钢管混凝土用氧化镁复合膨胀剂试验研究与工程应用

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

试验研究了20℃与40℃条件下,掺入氧化钙与不同活性氧化镁膨胀熟料水泥砂浆的限制膨胀率,在此基础上,采用应变计测试管内混凝土模拟实际温度历程下的应变历程,用以评价钙镁复合膨胀剂作用效果。结果表明,管内混凝土凝结硬化后早期经历了剧烈的温升与温降过程,而目前常用的氧化钙类膨胀剂活性高、水化快、温度敏感性强,与管内混凝土收缩历程不匹配,在温降阶段几乎没有补偿效果。将不同活性轻烧氧化镁与氧化钙熟料按特定比例混合制成一种新型膨胀剂用于管内混凝土,利用氧化镁的延迟膨胀性能,可分阶段、全过程补偿管内混凝土收缩,有效建立并存储膨胀预压应力。

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 ℃ and40 ℃ 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.