氯盐-硫酸盐内外源耦合腐蚀下偏高岭土掺量对现浇混凝土抗盐蚀性能的影响

Effect of metakaolin substitution on the salt corrosion durability of cast-in-place concrete subjected to combined chloride-sulphate attack

用偏高岭土等质量(5%、10%、15%、20%)替代水泥,同时掺入拌和水质量3%的NaCl试剂作为内腐蚀源制作现浇混凝土试件,开展试件在不同浓度(0、3%、5%、10%)Na_(2)SO_(4)溶液中的全浸泡腐蚀试验,探究氯盐-硫酸盐内外源耦合腐蚀下偏高岭土掺量对现浇混凝土抗盐蚀性能的影响。研究结果表明:(1)在同一侵蚀龄期,偏高岭土掺量为5%试件的表面剥蚀面积最小,强度损失最少,质量损失率最小,抵抗内外源耦合侵蚀的能力最强;(2)较高火山灰活性的偏高岭土替代部分水泥后,固化了混凝土内游离的Cl^(-),消耗了水化产物中的Ca(OH)_(2)生成了更多的C-S-H密实混凝土内部孔隙,阻碍了。的进一步扩散,减少了钙矾石(AFt)的生成,缓解了硫酸盐侵蚀导致的膨胀破坏;(3)过量偏高岭土的掺入减少了水泥含量,致使Ca(OH)_(2)的生成量降低,偏高岭土“二次水化”生成的C-S-H凝胶减少,进而降低了现浇混凝土内部的胶结性能。研究成果可为强盐渍土地区现浇混凝土的工程应用提供参考。

It involved replacing cement with varying proportions of metakaolin(5%,10%,15%,20%)and concurrently introducing NaCl reagent at 3%of the mixing water′s mass as an internal corrosion agent for the fabrication of in-situ concrete specimens.Total immersion corrosion tests were conducted on the specimens in Na_(2)SO_(4)solutions of varying concentrations(0,3%,5%,10%)to assess the influence of metakaolin incorporation on the salt corrosion resistance of cast-in-place concrete subjected to combined chloride-sulphate corrosion from both internal and external origins.The objective of the study was to explore the impact of kaolin incorporation on the resistance to salt corrosion in cast-in-place concrete,particularly under conditions of concurrent chloride-sulphate corrosion.The results show that:(1)At the same erosion age,the specimens with 5%metakaolin content have the smallest surface denudation area,strength loss,and mass loss rate,and the strongest resistance to coupled erosion from internal and external sources.(2)Replacing part of the cement with highly reactive metakaolin neutralized free Cl^(-)ions within the concrete,utilized Ca(OH)_(2),generated denser C-S-H gel formation within concrete pores,impeded SO_(4)^(2-)diffusion,calcium aluminate(AFt)formation,and mitigated expansion damage due to sulphate attack.(3)Excessive metakaolin in the mix decreased cement content,consequently diminishing Ca(OH)_(2)levels and inducing metakaolin′s“secondary hydration”,this reaction led to a depletion in C-S-H gel formation,thereby compromising the binding integrity of cast-in-place concrete.The researches can provide reference for the engineering application of cast-in-place concrete in areas with strong saline soil.