Volume and deviator creep of calcium-leached cement-based materials

This paper provides new experimental evidence of the specific volume creep and deviator creep of cement-based materials. Creep tests conducted on calcium-leached cement pastes and mortars under various triaxial loading conditions provide conclusive evidence of a specific short-term creep and a specific long-term creep. It is found that at least two competing dissipative mechanisms are at work in short-term creep of cement-based materials: (1) a creep relaxation mechanism in the calcium–silicate–hydrate (C–S–H) solid phase activated by microstress concentrations in the heterogeneous microstructure; and (2) stress relaxation by microcracking beyond a relatively small stress threshold. If the first dominates over the second, the short-term volume creep is contracting, and in the inverse case, a short-term dilating behavior is found. Furthermore, provided that microcracking stabilizes during the short-term creep, the long-term creep occurs at constant volume. Based on these results, we argue that the concept of a creep Poisson's ratio, which is commonly employed in engineering practice to extrapolate uniaxial creep tests to multiaxial stress conditions, should be abandoned when triaxial stress states affect the durability performance of concrete structures.