A sustainable enhancement of bio-cement using immobilised Bacillus sphaericus: Optimization, microstructural properties, and techno-economic analysis for a cleaner production of bio-cementitious mortars

Abstract The present study developed a cleaner production bio-cementitious mortars (BCM) using immobilised Bacillus sphaericus activity. In order to achieve a sustainable enhancement of BCM, the effect of curing in distilled water (DW as normal water), deposition medium (DM as controlled nutrient), and runoff water (RW as uncontrolled nutrient) was investigated compared to control cementitious mortars (CCM). The BCM production was optimised based on curing days (3–90 days) and setting time (225–340 min). The results revealed that the optimal conditions to generate BCM in different curing media were recorded after 84 days with 240 min of the setting time. The compressive strength ranged from 40 to 54 MPa in BCM, compared to 40.5–41.5 MPa in CCM, ISA was 0.1–0.08 mL/m2/s in BCM and 0.11–0.12 mL/m2/s in CCM, water absorption was 3.23%–2.54% in BCM and 8.08%–7.42% in CCM, porosity was 7.98%–5.99% in BCM and 13.70%–13.37% in CCM, weight was 3.35–85.88 g in BCM and 1.90–81.70 g in CCM, and water permeability was 1.87–1.1 m/s in BCM and 3.04–2.99 × 10–12 m/s in CCM. The consolidation of pore inside the BCM was due to sufficient nutrient for bacterial activity. This enabled continuous production of more CaCO3 to fill the pore. The microstructural test results proved the formation of the CaCO3 precipitation inside the cement matrix. This is parallel with the improvement of BCM performances by the modification of porosity and pore, especially for the sample cured in the runoff water which showed that the precipitation of CaCO3 were denser and strong. The techno-economic analysis revealed that the specific cost of bio-cementitious material production is estimated to be USD 46.12 per m3 with 45% of the IRR (the investment) efficiency and the payback period (PBP) of 10 years of the lifetime which indicate that the production of bio-cementitious material and is economically feasible.