Abstract
In recent years, many studies have been performed on the crack repairing technique in concrete or the protection of the concrete surface against sulfate ions. Bacterial immobilization and survival rate are the dominant influencing factors for the repair of concrete. In this study, a negative pressure method (NPM) was developed to forcibly remove air in the porous materials of concrete, which was applied for surface repair through bio-coating using Rhodobacter capsualtus. For normal repair—repair using the conventional simple soaking method (SSM) and repair through NPM—various evaluations of the concrete strength and durability were performed. Since a reinforced concrete (RC) structure for the application of these repair methods is a sewer pipe exposed to sulfate ingress, variations in concrete mass and strength were analyzed by the accelerated sulfate resistance test. The diffusion coefficient of the sulfate ion in the repair materials and the bacterial count after the accelerating test were also measured. In order to investigate the changes in the properties of the concrete hydrates, surface analyses with SEM, XRD, and TGA were carried out on the concrete under the repair layer after the tests. In all the experimental results, the bacterial immobilization rate was evaluated, and the high immobilization rate indicates the excellent shielding of sulfate ions as well as improves the survival rate of bacteria. This not only improves the service life of the coating repair but also extends the service life of the structure itself. As a result of analyzing the composition of concrete protected by different types of repair, the results most similar to the general concrete composition without sulfate attack were obtained in the case of applying NPM, which shows the least damage from sulfate attack.
Highlights
The X-ray diffraction (XRD) pattern of the sample taken from the concrete surface without exposure to sulfuric acid was indicated as the comparative data
In the concrete surface coated with the normal repair without bacteria mixing, the peak intensity of gypsum was high at approximately 11–12◦, 31◦ and 33◦
The peaks of gypsum were not relatively high in the concrete surface coated with slime bacteria-mixed repair
Summary
Concrete structures have the advantages of cost effectiveness and durability; calcium hydroxide inside cement may form ettringite or calcium carbonate, or may even be dissolved in the outer surface, as in the case of leaching, depending on the external environment [1,2]. Deterioration factors such as chloride attack and carbonation do not have a significant effect on hardened concrete, but bring forward the corrosion initiation time of the internal reinforcement and accelerate corrosion, which may lead to critical problems in terms of structural safety. The progress of the service life modeling of the sulfate attack was relatively slow because the formation of ettringite from the reaction between calcium hydroxide and sulfate ions expands the concrete volume, making quantitative modeling with a simple diffusion analysis difficult
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