摘要
水泥基材料早龄期碳化通常能够提高材料工程性能,然而早龄期碳化后水泥基材料基体环境发生变化,如何影响钢筋锈蚀过程和机制仍不明晰。为此,以内置0.7 mm直径钢丝的硫铝酸盐-硅酸盐(CSA-PC)复合水泥砂浆样品为研究对象,设置拆模后经历4、24 h和72 h 3种碳化时长,通过酚酞显色测量碳化深度并利用显影增强X射线断层扫描技术(XCT)表征砂浆毛细吸水过程;标准养护至28d后经历40次氯盐干湿循环,通过开路电位和腐蚀电流密度测量钢筋锈蚀过程;通过BSE-EDS和图像分析精细表征氯盐干湿作用后钢筋的腐蚀产物和微结构。结果表明:早龄期碳化降低了砂浆基体的碱度,标准养护至28 d,pH值仍低于钢筋形成钝化膜的碱度阈值;早龄期碳化能够提高砂浆基体抗渗性能,但显著降低开路电位,且腐蚀电流密度提高了近一个数量级;BSE-EDS分析显示,碳化后钢筋发生严重腐蚀,腐蚀坑深度最高达200μm和腐蚀面积占钢筋截面的20%;腐蚀产物迁移并填充钢筋周围砂浆基体,体积膨胀导致形成基体裂缝。研究结果表明复合砂浆早龄期碳化加速了钢筋锈蚀。
Introduction The alkaline nature of cementitious materials has high potential of carbon sequestration.Research has shown that carbonation curing to cementitious materials at early age can improve their strength and densify their microstructure.Consequently,it is expected that carbonation curing can enhance the durability of concrete structure.However,carbonation can naturalize the alkaline environment of concrete,raising risks of steel corrosion.The debate between the carbonation-induced microstructure improvement and the neutralization-raised corrosion risks has not been resolved yet.Therefore,it provides great incentives to understand if carbonation of cementitious materials at early age accelerates corrosion of steel bar or not.Methods A hybrid calcium-sulphoaluminate and Portland cement(CSA-PC)mortar was prepared to coat steel bars of 0.7 mm.Three carbonation durations of 4,24 h and 72 h were designed to treat the CSA-PC mortar.The alkalinity of the composite mortar after carbonation was characterized by phenolphthalein chromatography,and the water sorptivity of non-carbonated and carbonated mortar specimens was measured by using a contrast-enhancing X-ray computed tomography(XCT).The corrosion process of the steel bars was measured by open-circuit potential and corrosion current density up to 40 chlorine-salt drying-wetting(CSDW)cycles.The microstructure of the mortar and the corrosion rust distribution of the steel bars after the CSDW action were characterized by BSE-EDS and image analysis.Results and discussion Early-age carbonation significantly reduced the alkalinity of the mortar matrix,which recovered after standard curing up to 28 d but remained below the alkalinity threshold for the formation of passivation of steel(pH=11.5).Carbonation densified the pore structure of the hybrid cement mortar and reduced the capillary water absorption.The water sorptivity of the carbonated mortar specimens was significantly lower than that of the uncarbonated specimens as observed by XCT,indicating an improvement in the impermeability of the mortar matrix.After 10 CSDW cycles,the open circuit potential of the carbonated specimens decreased significantly and the corrosion current density increased by nearly one order of magnitude.The early-age carbonation significantly increased the probability and rate of corrosion of the steel bars in the mortar under cyclic CSDW actions.BSE-EDS analysis further showed that after carbonation,the rebars were severely corroded with corrosion pits up to 200μm in depth and 20%in area;corrosion products migrated and filled the mortar matrix around the rebars,generating cracks.Conclusions The alkalinity of the mortar matrix decreased after early age carbonation,following recovery to a certain value after standard curing,which remained below the alkalinity threshold for steel passivation.Carbonation was able to improve the compactness of the mortar matrix and enhance the material's impermeability.The open circuit potential of the carbonated material was lower and the corrosion current density was one order of magnitude higher after 10 CSDW cycles.Serious corrosion of the rebar occurred in the mortar after carbonation,the corrosion products migrated to the surrounding mortar matrix,and the volumetric expansion led to cracking of the matrix.The findings suggest that although early age carbonation may help to improve the performance of cementitious material matrix,it may be detrimental to the durability of reinforced concrete.
作者
邱月
兰燕
游秀菲
田野
曾强
QIU Yue;LAN Yan;YOU Xiufei;TIAN Ye;ZENG Qiang(College of Civil Engineering and Architecture,Zhejiang University,Hangzhou 310058,China)
出处
《硅酸盐学报》
北大核心
2025年第8期2351-2361,共11页
Journal of The Chinese Ceramic Society
基金
国家自然基金重点项目(52038004)
国家自然基金面上项目(52378268)。
关键词
水泥基材料
早龄期
碳化
锈蚀
微结构
cementitious materials
early age
carbonation
corrosion
microstructure
作者简介
第一作者:邱月(2002-),女,硕士研究生。E-mail:qiu27@zju.edu.cn;通信作者:曾强(1983-),男,博士,教授。E-mail:cengq14@zju.edu.cn。
