460.1 Quality Control/Quality Assurance
Under QC/QA, the contractor does the quality control (QC) testing while MoDOT does the inspection and quality assurance (QA) testing to verify the QC results. MoDOT is also responsible for independent assurance sampling (IAS) to verify that both QC and QA are performing the testing correctly. The contractor is paid based on the results of the QC tests. In addition, the contractor controls the materials, mix, and the plant and paving operations. The approved quality control plan (QC Plan) for Superpave mixes shall include the contact information of the contractor’s QC representative, lot and sublot sizes and how they will be designated, the test method for determining asphalt binder content, the number of cores to be cut for density determination, and the independent third party for dispute resolution. A QC Plan is not required for bituminous base (BB) and pavement (BP) mixes.
The inspector will do less sampling and testing, allowing more time for actual inspection. The inspector also has the authority to require the contractor to conform to the approved QC Plan as a part of the contract. The contractor's technicians and the MoDOT inspectors will be certified technicians, having demonstrated proficiency in sampling and testing the mix for the properties required in the QC/QA specifications.
Occasionally, the QC test may not represent the population or, due to individual differences in sampling and testing procedures, the QA and QC test results may not compare within the required limits. One of the first steps in resolution could be an immediate computation check, comparison of sampling and testing procedures, or split sample retests. Testing of the QC split sample or joint sampling and testing could determine if variations in the mix production or sampling and testing procedures are responsible for the differences. If resolution is not possible at the project level, either party may request that the approved independent third party test the mix. Third party test results will be binding upon both parties. The party whose results were incorrect will pay for the third party testing. Third party testing is costly and time consuming and should only be used when project level reconciliation is not possible.
It is not intended that any mix be produced outside the specification limits. Operating out of the specifications may reduce the contractor's pay and/or the pavement service life. When QC tests are out of specification tolerances, the contractor should adjust the production to bring the mix back in. When QA tests are out of specification tolerances, the contractor should be notified immediately. The contractor is responsible for deciding when adjustments are made to control the mix. Some test properties may be allowed to deviate beyond specification limits occasionally, provided that adjustments are made and the following tests show that production is back within limits.
Production may be required to cease if the QC or QA test results are either out of specifications far enough to indicate that the mix may be subject to failure or beyond the specification removal limits. Production should cease until the problem is corrected. An order record should be written describing the deficiency and the location and amount of mix affected. The contractor may elect to continue production in order to run more tests. If so, the order record should state that any mix produced after the order record was issued is at the contractor’s risk. Final disposition of the mix can then be made based on all tests and observations and may consist of acceptance at a reduced price or removal and replacement.
Superpave mixes contain a quality level analysis with statistically based incentive/disincentive pay factors. The QC tests are analyzed on each lot of mix and the pay is based on the percentage of the mix that statistically falls within the limits of the specifications. It is possible to have a given lot of mix with all tests falling within the specifications, but because of a large amount of deviation between test results, the percent within limits would be very low, giving the contractor a correspondingly low pay factor. Very consistent test results, with a correspondingly low standard deviation and high percent within limits, will produce high pay factors. Test results that are consistent may produce bonus pay factors while those that fluctuate within the specification limits will produce low pay factors.