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Understanding interactions between cementitious materials and microorganisms

Understanding interactions between cementitious materials and microorganisms

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Microorganisms can cause damage to building materials. They are mainly bacteria, fungi, and algae. Microorganisms' activity can cause material damage (biodeterioration), which can lead to chemical, mineral, and microstructural problems. The aesthetics of buildings can be affected by the proliferation of biological stains on roofs and facades, or the quality of indoor air. Microorganisms have the potential to heal materials and can be beneficial. Bio-based protective systems for building materials are being developed to explore their actions. Understanding the interactions between microorganisms and building materials is essential for developing safer, more durable, and better-quality structures in all environments. The durability and safety of concrete structures can be affected by microorganisms. This paper will present two examples. 


The biodeterioration and degradation of concrete in agro-food and agricultural environments is the first. The second example concerns the abiotic as well as biotic reactivity for nitrates in a repository of intermediate-level, long-lived radioactive wastes. This paper describes the methods used to understand and explore phenomenology in complex biogeochemical interactions. These studies include the development of experimental pilots and test methods to allow these explorations to take place. These studies also highlight current shortcomings in standardization and scientific literature.



A few general facts about microorganisms

Microorganisms, which are microscopic pioneer organisms in all aspects of life development, are found in soil, air, and water. Their metabolic functions, i.e. All the biochemical reactions that allow microbial cells to grow, reproduce, and react. A succession of redox reactions results in the creation of microbial biomass. This requires an energy source (light or the oxidation of chemical, organic, or inorganic compounds). An electron donor) and a source of carbon (organic or organic, i.e. CO 2. The main mode of classification for microorganisms is metabolism. This describes how microorganisms interact and react with their environment, including substrates (for instance, building materials). 


It is also dependent on the characteristics of an environment. The characteristics of an environment are a selection factor for the type of predominant microorganisms within a medium. In fully aerobic conditions, ammonium-rich environments will lead to significant nitrifying microorganisms (case of wastewater treatment plants with high solid retention times), while in sulfur-rich media, sulfur-oxidizing macroorganisms (SOM), will grow (cases involving the crown portion of sewer pipes). Microorganisms are capable of influencing the environment. This is in addition to their rapid adaptation to it. The surface of a substrate can be home to many populations that, by following each other, can cause chemical conditions to evolve towards more favorable levels. For example, the succession of acidophilic and neutrophilic SO can result in a decrease in concrete's pH. A biofilm is a form of microorganisms that is composed of aggregates of the organized microbial community held together by the polymers excrete. This makes them more resilient to extreme environmental conditions and variations.


Building materials can get microbial stains

Also, microorganisms can affect structures by their appearance. Colored microorganisms can cause facades to crumble or become invasive. These microorganisms are mostly algae or cyanobacteria. They are photoautotrophic microorganisms. They use light as an energy source, and mineral compounds as carbon sources (CO 2), and electron donors (photosynthesis). They can grow on only mineral supports like stone, concrete, or cementitious coverings (with a lower pH after carbonation or any other chemical weathering), and roofing tiles. These stains can be very ugly and cause damage to infrastructures. It all depends on the climate, environment, and architectural conditions. This type of attack can also be carried out by fungi. This can cause aesthetic and structural damage to building materials. In the case of highly regarded buildings, it may also lead to high cleaning costs and image prejudice. 


While the source of these alterations has been identified, research now focuses on the colonization mechanisms and the factors that influence them. Some research focuses on improving the bio-receptivity to materials to encourage the growth of microorganisms like algae and lichens, as well as higher plants that can enhance the appearance and thermal performance of buildings.


Indoor microbial proliferation

Indoor microorganisms can also cause indoor environment degradation. They are responsible for the production of allergens, allergens, and other metabolites, as well as for the growth of molds in building materials. Toxic effects and irritations, as well as other skin and respiratory diseases, can lead to health problems. It has a significant social and economic impact. Plasterboard, mortar, and other building materials have porous surfaces. Plasterboard, mortar, etc. are porous and often rough. These materials can be a support for the growth and proliferation of microorganisms in damp environments. Although microorganisms found in buildings are well-known, there are no studies that link the properties of conventional building materials to the nature of proliferation in terms of species and kinetics.



Building materials and microorganisms may interact in many settings. These interactions can affect the durability, safety, and aesthetics of multiple buildings and infrastructures. The two examples in this paper have shown that these phenomena cannot be explained by the chemical or geochemical reactions they might contain. The development of test methods to identify the interactions and to evaluate the performance of building materials under representative conditions is a technological challenge. This topic is the focus of several research projects currently underway, with different contexts in Construction. The test methods must be specific to the environmental conditions. Standardization must evolve to better take into account the building material-microorganism reaction, both from the perspective of test methods and formulation prescription (particularly regarding concrete). The next few years will be a time of great scientific progress in understanding biodeterioration mechanisms and biofilm's influence on the intensity and kinetics alteration. The impact of material properties on microorganism activity and their structuring into biofilm is important, but it is still poorly understood. Even though it can affect the durability of materials and products. These are critical steps in developing building materials that can withstand such harsh environments. This is the goal of RILEMTC 253-MCI. It was recently established to address all these issues and other topics, such as indoor microbial proliferation or bacteria-based protective systems. Research on microorganism-building materials interactions is a constant challenge. This requires multidisciplinary teams that include microbiologists as well as chemists, process engineering, and civil engineers. It is a fascinating and rewarding field that requires constant dialogue between researchers with different skills.



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