TY - CHAP A1 - Briendl, Lukas G. A1 - Galan, Isabel A1 - Steindl, Florian A1 - Röck, Rudolf A1 - Thumann, Maria A1 - Juhart, Joachim A1 - Baldermann, Andre A1 - Mittermayr, Florian A1 - Kusterle, Wolfgang T1 - Hydration processes of accelerated cementitious systems governing early strength development T2 - ICCC 2019: 15th International Congress on Chemistry of Cement, 16.-20.09.2019, Prague, Czech Republik Y1 - 2019 SP - 714 EP - 724 ER - TY - CHAP A1 - Galan, Isabel A1 - Thumann, Maria A1 - Briendl, Lukas G. A1 - Röck, Rudolf A1 - Steindl, Florian A1 - Juhart, Joachim A1 - Mittermayr, Florian A1 - Kusterle, Wolfgang ED - Beck, Thomas ED - Myren, Synnøve A. ED - Engen, Siri T1 - From Lab Scale Spraying to Real Scale Shotcreting and back to the Lab T2 - 8th International Symposium on Sprayed Concrete : Modern Use of Wet Mix Sprayed Concrete for Underground Support - Trondheim, Norwegen. - 11. - 14.06.2018 N2 - Before new mixes are sprayed in real scale applications, lab experiments have to be carried out to provide a basis for predicting a good performance in real scale. In many cases, to understand the correlations between the behavior in the lab and in real scale spraying, a further set of experiments after the real spraying is required. In this paper we present such a two way process for two new wet mixes, one with a very low tricalcium aluminate Portland cement and the other one with a CEM I with addition of ultra-fine calcite. Calorimetry and Shear-Modulus measurements were used in the lab to monitor hydration evolution. In the real scale spraying compressive strength was measured at periodic intervals up to 24 hours. The hydration of the sprayed samples was stopped at 3, 6 and 24 hours and samples were scanned with X-ray for the identification and quantification of the phases present. The results presented are used to discuss the extent to which lab experiments can predict the behavior of mixes in real scale and how small changes in the raw materials and the mixes can lead to quite different results. Y1 - 2018 UR - https://betong.net/wp-content/uploads/8th-Sprayed-Concrete_Web-Proceedings.pdf SN - 978-82-8208-060-6 SP - 139 EP - 153 ER - TY - CHAP A1 - Juhart, Joachim A1 - Briendl, Lukas G. A1 - Mittermayr, Florian A1 - Thumann, Maria A1 - Röck, Rudolf A1 - Kusterle, Wolfgang T1 - Optimierte Eigenschaften von Spritzbeton durch kombinierte Zusatzstoffe T2 - Tagungs-CD der Spritzbeton-Tagung 2018, 11.-12. Januar 2018, Alpbach, Tirol, CD-ROM Y1 - 2018 ER - TY - JOUR A1 - Steindl, Florian Roman A1 - Sakoparnig, Marlene A1 - Briendl, Lukas G. A1 - Thumann, Maria A1 - Galan, Isabel A1 - Juhart, Joachim A1 - Röck, Rudolf A1 - Saxer, Andreas A1 - Mittermayr, Florian A1 - Kusterle, Wolfgang T1 - ASSpC – Vier Jahre Forschung für dauerhaften Spritzbeton JF - Bautechnik Y1 - 2020 PB - Wilhelm Ernst & Sohn CY - Berlin ER - TY - JOUR A1 - Sakoparnig, Marlene A1 - Galan, Isabel A1 - Kusterle, Wolfgang A1 - Lindlar, Benedikt A1 - Koraimann, Günther A1 - Angerer, Thomas A1 - Steindl, Florian Roman A1 - Briendl, Lukas G. A1 - Jehle, Sebastian A1 - Flotzinger, Johannes A1 - Juhart, Joachim A1 - Mittermayr, Florian T1 - On the significance of accelerator enriched layers in wet-mix shotcrete JF - Tunnelling and Underground Space Technology 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. KW - Inhomogeneities KW - Pulsation KW - Concrete pumping KW - Layering KW - Accelerator KW - Shotcrete Y1 - 2023 U6 - https://doi.org/10.1016/j.tust.2022.104764 VL - 131 SP - 1 EP - 10 PB - Elsevier ER - TY - JOUR A1 - Steindl, Florian R. A1 - Mittermayr, Florian A1 - Sakoparnig, Marlene A1 - Juhart, Joachim A1 - Briendl, Lukas G. A1 - Lindlar, Benedikt A1 - Ukrainczyk, Neven A1 - Dietzel, Martin A1 - Kusterle, Wolfgang A1 - Galan, Isabel T1 - On the porosity of low-clinker shotcrete and accelerated pastes JF - Construction and Building Materials N2 - Although the number and size of interconnected pores have been identified as the most important aspects of concrete microstructure, comprehensive datasets on shotcrete porosity and pore size distributions are still scarce and their key controls are poorly investigated. In this study we investigate the effects of the spraying process, setting accelerator addition and mix design on the microstructure of real-scale dry- and wet-mix shotcrete and hand-mixed and sprayed accelerated pastes. A newly proposed deconvolution analysis of the pore size distributions, measured by mercury intrusion porosimetry, offers increased precision in determining the critical and median pore diameter parameters. In total >50 samples were analysed. Results show that the dry-mix shotcrete exhibits a shift towards coarser pore sizes (∼100–1 μm) than wet-mix shotcrete. Combinations of different supplementary cementitious materials are favourable for producing wet-mix shotcretes with refined pore structures. The addition of setting accelerators, up to 10 wt-% of binder mass, and the spraying process cause systematic variations in the pore volume and pore structure of (sprayed) paste and shotcrete. KW - Porosity KW - Shotcrete KW - Mercury Intrusion KW - Durability KW - SCMs Y1 - 2023 U6 - https://doi.org/10.1016/j.conbuildmat.2023.130461 SN - 0950-0618 VL - 368 PB - Elsevier CY - 14 ER - TY - JOUR A1 - Steindl, Florian Roman A1 - Galan, Isabel A1 - Baldermann, Andre A1 - Sakoparnig, Marlene A1 - Briendl, Lukas G. A1 - Juhart, Joachim A1 - Thumann, Maria A1 - Dietzel, Martin A1 - Röck, Rudolf A1 - Kusterle, Wolfgang A1 - Mittermayr, Florian T1 - Sulfate durability and leaching behaviour of dry- and wet-mix shotcrete mixes JF - Cement and Concrete Research N2 - Shotcrete is a material frequently used in underground constructions such as tunnels, where Ca leaching and sulfate attack are important durability issues. In this study, two test methods were employed to investigate the sulfate resistance and leaching behaviour of dry- and wet-mix shotcretes in sulfate solutions on a time-resolved basis. Tests on powdered samples showed the dissolution of AFm, portlandite and C-A-S-H, subsequently followed by the precipitation of calcite and ettringite. The extent of sulfate expansion of drill cores corresponded to the chemical response of the powder materials, particularly on the reactivity of Ca- and Al-containing hydrated cement phases. The use of high-purity metakaolin (7-10 wt%) in the shotcrete binder significantly decreased the sulfate durability, while high amounts of other SCMs such as blast-furnace slag and silica fume (> 20 wt%) had a positive effect on the durability of shotcrete. KW - ADMIXTURES KW - ALKALI-FREE KW - ATTACK KW - BLAST-FURNACE SLAG KW - concrete KW - Durability KW - Leaching KW - MECHANISM KW - METAKAOLIN KW - RESISTANCE KW - SCMs KW - Shotcrete KW - Sulfate attack KW - TEMPERATURE KW - THAUMASITE FORM Y1 - 2020 U6 - https://doi.org/10.1016/j.cemconres.2020.106180 VL - 137 IS - November SP - 1 EP - 19 PB - Elsevier ER - TY - JOUR A1 - Sakoparnig, Marlene A1 - Galan, Isabel A1 - Steindl, Florian Roman A1 - Kusterle, Wolfgang A1 - Juhart, Joachim A1 - Grengg, Cyrill A1 - Briendl, Lukas G. A1 - Saxer, Andreas A1 - Thumann, Maria A1 - Mittermayr, Florian T1 - Durability of clinker reduced shotcrete: Ca2+ leaching, sintering, carbonation and chloride penetration JF - Materials and structures N2 - The reduction of clinker use is mandatory to lower the negative environmental impact of concrete. In shotcrete mixes, similarly to the case of conventional concrete, the use of supplementary cementitious materials (SCMs) and proper mix design allow for the substitution of clinker without compromising the mechanical properties. However, the impact of the substitution on the durability of shotcrete needs to be further assessed and understood. The results from the present study, obtained from real-scale sprayed concrete applications, show a reduction of the Ca2+ leaching and sintering potential of clinker-reduced shotcrete mixes due to the presence of SCMs. This positive effect, crucial for low maintenance costs of tunnels, is mainly related to a reduced portlandite content, which on the other hand negatively affects the carbonation resistance of shotcrete. Additionally, the hydration of SCMs positively influences the chloride penetration resistance presumably due to a combination of microstructural changes and changes in the chloride binding capacity. Differences found in the pore size distribution of the various mixes have low impact on the determined durability parameters, in particular compared to the effect of inhomogeneities produced during shotcrete application. KW - Carbonate precipitation KW - Carbonation KW - Chloride penetration KW - Durability KW - Leaching KW - Shotcrete Y1 - 2021 U6 - https://doi.org/10.1617/s11527-021-01644-7 VL - 54 SP - 1 EP - 23 PB - Springer Nature ER -