Valorisation of Faecal Sludge-Derived Bio-Briquette Ash as a Potential Supplementary Cementitious Material for Sustainable Construction

Abstract

The increasing demand for sustainable construction materials and improved faecal sludge management has encouraged the exploration of waste-derived ashes as alternative supplementary cementitious materials. This study examined the use of Bio-Briquette Ash from faecal sludge as a supplementary cementitious material. Bio-briquettes with different binders (cassava peel and waste paper) and without binder were combusted in an open kitchen at 300–450°C, and the resulting ashes were analysed using X-ray fluorescence and X-ray diffraction techniques. The ash samples contained significant amounts of silica, alumina, and calcium oxide, with combined pozzolanic oxide contents (SiO₂ + Al₂O₃ + Fe₂O₃) ranging from approximately 67% to 70%, which is slightly below ASTM C618 requirement for pozzolanic materials. X-ray diffraction analysis showed that the ashes were dominated by crystalline quartz phases with limited amorphous content, indicating relatively low pozzolanic reactivity. In addition, the sulphate content exceeded the ASTM limits. The findings indicate that the bio-briquette ash produced under low-temperature combustion conditions does not meet the criteria for full compliance as a supplementary cementitious material. However, the ash shows potential for sustainable construction applications following further optimisation through controlled calcination, mechanical activation, or blended-cement systems. The mechanical and durability performances were not evaluated in this study.

Keywords: Circular economy; Pozzolanic materials; Thermal treatment; X-ray fluorescence; X-ray diffraction