Effect of SO42−, Cl− and Mg2+ on the system of C-S-H and Ca(OH)2

Abstract

Calcium silicate hydrate (C-S-H) and calcium hydroxide (CH) are fundamental hydrates in cement-based materials. The effects of Mg2+, Cl−, and SO42−, on C-S-H/CH system were investigated in this study. The results indicated that incorporating MgO into C-S-H/CH system can increase the mean chain length (MCL) of C-S-H and induce the formation of a Q3 cross-linking structure. When the C-S-H/CH system was attacked by saturated CaCl2, Ca(OH)2 and Cl− formed CaClOH, and the C-S-H tobermorite group transformed into Ca4Si5O13.5(OH)2. The decomposition process of Ca(OH)2 caused by SO42− was accelerated by high-temperature curing. When the system was exposed to the combined attack of saturated CaCl2 salts and magnesium cations, the higher the content of Mg(OH)2, the faster the degradation of the C-S-H. When exposed to the combined attack of saturated chloride and sulfate, corrosion led to the decalcification of C-S-H, and thus a decrease in the Ca/Si ratio. When saturated Mg(OH)2, CaSO4·2H2O, and CaCl2 synergistically attacked C-S-H, Cl− was reported to have the strongest corrosive effect.