混凝土超低温冻融循环损伤机理及控制措施

Mechanism and Improvement of Freeze-Thaw Deterioration of Concrete under Ultra-Low Temperature

通过冻融循环前后混凝土抗压强度、质量、表观及微观现象的改变揭示了其超低温冻融循环损伤机理。在此基础上,探究了抗冻剂和引气剂分别对混凝土超低温抗冻性的影响。根据试验结果可得到以下结论:1)循环最低温度越低,混凝土表面和内部结构劣化越严重,抗压强度降低越显著;2)混凝土超低温冻融循环损伤主要是由混凝土内部水结冰所致,在降温过程中,其体积膨胀对孔隙壁产生冻胀压力,使得孔隙逐渐增大、连通甚至出现裂缝,内部损伤逐渐累积使结构变得疏松;3)与抗冻剂相比,引气剂对混凝土超低温抗冻性的改善效果更好;4)抗冻剂和引气剂掺量分别不应大于水泥质量的5%和0.03%,两者在低温下的掺量宜为2%和0.02%~0.03%。

The deterioration mechanism of concrete under ultra-low temperature were investigateed by the change of compressive strength,mass,macro and micro phenomena before and after freeze-thaw cycles.The effect of antifreeze and air-entraining agent on the frost resistance of concrete is also provided.From the test results,the following conclusions are drawn:1)Freeze-thaw cycles of lower temperatures lead to more significant deterioration of concrete surface and micro structure as well as lower compressive strength;2)The deterioration of concrete can be attributed to the formation of ice.The pores enlarge and bridge due to the volumetric expansion of ice.The accumulation of damage leads to loose structure of concrete;3)The improvement on the frost resistance of concrete with air-entraining agent is better than that of concrete with antifreeze;4)The content of antifreeze and air-entraining agent shouldn’t excess 5%and 0.03%of cement mass,respectively.The proper content for antifreeze and air-entraining agent is 2%and 0.02%-0.03%.