粉煤灰混凝土钢筋腐蚀氯离子门槛值研究

Critical chlorides content for steel bar's corrosion initiation in fly ash concrete

为研究引起混凝土内钢筋锈蚀的氯离子临界门槛值,制作了15%、30%和45%三种粉煤灰替代率和0.1%、0.5%、1.5%、3.0%和5.0%五种氯离子含量的混凝土试件。在试件90d龄期分别测试了钢筋的腐蚀电位、腐蚀电流密度、阳极极化曲线、阴极极化曲线和混凝土电阻率、孔隙液pH值、自由氯离子含量等参数。试验结果表明:粉煤灰的添加与不同替代率对钢筋腐蚀的氯离子门槛值并无明显影响,粉煤灰混凝土与普通水泥混凝土的氯离子门槛值基本接近,约为胶凝材料重量的0.8%(自由氯离子);但当氯离子含量超过了,门槛值钢筋进入腐蚀状态之后,由于粉煤灰混凝土较低的氧扩散系数和较高的混凝土电阻率,粉煤灰混凝土较普通水泥混凝土对钢筋的腐蚀仍然能够提供较高的保护。

In order to study the chlorides critical value needed for the initiation of steel bar＇s corrosion, concrete specimens made of 3 kinds of fly ash replacement ratios （ 15%, 30% and 45% by weight of binder） and 5 kinds of chlorides contents （0.1%, 0.5%, 1.5%, 3.0% and 5.0% ） were fabricated.At the 90 days exposure time, steel bar＇s corrosion potential,corrosion current density,cathodic polarization curve,anodic polarization curve and concrete electrical resistivity,pH value of concrete pore solution and free chloride ions content were tested.Results indicate that the addition of fly ash and different replacement ratios have little effects on the chlorides critical value for steel bar＇s depassivation compared to ordinary Portland cement （ OPC ） concrete, which is around 0.8% by weight ofbinders in froe chloride ions form.However due to the lower oxygen diffusion capability and higher concrete resistivity, when steel bars start the onset corrosion fly ash concrete can still provide better protection to steel bar＇s anticorrosion than OPC concrete.