No abstract

The aim of this research is to produce self-healing cementitious composites based on the use of cylindrical capsules containing a repairing agent. Cementitious hollow tubes (CHT) having two different internal diameters (of 2 mm and 7.5 mm) were produced by extrusion and used as containers and releasing devices for cement paste/mortar healing agents. Based on the results of preliminary mechanical tests, sodium silicate was selected as the healing agent. The morphological features of several mix designs used to manufacture the extruded hollow tubes, as well as the coatings applied to increase the durability of both core and shell materials are discussed. Three-point bending tests were performed on samples produced with the addition of the above-mentioned cementitious hollow tubes to verify the self-healing effectiveness of the proposed solution. Promising results were achieved, in particular when tubes with a bigger diameter were used. In this case, a substantial strength and stiffness recovery was observed, even in specimens presenting large cracks (>1 mm). The method is inexpensive and simple to scale up; however, further research is needed in view of a final optimization.

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.