Effect of various bio-deposition treatment techniques on recycled aggregate and recycled aggregate concrete

When it comes to sustainable construction, recycling is one of the significant aspects to consider. Reusing waste from construction and demolition activities and utilizing recycled aggregate (RA) in construction appears to be a perfect solution. The major drawbacks in the effective utilization of RA in comparison to natural aggregate (NA) are its inferior properties like water absorption, strength, and adhered mortar. In this study, three biomineralization treatment techniques (spraying, single immersion, and double immersion) with three different cell concentrations of Bacillus sphaericus (1 × 103 cells/ml, 1 × 105 cells/ml, and 1 × 107 cells/ml) were applied for treating coarse recycled concrete aggregate (RCA). The treated coarse RCA was tested for water absorption, weight change, ultrasonic pulse resistance, and fragmentation resistance. In addition, the concrete mixes made with various treated coarse RCA were evaluated for compressive strength, permeability, water absorption, and resistance to the sulphate environment and economical aspect. As per the observations, the concrete mix containing double immersion treated RCA and bacterial cell count of 1 × 105 cells/ml provided almost equal 28 days of compressive strength compared to controlled mix concrete. The water absorption of RCA subjected to this treatment was 12% less than the untreated RCA. Also, the concrete made with these treated RCA showed equal 28 days of water absorption to controlled concrete. As per the economic analysis as well the concrete treated with double immersion and bacterial cell count of 1 × 105 cells/ml was found most effective. Treatment also had a positive effect on other properties of RCA and treated RCA concrete. It can be concluded that double immersion technique that is two-time immersion of untreated RCA in the grown bacterial culture for 24 h, and growth medium for three days of Bacillus sphaericus bacteria with cell concentration of 1 × 105 cells/ml is ideal for the effective treatment of RCA.