Technologies for Improving the Evaluation and Repair of Concrete Bridge Decks: Ultrasonic Pulse Echo and Polymer Injection

摘要

A significant number of concrete bridge decks, both public- and nonpublic use, in the United States are subjected to a variety of detrimental environmental conditions. Many of the decks are in northern regions and are subject to cold weather; some of these are subjected to further degradation from the applications of deicing salts. The current major distress noted is the occurrence of shallow delaminations resulting in horizontal voids below the surface of the decks. It appears the majority of the delaminations are caused by freezing and thawing action, by chloride attack that corrodes the reinforcement, and by alkali-silica reaction. All three attack mechanisms require the presence of moisture. Efforts to design and place a dense, impermeable concrete are hindered at times due to the porous nature of concrete. As the concrete ages, a micro system of tension cracks and other surface imperfections can develop, exposing the matrix to water and chloride infiltration. Water infiltration alone can lead to accelerated alkali-silica reaction and steel-reinforcement corrosion. Surface spalling not only reduces ride quality, but it leads to more serious problems including structural deterioration and failure. Many concrete sealers and penetrants on the market are designed to protect concrete by improving and enhancing its physical properties. Surface sealers such as silane, silicones, and siloxanes have been developed to prevent the infiltration of moisture and chlorides. Penetrants such as high molecular weight methacrylate (HMWM) and epoxies have been developed to penetrate and fill cracks and porous areas in the concrete, sealing it against the infiltration of air, water, and chloride. Once the concrete is effectively sealed, both the progression of alkali-silica reaction and the corrosion of the reinforcing steel are arrested. These materials are also designed to bond to the concrete and thus to the structural integrity of the concrete.