利用丝束电极技术研究海洋环境下裂缝混凝土中钢筋的锈蚀

Corrosion Behavior of Reinforcement Concrete with Cracks in Marine Environment Using Wire Beam Electrode technique

利用丝束电极技术研究0.1~0.3 mm裂缝砂浆保护下电极表面腐蚀电流分布与电化学阻抗谱。在海洋浪溅区对0.1~0.3 mm裂缝混凝土暴露700d,测试钢筋混凝土阻抗谱并计算腐蚀电流演变。结果表明:无裂缝砂浆中钢筋钝化时间大约为10~17 d,裂缝使得混凝土中钢筋钝化时间提前。混凝土中钢筋钝化与锈蚀均是由点到面的非均匀过程,裂缝使得氧气快速渗透至钢筋表面并在裂缝处形成阴极区;随着氯离子通过裂缝扩散至钢筋,裂缝处钢筋氧化形成若干阳极区。当横向裂缝小于0.1 mm时,海洋环境下的混凝土微细裂缝自愈合降低了氧气供给,使得裂缝处阳极区再次转化为阴极区从而延缓钢筋腐蚀。当横向裂缝为0.3 mm时,混凝土裂缝处钢筋快速锈蚀并向裂缝两边扩展,海洋浪溅区钢筋腐蚀速度可达到0.484μm/a。

Wire beam electrode(WBE) was used to investigate the corrosion behavior of rebar for mortar with cracks of 0.1–0.3 mm, and the distribution of galvanic current and EIS on WBE were tested. Also, a reinforced concrete with the similar cracks was also exposed to marine splash zone for 700 d, the Nyquist figures were examined and the corrosion current density evolution was calculated. The results indicate that the passivation time of rebar protected by non-cracking concrete is 10–17 d, and the existence of cracks in concrete accelerates the oxygen migration and promotes the passivation of rebar. The passivation and corrosion of rebar for concrete is an uneven process from pit to surface. The cathode zone is formed near the cracks firstly because oxygen can migrate from cracks to rebar surface. Chloride ions transport from cracks to rebar surface, forming the massive anode zones. For the transverse crack size of less than 0.1 mm, the micro-cracks of concrete will be self-healing and decrease oxygen supply when concrete is exposed to marine tidal and splash zone for a long term, and the anode zones near cracks will transfer to cathode zones and delay corrosion of rebar. For the transverse crack size of more than 0.3 mm, the corrosion of rebar in crack zones will occur quickly and extend to both sides of crack, and the corrosion rate of rebar in concrete is 0.484 μm/a when it exposed to splash zone.