海水环境下混凝土耐久性研究

RESEARCH ON THE DURABILITY OF CONCRETE IN MARINE ENVIRONMENT

采用岩相分析、X射线衍射分析、化学分析和扫描电镜/能谱分析等方法,对珠江三角沿海地区某30年跨海大桥桥墩混凝土开裂的原因及其耐久性问题进行研究。研究结果表明,该海工混凝土含有碱活性细集料,在海水环境下发生了碱-集料反应;海水的镁盐也侵蚀了混凝土,在粗裂缝的表面生成了大量的氢氧化镁沉淀;碱-集料反应与海水镁盐侵蚀等复合作用导致混凝土开裂。这是我国首例海水环境下混凝土因细集料发生碱-集料反应,并受镁盐侵蚀而造成复合破坏的报道。海工混凝土需综合考虑海水环境的影响,在选用集料时,应检测其碱活性,避免使用具有碱活性的集料。具有碱活性的细集料对混凝土耐久性的影响需引起重视。

The reason of cracking andthe durability problem in 30-year-old Pier of a-sea crossing bridge in coastal areas of the Pearl River Delta was studied by means of petrographic analysis, X-ray diffraction analysis, chemical analysis, scanning electron microscopy/energy dispersive analysis and other techniques. The results showed that there were active fine aggregates in the concrete, and alkali-silica reaction had occurred, the concrete had been eroded by magnesium salt in sea water and the sediments on the surface of the crude cracks contained a lot of magnesium hydroxide. The cracking in the concrete was caused by the compound damage of alkali-aggregate reaction and magnesium salt erosion. This is the first report in our country that the compound damage to the concrete in marine environment was caused by the alkali-aggregate reaction of fine aggregate and erosion of the magnesium salt. It was demanded strongly that the alkaline activity of aggregates be detected and the compound damage of the marine environment be generally considered in the ocean concrete projects. The influence of fine aggregates having alkaline activity on the durability of concrete should be taken seriously.