TY - JOUR
T1 - On the significance of accelerator enriched layers in wet-mix shotcrete
AU - Sakoparnig, Marlene
AU - Galan, Isabel
AU - Kusterle, Wolfgang
AU - Lindlar, Benedikt
AU - Koraimann, Günther
AU - Angerer, Thomas
AU - Steindl, Florian Roman
AU - Briendl, Lukas
AU - Jehle, Sebastian
AU - Flotzinger, Johannes
AU - Juhart, Joachim
AU - Mittermayr, Florian
PY - 2023/1
Y1 - 2023/1
N2 - 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.
AB - 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.
KW - Spritzbeton
KW - Beschleuniger
KW - Lagenbildung
KW - Pulsation
KW - Shotcrete
KW - Accelerator
KW - Layering
KW - Concrete pumping
KW - Pulsation
KW - Inhomogeneities
UR - http://www.scopus.com/inward/record.url?scp=85140138468&partnerID=8YFLogxK
U2 - 10.1016/j.tust.2022.104764
DO - 10.1016/j.tust.2022.104764
M3 - Article
SN - 0886-7798
VL - 131
JO - Tunnelling and Underground Space Technology
JF - Tunnelling and Underground Space Technology
M1 - 104764
ER -