Effect of the MgO/Silica Fume Ratio on the Reaction Process of the MgO⁻SiO₂⁻H₂O System.

Zhaoheng Li,Qijun Yu,Hao Liu,Yudong Xu,Jianwei Zhang,Jiangxiong Wei

doi:10.3390/ma12010080

Abstract

In order to clarify the effect of the MgO–silica fume (SF) ratio on the reaction process of the MgO–SiO2–H2O system, the reaction products and degree of reaction were characterized. Furthermore, the parameters of the reaction thermodynamics were calculated and the reaction kinetics were deduced. The results indicate that a large amount of Mg(OH)2 and small quantities of magnesium silicate hydrate (M–S–H) gels were generated upon dissolution of MgO. However, the M–S–H gels were continuously generated until the SF or Mg(OH)2 was consumed completely. For a MgO dosage less than 50% of the total MgO–SiO2–H2O system, the main product was M–S–H gel, while for a MgO dosage greater than 50%, the main product was Mg(OH)2. The results indicate that M–S–H gels have greater stability than Mg(OH)2, and the final reaction product was prone to be M–S–H gels. Based on the experimental values, an equation is proposed for the reaction kinetics of MgO.

Highlights

The MgO–SiO2 –H2 O system was developed as a novel cementitious material [1,2,3,4,5]
The main reason for this is that MgO produces a large amount of Mg(OH)2 in the later stage of the reaction
When mixed with silica fume (SF) and water, MgO hydrated to form brucite, which immediately reacted with dissolved silica to produce Magnesium silicate hydrate (M–S–H) gel

Summary

Introduction

The MgO–SiO2 –H2 O system was developed as a novel cementitious material [1,2,3,4,5]. Magnesium silicate hydrate (M–S–H) gel is the typical reaction product formed in the MgO–SiO2 –H2 O system [7,8,9,10,11,12,13,14]. M–S–H phase, which was identified as 4MgO·SiO2 ·8.5H2 O. Gollop [16] found that M–S–H gel forms in Portland cement pastes by magnesium sulfate attack, and characterized the gel as a poorly crystallized serpentine (3MgO·2SiO2 ·2H2 O). Brew [17,18] characterized chemically synthesized M–S–H gels and investigated the incorporation of cesium and potassium. Vandeperre et al [19] discovered that brucite (Mg(OH)2 ) could react with the amorphous silica present in pulverized fuel ash to form M–S–H gels

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Results

Conclusion