Expansive ultra-high performance concrete for concrete-filled steel tube applications

In this study, an expansive ultra-high performance concrete (UHPC) was prepared by combining use of lightweight aggregate (LWA) and CaO-expansive agent (EA) for concrete-filled steel tube applications. The coupled effects of LWA and EA on the volume stability, mechanical properties and microstructure of UHPC were systematically evaluated. The expansive stress of the outer wall of UHPC-filled steel tube was also determined. The test results showed that the EA and LWA could be effectively combined to produce a high expansive UHPC, and the internal curing effect of LWA mitigated the self-desiccation and promoted the hydration of EA, refining the pore structure of matrix. As a result, the expansive UHPC exhibited high levels of expansion and high mechanical properties. A maximum circumferential expansion of 308 μϵ and triaxial compressive stress of 3.65 MPa at 24 h could be obtained, which compacted the core UHPC and improved the interfacial bond between the steel tube and the UHPC.