New Mix Design Method for Hot-Mix Cold-Laid Mixtures

Hot-mix cold-laid (HMCL) asphalt mixes are crucial for maintaining asphalt pavements via blade-on/level-up patching. While the Superpave Gyratory Compactor (SGC) is widely used for hot-mix asphalt mixes due to its adjustable parameters and manageable compaction densities, the HMCL mix design still follows the Hveem mix design method, as per the Texas Department of Transportation (TxDOT) specification Item 334, using a Texas Gyratory Compactor. This study proposes a new HMCL mix design method that employs an SGC. This study examined five types of HMCL mixes, consisting of binders and aggregates commonly used in the industry. For each mix, three levels of binder content were determined following the TxDOT specification Item 334. These 15 laboratory-mixed HMCL mixes were then used to mold SGC specimens with four different compaction levels to establish the design gyration for SGC laboratory-molded densities in the range of 94.0 ± 1.5 percent. The study also found that the current specification may include mix designs with low compatibility. Specifically, the Hveem stability test in the specification was sometimes not sensitive to mix designs, leading to weak correlations with field performance. In developing a new mix design method, the Cantabro mass loss and IDEAL cracking and rutting tests were employed to characterize the resistance of mixes to raveling, cracking, and rutting. Binder contents significantly affected these test results. Moreover, mixes with low compactability were able to be excluded during testing specimen preparation. Therefore, the new HMCL mix design method using an SGC improved the current HMCL mix design method.