Strength and chloride resistance of mortars blended with SCBA: the effect of calcination and particle sizing on its pozzolanic activity

Abstract

Sugarcane bagasse was variously treated by three different processing protocols to improve the pozzolanic activity of the resulting sugarcane bagasse ash (SCBA). Three parameters were examined namely, the particle size, the calcination temperature and the duration of calcination. The resulting SCBA was blended with Portland cement to examine potential benefits upon the strength and chloride resistance of mortar specimens. As expected, the particle sizing and re-calcination, together imparted greater pozzolanic activity to SCBA. The results demonstrate that the optimal SCBA, possessing an acidic oxide (SiO2+Fe2O3+Al2O3) content over 70% and LOI can be reduced to 4.3%, resulted from grinding the boiler residue to 35 μm, followed by calcination for 90 min at 600 °C (P3-T90). In addition, the XRD test reveals that increasing the calcination temperature up to 600 °C could remove the residual carbon and other volatile compounds effectively. However, any further increase was noted to convert amorphous silica to cristobalite in SCBA itself and, also to enlarge the microcrack at ITZ in the hardened mortar. Furthermore, the optimal SCBA was found as P3-T90 in this study to produce the best blended mortar, as evident from an 18% increase in compressive strength, a 15% increase in flexural strength and a 43% decrease in chloride diffusion coefficient. This is firstly attributed to the improved pozzolanic activity and in turn, to the increasing C–S–H phase. Besides, the associated porosity and mean pore size were minimized to 15.78% and 36 nm, respectively.