Characterization of microbial-induced concrete corrosion by combining morphology observation and fluorescence staining

Biofilms play a crucial role in microbial-induced concrete corrosion (MICC), although their growth and composition vary depending on different environment. However, limited studies have been conducted on the corrosion process of MICC in tropical coastal sewer systems, specifically on the spatial microbial distribution within the concrete corrosion layer. This study utilized scanning electron microscopy, element mapping, and fluorescence microscopy to characterize the micro-morphology of biofilm and corrosion products, the element distribution in concretes using element mapping, and the spatial distribution of microorganisms inside deteriorated concretes, respectively. The results demonstrate that compared with the freshwater group, the seawater group with a high salt content is more favorable for biofilm adhesion to the concrete surface and induces more serious corrosion owing to the biological sulfur cycle reaction. The biological sulfuric acid produced by microbial metabolism corrodes concrete to produce gypsum and other corrosion products. Moreover, the surface and internal corrosion layers of concrete contain an abundance of Fe, a crucial element for microbial survival. Furthermore, fluorescence staining reveals a considerable number of microorganisms in concrete, and free proteins are widely distributed in the degraded hydration products, leading to microbial activity. This implies that microorganisms infiltrate the concrete through cracks and pores and proliferate within the concrete, hence aggravating bio-deterioration. Importantly, the combination of morphological observation and fluorescence analysis can provide a deeper understanding of the MICC process in seawater-containing sewage conditions.