In order to investigate the self-healing capability of fibre reinforced cementitious composites (FRCC), mechanical properties and surface morphology of crack in FRCC were studied. Three types of FRCC specimens containing (1) polyethylene (PE) fibre, (2) steel cord (SC) fibre, and (3) hybrid fibres composite (both of PE and SC) were prepared. These specimens, in which cracks were introduced by tension test, were retained in water for 28 days. The self-healing capability of the specimens was investigated by means of microscope observation, water permeability test, tension test and backscattered electron image analysis. It was found that many very fine fibres of PE were bridging over the crack and crystallization products became easy to be attached to a large number of PE fibres. As a result, water permeability coefficient decreased and tensile strength was improved significantly. Therefore amount of the PE fibre per volume was indicated to have a great influence on self-healing. Furthermore, by means of backscattered electron image analysis, it was also shown that the difference of hydration degree in each FRCC has only little influence on the self-healing capability in case of the employed test series.

Challenging studies of engineered self-healing and self-repairing functions in concrete structures are briefly reviewed. While self-healing of concrete has been studied for a long time, it was only recently noticed that some engineered technologies are useful to stimulate the potential of concrete to be self-healed. For example, fiber reinforced cementitious composites (FRCC) have a much higher potential of self-healing than ordinary concrete because of their capability to keep cracks thinner and also because of the bridging network system in cracks; a specific bio-chemical approach, i.e. the application of mineral-precipitating bacteria, is now available; and various mineral admixtures are useful for practical application. Furthermore, the new concept of self-repairing concrete, which is based on the design concept of intelligent materials, is reported. Self-repairing concrete is concrete that incorporates devices for achieving the three key functions of an intelligent material, (1) sensing, (2) processing, and (3) actuating. This paper is a state-of-the-art report on the recent development of engineered self-healing and self-repairing concrete.

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A fundamental study was carried out to develop a kind of smart concrete that has a self-healing system that incorporates a heating device. Self-diagnosis composite is employed as the heating device used to heat up cracked parts in the concrete. This heating device and a pipe made of heat-plasticity organic film containing a repair agent are embedded in the concrete. The film is melted through suitable heating. Selective heat around a crack can melt the film to allow the repair agent to fill up the crack and harden the repair agent in the crack. Three-dimensional thermal analysis and an experimental study were carried out to confirm the proposed method.

Experimental studies are carried out to evaluate the self-healing capability of FRCC using different types of synthetic fibers that have different chemical properties, i.e. poly vinyl alcohol (PVA), ethylene vinyl alcohol (EVOH), polyacetal (POM) and polypropylene (PP). FRCC specimens were subjected to tension tests in order to generate a crack, and the cracked specimens were immersed in water. In order to evaluate the effect of self-healing phenomena, permeability tests and microscopic observation were carried out. Microscopic observation revealed that the high polarity of synthetic composite has high potential of self-healing precipitation around fibers bridging a crack. Moreover, the coefficient of water permeability was generally reduced with this chemical precipitation, especially in the PVA series. However, even when it was confirmed by microscopic observation that precipitation had appeared and filled a crack, we found there is no recovery of water tightness in some cases, i.e. in the EVOH and POM series. It is confirmed that not only the chemical properties of fibers but also the geometrical properties of the crack surface, such as roughness, complexity and continuity, affect the capability of self-healing for water tightness.