Structural assessment of an ASR-affected reinforced concrete bridge

ASR (alkali-silica reaction) has long been acknowledged as a key consideration when designing concrete structures in South Africa. This study raises awareness of the influence of ASR on the structural behaviour of reinforced concrete bridge structures. Aggregate type plays a role in how the ASR develops over the structural life cycle. Greywacke aggregate is found to be prominent in ASR-affected structures within the Western Cape region, and in the structure that was investigated. ASR decreases concrete tensile strength, compressive strength, and E-modulus over time. To develop a standardised approach that can be replicated on other bridge structures, a simply supported rectangular reinforced concrete bridge deck slab was analysed. The slab was modelled according to the construction drawings, including the reinforcement detailing, to determine the ultimate shear and moment resistance according to the code (BS 1972) used for the original design, and current Eurocode standards, for both unaffected and ASR-affected concrete. Traffic load was determined from the relevant TMH7 standard, and from weigh-in-motion data collected at a station on the high-traffic-volume route crossing the bridge. Due to compressive strength being the least affected material property by ASR deterioration, the ultimate resistance to original design loads was found to be sufficient.