Testing the influence of filler type and content on thermal cracking of mastic

Abstract

Low-temperature cracking significantly affects durability of asphalt pavements. This research addresses the role of the mastic phase by experimentally evaluating the low-temperature cracking performance of selected bitumen and mastics with different filler types and contents. Their thermal contraction coefficient (αT), low temperature viscoelasticity, and strength properties are measured using standard tests like the dynamic shear rheometer (DSR) and fracture toughness tests (FTT). An enhanced laboratory technique, the annular restrained cold temperature induced cracking (ARCTIC) test, is employed to study combined thermal and mechanical effects on low-temperature cracking. The alignment of FTT with ARCTIC results highlights a good correlation between these methods for mastics with nearly the same αT. However, the insensitivity of FTT to αT raises concerns about its applicability to materials with significantly different αT, as it may not capture accurately their performance. The ARCTIC test is free of such a problem and even shows a higher sensitivity to the mastic composition. The findings demonstrate that the addition of filler significantly affects the resistance of mastic to low-temperature cracking by altering its αT. Additionally, the filler content, type, and gradation distinctly impact the thermal and mechanical characteristics of mastics, enhancing their ability to withstand lower temperatures more effectively than bitumen. In particular, adding 50% by volume of different filler types reduces the αT of mastic by 45 to 60% and results in 3 to 10 °C reduction in cracking temperature (Tcr) measured with the ARCTIC test.