Published online by Cambridge University Press: 25 February 2011
Submicroscopic cracking within cement paste is studied for monotonic and short-term sustained loading. Loading times range from 1.25 minutes to 4 hours. Water cement ratios of 0.3 and 0.5 are used. Specimens are loaded to preselected strains and immediately unloaded. The specimens are then sliced with a diamond saw and viewed in a scanning electron microscope. Crack traces are cataloged based on length, width and orientation. The crack traces are converted to three dimensional crack distributions, which are in turn used to determine the degree of softening due to cracking. The results indicate that for loading to a fixed strain, slow loading results in less cracking than rapid loading. However, at the same stress-strength ratio, rapid loading results in fewer cracks. The results indicate that the role of submicroscopic cracking in the nonlinear behavior of cement paste increases with strain rate.