Axial Compressive and Buckling Behavior of Concrete-Filled Steel Tubes Incorporating Recycled Coarse Aggregate, Plastic Waste, and Silica Fume

This study investigates the axial behavior of steel tubes filled with concrete incorporating a hybrid mix of natural coarse aggregate (NCA), recycled concrete aggregate (RCA), dune sand, and plastic waste (PW). The primary goal is to investigate the structural performance of concrete-filled steel tubes (CFSTs) filled with hybrid recycled aggregate concrete and assess the effectiveness of existing design codes in predicting their load-carrying capacity, and recommending adjustments as needed to enhance their predictive accuracy and reliability. Eight concrete mixes were prepared with the NCA replaced by 60% RCA (by volume) in all the mixes. PW (high-density polyethylene (HDPE) granules) replaced the fine aggregate at volumetric replacement ratios of 0%, 15%, 30%, and 45%. In addition, silica fume (SF) was used to partially replace the cement by 5% to compare the performance with mixes without SF. A total of nineteen steel tubes of similar dimensions were prepared. Each concrete mix was used to fill two steel tubes, resulting in a number of sixteen CFSTs. The remaining three steel tubes were left unfilled to serve as a reference. The results indicate that there is a reduction in the load-carrying capacity with the increase of PW content. The experimentally obtained failure loads were compared with six design codes. The comparison revealed that three design codes provided conservative predictions, while the other three overestimated the capacity, with the degree of overestimation increasing as the PW content increased. Consequently, a correction factor has been proposed to improve the accuracy of the non-conservative design codes.