Ultra Optimum Green Concrete Using High Volume Fly Ash Activated Systems
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Ultra Optimum Green Concrete Using High Volume Fly Ash Activated Systems Diego F. Velandia1,2, Cyril Lynsdale1, Fernando Ramirez3, John L. Provis4, German Hermida5 and Ana C. Gomez2 1 Department of Civil and Structural Engineering, University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield, S1 3JD, UK 2 Research and Development, Argos, Carrera 62 No. 19 - 04 , Bogotá, Colombia 3 Department of Civil and Environmental Engineering, Universidad de los Andes, Carrera 1 este No. 19A-40, Edificio Mario Laserna, Oficina ML 632, Bogotá, Colombia 4 Department of Materials Science and Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK 5 Sika Technical support, km 20,5 Autopista Norte, Tocancipa, Colombia ABSTRACT Environmental issues related to CO2 emissions have become a key focus for many different industries, including the cement and concrete industry. An environmentally optimized ‘green’ concrete can provide a much needed alternative to conventional concrete to reduce the carbon foot-print of the construction industry. This can be achieved through high Portland cement replacement by fly ash and with the inclusion of activators to enhance the rate of development of strength and other properties. This study evaluates different fly ashes and different activators (Na2SO4, lime and quicklime) that are added to enhance the reaction of the fly ash to achieve a comparable performance to that of standard Portland cement in mixes of much lower CO2 emissions. TGA, XRD and SEM are used to determine the development of hydration products and the consumption of portlandite by the fly ash. It is found that the amorphous content of the fly ash is an important parameter influencing compressive strength evolution. Based on the results, Na2SO4 as an activator, and a fly ash with high reactive SiO2 and Al2O3 contents and low Fe2O3 are found to provide the best options for producing a high volume fly ash matrix with the potential to show comparable behavior to a Portland cement control mix. INTRODUCTION In recent years, different possible solutions to reduce the carbon foot-print of concrete have been studied by cement and concrete researchers [1-13]. One of the solutions put forward is the inclusion of supplementary cementitious materials in high percentages for concrete production [2, 3]. To advance this concept, all important parameters need to be optimized to develop an ultra optimum green concrete (UOGC) as a low CO2 concrete alternative for the construction industry. The UOGC, investigated in this work, is based on a high volume fly ash concrete (HVFA), with added alkaline activators. Although this technology has been explored before [4], there are still many unanswered questions [5] which relate to why it has never yet been produced in sufficient volumes to compete with regular Portland cement concrete. Lack of detailed technical information, standards, and the evident need to further research its fresh and hardened properties and durability [6], are some of the
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