在盐湖环境中高强与高性能混凝土的抗冻性

FREEZINGTHAWING DURABILITY OF HIGH STRENGTH AND HIGH PERFORMANCE CONCRETE EXPOSED TO SALT LAKES

用快冻法研究了高强与高性能混凝土在水中和在西藏、内蒙古、新疆和青海盐湖卤水中的冻融耐久性,探讨了其冻融破坏机理。结果表明:在水中冻融时,活性掺合料严重降低了非引气高强混凝土的抗冻性,目前的非引气高性能混凝土不具备高抗冻性的特征,并非真正意义上的"高性能",其冻融破坏起因于单硫型水化硫铝酸钙向钙矾石转化时的膨胀压,不含活性掺合料的普通与高强混凝土的冻融破坏源于水冻胀压;在盐湖卤水中冻融时,引起混凝土冻融破坏的主导因素是盐结晶压,混凝土的抗卤水冻蚀性主要取决于盐结晶压的损伤负效应和卤水冰点降低的损伤正效应,而且与盐湖卤水的成分密切相关。高强与高性能混凝土具有很高的抗卤水冻蚀性,在盐湖地区属于高耐久性的混凝土,适用于不同类型的盐湖环境。

Freezing-thawing durability of high strength and high performance concretes exposed to salt lakes in the provinces of Xinjiang, Qinghai, Inner Mongolia, and Xizang were investigated by accelerated freezing-thawing, and the destructive mechanism was also discussed. The results show that the freezing-thawing durability of none-air-entrained high strength concrete (HSC) is reduced severely by adding of active additives when pure water is as freezing-thawing medium. Current none-air-entrained high performance concrete (HPC) is not high performance due to the poor freezing-thawing durability. Demolishment of concrete contained active mixture is caused by the expansibility occurred when calcium monosulphoaluminate hydrate is transformed to ettringite, while the demolishment of ordinary portland concrete (OPC) and HSC contained none-active mixture is caused by icing pressure. When the freezing-thawing medium is salt lake bittern, the damage is mainly due to the pressure induced by salt crystallizing. Bittern freezing-thawing durability of concrete is determined by balancing the disadvantageous effects caused by the pressure of salt crystallization and the advantageous effects of lowering ice point, and it is also closely related with the bittern composition. Bearing high bittern freezing-thawing durability, both HSC and HPC are applicable to various salt lakes.