MICROSTRUCTURAL EVALUATION OF A CONCRETE OVERPASS SYSTEM DURING REHABILITATION

Concrete durability and deterioration are so closely related that they ' must be considered together. Microstructural characterization, which has received limited attention in determining concrete durability, is used to determine the parameters of concrete overpass deterioration i n a major highway in Montreal, Canada. The highway crosses an importan t urban area and has been subjected to high concentrations of deicer s alts for 25 years. Sample of both concrete and rebar corrosion were ex amined by SEM/EDXA, XRDA, mercury porosimetry, and optical microscopy. A number of interesting features were noted, including a high ettring ite content at the paste-aggregate interface and the presence of unusu al deterioration products, such as thenardite and trona. Deicer salts and sulfates from vehicle exhaust are suggested as possible sources.