A Method for Predicting Asphalt Mixture Compactability and Its Influence on Mechanical Properties (0-5261-2)

This project aimed at providing better understanding of the factors affecting the uniformity and level of compaction; and the performance of asphalt pavements. TxDOT research report 0-5261-1 documented some of the findings of this research project. This research report documents the efforts and findings of experiments conducted with more test sections. In the first phase of this report, a number of field test sections were compacted, and field cores were extracted. These cores were scanned using X-ray Computed Tomography (X-ray CT) to capture the air void distributions in these cores. The air void distribution correlated well with the compaction effort across the mat. The compaction effort was found to be a function of the number of roller passes and the relative location of each pass across the mat. The Compaction Index (CI) developed in the TxDOT research report 0-5261-1 was used to quantify the compaction effort at any point in the pavement. This index combines the number of roller passes along with the effectiveness of each pass on the mat. The compactability of asphalt mixtures in the field correlated well with compactability of asphalt mixtures in the laboratory. The CI was used to quantify the compactability of asphalt mixtures in the field while the slope of the compaction curves obtained from Superpave Gyratory Compactor was used to quantify the compactability of asphalt mixtures in the laboratory. In the second phase of this report, the effect of different levels of compaction on the performance of asphalt mixtures was studied using a fracture mechanics approach and DEM models. The results showed that test specimens with less percent air voids performed better that the ones with higher percent air voids. In addition moisture-conditioned specimens performed worse than the dry ones at the same compaction levels. Furthermore, guidelines were developed to assist in predicting the compactability in the field based on laboratory measurements during the mixture design stage; and to improve the field compaction.