The effect of sodium carbonate on the formation of magnesium silicate hydrate

Practical application of magnesium silicate hydrate (M-S-H) cements is hindered due to their relatively slow setting time and low early strength development. Our previous study showed that the formation of the M-S-H binders can be accelerated by the addition of sodium bicarbonate (NaHCO3). To further understand the effect of carbonate additives on the M-S-H formation, sodium carbonate (Na2CO3) is tested in the title study. Aqueous solutions of Na2CO3 are used at different concentrations to hydrate a mixture of magnesium hydroxide (Mg(OH)2) and microsilica. The products are analysed by X-ray diffraction (XRD) and thermogravimetry (TG) to track the evolution of M-S-H and other phases; ex-situ pH measurements were also carried out. The obtained results indicated limited acceleration of M-S-H formation through addition of Na2CO3. The effects of pH, sodium and carbonate ions concentrations are further discussed.