Experimental analysis of self-healing cement-based materials incorporating extruded cementitious hollow tubes

In this work, new advances concerning the feasibility of extruded cementitious hollow tubes as containing/releasing devices for healing agents and their potential scaling up are presented. Specifically, sodium silicate and potassium silicate were evaluated as healing agents in terms of their ability to diffuse through cracks and of their ability to restore the initial mechanical properties of mortars. Their effect was investigated also in combination with the use of a hydrophobic coating applied to the inner surface of some of the hollow tubes to enhance the release of the healing agents along the crack path. A colorant was added to the sodium/potassium silicate solutions to help highlighting the fracture area covered by the healing agents, thus allowing a qualitative evaluation of the effect of the hydrophobic coating. Finally, image analysis was performed to correlate the mechanical strength/stiffness recovery to the area covered by the healing agent, as well as to the position of the tubes within the samples. On the whole, satisfactory results were obtained as far as restoration of the mechanical properties is concerned: the best performance was displayed when using cementitious hollow tube containing sodium silicate, with maximum values of bending load and stiffness recovery for the system of more than 70% and 50%, respectively.