Bio-stone

Abstract

Recycled concrete aggregates are obtained from materials used previously from a product or from construction. Recycled concrete aggregate (RCA) consists of original stone or sand, to which old cement paste are tightly bounded to it. Due to the porous nature of cement paste, RCA tends to have higher water absorption rate and decrease the strength grade of concrete.

In this research, Bacillus Pasteurii was chosen as it has the greatest potential for calcium carbonate precipitation even under extreme conditions.

The process of biologically inducing a layer of calcium carbonate on the exterior of construction materials is known as biodeposition. The calcium precipitation process depends on a few factors namely; calcium ion concentration, pH , bacteria concentration ( availability of nucleation sites) and temperature. Based on experiment conducted, the optimized conditions are as follow: 35°C , pH 9.5, calcium chloride concentration 16.80g/L and bacteria concentration 1x108 cell/mL. The biodeposition of calcium carbonate on the surface of recycled concrete aggregate has been observed under the optimal microscope under magnification of 64x.

In conclusion, optimization of the four factors managed to improve the biodeposition amount by a factor 8-15 times. Average reduction of water absorption increase from 8.44% to 14.85% after optimized conditions were used to conduct biodeposition. EDX also confirms that weight increase by biodeposition is calcium carbonate.

Further tests were recommended to include different types of bacteria such as Bacillus Subtilis or Bacillus sphaericus. Future tests could be conducted on the type of crystal deposited under different conditions. Attachments efficiency of the crystal calcium carbonate onto the recycled concrete aggregates with regards to ITZ could also be explored. Lastly, treated recycled concrete aggregates could be cast into concrete slabs and sorptivity, tensile test and chloride ponding tests could be conducted to further understand the impacts of bacillus pasteurii has on those factors.