Mechanical properties of the concrete with recycled coarse aggregate surface treated by microbes

Purpose: Scarcity in the construction aggregates necessitated the use of suitable alternative materials such as recycled aggregates. However, the higher porosity of recycled aggregates due to the presence of adhered mortar affects its quality resulting in limited utilization. The purpose of this paper is to investigate the use of Bacillus subtilis to enhance the properties of the recycled coarse aggregate (RCA). The strains of the bacterial species were collected from the Gene bank, Chandigarh, and cultured to 105 cells/ml to treat the RCA. Design/methodology/approach: The concrete mixtures are prepared with 0%, 50% and 100% of treated and untreated RCA by mortar mixing approach. The concrete specimens are tested for compressive strength, split tensile strength, flexural strength and elastic modulus at 7, 14 and 28 days, respectively. Findings: Microbial treatment to RCAs increased the weight of the aggregate and decreased the water absorption of the aggregates. The optimal replacement of RCA was observed to be 50% and the strength of the concrete with 50% of treated RCA was comparable to the normal aggregate concrete. The CaCO3 precipitation by bacterial species fills the pores on the RCA and thus increasing the strength of the concrete. Originality/value: The originality of the research is to produce concrete with waste recycled aggregate treated by bacteria to overcome the problem of scarcity in construction materials.