Stress Relaxation and Creep Nanoindentation for Cement Paste

Abstract

Feedback-controlled statistical-based nanoindentation creep and stress relaxation tests are performed on cementitious material to characterize the viscoelastic properties. Closed-form linear viscoelastic analytical solutions are derived based on the elastic–viscoelastic correspondence principle to study the creep and stress relaxation response. The solution developed to model the relaxation behavior is inverted in the transform domain to obtain the creep response, thus cross-validating the stress relaxation solution. The viscoelastic properties obtained from testing hardened cement paste and standard polycarbonate indicate strong agreement between the measured and fit data. The creep compliance curve developed as the inverse of stress relaxation function shows good correlation with creep compliance curves obtained by the analytical viscoelastic solution. Additionally, the nanoindentation-based stress relaxation test appears to provide more converged data compared with creep tests; hence, the study proposes nanoindentation as an additional and efficient tool to characterize the stress relaxation of cementitious materials.