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CIGMAT Report: Center Studies Concrete Coatings And Repair Methods For Corroded Steel Piles
Corrosion in reinforced concrete is influenced by three mechanisms as diffusion, corrosion and deterioration; but the diffusion period is the most critical (Liu and Vipulanandan 2003; Mebarkia and Vipulanandan 1995; Cady et. al. 1984). It must be noted that the deterioration stage will not start if the moisture, oxygen and/or chloride concentration levels are relatively low (Zemajtis et. al. 1998). Since reinforcement corrosion is dependent on the availability of moisture, oxygen, sulfate and chlorides, any methodology to reduce their ingress into the concrete mass will reduce concrete deterioration (Liu and Vipulanandan 2003 and 2004).
Several methods are used in protecting concrete surfaces including coating the concrete. Coating materials used in protecting concrete from corrosive environments include epoxies, methacrylate, urethane, silicate, siloxane and silanes (Vipulanandan and Issac, 2008; Vipulanandan et al. 2002(b), 2005). The primary function of a surface treatment is to prevent capillary action at the surface, thus preventing the migration of water and chloride ions into the concrete. Surface treatments materials used for protecting reinforced concrete structures include sealers and coatings. The general difference between sealers and coatings is that sealers penetrate the concrete surface and block the capillary pores, whereas coatings do not penetrate the concrete surface but form a thick film on the surface.
Concrete sealers can be divided into two main groups: pore blockers and hydrophobic agents (such as silanes and siloxanes). Hydrophobic sealers penetrate the concrete to some degree, while pore blocking sealers provide little penetration and instead form a thin film on the concrete’s surface. Pore blockers are further distinguished by their ability to partially or fully fill the surface pores; a capability not shared by hydrophobic agents (Wohl and LaFraugh, 1990). Concrete sealers work in two ways. First they substantially reduce the absorption of chloride ions and moisture. Secondly, they allow the progressive internal drying of concrete by reducing the rate of moisture gain from the environment. Hence the sealer protects the concrete and makes it breathable. Most sealers are not permanent; hence periodic reapplications may be necessary to maintain the protective properties of the sealers (Vipulanandan et al. 2008; Klahorst et al. 2004; Perkins 1997; Wohl and LaFraugh, 1990). To provide long-term durability by protecting the sealers and avoid their reapplication, the potential of resisting chloride and moisture intrusion by a combination of sealer with coating was investigated in the current study.