In situ Ca(OH)2 consumption of TEOS on the surface of hardened cement-based materials and its improving effects on the Ca-leaching and sulfate-attack resistivity

Ca(OH)(2) (CH) is a critical constituent that influences the durability of cement-based materials. By taking the advantages of the in situ hydrolysis of tetraethoxysilane, TEOS, and the in situ consumption of CH at the surface of hardened cement-based material, this work studied the effects of TEOS-treatment on the CH-related durability, i.e., the calcium-leaching and sulfate-attack resistivity. Results suggested that TEOS can penetrate into hardened cement-based material more easily than water. Thermogravimetric analysis showed that TEOS consumed CH on the surface of hardened cement-based material, resulting in a gradient distribution of CH, and benefited the CH-related durability. The loss of compressive strength of mortar samples suffering decalcification was reduced by TEOS-treatment, and the lower Ca-leaching of the TEOS-treated sample introduced by the reduction of CH content and the polymerization of C-S-H gel (shown by NMR results) could be two of the critical reasons. XRD results showed that the formation of the gypsum on the surface of cement-based material that cured in Na2SO4 solution could be reduced by the in situ consumption of CH of TEOS, which benefited the reduction of the loss of the compressive strength in the corrosive environment. It can be deduced from this study that the in situ consumption of CH of TEOS on the surface of hardened cement-based material would favor the improvement of the durability, showing its potential for surface-treatment of hardened cement-based material. (C) 2016 Elsevier Ltd. All rights reserved.