The phase composition and microstructure development of a construction composite made from sewage sludge and biomass ash

Waste from one industry can often serve as raw material for another. Previous research has shown that sewage sludge stabilized with biomass ash can form a construction composite with “Controlled Low-Strength Material” properties. This study focuses on the microstructural properties of such composites over time, investigating changes in phase composition and pore size distribution, as well as susceptibility to carbonation. Techniques such as X-ray powder diffraction, Fourier transformation infrared spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, mercury porosimetry, and nitrogen gas sorption were employed. Results indicated that ash, a fine-grained, calcium-rich material, promotes new phase formation when combined with sewage sludge. Over time, common hydration phases like C-A-H and C-(A-)S-H were identified. The research demonstrated a direct correlation between microstructure development and phase evolution in the construction composite.