Microorganism Precipitation in Enhancing Concrete Properties

Abstract

Microorganism is an unique living element and has the ability to precipitate minerals through the process of biomineralisation. The precipitation process occured naturally and most of the precipitated products are very important compound composed of such as carbon, nitrogen, oxygen, sulphur, phosphorus and silica. So far, concrete incorporated with microorganism that able to precipitate calcium carbonate (calcite) was reported. However, little information on silica precipitation and its effect on concrete properties has been revealed. In this present study, the concrete specimens were incorporated with Bacillus subtilis silica adsorbed in their cell wall. Concrete specimens with five different concentration of Bacillus subtilis cell which are 104, 105, 106 and 107 cell/ml and control (without Bacillus subtilis) were cast. The experimental investigation aims to prove that the silica precipitated by this microorganism can enhance the concrete properties namely its compressive strength and resistance to carbonation. The microstructure of the concrete contained Bacillus subtilis was also examined. It appears that the inclusion of Bacillus subtilis into the concrete enhanced the compressive strength. The concentration of 106 cell/ml was found to be the optimum concentration to give most enhanced effect to the compressive strength. However the effect of including Bacillus subtilis to the resistance to carbonation of the concrete specimen is found to be insignificant.