Reaction products of MgO and microsilica cementitious materials at different temperatures

Abstract

The paste was prepared by mixing MgO, microsilica and H 2 O in the presence of water reducer at different reaction ratios and temperatures, and characterized by XRD, DTA, TGA, IR, and solid-state 29Si NMR. The experimental results showed that, besides Mg(OH) 2 , magnesium silicate hydrate (M-S-H) was formed at a low temperature such as 25 and 50 ℃. At a high temperature of 100 ℃, Mg(OH) 2 can be further transformed into M-S-H completely, for instance, within ca. 1 month in an excess of microsilica. The average composition and structure of M-S-H was mainly related to the reaction mixture and curing temperature and was discussed in detail.

Reactive magnesia cement

“…The formation of MSH as the reaction product between reactive MgO and microsilica at room temperature confirmed the findings of others (Wei et al, 2006(Wei et al, , 2011. Ongoing studies, using different source raw materials, giving a pH range of the blends of between 9.0 and 11.7, further showed that the reaction rate is significantly affected by the characteristics of the MgO, in particular its reactivity and pH (Jin, forthcoming) where the reactivity indicated the amount of brucite available for reaction and the pH determined the solubility of the microsilica in water.…”

Some New Perspective on the Reaction Mechanism of MgO–SiO2–H2O System

“…The exothermic peaks occur at about 850°C with no weight loss. It should account for the crystallization of M–S–H gels to form 2MgO·SiO 2 . The endothermic peak at about 400°C and the exothermic peak at about 850°C are not apparent for the samples aged at short time, indicating that the hydration of MgO are not sufficient.…”

“…It has also been used in the field of encapsulation of nuclear or metal containing wastes and contaminant immobilization . Therefore, MgO–SiO 2 –H 2 O system has significant potential practical applications and now becomes a hot topic …”

Role of sodium hexametaphosphate in MgO/SiO2 cement pastes

“…The structure of M-S-H gel produced by reacting MgO and silica fume (SF) with water has recently been reported using x-ray diffraction, IR spectra, DTA-TGA-EGA and NMR studies [9][10][11]14].…”

“…The addition ofNa-HMP to the mix water has been reported to significantly improve the rheology and properties of MgO/SF pastes and mortars and this enables the production of materials with high strength, high density and low porosity [10,13].…”