Performance of Epoxy-Injection and Microorganism-Based Crack-Healing Techniques on Cracked Flexural Members

Reinforced concrete (RC) members are designed to crack and the crack width usually remains within the service limit; however, these micro-cracks make structures susceptible to the infiltration of aggressive substances, especially near the coastline. Thus, the healing of these cracks is necessary before they further widen and spread. This study focused on the development and application of a crack-healing solution using microorganisms of the class bacillus; healing was observed through a crack-sensing camera. The aim was to regain the load-carrying capacity of the concrete member to meet the serviceability limit state requirements after healing the crack. The performance of the crack-healing solution was compared with the epoxy-injection method. Five full-scale RC beams of 100 × 200 × 1800 mm in dimension were cast using concrete designed with a cylindrical compressive strength of 21 MPa. After curing for up to 28 days, the beam specimens were tested and subjected to four-point bending to produce a flexural crack of width 1–3 mm. One of the beams was treated to fill the crack by injecting epoxy, while the three other similar beams were treated using a crack-healing solution consisting of bacteria (Bacillus subtilis), nutrient (calcium nitrate), and transporting agents. The healing solution was applied directly to the opened crack with silica gel and with cement slurry in three similar beams cracked under flexural load. The cracks in the beam treated with the crack-healing solution were sealed and kept moist for a further 14 days. After curing, all of the beams including the control (without treatment) were tested again and were subjected to four-point bending until failure to observe the effect of the crack repairs on the flexural response. It was observed that both systems were equally good at enhancing the serviceability limit state and improving the load-carrying capacity.