Sustainable production of concrete with treated alum sludge

Abstract

• Incorporation of AS in concrete could be useful in protecting the environment. • The inclusion of AS tends to increase the water demand of concrete. • The mechanical properties decrease with the increase of AS substitution. • The inclusion of the AS tends to enhance the durability properties of concrete. A huge amount of unwanted sludge produced daily from water and wastewater treatment plants and disposed into landfills which cause a numerous environmental challenges. This study aims to investigate the effect of replacing cement by alum sludge (AS) on the performance of normal concrete. The replacement levels of the AS by weight of cement were: 0%, 2%, 4%, 6%, and 8%. Slump test was performed on fresh concrete to measure workability. The mechanical and durability properties were investigated on two concrete curing ages (after 7 days and 28 days). The scanning electron microscopy (SEM) test was carried out after 28 days of curing. Results showed that, the mechanical strengths and workability of concrete tend to decrease as the replacement level of cement with the AS increases. The optimal mechanical strengths were indicated at 4.0% replacement level of cement by AS with the addition of 2% superplasticizer (SP). The reduction in the optimal compressive and flexural strengths were up to 25.6% and 6.5% compared with the control mix after 28 days of curing, respectively. In addition, the treated AS enhances the durability properties of concrete at all ages. The lowest water absorption percentage (1.06%), gas permeability (1.03 × 10 −16 m 2 ) and chloride penetration (5 mm) were associated with the highest replacement level of cement with AS (8%) and addition of 2% SP, after 28 days of curing period. Overall, incorporation of treated AS in concrete production could be useful in protecting the environment by reducing the volume of alum sludge in the landfill.