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Thermodynamic modeling of silica dissolution kinetics of quartzitic aggregates stored in highly alkaline solution

  • Knowledge's on the dissolution behaviour of SiO2-containing aggregates are the basis for understanding damaging processes regarding ASR. Because of many influences, the solubility of aggregates has still needs to be determined by dissolution experiments. This article is about the reliably modeling of silica dissolution of relatively pure SiO2 containing aggregates in alkaline solutions. Therefore, quartz, quartzite, opal sandstone and flint with different silica modifications were chosen. A kinetic model based on the surface area was derived and numerous thermodynamic data from different authors were evaluated. The surface area of the aggregate grains were determined by an adapted BET method. For this measurement, the original grain sizes were used as they are also used so in concrete. These aggregates were stored in 0.1 mol and 1.0 mol KOH solution at 40°C and 80°C respectively. The dissolution experiments too were performed with grains in the original particle sizes. The concentration of silica in the liquid phase was measured byKnowledge's on the dissolution behaviour of SiO2-containing aggregates are the basis for understanding damaging processes regarding ASR. Because of many influences, the solubility of aggregates has still needs to be determined by dissolution experiments. This article is about the reliably modeling of silica dissolution of relatively pure SiO2 containing aggregates in alkaline solutions. Therefore, quartz, quartzite, opal sandstone and flint with different silica modifications were chosen. A kinetic model based on the surface area was derived and numerous thermodynamic data from different authors were evaluated. The surface area of the aggregate grains were determined by an adapted BET method. For this measurement, the original grain sizes were used as they are also used so in concrete. These aggregates were stored in 0.1 mol and 1.0 mol KOH solution at 40°C and 80°C respectively. The dissolution experiments too were performed with grains in the original particle sizes. The concentration of silica in the liquid phase was measured by ICP-OES. The model based on a comparison of calculated and experimental determined silica concentrations, because some parameters of the differential equations are still unknown. The model includes the temperature and molarity dependence of the silica dissolution. The model also takes into account the influences of the SiO2 structures and can vary between crystalline and amorphous SiO2 in a wide range. Thermodynamic data suitable for modeling are recommended. In future, these dissolution calculations shall be extended to other non-pure quartzitic aggregates. Instead of time-consuming ASR concrete prism tests the silica dissolution rates may be used then to indicate quickly the ASR sensitivity of aggregates. Of course, it will be possible to distinguish between innocuous, medium and highly reactive grains.show moreshow less

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Metadaten
Author: Klaus-Jürgen HüngerGND, Mario Kositz
ISBN:978-972-49-2315-4
Title of the source (English):Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete
Publisher:LNEC
Document Type:Conference publication not peer-reviewed
Language:English
Year of publication:2021
Tag:alkali silica reaction; kinetic modeling; quartzite aggregates; silica dissolution; thermodynamic data
First Page:1447
Last Page:1458
Faculty/Chair:Fakultät 6 Architektur, Bauingenieurwesen und Stadtplanung / FG Baustoffe und Bauchemie
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