Effect of sewage sludge ash on mechanical properties, drying shrinkage and high-temperature resistance of cement mortar

The treatment and disposal of sewage sludge ash (SSA) have emerged as crucial environmental concerns. This study delves into the profound impact of substituting SSA for sand in cement mortar, examining fresh and mechanical properties, drying shrinkage, and high-temperature resistance. Analyzing the SSA-modified mortar through X-ray diffraction (XRD) and scanning electron microscopy (SEM), the research reveals that the porous nature of sludge ash marginally influences the hydration rate and degree by adsorbing ions or encapsulating cement particles. While the SSA leaching solution has only a neglectable impact on the hydration rate. The workability is enhanced with the increase of the addition of excess water. Meanwhile, although the presence of excess water indirectly increases the w/c ratio of mortar, mortar with 5 % and 10 % SSA exhibit superior mechanical performance due to denser microstructure. Porous structures of SSA and more excess water in higher SSA content result in the rise of mortar drying shrinkage. When the sintering temperature reaches 800 °C, the high-temperature resistance of mortar with 20 % SSA is greater than that of the control group. The rough surface of SSA effectively fills cracks induced by elevated temperatures and improves the friction reaction, contributing to enhanced performance.