Concrete, a mixture of sand, cement and aggregates, is a remarkable material that can be shaped in almost every form and that can be produced at relatively low costs compared to other construction materials. Because of all of these advantages, concrete is currently the most widely used material after water. Despite its numerous assets, concrete present one major drawback: its production emits a lot of CO2. This comes from the production of cement, which needs to heat up to 1450°C and because of the decarbonation of limestone (CaCO3). Scientists estimated that cement is responsible for 5 to 8% of anthropogenic CO2 emissions. In a context of global warming, it is therefore necessary to reduce the CO2 emissions during the production of cement. Several solutions are currently studied, and one of them consist in using alternatives binders based on Magnesium. Magnesium is an abundant mineral on Earth which can be extracted from different rocks. It can be extracted as magnesium oxide (MgO) and also as hydrated magnesium carbonate (referred as HMC). By mixing MgO and HMC with water, hydration and carbonation will happen in the mix and develop strength.  The obtained cement is called HMC cement. The main advantage of HMC cement is that its production does not emit CO2 and it can act as a carbon sink thanks to the carbonation reaction that occurs during the process of hardening. Developing HMC cements requires to take into account several parameters, and one major challenge to take up is the control of the kinetics. Indeed, the cement has to harden in a range of time which is relatively fast, but also not too short. This is why one part of the project focuses on the speed of the reaction in HMC cements, and how minor additives can affect it. These knowledge can be used to improve the setting time of a HMC cement without deteriorating its properties.

Contact: Clélia Bouchaud, Barbara Lothenbach

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