Hot-Mix Asphalt Sampling Techniques and Methods of Acceptance - State DOT's Practice

Hot-mix asphalt (HMA) sampling is a critical step in quality control and quality assurance (QC/QA) programs to ensure that the tested material is representative of the installed product. Samples of HMA in Illinois are currently taken from a truck at the plant. This sampling method allows for a quick turnaround time since the QC laboratory is usually located at the plant. However, it may be difficult to obtain a representative sample since most of the sample is taken from the top of the pile and on the side closest to the sampling platform. In addition, this sampling method does not account for any additional asphalt absorption taking place during transportation and placement. The concept of moving the sample location to the job site offers the potential to address the weaknesses cited above. However, there are a number of different approaches, each with advantages and disadvantages. The objective of this study was to produce a review of successful methods and practices currently used to sample HMA during production and installation. This included visiting other states and collecting sufficient data to draw a final recommendation for the optimum technique to be adopted for HMA sampling in Illinois. The conclusion of the field visits is that sampling behind the paver is being successfully conducted by many states without difficulty. Based on the site visits conducted in this study, the roadway sampling procedure adopted by Michigan DOT was recommended for possible implementation in Illinois. In addition to this sampling technique, sealed bags adopted by Iowa DOT may be used, if necessary, to safely transport samples from the field to the laboratory.