Comparative Assessment of Algae- and Bacteria-Modified Mortar for Matrix Densification
摘要
Bio-mediated modification of cementitious materials has gained attention as a sustainable approach for enhancing microstructural development and matrix densification. Although bacterial species such as Bacillus subtilis have been extensively investigated for calcium carbonate precipitation, cyanobacteria such as Spirulina sp. present potential advantages due to their alkaline tolerance and mineral nucleation capability. Nevertheless, their behaviour in cementitious matrices under different water-cement (W/C) ratios and replacement levels is not yet fully understood. This study evaluates the influence of partial cement replacement using Spirulina sp. and Bacillus subtilis on the densification of cement mortar matrices. Mortar specimens were prepared with microbial replacement levels of 1%, 2%, and 3% at W/C ratios of 0.4, 0.45, and 0.5. Matrix densification was assessed by measuring percentage weight gain, density variation, compressive strength, and mineralogical characterization via X-ray diffraction (XRD). Among the investigated mixtures, the highest weight gain was observed at 2% Spirulina sp. (2.34%) at W/C 0.45, while 1% Bacillus subtilis showed a superior weight gain of 4.54% at W/C 0.50. The density increased by 84 kg/m3 for bacterial specimens and 43 kg/m3 for algal specimens after 28 days. The maximum compressive strength achieved was 32.26 MPa for Bacillus subtilis at W/C 0.45 and 24.68 MPa for Spirulina sp. at W/C 0.4, both at 3% replacement. XRD analysis confirmed the formation of calcite and portlandite, indicating bio-mediated mineral deposition. These findings show that both bacterial and algal systems improve matrix densification, suggesting promising potential as sustainable bioadditives for cement-based materials.