Effects of biochar and polypropylene fibre on mechanical behaviour of cement‐solidified sludge

Abstract

AbstractCement solidification is a conventional method in sludge treatment. In order to improve the efficiency and sustainability of this process, biochar and polypropylene fibre were utilized with cement in this study. Biochar (0%, 2%, 5%, 7%, 10%, 15% and 20%, w/w) and fibre (0%, 0.05%, 0.1%, 0.2% and 0.4%, w/w) at different mass dosages were added to cement‐sludge system at two initial water contents (120% and 150%, w/w). A series of unconfined compression tests were carried out to investigate the effects of biochar and polypropylene fibre on the mechanical behaviour of cement‐solidified sludge. Scanning electron microscopy (SEM) was used to analyse the mechanism of biochar and polypropylene fibre in changing the mechanical properties of cement‐solidified sludge. Experimental results show that the addition of biochar can significantly promote cement hydration and reduce the water content of sludge after curing, thereby compacting the soil and increasing the unconfined compression strength (UCS) of the mixture. Moreover, when fibre contents increase from 0% to 0.4%, the UCS increases dramatically first and then decreases, peaking at 0.1%. The addition of fibre changes the brittle behaviour and improves the ductility of the samples, with residual strength significantly increased. The moisture regulation effect by biochar and the ‘bridge’ effect by fibre may be the key mechanisms to improve the mechanical properties of cement‐solidified sludge.