Evaluation of Effect of Sodium Silicate and Bacillus Pasteurii in Self-Healing Ability of Concrete

One of the major defects of hardened concrete is crack. Cracks allow water to permeate into concrete and it could corrode the reinforcing steel fibres. Concrete liquid retaining structures do not function properly if cracks are not controlled. This study examines the effectiveness of sodium silicate and bacillus pasteurii mixed in concrete to control its cracks. The objectives are to determine the healing ability of sodium silicate gel, spore bacillus pasteurii, and solution of bacillus pasteuriii when mixed with concrete. Laboratory experimental methods were adopted for the research. The index properties of the materials were determined. Mix ratio of 1:2:4 was adopted for the concrete mixes. Results indicate that over 92 % of the concrete specimens tested show a reduction in water absorption. The cube specimens containing sodium silicate gel has an average density of 2440 kg/m3 before healing and decreased to 2437 kg/m3 after healing with an average compressive strength of 25.56 N/mm2. This strength approximately equals the value of control cube specimens of 25.18 N/mm2. Specimens that contained bacillus pasteurii have average10.0% gain in compressive strength compared to the control specimens. The concrete specimens that contained bacillus pasteurii showed physical evidence of crack sealing. Specimens containing sodium silicate showed no physical signs of healing of the induced cracks. Specimens containing bacillus pasteurii manifested autogenous as well as autonomous healing in both spore and solution state. This is evident by the decrease in water absorption of the concrete. Bacillus pasteuriiis compatible in incorporation into fresh concrete through media such as glass wares, glass tubes and light weight expanded clay aggregates (LECA), for later healing processes. It is also capable of surviving extreme alkaline environment and forming spore without contamination. Bacillus pasteurii in spore state is therefore recommended for addition in concrete to achieve self-healing.