Nano silica, a new pozzolanic material, due to having a high specific surface, constitutes a strong adhesion agent in concrete and like pozzolan, fills the micro fractures and capillary pores, and thus increases the density, reduces the permeability, and enhances the strength and durability. But in the event of fracturing of the already treated concrete, the nano silica treatment appears to perform poorly.Thus, in the current work, a new nano silica type material with polymer core and silica shell –the nanocapsule – was introduced together with the synthesizing procedure. In order to investigate the improvements that nanocapsulecould do to the concrete properties, such as self-healing, specimens with 10 percent cement, with and without thenanocapsule treatment, were put to tests. Fractures were introduced by subjecting the specimens to 150 cycles of freezing and thawing before being evaluated for durability and strength using the ultrasonic pulse velocity and the compressive strength tests. FESEM imaging was carried out on a healed fracture and on nanocapsule while TEM imaging was carried out on nanaocapsule in order to appraise the formations at microstructure level. The ultrasonic pulse velocity and compressive strength were both found enhanced in the case of treated specimens. With increasing time, the ultrasonic pulse velocity for fractured, treated specimens was found approaching that of the intact, treated specimens which is evidence of the self healing progress brought by the treatment. The microstructure images also proved the materialization of the nanocapsule.
