Bond–slip behavior of eolian‐sand micro‐expansive <scp>CFSTs</scp> : Experimental tests and analytical modeling

Abstract This study experimentally and analytically investigates the interfacial bond–slip behavior between square steel tubes and eolian‐sand micro‐expansive concrete for application in concrete‐filled steel tube ( CFST ) structures in arid and semi‐arid regions with natural sand scarcity. Sixteen push‐out tests were performed on square CFST specimens, with width‐to‐thickness ratio, eolian‐sand replacement ratio, and expansive‐agent dosage as the main variables. The results show that the interfacial bond–slip evolution can be divided into three stages ( OA – AB – BCD ), and that reducing the width‐to‐thickness ratio increases the peak bond strength by up to 56.7%. An optimal eolian‐sand replacement level of about 35% and expansive‐agent dosages of 8%–12% were identified, which enhance bond performance through improved matrix densification and beneficial self‐stress, whereas higher replacement levels and overdosed expansive agent lead to microcracking and bond degradation. A parameterized three‐stage bond–slip constitutive model was proposed, with model parameters explicitly related to wall thickness, eolian‐sand content, and expansive‐agent dosage; the predicted curves agree well with the test results. The findings provide mechanistic insight and design guidance for CFST structures utilizing eolian‐sand concrete.