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

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 Q(3) 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), CaSO4.2H(2)O, and CaCl2 synergistically attacked C-S-H, Cl- was reported to have the strongest corrosive effect. (C) 2021 Elsevier Ltd. All rights reserved.