Combined Use of Sewage Sludge Ash and Silica Fume in Concrete

Abstract

The lack of adequate space for sewage sludge disposal has become a significant challenge in many countries. Landfilling and using sewage sludge as fertilizer in agricultural lands are the main methods for disposal. However, these methods can result in soil and groundwater contamination as well as heavy metal and microbial pollution in soil. An alternative disposal method is using sewage sludge ash (SSA) in concrete production. If the sludge ash is reactive, it can replace a portion of cement in concrete; otherwise, it can be used as a filler. In the present study, X-ray fluorescence (XRF) experiments were conducted to determine the elemental composition of sewage sludge. Then, the sewage sludge was incinerated, and XRF and X-ray diffraction (XRD) tests were performed on the resulting sewage sludge ash. The ash was utilized in different proportions in the mortar and concrete specimens, and compressive strength tests were conducted on the resulting specimens. The results indicate that using 20% SSA instead of cement resulted in a 25% reduction in compressive strength in concrete specimens. However, the combination of 10% silica fume and 10% SSA was the optimal combination to compensate for the reduction in compressive strength caused using SSA.