Suitability of Biocement Produced by Isolated Micro-Organisms as a Cementing Material in Mortar

Abstract

This research aimed at partial replacement of Ordinary Portland Cement (OPC) with biocement obtained from biocementation processes induced by microorganisms for production of mortar. Urease positive bacteria were identified, cultured and feed into solutions containing a sterile mix of CaCl2 (0.75M) and urea (1M); 50 litres of this was produced. Mortar prisms of 40 mm x 40 mm x 160 mm were cast using a mix ratio of cement to sand of 1:3. A total of 54 prisms were cast and cured in water for 7, 21 and 28 days. OPC was replaced by biocement containing 20% pulverized fired clay at 10, 20, 30 and 50%. Bacillus Licheniformis isolated from bovine faeces was identified as urease positive micro-organism suitable for calcite precipitation producing at a rate of approximately 0.67g/hour. Results revealed that bacteria cells increased the compressive strength of mortar by 20% and the combined effect of bacteria cells, pulverized fired clay and biocement increased the compressive strength by 43.6% at 10% replacement. It was generally concluded that bacillus Licheniformis can precipitate CaCO3 through urea hydrolysis and bacteria cells as well as biocement containing 20% pulverized fired clay at 10 and 20% partial replacement increased the compressive strength of mortar, therefore suitable for mortar production where design compressive strength are desired.