钢筋混凝土中氯盐和硫酸盐耦合侵蚀研究进展

Coupling Erosion of Chlorides and Sulfates in Reinforced Concrete:a Review

钢筋混凝土被广泛应用于公共建筑和大型基础设施的建设中,但其在服役中常常面临氯盐和硫酸盐的侵蚀,尤其是在滨海和盐渍环境中,其耐久性能将迅速下降,因此有必要探究硫酸盐和氯盐在耦合侵蚀过程中的相互影响,以及二者对混凝土劣化和钢筋锈蚀的影响。本文从钢筋混凝土中单一氯盐和硫酸盐的侵蚀机理出发,从混凝土因离子传输和基体膨胀而导致的劣化、耦合侵蚀所导致的钢筋锈蚀两个方面总结了相关研究成果。明确硫酸盐侵蚀对氯离子扩散的影响是理解氯盐和硫酸盐耦合侵蚀机理的关键,需考虑硫酸盐对结合氯离子的释放以及硫酸盐侵蚀对混凝土孔隙和开裂影响所产生的叠加效应。基于此,该影响可分为促进、抑制、促进三个阶段。氯盐缓解混凝土中硫酸盐侵蚀的前提是氯离子对混凝土材料本身无侵蚀作用,缓解的原因主要在于氯离子能够先于硫酸根离子与单硫型水化硫铝酸钙(AFm)反应生成弗里德尔盐(Friedel’s salt,也称为Friedel盐)。硫酸盐和氯盐耦合侵蚀下钢筋的锈蚀问题需要结合硫酸盐对氯离子的影响机理做进一步的分析,同时也有必要研究硫酸盐对钢筋的直接锈蚀问题。最后,将钢筋混凝土作为一个整体,从实验和数值两种角度对其在氯盐和硫酸盐共同作用下的耐久性研究进行展望,以期为滨海和盐渍环境中的新建钢筋混凝土基础设施的耐久性设计和既有结构的安全性评估提供参考。

Reinforced concrete is widely used in the construction of public buildings and large-scale infrastructure,but it is often eroded by chloride and sulfate in service,especially in marine and saline environments.The durability of the reinforced concrete structures under sulfate and chloride environment is rapidly degraded due to the dual attack.Under this condition,it is necessary to investigate the interaction between sulfate and chloride during the binary erosion process and its effect on the concrete deterioration and steel corrosion.Based on the degradation mechanism of the reinforced concrete under single chloride erosion or sulfate attack,this review offers a retrospection of the research efforts with respect to concrete deterioration and steel corrosion.Sulfates have been found capable of reducing the capacity of the chemical binding of chloride ions by the priority of the reaction between sulfate ions and AFm and the decomposition of the Friedel’s salt.To investigate the influence of sulfates on chloride diffusion,the effect of sulfates on chloride binding and the effect of sulfate two-stage erosion on concrete porosity need to be synthetically considered.And the effect of sulfate attack on chloride diffusion can be divided into three stages:promotion,inhibition and then promotion.The premise of chlorides’alleviation of sulfate attack on concrete is that chlorides have no corrosive effect on concrete material itself,and the key is that chloride ions react with AFm before sulfate ions to form Friedel’s salts.As for the corrosion of steel in concrete under dual attack,further analysis needs to be carried out with the influence of sulfates on chloride binding and diffusion,and it is necessary to study the effect of sulfate attack on steel corrosion.Finally,the durability of reinforced concrete as a whole under the combined action of chlorides and sulfates is prospected through experiment or numerical simulation,which can provide a better insight for the durability design of new reinforced concrete structures and the safety assessment of existing structures in marine and saline harsh environments.