Water treatment sludge as a partial cement replacement material: preliminary investigations and future perspectives

The amount of alum sludge (AS), a byproduct of drinking water treatment plants, is significantly increasing due to a higher potable water demand. Concomitantly, it is becoming more difficult to efficiently dispose of AS, especially, considering its environmental implications. Hence, this study investigated the potential of alum sludge as a sustainable supplementary cementitious material (SCM) in concrete. Furthermore, some preliminary laboratory investigations are carried out regarding characterization and utility of a locally sourced AS as a SCM. Initially, some of the physio-chemical characteristics of the pristine and calcined AS revealed a relatively high aluminium content and the formation of amorphous aluminate when AS underwent calcination at 800 °C. Concrete cylinders incorporating the 10% calcined AS, in addition to 10% MK, achieved 77% of the 28-day compressive strength as compared to the control sample. Analysis of ultimate load capacity highlighted the influence of curing time and the slower reaction kinetics of the AS pozzolans. Through appropriate comparison of the relevant literature precedents and the experimental findings, this study also provided some pertinent recommendations for future avenues of research.