Effects of mineral admixtures on time-dependent behavior of high-strength self-compacting concrete-filled steel tubes

High-strength self-compacting concrete-filled steel tubes (HSCFST) have been widely used in high-rise buildings and long-span bridges due to their high workability, high compressive strength, and excellent seismic performance. To achieve those high performances, mineral admixtures, such as silica fume, fly ash, and ground granulated blast furnace slag (BFS), are commonly incorporated in the concrete mix. Yet the mineral admixture effects on creep behavior of HSCFST have not been well studied. In this paper, 524-day creep tests were conducted on eighteen specimens. The mineral admixture effects on the creep development trend of HSCFST were investigated, and the compounding effects between the mineral admixtures on the final value of the HSCFST creep were quantified. Using equivalent compressive strength, the creep model of the Eurocode was modified to account for the mineral admixture effects on both the development trend and the final value of HSCFST creep. Investigation shows that: (1) all three mineral admixtures significantly accelerate creep development rate, which can lead to a 55 % overestimation of HSCFST creep at the 50-year service time using the existing concrete creep models; (2) the fly ash and silica fume have a significant compounding effect on HSCFST creep, while little compounding effect exists between the BFS and silica fume; (3) the modified EC2 model can well predict both the development trend and the final value of HSCFST creep, with a 0.980 mean value, 0.164 coefficient of variation.