Experimental analysis of biocementation technique for sealing cracks in concrete water storage tanks

Water supply systems are vital infrastructures that provide an indispensable public service to society. An important percentage of water losses is caused by the development of cracks in water storage tanks, so efficient crack sealing repair works must be investigated. Biocementation has been used with good results for sealing cracks in many construction concrete infrastructures (e.g., buildings), as an alternative to standard materials, such as polymeric resins and cement mortars. This research aims at the experimental evaluation of biocimentation effectiveness in terms of watertightness for sealing cracks structures in contact with pressurized water, to be further applied to repair cracks in water storage tanks. Biocementation treatment is applied in cracks artificially created in small rectangular concrete plates 4 cm thick, with three crack widths (i.e., 0.1, 1 and 10 mm) to cover different real cases in which the repair with this technique is viable. The 10 mm width cracks were filled with sand before the treatment. Different rounds of bacteria Sporosarcina pasteurii are applied, being the efficiency of the treatment investigated by performing watertightness tests through variable water head tests starting at 10 kPa (1 m of water). Dissolution is discarded through measurements of ultrasonic pulse velocities before and after the watertightness tests and the results are explained by images of thermographic camera. The presence of biocement is confirmed by mineralogical analysis of the precipitate extracted from the cracks after breaking the plates through bending tests. Obtained results are very promising since the biocement precipitated can completely stop water flow in the 0.1 mm cracks and, for the cracks with 1 mm and 10 mm widths, the treatment can reduce the initial flow rate, on average, by 95% and 98%, respectively. The performance of the 10 mm width cracks previously filled with sand was similar to that of the 1 mm cracks, where no sand was used. The material strength recovered after the treatment is not as good as desirable: although a maximum recovery of 95.5% of the initial strength (average values) is found for the smallest crack width and it was almost null for the other two crack widths. These results demonstrate that the technique is effective when watertightness is required, but not when material strength must also be recovered. Further research is required to investigate the maximum water pressures that can be applied to each case, eventual effects of biocimentation on water quality and the durability of the treatment.