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Untersuchungen zur Korrelation von AKR induzierten Dehnungen und der Löslichkeit von Gesteinskörnungen unter Berücksichtigung von NaCl; Teil 2
Alternative Wege zur Ermittlung des AKR-Schädigungspotenzials von Gesteinskörnungen für Beton
Kositz, Mario / Hünger, Klaus-Jürgen
Die Alkali-Kieselsäure-Reaktion (AKR) stellt nach wie vor ein Problem für die Dauerhaftigkeit von Betonbauteilen dar. Die Prüfung von Gesteinskörnungen bei der Verwendung im Beton wird in der Alkali-Richtlinie vom DAfStb und dem Allgemeinen Rundschreiben Straßenbau (ARS) vom BMVI geregelt. Üblicherweise werden dazu Mörtel- bzw. Betonprobekörper, die die zu prüfende Gesteinskörnung enthalten, unter AKR beschleunigenden Bedingungen gelagert, die Dehnung gemessen und mit Grenzwerten verglichen. Diese Verfahren sind teilweise sehr aufwändig. Eine Alternative bietet ein am Fachgebiet Baustoffe und Bauchemie der BTU-Cottbus-Senftenberg in den vergangenen Jahren entwickeltes chemisches Prüfverfahren direkt an der Gesteinskörnung. Dieser Beitrag zeigt das Potenzial des weiterentwickelten sogenannten modifizierten BTU-Tests im Vergleich mit den derzeit standardisierten Prüfverfahren.
Investigations on the correlation of ASR induced strains and the solubility of aggregates under consideration of NaCl; part 1
The contribution presents a novel correlation of ASR-induced strains of concrete specimens with the SiO2,Üb solubility parameter of the modified BTU test (named after the Brandenburg Technical University in Cottbus). Assumptions and findings from previous research work are taken into account and confirmed by means of mathematical regression. Furthermore, the influence of alkali impingement by NaCl on the strains and solubilities is shown. The regression analysis is able to correlate the strains and maximum crack width of the 40 °C concrete test, the strains of a 40 °C concrete test with alkali addition (0 % and 3 % NaCl) and the 60 °C concrete test with alkali addition (0 %, 3 % and 10 % NaCl) with chemical and physical aggregate parameters. Required parameters are aggregate solubility, aggregate surface area , acceleration factor and alumino-silicate bond factor. The regression analysis shows that the alumino-silicate bond factor 1.4 is valid for stationary and transient (cyclic alternating) conditions at 40 °C even with NaCl addition. At a temperature of 60 °C with and without alkali supply, nBF reduces towards zero, since the concentration of dissolved aluminium from the aggregate also tends towards zero. Thus, the self-inhibition process of aggregates due to Al2O3 on ASR disappears. For the test methods without NaCl addition (40 °C concrete test, 40 °C concrete test with alkali addition 0 % NaCl and 60 °C concrete test with alkali addition 0 % NaCl), the 0 % NaCl concentration in the modified BTU test is decisive. In the 40 °C concrete test with alkali addition and 3 % NaCl, a 0.5 % NaCl addition shows the best agreement in the modified BTU test. In the 60 °C concrete test with alkali addition, a modified BTU test with 1 % NaCl is always sufficient for both 3 % and 10 % NaCl. Excessively high NaCl concentrations in the modified BTU test (10 %) are not effective. In future research projects, the number of aggregates and rock types should be significantly expanded.
Investigations on the correlation of ASR induced strains and the solubility of aggregates under consideration of NaCl; part 1
The contribution presents a novel correlation of ASR-induced strains of concrete specimens with the SiO2,Üb solubility parameter of the modified BTU test (named after the Brandenburg Technical University in Cottbus). Assumptions and findings from previous research work are taken into account and confirmed by means of mathematical regression. Furthermore, the influence of alkali impingement by NaCl on the strains and solubilities is shown. The regression analysis is able to correlate the strains and maximum crack width of the 40 °C concrete test, the strains of a 40 °C concrete test with alkali addition (0 % and 3 % NaCl) and the 60 °C concrete test with alkali addition (0 %, 3 % and 10 % NaCl) with chemical and physical aggregate parameters. Required parameters are aggregate solubility, aggregate surface area , acceleration factor and alumino-silicate bond factor. The regression analysis shows that the alumino-silicate bond factor 1.4 is valid for stationary and transient (cyclic alternating) conditions at 40 °C even with NaCl addition. At a temperature of 60 °C with and without alkali supply, nBF reduces towards zero, since the concentration of dissolved aluminium from the aggregate also tends towards zero. Thus, the self-inhibition process of aggregates due to Al2O3 on ASR disappears. For the test methods without NaCl addition (40 °C concrete test, 40 °C concrete test with alkali addition 0 % NaCl and 60 °C concrete test with alkali addition 0 % NaCl), the 0 % NaCl concentration in the modified BTU test is decisive. In the 40 °C concrete test with alkali addition and 3 % NaCl, a 0.5 % NaCl addition shows the best agreement in the modified BTU test. In the 60 °C concrete test with alkali addition, a modified BTU test with 1 % NaCl is always sufficient for both 3 % and 10 % NaCl. Excessively high NaCl concentrations in the modified BTU test (10 %) are not effective. In future research projects, the number of aggregates and rock types should be significantly expanded.
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beton 4/2021 ab Seite 120
Herausgeber des Artikels:
beton
bis beton 4/2022: Verlag Bau+Technik GmbH
ab beton 5/2022: Concrete Content UG
Wuppertal / Schermbeck
Tel: +49 (0) 2 02 7 69 92 69
Fax: +49 (0) 2 02 7 69 92 70
beton
bis beton 4/2022: Verlag Bau+Technik GmbH
ab beton 5/2022: Concrete Content UG
Wuppertal / Schermbeck
Tel: +49 (0) 2 02 7 69 92 69
Fax: +49 (0) 2 02 7 69 92 70