of the NCDOT Standard Specifications and all applicable Project or Standard Special Provisions provide for Quality Control and Quality Assurance of asphalt pavements by use of a Quality Management System (QMS). The basic concept of this process is that the Contractor performs adequate testing and inspection to insure a quality asphalt pavement and the Department performs adequate testing and inspection to insure that the Contractor’s results are accurate. This system requires both the Department and the Contractor to have technicians that are competent in production, construction, testing, and inspection of asphalt pavements. The general idea is for the Contractor to perform the necessary tests and inspection to insure the likelihood that all mix meets the Specifications instead of “after-the-fact” testing to see if it does meet the Specifications. This approach gives the Contractor much more control over his total operations. He is responsible for his product from the design of the mix to the final acceptance of the pavement. The Department simply monitors his process to be sure that what he is doing is adequate and accurate; and, then performs independent testing to verify the quality of the end product.
The Contractor’s responsibility under the QMS process is referred to as Quality Control (QC). The Department’s responsibility under the QMS process is referred to as Quality Assurance (QA). The Contractor is responsible to provide competent personnel to perform his quality control and the Department is responsible to provide competent personnel to perform their quality assurance. The requirements and details of certification for these personnel to perform the QC/QA work is given in
The requirements for the Contractor’s QC sampling and testing are contained in
of the Specifications and
. The frequency of these activities may vary with the process and the materials. When test results vary from the design and/or specifications, changes to the process shall be made. The frequency of the appropriate QC activities shall be increased until the proper conditions have been restored. The Department’s minimum frequency requirement for QA sampling and testing is specified in
and is covered in detail later in this manual.
The Contractor may utilize innovative equipment or techniques not addressed by the specifications or these provisions to produce or monitor the production of the mix, subject to approval by the Department's Engineer.
QMS is a total process that encompasses the Contractor’s mix design, the QC testing and inspection, and the Department’s quality assurance and acceptance of the Contractor’s process and procedures. Each of these aspects of the total process will be addressed in detail later in this manual. While all of these are very important, the real success of this program is that the Contractor and the Department carry out every aspect of the process such that a quality asphalt pavement is the final product.
|1.2 Contractor’s Quality Control Plan|
The Contractor will not be required to submit a written quality control plan to the Department; however, the Contractor, at a minimum, shall perform all quality control activities required by the specifications as well as accepted asphalt industry quality control practices and procedures.
|1.3 Asphalt QMS Technician Qualifications and Certifications|
The technician's role is extremely vital in every road construction project, especially in asphalt construction. He has the job of ensuring that the pavement design as described in the plans and specifications produces a strong, durable, and reliable pavement on the roadway. The technician's job is one that demands knowledge, awareness, keen observational skills, and diplomacy. It is among the toughest jobs in the construction industry.
Most road and highway construction in North Carolina is performed under contract. One party (the Contractor) agrees to perform certain work that meets specified standards. In return for this work, the Contractor is paid by the other contractual party (the owner) who is often a local, state or federal government agency. The contract between Contractor and owner includes plans and specifications that must be followed during pavement construction and be met by the finished product. Whether or not these requirements are fulfilled determines the quality level of the finished pavement and how well the pavement will serve the public.
Because asphalt pavement construction is often complex, plans and specifications are often detailed and lengthy. Ensuring that the plans are followed precisely demands the owner and the Contractor have an agent acting as their eyes and ears, and who is on-hand throughout the construction process. That agent is the asphalt technician. It is the technician's duty to see that construction operations produce the results called for by the plans and specifications. In this capacity, both the DOT's technician and the Contractor's technician have certain areas of responsibility to identify deviations from project specifications and to see that they are corrected immediately. In any case, neither technician has the authority to change or modify the contract or specifications.
Knowledge is the path every technician must follow to improve his performance and capability. Whether a technician is new to the job or seasoned, his learning never stops. New developments that affect his job are constantly appearing. Additionally, every technician needs to refresh his knowledge periodically and to brush up on procedures that are used infrequently. This manual is a good source of refresher information, as well as a basic text for training the new asphalt technician.
A manual alone, however, is not enough. It must be used in conjunction with other learning tools. The most effective learning tool is on-the-job training. The job site is where things are happening that a technician must know. It is the ideal place to observe, to ask questions, to get answers. On the job, the new technician develops inspection skills first-hand and discovers what occurs during asphalt mix construction and why certain methods achieve certain results. Combined with this course of instruction, on-the-job training provides the technician with the necessary tools to carry out his duties and responsibilities.
1.3.2 PURPOSE OF INSPECTION AND TESTING
The purpose of inspecting and testing asphalt construction is to ensure the quality of the work meets project requirements and specifications. To accomplish this, the asphalt technician must be familiar with the parts of the construction contract that apply to his job.
contract is the agreement between the owner or contracting agency and the Contractor. It states the obligations of both parties, including labor, materials, performance and payment. While there are many documents that make up the construction contract, the technician is concerned primarily with the plans and specifications. Together, plans and specifications explain requirements that the Contractor must fulfill to build a satisfactory pavement and get paid in full for his work.
Plans are the contract documents that show the location, physical aspects, details and dimensions of the work. The plans include layouts, profiles, cross-sections and other details.
Specifications are the written technical directions and requirements for the work; also, the standard specifications and the special provisions complement the plans by providing instructions that are not specifically indicated on the drawings. Specifications are the means of communication among the designer, the Contractor, and the technician. Specifications include Standard Special Provisions and Project Special Provisions, which simply are revisions to the specifications.
1.3.3 DOT TECHNICIAN'S AUTHORITY
The Division Engineer or project Resident Engineer assigns the DOT’s technicians, and their authority is stated in the Standard Specifications under Duties and Authority of the Inspector
. The Technician assists the Engineer in determining that the work done and the materials used meet contract requirements. The Technician has the authority to reject defective materials and to advise the Contractor that payment will be withheld for work that is being done improperly. The Engineer may delegate additional authority to him; however, the Technician is not authorized to make any final acceptance of the work. The technician is generally responsible to ensure that the contractor is utilizing good construction practices in order to deliver a satisfactory product at a reasonable cost.
1.3.4 DOT TECHNICIAN'S RELATIONSHIP WITH CONTRACTOR
It is required by the Specifications that a preconstruction conference be held between the inspection and engineering personnel of the owner and the Contractor's supervisory personnel. At such a meeting the plans and specifications are reviewed, material deliveries and construction techniques discussed, traffic control procedures agreed upon, specific project responsibilities and lines of authority defined, and any other necessary items that may have a bearing on the project are discussed.
One of the most important aspects of the technician's job is his relationship with the Contractor. This relationship affects the management of the project. A good personal rapport assists the Technician in resolving problems that might arise. When dealing with the Contractor and his personnel, the Technician should be friendly, but he must be firm and impartial in making decisions. If the Technician experiences difficulties with the Contractor, he should immediately inform the Engineer.
The Technician will assist himself, as well as the Contractor, by trying to understand the project from the Contractor's point of view. The Technician is primarily interested in quality (how good the pavement is); the Contractor is primarily interested in quantity (how much pavement is placed in a given time). Under no condition should the Technician permit a reduction in quality in the interests of quantity. However, as long as pavement quality is maintained, the Technician should assist the Contractor's efforts to place asphalt mix as efficiently as practical and within specifications.
The Technician has the obligation to influence the construction process so that the best possible roadway is constructed. He cannot simply take a passive role when observing a problem. He must be willing to help solve it. For example, after observing a particular situation, the Technician may be able to suggest a change in procedures that could improve the quality of the work while increasing the efficiency of the operation. Such a suggestion benefits both the Contractor and the Department of Transportation.
When offering assistance in solving problems, however, the Technician must be careful to avoid involving himself in the supervision of construction. He should avoid giving the impression that he wants to control the work, and he must never issue an order to the Contractor's workers. Assuming supervision of the work puts the Technician in the undesirable position of judging the quality of work by means that he dictated.
1.3.5 QUALIFICATIONS OF QC AND QA TECHNICIANS
The personal attributes required of a technician go beyond those expected of an ordinary workman. The technician must be honest. He must conduct himself in a fair and straightforward manner. While under stress, he must be able to maintain his composure and make good decisions. He must have keen common sense for making competent decisions. He must be frank and sincere in his relationships with people and must be a skilled diplomat, able to handle tough situations without arousing hostility. Above all, he must be observant and be capable of keeping good records.
Some technical study and construction experience is helpful. As a minimum, however, the technician must be able to perform accurate mathematical calculations and should be familiar with the fundamentals of engineering equations. It is essential that he knows how to read and understand plans, specifications and other contract documents in order to understand requirements of the work. Although not responsible for the design of roadways, the technician should understand the basic engineering principles involved. He should be familiar with the characteristics of materials and know the principles of material testing, including the interpretation of test results.
The technician must have specialized knowledge pertaining to his particular job. For example, a plant technician must have a thorough working knowledge of asphalt plants, but he must also have a broad general knowledge of asphalt materials, production, and construction procedures. Practical experience with asphalt mix production, roadway construction, and asphalt laboratory testing is a valuable asset.
If all the qualifications of a technician could be reduced to four, they would be: (1) knowledge, (2) common sense, (3) observational skills, and (4) courtesy. The basic summary of each is presented below.
(1) Knowledge--The technician must know about the work that he is inspecting. He should be familiar with materials, equipment and asphalt pavement construction procedures. The more knowledgeable a technician is, the better prepared he is to perform his duties.
(2) Common Sense--A good technician must have abundant common sense. While common sense is no substitute for knowledge, it is the means of interpreting the specifications to properly enforce their intent. Common sense grows out of knowledge, but it cannot be learned out of a book.
(3) Observational Skills--A technician can act only on what he observes. What is not seen is missed. Thus, it is important not only for a technician to look carefully at everything going on around him, but also to see what he looks at. "Seeing" in this context means thinking carefully about what the eyes observe. Without seeing, a technician can observe an incorrect condition and not realize it.
(4) Courtesy--A major part of the technician's job is to inform others when unsatisfactory conditions exist or when the specifications are not being met. Both parties expect valid criticism and objections from the other, yet the manner of presenting comments can often become the source of poor relations between Contractor and technician. Experience shows that it is not what is said, so much as the way it is said that is important. Gruff, bossy and sarcastic comments are unacceptable from any technician, even if given in answer to aggravating remarks from others.
Once Contractor-DOT relations deteriorate, the work suffers. Since the technician's primary concern is to preserve the quality of the work, he should show common courtesy at all times, even when tempted not to do so. Although desired qualities for prospective technicians can be listed, the bottom line is this: To do a professional job, the technician must want to do a good job, know how to do it, and go about it in a manner that contributes favorably to the project.
1.3.6 QMS TECHNICIAN REQUIREMENTS
On Quality Management System projects, all asphalt plant mix testing technicians (both Contractor & DOT) are required to be certified through the Department's current Asphalt Technician Certification Program. All plant technicians (both Contractor and DOT) must be certified as Plant technicians. Certified QMS Level I Plant Technicians are testing personnel and are required to be at the plant site at all times during production of material for the project. A plant operator who is a certified Asphalt Plant Technician Level I may be utilized to meet this requirement when daily production for each mix design is less than 100 tons provided the randomly scheduled increment sample as defined in
is not within that tonnage. When performing in this capacity, the plant operator will be responsible for all quality control activities which are necessary and required. Absences of the Level I Technician, other than those for normal breaks and emergencies must be pre-approved in writing by the appropriate QA Supervisor or his designated representative(s). Any extended absence of the Technician that has not been approved will result in immediate suspension of production by the Engineer. All mix produced during an unexcused absence of the Level I technician will be accepted in accordance with
of the Specifications. The Contractor is also required to have readily available (on-call) a QMS Level II Plant Technician responsible for making process control adjustments and solving mix problems. He must be located such as to be able to respond to all plant mix problems in a timely manner. The Department will have at least one certified QMS Level II Plant Technician on its' Quality Assurance (QA) team as well as several Level I Technicians. Either a QC or QA Level II Technician may also function as a Level I Technician, in which case he/she would fulfill the requirements for both the Level I and II technicians.
All Roadway Technicians are required to be certified through the Department’s current certification program. The Contractor is required to have at least one certified roadway technician on the project at all times during normal laydown operations. This person is responsible for monitoring all roadway paving operations and all quality control processes and activities, to include stopping production or implementing corrective measures when warranted. The Contractor’s technician(s) must meet the same requirements as DOT personnel and will be certified by the same certification program. A certified DOT Roadway Technician will also be on-site at all times during paving operations.
The Department's Certification Program for QMS plant and roadway technicians is managed by the Materials and Tests Unit's Asphalt Laboratory. This section will maintain a listing of all plant and roadway QMS personnel certified by NCDOT. This listing will be maintained in an internal computer database (HiCAMS).
The Asphalt Laboratory may be contacted at
(919) 329-4060 for further instructions on how to access this information. This listing may be used to verify certification of personnel working on QMS projects.
It is required that both DOT and Contractor Density Gauge Operators be certified through the Department’s current QMS Density Gauge Technician’s Program. The Department’s Certification Program for QMS Density Gauge Technicians is managed by the Soils Engineer of the DOT M&T Unit. The Soils Engineer will maintain a listing of all certified QMS Density Gauge Technicians and may be contacted at
(919) 329-4150 for verification of these. This listing will also be maintained in a computer database, and is accessible via the NCDOT’s Materials & Tests website.
The QMS Specification requires that the Contractor design his own asphalt mixes. He may do so by use of his own personnel or by hiring an approved company to do it for him. Whichever the case, any technician performing mix designs for use on NCDOT specification projects must be certified through the Department’s current mix design certification program. This certification program is managed by the Asphalt Design Engineer of the Department’s Materials and Tests Unit. The Asphalt Design Engineer may be contacted at
(919) 329-4060 for verification of a technician’s mix design certification.
An organizational chart, including names, telephone numbers, and current certification numbers of all the Contractor's personnel responsible for the quality control program shall be posted in the Contractor's laboratory while the asphalt paving work is in progress.
1.3.7 NCDOT ASPHALT TECHNICIAN CERTIFICATION PROGRAM
The certification of asphalt technicians is a program by which it can be reasonably assured that both the DOT's quality assurance personnel and the Contractor's quality control personnel are knowledgeable and qualified to perform the required sampling, testing and inspection of asphalt mixtures and pavements. Certification will also include a general knowledge of the techniques and equipment used in the construction of asphalt pavements, including asphalt plant operations, placement operations and compaction operations. Under the NCDOT program, a technician may be certified in either mix design techniques, plant operations, roadway operations, density gauge operations, or all of these. Certification in either area will include some overlap into the other area. For example, a certification in plant operations will include a basic knowledge and understanding of roadway procedures, etc. This is required since it can be readily seen that proficiency in one area requires some general knowledge of the overall operation.
The certification program will be operated on a continuing basis. There will be classes and examinations scheduled throughout each year. In addition, there will be an “on-the-job” training program for Level I plant & roadway technicians. The Asphalt Design Engineer will provide applications for and maintain a master training schedule of all related classes. Both the applications and schedule may be downloaded from the Materials and Tests Unit’s web site located at the following web address:
Enrollment procedures for these training classes are included at the end of this Section. All certifications will generally be effective for four years beginning from the date of passing the certification test and then must be renewed. Details for renewal of certifications are covered later in this section.
2. Types of Certifications
Listed next are the different types of certifications related to asphalt pavements and a basic job description for each. As mentioned previously, a technician may be certified as any one or more of these, or possibly all of these. As noted in the prerequisites listed later, some certifications require a lower level certification before advancement to the next level of certification.
A. QMS Certifications
1. QMS Level I Plant Technician - A Technician trained and competent in testing and inspection of asphalt mix at the plant.
2. QMS Level II Plant Technician - A Technician trained and competent in making mix adjustments and solving asphalt mix problems.
QMS Mix Sampling Technician - A Technician trained and competent in sampling of asphalt mix at the plant.
4. QMS Roadway Technician - A Technician trained and competent in roadway laydown, compaction, and density procedures.
5. QMS Density Gauge Operator - A Technician trained and competent in the use of a density gauge in accordance with the QMS specification.
6. Mix Design Technician - A Technician trained and competent in the area of asphalt mix design procedures.
B. QMS Certification Requirements
The basic requirements for these five types of certifications are listed as follows:
A. QMS Level I Plant Technician
1. Prerequisite(s): Introduction to Asphalt Pavements Course with Passing Exam.
Step 1: Level I Plant Technician OJT Program (See Section 12 for the QMS-3 checklist with instructions)
Step 2: Level I Plant Technician Class with Passing Exam
3. Experience Requirement: Minimum 10 working days per OJT Program *
B. QMS Level II Plant Technician
CURRENT LEVEL I PLANT TECHNICIAN
1. Prerequisite(s): Minimum of 1 year‘s experience as Level I Plant Technician
Step 1: Approved Mix Design Course with Passing Exam
Step 2: Level II Plant Technician Class with Passing Exam
3. Experience Requirement: One (1) year as Level I Technician or Equivalent
Experience as Determined by Asphalt Design Engineer.
C. QMS Mix Sampling Technician
Step 1: Attend I Day Training Class
Step 2: Pass Written Exam and Complete Hands on Training
D. QMS Roadway Technician
1. Prerequisite(s): Introduction to Asphalt Pavements Course with Passing Exam.
Step 1: Roadway Technician OJT Program (See Section 12 for the QMS-5 checklist with instructions)
Step 2: Roadway Technician Class with Passing Exam
3. Experience Requirement: Minimum 10 working days per OJT Program **
* In lieu of the 10-day minimum training and the minimum requirements in Parts II, III and IV of the OJT Checklist, a current asphalt plant mix testing certification from another State or other approved testing agency may be substituted. In this case, a copy of the certification shall be attached to the back of the OJT checklist. In addition, the OJT technician must perform one repetition of all requirements in Parts II, III, and IV in the presence of a certified plant technician prior to the check off by a final review technician. All other requirements of this OJT checklist shall be completed as specified.
** In lieu of the 10-day minimum training, either of the following may be substituted:
1) a current roadway paving certification from another state or other approved testing agency, or
2) Certification verifying a minimum of 1 year asphalt roadway paving experience from a supervisor who has direct knowledge of the applicant's roadway paving experience. In either case, the appropriate certification shall be attached to the back of the OJT checklist and included with the class application package. All other requirements of the OJT checklist shall be completed in full as specified, including the Final Review Check off by an Approved Final Review Technician.
E. QMS Density Gauge Operator
a. Prerequisite(s): NCDOT Nuclear Safety Training Course
b. Training: QMS Density Gauge Technician Course with Passing Exam.
c. Experience Requirement: "Hands-on" QMS training after completion of class.
2. NON - NCDOT TECHNICIANS
a. Prerequisite(s): Nuclear Safety Training Course
b. Training: QMS Density Gauge Technician Course with Passing Exam.
c. Experience Requirement: "Hands-on" training after completion of class.
(a) QMS Level I or II Technician OR
(b) Completion of the Level I OJT Program and Enrollment in a Level I Class OR
(c) Equivalent Experience as Determined by the Asphalt Design Engineer.
(d) Completed Aggregate Consensus Properties Checklist
Step 1: Approved Mix Design Course with passing exam
Step 2: Check-off on Aggregate Consensus Property Tests (Contact Local QA Supervisor for Details)
Step 3: NCDOT Mix Design Certification Class including Passing Exam.
A certificate will be issued for each type certification. Initial certification will generally be effective for five (5) years beginning from the date of passing the appropriate written exam until December 31st of the 5th year. A Mix Sampling Technician Certification has no expiration date. Failure of an exam will require the person to re-attend the regular class and pass the exam to become certified / re-certified. Upon two consecutive failures of the exam, the person will be required to perform the OJT (On-the-Job-Training) prior to re-attending the full class and taking the exam, unless otherwise approved by the Asphalt Design Engineer. Upon satisfactory completion of all requirements, the technician will be issued a certificate.
It should be noted that there is no certification for the Introduction to Asphalt Pavements Course. This is a very basic asphalt course designed to provide general knowledge of both plant and roadway operations to personnel with little or no experience. It is a prerequisite for several other certifications; therefore, a “completion” certificate will be issued to verify satisfactory completion. An online exam will be given at the end of the course and will be used to judge satisfactory completion.
3. Renewal Certification
A technician is required to renew his certification prior to the expiration of the current certificate. If a Technician’s certification expires, he will not be permitted to perform the duties of this expired QMS Certification until renewal occurs. He will also be required to complete all initial requirements as outlined above. Requirements for renewal of certifications are as follows.
Level I & II Plant Technicians: Attend the Level I or Level II plant Technician class including passing a written exam.
Roadway Technicians: Attend the regular roadway technician class including passing a written exam.
Density Gauge Operators: Attend the regular density gauge operators class, including passing a written exam, and a "hands-on" checkoff.
Mix Design Technicians: Attend the regular mix design certification class including passing a written exam.
4. Loss of Certification by Suspension or Revocation
All certified technicians are subject to loss of their certification by suspension or revocation. The primary reason for the loss of a certification would be the falsifying of test results, records and/or reports. Other reasons that might lead to loss of certification include insubordination, gross negligence and apparent incompetence on the part of the technician. All reported occurrences of violations, misuse or abuse of this certification will be documented by the appropriate person(s).
The NCDOT Asphalt Design Engineer may suspend or permanently revoke any certification. Suspension or revocation of a certification will be sent by certified mail to the technician, the Quality Control Manager and the Corporate Head of the company that employs the technician.
A technician has the right to appeal any adverse action which results in suspension or permanent revocation of certification by responding, in writing, to the State Materials Engineer within 10 calendar days after receiving notice of the proposed adverse action. Failure to appeal within 10 days will result in the proposed adverse action becoming effective on the date specified on the certified notice. Failure to appeal within the time specified will result in a waiver of all future appeal rights regarding the adverse action taken. The technician will not be allowed to perform duties associated with the certification during the appeal process.
The State Materials Engineer will hear the appeal and make a decision within 7 days of hearing the appeal. Decision of the State Materials Engineer shall be final and shall be made in writing to the technician.
If a certification is temporarily suspended, the technician must pass any applicable written examination, any proficiency examination, and other requirements as required by the Engineer prior to having the certification reinstated.
1.3.8 NCDOT ASPHALT TECHNICIAN CERTIFICATION - ENROLLMENT PROCEDURES
The Department requires all students to enroll in the appropriate class(es) prior to attendance. Below are the guidelines for class enrollment. It is extremely important that these guidelines be followed in order to ensure correct enrollment data.
1. Students will only be enrolled by submission of application, applicable fee, and all other required documents. Class space or slots will not be held or reserved.
2. Mailed or online applications are accepted for enrollees. No faxed applications will be accepted.
3. Required verification of prerequisites must be marked on and/or attached to the application form. Applicants must meet all prerequisites at time of application submittal.
4. Non-NCDOT agencies must attach a non-refundable check(s) to the application. NCDOT Divisions / Units funds will be drafted to cover their fees.
5. When registering multiple students, send one check per class. One check per student is preferred.
6. Registration form & payment must be received no more than 90 and no less than 7 calendar days prior to class start date, unless otherwise noted. Application(s)/check(s) will be returned if not received within this time frame.
7. NCDOT personnel registered through HiCAMS are not enrolled until all required documentation is received and approved by the Materials & Tests Unit. Non-NCDOT personnel are not enrolled until all required documentation is received and approved via hard copy. Confirmation notices will be sent to all enrolled students. If confirmation notice is not received within 5 business days of class start date, notify the appropriate class contact person.
8. Substitution, deletion or transfer of enrolled students must occur no later than 5 business days prior to class start date, and must be approved by the Materials & Tests Unit conducting the class. If substitution or transfer of an enrolled student is allowed, a new confirmation notice will be furnished.
9. Absent students Will Not be transferred to another class. If enrollment is desired for a different class, the enrollment process must be repeated for that student, including payment of the fee.
10. Applications received after a class is full will be returned. Maximum class size depends on the classroom size.
11. Level I, Level II, and Mix Design Certification Classes are subject to cancellation if not more than 10 students are registered within 7 calendar days of class start date.
12. QMS Roadway Classes are subject to cancellation if not more than 20 students are enrolled within 7 calendar days of class start date.
13. Students attending a class but failing to pass the exam must repeat the enrollment process and pay the class fee and attend the class again before taking the exam. These applicants should mark "Retest" on their application.
14. Any student attending the class but not taking the exam for a valid reason, shall have 10 calendar days to take the exam without having to reattend the class. This must be coordinated through the Materials & Tests Asphalt Laboratory.
(1) Either attach copy of Introduction to Asphalt Pavements certificate of completion or email confirmation of completion
(2) Attach front & back pages of completed OJT checklist to application. Applicants using exception for being certified in another state must attach copy of that certification. Applicants utilizing the exception for 1 year's roadway paving experience, must attach the experience certification.
(3) Attach copy of Mix Design Course certificate.
(4) Attach copy of Level I Plant Technician certificate.
|1.4 QMS Laboratory Technician Assessment Program|
The mission of the Assessment Program is to determine the competency of the Quality Control and the Quality Assurance technicians in the QMS program by observation and by comparison of sampling and testing results.
1.4.2 TECHNICIAN ASSESSMENTS
It is the intent of this program to validate the competency of the personnel performing quality control and quality assurance testing of Asphalt Mix and QA/QC Laboratory Equipment used in the QMS program is in compliance with specifications. In order to determine this competency, the following rating system will be used to grade QMS technicians:
• Satisfactory – all test procedures are performed with no corrections or exceptions.
• Acceptable with Exceptions – while performing test procedures, the technician made mistakes, but did not or could not make corrections during the procedure. The technician will be reassessed.
• Unsatisfactory – while performing test procedures, the technician made mistakes and did not make corrections during the procedure. The technician demonstrated a lack of knowledge about the testing procedures. This may require remedial training, and could result in suspension of certification. The technician will be reassessed.
A review by the Engineer may be performed prior to any action in the case of an unsatisfactory assessment. Any unsatisfactory assessments that the Engineer regards as requiring more than remedial training, or if remedial training has not been effective, will be brought to the attention of the Review Committee. A reassessment will be performed on any technician that receives any rating other than satisfactory. It will be the determination of the Engineer if the reassessment process should include an additional material correlation. An assessment can be performed at any time regardless of the fact that the material is being transported to a NCDOT project or private work.
The technician will be allowed two postponements in the event of an emergency that prevents him/her from meeting an agreed upon assessment schedule. If the assessor has made three attempts to assess the technician, or if the requested postponement does not fit the definition of an emergency, the Engineer will immediately notify the technician’s supervisor to set a date and time for the assessment. An emergency, in this case, would be defined as an event requiring the complete attention of the technician to the exclusion of performing any testing.
The following guidelines shall be used in determining assessment frequencies for personnel:
A) All Level I and Level II Technicians are eligible to be assessed.
B) QA Supervisors shall be assessed once a year.
C) All Final Review Technicians shall be assessed once a year.
D) All technicians who are actively testing asphalt mix are subjected to be assessed.
All personnel being assessed shall perform all sampling in accordance with
. In addition, an IA portion of the sample will be taken at the same time as the QC or QA sample. In conjunction with QA approval an additional sample may be directed at any time and any location during production (in lieu of the next randomly scheduled sample for that increment).
All personnel being assessed shall perform all tests in accordance with their respective procedures as stated in
All equipment used in the testing must be properly calibrated and maintained as required by
prior to the QC or QA technicians performing the tests. The assessor will perform an equipment assessment during which they will verify the calibration of the testing equipment. The equipment assessment will typically be performed during the scheduled technician assessment visit. If during the assessment visit, equipment is found to out of specification, the equipment must be brought into compliance or replaced as per the requirements of
. Once the equipment issue has been resolved, notify the assessor so the assessment can be completed. If the laboratory fails to comply with the above requirements, the Engineer may stop production as detailed in
If the verification determines that the equipment is out of calibration, testing of the mix shall stop and cannot resume until the equipment is brought into compliance or is replaced by equipment that is within compliance.
1.4.7 LOSS OF CERTIFICATION
All certified technicians are subject to the loss of certification by suspension or revocation as defined in Section 1.3.7
. In addition, the following provisions shall apply to any technician assessed under this program.
If the technician receives an unsatisfactory on any procedure, the assessor will review all parts of each test method that were performed incorrectly to ensure that the technician clearly understands their mistakes. A reassessment will be required only on those test procedures that received an unsatisfactory. Following any unsatisfactory assessment, the QC Manager/QA Supervisor will be notified by e-mail.
The technician will have the option of performing the reassessment for each unsatisfactory procedure on the same day if mutually agreed upon by the assessor and the technician. [A Process Control (PC) sample can be used for this purpose]. However, the technician can request that the reassessment occur at a later date. If this option is used by the technician, the QC Manager/QA Supervisor should review the assessment with the technician and perform whatever corrective actions they deem necessary within ten (10) calendar days. The Engineer will contact the assessor who will then perform a reassessment within ten (10) calendar days.
Failure by the technician to perform the proper methods after reassessment will result in an overall rating of Unsatisfactory and the following actions may occur:
Failure of the QC/QA technician to satisfactorily complete the reassessment may result in the suspension of the technician’s certification. Notification of the suspension will be in the form of a letter to the company’s management or the appropriate Division Engineer. Once a technician’s certification is suspended, he/she will be required to complete the OJT program and have a satisfactory assessment before their certification will be reinstated. However, the technician can appeal, but the certification will remain suspended until the appeal process is completed. If the assessment following the OJT process is unsatisfactory, the technician’s certification will be revoked. However, the technician can request a hearing with the Review Committee. The Review Committee will review the assessment documentation, as well as any other documentation deemed necessary. The Review Committee can request that additional OJT be performed, overturn the reassessment and have a new assessment performed, or they can uphold the revocation of certification.
Revocation of the technician’s certification may occur if an unsatisfactory reassessment occurs after the OJT completion. Also, if the technician has two suspensions in the same certification period, their certification may be revoked. The final revocation decision will be made by the Review Committee and will be effective on the date of the letter sent to the technician. Copies of the letter will be sent to the producer, the Division Engineer, the Division QA Supervisor and FHWA.
3. Reinstatement of Certification:
All certified technicians may regain their certification in the manner defined in
At the completion of the assessment, the assessor will retain the IA portion of the sample and a copy of the QC or QA worksheet. This sample will be returned to either the Central Asphalt Laboratory or to an appropriate M&T Regional Laboratory. The sample information will be entered into HiCAMS by the assessor. Upon completion of the tests, the assessor will correlate the results. Depending on the outcome of the sample correlation, an investigation may be conducted to determine the cause of any testing disparity.
At the completion of each assessment, the assessor will provide a completed hard copy of the M&T 901 form to the assessed technician. The assessor will also send a follow-up copy via email to the QC Manager/QA Supervisor after each assessment.
|1.5 Ethics and Falsification|
False statements, misrepresentations, false reporting, or false claims made concerning the acceptability of materials on highway projects are prohibited by North Carolina General Statutes and the United States Code of Federal Regulations.
Fraudulent activities include: falsification of test results, false documentation of observations, falsification of inspection records, adjustments to the process, discarding of samples and/or test results, or any other deliberate manipulation of the facts. Such activities will result in the revocation of the applicable person’s QMS certification. In addition, state and/or federal authorities may also pursue criminal charges. The Engineer will determine acceptability of the mix and/or pavement represented by the falsified results or documentation. If the mix and/or pavement in question is determined to be acceptable, the Engineer may allow the mix to remain in place at no pay for any asphalt mix, binder, or other mix components. If the mix and/or pavement represented by the falsified results is determined not to be acceptable, it shall be removed and replaced with mix that meets the Specifications.
1.5.1 NORTH CAROLINA REQUIREMENTS
The following is set forth in G.S. § 136-13.2, “Falsifying Highway Inspection Reports”:
(a) Any person who knowingly falsifies any inspection report or test report required by the Department of Transportation in connection with the construction of highways, shall be guilty of a Class H felony.
(b) Any person who directs a subordinate under his direct or indirect supervision to falsify an inspection report or test report required by the Department of Transportation in connection with the construction of highways, shall be guilty of a Class H felony.
1.5.2 FEDERAL REQUIREMENTS
Any suspected fraudulent activity – whether it involves a Federal or State employee, contractor, subcontractor, or any other participant in a Federally-assisted highway project – should be reported to the Office of the Inspector General (OIG) Office of Investigations, USDOT. The OIG is responsible for investigating charges of fraud, waste, and abuse in FHWA programs.
Code of Federal Regulations (23 CFR 635.119) requires that the Office of Inspector General (OIG) will maintain a hotline for receiving allegations of fraud, waste, abuse, or mismanagement in U.S. Department of Transportation (DOT) programs or operations. Allegations may be reported 24 hours a day, seven days a week by DOT employees, contractors, or the general public. The FHWA Fraud Notice (Form FHWA 1022) is required to be posted on all Federally-Funded Construction Projects. This awareness poster points out the consequences of impropriety on the part of any Contractor or Department employee working on Projects.
|2.1 General Description of Asphalt Paving Materials / Pavements|
Asphalt pavements are composed of three basic components - 1) asphalt binder, 2) aggregates, and 3) air voids. Aggregates are generally classified into two groups - coarse and fine, and normally constitute 90 to 96 percent by weight of the total mixture. Asphalt binders are classified by various grading systems and normally constitute 4 to 10 percent of the total mixture. Probably the most important but often overlooked component of an asphalt mix is air voids. In this section, only asphalt binder, aggregates and other additives are discussed. Air voids and the role it has in asphalt mixtures and pavement performance will be discussed in later sections of this manual.
There are many different types of asphalt and many different types of aggregates. Consequently, it is possible to make different kinds of asphalt pavements. Among the most common types of asphalt pavements are:
* Dense-Graded Hot Mix Asphalt (HMA);
* Warm-Mix Asphalt (WMA);
*Open-Graded Asphalt Friction Course; Permeable Asphalt Drainage Course
* Ultra-Thin Bonded Wearing Course
* Asphalt Surface Treatments;
* Emulsified Asphalt Mixes (Cold Mixes);
* Others, SMA, In-Place Recycled Mixes (both hot and cold)
This manual primarily addresses dense-graded asphalt concrete which is a paving material that consists of asphalt binder and mineral aggregate with appropriate air voids. The asphalt binder, either an asphalt cement or a modified asphalt cement, acts as a binding agent to glue aggregate particles into a dense mass and to waterproof the mixture. When bound together, the mineral aggregate acts as a stone framework to impart strength and toughness to the system. The performance of the mixture is affected both by the properties of the individual components and the combined reaction in the system.
|2.3 Technician Responsibilities|
The Contractor’s Quality Control technicians and the DOT’s Quality Assurance technicians are responsible for the way asphalt and aggregate materials are handled, stored, sampled, mixed, hauled, placed, and compacted. They have responsibilities to check such things as material sources, grades, types, temperatures, and moisture contents. Both must also be fully capable of reviewing and interpreting mix design data, laboratory test results and specifications, when necessary, as well as being able to perform sampling and testing.
The technician will be unable to perform his job without a working knowledge of the materials from which an asphalt concrete pavement is made, particularly material characteristics and their role in pavement performance. He must also understand how improper handling of materials can adversely affect their properties and ultimately, their behavior in the finished pavement. Having such information will give him the confidence to make proper day-to-day decisions and will eliminate the role of guesswork in the job, ensuring that good quality control is maintained.
Materials inspection and control demands accurate and thorough documentation. Facts, figures, dates, names, locations, and conditions are important elements in daily record-keeping. Experience has taught us over the years that a scrap of information that seems unimportant when recorded can later turn out to be the very piece of information needed to analyze a serious problem.
|2.4 Asphalt Materials|
As mentioned earlier, one of the basic components of asphalt mixes is asphalt binder. Asphalt binder at normal atmospheric (ambient) temperatures is a black, sticky, semi-solid, highly viscous, cementitious material. Asphalt binder is typically a solid to semisolid at normal air temperatures and becomes a liquid at high temperatures. Asphalt is made up largely of a hydrocarbon called bitumen and therefore is often called a bituminous material. Because asphalt binder is sticky, it adheres to aggregate particles and can be used to cement or bind the aggregate in an asphalt concrete mixture. Asphalt binder is an excellent waterproofing material and is unaffected by most acids, alkalis, and salts. This unique combination of characteristics and properties is a fundamental reason why asphalt is an important paving material.
2.4.2 REFINING CRUDE PETROLEUM
Asphalt is a constituent of crude petroleum (crude oil). Most crude oil sources contain some asphalt. However, some crude oil sources may be almost entirely asphalt and some crude oils contain little or no asphalt. The primary source for asphalt cement used in the United States today is from the refining of crude petroleum (crude oil). Crude petroleum from oil wells is separated into its constituents or fractions in a refinery. (see Fig. 2-1). Accordingly, asphalt is obtained as a residue or residual product, and is valuable and essential for a great variety of engineering and architectural uses. Petroleum asphalt for use in pavements is usually called paving asphalt, or asphalt binder to distinguish it from asphalt made for non-paving uses, such as roofing and industrial purposes.
2.4.3 CLASSIFICATION AND GRADING OF PAVING GRADE ASPHALTS
Paving grade asphalts are classified into three general types:
(1) Asphalt Cements (Binders)
(2) Emulsified Asphalts
(3) Cutback Asphalts*
*It should be noted that North Carolina Specifications do not allow for any use of cutback asphalts primarily due to environmental concerns.
Asphalt Binder is the residual by-product from the distillation process. Emulsified asphalts and cutback asphalts are then made from asphalt cements and are frequently referred to as liquid asphalts. Included in the Standard Specifications and Special Provisions are the specific requirements for the various grades and types of asphalt materials. Figures 2-3 and 2-4 included in this manual summarize the various grades and typical applications of asphaltic materials used in pavement construction by the NCDOT. However, the technician should always review the project special provisions to determine if there are any additional grades or specific requirements which must be utilized on a specific project. Paving grade asphalt binder must be made fluid (liquefied) for handling and use during construction operations, such as pumping through pipes, transporting in tanks, spraying through nozzles and mixing with aggregate. Asphalt binder can be made temporarily fluid (liquefied) for construction operations in three ways:
heating the asphalt binder with indirect heat in a storage tank: After construction operations (mixing, spraying, etc.) the hot liquid asphalt binder cools and changes from a fluid back to a semi-solid condition at ambient air conditions. During the heating process the asphalt binder temperature must not exceed the manufacturers recommended temperature. If the asphalt binder is overheated, a process known as oxidation will occur. Oxidation causes the asphalt to become more brittle, leading to the term oxidative, or age, hardening. Oxidation occurs more rapidly at higher temperatures. A considerable amount of hardening occurs during mix production, when the asphalt binder is heated to facilitate mixing and compaction. When pavement construction operations are finished, the asphalt binder cools and reverts to its normal semi-solid condition and functions as the cementing and waterproofing agent that makes the pavement stable and durable.
emulsifying the asphalt with water: Emulsified asphalts are a mixture of asphalt cement, water, and an emulsifying agent (such as soap). While asphalt and water ordinarily do not mix, they can be made to mix by mechanically milling asphalt in a colloid mill with water and a small amount of emulsifying agent under high pressure. The resulting product, called emulsified asphalt, is a fluid and can be handled and sprayed at relatively low temperatures. Emulsified asphalts are normally liquid at room temperature. After application, the water evaporates and the asphalt particles coalesce (join together) into a continuous film that bonds the aggregate particles together. When the water and asphalt separate, it is said that the emulsion breaks or sets and the asphalt residue remains.
dissolving the asphalt with a petroleum solvent such as naphtha, gasoline, kerosene, or diesel oil: Mixing the solvent with the asphalt liquefies the asphalt at ambient air temperatures such that it can be sprayed or mixed with aggregate during construction. The solvent then evaporates over time, the residual asphalt returns to its semi-solid state and performs its intended function. As noted earlier, cutback asphalts are not used by NCDOT because of environmental concerns.
(A) Asphalt Binders
Performance Grade “binder” specifications are based on tests which measure physical properties of the asphalt “binder” that can be related directly to field performance by engineering principles. The tests are conducted at temperatures encountered by in-service pavements. These “binder” specifications have now been adopted by AASHTO and are referenced under AASHTO M 320.
Performance graded (PG) binders are designated with grades such as PG 64-22. The first number, 64, is often called the “high temperature grade.” This means that the binder would possess adequate physical properties to perform satisfactorily at least up to 64ºC (147ºF). This would be the high pavement temperature corresponding to the climate in which the binder is actually expected to satisfactorily serve. Likewise, the second number, -22, is often called the “low temperature grade” and means that the binder would possess adequate physical properties in pavements to perform satisfactorily at least down to -22ºC (-8ºF).
Additional consideration in selecting the grade to be used is given to the time of loading (vehicle speed on open highway, city streets, intersections, etc.) the magnitude of loads (heavy trucks), and at what level the material is within the pavement structure. Figure 2-3 shows the current binder grades in AASHTO M 320. Under these specifications, the binder grade used in standard asphalt mix pavements in North Carolina is Performance Grade 64-22 (PG 64-22). Other grades are required under certain conditions, such as heavy traffic and in recycled mixes.
(B) Emulsified Asphalts
Another method to liquefy the asphalt is to emulsify the asphalt in water. Asphalt liquefied by this method is known as emulsified asphalt. With emulsified asphalt, the basic idea is that the water will escape by absorption and evaporation, leaving the asphalt binder to do its job.
The object is to make a dispersion of the asphalt binder in water, stable enough for pumping, prolonged storage, and mixing. Furthermore, the emulsion should break down quickly after contact with aggregate in a mixer, or after spraying on the roadbed. Upon curing, the residual asphalt retains all of the adhesive, durability, and water-resistant properties of the asphalt binder from which it was produced.
By proper selection of an emulsifying agent and other manufacturing controls, emulsified asphalts can be produced in several types and grades. By choice of emulsifying agent, the emulsified asphalt can be anionic (asphalt globules electro-negatively charged) or cationic (asphalt globules are electro-positively charged) or nonionic (asphalt globules are neutrally charged). In practice, the first two types are ordinarily used in roadway construction and maintenance activities. The letter “C” in front of the emulsion type denotes cationic. The absence of the “C” denotes anionic or nonionic. For example, RS-1 is anionic or nonionic and CRS-1 is cationic.
Because particles having a like electrostatic charge repel each other, the asphalt globules are kept apart until the emulsion is deposited on the surface of the aggregate particles. At this point, the asphalt globules coalesce (join together) through neutralization of the electrostatic charges or water evaporation. Coalescence of the asphalt globules occurs in rapid and medium-setting grades. When this coalescence takes place, it is referred to as "breaking" or "setting".
Emulsions are further classified on the basis of how quickly the asphalt will coalesce; i.e., revert to asphalt binder. The terms RS, MS, and SS have been adopted to simplify and standardize this classification. They are relative terms only and mean rapid-setting (RS), medium-setting (MS), and slow-setting (SS). The tendency to coalesce is closely related to the mixing of an emulsion. An RS emulsion has little or no ability to mix with an aggregate, an MS emulsion is expected to mix with coarse but not fine aggregate, and an SS emulsion is designed to mix with fine aggregate.
Additional grades of high-float medium-setting anionic emulsions, designated HFMS, have been added to standard AASHTO and ASTM specifications. These grades are used primarily in cold and hot plant mixes, coarse aggregate seal coats, road mixes, and tack coats. High float emulsions have a specific quality that permits a thicker film coating without danger of runoff. A quick-set type of emulsion (QS) has been developed for slurry seals. Its use is rapidly increasing as the unique quick-setting property solves one of the major problems associated with the use of slurry seals.
(C) Cutback Asphalts
As noted earlier, cutback asphalts are not used by NCDOT because of environmental concerns and therefore are not discussed further in this Manual.
2.4.4 CHARACTERISTICS OF ASPHALT
The characteristics of asphalt binder under varying temperatures, rates of loading, and stages of aging determine its ability to perform as a binder in the pavement system. The tests and specifications used to measure and control these characteristics are discussed in Performance Graded Asphalt Binder Specification and Testing, (SP-1), The Asphalt Institute.
2.4.5 TESTING PROPERTIES OF PERFORMANCE GRADED ASPHALT BINDERS
A key feature in the Performance Grading system is that physical properties are measured on binders that have been laboratory aged to simulate their aged condition in a real pavement. Various tests are used for determining and measuring the properties of an asphalt binder. The ASTM and AASHTO references that describe in detail the equipment and procedures required to conduct these tests are available from a number of sources. These tests are normally conducted by the asphalt supplier or the Materials and Tests Laboratory in Raleigh. The specifications require that the Contractor furnish a certified delivery ticket for all asphalt materials to be used on a project (See
Article 1020-1 of the Standard Specifications).
2.4.6 SPECIFIC GRAVITY OF ASPHALT BINDER
Specific gravity is the ratio of the weight of any volume of a material to the weight of an equal volume of water, both at a specified temperature. As an example, an aggregate with a specific gravity of 2.653 weighs 2.653 times as much as water. Asphalt binder has a specific gravity of approximately 1.030 at 60° F (15.6° C).
The specific gravity of an asphalt binder is not normally indicated in the job specifications. Nonetheless, knowing the specific gravity of the asphalt binder being used is important for two reasons. Asphalt binder expands when heated and contracts when cooled. This means that the volume of a given amount of asphalt binder will be greater at higher temperatures than at lower ones. Specific gravity measurements provide a means for making temperature-volume corrections, which are discussed later.
: Silicone is used in asphalt because of its foam suppressing capabilities and also because it helps prevent the tearing and pulling of an asphalt mix behind the paving machine. Section 620-3
of the Standard Specifications requires that silicone is to be added to asphalt binder used in all surface course mixtures, including open-graded asphalt friction courses, unless otherwise directed. The silicone is added at the rate of 1 ounce per 2000-2500 gallons (4 ml per 1000-1250 liters) of asphalt binder and may be added either at the asphalt plant or at the supplier's terminal when so noted on the delivery ticket. The silicone should be adequately circulated throughout the asphalt binder storage tank prior to use. The brand used must have been previously approved by the Department. A listing of approved sources of silicone may be obtained through the M&T Lab in Raleigh, N.C.
(B) Anti-Strip Additive: Heat stable liquid chemical or hydrated lime anti-strip additives are required to be incorporated into asphalt mixes in an effort to prevent the separation of the asphalt from the aggregate particles (stripping). Chemical anti-strip additives are blended with the asphalt binder prior to introduction of the binder into the aggregate. Hydrated lime is blended with the aggregate prior to the aggregate entering the dryer.
All mixes including recycled mixes require either chemical or lime anti-strip additive or a combination of both. The technician should always refer to the JMF to determine the type, rate required and the brand specified. The Contractor may use a different brand or grade, provided the proper TSR testing has been performed with satisfactory results prior to its use. If a different rate is required, the Contractor must obtain a new JMF.
(C) Warm-Mix Asphalt Additives: Chemical additives that allow for lower mixing and placement temperatures. These additives are commonly categorized as: foaming agents, surfactants, or wax-based agents. The technician should always refer to the JMF to determine the type, rate required and the brand specified.
2.4.8 ASPHALT BINDER STORAGE
The asphalt binder storage capacity at the plant must be sufficient to allow uniform plant operation. Where more than one grade of asphalt binder is required for a project, at least one tank will be needed for each grade or the tank must be completely emptied before a different grade is added. Different grades must not be mixed.
Asphalt contents of storage tanks must be capable of being measured so that the amount of materials remaining in the tank can be determined at any time. This is necessary in order to determine the amount of an additive to be added, when required. They also must be heated to keep the asphalt fluid enough to move through the delivery and return lines; however, the maximum storage temperature should not exceed the supplier’s recommendation. Heating is done either electrically or by circulating steam or hot oil through coils in the tank. Regardless of the heating method used, an open flame must never come in direct contact with the tank or contents. Where circulating hot oil is used, the oil level in the reservoir of the heating unit should be checked frequently. A drop in the level could indicate leakage of the hot oil into the tank, leakage which results in contamination of the asphalt. All transfer lines, pumps and weigh buckets also must have heating coils or jackets so that the asphalt will remain fluid enough to pump. One or more thermometers must be placed in the asphalt feed line to ensure control of the asphalt temperature, as it is being introduced into the mixer or drum. The asphalt tanks must be equipped with a circulation system capable of uniformly dispersing and mixing additives throughout the total quantity of asphalt binder in the tank.
Adequate pumps must be furnished so that asphalt binder can be unloaded from tankers and still continue to operate the plant. A sampling valve or a spigot must be installed in the circulating system or tank to allow sampling of the asphalt. When sampling from the circulating system, exercise extreme care, as pressure in the lines may cause the hot asphalt binder to splatter.
Safety: Asphalt binder, if heated to a high enough temperature, will flash in the presence of a spark or open flame. The Minimum Flash Point temperature specified for all performance graded (PG) asphalts is 446°F (230°C). This temperature is well above the temperatures normally used in paving operations; however, to be sure there is an adequate margin of safety, the flash point of the asphalt should be known.
2.4.9 DELIVERY AND ACCEPTANCE OF ASPHALT MATERIALS
Obtain Performance graded asphalt binder (PGAB) only from sources participating in the Department’s Quality Control/Quality Assurance (QC/QA) program. The PGAB QC/QA program is designed to give Producers or Suppliers more responsibility for controlling the quality of material they produce and to utilize the QC information they provide in the acceptance process by the Department. It requires Producers or Suppliers to perform QC sampling, testing, and recordkeeping on materials they ship for use by the Department. Also, it requires the Department to perform QA sampling, testing, and recordkeeping to confirm the performance of the Producer’s quality control plan set forth in the QC/QA program.
require that asphalt materials used in asphalt pavement construction be tested and certified as meeting all applicable specification requirements. This certification for acceptance purposes is furnished with each delivered load of material, subject to certain conditions outlined in the specifications.
This Article of the specifications also requires that all asphalt transport tankers, rail, and truck tankers must have a sampling valve in accordance with Asphalt Institute Publication MS-18,
Sampling Asphalt Products for Specification Compliance
and ASTM D 140 or a comparable device acceptable to the Engineer. A picture of a typical sampling device is shown in Figure 2-2.
The sample must be taken from the sampling device on the transport tanker. Sample containers must be new and are available from the M & T Laboratory. Glass containers should not be used. The sample container should not be washed, rinsed out, or wiped off with oily cloths. The top of the container must fit securely. In obtaining a sample from the sampling valve, approximately 1 gallon (4 liters) of the asphalt material should be drawn from the valve and discarded for sampling purposes. The container should then be filled from the valve and the lid securely fastened to the container. Samples shall not be transferred from one container to another. The sample should then be forwarded to the Materials and Tests Unit with the appropriate sample identification cards.
This Article also outlines the information that is to be shown on load delivery tickets for all asphalt materials. Also included is an example statement of certification forms which must be included on the delivery ticket. The Contractor must furnish a ticket from the supplier, which includes a statement of certification of the grade and amount of asphalt material, including a statement relative to the brand, grade, and quantity or rate of anti-strip additive added to the material. In addition, a separate statement of certification that the tanker was clean and free of contaminating material is required from the transporter on the ticket. Each certification shall be signed by an authorized representative of the supplier or transporter. These certifications may be either stamped, written, or printed on the delivery ticket, or may be attached to the delivery ticket. Failure to include or sign the certifications by either the supplier or transporter will be cause to withhold use of the material until a sample can be taken and tested, except where an alternative testing and invoicing procedure has been preapproved by the Engineer.
It will not be necessary to fill out Materials Received Reports (MRRs) for asphalt binder or emulsions. All asphalt materials will be accepted by certification in accordance with
of the Standard Specifications and the following procedures. When a shipment of asphalt binder is received at the asphalt plant, a copy of the bill of lading will be furnished to the QA Supervisor, attached to the appropriate QC-1 report from that plant, and maintained in the appropriate plant file within the QA Lab. Detailed procedures for maintaining bills of lading for prime and tack coat materials are covered in
M&T Unit representatives will take verification samples from the asphalt terminals, which will be logged in and tested at the M&T central facility with results entered into an Asphalt Materials Database. If a sample fails but the failure is considered by the Engineer to be immaterial, the terminal will be notified of the test results and allowed to continue shipping, provided corrective action is taken. Samples will continue to be taken at the normal frequency.
If a sample fails and the failure is considered by the Engineer to be significant, the terminal will be notified of the results and they will be instructed to discontinue shipments and take corrective action. M&T will resample and retest the material at the terminal. Any materials from this batch in a Contractor’s storage tank will be evaluated for acceptability.
In the case of a significant material failure, the Engineer will send a failure notification form to all QA Supervisors. The QA Supervisors will review the bills of lading in their files to determine if they have received any material from that batch. If so, they will notify the appropriate Resident Engineers. They will then review the appropriate QC records for any possible related test deviations. The failure notification form will include an investigation section to be filled out by the QA Supervisor. They should include information concerning test deviations and any actions they took concerning or involving the Resident Engineers on this form and attach it to the appropriate bill of lading and QC-1 report in their file and send a copy to the Testing Engineer.
Resident Engineers will not be receiving direct notification of failures from the Engineer because there is no way he can determine who should receive the notifications. By sending these notifications to the QA Supervisors, a relatively small number of forms can be sent out and the appropriate Resident Engineers will be notified by the QA Supervisors. All actions taken by the QA Supervisors and Resident Engineers will be noted by the Asphalt Design Engineer in the binder database summary.
Performance-Graded Binder Grades (from AASHTO M 320)
2.4.10 TEMPERATURE-VOLUME RELATIONSHIPS OF ASPHALTS
As with all liquids and most solids, asphalt expands when heated and contracts when cooled. These changes in volume must be taken into consideration because, regardless of the temperature at which asphalt is shipped and stored, the basis for buying and selling asphalt materials, for making asphalt plant settings and mix design calculations is the asphalt's volume and specific gravity at 60°F (15.6°C).
The calculation involved is rather simple. It requires that two pieces of information be known:
• The temperature of the asphalt when used.
• The asphalt specific gravity or Group No. @ 60°F (15.6°C).
The asphalt temperature and specific gravity are used to locate the proper correction factor on one of the following tables. These tables have been in use for at least three decades and are the only data currently available for temperature corrections above 300°F (149°C). (See Figure 2-5)
When the Technician knows the asphalt temperature and the necessary correction factor, the following formula is used to calculate the asphalt volume at 60°F (15.6°C):
The following example illustrates how the calculation is made:
A truck has just delivered 5,000 gallons (19,000 liters) of asphalt at a temperature of 300°F (149°C). The Specific Gravity (Sp.Gr.) of the asphalt is 0.970. What would the asphalt's volume be at 60°F (15.6°C)?
Because the asphalt Specific Gravity is above 0.966, the tables for Group O (Figure 2-5) are used to find the correction factor. For 300°F (149°C), the correction factor listed is 0.9187.
Therefore, V60 = 5,000 gallons x 0.9187 V60 = 19,000 liters x 0.9187
= 4,594 gallons or = 17,455 liters
The volume of the particular asphalt at 60°F (15°C) is therefore, 4,594 gallons (17,455 liters).
|2.5 Mineral Aggregates|
The amount of mineral aggregate in asphalt paving mixtures is generally 90 to 96 percent by weight and 75 to 85 percent by volume. Mineral aggregate is primarily responsible for the load supporting capacity of pavement. Asphalt pavement performance is also heavily influenced by aggregate characteristics and properties. Mineral aggregate has been defined as any hard, inert mineral material used for mixing in graduated particles or fragments. It includes sand, gravel, crushed stone, slag, rock dust or powder. Aggregates may also include recycled materials, such as reclaimed asphalt pavement (RAP) or reclaimed asphalt shingle material (RAS).
2.5.2 SOURCES OF AGGREGATES
Aggregates for asphalt paving are generally classified according to their source or means of preparation. They include natural aggregate (pit or bank-run aggregates), processed aggregates (from quarries), synthetic or artificial aggregates (manufactured), and recycled aggregates. A listing of approved sources of aggregates may be obtained through the M&T Lab in Raleigh, N.C.
a. Natural Aggregates: Gravel and sand are natural aggregates and are typically pit or bank-run (river deposits) material. Exposed rocks are eroded and degraded by many processes of nature, both physical and chemical. The products of the degradation processes are usually moved by wind, water, or moving ice, and deposited as a soil material in various landforms.
b. Processed Aggregate: Processed aggregate includes both quarried aggregate and natural gravel or stone that has been crushed and screened to desired sizes. Natural gravel is usually crushed to make it more suitable for use in asphalt paving mixtures and to meet specification requirements for fractured faces. The quality may be improved by crushing, which changes the surface texture of the particles, changes the rounded particle shapes to angular shapes, and improves the distribution and range of particle sizes.
c. Synthetic or Artificial Aggregates: Aggregates resulting from the modification of materials, which may involve both physical and chemical changes, are sometimes called synthetic or artificial aggregates. They may take the form of the by-product that is developed in the refining of ore, or those specially produced or processed from raw materials for ultimate use as aggregate.
d. Recycled Aggregates: These are salvaged aggregates obtained from the reclaiming of existing pavements (both asphalt and concrete), from waste shingle manufacturing material, or from other sources. Normally, recycled aggregate from pavements are obtained by milling an existing pavement or by breaking up the pavement and then processing the material through a crusher. Waste shingle material is obtained by processing manufacturing waste by grinding and screening to acceptable sizes.
2.5.3 EVALUATING THE QUALITY OF AGGREGATES
To specify aggregate gradation, the 0.45 power gradation chart is used with control limits to specify the mix gradation limits and to develop a design aggregate structure. A design aggregate structure must pass between the control points. The maximum density gradation is drawn from the 100 percent passing the maximum aggregate size through the origin. Maximum aggregate size is defined as one size larger than the nominal maximum aggregate size. Nominal maximum size is defined as one size larger that the first sieve size to retain more than 10 percent. The design aggregate structure approach ensures that the aggregate will develop a strong, stone skeleton to enhance resistance to permanent deformation while achieving sufficient void space (VMA) for mixture durability. Standard sizes of coarse and fine aggregate are shown in Table 1005-1 of the Standard Specifications (See Table 1005-1 at the end of this Section). Other requirements for aggregates for asphalt pavements can be found in
of the Specifications.
Selecting an aggregate material for use in an asphalt pavement depends upon the availability, cost, and quality of the material, as well as the type of construction that is intended. Mineral aggregates play a key role in asphalt mix performance. Two types of aggregate properties are specified: source properties and consensus properties.
Source properties are those which are often used to qualify local sources of aggregate. These tests must be completed prior to allowing the use of any particular aggregate in an asphalt mix. These properties are determined on the
individual components rather than the aggregate blend. The source properties are:
(1) Toughness: Toughness is the percent loss of materials from an aggregate blend during the Los Angeles Abrasion test. The procedure is stated in AASHTO T 96, “Resistance to Abrasion of Small Size Coarse Aggregate by Use of the Los Angeles Machine.” This test estimates the resistance of coarse aggregate to abrasion and mechanical degradation during handling, construction, and in-service performance.
(2) Soundness: Soundness is the percent loss of materials from an aggregate blend during the sodium sulfate soundness test. The procedure is stated in AASHTO T 104, “Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate.” This test estimates the resistance of aggregate to weathering while in-service. It can be performed on both coarse and fine aggregate.
(3) Deleterious Materials: Deleterious materials are defined as the weight percentage of contaminants such as shale, wood, mica, and coal in the blended aggregate. This property is measured by AASHTO T 112, “Clay Lumps and Friable Particles in Aggregates.” It can be performed on coarse and fine aggregate.
Once the aggregate sources have been selected and the source properties approved for use in asphalt mixes, an aggregate blend will be determined. The aggregate blend will consist of the percentages needed to meet the Job Mix Formula. Once the blend is determined, the following consensus properties will be analyzed to determine if the blend conforms to NCDOT requirements.
Consensus properties are those properties which are critical in achieving high performance asphalt pavement. These properties are determined on the
aggregate blend rather than individual components. They are:
(1) Coarse Aggregate Angularity (Fractured Faces): This property ensures a high degree of aggregate internal friction and rutting resistance. It is defined as the percent by weight of aggregates larger than 4.75 mm with one or more fractured faces. Coarse aggregate angularity is to be determined in accordance with ASTM D 5821. The Specifications include the minimum requirements for coarse aggregate angularity for each mix type.
(2) Fine Aggregate Angularity: This property ensures a high degree of fine aggregate internal friction and rutting resistance. It is defined as the percent air voids present in loosely compacted aggregates smaller than 2.36 mm. Higher void contents mean more fractured faces. The test procedure used to measure this property is AASHTO T 304 (Method A). The Specifications include the minimum requirements for fine aggregate angularity (uncompacted void content) for each mix type.
(3) Flat and Elongated Particles: This characteristic is the percentage by weight of coarse aggregates that have a ratio of maximum to minimum dimension greater than a specified value. Elongated particles are undesirable because they have a tendency to break during construction and under traffic. The test procedure used is ASTM D 4791 (Section 8.4), “Flat and Elongated Particles in Coarse Aggregate” and it is performed on coarse aggregate larger than 4.75 mm sieve. The Specifications state that the maximum allowed Flat and Elongated Particles is 10% by weight at a 5:1 ratio for all mix types except S 4.75A, SF 9.5A, and S 9.5B.
(4) Clay Content (Sand Equivalent): Clay content is the percentage of clay material contained in the aggregate fraction that is finer than a 4.75 mm sieve. It is measured by AASHTO T 176, “Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test.” The sand equivalent value is computed as a ratio of the sand to clay height readings expressed as a percentage. The Specifications include the minimum sand equivalent requirements for each mix type.
(A) When aggregates are used for Portland cement concrete, asphalt treatment, and asphalt plant mix, the requirements pertaining to material passing the No. 200 sieve are as follows:
When tested during production, the amount of material passing the No. 200 sieve shall be no greater than 0.6%. When tested in a stockpile at the quarry site, the amount of material passing the No. 200 sieve shall be no greater than 1.0%.
When tested at the job site before use, the amount of material passing the No. 200 sieve shall:
be no greater than 1.5% for aggregate used in Portland cement concrete or asphalt surface treatment.
be no greater than 2.0% for aggregate used in asphalt plant mix.
If a stockpile at the job site is found to contain in excess of the specified amount of material passing the No. 200 sieve before use, the Engineer may approve its use provided:
For aggregate used in Portland cement concrete, the total percentage by weight passing the No. 200 sieve in the combined coarse and fine aggregate in the mix does not exceed 2.0%, and provided no increase in water-cement ratio is required by the use of this aggregate.
For aggregate used in asphalt plant mix, the total percentage by weight of minus No. 200 material in the plant mix being produced, as determined by the extraction test, can be maintained within the limits allowed by the job mix formula.
For ABC and ABC(M), in addition to the gradation requirements, the material passing the No. 40 sieve shall not have a LL in excess of 30 nor a PI in excess of 6. For ABC used in asphalt plant mix, when tested during production, in a stockpile at the quarry site or at the job site before use, the amount of material passing the No. 200 sieve shall be from 0.0% to 12.0% by weight and the gradation requirements for material passing the No. 10 sieve (soil mortar) required in
for ABC will not apply. For ABC not used in asphalt plant mix, the gradation requirements for material passing the No. 10 sieve (soil mortar) will be as required in
|3.1 Designing an Asphalt Pavement Structure (Thickness)|
Pavements constructed of asphalt mix are typically designed based on traffic projections over a 20 year period. Yet despite our best efforts, it is not uncommon to see severe rutting and cracking in asphalt pavements well before then as environmental conditions and heavy traffic loading take their toll. The result: rougher rides, higher user costs, higher pavement maintenance and rehabilitation costs, and more work zones for motorists to negotiate. In order to provide a pavement which will serve its intended purpose for a reasonable time at a reasonable costs, Engineers must utilize proper design procedures based on projected traffic over the design period and consider the environmental conditions, subgrade strength, material properties and other factors that will allow construction of a pavement that will perform satisfactorily. When designing and building a road for all-weather use by vehicles, the basic objectives are to:
(a) Have sufficient total thickness and internal strength to carry expected traffic loads.
(b) Prevent the penetration and/or internal accumulation of moisture, and
(c) Have a top surface that is smooth, skid resistant, and resistant to wear, distortion and deterioration by traffic, weather and deicing chemicals.
The subgrade ultimately carries all traffic loads; therefore, the structural function of a pavement is to support a wheel load on the pavement surface and transfer and spread that load to the subgrade, without over-taxing either the strength of the subgrade or the internal strength of the pavement itself. Figure 3-1 shows the wheel load being transmitted to the pavement surface through the tire. The pavement then spreads the wheel load to the subgrade which reduces the stress applied to the subgrade. Figure 3-2 shows how a wheel load, W, slightly deflects the pavement structure, causing both tensile and compressive stresses within the pavement. By proper selection of pavement materials and with adequate pavement thickness and strength, the stress at the bottom of the pavement will be small enough to be easily supported by the subgrade and the pavement will be able to resist the internal stresses caused by the loading.
Spread of Wheel-Load Through Pavement Structure
In determining pavement thickness, the following factors are considered:
(a) Traffic - The amount of traffic predicted to use the facility. The number of trucks predicted to use the highway is particularly important, as one pass of a tractor-trailer truck equals approximately 4,000 passenger vehicles;
(b) Soil Support Value - The soil subgrade strength, i.e., the type of soil of which the subgrade is composed - sand, clay, silt, etc.;
(c) Regional Factor - Accounts for the effect of various climatic conditions. For instance, the effect and number of freeze-thaw cycles in the mountain region will require a thicker pavement structure than the milder climate in the eastern part of the state;
(d) Strength and other influencing characteristics of the materials available or chosen or the layers or courses in the total asphalt pavement structure;
From these factors, a structural number is calculated. The structural number is an index number derived from an analysis of traffic, soil conditions, and regional factors. This number is used to determine the thickness of the total pavement and the thickness of the various layers. The following is a relative comparison of strength of various asphalt mix layers to each other and to other base types:
• 1 inch (25 mm) asphalt surface or intermediate layer
≅ 1½ inches (37.5 mm) asphalt base
• 1 inch (25 mm) asphalt surface or intermediate layer
≅ 3 inches (75 mm) aggregate base course
• 1 inch (25 mm) asphalt surface or intermediate layer
≅ 2 inches (50 mm) cement treated ABC
Obtaining the specified thickness of each pavement layer during construction is critical in order for the pavement to perform for the design life. As pavement thickness increases, small increases greatly extend the pavement life. For instance, one half inch (12.5 mm) less surface course potentially can reduce the pavement life from 20 years to 15 years. Therefore, the roadway technicians should be aware of the thickness required of each layer as specified by the plans and typical sections and the importance of obtaining that thickness in the completed pavement structure.
|3.2 Asphalt Mix Types|
An asphalt pavement structure consists of all courses or layers above the prepared subgrade or foundation. The upper or top layer(s) is the asphalt surface course. The surface course(s) may range from less than an inch (25mm) to several inches (mm) in thickness. The surface course is a high density layer designed to prevent penetration or internal accumulation of moisture. It is also designed to be skid resistant, resistant to wear, distortion, and deterioration by traffic, weather and deicing chemicals and is made using a relatively small maximum size aggregate. The layer placed immediately below the surface course is the intermediate course. The intermediate course is a high density material and is made using a slightly larger maximum size aggregate. When the expected traffic is very high or other conditions dictate, an asphalt base course may be utilized. The base is also a high density material and is made using an even larger maximum size aggregate. The base is an important structural strength element of a pavement. Its main purpose is to distribute traffic wheel loads over the subgrade and, therefore, is almost entirely designed for that purpose. Base course mixes can be constructed in relatively thick layers at a reasonable cost due to the large aggregate size and therefore, require a lower asphalt binder content. The thickness of the base course is usually dependent upon the overall strength requirements for a particular pavement based upon the anticipated traffic loading.
Listed in the following table are the asphalt mix types. The first letter of the mix type designation indicates the type of mix (Surface, Intermediate and Base), the number indicates the nominal aggregate size in millimeters, and the letter at the end indicates the level of traffic loading which the mix is designed to carry with satisfactory performance. Traffic loading is expressed in Equivalent Single Axle Loads (ESALs). As an example, an S 12.5 C mix is a surface mix with a nominal maximum aggregate size of 12.5 mm and a design loading of 3 to 30 million ESALs and will be produced using a PG 70-22 asphalt binder.
Asphalt Mix Types
ESAL Range (Million)||
Binder PG Grade|
|SA-1||Surface Course||Less than 0.3||64-22|
|S 4.75A||Surface Course||Less than 1.0||64-22|
|SF 9.5A||Surface Course||Less than 0.3||64-22|
|S 9.5B||Surface Course||0.3 to 3||64-22|
|S 9.5C||Surface Course||3 to 30||70-22|
|S 9.5D||Surface Course||More than 30||76-22|
|S 12.5C||Surface Course||3 to 30||70-22|
|S 12.5D||Surface Course||More than 30||76-22|
|I 19.0B||Intermediate Course||Less than 3||64-22|
|I 19.0C||Intermediate Course||3 to 30||64-22|
|I 19.0D||Intermediate Course||More than 30||70-22|
|B 25.0B||Base Course||Less than 3||64-22|
|B 25.0C||Base Course||More than 3||64-22|
|3.3 Pavement Layer Depth Guidelines (For Pavement Design Purposes)|
PAVEMENT LAYER DEPTH GUIDELINES (FOR PAVEMENT DESIGN PURPOSES) (1)
Single Lift Depths (Min. - Max.)
Max. Layer Total Depths|
|SA-1||0.5 - 1.0 in.||2.0 in.|
|S 4.75A||0.5 - 1.0 in.||2.0 in.|
|SF 9.5A||1.0 - 1.5 in.||3.0 in.|
|S 9.5 X||1.5 - 2.0 in.||3.0 in.|
|S 12.5 X||2.0 - 2.0 in.||4.0 in.|
|I 19.0 X||2.5 - 4.0 in.||4.0 in.|
|B 25.0 X||3.0
(3) - 5.5 in.||No Restrictions|
(1) From NCDOT Pavement Management Unit.
(2) Minimum layer thickness is at least 3 times the nominal maximum aggregate size.
(3) For B 25.0 X placed on unstabilized subgrade, minimum lift thickness is 4.0 in. (100 mm)
|3.4 Application Rates of Spread per Inch Depth|
Single Layer Thickness/Rate
|SA-1||100||0.75 in @ 75 lbs/sy|
|S 4.75 A||100||0.75 in @ 85 lbs/sy|
|SF 9.5 A||110||1.25 in @ 138 lbs/sy|
|S 9.5 X||112||1.50 in @ 168 lbs/sy|
|S 12.5 X||112||2.00 in @ 224 lbs/sy|
|I 19.0 X||114||2.50 in @ 285 lbs/sy|
|B 25.0 X||114||3.00 in @ 342 lbs/sy|
(1) Always refer to the contract and/or typical sections for the specified average rate and approximate depth.
(2) Approximate Minimum Thickness; lower rates may be used for leveling courses.
|3.5 Typical Asphalt Binder Contents (By Weight of Total Mix)|
PG 64-22 ||
PG 70-22 ||
PG 76-22 |
|SA-1||6.8%|| || |
|S 4.75 A||7.0%|
|SF 9.5 A||6.7%||S 9.5 C||5.9%||
S 9.5 D||5.7%|
|S 9.5 B||6.0%||S 12.5 C||5.6%||
S 12.5 D||5.2%|
|I 19.0 B & C||4.8%||
I 19.5 D||
|B 25.0 B & C||4.5%|| |
|OGAFC, Type FC-1||6.1%||
OGAFC, Type FC-1 Mod.||6.1%|
|PADC, Type P-57||2.5%|||
|PADC, Type P-78M||3.0%||OGAFC, Type FC-2 Mod.||6.1%||AQMSM-03-05||Approved|
|Example Roadway Typical Section||AQMSM-03-06||Approved|
|4.1 Introduction to Mix Design|
As stated in
, an asphalt mixture is composed of three basic components: 1) asphalt binder, 2) aggregates and 3) air voids. Mineral filler, additives, and other modifiers are used when needed or required. The asphalt material, which can be asphalt binder, modified asphalt binder, emulsified liquid asphalt or some other form of asphaltic material, acts as a binding agent to glue the aggregate particles into a cohesive mass. Asphalt Concrete is a paving material that consist primarily of asphalt binder and mineral aggregate and is mixed in an asphalt mix plant or by some other procedure. When bound by the asphalt binder, the mineral aggregate acts as a stone framework to impart strength and toughness to the system. Because it is relatively impervious to water, the asphalt binder also functions to waterproof the mixture. Because asphalt mix contains both asphalt binder and mineral aggregate, the volumetric properties and subsequently the behavior of the mixture is affected by the properties of the individual components and how they react with each other in the system. In order to determine if the behavior and performance of the mixture under traffic will be satisfactory, a mix design must be performed to determine the proper combination of the individual materials prior to beginning mix production.
|4.3 Performance Characteristics Considered in Mix Design|
Asphalt pavements function properly when they are designed, produced and placed in such a manner as to give them certain desirable performance characteristics. These characteristics contribute to the quality of asphalt pavements. These include permanent deformation (rutting) resistance, durability, flexibility, fatigue resistance, skid resistance, impermeability, workability and economics.
Ensuring that a paving mixture has each of these properties is a major goal of the mix-design procedure. Therefore, the technician should be aware of what each of the properties is, how it is evaluated, and what it means in terms of pavement performance. These properties are discussed below.
4.3.1 PERMANENT DEFORMATION (RUT RESISTANCE)
The ability of an asphalt mix to resist permanent deformation from imposed loads. Unstable mixes are marked by channeling (ruts), corrugations (washboarding), pushing and shoving in the pavement. Rut resistance is dependent upon both internal friction of aggregate and cohesion within the mix.
Internal friction is dependent on particle shape, surface texture, gradation of aggregate, density of mix, binder grade and quantity of asphalt. Rut resistance results from a combination of the frictional forces within the aggregate structure and the interlocking resistance of the aggregate in the mix. Frictional resistance increases with the surface roughness of the aggregate particles and with the area of particle contact. Interlocking resistance is dependent upon particle size and shape.
The figure above demonstrates that with more angular (cubical) particle shape and more contact between particles greater resistance to rutting and permanent deformation is achieved. For any given aggregate, the rut resistance increases with the density of the confined particles, which is achieved by dense gradations and adequate compaction. Excessive asphalt in the mix tends to lubricate the aggregate particles and lower the internal friction of the stone framework.
Cohesion is that binding force that is inherent in the asphalt mixes. The asphalt serves to maintain contact pressures developed between aggregate particles. Cohesion varies directly with the rate of loading, loaded area, and viscosity of the asphalt. It varies inversely with the temperature. Cohesion increases with increasing asphalt content up to a maximum point and then decreases.
Durability is how well an asphalt mix resists disintegration by weathering and traffic. Included under weathering are changes in the characteristics of asphalt such as oxidation, volatilization and changes in the pavement and aggregate due to the action of water, including stripping, freezing and thawing. Durability is generally enhanced by high asphalt contents, dense aggregate gradations, and well-compacted, impervious mixes. One argument for an increased amount of asphalt is the resultant thicker asphalt film coating around the aggregate particles. Thicker films are more resistant to age-hardening. Another reason for an increased amount of asphalt is to reduce the pore size of the interconnected voids or to seal them off in the mix, making it more difficult for air and water to enter the interior of the mix and cause damage. To resist the action of water, the same requirements (dense-graded aggregates, high asphalt contents, and adequate compaction) apply. It is desirable to use aggregates that retain an asphalt coating in the presence of water.
Sufficient asphalt must be incorporated in the mix to provide bonding properties adequate to resist the abrasive forces of traffic. Insufficient asphalt may result in aggregate being dislodged from the surface. This is known as raveling. Abrasion may also take place if the asphalt has become brittle. Overheating of asphalt in the mixing process is a cause of brittleness, which leads to pavement disintegration. A mix having a high asphalt content with voids completely filled with asphalt would provide the ultimate in durability. However, this would be undesirable from the standpoint of rut resistance. When placed in the roadway, the mix would rut and displace under traffic. Bleeding or flushing of asphalt to the surface would also take place, thereby reducing skid resistance.
Maximum rut resistance is not reached in an aggregate mass until the amount of asphalt coating the particles has reached some critical value. Additional asphalt then tends to act as a lubricant rather than a binder, reducing rut resistance of the mix, even though durability may be increased. It is necessary to compromise by keeping the asphalt content as high as possible while maintaining adequate rut resistance.
This is the ability of an asphalt mix to conform to gradual settlements and movements of the base and subgrade. Differential settlements in the fill embankment occasionally occur. Thus, it is impossible to develop uniform density in the subgrade during construction because sections or portions of the pavement tend to compress and settle under traffic. Therefore, the asphalt pavement must have the ability to conform to localized and differential settlement without cracking. Generally, flexibility of the asphalt mix is enhanced by high asphalt content and relatively open-graded aggregates.
4.3.4 FATIGUE (CRACKING) RESISTANCE
The ability of asphalt pavement to withstand repeated flexing of the pavement structure caused by the passage of wheel loads. Tests have shown that the quantity of asphalt is extremely important when considering the fatigue resistance of a pavement. As a rule, the higher the asphalt content, the greater the fatigue resistance. Tests indicate that low air-void content asphalt mixes have more fatigue resistance than higher air-void content mixes. Well-graded aggregates that permit higher asphalt content without causing flushing or bleeding in compacted pavement should be incorporated in the mix.
The ability of an asphalt surface, particularly when wet, to provide resistance to slipping or skidding of vehicles. The factors for obtaining high skid resistance are generally the same as those for obtaining high stability. Proper asphalt contents and aggregates with a rough surface texture are the greatest contributors. However, not only must the aggregate have a rough surface texture, it must also resist polishing. Aggregates containing non-polishing minerals with different wear or abrasion characteristics provide continuous renewal of the pavement's texture, maintaining a skid-resistant surface. Examples of non-polishing aggregates are granites, crushed gravel, silica sands and slag. An example of a polishing type aggregate is limestone. Mixes so rich in asphalt as to fill the voids in the compacted pavement will probably cause asphalt to flush to the surface, which is called bleeding. Asphalt on pavement surface can cause slippery conditions.
The ability an asphalt pavement to provide resistance to the passage of air and water into or through the pavement. While the void content may be an indication of the susceptibility of a compacted mix to the passage of air and water; of more significance is the interconnection of voids and their access to the surface. Imperviousness to air and water is extremely important from the standpoint of lasting durability.
4.3.7 LOW TEMPERATURE / SHRINKAGE CRACKING
The ability of an asphalt pavement to resist low temperature/shrinkage cracking. Low temperature/shrinkage cracking is caused by adverse environmental conditions rather than applied traffic loads. It is characterized by surprisingly consistently spaced transverse cracks (perpendicular to the direction of traffic). It is caused by a build-up of tensile stresses as the pavement shrinks due to extremely cold weather or due to shrinkage caused by oxidation (aging) of the pavement. Hard asphalt binders or binders which have hardened (oxidized) due to high void content in the as constructed mix are more prone to low temperature cracking.
The ease with which an asphalt mix may be placed and compacted. With careful attention to proper design and with the use of machine spreading, workability is not a problem. At times, the properties of the aggregates that promote high rut resistance make asphalt mixes containing these aggregates difficult to spread or compact and may promote segregation. Since workability problems are discovered most frequently during the paving operation, mix design adjustments should be made quickly to allow the job to proceed as efficiently as possible.
The cost of the in-place pavement must be considered. Mix components, production and placement costs, haul distances, safety considerations, quality, expected pavement performance and other factors need to be evaluated when selecting the final mix design.
|4.4 The Mix Design Process|
The mix design process is based on volumetric proportioning of the asphalt and aggregate materials and laboratory compaction of trial mixes using the Superpave Gyratory Compactor (SGC). The basic mixture design procedures consist of an evaluation of the following characteristics once the type and amount of traffic and the environmental conditions under which the pavement will be expected to perform have been determined:
4.4.1 AGGREGATE PROPERTIES AND GRADATION REQUIREMENTS
Aggregate physical properties for asphalt mixes are specified on the basis of both “consensus” (blend) properties and “source” (individual) properties. These criteria are discussed in more detail in
To specify gradation, the 0.45-power gradation chart is used with control points on various sieves to define a permissible gradation of the designated mix type. Control points function as master ranges through which gradations must pass. Control points are placed at the nominal maximum size sieve, an intermediate size sieve (2.36 mm), and the smallest sieve (0.075 mm). The control points vary, depending on the nominal maximum size of the mix. This chart uses a unique graphing technique to judge the cumulative particle size distribution of an aggregates blend. The vertical axis of the chart is the percent passing. The horizontal axis is an arithmetic scale of sieve sizes in millimeters, raised to the 0.45 power
An important feature of the 0.45-power chart is the maximum density gradation. This gradation plots as a straight line from the maximum aggregate size through the origin and uses the following definitions with respect to aggregate size:
Maximum Size: One sieve size larger than the nominal maximum size.
Nominal Maximum Size: One sieve size larger than the first sieve to retain more than 10 %
(Mix types are defined in terms of their nominal maximum aggregate size;
for example, an I 19.0C mix has a nominal maximum aggregate size of 19.0 mm.)
The maximum density gradation represents a gradation in which the aggregate particles fit together in their most dense possible arrangement. In general, this is a gradation to avoid because there will most likely be inadequate void space within the aggregate structure to allow adding adequate asphalt binder in order to develop sufficiently thick asphalt films for a durable mixture and still maintain the desired air void content. The design gradation should lie between the control points and meet the aggregate gradation requirements detailed in
4.4.2 ASPHALT BINDER GRADE SELECTION AND REQUIREMENTS
The binder grade selection process utilizes procedures that directly relate laboratory analysis with laboratory performance. In general, mix design guidelines specify that the binder grade to be used in a mix be initially selected based on the climate (average high and average low temperatures), in which the pavement will be performing. The guidelines then recommend the high temperature grade be adjusted (upward) based on other factors, such as the amount and type of traffic loading, operating speed of the traffic, and position of the pavement layer within the pavement structure. The designation, called Performance Grading (PG) contains two temperatures: the average 7 day high pavement temperature and the average 7 day low temperature. The high temperature is important because rutting failure occurs when the pavement is hot and becomes soft. Two other effects that increase rutting potential are very high traffic or very slow traffic. These factors increase the likelihood of rutting, and by raising the specified high temperature of the binder, the rut resistance will increase. The low temperature number indicates the low temperature cracking properties of the binder. The lower the second number, the greater the ability the binder has to resist cracking due to shrinkage caused by freeze/thaw cycles. These guidelines have been taken into consideration when specifying the binder grades to be used in the various mixes used in North Carolina. See
for the PG grade required for the various mix types specified by NCDOT.
PG 64-22 was selected as the “standard” grade for North Carolina based on climatic conditions.
4.4.3 MIXTURE VOLUMETRIC PROPERTIES AND REQUIREMENTS
A major factor that must be taken into account when considering asphalt mixture behavior is the volumetric properties of the mixture. Mixture volumetric requirements consist of air voids (VTM), voids in the mineral aggregate (VMA), voids filled with asphalt (VFA) and effective asphalt content (Pbe). These volumetric properties for NCDOT mixes are illustrated in Figure 4-2.
Air void content (VTM) is an extremely important property because it is used as the basis for selecting the asphalt binder content. The design air void content is usually 4.0 %; however, the mix designer should always check the specifications.
Voids in the mineral aggregate (VMA) is defined as the sum of the volume of air voids and effective (i.e., unabsorbed) binder in a compacted sample. It represents the void space between the aggregate particles. Specified minimum values for VMA at the design air void content of 4.0 % are a function of nominal maximum aggregate size.
shows mix VMA requirements.
Voids filled with asphalt (VFA) is defined as the percentage of the VMA containing asphalt binder. Consequently, VFA is the volume of effective asphalt binder expressed as a percentage of the VMA. The acceptable range of design VFA at 4.0 % air voids is a function of traffic level as shown in
Effective asphalt content (Pbe) is defined as the total asphalt content of a paving mixture minus the portion of asphalt absorbed into the aggregate particles (see Fig. 4-3).
Obtaining the correct air void content is critical in both mix design and the in-service performance of a pavement. As discussed in Section 2, asphalt binder expands and contracts with variations in temperature. In hot weather, air voids in the mix provide room for the expanding asphalt binder. If there are not enough voids within the mix to allow for the expansion, the asphalt binder expands to fill all existing voids, and then begins pushing the aggregate particles apart, reducing aggregate interlock and contact friction. This causes the pavement to become unstable, more susceptible to pushing, shoving, and rutting. The binder eventually may bleed or flush to the surface. This significantly reduces the skid resistance of the pavement.
Imperviousness to air and water is extremely important for the mix to be and remain durable. If the air void content is too high, the air voids may interconnect and allow water and air to penetrate into the mix. Water penetration may cause the asphalt binder to strip from the aggregate. Exposing asphalt binder to both water and air will cause it to oxidize more rapidly, causing it to become hard and brittle, and therefore resulting in early fatigue failure.
4.4.4 DUST TO EFFECTIVE BINDER RATIO
Another mixture requirement is the dust to effective binder ratio. This is computed as the ratio of the percentage by weight of aggregate finer than the 0.075 mm sieve (by washing) to the effective asphalt content expressed as a percent by weight of total mix. Effective binder content is the total binder used in the mixture less the percentage of absorbed binder. Dust / Binder Ratio is used during the mixture design phase as a design criteria. Specifications require the dust / effective binder ratio to be in the range of 0.6 to 1.4, inclusive, for all NCDOT asphalt mixtures.
4.4.5 MOISTURE SUSCEPTIBILITY
Moisture Susceptibility, also known as
stripping, is the separation of the asphalt film from the aggregate through the action of water and may make an aggregate material unsuitable for use in asphalt paving mixes. Such material is referred to as hydrophilic (water loving). Siliceous aggregates such as quartzite and some granites are examples of aggregates that may require evaluation of stripping potential. Aggregates that exhibit a high degree of resistance to asphalt film stripping in the presence of water are usually most suitable in asphalt paving mixes. Such aggregates are referred to as hydrophobic (water hating) aggregates. Limestone, dolomite, and traprock are usually highly resistant to asphalt film stripping. Why hydrophobic or hydrophilic aggregates behave as they do is not completely understood. The explanation is not as important as the ability to detect the properties and avoid use of aggregates conductive to asphalt stripping.
The moisture susceptibility test used to evaluate asphalt mix for stripping is
. This test serves two purposes. First, it identifies whether a combination of asphalt binder and aggregate is moisture susceptible. Second, it measures the effectiveness of anti-stripping additives.
4.4.6 PERMANENT DEFORMATION (RUT RESISTANCE)
One of the major objectives of mix design is to provide pavements which would be highly resistant to permanent deformation (rut resistance). As stated earlier, rut resistance is the ability of an asphalt mix to resist permanent deformation from imposed loads. This is especially important for surface mixes since this is where the wheel loads are concentrated and the potential for rutting is greatest. The aggregate and binder specifications are established such that a rut resistant mix should be obtained; however, once a mix has been designed based on the specified criteria, the mix should be physically tested to evaluate the anticipated performance under traffic. To accomplish this objective the Department will perform rut resistance evaluation on surface mix specimens prepared by the Contractor as a part of the mix design process.
In addition to the required mix design submittal forms, the Contractor will prepare and deliver six (6) Gyratory Compactor specimens to the Department’s Central Asphalt Laboratory for the following surface mix types: S4.75A, SF9.5A, S9.5B, S9.5C, S9.5D, S12.5C and S12.5D. The Contractor will prepare these specimens using lab produced mix in accordance with
. These specimens shall be compacted to a height of 75 ± 2 mm and to a void content (VTM) of 4.0% ± 0.5%
(except, S4.75A rut specimens should be compacted to a VTM of 5.0% ± 0.5%)
. These specimens will be tested for rutting susceptibility using the Asphalt Pavement Analyzer in the Materials and Tests Central facility. The maximum rut depth allowed for the various surface mixes is specified in
|4.5 NCDOT Mix Design Procedures|
The Contractor is required to design the asphalt mix and to obtain an approved Job Mix Formula (JMF) issued by the Department. A mix design and proposed JMF targets for each required mix type and combination of aggregates must be submitted both in writing and in electronic format to the NCDOT Asphalt Design Engineer for review and approval at least 10 days prior to start of asphalt mix production.
The mix design must be prepared in an approved mix design laboratory by a certified
Mix Design Technician. The design laboratory must be approved by the Asphalt Design Engineer prior to submission of the mix design. The mix design shall be prepared in accordance with AASHTO R 35, “Superpave Volumetric Design for Asphalt Mixtures” as modified by the Department, recommended procedures in the Asphalt Institute publication "Superpave Series No. 2 (SP-2, 3rd edition) Mix Design Manual” and the latest edition of Department mix design computer programs, policies, procedures, and forms. The request for the AMD/JMF approval will be submitted to the Mix Design Engineer on Form QMS-1 (see Page 4-19) with attached design data, proposed JMF target values, and forms as noted. In addition, the Contractor is required to submit the design data in electronic form using the Department’s mix design program.
Prepare all proposed mix design data in accordance with Department policies and procedures including but not limited to, the following information:
Source and percentage of each aggregate component to be used in the design aggregate blend gradation, including RAP and RAS.
Percentage of asphalt binder in RAP and RAS.
Gradation of each aggregates component, including RAP and RAS.
The following aggregate properties: current bulk specific gravity (Gsb
), current apparent specific gravity (Gsa
) and absorption of the individual aggregate components to be used when tested in accordance with AASHTO T84 and T85, except report the effective bulk specific gravity (Gse
) of RAP and RAS aggregate as determined by
. Report coarse aggregate angularity, fine aggregate angularity, flat and elongated percentages, and sand equivalent for the total aggregate blend.
Source(s), modification method, and percent of modifier by weight of asphalt binder, if modified.
Supplier, source, grade, and equi-viscous mixing and compaction temperatures of the asphalt binder. Determine equi-viscous temperatures using the rotational viscometer in accordance with ASTM D4402 corresponding to the following recommended viscosity ranges:
Range for mixing = 0.150 to 0.190 Pa-s
Range for compaction = 0.250 to 0.310 Pa-s
When PG 76-22 or other modified binders are used, base the temperatures on the documented supplier’s recommendations.
Brand name, manufacturer, shipping point, and percentage of anti-strip additive used in the mix design. Determine TSR data in accordance with
Target value for percent passing each standard sieve for the design aggregate gradation. Data will show the percent passing for all standard sieves listed in Table 610-1 for the specified mix type. Show the percentages in units of one percent of aggregate passing, except for the 0.075 mm (No. 200) sieve, show in units to one-tenth of one percent. Base percentages on the dry weight of aggregate determined in accordance with
NCDOT-T-11 and NCDOT-T-27
Volumetric properties of the compacted mixture calculated on the basis of the mixture's maximum specific gravity as determined by
. The mixture shall be aged in accordance with AASHTO R 30 and the bulk specific gravity of specimens determined by
, for each asphalt content tested. Determine and report properties in accordance with the requirements of AASHTO R 35 except as modified herein, and Department Mix Design Policies and Procedures.
(10) Graphical plots of percent asphalt binder by total weight of mix (Pb) versus the following properties at the design number of gyrations, Ndes, specified:
(a) SGC bulk gravity, Gmb @ Ndes
(b) % Gmm @ Nini
(c) Voids in total Mix (VTM)
(d) Voids Filled With Asphalt (VFA)
(e) Voids in Mineral Aggregate (VMA)
(f) % Compaction vs. Log of Gyrations
(11) Graphical plot of the design aggregate gradation (design blend) on FHWA 0.45 power chart showing the applicable control points, and maximum density line. Plot all standard sieves for the applicable mix type.
(12) Proposed target value of asphalt binder content by weight of total mix and specification design properties at that percentage.
When the mix design is submitted, include the original recording charts detailing the TSR results to the Asphalt Design Engineer in accordance with
. In addition, when requested by the Asphalt Design Engineer, the Contractor must submit representative samples of each mix component, including RAP, RAS, mineral filler, asphalt binder, chemical anti-strip additive and hydrated lime to the Department’s mix design laboratory.
In addition, the Contractor will prepare and deliver six (6) Gyratory Compactor specimens to the Department’s Central Asphalt Laboratory for the following surface mix types: S4.75A, SF9.5A, S 9.5B, S 9.5C, S 9.5D, S 12.5C and S 12.5D. These specimens are used for rut testing.
|4.6 The Job Mix Formula|
NCDOT Specifications require that all asphalt plant mixes, either virgin or recycled, be proportioned and graded such that they meet the requirements of a job mix formula approved and issued by the Department. This job mix formula will be based on a mix design performed by the Contractor and approved by the Materials and Tests Asphalt Lab. Once the Asphalt Design Engineer has evaluated and/or confirmed the data, the mix design will be approved if it meets specifications. The mix design and job mix formula target values must be within the design criteria for the particular type of asphalt mixture specified. The source and grades of material, blend proportions of each of the various aggregates used, specific gravity information, and other applicable data and notes will be given on the formula. Specific details on “Master” job mix formula procedures are discussed below.
Once the JMF has been approved and production is ready to begin, the component materials must be combined in such proportions that the completed mixture meets the specification requirements for the particular mix type specified. During production the materials are heated and blended together in an asphalt mix plant such that the mixture is uniformly mixed and coated with asphalt binder. The mixture is then transported to the roadway where it is spread, finished and compacted to the required grades, thickness and typical section required by the plans and contract.
The job mix formula (JMF) gradation target values will be established within the design criteria specified for the particular type of asphalt mixture to be produced. The JMF asphalt binder content will be established at the percentage which will produce voids in total mix (VTM) at the midpoint of the specification design range for VTM, unless otherwise approved. The formula for each mixture will establish the following: blend percentage of each aggregate fraction, the percentage of reclaimed aggregate, if applicable, a single percentage of combined aggregate passing each required sieve size, the total percentage (by weight of total mixture) and grade of asphalt binder required by the specifications for that mix type as in
unless otherwise approved by the Engineer, the percentage and grade of asphalt binder actually to be added to the mixture (for recycled mixtures), the percentage of chemical anti-strip additive to be added to the asphalt binder or percentage of hydrated lime to be added to the aggregate, the temperature at which the mixture is to be discharged from the plant, the required field density, and other volumetric properties.
The mixing temperature during production at the asphalt plant will be established on the job mix formula. The mixing temperature is based on the grade of asphalt binder required by the specifications for a specific mix type as in
, unless otherwise approved by the Engineer. The mixing temperatures will be different depending on which grade of asphalt binder is being used.
At the end of this section are examples of the currently approved computer generated mix design forms and supporting mix design data forms for the Contractor's use in preparing and submitting Mix Design/JMF request. The Contractor is required to use and therefore, must obtain from the Department, at no charge, the Mix Design computer spreadsheet program that will perform the calculations and generate the completed forms once the appropriate data has been entered. To obtain a copy of this spreadsheet, contact the Asphalt Design Engineer at
|Superpave Aggregate Gradation Criteria (Table 610-2)|
(Percent Passing Control Points)
Mix Type (Nominal Max. Aggregate Size) |
4.75 mm ||
9.5 mmA ||
12.5 mmA ||
19.0 mm ||
25.0 mm |
A. For the final surface layer of the specified mix type, use a mix design with an aggregate blend gradation above the maximum density line on the 2.36 mm and larger sieves.
B. For Type SF9.5A, the percent passing the 2.36 mm sieve shall be a minimum of 60% and a maximum of 70%.
|Superpave Mix Design Criteria (Table 610-3)||AQMSM-04-08||Approved|
|Maximum Recycled Binder Replacement Percentage (RBR%) (Table 610-4)|
MAXIMUM RECYCLED BINDER REPLACEMENT PERCENTAGE (RBR%)
|Recycled Material||Intermediate & Base Mixes||
Surface Mixes||Mixes Using PG 76-22|
|RAP or RAP/RAS Combination||45%||40%||18%|
|4.7 NCDOT “Master” Job Mix Formula Procedures|
Once a mix design for a specified mix type has been approved, and if the Asphalt Design Engineer is in concurrence with the design and proposed target values, the JMF data will be entered into the NCDOT HiCAMS computer system. This "Master" JMF will be for a specific plant and will serve for all projects on which that given JMF for the specified mix type is to be used. The Contractor will then place one copy of this AMD/JMF assembly on file at the asphalt plant QC field laboratory for use by all QMS personnel. It is suggested that a bulletin board, preferably with a glass enclosure or a durable notebook with transparent plastic sheeting be used for this purpose. In situations where the JMF is to be used for DOT work and no lab is present, the JMF should be placed on file in the plant control room.
This is the JMF that both the Contractor QC and the DOT QA personnel will be using for producing and testing the mixture, respectively. This JMF will possibly be used for a significant period of time and must be kept in a safeguarded manner. This posted copy will be readily available to all QC/QA personnel and will also serve for all projects until voided or revisions are authorized by the Asphalt Design Engineer or his representative.
When the Contractor is ready to begin producing mixture, he will advise the QA Supervisor which JMF he intends to produce. Inasmuch as there will very likely be several valid JMF's for a given mix type at each plant using different material sources and combinations, the Contractor must use caution to ensure that the appropriate materials as required by the formula are being used. In addition, he must ensure that the latest version of the formula is being used and the correct JMF number is being recorded on weight tickets. The QA Supervisor will compare his test results with this JMF for compliance with specifications.
As a JMF is revised in the field for whatever reasons, the Asphalt Design Engineer will send to the Contractor an updated copy showing the revisions and the effective date. The Contractor must make certain that these updated copies are posted in the field lab as quickly as possible and that the voided copies are removed. (There may be situations where verbal approval is given by the Asphalt Laboratory prior to the actual posting of the JMF data). While it would be desirable to have the valid JMF posted at the plant at all times, it is realized that delays due to mailing will occur. Verbal approval can be given in these situations but everyone must strive to keep this to a minimum. Master Job Mix Formulas for the standard mix types covered by the specifications will not be issued directly by the Asphalt Design Engineer for a specific project unless some special circumstance exists.
Included in this Manual are examples of both virgin mix JMF's and recycled mix JMF's. Note that the owner's name, plant location, and plant certification number shown on the JMF are the same as shown on the plant certification certificate. JMF's will indicate a specific anti-strip additive supplier, brand, and rate and must be used unless otherwise approved by the Engineer.
|4.8 Composition of Recycled Mixtures (JMF)|
When the Contractor elects to use a recycled mixture on a project, he must submit to the Department's Materials and Tests Unit his proposed mix design and JMF target values in accordance with
of the Standard Specifications and this Manual. The reclaimed asphalt materials (RAP or RAS) shall be tested for the following properties: (1) asphalt content, (2) aggregate gradation, (3) aggregate effective specific gravity, and (4) asphalt viscosity and performance grade (PG) of the RAP asphalt, if more than 30% RAP is proposed.
The gradation of the reclaimed aggregates is analyzed to determine the gradation of the virgin aggregates required. Using the gradation of the aggregate from the RAP material and the new aggregates, the approved design lab will design a combined gradation meeting the specifications. The asphalt content of the RAP material is used to determine the amount of asphalt binder to be added in the recycled mixture. The performance grade parameters of the asphalt in the RAP material (if more than 30%) will determine the required grade of the additional asphalt binder in the recycled mixture. The new asphalt binder added to the recycled mix serves two purposes. It increases the total asphalt content to meet the requirements of the mix and it blends with the aged asphalt in the reclaimed portion of the mix to yield an asphalt meeting the desired specifications.
Reclaimed asphalt pavement (RAP) may constitute up to 50% of the total material used in recycled mixtures, except for mix Type S 12.5D, Type S 9.5D, and mixtures containing reclaimed asphalt shingle material (RAS). Reclaimed asphalt shingle (RAS) material may constitute up to 6% by weight of total mixture for any mix. When both RAP and RAS are used, do not use a combined percentage of RAS and RAP greater than 20% by weight of total mixture, unless otherwise approved. When the percent of binder contributed from RAS or a combination of RAS and RAP exceeds 20% but not more than 30% of the total binder in the completed mix, the virgin binder PG grade shall be one grade below (both high and low temperature grade) the binder grade specified in
for the mix type, unless otherwise approved. When the percent of binder contributed from RAS or a combination of RAS and RAP exceeds 30% of the total binder in the completed mix, the Engineer will establish and approve the virgin binder PG grade. Use approved methods to determine if any binder grade adjustments are necessary to achieve the performance grade for the specified mix type.
For Type S 12.5D and Type S 9.5D mixes, the maximum percentage of reclaimed asphalt material is limited to 20% and shall be produced using virgin asphalt binder grade PG 76-22. For all other recycled mix types, the virgin binder PG grade shall be as specified in
for the specified mix type. When the percentage of RAP is greater than 20% but not more than 30% of the total mixture, use RAP meeting the requirements for processed or fractionated RAP in accordance with the requirements of
. When the percentage of RAP is greater than 30% of the total mixture, use an approved stockpile of RAP in accordance with
. Use approved test methods to determine if any binder grade adjustments are necessary to achieve the performance grade for the specified mix type. The Engineer will establish and approve the virgin asphalt binder grade to be used.
Samples of the completed recycled mixture may be taken by the Department on a random basis to determine the PG grading on the recovered asphalt binder in accordance with AASHTO M 320. If the grading is determined to be a value other than specified in
for the required mix type, the Engineer may require the Contractor to adjust the grade and/or percentage of additional asphalt binder, and/or the blend of reclaimed material to bring the grade to the specified value.
Once the total asphalt demand has been determined, the amount of new asphalt binder to be added in the recycled mixture is then calculated. This quantity equals the calculated asphalt demand minus the percentage of asphalt in the reclaimed asphalt pavement. Trial mix designs are then made using the mix design procedures to determine the estimated design asphalt content. The same design criteria are used for recycled mixes as are used with virgin mixes of the same type.
The Job Mix Formula will establish the percentage of reclaimed aggregate, the percentage of each additional aggregate required, a single percentage of combined aggregate passing each sieve size, the total percentage of asphalt binder in the mixture, a single percentage of additional asphalt material to be added, the percentage of chemical anti-strip additive to be added to the additional asphalt material or percentage of hydrated lime to be added to the aggregate, a single temperature at which the mixture is to be discharged from the plant, the required field density, and other volumetric properties. In addition, the Job Mix Formula will establish the blend ratio and percent binder in the RAP. Should a change in the source of virgin aggregate be made, a new job mix formula will be required before the new mixture is produced.
Should a change in the source or properties of the RAP be made, a new mix design and/or JMF may be required based on the requirements of
of the Standard Specifications (see Section 8.3
Samples of the completed recycled asphalt mixture may be taken by the Department on a random basis to determine the performance grading on the recovered asphalt binder in accordance with AASHTO M 320. If the viscosity is determined to be out of this specified range, the Engineer may require the Contractor to adjust the additional asphalt material formulation and/or blend of reclaimed material to bring the viscosity within the allowable range.
|4.9 Project File Job Mix Formula Procedures|
Job Mix Formulas (JMF) are maintained in the Highway Construction and Materials System (HiCAMS), including revised and voided JMF’s. HiCAMS automatically pulls information from the JMF to calculate the quantity of asphalt binder to be paid based upon the quantity of plant mix material placed and JMF in effect at the time the work is performed. Since copies of those JMF can be obtained at any time, the Resident Engineer is not required to maintain paper copies of the JMF within the project Files.
When a given JMF is revised, the void date will be entered on the voided formula by the Asphalt Design Engineer's office and this date will appear on all copies obtained through the computer after that date. The new or revised JMF will show the new number assigned and the effective date. This new JMF will be entered into the computer system and the cycle repeated as noted in the "Master" JMF procedures. Again, it is critical that the QC technician has the correct JMF number and shows same on his daily reports. If the JMF is revised, the technician at the plant will be advised of the new JMF number at that time and will note the revised number and date on the copy posted at the plant. This revised JMF will be used until the Contractor receives and posts the new JMF at the plant.
A listing of all Job Mix Formulas issued to a specific asphalt plant can be obtained from the local QA Supervisor. It should be noted that this listing shows all Job Mix Formulas issued to a plant including any "voided" formulas. Therefore, everyone must be careful to assure that the Contractor is using the most current JMF and not a voided formula.
4.9.1 MIX TYPE DESIGNATIONS
|Asphalt Concrete Surface Course, Type SA-1||SA-1||RSA-1|
|Asphalt Concrete Surface Course, Type SF 9.5 A||SF 9.5 A||RSF 9.5 A|
|Asphalt Concrete Surface Course, Type S 9.5 B||S 9.5 B||RS 9.5 B|
|Asphalt Concrete Surface Course, Type S 9.5 C||S 9.5 C||RS 9.5 C|
Asphalt Concrete Surface Course, Type S 9.5 D||S 9.5 D||RS 9.5 D|
|Asphalt Concrete Surface Course, Type S 12.5 D||S 12.5 C||RS 12.5 C|
|Asphalt Concrete Surface Course, Type S 12.5 D||S 12.5 D||RS 12.5 D|
|Asphalt Concrete Surface Course, Type I 19.0 B||I 19.0 B||RI 19.0 B|
|Asphalt Concrete Surface Course, Type I 19.0 C||I 19.0 C||RI 19.0 C|
|Asphalt Concrete Surface Course, Type I 19.0 D||I 19.0 D||RI 19.0 D|
|Asphalt Concrete Surface Course, Type B 25.0 B||B 25.0 B||RB 25.0 B|
|Asphalt Concrete Surface Course, Type B 25.0 C||B 25.0 C||RB 25.0 C|
4.9.2 JOB MIX FORMULA NUMBERING SYSTEM
Job Mix Formula numbers will be 9 digits with a 4 character code at the end. This is the number shown on the JMF posted at the plant and shown on all appropriate reports. Job Mix Formulas are accessible by QA Supervisors and Resident Engineers through HiCAMS.
where: xx = Calendar Year
yyyy = Sequential number assigned by HiCAMS System
a = plant number, (1 for 1st plant 2 for a 2nd plant, etc.)
b = anti-strip percentage (2 for 0.25%, 5 for 0.5% etc.)
c = JMF revision number
defg = Code for Mix Type (see the following Table)
|4.10 Asphalt Mix Design and Testing Calculations / Formulas|
(from Asphalt Institute’s, SP-2, 3rd ed.)
|5.1 Basic Operation of an Asphalt Plant|
Asphalt paving mixes made with asphalt binder are prepared at an asphalt mixing plant. Aggregates are blended, heated and dried, and mixed with asphalt binder to produce a hot asphalt paving mixture. The mixing plant may be small and simple or it may be large and complex, depending on the type and quantity of asphalt mixture being produced. The plant may be stationary (permanent) or portable.
|5.2 Types of Asphalt Plants|
Asphalt plants are basically of three general types:
(1) Batch plant; (2) Drum mix plant; (3) Continuous mix plant
The specifications include specific equipment requirements for each type plant. However, the two most common types of asphalt plants are
batch plants and
drum mix plants and will be discussed in detail in this manual. Continuous mix plants are not covered, since these are very similar to Batch Plants. They are essentially batch plants that are controlled by the cold feeds.
|5.3 Certification of Asphalt Plants|
All plants used to produce asphalt mix for DOT projects are certified by the Division of Highways as meeting the requirements of the specifications. The initial inspection for plant certification will be made by the Asphalt Design Engineer or his representative upon request from the Contractor. A certificate of compliance, (Figure 5-1), including a copy of the certification checklist, will be issued to the plant owner. The Certificate
shall be displayed in the plant control room. This certification is effective from the date of issuance and is non-expiring, subject to continued compliance. Any plant which is significantly modified, relocated or which changes ownership must be recertified prior to use and a new certificate issued.
A list of all certified Asphalt Plants is available by contacting the Asphalt Laboratory or using the “Producer/Supplier” website at:
Changes in certifications and the addition of new certifications will be updated in the system as they occur by the Asphalt Design Engineer. Updated listings will be furnished periodically to each Division QA Supervisor, or to anyone upon request.
At the beginning of each season, and any time deemed necessary by the Engineer, each plant site will be checked for compliance with the specifications. This check will be performed by the QA supervisor or his representative and documented in writing in a daily log or diary. When QA Supervisors find anything out of compliance with the specifications, it should be documented in writing. The Contractor and the Asphalt Design Engineer shall be notified immediately.
This certification covers all plant equipment, including recycling equipment. This certification does not certify the Contractor’s Quality Control Laboratory nor does it ensure the plant’s mix quality. Field Lab tests performed during production is required to ensure mix quality. The plant certification also doesn’t ensure accuracy of weighing devices. Refer to the appropriate section of this manual for specific requirements of weighing devices.