Microbial Participation in the Formation of Calcium Silicate Hydrated (CSH) from Bacillus subtilis

Primary hydration of cement induces the formation of calcium silicate hydrated (C-S-H) gel and the latter contributes towards the strength development of concrete. The secondary hydration derived from pozzolanic materials such as silica fume is dependent upon the formation of C-S-H gel of the primary cement hydration reaction. The additional formation of C-S-H gel as a result of second hydration process, densities the cement microstructures producing low permeability concrete. However, the silica fume is considered expensive material and its availability is limited. Therefore, it is essential to utilise living elements as an alternative agent to form the C-S-H gel. In the present study, the untreated Bacillus Subtilis and chemically modified Bacillus subtilis (CMBS) were prepared. CMBS was prepared by reacting with ethylenediamine to modify its cell wall to become electropositive facilitating the binding of the silicate during the incubation process. The cell was then incubated in the Si solution (Na2SiO3.5H(2)O) for 10 days which enables the SiO32- (silica ion) from the solution to be bonded with the cell wall. The C-S-H gel is expected to be formed from the bonded silica of the cell wall when mixed with saturated calcium hydroxide solution which the latter simulates the concrete environment. The presence of C-S-H gel was then substantiated using X-Ray Diffraction (XRD) analysis. In another series of study, the difference concentration of Bacillus subtilis were incorporated into the grade 30 concrete specimens and the compressive strength up to 60 days of age were tested. The results showed that the silicate was adsorbed by Bacillus subtilis and there is no difference in the amount of Si adsorbed between untreated Bacillus subtilis and CMBS. The incorporation of Bacillus subtilis into the concrete enhanced the compressive strength and the concentration of 10(6) cell/ml was found tSo be the optimum concentration. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Universiti Teknologi MARA Perak and Institution of Surveyors Malaysia (ISM)