Evaluating the Impact of Durability-Integrated Concrete Mix Design on the Seismic Performance of RC Structures

The influence of durability on the seismic performance of reinforced concrete (RC) structures is often evaluated through indirect comparisons, where variations in strength between durable and less durable concrete obscure the true impact of durability. To address this limitation, this study proposes a framework for the mix design of durable concrete with strength-matched non-durable counterparts. By ensuring comparable strength, the differences in seismic performance can be directly attributed to durability effects rather than strength disparities. The framework is demonstrated through a comparative assessment of a five-storey moment resisting RC frame with durability-optimized, more durable concrete (MDC) against a strength-matched, less durable concrete (LDC) counterpart subjected to progressive degradation over subsequent years (e.g., 10, 30, and 50 years). The governing degradation phenomenon for concrete is considered to be chloride attack, and the corrosion in reinforcement is assumed to be uniform. The pushover curves are individually developed at various ages for structures conforming to the above two concretes, which only have durability disparities. The resulting variation in the ductility capacity against age is compared to showcase the effectiveness of the proposed mix design framework. A significant reduction in global and local ductility is observed for LDC with age, for example, about a 50% reduction at 50 years. Meanwhile, the overall reduction for MDC at the same age (i.e., 50 years) is only 20%. The findings show that neglecting durability can overestimate long-term capacity, highlighting the need for a durability-based proposed mix-design framework.