Immobilization of (bio-)healing agents for self-healing concrete technology: Does it really ensure long-term performance?

For more than two decades, with steadily increasing intensity, the focus of scientific research, mainly on the laboratory scale but also in the field conditions, has been the applicability of microbiologically induced calcite precipitation processes in the technology of self-healing concretes. In the existing literature, achievements have been presented concerning the factors affecting the ureolytic activity of potential bacterial strains and their survival throughout the life of cementitious composites and structures manufactured from them. In recent years, one of the important questions is the possibility of protecting bacterial cells by their immobilization on carrier materials. The objective of the presented work is to provide a comprehensive understanding of recent developments in the field of self-healing concretes, in particular through the use of bio-healing agents. The analysis of 195 literature records allowed to characterize the basics of healing of cracked surfaces, to identify the limiting factors for the application of this method and finally, to present methods protecting bacteria from the unfavorable environment of cementitious composites by classifying carrier materials and methods of bio-agents production. The article's important novelty is firstly the tabulation of the preparation method of (bio-)healing agents (by impregnation of carrier materials, including their distinction) and secondly overview of their addition's influence on the parameters and self-healing abilities of cement composites.