Compressive strength of cement paste as a function of loading rate: Experiments and engineering mechanics analysis

Uniaxial compressive strength of cement paste increases with increasing loading rate. Two experimental campaigns are described: 2-day-old cement paste samples are tested by using quasi-static stress rates. 6-month-old and oven-dried cement paste samples are tested by using quasi-static and high-dynamic strain rates. As for the analysis of the former tests, we develop a nonlinear viscoelastic-brittle model. It explains our test data very well, and it suggests that strength decreases with decreasing loading rate, because the duration of the test increases and this provides the possibility for creep-related damage mechanisms to reduce the strength of the material. As for the analysis of the latter tests, we develop an elasto-brittle model considering crack propagation, at the Rayleigh wave speed, in loading direction. The model is free from fitting parameters and explains our measurements very well, indicating that high-dynamic strength increase is a structural effect.