Lime-hemp concrete (LHC) enhancement using magnesium based binders

Abstract

The major CO2 emitting countries have concluded an agreement aimed at reducing the CO2 emissions at the Paris Climate Conference 2015. However, the emission levels are still on the rise. As the building material industry is one of the largest producers of CO2, it should find solutions to limit these emissions, such as development of new materials with negative CO2 balance and low thermal conductivity for energy saving during lifespan. The lime-hemp concrete (LHC) could be one of the solutions as it has negative CO2 emissions balance (up to 80 kg/m2) and low thermal conductivity (0,07-0,09 W/m*K). Even though, the LHC has been gaining popularity and recognition over the past years, it is still not used enough to contribute significantly to lowering the global CO2 emissions. One of the reasons is the low mechanical strength of this material that can be mostly used only with supportive load bearing frame appropriate for the low rise buildings. It could be improved by enhancing the binder strength either through supplementing or substituting it with the magnesium based binders. Made of calcined MgO with possible additions of magnesium salts or other hardeners, the early and overall compressive strength shown by these binders is greater compared to hydraulic lime binders used in the LHC. The magnesium based binders also remain unaffected by the organic water soluble constituents that react with calcium ions in hydraulic lime, thus delaying or preventing hydration process. Various MgO binders are tested in this research, focusing mainly on mechanical strength and thermal conductivity, in order to understand the effect that adding the magnesium binders has on important LHC properties. The obtained results suggest that the MgO binders are viable alternative to hydraulic lime as their superior compressive strength allow for lower amount of binder to be added thus enhancing thermal conductivity or giving material wider possible use due to this strength increase.