Effect of Naturally Occurring Salts on Tensile and Shear Strength of Sealed Granular Road Pavements

Abstract

Areas affected by dryland salinity in Australia are predicted to more than double over the next 40 years as a result of land use and climatic changes. This presents a significant risk to road asset managers because the concentration of salts within road pavements has been shown to cause damage to pavements and surfacings. The present study explores the impact of dryland salinity on road pavements by assessing the effect of naturally occurring salts on the tensile and shear strength of a sealed granular pavement. Microstructure analysis techniques using scanning electron microscopy and mercury intrusion porosimetry were employed to analyze tested specimens to explain the physical mechanisms that occur as a result of salt concentration. The presence of natural salts was found to have a positive effect on granular pavements but a negative impact on bituminous surfacings. While in solution, salts were found to have a very small positive effect on the tensile strength of the pavement material, which is likely related to clay chemistry interactions. Upon crystallization, salts were observed to form bonds within the pores of the pavement material, which led to a significant increase in tensile strength and a moderate increase in shear strength. However, at the interface between the surfacing and the pavement material, whisker-shaped crystals were observed to grow from the bitumen. Interestingly, the chemical composition of the two types of crystals observed was found to be completely different, despite occurring within the same specimens, under the same conditions. The implications of these findings for road pavements in high-saline areas are also discussed.