BioResComp - Biogenic corrosion resistant geopolymer - concrete composites for sewer applications

Microbial induced concrete corrosion (MICC) is accounted for ~40 % of the degradation of concrete based subsurface wastewater infrastructure globally. A further problem is the toxic outgazing, which poses a serious health hazard. In Germany a use of 450 Mil. Euro for repair measures of MICC-damaged sewer systems are documented each year. The number of unreported cases is suspected to be significantly higher. At present there are two usual ways, how to repair such sewer constructions: Firstly by mounting inliners made from plastic and secondly by coating the inner surfaces. The latter is mostly realised by the use of organic polymer-modified mortars and synthetic resins (i.e. epoxy). A great number of such measures of repair turned out to be costly and non-durable. This is the reason why alternative materials, especially inorganic ones based on the silicate-technology, were developed and launched. These materials are used for making very thin (up to 3mm) coatings. Their long-lasting protective function has not been proven yet. Conventional sulphate attack happens via fluid transport whereas MICC progresses due to the transport and diffusion of aggressive gases such as H2S and CO2 and subsequent microbial transformations. Thin coatings from silicate-based inorganic materials are generally water-proof but permeable to gas and therefore they cannot sufficiently work as a MICC barrier for the standard concrete beyond. One of the most acid-resistant silicate-based materials are Geopolymers. However, their physical and microstructural properties vary in a wide range depending on their composition. If Geopolymers are mixed with aggregates, one gets Geopolymer Concrete (GPC). The project consortium developed specific compositions of GPC, highly resistant against MICC. Further previous research work pointed out, that certain metallic admixtures significantly inhibit the growth of relevant bacteria steering this highly corrosive attack of concrete. Based on these findings the outlined project BioResComp deals with the idea to use such innovative bacteriostatic Geopolymer Concrete as a more solid construction material instead of thin coating applications for both, repair measures and new construction of waste-water buildings. One can expect that constructing without any standard concrete will not be an economic future way. Therefore, the project proposes a new composite technique by combining a standard concrete part with a GPC part. The key of this technique is a very strong bond between the two materials. Main goal of the project is to study the mechanical composite behavior and the resistance of composites to MICC. A multi-disciplinary and mainly experimental research approach will help to get a comprehensive understanding of all the interdependencies between material composition, GPC-thickness, bond behavior, crack formation, bacterial growth and the corrosion mechanisms. We follow the hypothesis, that at certain thicknesses of the new bacteriostatic GPC layer (typically a few centimeters) a balance between the microbial growth (attack) and the corresponding resistance of the composite system will come into being.