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This research explores the innovative integration of Microbially Induced Calcite Precipitation (MICP) with traditional cement stabilization to address the strength and durability challenges of alluvial sandy soils. The primary objective is to enhance soil properties while introducing a sustainable, bio-inspired technique for compressed earth block (CSEB) fabrication. Sandy soil samples were sourced from Anowara, Chattogram, and mixed with 10% garden soil to support bacterial activity. The study examined the impact of varying content ratios, curing periods, and mellowing periods of MICP treatment on the micro-mechanical properties of the soil. Analytical techniques, including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA), were employed to evaluate microstructural and chemical transformations, alongside 16S metagenomic sequencing to analyze bacterial community dynamics.
The mechanical tests demonstrated substantial improvements in soil strength, with dry unconfined compressive strength, split tensile strength, and flexural strength increasing by 113%, 95.84%, and 133.86%, respectively. MICP treatment enhanced water absorption resistance by 59.2% and improved durability under dry-wet cycles. SEM and EDS analyses revealed reduced voids and the formation of calcite crystals and cement hydration products that bridged soil particles. FTIR results confirmed stronger calcite and hydration-related spectral peaks, correlating with observed strength and durability enhancements. DSC and TGA results indicated significant calcite content, with a notable weight loss above 600°C. A 101.53% increase in calcite content was achieved in 5-day treated samples with 8% cement content. 16S sequencing highlighted the enrichment of urease-positive bacteria, particularly Sporosarcina and Bacillus genera, with Firmicutes dominance in MICP treated cement-stabilized blocks. Life cycle analysis (LCA) further revealed that CSEBs are 14.69% more cost-effective and environmentally sustainable compared to fired clay bricks (FCBs).
Optimal results were achieved with 6% cement content by weight and a 5-day mellowing period. This study underscores the potential of combining MICP bio-stimulation with traditional cement stabilization to establish an effective protocol for partial cement replacement, advancing sustainable construction practices. |
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