Q1. Does the Form 312-R need to be signed by the contractor prior to submittal to the Mix Design Engineer?
Q2. Do test data results need to be submitted when submitting a new mix design for approval?
A2. Yes, when there is no previous history of the mix or if any major changes are made as defined by
Section 1000-3 of the specifications.
Q3. Who needs to submit the 312-R form to the Mix Design Engineer?
A3. The projects Resident Engineer.
Q4. How many days in advance should a concrete mix design submittal be sent to the Concrete Mix Design Engineer?
A4. A minimum of 30 days in advance.
Q5. What if the aggregate source supplying aggregate at my plant is not on the NCDOT approved list?
A5. You can not produce for NCDOT and must get an approved source to supply your plant with aggregate in compliance with NCDOT Specifications.
Q6. Do I need to record the actual batch quantities and the individual batch weights?
A6. Yes, all quantities and weights must be computer generated or hand printed, but must be recorded for each batch produced (policy letter dated August 29, 2000).
Q7. What certification do I need to batch concrete for NCDOT?
A7. All batchers who produce concrete for NCDOT, must keep a current Concrete Field Technician and Concrete Batching Technician Certification.
Q8. If my Concrete Batch Technician Certification is current, do I need to keep my Field Technician Certificate current?
A8. It is
mandatory to keep both certifications current or you will have all certifications revoked.
Q9. Question: Do I need to perform a moisture content on coarse aggregate?
A9. Yes, the certified batcher is required to perform moisture contents by the drying method on both fine and coarse aggregate a minimum of twice a day or whenever deemed necessary. These moisture calculations are to be recorded, documented and stored with the producer’s copy of the batch weight tickets.
Q10. What if the moisture the batcher computes is different from the moisture the computer indicates?
A10. The batcher must have the capability to change/update the moisture contents for both fine and coarse aggregate
prior to batching. This correction is to be performed at the batching facility and not at the central dispatch location.
Q11. What if the moistures are not changed in the computer?
Q11. The batcher and plant certifications will be investigated. Pending the investigation, disciplinary actions may be implemented towards the facility.
Q12. Does the batcher need to review the approved mix design?
A12. Yes, the certified batcher is responsible for all production of concrete. All sources of materials should be correct on site and approved by NCDOT. If any producer / facility source on the mix design is different than on site, you must submit a new mix design or get the approved materials.
Q13. What paperwork is required on the materials?
A13. The plant is responsible for and must supply current copies of certifications for all cement, fly ash, slag, fine and coarse aggregates, all admixtures, and the water source. In addition, all sources must be on the “NCDOT Approved List”.
Q14. How does the DOT keep track of mix designs?
A14. By use of two electronic databases. The Concrete Mix Design database is a plant-by-plant list of mix designs accepted for each plant. Data on each mix design includes mix number, class, proportions, mix properties, material sources, and material properties. Acceptance of a mix design in this database does not constitute its acceptance for any contract. Assignment of mix designs to contracts involves a separate submittal, review and acceptance procedure via the Concrete Mix Contract Assignment database. Mix designs must be in the Concrete Mix Design database to qualify for assignment to a contract.
Upon written request from the Engineer for specific mix designs to be assigned to a contract, the Physical Testing Engineer reviews and assigns these mix designs in the Concrete Mix Contract Assignment database. This database shows the list of mix designs assigned to each contract. Requests for mix design approval for contracts outside the scope of HiCams are handled similarly except that the Concrete Mix Contract Assignment database is not used, in which case approved hard copies are returned to the Engineer for distribution.
Q15. How do I submit a mix design for the Mix Design database?
A15. Complete Materials and Tests
Form 312U (English units only) and e-mail it to the Materials and Tests Concrete Mix Design Engineer and carbon copy the
Structural Materials Laboratory Engineer.
Q16. How do I submit mix designs for a contract?
A16. It is the contractor’s responsibility to submit such requests to the DOT Resident Engineer administering the contract. The contractor should request the concrete producer to complete M & T
Form 312R, Mix Design Request Form, for each plant he plans to use to supply concrete and forward these forms to him for submittal to the Engineer.
Q17. My ACI Certification is good for another year, but my Field Technician certification expired this year. May I continue to test concrete and batch concrete for another year (provided my Batch Certification is good for another year)?
A17. Once the Field Technician Certification expires, all DOT certifications associated with it expire. While the ACI certification may still be current, NCDOT requires a current Field Technician certification for testing sampling and producing concrete. The ACI is a component of the Field Technician certification.
Q18. My truck driver who is field tech certified informed me the concrete was not sampled properly during acceptance testing by project personnel. What should I do?
A18. Once an error of this type is exposed, immediately notify the project personnel. In addition, inform the M&T Concrete Technician of the problem. Document the specific procedure you feel was run incorrectly. Keep a record including date, ticket number, project, and structure where the concrete is placed.
Q19. Do I physically have to be present in the batch room when concrete is batched for a NCDOT project? May I be on the premises, monitoring the batch process via two-way radio?
A19. The batcher must be physically present during batching of concrete on a NCDOT project. The certified batcher should be the one actually batching the concrete, not supervising someone who is not certified.
Q20. I just discovered the wrong mix design was used to batch concrete for a NCDOT project. Whom do I notify about this mistake? Will I lose my certification?
A20. Once an error of this type is discovered, immediately notify project personnel. The M&T concrete technician should also be informed of the error. Depending on the circumstances, the error will not necessarily lead to loss of your certification. The batcher should still maintain all required documentation. The
M&T 903 form should reflect the mix design that was used. The worst possible thing to do in this case is to attempt to alter records to cover up the mistake.