Durable and sustainable shotcrete

Nowadays there is a special need to develop “new” construction materials to reduce the environmental footprint of structures. Investigations focus on durability of constructions and the use of sustainable materials and the reduction of CO2 emission (especially of the binder). Constructions have to be sustainable and durable. This will lead to low maintenance work and costs as well as a good life cycle performance. The aim of the Austrian research project „Advanced and Sustainable Shotcrete - ASSpC“ is to improve shotcrete mix design regarding durability and sustainability. There are different ways which may lead to success, one possibility is to replace part of the clinker content in the binder with supplementary cementitious materials. But it is crucial that new mix designs fulfil the technical requirements on site concerning workability and early age strength development, too. One central issue of the research project is to investigate how the pumpability of shotcrete can be determined in lab. At the moment there is no proven method available to measure the pumpability of shotcrete. Several test methods are used to determine the stability, tendency to segregation, bleeding and of course the consistency of concrete. Common test methods like the spread flow table and V-funnel flow time are used as well as two point test methods like the concrete rheometer eBT2 and Sliper. The segregation tendency is evaluated by the filter pressing test and the bucket setting test. Results from lab will be compared to results from site to define threshold values and parameters which describe the pumping characteristics of shotcrete base mix. In addition to that the early age strength development of the shotcrete mix design is investigated with the Minishot System designed by Sika. The shotcrete system is downscaled to a mini spray unit. In opposite to common test methods it is not necessary to mix the accelerator into the cement paste or mortar, but it will be added at the nozzle. The paste is sprayed by a downscaled nozzle and thus a realistic shear stress can be achieved. The paste is applied to a pulsment ultrasound spectrometer and the shear modulus development is measured continuously over time. The results can be linked to the strength development of shotcrete. The paper presents the tests procedures mentioned above in detail as well as first results with different shotcrete mix-designs

Investigations regarding the pumping process of wet-mix shotcrete improvement and upgrading of underground traffic structures

Workability is a physical property of fresh concrete, which can’t be described with only one single parameter or measured with one single test method. Pumpability and sprayability plays an important role for wet-mix sprayed concrete. The material must be conveyed through the pipe without changing its properties and mix proportion. The mix should leave the nozzle in a uniform stream intermixed homogeneously with the accelerator. When concrete is pumped through a pipe, a thin layer of paste is lubricating the wall of the pipe. The interaction of the lubricating layer and the pipe wall is of great importance for pumpability. The shear of the layer allows the slipping of the concrete and leads to a reduction of the required pumping pressure. In this presentation a sliding pipe rheometer “Sliper” is used to determine the pumping capacity of concrete. The Sliper consists of a pipe and a guided piston which is standing on the ground. A pressure sensor is integrated onto the piston. When the pipe is sliding downwards, the pressure in the pipe as well as the speed of the pipe are recorded. Rheological parameters as well as the supposed pumping pressure may be estimated. The cohesiveness of concrete is important to avoid blockages in the conveying pipe. Blockages can occur, when the paste separates from the aggregate skeleton because of a high pressure in the pipe. The stability of the wet-mix was determined by a filter pressing test. Mixes tested by the Sliper and the filter press were then sprayed with a wet-mix shotcrete machine Sika PM 500. This machine was equipped with seven pressure sensors, which could monitor the pressure over time. The sensors measured the pressure of the hydraulic system, the mix at the beginning and end of the pumping line, the pressure of the accelerator shortly after the pump and at the end of the hose, the pressure of the air and finally the pressure in the aerosol converter. Simultaneously, the spraying was filmed by a high-speed camera. This slow-motion recording shows the homogeneity and pulsation of the spray jet. At its best, shotcrete should emerge from the nozzle in a steady, uninterrupted flow. Different durable and sustainable mixes, developed under the Austrian research project ASSpC, were sprayed at different output of the shotcrete machine. The results and lessons learned from the results will be final part of the presentation

Estudio de las reacciones de hidratación temprana en el hormigón proyectado

[ES] El hormigón proyectado es un tipo de hormigón especial utilizado como soporte de rocas durante la construcción de túneles y excavación de minas, entre otras aplicaciones. Sus principales características son el fraguado rápido y el desarrollo de una resistencia mecánica muy alta a edades tempranas, lo cual permite que el hormigón se fije a la base sin necesidad de un soporte extra, endureciéndose en pocos minutos. Las reacciones de hidratación que ocurren en las primeras horas en el hormigón proyectado determinan el desarrollo de las propiedades mecánicas y su estudio es de crucial importancia para entender y optimizar el comportamiento de este tipo de hormigones. El estudio de estas reacciones, sin embargo, resulta relativamente complicado por varias razones: (i) el hormigón proyectado endurece muy rápido, lo cual dificulta su manejo durante los ensayos experimentales, y (ii) composiciones similares mezcladas en el laboratorio no se comportan de la misma forma que las proyectadas. En este trabajo se presenta una metodología experimental desarrollada para el estudio de las reacciones de hidratación que ocurren en el hormigón proyectado durante las primeras horas y su correlación con la resistencia mecánica.Los resultados que aquí se presentan forman parte del proyecto ASSpC (Advanced and Sustainable Sprayed Concrete) financiado por la ‘Sociedad austriaca para la tecnología de la construcción’ ÖBV y la ‘Agencia para la promoción de la investigación en Austria’ FFG (proyecto numero 856080). Los autores agradecen a SIKA Technology AG su colaboración para la realización de ensayos en sus instalaciones.Galan Garcia, I.; Stauffacher, A.; Mittermayr, F.; Thumann, M.; Kusterle, W.; Juilland, P.; Stenger, C.... (2018). Estudio de las reacciones de hidratación temprana en el hormigón proyectado. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 383-392. https://doi.org/10.4995/HAC2018.2018.6907OCS38339

Anpassung der Verarbeitungseigenschaften von Frischbetonmischungen für die Entwicklung von Spritzbetonen mit reduziertem Versinterungspotential

Die Entstehung von Versinterungen in den Entwässerungssystemen nicht druckwasserhaltender Tunnelbauwerke wird u. a. durch den Kontakt des Bergwassers mit zementgebundenen Materialien beeinflusst. Ein Ansatz um die Entstehung von Versinterungen zu reduzieren ist die Optimierung der Spritzbetonrezeptur. Die Änderungen der Bindemittelzusammensetzung des Spritzbetons haben Auswirkungen auf den Klinkergehalt, den Wasserbedarf und den Leimgehalt und damit auch auf die Verarbeitbarkeit der Frischbetonmischung. Darüber hinaus werden die Frühfestigkeitsentwicklung und die 28 d Druckfestigkeit des Spritzbetons beeinflusst. Im Rahmen dieser Arbeit konnte gezeigt werden, welche Aspekte bei der Entwicklung von Spritzbetonen mit einem reduzierten Versinterungspotential berücksichtigt werden müssen, um auch die genannten baupraktischen Anforderungen zu erfüllen

Enantioselective biocatalytic synthesis of (S)-monastrol

Alfaro Blasco M, Thumann S, Wittmann J, Athanassios G, Gröger H. Enantioselective biocatalytic synthesis of (S)-monastrol. BIOORGANIC & MEDICINAL CHEMISTRY LETTERS. 2010;20(15):4679-4682.The first enantioselective biocatalytic synthesis of (S)-monastrol has been developed via an unexpected and unusual enzymatic pathway as suitable route. Whereas attempts for a direct hydrolysis of racemic monastrol were not successful, formation of racemic O-butanoyl monastrol and subsequent enantioselective hydrolysis furnished O-butanoyl (S)-monastrol with 97% ee. Cleavage of the O-butanoyl moiety then gave the desired (S)-monastrol with 96% ee. (C) 2010 Elsevier Ltd. All rights reserved