@inproceedings{JuhartBriendlRoecketal., author = {Juhart, Joachim and Briendl, Lukas G. and R{\"o}ck, Rudolf and Galan, Isabel and Thumann, Maria and Mittermayr, Florian and Kusterle, Wolfgang}, title = {Performance optimization of shotcrete by combined fillers}, series = {ICCC 2019: 15th International Congress on the Chemistry of Cement, ICCC 2019, 16.-20.09.2019, Prague, Czech Republik}, booktitle = {ICCC 2019: 15th International Congress on the Chemistry of Cement, ICCC 2019, 16.-20.09.2019, Prague, Czech Republik}, pages = {1387 -- 3872}, language = {en} } @article{SakoparnigGalanKusterleetal., author = {Sakoparnig, Marlene and Galan, Isabel and Kusterle, Wolfgang and Lindlar, Benedikt and Koraimann, G{\"u}nther and Angerer, Thomas and Steindl, Florian Roman and Briendl, Lukas G. and Jehle, Sebastian and Flotzinger, Johannes and Juhart, Joachim and Mittermayr, Florian}, title = {On the significance of accelerator enriched layers in wet-mix shotcrete}, series = {Tunnelling and Underground Space Technology}, volume = {131}, journal = {Tunnelling and Underground Space Technology}, publisher = {Elsevier}, doi = {10.1016/j.tust.2022.104764}, pages = {1 -- 10}, abstract = {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.}, language = {en} } @inproceedings{GalanThumannBriendletal.2018, author = {Galan, Isabel and Thumann, Maria and Briendl, Lukas G. and R{\"o}ck, Rudolf and Steindl, Florian and Juhart, Joachim and Mittermayr, Florian and Kusterle, Wolfgang}, title = {From Lab Scale Spraying to Real Scale Shotcreting and back to the Lab}, series = {8th International Symposium on Sprayed Concrete : Modern Use of Wet Mix Sprayed Concrete for Underground Support - Trondheim, Norwegen. - 11. - 14.06.2018}, booktitle = {8th International Symposium on Sprayed Concrete : Modern Use of Wet Mix Sprayed Concrete for Underground Support - Trondheim, Norwegen. - 11. - 14.06.2018}, editor = {Beck, Thomas and Myren, Synn{\o}ve A. and Engen, Siri}, isbn = {978-82-8208-060-6}, pages = {139 -- 153}, year = {2018}, abstract = {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.}, language = {en} } @inproceedings{JuhartBriendlMittermayretal., author = {Juhart, Joachim and Briendl, Lukas G. and Mittermayr, Florian and Thumann, Maria and R{\"o}ck, Rudolf and Kusterle, Wolfgang}, title = {Optimierte Eigenschaften von Spritzbeton durch kombinierte Zusatzstoffe}, series = {Tagungs-CD der Spritzbeton-Tagung 2018, 11.-12. Januar 2018, Alpbach, Tirol, CD-ROM}, booktitle = {Tagungs-CD der Spritzbeton-Tagung 2018, 11.-12. Januar 2018, Alpbach, Tirol, CD-ROM}, language = {de} } @article{SteindlMittermayrSakoparnigetal., author = {Steindl, Florian R. and Mittermayr, Florian and Sakoparnig, Marlene and Juhart, Joachim and Briendl, Lukas G. and Lindlar, Benedikt and Ukrainczyk, Neven and Dietzel, Martin and Kusterle, Wolfgang and Galan, Isabel}, title = {On the porosity of low-clinker shotcrete and accelerated pastes}, series = {Construction and Building Materials}, volume = {368}, journal = {Construction and Building Materials}, publisher = {Elsevier}, address = {14}, issn = {0950-0618}, doi = {10.1016/j.conbuildmat.2023.130461}, abstract = {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.}, language = {en} } @inproceedings{JuhartBriendlMittermayretal., author = {Juhart, Joachim and Briendl, Lukas G. and Mittermayr, Florian and R{\"o}ck, Rudolf and Thumann, Maria and Kusterle, Wolfgang}, title = {Mischungsentwicklung von nachhaltigem Spritzbeton mit kombinierten Zusatzstoffen}, series = {Beton Graz '18 : 4. Grazer Betonkolloquium : 20./21. September 2018}, booktitle = {Beton Graz '18 : 4. Grazer Betonkolloquium : 20./21. September 2018}, publisher = {Verlag der Technischen Universit{\"a}t Graz}, address = {Graz}, isbn = {978-3-85125-621-5}, pages = {139 -- 152}, abstract = {Spritzbeton ist nachhaltig, wenn er sowohl umweltfreundlich als auch dauerhaft ist. Traditionelle Mischungszusammensetzungen f{\"u}r Spritzbeton enthalten einen hohen Anteil an fein gemahlenem Portlandzement und an Erstarrungsbeschleunigern. Beide Komponenten sind f{\"u}r eine sehr schnelle Festigkeitsentwicklung, aber auch hohe Umweltauswirkungen (wie CO2-Emissionen, Prim{\"a}renergiebedarf) verantwortlich. Portlandzement ist ein hervorragendes Bindemittel, bringt aber ein hohes Versinterungspotenzial und bei normaler Zusammensetzung einen geringen Widerstand gegen chemischen Angriff, wie zum Beispiel den Sulfatangriff aus dem Bergwasser, mit sich. Hingegen k{\"o}nnen latent hydraulische und puzzolanische Zusatzstoffe die Dauerhaftigkeit erh{\"o}hen, sind aber auch f{\"u}r eine langsame Festigkeitsentwicklung bekannt. Im Beitrag wird ein neues Konzept des Mischungsentwurfs vorgestellt, das auf der Auswahl geeigneter Zusatzstoffe (i.e. feinste Kalksteinmehle, die die Hydratation beschleunigen, kombiniert mit gemahlenem H{\"u}ttensand und Puzzolanen), der Optimierung von Packungsdichte und Wasserbedarf sowie einem optimalen Mischungsverh{\"a}ltnis aller Feinstoffe beruht. Es wird an exemplarischen Mischungszusammensetzungen gezeigt, welche Eigenschaften bzw. Leistungsmerkmale in Labortests sowie in großmaßst{\"a}blichen Spritzversuchen erreicht werden k{\"o}nnen.}, language = {de} }