Review on the effect of sewage sludge ash on the properties of concrete

Sewage sludge disposal is a complicated task which requires considerable planning and investment. Unsafe disposal of sludge has the potential to pollute underwater sources due to the leaching of hazardous heavy metals and pathogens. The potential of recycling of sewage sludge as a construction material can help alleviate the problems associated with sewage sludge disposal and prevent environmental degradation. The present study aims to provide an assessment of the effect of sewage sludge ash on the properties of concrete as a partial replacement of cement and sand in concrete. The effectiveness of the pozzolanic activity of the sewage sludge ash is found to be dependent on the incineration process. The sewage sludge ash delays the setting time and reduces the early strength of concrete due to low pozzolanic activity, however, application of certain treatments and the use of accelerators can mitigate this effect. As observed in various studies, sewage sludge ash content of 5–10 % in concrete provides better compressive strength and comparable splitting tensile and flexural strength performance. It is also suggested that sewage sludge ash-based concrete provides improved durability performance, including reduced water permeation, improved freeze-thaw resistance and better chloride resistance. Based on the findings, it is suggested that sewage sludge ash in concrete offers satisfactory performance with the potential to reduce the environmental impact by lowering cement content. Sewage sludge ash usage in concrete can also tackle the issue of sludge disposal. However, safety validation through leaching tests is required before its application in concrete manufacturing.