Bio Concrete a bacteria based self-healing concrete

Abstract

Concrete is the most extensively used building material. Cracks are responsible for the deterioration of concrete structures. The use of biological techniques and processes in the concrete has lead to the invention of a new building material, bio-concrete. The present study focuses on isolation and screening of spore forming, calcite mineral precipitating bacteria and analyzes the effect of potential bacterial strain embedded on the strength and crack healing characteristics of concrete. Here, a total of 15 soil samples were collected from the various locations of Himachal Pradesh, India. The bacterial strain Bacillus megaterium MTCC 1684, procured from Microbial Type Culture Collection and Gene Bank (MTCC), Chandigarh, India was used as the standard culture to compare the results with selected isolates. The first phase of investigation focuses on the culturing of bacteria. For this, enrichment culture technique was performed in Luria Broth as a nutrient medium and further processed on Urea Broth. Then, 26 distinct bacterial isolates were further processed for screening to select potential bacterial isolates. Finally 2 isolates were selected based on urease assay and calcite precipitation results. M20 concrete specimens were prepared with water/cement ratio of 0.45 and the concentration of bacterial cells embedded in concrete was 107 to 108 cell/ml of mixing water. The cracks were induced in the concrete specimens by introducing a thin copper plate of thickness 0.3 mm to 0.5 mm in the fresh concrete paste up to a depth of 10 mm to 15 mm. The compressive strength test, splitting tensile strength test, flexural strength test and visual inspection of crack healing were performed on concrete specimens incorporated with and without bacteria. It was observed that concrete prepared with isolate 3 bacterial cells reported greatest increment in compressive strength (17.28%), split tensile strength (27.76%) and flexural strength (35.03%) as compared to the control concrete specimens. Also, the maximum healable crack width for isolate 3 concrete was 0.3 - 0.4 mm, for standard concrete: 0.2 - 0.3 mm and it was only 0.1 - 0.2 mm for control concrete specimens. Therefore, it was concluded that Isolate 3 concrete can be successfully used in the crack remediation of concrete structures.