Coupled effect of PP fiber, PVA fiber and bacteria on self-healing efficiency of early-age cracks in concrete

Both bacteria and fiber can promote self-healing of cracks in concrete by accelerating calcium carbonate precipitation. Calcium carbonate in bacterial concrete grows from section surfaces of cracks, which might be altered after incorporating fibers. Therefore, this paper investigated coupled effect of PP fiber, PVA fiber and bacteria on self-healing efficiency of concrete. Optical density of bacteria cultivated in medium containing fiber was measured by using multifunction microplate reader, results showed that PP fiber and PVA fiber resulted in decrease of bacteria concentration. In addition, calcium carbonate induced by bacteria was synthesized in solution with fiber and characterized by using X-ray Diffraction, FTIR and particle size analyzer. Results revealed that the polymorphs of calcium carbonates were all calcite, while calcite generated in solution with PVA fiber showed lager particle size. In bacterial fiber reinforced concrete, crack width of 300-500 mu m was obtained and autogenous healing performance was evaluated. The results showed that although repair ratio of crack area for specimens with bacteria and fiber was slightly lower than that with bacteria only, water tightness and flexural strength regain ratio were improved evidently. By measuring the amount of calcium ions in repair medium and observing calcium carbonate distribution in the cracks, it could be concluded that PP fiber and PVA fiber were conductive to calcium leaching and calcium ions utilization. Deposition was attached on surfaces of fibers and can even be observed on PVA fibers inside of cracks, which was due to effect of polarity groups and cell structure of polyvinyl alcohol fiber on calcium carbonate nucleation. Therefore, the study suggests that coupled effect of PP fiber, PVA fiber and bacteria has potential to enable excellent self-healing performance in concrete. (C) 2019 Elsevier Ltd. All rights reserved.