不同pH值模拟混凝土孔隙液中镀锌层的阳极特性逆转

Reversion of Anode Characteristics of Galvanizing Coating in Simulated Concrete Pore Solution with Different pH Values

在不同pH值的混凝土中镀锌层显示有阳极逆转现象,其对基体钢的保护作用出现变化。以回填海沙导致近海陆地混凝土建筑镀锌钢管的局部腐蚀为例,模拟其实际工况,将镀锌试样置于6种不同的模拟混凝土孔隙液中,将去锌层钢基置于3.5%NaCl中性溶液中浸泡24 h,用盐桥连接电解池,测定2种试样间的电位-时间曲线和电偶电流值,并与无预浸泡的相应值对比。结果表明:(1)当镀锌层在含有Cl-的中性溶液及pH=10.0,11.0的Ca(OH)2溶液中时,对钢基体起到了牺牲阳极的保护作用;(2)当镀锌层在pH=12.0的Ca(OH)2溶液中时,无论是否预浸泡其电位均出现逆转现象,且电偶电流值为正值,反而会促进钢基体的腐蚀;(3)在pH=12.5的Ca(OH)2溶液中,无预浸泡时镀锌层对去锌层钢基有保护作用,预浸泡24 h后初始阶段具有保护作用,1 650 s后时出现逆转,不仅已失去对钢基体的保护作用,反而会加速其腐蚀。

The backfill of the sand from the sea causes the local corrosion of galvanized steel pipes used in concretebased buildings near the coast.Galvanized specimens were immersed into 6 kinds of simulated concrete pore solution with different values,while the steel substrate without galvanizing coating was immersed in the aqueous solution of 3.5%NaCl for 24 h.After the electrolysis cell was linked with an electrolytic bridge,the potentialtime curves between the two kinds of specimens as well as the current of the galvanic couple were measured and compared with those in the absence of preimmersion.It was found that,in neutral solution containing Cl-and saturated Ca(OH)2 solution with pH=10.0,11.0,the galvanizing coating acted as a sacrificial anode to well protect the steel substrate.However,in saturated Ca(OH)2 solution with pH=12.0,whether the galvanizing coating was preimmersed or not,its potential tended to reverse and relevant galvanic couple current was positive,which indicated that in this case the galvanizing coating accelerated the corrosion of the steel substrate.Moreover,in saturated Ca(OH)2 solution with pH=12.5,the galvanizing coating without preimmersion was able to protect the steel substrate;and still in such Ca(OH)2 solution,the galvanizing coating after 24 h of preimmersion could protect the steel substrate only at the early stage,and lost the ability after about 1 650 s of test while the corrosion of the steel was contrarily accelerated thereafter.