The influence of sugarcane bagasse ash on the microstructure of autoclaved cementitious material: Comparative study with amorphous and crystalline silica

Abstract

This study aimed to investigate the effects of a partial replacement (25 wt%) of Portland cement with sugarcane bagasse ash (SCBA) on the microstructure of cement pastes. The effects were compared with those of pastes containing amorphous (silica fume) or crystalline (crushed quartz) silica. Two curing methods were used for the pastes: conventional curing (25 °C and RH > 95%) and autoclave curing (220 °C under 2.1 MPa for 8 h). The microstructure of the pastes was characterized by XRD, SEM, FTIR, and the hardness and elastic modulus of their C–S–H regions. The results showed that the pastes cured at room temperature exhibited similar microstructure development, showing little or no reaction, even though silica fume is a highly reactive pozzolanic material. Differently, the hardness of the pastes containing silica fume, SBCA and crushed quartz replacement for cement increased approximately threefold after autoclave curing, while, in contrast, the reference sample, no cement replacement, showed no improvement. This is attributed to the formation of tobermorite and xonotlite. The presence of Al in the SCBA allowed the formation of tobermorite under the autoclave curing conditions (220 °C, 2.1 MPa for 8 h), and in this case, the SCBA exhibited behavior between silica fume and fine quartz.

Keywords

• Agro-industrial waste
• Supplementary cementitious materials
• Microstructure
• Hydrothermal curing
• Sustainable cements