Microstructural Evolution Mechanism of C-（A）-S-H Gel in Portland Cement Pastes Affected by Sulfate Ions
来源期刊：Journal Of Wuhan University Of Technology Materials Science Edition2018年第3期
论文作者：张高展 ZHANG Xiaojia 丁庆军 HOU Dongshuai LIU Kaiwei
文章页码：639 - 647
摘 要：The microstructural evolution of C-（A）-S-H gel in Portland cement pastes immersed in pure water and 5.0 wt% Na2SO4 solution for different ages was comparatively investigated, by means of 29 Si NMR spectroscopy, and SEM-EDS analysis. Additionally, molecular dynamics simulation was performed to study the aluminum coordination status and interaction of sulfate ions in C-（A）-S-H gel. The results showed significant changes in the microstructural evolution of C-（A）-S-H gel in Portland cement paste. Sulfate attack has decalcifying and dealuminizing effect on C-（A）-S-H gel which is evident from increase in mean chain length（MCL） and decrease in Ca/Si & Al[4]/Si ratios of C-（A）-S-H gel. Additionally, Molecular dynamics simulation proves that Al[4] substituted in silicate chains of C-（A）-S-H gel is thermodynamically metastable, which may explain its migration from the silicate chains and transformation to Al[6], thus lowering the Al[4]/Si ratio of C-（A）-S-H gel. SO42-ions can carry the interfacial Ca2+ ions into the pore solution by the diffusion-absorption-desorption process, which unravels the mechanism of sulfate attack on C-（A）-S-H gel.
张高展1，ZHANG Xiaojia1，丁庆军2，HOU Dongshuai3，LIU Kaiwei1
1. Advanced Building Materials Key Laboratory of Anhui Province, Anhui Jianzhu University2. School of Materials Science and Engineering, Wuhan University of Technology3. Department of Civil Engineering,Qingdao Technological University
摘 要：The microstructural evolution of C-（A）-S-H gel in Portland cement pastes immersed in pure water and 5.0 wt% Na2SO4 solution for different ages was comparatively investigated, by means of 29 Si NMR spectroscopy, and SEM-EDS analysis. Additionally, molecular dynamics simulation was performed to study the aluminum coordination status and interaction of sulfate ions in C-（A）-S-H gel. The results showed significant changes in the microstructural evolution of C-（A）-S-H gel in Portland cement paste. Sulfate attack has decalcifying and dealuminizing effect on C-（A）-S-H gel which is evident from increase in mean chain length（MCL） and decrease in Ca/Si & Al[4]/Si ratios of C-（A）-S-H gel. Additionally, Molecular dynamics simulation proves that Al[4] substituted in silicate chains of C-（A）-S-H gel is thermodynamically metastable, which may explain its migration from the silicate chains and transformation to Al[6], thus lowering the Al[4]/Si ratio of C-（A）-S-H gel. SO42-ions can carry the interfacial Ca2+ ions into the pore solution by the diffusion-absorption-desorption process, which unravels the mechanism of sulfate attack on C-（A）-S-H gel.
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