基于钙镁复合膨胀的无收缩混凝土技术研究与应用

Research and application of non-shrinkage concrete technology based on CaO and MgO composite expansion agent

避免管内混凝土收缩脱空是保障钢管混凝土拱桥施工质量且进一步增加跨径的关键措施之一。试验研究了掺入不同配合比的钙镁复合膨胀剂管内混凝土,在恒温和变温条件下的体积变形与力学性能。结果表明:总掺量不变的情况下,20℃恒温时管内混凝土膨胀率随CaO掺量增加而明显增大,模拟实际工程的典型变温条件下,复合膨胀剂中MgO掺量为50%时,管内混凝土最终可残余约22με的膨胀变形,可实现钢管混凝土结构无收缩。外约束作用可提高掺入膨胀剂的管内混凝土抗压强度,不同龄期较自由状态提高了4.5%~7.7%。

Ensuring the compactness of the in-tube concrete without de-bonding and separation caused by shrinkage is of importance guaranteeing the construction quality of concrete-filled steel tube(CFST)arch bridge and promoting the further improvement of its span.This study investigated the deformation and mechanical properties of in-tube concrete containing CaO and MgO-based expansion agents with different mix ratio under both the constant temperature and varying temperature.The results showed that when the total mixing proportion was unchanged,the expansion of in-tube concrete was significantly increased with the increase of CaO dosage under the constant temperature of 20℃.Under the varying temperature condition consistent with the actual engineering,when the MgO dosage in composite expansion agents was 50%,the final residual expansion of in-tube concrete was about 22με.It can be seen that a suitable expansion component mix ratio can achieve no shrinkage in CFST structures.The external constraint of the steel tube can improve the compressive strength of in-tube concrete prepared with expansion agents by 4.5%to 7.7%at different ages.