Crystalline Admixture as Healing Promoter in Concrete Exposed to Chloride-Rich Environments: Experimental Study

The requirements on service life of reinforced concrete structures, as prescribed by design codes, may be difficult to be fulfilled in highly aggressive environments such as marine ones, in which premature degradation is most likely to occur. In the aforementioned situations, to avoid expensive repair activities, different protective systems, including, among the others, self-healing concrete, could be adopted. Researchers have found self-healing as a way to face degradation problems in chloride-rich environments. If a significant degree of crack sealing can be achieved, the physical properties of a cracked element can trend back to those of an identical uncracked element, which may also result in a slower penetration rate of aggressive substances. The main problem in exploiting this methodology is related to its reliability. In this context, an experimental program aimed at investigating the effectiveness of crystalline admixtures as healing stimulating agent in chloride-rich environments was carried out. The influence of the exposure conditions on the compressive strength development and on its recovery in predamaged specimens was first analyzed. Afterwards, crack sealing and chloride permeability of sealed cracks were evaluated for specimens continuously immersed or subjected to wet/dry cycles in a 16.5% NaCl aqueous solution. Both an enhanced recovery of compressive strength and an improved crack sealing ability were observed for samples containing the healing agent. A microstructure study of the healing products was conducted by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis as well.