Response and Modeling of Steel Tubes Filled with Recycled Fine and Coarse Aggregate Concretes under Long-Term Loading

The engineering properties of concrete with recycled aggregates (RAC) can vary more widely than normal aggregate concretes (NAC). Because concrete-filled steel tubes do not rely solely on the concrete in compression, using RAC in a concrete-filled steel tube (RACFST) is a sustainable structural solution. Most work has focused on using only coarse recycled aggregate (CRA), but with virgin sand supplies decreasing, there is a need to use fine recycled aggregate (FRA). Meanwhile, the long-term deformation of RACFST may be notably affected by FRA. A research program was undertaken to investigate the impact of FRA on the time-dependent behavior for the RACFST. Study parameters included CRA replacement ratio (r(C)), FRA replacement ratio (r(F)), and concrete strength (f(cm)). The experimental results showed that the FRA and CRA had a modest compounding effect (i.e., the FRA effect depends on r(C)) in RACFST, but this effect can be more pronounced for lower-strength concretes. Using RAC increases the scatter in the deformability but does not affect the rate of creep development. A creep model for NAC was then modified to predict the long-term deformation of RACFST. A parametric study was carried out to evaluate the time-dependent effects of the RACFST with other untested parameters. (C) 2021 American Society of Civil Engineers.