A Review of Early-Age Properties of Cement-Based Materials

Immediately after placement, gravitational forces and the local drying environment begin to influence the (micro)structure of a cement paste, mortar, or concrete. Depending on the mixture’s water-to-cementitious materials mass ratio (w/cm) (and aggregate volume fraction), the initial freshly cast material may be thought of either as a concentrated suspension of rigid particles in water or as a granular water-filled porous media. In the former case, significant settling will be expected to occur, accompanied by bleeding. For present-day portland cement pastes without admixture additions, for example, measurable bleeding and settling are generally observed for water-to-cement ratios (w/c) > 0.4. As the solid particles settle and a corresponding volume of water rises to the top of the specimen, a microstructural (porosity/density) gradient will be established through the thickness of the specimen. In addition to the concentration and particle size distribution (PSD) of the solids, the details of this gradient will depend also on the evaporative water loss from the specimen’s top surface, e.g., the drying conditions.