Phase, structure, and hygroscopic property evolutions of alkali-silica reaction gels under freeze drying

IF 10.9 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement and Concrete Research Pub Date : 2024-10-09 DOI:10.1016/j.cemconres.2024.107692

Arkabrata Sinha, Jianqiang Wei

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引用次数: 0

Abstract

Alkali-silica reaction (ASR), a detrimental process causing volume expansion and cracking in concrete by forming hygroscopic and swellable gel-like products, has been a long-standing challenge faced by concrete structures across the world. Understanding the underlying mechanisms of formation, moisture uptake and swelling of ASR gels requires thorough characterizations, where an appropriate drying method to remove free water and stop the reactions in the samples is essential. This study aims to elucidate the effect of freeze-drying, an emerging drying technique increasingly employed in sample preparations, on the phase, molecular structure, and moisture absorption behavior of ASR gels. Towards this end, six ASR gels with three calcium-to-silica (Ca/Si) ratios (0.1, 0.3, and 0.5) and two alkali-to-silica [(Na + K)/Si] ratios of 0.3 (low-alkali gels) and 1.0 (high-alkali gels) were studied. The results indicate that the chemical bonds and mineral components of ASR gels can be maintained during the removal of free and loosely bound water in freeze drying, while slight changes in crystallization and relative contents of alkali-silicate hydrate and calcium silicate hydrate phases were observed, in particular, for the high-alkali ASR gels. Although slight decreases in Q¹, Q^2, and Q³ silica polymerization sites and increases in the mean chain length and degree of polymerization were observed from the nuclear magnetic resonance (NMR) spectroscopy, the intrinsic layered silicate structure of ASR gels remains. The moisture absorption of low-alkali and high-alkali ASR gels was found to be governed by gel pores and mesopores, respectively. After freeze-drying, slight increases in moisture sorption (a 6.8 % increase in absorption and a 2.2 % decrease in desorption) and enhanced hysteresis were observed from the low-alkali gels. The high-alkali gels, however, showed a slight decrease in hygroscopicity along with a 16.6 % reduction of mesopores.

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冷冻干燥条件下碱硅反应凝胶的物相、结构和吸湿性能演变

碱硅反应（ASR）是通过形成吸湿性和膨胀性凝胶状产物而导致混凝土体积膨胀和开裂的有害过程，是全球混凝土结构长期面临的挑战。要想了解 ASR 凝胶的形成、吸湿和膨胀的基本机制，就必须对其进行全面的表征，其中必须采用适当的干燥方法去除游离水并停止样品中的反应。冷冻干燥是一种新兴的干燥技术，在样品制备过程中被越来越多地采用，本研究旨在阐明冷冻干燥对 ASR 凝胶的相位、分子结构和吸湿行为的影响。为此，研究人员研究了六种 ASR 凝胶，它们的钙硅比（Ca/Si）分别为 0.1、0.3 和 0.5，碱硅比（(Na + K)/Si] 分别为 0.3（低碱凝胶）和 1.0（高碱凝胶）。结果表明，ASR 凝胶的化学键和矿物成分可在冷冻干燥过程中去除自由水和松散结合水的过程中保持不变，同时观察到结晶和碱硅酸盐水合物及硅酸钙水合物相的相对含量发生了轻微变化，尤其是在高碱 ASR 凝胶中。虽然从核磁共振（NMR）光谱中观察到 Q1、Q2 和 Q3 硅聚合位点略有减少，平均链长和聚合度有所增加，但 ASR 凝胶的固有层状硅酸盐结构依然存在。研究发现，低碱和高碱 ASR 凝胶的吸湿性分别受凝胶孔隙和中孔的支配。冷冻干燥后，低碱凝胶的吸湿性略有提高（吸湿性提高 6.8%，解吸性降低 2.2%），滞后性也有所增强。然而，高碱凝胶的吸湿性略有下降，中孔减少了 16.6%。

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来源期刊

Cement and Concrete Research 工程技术-材料科学：综合

CiteScore

20.90

自引率

12.30%

发文量

318

审稿时长

53 days

期刊介绍： Cement and Concrete Research is dedicated to publishing top-notch research on the materials science and engineering of cement, cement composites, mortars, concrete, and related materials incorporating cement or other mineral binders. The journal prioritizes reporting significant findings in research on the properties and performance of cementitious materials. It also covers novel experimental techniques, the latest analytical and modeling methods, examination and diagnosis of actual cement and concrete structures, and the exploration of potential improvements in materials.