半暴露桥墩混凝土受硫酸钠破坏的研究

Study on the Sulfate Attack on Concrete of Pier by Na_(2)SO_(4)

当铁路桥墩半暴露在含有硫酸钠的水环境中时,硫酸钠溶液通过灯芯效应传输至桥墩水分蒸发区。而混凝土水灰比的变化会改变混凝土内部孔隙结构,从而影响半浸泡在硫酸钠溶液中混凝土内部溶液的灯芯效应传输过程,进而影响进入到混凝土中硫酸根离子含量。文章固定环境条件(20℃,RH55%),将5组水灰比为0.35、0.40、0.45、0.50、0.55的混凝土半浸泡在5%的Na_(2)SO_(4)溶液中,连续测试混凝土试件水分蒸发速率和进入固化在混凝土内部的硫酸根离子含量,试验结果显示,半浸泡90 d后,水灰比为0.50和0.55的混凝土水分蒸发区出现了明显的剥落破坏,进入这2种混凝土中的硫酸根离子含量也显著大于进入水灰比为0.35、0.40和0.45这3种混凝土中的含量;随着水灰比降低,进入混凝土中硫酸根离子的含量并没有呈现随着水灰比的降低而减少的显著特点,水灰比为0.45的混凝土中水分蒸发速率小,进入混凝土内部的硫酸根离子含量也最少。

When the piers are partially exposed to the waterenvironmentcontaining Na_(2)SO_(4),the water containing Na_(2)SO_(4) is absorbed into and reaches the exposure zone concrete of the piers by the wick action.However,the wick action is controlled by the pore structure of concrete,and the pore structure will be changed due to different W/C ratio.In the present paper,5 concrete specimens with different W/C ratios of 0.35,0.40,0.45,0.50 and 0.55 were partially immersed in the 5% Na_(2)SO_(4) solution under the condition of 20℃ and RH 55%.After 90d exposure,the test results indicated that the water evaporation ratio and total SO_(4)^(2-) content in concrete specimens did not fall following the W/C ratios decrease.The concrete with W/C ratio of 0.45 showed the lowest evaporation ratio and least SO_(4)^(2-) content.The concrete specimens with W/C ratios of 0.50 and 0.55,where much higher SO_(4)^(2-) content was checked,showed obvious damage observation.