Effect of CaO and MgO based expansive agent on deformation and mechanical properties of concrete-filled steel tubes

Abstract The separation problem between core concrete and steel tube is one of the main bottlenecks restricting the construction of super large-span concrete-filled steel tubular arch bridges. One of the main measures to solve this problem is to prepare micro expansive core concrete by using the shrinkage compensation property of expansive agent. This study investigated the deformation and mechanical properties of core concrete containing CaO-based and MgO-based expansive agent under both the constant temperature and the varying temperature. The results showed that concrete containing CaO-based and MgO-based expansive agents can produce remarkable expansion which increases with the increase of CaO-MgO ratios under the constant temperature of 20 °C, but decreases with the increase of CaO-MgO ratios under the varying temperature. Through the restraint from the steel tube can reduce the expansion value, proper selection of CaO-MgO ratio can still produce enough expansion in core concrete to compensate autogenous and thermal shrinkage, with the concrete still in expansion state when the temperature finally stabilizes. Thus it is beneficial to maintain the integrity between the core concrete and the steel tube. The results obtained will provide guidance for the application of this kind of expansive agent in concrete-filled steel tube structure.