Methodological approaches for the structural, chemical, and microbial analysis of microbial biofilms developed on the surface of cementitious materials: Overview and future prospects

Biofilms are the predominant living presence of micro-organisms in the environment, and on the surfaces of cementitious materials. This protective organization gives the microorganisms a certain resilience. But above all, the formation of biofilms on the surface of cementitious materials favours the phenomenon of biodeterioration, which is very prevalent in the field of civil engineering, or in the medical field, in orthodontics and orthopaedic surgery on dental or bone cements. In order to instigate and combat the development of biofilms on cementitious materials, in-depth research studies are being conducted to gain an understanding of the basic mechanisms of biofilm formation and material deterioration. Therefore, analytical techniques have been developed to describe the chemical compositions, structural characteristics and microbial diversity of biofilms formed on cementitious materials. This review article presents the state of the art in terms of technical developments, which provide extensive information on the spatial structure, chemical composition and microbial populations within the biofilm. In addition, it provides a critical analysis of the use and limitations of all these techniques, in order to help the multidisciplinary scientific community to make a judicious and appropriate scientific decision. Finally, new methods, already exploited in other fields of investigation of microbial biofilms, are also discussed. In particular, we have highlighted how the physico-chemical characterization of pH and chemical transport phenomena within a biofilm could help to understand the mechanisms involved in the interactions between biofilms and reactive cementitious materials. Article Structure: The article is organized in 5 parts. A first part introducing the problematics of the subject and the structure of the article. A second part focused on the techniques employed to study the spatial structure and the chemical composition of biofilms formed on cementitious materials. A third part focused on the methods used to quantify and identify the microorganisms in biofilms formed on cementitious materials. The fourth part focuses on approaches not yet used but which would be useful to develop for the study of biofilms formed on cementitious materials. Finally, the last part summarises the key points of the article and provide future directions for the research on biofilms formed on cementitious materials.