Comparative Performance of the SMAC Made with the SBS- and ST-Modified Binders

Styrene-butadiene-styrene (SBS) and starch (ST) have been used by many to modify asphalt cement and to improve the properties of asphalt concrete. In this investigation, SBS and ST were used to modify asphalt cement. The basic properties of modified asphalt binders and stone mastic asphalt concrete (SMAC) containing such asphalt binders were studied and compared with those of asphalt cement. Marshall stability, Marshall Quotient, tensile strength, tensile strength ratio, rutting resistance, flexural strength, and resilient modulus were carried out on the SMAC. A mechanistic-empirical design approach was used for estimating the improvement in service life of the pavement or reduction in thickness of SMAC and base layer for the same service life due to modification the SMAC. In addition, an optimization table was prepared to select the type of SMAC for any field applications. The analyzes of test results show that the performance of SBS-modified SMAC is slightly better when compared to ST-modified SMAC. The temperature susceptibility can be reduced by the inclusion of SBS and ST in the SMAC. The results of multilayer elastic analysis presented herein indicate that the pavement consisting of SBS and ST-modified SMAC as a surface layer is beneficial in reducing the construction materials. Actual savings would depend upon the option exercised by the designer for reducing the thickness of an individual layer.