Experimental research and engineering application of MgO compound expansion agent in concrete filled steel tube.

An experimental investigation on the restrained expansion rate of cement mortars which were prepared by mixing calcium oxide (CaO)expansion clinker and magnesium oxide (MgO)expansion clinkers with different active reaction time at 20°C and 40°C was carried out. Then the strain history of concrete filled steel tube (CFST)was tested under mock temperature history of actual situation by using concrete strain meter to evaluate the effect of calcium oxide (CaO)and magnesium oxide (MgO)compound expansion agent (EA). The results indicated that CFST has experienced drastic temperature rise and drop process at its early age. However, the currently used calcium oxide expansion agents have characters of high activity, fast hydration, and strong temperature sensitivity, which do not match the shrinkage process of CSFT, they couldn't compensate CFST shrinkage at temperature drop stage effectively. Light burned MgO clinkers with different active reaction time and light burned CaO clinker were compounded in a certain ratio as a new kind of concrete expansion agent which was applied in CFST, the delayed expansion performance of magnesium oxide can be used to compensate the shrinkage of CFST in stages and throughout the process. Therefore, the expansion prepressing stress from core concrete to steel tube wall has been established and maintained effectively. [ABSTRACT FROM AUTHOR]