Tests and methods of evaluating the self-healing efficiency of concrete: A review

To achieve the extended service life of the concrete material, expansive chemicals and microbial induced calcium carbonate precipitation are used, which induced autonomous healing of cracks in concrete. Various approaches are adopted to develop self-healing cement based materials, where experiments are conducted to establish a new method of self-healing. However, comprehensive evaluations of self-healing efficiency are not performed at the level of macro-, micro- and nano scale. Existing approaches evaluated the self-healing efficiency at the macrostructure level. These are based on the durability criterion of water absorption, chloride and acid resistance. Tests at microstructure level are commonly performed to maximize the reliability of the results. Only few tests are conducted at the nanostructure level. It is worth to review all the available tests and methods on self-healing efficiency assessment of cement based materials to develop innovative experimental strategy. Use of supplementary cementing materials, polymers and microorganisms are the most familiar approaches to achieve effective self-healing. Determining the effect of self-healing to successfully sealing the crack width is the key issue. So far, a crack of maximum size of 0.97 mm is healed. Visual observation based on microscope, digital imaging and camera photographs are the primary techniques to assess the width of the filled cracks. Yet, only couple of researches reported on the healing of crack depths of 32 mm and 27.2 mm. Besides, only one report acknowledged the healing of crack length of 5 mm.