Use of silica fume and natural volcanic ash as a replacement to Portland cement: Micro and pore structural investigation using NMR, XRD, FTIR and X-ray microtomography

This work investigates the effectiveness of the use of volcanic ash along with silica fume as a partial replacement for Portland cement. Multiple mix combinations of volcanic ash, silica fume and Portland cement were examined using various pore and microstructure characterization techniques. Hardened cement pastes were cured for 28 days and their pore and microstructures were examined using X-ray Microtomography, Magic Angle Spinning (MAS) Nuclear magnetic resonance (NMR) for ²⁷Al and ²⁹Si, X-ray Diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR). Microstructure examination of mixes prepared with volcanic ash, silica fume and Portland cement revealed the co-existance of calcium silicate hydrate (C-S-H) and calcium–alumino-silicate-hydrate (C-A-S-H) gels, along with other hydration products that led to a reduction in porosity and densification of the cement matrix. These findings indicate that volcanic ash along with silica fume is a viable substitute for Portland cement up to 40% and provides a sustainable, cost effective and environmentally friendly solution to volcanic ash disposal.