Dimensional change and elastic behavior of layered silicates and Portland cement paste

The role of water in hydrated Portland cement paste (hpc) is germane to understanding the nature of nanostructure – property relationships of the material. The irreversible dimensional changes of hpc and phase pure C–S–H that occur on wetting and drying are dissimilar to those observed for other silicate minerals of interest to cement science. This irreversibility in hpc is also observed for the modulus of elasticity parameter. Length change, mass change and modulus of elasticity isotherms (including drying–wetting cycles) were determined for specimens of hpc, Ca-montmorillonite and 1.4 nm tobermorite. Length change and modulus of elasticity versus mass loss curves were also obtained for phase pure C–S–H (C/S = 0.8, 1.0 and 1.5). All the isotherms exhibit significant irreversible behavior. Similarities and differences in the nature and character of the isotherms and the relevance of the C–S–H data are discussed. Inferences are made with respect to the nanostructural nature of hpc, its dimensional response in aqueous media and the correspondence in behavior of synthetic C–S–H and that formed in hpc. It is apparent that hpc has unique characteristics that are responsible for stability.