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

Abstract

This paper presents a quantitative study of the effect of 5 and 7.5% of nano silica (nS), 2.5 and 5% of nanoalumina (nA) and 2.5 and 5% of nanocalcium carbonate (nCC), on the properties of very high-volume fly ash cement composites (VHVFA-CC), replacing 80% of cement. Compressive strength test, 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 composites. The results show that the addition of nS to VHVFA-CC significantly improves its compressive strength and considerably increases the formation and thermal stability of silica-rich hydrogarnet [Ca3(AlxFe1−x)2(SiO4)y(OH)4(3−y)], which increases with the increase in nS content. The addition of nCC to VHVFA-CC 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 addition of nA though improves the hydration/pozzolanic reaction of VHVFA-CC, resulting in the improvement of compressive strength, but only if added in small quantities (i.e. 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.

Keywords:

• Nano silica
• nano alumina
• nano calcium carbonate
• fly ash
• X-ray diffraction
• thermogravimetric analysis
• scanning electron microscopy
• rietveld analysis

Acknowledgement

The authors fully acknowledge the scientific and technical support provided by the Microscopy & microanalysis facility, Rheology and material characterisation facility and the X-ray facility at RMIT University. The authors would like to thank Cement Australia for providing the material support to carry out this research.