A quantitative study on the effect of nano SiO2, nano Al2O3 and nano CaCO3 on the physicochemical properties of very high volume fly ash cement composite

This paper presents a quantitative study of the effect of 5% and 7.5% of nano silica (nS), 2.5% and 5% of nano alumina (nA) and 2.5% and 5% of nano calcium carbonate (nCC), on the properties of low calcium class F very high volume fly ash (VHVFA) cement composites, replacing 80% of cement. Compressive strength test along with thermogravimetry, quantitative x-ray diffraction, and scanning electron microscopy were undertaken to study the effect of various nanomaterials on the physicochemical behaviour of VHVFA cement blends. The results show that the addition of nS significantly improves the compressive strength of VHVFA cement composites and considerably increases the formation and thermal stability of silica-rich hydrogarnet phase [Ca3(AlxFe1 - x)2(SiO4)y(OH)4(3 - y)], which increases with the increase in nS content. The addition of nCC to VHVFA cement composite does not show any effect on the pozzolanic reaction at 7 days of curing but at 28 days considerably improves its pozzolanic reaction, which increases with the increase in nCC content. The performance of nCC in improving the mechanical properties is less pronounced than that of nS. The addition of nA though improves the hydration/pozzolanic reaction of VHVFA cement composite, resulting in the improvement in compressive strength, but only if added in small quantities (2.5% or less). If it is added in higher amounts, it promotes the formation of Al(OH)3 gel that severely inhibits the hydration/pozzolanic reaction within the cement matrix. nA shows inferior performance compared to that of nS and nCC.