Ultrasonic investigation on the fracture-healing mechanism due to alkaline silicate solutions

The interaction between a cracked cementitious matrix and an alkaline silicate solution was analyzed via linear and nonlinear ultrasonic techniques in order to investigate its evolution in time and provide insight to develop effective material solutions for self-healing concrete applications. The behavior of the alkaline silicate solution in contact with the cracked cementitious matrix was analyzed on its own or in the presence of specific additives aimed at improving its water-resistance, and in comparison with two other fluid compounds. In all cases, the resonant behavior and the linear acoustic transmission properties of the cracked system were shown to evolve in time in the presence of the healing solutions, tending to an asymptotic condition related to the completion of the healing reactions. The analysis of the nonlinear acoustic behavior suggested that the healing mechanisms could be characterized by different stages, occurring at different time scales. The mechanical characterization tests performed at the end of the healing processes allowed to quantify the extent of performance recovery.