Effect of Sulfate Attack on C-S-H Microstructure in Hardened Portland Cement Pastes

• 作 者: DING Qingjun ZHANG Gaozhan HU Chenguang HU Shuguang
• 机 构: SchoolofMaterialsScienceandEngineering,WuhanUniversityofTechnology,Wuhan430070,ChinaCollegeofMateria
• 出 处: The 14th International Congress on the Chemistry of Cement (
• 发表日期: 2015年10期
• 关键词: Sodium sulfate cement C-S-H microstructure Al3+coordination

　　Based on the practical situation of serious deterioration for concrete materials performance in sulfate attack environment of our Ocean and Western regions, by using the 29Si and 27A1 Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) combined with deconvolution technique, effect of 5wt% sodium sulfate on C-S-H microstructure in Portland cement was investigated.The results show that sulfate attack can promote the hydration of silicate minerals, and the mean chain length (MCL) of C-S-H increases with the corrosion age.Compared with no corrosion, the increase amplitude of MCL under SO42-corrosion is greater before 28d, and slows down gradually after 28d.At early age(3d), sulfate attack enhances the hydration of silicate minerals, and promotes the incorporation of 4-coordinated A13+(Al[4]) into C-S-H structure, thus increasing the degree of Al3+ substituting for Si4+(Al[4]/Si).With the corrosion age, dealuminzation to calcium aluminosilicate hydrate (C-A-S-H) by SO42-ions is gradually discovered, which decreases the Al[4]/Si and promotes Al[4] transforming into 6-coordinated A13+(Al[6]), while, the formed vacancies by dealuminzation are occupied by [SiO4] tetrahedra, the MCL of C-S-H doesnt decrease with it.