Influence of limestone addition on calcium leaching mechanisms in cement-based materials

In order to investigate the mechanisms of calcium leaching and their implications on the long-term durability of cement-based materials, four different systems (C₃S, C₃S+C₃A+CaSO₄·2H₂O, C₃S+C₄AF+CaSO₄·2H₂O, and Portland cement) were prepared, mixed with water, and cured for several weeks. Four percentages of calcium carbonate addition (0%, 5%, 10%, and 20%) were used in the preparation of these systems. In all cases, the water/solid ratio was fixed at 0.5. At the end of the curing period, 1-mm thick samples were cut and immersed in distilled water. The kinetics of degradation was assessed by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) analysis after 10, 20, 40, and 90 days of immersion. The volumetric stability was also followed by length-change measurements. Test results clearly indicate that the mechanisms of leaching are directly affected by the mineralogical composition of the system, in particular by the calcium carbonate content.