Effect of Carbonation on the Microstructure and Moisture Properties of Cement-Based Materials

We provide a comprehensive understanding of the eff cts of carbonation on the microstructure, and the moisture properties of cement-based materials m de of ordinary Portland cement (OPC) and fly ash (FA). The bulk porosity is measured on a large panel of non-carbonated or fully carbonated cement pastes and concrete specimens by hydrostatic weighing and by mercury intrusion porosimetry (MIP). The carbonatable amount of CH and C-S-H (corresponding to the maxim um degree of carbonation that is reached for these hydration com pounds) is assessed when the carbonation mechanism is considered stabilised. The induced red uction in porosity is correlated with the calcium carbonate (CC) content quantified by thermogravimetric analysis (TGA) and associated both with CH and C-S-H carbonation. The identified variation of molar volume occurring during the C-S-H carbonation is dependent on the CO 2 concentration and is different if pozzolanic C-S-H are considered since for this latter a negative differe nce of solid volume can be observed. The effect exerted by carbonation on the pore size distributio n (PSD) is also elucidated by means of MIP and by analysing the diagrams of the spin-lattice relaxati on time (T1) determined by Nuclear Magnetic Resonance of proton H (NMR). The proportion of coar se capillary pores (radius>100 nm) increases with the degree of carbonation for materials of a h igh water/cement (w/c) ratio although a systematic reduction in total porosity for OPC systems is stil l measured. Moreover, this paper discusses the influence of carbonation on the water vapor desorpt i n isotherms (WVDIs). An analysis of the T 1diagrams and the WVDIs of carbonated and non-carbon ted materials made of OPC shows that the same fine-textured morphology of the C-S-H seems re mains in spite of a partial decalcification and polymerisation.