Magnesium oxide based binders as low-carbon cements
Author(s)
Zhang, Fei Hannah Doig
Type
Thesis or dissertation
Abstract
Portland cement (PC) is a fundamental component of the construction industry. However, its
manufacturing process is responsible for ~5 % of global anthropogenic CO2 emissions. Given
current demand for PC which is expected to triple by 2050, there is an urgent need for the
production of alternative binders with a lower carbon footprint. One type of such alternative
binder are magnesium oxide (MgO) based cements. This research has investigated the
properties of three novel magnesium oxide based cement systems as potential binders that
could be used for some standard cement applications.
Previous research at Imperial College London found that the addition of a hydrated
magnesium carbonate to MgO prior to hydration resulted in the production of setting and
strength gaining samples. One of the main objectives of this research was to understand how
the addition of magnesium carbonate gave the system cement-like properties and to
investigate the types of strength possible from a basic system as well as to identify the main
parameters that affect strength, thus allowing for future optimisation. It was found that the
presence of carbonate and its effect upon the system pH alters the type of Mg(OH)2 formed,
giving a more stable microstructure that accounts for the strengths achieved. The type of
MgO was found to be an important parameter, as was particle size. Due to water demand, a
10 % carbonate – 90 % MgO mix was chosen as the optimum mix.
The second system studied was the silica (SiO2) – MgO system. This was investigated in
order to assess the potential of the reaction between MgO and silica to form M-S-H gel and to
study the mechanism of formation of reaction products. It was found that reactive MgO and
amorphous silica can react together upon hydration to form a mixture of M-S-H gel and
Mg(OH)2, dependent upon the SiO2/MgO ratio. These systems have considerable
compressive strengths the extent of which depends upon the type of silica. An optimum mix
of 30 % silica – 70 % MgO (by dry weight) was found
Finally, a simple ternary system of magnesium carbonate - silica - MgO was investigated in
order to assess if the presence of the combination of both ‘additives’ could create a better
system than either of the two-component systems. Strength results suggested that there is no
added benefit to the system in combining the two-component systems. For all three systems
studied, the high w/s ratios required were found to be a significant limiting factor.
manufacturing process is responsible for ~5 % of global anthropogenic CO2 emissions. Given
current demand for PC which is expected to triple by 2050, there is an urgent need for the
production of alternative binders with a lower carbon footprint. One type of such alternative
binder are magnesium oxide (MgO) based cements. This research has investigated the
properties of three novel magnesium oxide based cement systems as potential binders that
could be used for some standard cement applications.
Previous research at Imperial College London found that the addition of a hydrated
magnesium carbonate to MgO prior to hydration resulted in the production of setting and
strength gaining samples. One of the main objectives of this research was to understand how
the addition of magnesium carbonate gave the system cement-like properties and to
investigate the types of strength possible from a basic system as well as to identify the main
parameters that affect strength, thus allowing for future optimisation. It was found that the
presence of carbonate and its effect upon the system pH alters the type of Mg(OH)2 formed,
giving a more stable microstructure that accounts for the strengths achieved. The type of
MgO was found to be an important parameter, as was particle size. Due to water demand, a
10 % carbonate – 90 % MgO mix was chosen as the optimum mix.
The second system studied was the silica (SiO2) – MgO system. This was investigated in
order to assess the potential of the reaction between MgO and silica to form M-S-H gel and to
study the mechanism of formation of reaction products. It was found that reactive MgO and
amorphous silica can react together upon hydration to form a mixture of M-S-H gel and
Mg(OH)2, dependent upon the SiO2/MgO ratio. These systems have considerable
compressive strengths the extent of which depends upon the type of silica. An optimum mix
of 30 % silica – 70 % MgO (by dry weight) was found
Finally, a simple ternary system of magnesium carbonate - silica - MgO was investigated in
order to assess if the presence of the combination of both ‘additives’ could create a better
system than either of the two-component systems. Strength results suggested that there is no
added benefit to the system in combining the two-component systems. For all three systems
studied, the high w/s ratios required were found to be a significant limiting factor.
Date Issued
2012
Date Awarded
2013-02
Advisor
Vlasopoulos, Nikolaos
Cheeseman, Chris
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)