IS THERE A MARKET FOR SELF-HEALING CEMENT- BASED MATERIALS?

Cement-based building materials are, by definition, made of cement. Cement particles react with water Producing hydration products. These products “glue” cement and aggregate particles together to a cement paste, mortar or concrete. The resulting material is a brittle system, susceptible to cracking under external loads and/or imposed deformations. Cracks are supposed, and known, to jeopardize the strength, stiffness, durability and service life of concrete structures. The majority of degradation studies reveal that transport processes in concrete are the main cause of durability problems. The presence of cracks will increase the transport of aggressive substances into the concrete, thus increasing the risk of degradation of the material. Given the relatively high brittleness of cement-based systems the formation of cracks is almost unavoidable. If it were possible to close or fill these cracks through a self-healing mechanism the service life of concrete structures could increase substantially. In this contribution examples are presented of proven and potential self-healing of cement-based materials. It will be explained how the heterogeneous nature of cement-based systems can be considered as an asset when it comes to realization of built-in self-healing features. In this respect concrete can be considered as a material different from other building materials since heterogeneity-induced cracking can be considered as an inherent feature of concrete. This unavoidable cracking is, as far as its consequences for the performance of the material are concerned, allowed for in all codes implicitly by well-documented material factors. If this cracking could be used as trigger for starting, or intensifying, a self-healing process, the magnitude of material factors could be reduced, thus reducing building costs and saving raw materials. Finally it will be mentioned briefly that selfhealing could contribute to better esthetic performance of concrete.