Optimum Design of Mixture Proportion and Microscopic Analysis of Cement-Stabilized Macadam by Rubber Powder and Fiber

Abstract

Abstract Based on the orthogonal test method, the mixture proportion design of cement-stabilized macadam (CSM) modified with rubber powder and fiber is studied. With strength and dry-shrinkage as key indices, the influence of length of polyvinyl alcohol (PVA) fiber, fiber content, particle size of rubber powder, and rubber powder content on the performance of CSM is analyzed, and the optimum mixing proportion is determined. Based on this, the modification mechanism of CSM by rubber powder and fiber is further studied from a micro perspective. The results show that the 7-day unconfined compressive strength of CSM gradually increases with the increase of fiber length. With the increase of fiber content, the compressive strength shows a trend of first increasing and then decreasing. The 7-day unconfined compressive strength of CSM gradually increases with the increase of rubber powder mesh size and linearly decreases with the increase of rubber powder content. The 28-day average dry-shrinkage coefficient of CSM shows a trend of first decreasing and then increasing with the increase of fiber length and fiber content, and gradually increasing with the increase of rubber powder mesh number and rubber powder content. Considering the strength and shrinkage characteristics, the optimum mixing parameters are 40 mesh rubber powder, 0.5 % rubber powder, 18-mm fiber length, and 1.2-kg/m3 fiber content. Scanning electron microscopy results show that there is a gap between the rubber powder and the cement matrix, and the interface between the two is discontinuous, with weak bonding, resulting in a decrease in the compressive strength of CSM. PVA fiber can improve the toughness of CSM. It has good adhesion with cement matrix. It forms a three-dimensional network support structure in the CSM mixture and can restrain water loss in the cement matrix, thus greatly improving the cracking resistance of CSM.