Synthesis and characterization of alkali-silica reaction products

Author(s): Z. Shi, B. Lothenbach, A. Leemann
Paper category: Proceedings
Book title: Proceedings of the International Conference on Sustainable Materials Systems and Structures (SMSS2019) Durability, Monitoring and Repair of Structures
Editor(s): Ana Baričević, Marija Jelčić Rukavina, Domagoj Damjanović, Maurizio Guadagnini
ISBN: 978-2-35158-217-6
e-ISBN: 978-2-35158-218-3
Publisher: RILEM Publications SARL
Publication year: 2019
Pages: 208-213
Total Pages: 813
Language: English

Abstract: Despite of numerous investigations on alkali-silica reaction (ASR), its mechanism is still not explicitly understood due to the difficulties to monitor the reaction and to characterize the tiny amount of ASR products in concrete. In this study, ASR products are synthesized using samples with initial Ca/Si ratio of 0.3 and Na/Si ratios of 0, 0.25, 0.5, 0.75 and 1 and equilibrated for 90 days in the presence of a surplus of water at 80 oC. The obtained reaction
products are dried and subsequently characterized by X-ray powder diffraction (XRD) and thermogravimetric analysis (TGA). The pH and chemical composition of the solution for each sample are also measured by pH meter and ion chromatography (IC). The results show that calcium-silicate-hydrate (C-S-H) is formed at low and very high Nainitial/Si ratios (i.e., 0, 0.25 and 1) at a Ca/Si ratio of 0.3. With the same Ca/Si ratio, crystalline ASR products, namely Na-shlykovite which has similar XRD pattern as K-shlykovite, are formed at the intermediate Na/Si ratios of 0.5 and 0.75. The calculated saturation indices with respect to C-S-H and amorphous silica are generally consistent with the phases precipitated as seen from XRD. Mass balance calculations indicated a Ca/Si from 0.3 to 0.5 and a Na/Si from 0.2 to 0.3 in the solid phase for the samples where Na-Shlykoveite was the main solid. The good agreement of these molar ratio with those observed in field samples of ASR products tentatively indicates that the obtained shlykovite-like phase could be in fact a synthetic proxy for ASR products.

Online publication :2019
Publication type : full_text
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