Comparative Study on Performance of Wax-Modified and Typical SMA Mixtures

Abstract

Stone-matrix asphalt (SMA) is a type of hot-mix asphalt that can reduce the cost of maintenance and rehabilitation of pavements through decreasing the amount of permanent deformation during its service life. In addition, warm-mix asphalt (WMA) has been recently used to reduce the mixing and compaction temperatures of asphalt concrete and potentially decrease the initial cost of asphalt mixtures, especially in countries for which energy costs are high. The primary purpose of this research is to combine these technologies to produce more efficient asphalt mixtures. To this end, two different additives [cellulose fiber and styrene-butadiene-styrene (SBS)] were used to construct typical SMA mixtures, and a type of WMA additive (wax) was used to prepare warm SMA specimens. Modified binders were subjected to binder properties tests. Mixture performance tests, including the Marshall, indirect tensile strength, moisture susceptibility, dynamic creep, and resilient modulus tests were also performed to evaluate the performance properties of different types of SMA mixtures. A mechanistic-empirical design procedure was conducted to investigate the benefit of modification. The results indicate that Fischer-Tropsch (FT) wax is capable of enhancing the base binder properties. Although different percents of wax could reduce the amount of binder drain down, this reduction was not adequate. Consequently, the use of an additional additive may be necessary. The effect of wax on the performance properties of SMA mixtures was also insignificant, although there were some improvements. Moreover, by comparing the test results, good correlations were obtained between various performance properties of SMA mixtures, all of which were significant. The use of cellulose fiber, SBS, and FT wax would respectively increase the service life of the pavement 1.08, 1.243, and 1.154 times more than the corresponding unmodified mixtures.