Application of soil bacteria to improve compressive strength of Portland cement
In order to control the demand for the use of Portland cement as well as to increase the durability of structure, although commercial admixtures are available that imparts additional cost for the construction projects. To enhance the mechanical property of Portland cement, a greener alternative solution needs to be investigated. Bacteria deposits calcium carbonate by the phenomenon called bio-cementation or microbiologically induced calcite precipitation (MICP). The present study aimed to analyse the improvement in compressive strength of ordinary Portland cement (OPC 53 grade) by addition of soil bacterial solution. In all casting for nine cubes each for controlled and bio-OPC were carried out. Experimentally, three cubes from each set were studied for compressive strength at the age of 7, 14 and 28 days. The effect of peptone and lentil seed as the protein source to soil bacteria was also analysed. At the age of 28 days, as compared to the controlled OPC 53 grade cubes, on an average 15.26 and 15.73 % improvement in compressive strength was estimated for peptone and lentil based bio-OPC respectively. Scanning electron microscopy (SEM) study was carried out and revealed the precipitation of calcite in the microbial amended cement specimen. The growth of calcite crystals within the pores of the cement matrix was observed. As compared to peptone solution, the lentil seeds are cost effective protein source to the soil bacteria and also impart in gaining more strength. The approach of bio-cementation is found to be commercially viable and environment friendly technique.