Effects of carbonation on pore structure and diffusional properties of hydrated cement pastes

Steady-state diffusion kinetics of dissolved oxygen and chloride ions were studied in well-cured, partially dried, non-carbonated and fully carbonated specimens of OPC, OPC/30% PFA and OPC/65% BFS pastes. Pore size distribution, total porosity and coarse capillary porosity data for the specimens were also determined. The diffusion resistances of all the materials were adversely affected by pre-drying and carbonation, but the effects were considerably more severe for the blended cements than for the OPC. This was associated with coarsening of the pore structures of the various pastes to differing extents as a result of pre-drying and carbonation. Diffusion rates of both chloride and oxygen in all three carbonated materials appeared to be controlled by a common, purely physical mechanism. (C) 1997 Elsevier Science Ltd.