Sealing efficiency of cement-based materials containing extruded cementitious capsules

The intensive use of cement-based building materials is a growing concern in terms of environmental impact, since they significantly contribute to the global anthropogenic CO2 emissions. The development of self-sealing cementitious materials could be a possible approach to improve the structural durability and thus reduce overall cost and environmental impact. In the present work, the efficiency of a self-sealing system using extruded cementitious capsules was experimentally investigated, and different healing agents were tested (specifically, a water-repellent agent, a polyurethane precursor and a solution of silica gel immobilized ureolytic bacteria). The self-sealing efficiency was evaluated in terms of capability to autonomously seal localized cracks induced in a controlled way. An active crack width control technique was adopted during the cracking procedure, in order to reduce the variation of the crack width within a series of specimens. Water permeability and capillary water absorption tests were performed to quantify the crack sealing ability, along with qualitative visual analysis of the crack faces. Positive results were achieved when using the water-repellent agent in water absorption tests, the bacterial agent in water-flow tests and the polyurethane precursor in both cases. This suggests that the proposed self-sealing system is sufficiently versatile to be used with different healing agents and that it can be effective in prolonging the material functionality by selecting the most appropriate agent for the real operating conditions.