Expansive Behavior in Circular Steel Tube Stub Columns of SCC Blended with CFB Bottom Ashes

This work provides a systematic analysis of the expansive and load-deformation behaviors in circular steel tube stub columns (CSTCs) of self-compacting concrete (SCC) blended with ground circulating fluidized bed (CFB) bottom ashes (BAs). A series of SCCs with different expansive properties was fabricated by adding CFB-BAs. As the dosage of CFB-BAs increased, the time-dependent circumferential and axial strains increased. The expansive and load-deformation behaviors of cured SCCs filling the CSTCs were evaluated. Time-dependent expansive strain (TDES) measurements revealed that the expansive behavior in both the circumferential and axial directions had the same variation trend. The circumferential TDES values were much larger than the axial values. The axial load-displacement relations indicated that the specimen with 30% CFB-BAs had a 34% higher ultimate load, and it had a 54% higher ultimate load when 1.5% sodium sulfate was added to the specimen. The prestress had a significant impact on the ultimate capacity of concrete-filled steel tubes (CFTs). However, the ultimate capacity still was determined by the compressive strength of the core concrete, and it was not directly proportional to the initial prestress. The specimen with a 4-mm wall thickness and 30% CFB-BAs gained the most ultimate stress, indicating that the wall thicknesses of steel tubes had a distinct influence on the load-deformation behavior.