An experimental study on the micromechanical behavior of pumice

Abstract

Pumice has a large potential to be used in structural and geotechnical engineering projects as a lightweight aggregate, and it is a material of unique characteristics. Gravel-sized pumice from Yunnan, China, was examined in the present study with a custom-built micromechanical apparatus investigating the properties of pairs of grains at their interfaces subjected to monotonic and cyclic tests under different saturation states. Based on interferometer measurements, the vesicular surface of the pumice was characterized to be very rough. From the interface micromechanical experiments, it was shown that the virgin surfaces appeared to be very soft under normal loading tests, during which micro-asperity breakage was caused. After preloading and preshearing, the normal load–displacement curves became much smoother and the Young’s moduli, which remained relatively low in magnitude compared with other geo-materials previously studied, could be quantified applying the Hertzian model. Large hysteretic loops were observed from cyclic normal load tests. Plastic displacements dominated the first normal loading cycle, while elastic displacements prevailed in the subsequent cycles. High values of the apparent coefficient of friction were observed from the monotonic shearing tests. A modification of the power value of the Mindlin and Deresiewicz model was necessary to be applied during the fitting of the experimental data so that theoretical and laboratory curves could match. It was shown that this power had a direct correlation with the coefficient of friction.