Biogenic Calcite Production From Bacillus Subtilis: Characterization and Potential for Sustainable Self-healing Construction Materials
DOI:
https://doi.org/10.64321/jcr.v3i4.10Keywords:
Bio-concrete, Bacillus subtilis, Rice Husk Ash, Calcite, MICCP, SEM, EDX, XRDAbstract
The self-healing mechanism in bio-concrete is attributed to Microbial Induced Calcium Carbonate Precipitation (MICCP). However, direct confirmation of the precipitated phase is required. This study identified crystals harvested from 90-day bio-concrete containing Bacillus subtilis and rice husk ash (RHA) using SEM, EDX and XRD.SEM revealed rhombohedral crystals with well-defined facets diagnostic of calcite, forming cluster-like networks that bridged pores and cracks. EDX showed Ca and C at 35.28% and 37.76% respectively, giving a Ca:C ratio of 1:1.07, within the ± 15% tolerance for CaCO3 confirmation. The spectrum displayed C Kα, O Kα and Ca Kα peaks consistent with CaCO3. XRD confirmed the phase as calcite with sharp peaks at 2θ = 30.018ᴼ (104), 36.52ᴼ, 39.93ᴼ, 43.72ᴼ, 48.09ᴼ and 49.14ᴼ. Quantitative analysis showed 83(4)% calcite with minor albite and quartz. The (104) peak gave an average crystallite size of 28.6 nm by the Debye-Scherrer equation. Absence of aragonite and vaterite confirmed exclusive calcite formation. Thus, rhombohedral morphology, 1:1 Ca:C stoichiometry, Ca-C-O signature, and calcite XRD pattern confirm that B. subtilis precipitated calcite through MICCP, responsible for pore filling and crack bridging in RHA-modified bio-concrete.
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