Adhesion of Biofilm to Mortar Surface with Protective Coating in Seawater Environment and the Influence on the Mortar Performance

To improve the corrosion resistance and mechanical properties of mortars in seawater, this work explored the evolution of biofilm adhered on mortar surfaces with different protective coatings and the mortar properties in the seawater environment. Sulfur-oxidizing bacteria were selected as experimental strains, and epoxy resin and polyurethane as protective coatings. The performance of each group of samples was tested from the 15th day to the 120th day at intervals of 15 days. The evolution and morphology of the biofilms were measured by scanning electron microscopy (SEM), a common camera, ultraviolet-visible spectroscopy (UV-Vis), and ultra-deep field microscope. The properties and microstructure of the mortars were determined by X-ray diffractometer (XRD), thermogavimetric analyzer (TG), energy dispersive spectroscopy (EDS), and electro-hydraulic pressure laboratory machines. The results show that: (1) In a seawater environment, protective coatings can effectively impede the adhesion of biofilms, and the beginning of the rapid growth period of the biofilms is delayed from day 30 to day 60. (2) On day 120, the highest dehydration rate of 0.61% is for the uncoated specimen. In contrast, the epoxy resin group experienced a dehydration rate of 0.57%, and the polyurethane group a dehydration rate of 0.53%. This indicates that a polyurethane coating can effectively hinder the entrance of corrosive media from the seawater, alleviate the tendency of the mortar to swell, delay the corrosion process of the mortar in the seawater, and provide some degree of protection for the mortar.