冻融和碳化作用对混凝土氯离子侵蚀的影响

对4种不同配比混凝土先后进行冻融循环(0,50,150次)、加速碳化(0,1,2星期)和氯离子侵蚀,以研究冻融、碳化作用对混凝土氯离子侵蚀的影响.通过压汞法和选择电极法分别测定不同作用后混凝土的孔径分布和氯离子含量及其毛细吸收变化情况.结果表明:冻融循环增大混凝土孔隙率,作为混凝土损伤的动力源,为氯离子侵蚀创造更为有利的条件;冻融次数越多,造成的氯离子侵蚀越严重;碳化反应破坏混凝土基体原有的过滤机制,并促进Friedel盐分解,使氯离子含量增多;冻融与碳化均不同程度增大混凝土毛细吸水性能,两者共同作用较单独作用时的氯离子侵蚀严重得多.对混凝土结构进行耐久性设计和使用寿命预测时,必须考虑和引进冻融、碳化及其他因素的复合作用.

Influence of freeze-thaw cycles and carbonation action on chloride penetration into concrete

Four different types of concrete were studied after exposure to freeze-thaw action (0, 50, 150 cycles) and accelerated carbonation (0, 1, 2 weeks) to investigate their effects on chloride penetration into concrete. By mercury intrusion porosimetry and chloride sensitive electrode, pore radius distribution and chloride content were determined for the concrete after different actions. Results show that increased porosity, which is induced by freeze-thaw cycles, accelerates the process of chloride penetration into concrete; and the deterioration becomes more severe with increasing number of frost cycles. Carbonation action destroys the filter system of concrete matrix for chloride ingress, reduces the pH value inducing chloride from decomposition of "Friedel Salt" , which cause increasing of chloride concentration. Capillary absorption of concrete is increased by freeze-thaw action and carbonation more or less. And chloride penetration becomes more severe than under single action. Freeze-thaw action, carbonation, and other deterioration factors should be taken into account when durability design and service life prediction of concrete structures are dealt with.