Abstract:
A partially encased composite (PEC) column is an H-shaped steel column with concrete infill between the flanges of the steel section. The use of recycled concrete aggregate (RCA) in PEC columns can offer significant sustainability benefits by reducing waste and lowering the environmental impact on construction. This study presents a series of tests on short PEC columns to investigate the effects of RCA on compressive strength and failure behavior of PEC columns cast with recycled concrete aggregate (RCA). A total of 30 PEC columns and three bare steel columns were tested under concentric and eccentric axial compression loads. The test incorporated five RCA replacement ratios (0%, 25%, 50%, 75%, and 100%) and three link spacing-to-depth ratios (0.33, 0.5, and 0.67). For the eccentrically loaded columns the compressive axial load was applied at a constant eccentricity ratio about the weak axis of the steel section. The failure mode, load-strain behavior and load capacity were assessed to evaluate the effect of the RCA ratio and link spacing.
Five concrete mix ratios were cast with variable RCA replacement ratios. The concrete strength was measured for each mix ratio, and the strength of concrete incorporating RCA was comparable to that of concrete made with natural aggregates. Since the source concrete for the RCA had a relatively high strength, the overall compressive strength of concrete with RCA did not decrease significantly. The failure mode was similar for all the PEC columns: crushing of concrete, and buckling of steel flanges. The test results indicate that columns become more brittle when the RCA ratio exceeds 50% since RCA contains microcracks. However, under concentric loading, the effect of the RCA ratio on column strength was negligible across different link spacing. Incorporating RCA resulted in a maximum 6% drop in strength. An increase in link spacing reduced the ultimate load for all columns, attributed to the reduced lateral stiffness and stability with wider link spacing. The initial stiffness was also comparable for different RCA ratios and link spacings. Increasing the RCA ratio increased the strain at peak load, especially for smaller link spacings, due to RCA impurities. All PEC columns outperformed bare steel columns in terms of strength and stiffness. The current design guidelines for PEC columns with natural aggregate concrete can be safely used to predict the capacity of the PEC columns incorporating RCA.
For eccentric loading, the effect of the RCA ratio varied with concrete confinement. At lower link spacing, the RCA had minimum impact on the compressive and flexural strength of the concrete. As the link spacing increased, the compressive and flexural strength decreased with the increase of the RCA ratio. A maximum of 12% reduction in strength was observed for PEC columns with higher link spacings. RCA ratio minimally affected initial stiffness at low link spacing but slightly reduced it at higher spacing. Post-peak responses were similar across RCA ratios. The theoretical load-moment interaction diagram was found to align well with the test results for the eccentrically loaded columns. These findings enhance sustainable building techniques by illustrating that RCA can be utilized efficiently in PEC columns without a considerable decline in strength and stiffness.