Prediction of Asphalt Cement Content of Compacted Hot-Mix Asphalt Specimens Using Nuclear Gauges

Determining asphalt cement (AC) content of hot-mix asphalt (HMA) for quality control/quality assurance using extraction methods is a lengthy, time-consuming, and hazardous process. A demand for a faster and safer method led to the development of different nuclear gauges capable of predicting the AC content of HMA samples. Measuring the AC content of compacted specimens by nuclear gauges is a new technique whose feasibility was evaluated. A total of 216 Marshall compacted specimens were cast and tested in an attempt to develop correction models. The study program investigated the effect of various HMA parameters on the measured AC content, including aggregate gradation and type, air void content, moisture content, AC content, and specimen weight. Specimens were prepared at two different mix design formulas using AC-30 and compacted at two different compaction efforts to investigate the effect of air voids. Specimens (1200 g each) used for calibration were prepared at 3 to 7 percent AC content, whereas specimens prepared for measurements were prepared at 4 to 6 percent. Quartzite and diabase aggregate were used as open and dense graded in prepared mixes. Three levels of moisture content in HMA were evaluated. Different calibration models were developed for different asphaltic mixtures. The evaluated nuclear gauge for measuring AC content for compacted HMA specimens produced satisfactory results when the parameters of tested and calibration parameters were the same. The study found that specimen weight is the most significant factor. Other parameters have different degrees of influence on the measured AC content. Statistical models were developed to correct for the evaluated parameters.