不同水灰质量比混凝土早期受冻氯离子扩散系数实验

摘要

The paper aims to analysis of structure of concrete at early frost damage mechanisms and solves concrete durability problems. The NEL method is applied to test the electrical conductivity to calculate out Cl- diffusion coefficient of three kinds of concrete in the water to cement ratios of 0. 38,0. 44,0. 50 which standard curing periods were respectively 1 ~5 days,then curing periods at -5 ℃/ -20 ℃ were 7 days,last curing 0/27 -23 days in standard condition. And simultaneity compressive strength was tested. The results indicated that the Cl- diffusion coefficient of early age concrete at the frozen temperature of - 20 ℃ was lower than that of - 5 ℃. The Cl- diffusion coefficient of concrete in standard curing condition after early age at -20 ℃ was lower than curing 28 d in standard curing condition. The Cl- diffusion coefficient of concrete at -5 ℃ lower than that at -20 ℃ under identical condition;The compressive strength of concrete at-5 ℃ was higher than that at -20 ℃ under identical condition. The Cl- diffusion coefficient of concrete in the water to cement ratios of 0.50 curing in standard condition after early age at the frozen temperature (SCAFT)reached to its peak at 3 d. The Cl- diffusion coefficient of concrete in the water to cement ratios of 0. 38 reached to its valley at 3 d. The compressive strength of concrete at SCAFT was increasing along with curing age, and the increase was getting less at 2 - 4 d. The cause of early damage of the concrete in condition of high water cement ratio(W/C)and -20 ℃ were frost heave force,and the cause of early damage of the concrete in condition of low W/C and -5 ℃ were moisture transfer and drying force. The concrete curing periods were 3 d reached the structure of resistant critical strength.%目的 分析混凝土早期结构受冻损伤机理,解决混凝土耐久性问题.方法 水灰质量比分别为0.38、0.44、0.50的混凝土试件在标准条件下养护到1～5d,-5℃、- 20℃冻7d,即时恢复标准养护累计28 d后,采用NEL法测试混凝土饱盐电导率,计算Cl-扩散系数.同时测试试件强度.结果 -20℃早期受冻后的Cl-扩散系数比-5℃早期冻的Cl-扩散系数后要小.-20℃早期冻后恢复标养的Cl-扩散系数比标养28 d的Cl-扩散系数小,-5℃冻后恢复标养的Cl-扩散系数比同条件-20℃的Cl-扩散系数小；-5℃冻后恢复标养的强度比同条件-20℃的强度大.早期受冻后恢复标养,水灰质量比为0.50的混凝土在预养3d时出现峰值,而水灰质量比为0.38的混凝土在预养3d时出现低谷.混凝土冻后恢复强度随预养护龄期增长而增大,在预养2～4d强度增长平缓.结论 水灰质量比大、- 20℃混凝土早期受冻损伤是以结冰冻胀破坏为主的,水灰质量比小、-5℃混凝土早期受冻损伤是以迁移干燥破坏为主的.混凝土预养3d对应的结构应是混凝土抗冻临界结构.