Low Temperature Crack Resistance of Stone Mastic Asphalt Affected by Its Nominal Maximum Size and Asphalt Binders

To study the effect of nominal maximum particle size (NMS) of stone mastic asphalt (SMA) gradation and a mixed modified asphalt binder on the low temperature crack resistance of SMA, SMA asphalt mixtures with three different NMS, two styrene-butadiene-styrene (SBS) and crumb rubber modifier (CRM) hybrid-modified asphalt binders were designed.Thermal strength restrained specimen test (TSRST) and bending beam test (BBT) were performed on the mixtures. The freezing-fracture temperature and strength from TSRST, bending tensile strain and stiffness from BBT at low temperature were evaluated. Finally, an intrinsic relationship was established between these properties obtained from the two tests. The results showed that the following: (1) the SMA-5, the best of all the three NMS, has a freezing-fracture temperature of −31.5 °C, which is 18.9% and 48.6% lower than those of SMA-10 and SMA-13, respectively, while its freezing fracture strength is 6.15 MPa, which is 95.2% and 243.6% higher than those of SMA-10 and SMA-13, respectively; (2) the bending failure strain of SMA-5 is 4649 με, which is higher than those of SMA-10 and SMA-13 by 11.3% and 21.9%, respectively; (3) increased CRM dose in the SBS-modified SMA improves the crack resistance at low temperature; (4) the bending failure strain of the SMA has the best correlation with the freezing-fracture temperature, with a correlation coefficient of about 0.8.