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混凝土中掺入适量外加剂,能改善混凝土的性能、加快施工进度或节约水泥。如果对外加剂性能了解不够、掺配操作不当或掺量不准,混凝土便会出现异常现象。我们在混凝土施工中就遇到了这样的问题,现总结如下。 1 假凝 当水泥中含有半水石膏,而所选用的外加剂与之不适应时,搅拌后刚出机混凝土便失去流动性(假凝)。防治方法为:减少外加剂掺量,降低搅合温度,更换外加剂或水泥。 2 速凝 新拌混凝土出机后十几分钟便初凝。此现象多出现在使用木钙减水剂时,原因是木钙被水泥中的氟石膏吸附生成铝酸三钙而加速水化。防治方法为:氟石膏水泥不能掺用木钙减水剂。 铁道建筑技术1994年第4期
Mixing proper amount of additives in concrete can improve the performance of concrete, speed up construction progress or save cement. If the performance of the admixture is not well understood, the dosing operation is not properly performed or the amount of admixture is inaccurate, the concrete will be abnormal. We encountered such problems in concrete construction and are summarized below. 1 Fake coagulation When the cement contains hemihydrate gypsum, and the selected additive is not compatible with it, the concrete that has just been stirred will lose its fluidity (false coagulation). Prevention methods include: reducing the amount of admixture, reducing the stirring temperature, and changing the admixture or cement. 2 Quick-setting The fresh concrete will start to condense after ten minutes. This phenomenon is mostly caused by the use of wood calcined water reducers, because the wood calcium is adsorbed by the fluorine gypsum in the cement to form tricalcium aluminate and accelerate hydration. The prevention and control method is: Fluorine-gypsum cement can not be mixed with wood calcium water reducer. Railway Construction Technology No. 4 of 1994