海洋环境下低合金钢筋在碱激发矿渣混凝土中的耐蚀性与腐蚀机理

With the increasing environmental pollution, alkali-activated slag (AAS) has got more and more attention. Because cement manufacture is a process which has high energy consumption and high pollution, AAS has been proved to be a good alternative to ordinary Portland cement (OPC). Many studies have been carried out on the hydration mechanism, microstructure and performance of AAS. However, the studies concerning the durability of AAS are rarely found in literature so far, especially for steel corrosion behavior in AAS, which is one of the reasons for its limitation of engineering application. Accordingly, in order to investigate the electrochemical behaviors (passivation and corrosion) of reinforcing steel in AAS concrete and to reveal the corrosion mechanism, the studies on the corrosion behaviors of low-alloy steel will be carried out by indoor accelerated corrosion tests, indoor long-term natural corrosion tests and outdoor long-term natural corrosion tests at marine exposure station. Firstly, the corrosion initiation and corrosion propagation of low-alloy steel in AAS materials can be characterized by various electrochemical measurements (linear polarization resistance and electrochemical impedance spectroscopy, et al.), on the basis of the results, the corrosion mechanism of low-alloy steel can be revealed. Secondly, the transport process of corrosion products within AAS concrete cover and the distribution of different corrosion products will be monitored and surveyed by X-ray computed tomography and surface analysis techniques (SEM/EDS and Raman spectroscopy, et al.). Finally, a non-uniform mathematical model and numerical modeling of the damage and crack of AAS concrete cover induced by steel corrosion will be proposed, highlighting the corrosion mechanism of steel and the transport characteristics of different corrosion products in AAS concrete. The research results will provide technical supports for the engineering application of AAS and low-alloy steel in marine environment, not only considering energy conservation and emission reduction but also prolonging the service life of AAS concrete structures.

碱激发矿渣体系比硅酸盐水泥体系节能环保，近年来日益受到关注。目前在碱激发矿渣的水化机理、微结构及性能等方面已开展了大量的研究，但对于钢筋在该体系中的腐蚀行为却缺乏系统的研究和了解，这也成为阻碍其工程应用的主要原因之一。为探明钢筋在碱激发矿渣混凝土中的钝化与腐蚀行为并揭示其腐蚀机理，本申请拟开展在室内加速腐蚀、室内长期腐蚀与海洋环境长期腐蚀条件下碱激发矿渣混凝土中低合金钢筋的腐蚀行为研究。应用多种电化学方法（极化电阻与电化学阻抗谱等）监测碱激发矿渣中低合金钢筋的腐蚀诱导与扩展行为从而揭示低合金钢筋的腐蚀机理；通过X-CT技术与多种表面分析技术（扫描电镜与拉曼光谱等）研究腐蚀产物在基体中的分布特征与传输行为；建立碱激发矿渣混凝土非均匀损伤与钢筋锈胀开裂数学模型并进行数值模拟。研究成果将为配筋碱激发矿渣混凝土在海洋环境中的应用提供理论和技术支撑，在节能减排的基础上延长混凝土结构的服役寿命。

相比于硅酸盐水泥，碱激发矿渣材料的使用能降低二氧化碳排放和能源消耗，从而起到节能环保的作用。目前，国内外在碱激发矿渣材料中钢筋的钝化与腐蚀行为方面缺少系统的研究。而对于海洋恶劣环境，尚未有文献报道耐蚀合金钢筋在碱激发矿渣材料中的耐蚀性研究。这些因素成为了阻碍碱激发矿渣材料工程应用的重要原因。.为此，本项目通过电化学测试法，微结构表征技术以及化学成分表征技术等方法从以下四个方面进行研究：（1）海洋环境中耐蚀合金钢筋的耐蚀理论与关键应用技术；（2）碱激发矿渣萃取液中钢筋的电化学行为与腐蚀产物表征；（3）碱激发矿渣砂浆中钢筋的钝化与腐蚀机理；（4）海洋环境长期自然腐蚀情况下碱激发矿渣材料中钢筋的腐蚀行为与锈胀开裂机理。.本项目取得了以下研究结果：（1）揭示了耐蚀合金钢筋在混凝土孔溶液中的自发钝化机理，阐明了不同合金含量耐蚀合金钢筋的氯盐点蚀特征；（2）阐述了混凝土中耐蚀合金钢筋表面致密锈层的形成过程以及耐蚀机理，并进一步分析了混凝土锈胀开裂特征；（3）发现了碱激发矿渣材料能促使钢筋表面生成絮状沉淀物和致密锈层，显著提升钢筋的耐氯盐点蚀能力，从而证实了碱激发矿渣适用于海洋氯盐环境；（4）揭示了碱激发矿渣材料会抑制钢筋钝化膜的生成，对耐蚀合金钢筋与不锈钢钢筋钝化膜的负面作用尤为显著；（5）基于海洋环境长期自然腐蚀研究阐明了碱激发矿渣材料中钢筋锈蚀诱导的保护层锈胀开裂机理，探明了在海洋大气区服役的碱激发矿渣材料容易被碳化，而海洋浸没区的碱激发矿渣材料能较好地保护钢筋。.通过本项目的系统研究验证了钢筋与碱激发矿渣材料在海洋环境中共同服役的适用性，为推广碱激发矿渣材料在海工钢筋混凝土结构中的应用提供必要的理论基础与技术支撑，在节能减排的基础上延长钢筋混凝土结构的服役寿命。