Behavior of recycled aggregate concrete-filled basalt and carbon FRP tubes

This paper presents the results of an experimental study on the axial compressive behavior of concrete-filled FRP tubes (CFFTs), prepared using different amounts of recycled concrete aggregate (RCA). Thirty-six CFFTs were tested under axial compression. The effects of the RCA replacement ratio, specimen cross-sectional shape, FRP type, and concrete strength were studied. The results suggest that the axial stress-strain behavior of CFFTs is affected by the amount of RCA, which particularly affects the ultimate axial strain and FRP hoop rupture strain. For a given in-place concrete strength, an increase in RCA content leads to a decrease in compressive strength and an increase in ultimate axial strain of FRP-confined concrete. The results also indicate that the increased RCA content leads to a decrease in the hoop rupture strain of CFFTs. CFFTs manufactured with carbon FRP tubes instead of basalt FRP tubes and CFFTs with circular cross-sections instead of square cross-sections develop a higher compressive strength and lower ultimate axial strain. The effects of specimen cross-sectional shape and FRP type on the axial compressive behavior of CFFTs vary with RCA content.