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Magnesium oxide based binders as low-carbon cements

By Fei Hannah Doig Zhang

Abstract

Portland cement (PC) is a fundamental component of the construction industry. However, its\ud manufacturing process is responsible for ~5 % of global anthropogenic CO2 emissions. Given\ud current demand for PC which is expected to triple by 2050, there is an urgent need for the\ud production of alternative binders with a lower carbon footprint. One type of such alternative\ud binder are magnesium oxide (MgO) based cements. This research has investigated the\ud properties of three novel magnesium oxide based cement systems as potential binders that\ud could be used for some standard cement applications.\ud Previous research at Imperial College London found that the addition of a hydrated\ud magnesium carbonate to MgO prior to hydration resulted in the production of setting and\ud strength gaining samples. One of the main objectives of this research was to understand how\ud the addition of magnesium carbonate gave the system cement-like properties and to\ud investigate the types of strength possible from a basic system as well as to identify the main\ud parameters that affect strength, thus allowing for future optimisation. It was found that the\ud presence of carbonate and its effect upon the system pH alters the type of Mg(OH)2 formed,\ud giving a more stable microstructure that accounts for the strengths achieved. The type of\ud MgO was found to be an important parameter, as was particle size. Due to water demand, a\ud 10 % carbonate – 90 % MgO mix was chosen as the optimum mix.\ud The second system studied was the silica (SiO2) – MgO system. This was investigated in\ud order to assess the potential of the reaction between MgO and silica to form M-S-H gel and to\ud study the mechanism of formation of reaction products. It was found that reactive MgO and\ud amorphous silica can react together upon hydration to form a mixture of M-S-H gel and\ud Mg(OH)2, dependent upon the SiO2/MgO ratio. These systems have considerable\ud compressive strengths the extent of which depends upon the type of silica. An optimum mix\ud of 30 % silica – 70 % MgO (by dry weight) was found\ud Finally, a simple ternary system of magnesium carbonate - silica - MgO was investigated in\ud order to assess if the presence of the combination of both ‘additives’ could create a better\ud system than either of the two-component systems. Strength results suggested that there is no\ud added benefit to the system in combining the two-component systems. For all three systems\ud studied, the high w/s ratios required were found to be a significant limiting factor.Imperial Users onl

Publisher: Civil and Environmental Engineering
Year: 2013
OAI identifier: oai:spiral.imperial.ac.uk:10044/1/11000

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