Response and Modeling of Steel Tubes Filled with Recycled Fine and Coarse Aggregate Concretes under Long-Term Loading
Mu-Zi Zhao, Yuyin Wang, Dawn E. Lehman, Yue Geng, Charles W. Roeder
Abstract
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 (rC), FRA replacement ratio (rF), and concrete strength (fcm). The experimental results showed that the FRA and CRA had a modest compounding effect (i.e., the FRA effect depends on rC) 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.