Gel nanostructure in alkali-activated binders based on slag and fly ash, and effects of accelerated carbonation
Gel nanostructure in alkali-activated binders based on slag and fly ash, and effects of accelerated carbonation
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DOI：
10.1016/j.cemconres.2013.06.007
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发表时间：
2013-11-01
影响因子：
11.4
通讯作者：
van Deventer, Jannie S. J.
中科院分区：
文献类型：
--
作者：
Bernal, Susan A.;Provis, John L.;van Deventer, Jannie S. J.
通过矿渣和粉煤灰的碱活化形成的粘合剂，包括“粉煤灰地质聚合物”，作为低排放混凝土生产的粘合剂提供有吸引力的性能。然而，在加速碳酸化测试期间引起的pH值和孔隙溶液化学变化提供了不切实际的低使用中抗碳酸化性预测。在加速碳酸化之后，碱活化炉渣系统中剩余的铝硅酸盐凝胶高度聚合，与脱钙机理一致，而基于粉煤灰的粘合剂主要通过碱金属盐（在升高的CO2浓度下的碳酸氢盐，或在自然暴露下的碳酸盐）从孔溶液中沉淀而碳酸化，通过核磁共振光谱法可识别的粘合剂凝胶几乎没有变化。在活化粉煤灰/矿渣共混物中，形成两种不同的凝胶（C-A-S-H和N-A-S-H）;在加速碳酸化作用下，N-A-S-H凝胶表现出与粉煤灰基体系相似的性质，而C-A-S-H凝胶的脱钙作用与碱活化矿渣相似。这为耐久性优化和开发适当的测试方法提供了新的范围。(C)2013爱思唯尔有限公司保留所有权利。
Binders formed through alkali-activation of slags and fly ashes, including 'fly ash geopolymers', provide appealing properties as binders for low-emissions concrete production. However, the changes in pH and pore solution chemistry induced during accelerated carbonation testing provide unrealistically low predictions of in-service carbonation resistance. The aluminosilicate gel remaining in an alkali-activated slag system after accelerated carbonation is highly polymerised, consistent with a decalcification mechanism, while fly ash-based binders mainly carbonate through precipitation of alkali salts (bicarbonates at elevated CO2 concentrations, or carbonates under natural exposure) from the pore solution, with little change in the binder gel identifiable by nuclear magnetic resonance spectroscopy. In activated fly ash/slag blends, two distinct gels (C-A-S-H and N-A-S-H) are formed; under accelerated carbonation, the N-A-S-H gel behaves comparably to fly ash-based systems, while the C-A-S-H gel is decalcified similarly to alkali-activated slag. This provides new scope for durability optimisation, and for developing appropriate testing methodologies. (C) 2013 Elsevier Ltd. All rights reserved.