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On the significance of accelerator enriched layers in wet-mix shotcrete

  • The application process, which gives shotcrete its name is a robust and established method, dating back to the beginning of the 20th century. Since then, the spraying process has been significantly enhanced. However, during the last decades no major technical changes have been made. In this study the wet - mix shotcrete process including the dosing of accelerator was investigated. For this, we monitored the concrete and accelerator pressure with 5 sensors in the pumps and pipes, and analysed the accelerator distribution in the hardened shotcrete matrix. The recorded pressure fluctuations clearly indicated that the pumping of the concrete with a double-piston pump led to flow pulsations. The pressure along the accelerator pipes, controlled by a peristaltic pump, was not steady either. However, the accelerator flow pulsation had a higher frequency than that of the concrete flow. This misalignment led to changes in the accelerator to concrete ratio during the spraying process. The impact of these incongruent concrete and accelerator flows on the resulting hardened shotcrete was visually analysed with the use of 0.02 % uranin as fluorescent tracer added to the accelerator. The tracer distribution showed that changes in the accelerator/concrete ratio led to the formation of ‘accelerator layers’, layers with higher accelerator concentrations in the hardened shotcrete. These layers show differences in chemistry, mineralogy and open porosity compared to the rest of the shotcrete matrix. The presence of accelerator enriched layers can have detrimental effects on the shotcrete properties, especially affecting the durability and mechanical performance. In consequence, we recommend a revision of the shotcrete process to eliminate these inhomogeneities.

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Metadaten
Author:Marlene Sakoparnig, Isabel Galan, Wolfgang KusterleORCiDGND, Benedikt Lindlar, Günther Koraimann, Thomas Angerer, Florian Roman Steindl, Lukas G. Briendl, Sebastian Jehle, Johannes Flotzinger, Joachim Juhart, Florian Mittermayr
DOI:https://doi.org/10.1016/j.tust.2022.104764
Parent Title (English):Tunnelling and Underground Space Technology
Publisher:Elsevier
Document Type:Article
Language:English
Year of first Publication:2023
Release Date:2022/10/29
Tag:Accelerator; Concrete pumping; Inhomogeneities; Layering; Pulsation; Shotcrete
Volume:131
Article Number:104764
First Page:1
Last Page:10
Institutes:Fakultät Bauingenieurwesen
Fakultät Bauingenieurwesen / Labor für Baustoffe
Begutachtungsstatus:peer-reviewed
research focus:Gebäude und Infrastruktur
OpenAccess Publikationsweg:Hybrid Open Access - OA-Veröffentlichung in einer Subskriptionszeitschrift/-medium
Licence (German):Creative Commons - CC BY - Namensnennung 4.0 International