Impact of Clay Contamination on Rutting Performance of Asphalt Mixtures

Natural sands improve the sustainability of asphalt mixtures by enhancing workability and lowering the required asphalt binder and manufactured fine aggregates. One of the primary concerns with incorporating natural sands in a mixture is the potential for clay contamination. Harmful active clays swell when in contact with moisture and diminish the bonding between the aggregate and asphalt binder. This paper investigates the impact of clay contamination on the performance of asphalt mixtures with respect to rutting and moisture susceptibility. Twenty-one combinations of passing no. 200 sieve (minus 0.075 mm) material with various contamination levels were prepared using inactive (i.e., calcium carbonate and dolomite) and active (i.e., bentonite and natural) clays. The methylene blue value (MBV) was used to classify the level of chemical activity of those combinations. Each of the 21 permutations was added to a reference Superpave mixture to produce asphalt mixture specimens. The rutting and moisture susceptibility of each mix were then evaluated by subjecting them to Hamburg wheel tracking tests. X-ray diffraction (XRD) was also used to characterize the mineral composition of the inactive and active clay materials used for this study. The experimental results showed that mixtures having a MBV above 6 mg/g are most likely to suffer rutting and moisture damage. Moreover, XRD testing corroborated that the active clays used in this study contained detrimental minerals to asphalt mixture performance, such as sulfuric acid, quartz low, and microline.