Mechanical Properties of Lightweight Alum Sludge Aggregate Concrete

Disposal of alum sludge (AS) in such an economical and environmental friendly way is a major challenge that water treatment plants around the globe had to deal with. AS cannot be dumped into landfills as it contains heavy metals which are harmful to the environment. In this study, alum sludge is utilised as partial replacements (0, 5 and 10%) of natural granite coarse aggregate (by mass) to form a lightweight concrete. The water/cement ratio is 0.65. The water absorption of the alum sludge is 22.06%. The slump, density, compressive strength and split tensile strength of the lightweight alum sludge aggregate concrete (LASAC) reduce as the AS aggregate content increase. The density of the 10% AS aggregate concrete is 2185.3 kg/m3. The compressive strength reduced from 25.6 MPa to 16.7 MPa and 14.2 MPa at 0, 5 and 10% replacement of AS aggregate respectively. The 2.18 MPa tensile strength of the control concrete reduced to 1.53 MPa at 10% replacement of AS aggregate. But as for the flexural strength, it increases from 5.42 MPa for the control up to 5.55 MPa and 5.63 MPa for 5 and 10% replacement of AS aggregate respectively. Results show that strength of alum sludge lightweight aggregate concrete is better than lightweight crumb tyre aggregate concrete and is at par with oil palm coconut shell aggregate concrete.