Chloride Permeability of Concrete Deteriorated by Freezing and Thawing

骨料类型（天然和人工轻骨料），类型的投标人（波特兰水泥，闪光和粉末状高炉矿渣），水胶比（65%，55%和45%）和混凝土的年龄，其中冻融循环开始（28和3天）对氯离子渗透性恶化的混凝土冻融的影响进行了测试，由AASHTO标准T277中描述的方法。对没有夹带空气的混凝土和夹带空气为3.5%、5.5%和7.5%的混凝土进行了试验。试验结果表明：（1）在天然骨料混凝土中，掺入5%左右的空气，对防止混凝土因冻融而劣化导致的氯离子渗透性增加是相当有效的。对于不含外加剂的混凝土和掺有粉煤灰的混凝土，所需的最小含气量约为0.5%、5.5%和3.5（水泥的30%）和掺有粉状高炉矿渣的混凝土（水泥的70%）。2）如果是人工轻骨料混凝土，（在完全被水饱和的状态下），掺入7.5%空气不能有效地防止由于混凝土劣化而导致的氯离子渗透性的增加。3）掺有粉末状爆炸物的混凝土-与普通混凝土和掺矿渣混凝土相比，矿渣混凝土的氯离子渗透性显著降低。4）普通混凝土和轻质混凝土的氯离子渗透性均随水灰比的降低和混凝土龄期的延长而降低。

The effects of type of aggregate(natural and artificial lightweight aggregate), type of bider(portland cement, flash and powdered blast-furnace slag), water-binder ratio(65, 55 and 45 percent)and the age of concrete to which freeze-thaw cycles are initiated(28 and 3 days)on chloride permeability of concrete deteriorated by freezing and thawing were tested by the method described in the AASHTO Standards T277. Concrete without entrained air and concrete with entrained air of 3.5, 5.5 and 7.5 percent were tested. Grades of deterioration were controlled by the number of cycles of freeze-thaw cycle test.The followings were revealed from the test results :1)In case of concrete with natural aggregate, entrainment of air up to around 5 percent is considerably effective to prevent increase of chloride permeability due to deterioration of concrete accompanied by freezing and thawing. Required minimum air contents are approximately, O, 5.5 and 3.5 percent for concrete without admixture, concrete admixed with flyash(30 percent of cement)and concrete admixed with powdered blast-furnace slag(70 percent of, cement), respectively.2)In case of concrete with artificial lightweight aggregate(in state of completely saturated with water), entrainment of air up to 7.5 percent is not effective to prevent increase of chloride permeability du to deterioration of concrete.3)Concrete admixed with powdered blast-furnace slag showed remarkably less chloride permeability as compared with ordinary concrete or concrete admixed with flash.4)Less chloride permeability, in both ordinary and lightweight concrete, was observed in lower water-cement ratio, and in later age of concrete.