Laboratory observation of engineering properties and deformation mechanisms of cemented rubber-sand mixtures

Abstract

This paper presents details of a study that deals with investigation of compression behaviors, stiffness properties, and microstructural characteristics of lightly cemented and uncemented rubber-sand mixtures. The rubber-sand mixtures specimens were prepared with various sand volume fractions to evaluate its effects on the engineering properties. The specimens were subjected to different levels of vertical stress under K0 condition and the shear wave velocity (Vs) was measured simultaneously by bender elements during the compression process. Investigations were carried out with respect to the effect of sand fraction and the level of vertical stress on the overall rubber-sand mixtures properties including stress-strain characteristics, Vs, and small strain shear modulus (G0). In addition, scanning electron microscopy analysis was conducted to understand the variations in microstructure and the deformation mechanisms controlling the changes in engineering properties of the cemented rubber-sand mixtures. The study reveals that sand fraction has a considerable influence on the mass density (ρ), stress-strain characteristics, and stiffness properties of cemented and uncemented mixtures. These changes are attributed to the remarkable difference of engineering properties between shredded rubber and sand particles. The vertical strain presents three behavior regions as a function of stress in semi-log scale for lightly cemented rubber-sand mixtures: bonding control, bonding degradation, and stress control. Residual strain of the specimen decreases with an increase in sand fraction, and its value of cemented specimen is much lower than that of uncemented specimen. The Vs and G0 dramatically increase with an increase in sand fraction and vertical stress. A good linear relationship is proposed between Vs and vertical stress for uncemented rubber-sand mixtures. Additional loading of the vertical stress decreases the increment of Vs as a result of bonding degradation. The response of stress-strain and Vs can be employed as indicators of cementation degradation. Two different deformation mechanisms: rubber particles deformation and the force chains generated by sand particles were proposed for rubber-sand mixtures with different sand fractions. Rubber particles sustain loads and suffer a dramatical shape change when mixtures with a small amount of sand, whereas they play an important role in preventing the buckling of sand particle chains with high sand fraction.