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

In order to investigate the mechanisms of calcium leaching and their implic ations on the long-term durability of cement-based materials, four differen t systems (C3S, C3S + C(3)A+ CaSO4. 2H(2)O, C3S + C(4)AF + CaSO4. 2H(2)O, a nd 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/so lid ratio was fixed at 0.5. At the end of the curing period, 1-mm thick sam ples 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 stabi lity was also followed by length-change measurements. Test results clearly indicate that the mechanisms of leaching are directly affected by the miner alogical composition of the system, in particular by the calcium carbonate content. (C) 2001 Elsevier Science Ltd. All rights reserved.