Characterization of surface mechanical properties of various aggregates from micro scale using AFM

Abstract

In this study, the micromechanical properties of aggregates, including the surface energy, nanohardness, and elastic modulus, were investigated using an atomic force microscope (AFM). The Surface energy was quantitatively evaluated by applying a surface energy model, whereas the surface nanohardness and elastic modulus were quantitatively evaluated using the contact-mechanics model. Further, the effects of the aggregate chemical composition and limewater treatment on the surface micromechanics were explored. Four natural aggregates, one recycled concrete aggregate (RCA), and one recycled brick aggregate (RCB) were used for the experiments, for every aggregate, we investigated two states, the original state and that after the limewater treatment. Results showed that the alkaline components (Al2O3 and CaO) on the surface of the aggregate have a positive effect on surface energy, whereas the acidic component (SiO2) has a negative effect. The difference in aggregate composition results in the surface energy of the original basalt, limestone, and diabase being three to four times those of the original granite, RCA, and RCB, respectively. Therefore, after limewater treatment, the surface energies of basalt, diabase, granite, and RCA increased by 18.20%, 12.73%, 71.61%, and 95.45%, respectively, whereas those of limestone and RCB decreased by 10.06% and 8.56%, respectively. The increase in SiO2, Al2O3, and CaO contents have a positive effect on nanohardness and a negative effect on elastic modulus. After limewater treatment, the nanohardness of limestone was found to have increased, whereas those of the remaining five aggregates (basalt, diabase, granite, RCA, and RCB) had decreased. The CaCO3 attached to the aggregate surface, causing the nanohardness (1.5–7.0 GPa) and elastic modulus (21–32 GPa) of the six aggregates to approach each other.