Nondestructive Evaluation of Autonomic Crack Healing in Concrete Using Ultrasonic Wave Propagation

Abstract

Cracks in concrete structures are unavoidable, resulting in the deterioration of concrete structures. An effective way to heal cracks, integrated with a suitable monitoring method, is of great significance. This research explores and demonstrates the autonomic healing and simultaneous ultrasonic monitoring of thin cracks using silica-based chemical agents. The sensitivity of ultrasonic waves to the change in the elastic properties of the medium through which it propagates is used to monitor the progressive healing of cracks in concrete. An increase in the ultrasonic pulse transmission (UPT) signal strength with the progression of healing in cracked concrete was used to interpret the condition of the crack. The ultrasonic results were validated by visual observations, an increase in compressive strength and a reduction in water permeability. Further, the efficacy of silica-based chemical healing agents in crack-healing concrete was also verified by microstructural scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) tests. The study successfully demonstrates the efficacy of sodium silicate as an effective chemical healing agent in cementitious materials, with the healing process well picked up by ultrasonic pulse transmission measurements. The results of the study indicate that the utilization of sodium silicate as a healing agent in civil structures, integrated with the nondestructive monitoring of the healing process using the ultrasonic pulse transmission technique, represents an innovative approach to enhancing the durability and sustainability of concrete structures. Some practical applications include the following (1) the strength and life span of concrete bridges can be improved by integrating a crack repairing system with sodium silicate and monitoring through ultrasonic methods; (2) a sodium silicate solution can be injected into masonry substrate and mortar joints of historical buildings where cracks and weathering action have compromised the structural stability, and ultrasonic transducers can be strategically placed to monitor the healing progression and restoration process; and (3) this technique can be used to improve the resilience of marine structures by using sodium silicate as a healing solution in underwater concrete structures and combining it with ultrasonic monitoring.