660-1 DESCRIPTION
This section of the Specifications covers all types of asphalt surface treatments (AST). Surface treatments consist of one or more applications of an asphalt material and one or more applications of aggregate cover material on a prepared surface.
Surface treatment provides a waterproof cover over its base and provides resistance to the abrasion of traffic. It is not intended in itself to greatly increase the strength of the base or pavement.
Surface treatments have many functions. They will provide long-lasting economical surfaces for granular base roads having light and medium traffic volumes. They will help prevent surface water from penetrating granular bases and old pavements that have become weathered or cracked. Surface treatments will plug voids and also coat and bond loose mineral aggregate particles. They will renew a surface and restore skid resistance to traffic on pavements in which the surface aggregates have become polished. They are sometimes used to provide delineation and rumble effect between mainline pavements and shoulder pavements. Mat coats may be used as a crack absorbing layer between an existing concrete pavement and asphalt overlay.
660-2 MATERIALS
The Technician should always refer to the Special Provisions in the contract since in some instances the specific grade of asphalt and/or size of aggregate and application rates will be specified. When the grade of asphalt material and/or aggregate to be used is not specified in the Special Provisions, this article gives a list of materials from which the Contractor may select with certain restrictions. See
Sections 1012 and
1020 of the Materials Division of the Specifications for aggregate and binder requirements (see also
Table 660-1 in the Standard Specifications).
Clean aggregate is extremely important in surface treatment work. If the aggregate particles are dusty or coated with silt or clay, the asphalt may not bond, since the dust produces a film which prevents adhesion to the aggregate. See the remarks and footnotes concerning AST aggregates in
Table-1005-1 of the Standard Specifications.
660-3 WEATHER AND SEASONAL LIMITATIONS
Weather conditions are critical to the successful placement of surface treatments. Hot and dry weather is best for the application of surface treatments. The surface of the base must be dry in order to obtain satisfactory results from the application of the asphalt material. The combination of water or wet surface, fresh surface treatment, and traffic will result in the loss of the cover aggregate.
Should the Contractor feel that there are extenuating circumstances and justifications to waive the seasonal restrictions, he should be advised to make written request to the Engineer giving such circumstances and justifications. Upon receipt of any such request, the Engineer should forward the Contractor's request along with his own recommendations and reasons for such recommendations to the Division Engineer.
660-4 SURFACE PREPARATION
The surface to be treated must be clean of all foreign and deleterious matter and must be dry before the asphalt material is applied. This is essential to the successful performance of surface treatment. The surface is normally cleaned by the use of a rotary broom and a certain amount of handwork may be necessary in order to properly clean a base or surface. Any damaged or defective areas in a primed surface should be repaired prior to the application of the asphalt material.
660-5 ACCEPTANCE OF ASPHALT MATERIALS
The Department reserves the right to sample and test any asphalt material shipment regardless of whether a certification is furnished. If the material appears questionable, it should be sampled. The asphalt emulsions should not be diluted or mixed with water, solvents, or other materials prior to application.
660-6 APPLICATION EQUIPMENT
An asphalt distributor is typically used to apply the asphalt emulsion to the existing surface prior to the application of the aggregate. Refer to
Article 600-5 of the Specifications and this
Manual for the requirements of the distributor.
A self propelled, pneumatic-tired aggregate spreader is used in conjunction with the distributor on surface treatments. A spreader in good working condition and properly operated will conserve aggregate and produce a uniform spread. The self propelled spreader provides a uniform and continuous application of cover aggregate and is able to keep up with the asphalt distributor. Aggregate trucks dump their load into a receiving hopper in the rear of the spreader and are pulled along by the spreader as it moves forward. Belt conveyors carry the aggregate to the front of the spreader machine where it is dropped into a spreading hopper.
The spreader must be capable of spreading the aggregate over the full lane width of the applied asphalt material in a single pass.
660-7 APPLICATION OF ASPHALT MATERIALS
When the grade of asphalt material is not specified in the Special Provisions, the Contractor may select any grade of asphalt shown in
Table 660-1 for the type of treatment being constructed. The rates of application are based on asphalt material at the application temperatures specified.
The Technician should make certain that the asphalt material is being applied uniformly and at the temperature and within the rates specified in
Table 660-1. A lack of adequate asphalt material in surface treated pavements, including paved shoulder construction, contributes greatly to the loss of the cover aggregate when exposed to traffic. The correct grade, amount and temperature of the asphalt material will when being applied be fluid enough to spray properly and cover the surface uniformly but will be viscous enough to remain in a uniform layer. It also will not puddle in depressions or run off the crown and after rolling and curing will hold the aggregate tightly to the road surface to prevent dislodging by traffic and will not bleed or strip with changing weather conditions.
660-8 APPLICATION OF AGGREGATES
This article of the Specifications gives the aggregate size and application rate for each type mat or seal of coat (see
Table 660-1). This article also gives the Engineer the authority to require the Contractor to weigh a sufficient number of loads of aggregate prior to spreading to verify that the rate of application is within the required limits indicated in this table or the Special Provisions.
The cover aggregate shall be spread uniformly, immediately after the asphalt application. This is of utmost importance in obtaining adequate retention of the aggregate when exposed to traffic. The aggregate must be applied before the asphalt begins to “break.” The aggregate cannot be applied too quickly but can most definitely be applied too late. This requires enough trucks loaded with the aggregate to be standing by and careful planning and coordination by the Contractor so that there will be no delays once the asphalt is applied. Careful timing and coordination are absolutely necessary to produce the desired results.
Immediately after application, the aggregate should be set in place by rolling to produce a smooth, tight surface of even texture. As soon as the asphalt has a definite set or hardening, rolling should be discontinued so that the roller will not break the bond between the surface and the aggregate.
660-9 CONSTRUCTION METHODS
(A) ASPHALT MAT COAT
The surface upon which mat coat or seal coat is to be applied must be clean. Cleaning is normally accomplished by the use of a power rotary broom. It may sometimes be necessary to utilize blowers and flushing equipment to clean a surface prior to the asphalt application. The surface should also be dry prior to the application of asphalt material.
It is a requirement of this article of the Specifications that a string line be placed by the Contractor and used as a guide for application equipment unless otherwise permitted by the Engineer.
The nozzles of the spray bar should be kept clean and properly adjusted at all times. If one or more nozzles should become blocked during application, the distributor must be stopped and the nozzles cleaned out.
All mat coat and seal coat shall be placed in full lane widths unless otherwise permitted by the Engineer. When asphalt materials are applied for less than the full width of the treatment, a suitable longitudinal joint should be provided. To prevent aggregate from building up on the longitudinal joint, the edge of the aggregate spread should coincide with the edge of the full thickness of applied asphalt. This allows overlapping of the partial thickness of applied asphalt when the adjacent width is sprayed with asphalt. The partial thickness is a result of the outside nozzle spray being only partially overlapped. The width of the asphalt strip left exposed varies depending upon the nozzle spacing and the lap pattern used. If possible, the longitudinal joint should be along the centerline of the pavement being treated. An established line ensures a straight longitudinal joint. Anticipated aggregate needed for the intended treated area should be on hand before starting the asphalt application. When the distributor moves forward to spray asphalt, the aggregate spreader should follow immediately behind. The sprayed asphalt should be covered with aggregate as soon as possible but in no case should more than 5 minutes elapse before coverage begins.
Rolling must be done immediately after the aggregate has been uniformly spread. Rolling seats the aggregate in the asphalt and thus promotes the bond necessary to resist traffic stresses.
This article of the Specifications requires the initial coverage to be done with a steel wheel roller. The Technician should closely observe the beginning of this initial coverage to determine if the aggregate is being crushed appreciably. If crushing is occurring, the use of a lighter steel wheel roller should be required. The rolling is then completed with a pneumatic-tired roller. The coat should be rolled until the aggregate is properly seated. As soon as the asphalt has a definite set or hardening, rolling should be discontinued to prevent the bond between the surface and the aggregate being broken by the roller. Rolling normally begins at the outer edge of the surface treatment and proceeds in a longitudinal direction working towards the center of the road. Each trip with the roller should overlap the previous trip by about
1/2 the total width of the roller wheels. The Engineer may direct other rolling patterns.
In beginning the distribution of each load of asphalt material, the proper joint shall be made with the preceding application. Building paper or other suitable material shall be spread at all starting points in order that the distributor nozzles may be operating at full force when the asphalt application begins and ends. This same procedure should be followed at intersections and junctions with other pavements. The paper should be removed immediately after use and properly disposed of by the Contractor. Excess asphalt material should be removed or corrected in a satisfactory manner. Irregular areas which cannot be covered with asphalt material directly from the distributor spray bars shall be covered by means of a hand hose equipped with a nozzle.
In applying asphalt material adjacent to structures, the Contractor should use effective means of protecting the structure from spray by asphalt material.
This article of the Specifications states that traffic may be permitted on the mat coat immediately after the rolling is complete. The excess aggregate should be broomed off prior to placement of traffic to prevent damage to vehicles from loose aggregates. Speed of the traffic should be restricted to
25 miles per hour or less for several hours.
(B) ASPHALT SEAL COAT
This article of the Specifications specifies the construction methods that are to be used in the construction of all seal coats.
The Engineer should refer to the contract to determine the size of aggregate and the type of seal coat that is required by the contract for each section to be sealed.
The seal coat aggregates should have been tested and approved prior to their incorporation into the seal coat. They should be drained of all free moisture. It is important that the aggregate be clean. If aggregates are dusty or coated with silt or clay, a film is present which will prevent proper asphalt adhesion. Good adhesion between aggregate and asphalt and retention of this adhesion are essential to surface treatment success. Best adhesion is obtained when aggregates are clean and reasonably dry. Some moisture can be tolerated in warm, dry weather that promotes rapid drying.
The width of seal coat construction, joint construction, and application of asphalt and aggregate shall be as explained previously in
Subarticle 660-9(A) of the Specifications and this
Manual.
Rolling for all seal coats shall be accomplished as described in the following paragraph, except that only the pneumatic-tired roller shall be used on sand seal.
Rolling shall be done immediately after the aggregate has been uniformly spread. Initial rolling shall consist of one complete coverage with a steel wheel roller after which pneumatic-tired rollers shall be used. Rolling shall continue until the aggregate is thoroughly keyed into the asphalt. A final coverage with the steel wheel roller may be required to provide a satisfactory finished surface. The use of rollers that result in excessive crushing of the aggregate will not be permitted. The rollers shall be designed to prevent picking up the material. The use of combination steel wheel and pneumatic- tired rollers will not be permitted. Two individual rollers shall be used.
When directed by the Engineer, the Contractor shall apply blotting sand in accordance with the provisions of
Section 818.1)
Straight Seal
Straight seal is a term used to describe a treatment that consists of one application of liquid asphalt and one application of aggregate. The thickness of the treatment is about the same as the nominal maximum size of aggregate particles. It is essential that the aggregate is clean and that it be spread before the liquid asphalt begins to break or set. If the aggregate is excessively damp, no retention will develop until it dries.
Excess aggregate should be broomed from the surface immediately after the initial set of the asphalt and before traffic is placed upon the seal if possible. Brooming is usually best accomplished early in the day when the pavement surface and the asphalt binder are cool.
2) Split Seal
Split seal is a double application of asphalt and aggregate followed by rolling, as noted previously.
Immediately after the first application of seal aggregate has been made uniform, the remainder of the required amount of asphalt material and seal coat aggregate shall be applied and the seal coat shall be rolled as previously described.
3)
Triple Seal
Triple seal is a triple application of asphalt and aggregate followed by rolling as noted previously.
4)
Slurry Seal
Slurry Seal is a mixture (slurry) of aggregates and asphalt emulsion that is applied by a spreader in a single thin layer.
5)
Sand Seal
The full-required amount of asphalt material shall be placed in one application and immediately covered with the seal coat aggregate. The full required amount of aggregate shall be uniformly spread in
one application and all non-uniform areas shall be corrected prior to rolling.
Immediately after the aggregate has been uniformly spread, rolling shall be done as previously described.
When directed by the Engineer, excess aggregate material shall be broomed from the surface of the seal coat.
When the sand seal is to be constructed for temporary sealing purposes only and will not be utilized by traffic, other grades of asphalt material meeting the requirements of
Articles 1020-6 or
1020-7 may be utilized in lieu of the grade of asphalt required by
Table 660-1 when approved by the Engineer.
(C) ASPHALT MAT AND SEAL
The mat coat shall be constructed in accordance with
Subarticle 660-9(A) using the size aggregate required by the contract.
The seal coat shall be constructed in accordance with
Subarticle 660-9(B) using the type seal required by the Project Special Provisions.
(D) CAPE SEAL
The seal coat shall be constructed in accordance with
Subarticle 660-9(B) using the size aggregate required by the contract.
The slurry seal shall be constructed in accordance with
Subarticle 660-9(B)(4) using the type slurry seal required by the Project Special Provisions.
660-10 MAINTENANCE AND PROTECTION
The Contractor is responsible for the maintenance and protection of surface treatment until such time as the Department accepts the work for maintenance. He should make all necessary repairs immediately to the satisfaction and under the supervision of the Engineer.
660-11 MEASUREMENT AND PAYMENT
Surface treatments will be paid on a square yardage basis. In measuring the quantity, the number of square yards will be determined using the actual length constructed and the width required by the project plan details or as directed by the Engineer.
A replacement of satisfactory completed surface treatments made necessary by defects in the subgrade or base which were constructed by others will be paid for under this article.
No reduction in compensation will be made when the Engineer directs the application rates of asphalt material to be less than the minimum indicated in
Table 660-1 of the Specifications.
Blotting sand will be paid for as provided in
Article 818-4 of the Specifications. It should be noted that additional payment would not be made for blotting sand where the blotting material is a component of any Asphalt Seal Coat, Asphalt Mat and Seal, or Cape Seal.
ADDITIONAL RESOURCES
