Measuring and modeling the time-dependent response of cementitious materials to internal stresses.

摘要

Recent advances in shrinkage modeling have worked toward modeling autogenous and drying shrinkage as mechanical responses to internally applied stresses. In this thesis, previous modeling work is extended such that autogenous shrinkage of cement paste is considered as a viscoelastic response to internally applied stresses. In addition, concrete shrinkage is modeled from a composite approach considering the viscoelastic properties of the cement paste matrix and the complex paste-aggregate interaction that results in internal stresses affecting the composite deformation. Finally, permeability is indirectly measured by considering the short-term time-dependent response of saturated cementitious materials to hydrostatic pressure as related to internal stresses and the rate of fluid flow within the material. The primary finding from this thesis is that the transient deformation of concrete or cement paste may effectively be modeled as a mechanical response to internally applied stresses. In certain cases, it is necessary that the aging, viscoelastic properties of the cement paste be accounted for. To this end, the viscoelastic constitutive properties of four cement pastes and concrete mixtures have been measured and modeled using two different constitutive models. Measured viscoelastic properties from multi-axial compression were not in full agreement with results from uniaxial compression, which provides some insight into the mechanisms of time-dependent behavior of cementitious materials.