膨胀剂掺量和应力比对钢管混凝土徐变性能的影响

Effect of interaction between expanding agent proportion and stress ratio on creep characteristics of concrete filed steel tube

为了研究膨胀剂掺量和应力比对钢管混凝土徐变性能的影响,进行膨胀剂掺量分别为4%,8%和12%共3种情况下的钢管混凝土徐变应变试验,测试钢管与混凝土整体纵向变形随时间的分布规律。同时进行应力比分别为0.15,0.31,0.33,0.37和0.74共5种情况下的徐变试验,测试在相同荷载下,不同应力比钢管混凝土应变变化规律。研究结果表明:膨胀剂掺量对钢管混凝土徐变应变的影响由小到大依次为12%,8%和4%,但是徐变应变并不是随着膨胀剂掺量的增加而呈比例减少;徐变应变随着应力比的增加而增加。应用扫描电镜二次电子成像观测及能谱成分分析膨胀剂的作用机理,得出膨胀剂反应生成钙矾石,其微膨胀可以补偿收缩;同时钙矾石填充在结构孔隙中,使水泥石更加致密。通过应力比对钢管混凝土徐变影响的机理分析,得出混凝土应力随着应力比的增加而增大,同时随着壁厚的增加,钢管对混凝土的侧向约束增加,限制了混凝土徐变变形。

In order to study the effects of expansive agent dosage and stress ratio on creep performance of concrete filled steel tube, three creep strains were tested on concrete filled steel tube under 4%, 8% and 12% expansive agent dosage respectively, and the distribution regularities were tested for the overall longitudinal deformation of steel tube and concrete over time. Meantime, five creep tests under stress ratios of 0.15，0.31，0.33，0.37 and 0.74 respectively were conducted to test the strain change rules of concrete filled steel tube under the same load but different stress ratios. The test results show that the expansive agent dosage has different creep and strain effects on concrete filled steel tube, in an order of from small effect to large one, being 12%, 8% and 4% dosage; however, creep and strain do not decrease proportionately with the increase of expansive agent dosage, but increase with the increase of stress ratio. It can be concluded from the secondary electron imaging observation via scanning electron microscope and acting mechanism of expansive agent analyzed by energy spectrum component analysis that microdilatancy of expansive agent may provide compensating and shrinkage when reacting to generate ettringite, which fills in the structural pore space at the same time to make the cement stones more compact. Moreover, through the mechanism analysis on the creep effects of stress ratio on concrete filled steel tube, the research results can provide that the stress of concrete increases with the increase of stress ratio, and with the increase of wall thickness, steel tube strengthens lateral restraint on concrete, so as to restrict the creep deformation of concrete.