The dependence of the global construction sector on concrete, derived mainly from Portland cement clinker (PCC), presents significant environmental challenges. The cement manufacture accounts for approximately 8% of global anthropogenic CO2 emissions, caused mainly by the calcination of limestone, which takes place at temperatures above 1400 °C, and the subsequent clinker formation process. Efforts to reduce this carbon footprint have led to the exploration of alternative clinkers. An alternative approach involves carbonation processes that sequester CO2 in magnesium oxide (MgO)-based materials, resulting in the formation of magnesite (MgCO3) or hydrated magnesium carbonates (HMC) such as hydromagnesite, Mg5(CO3)4(OH)2·4H2O, and nesquehonite, MgCO3·3H2O.

MgO can be obtained from minerals such as olivine and serpentine, or from waste products such as brines. The used of Mg-silicates or Mg-containing brines to obtain MgO does not release fossil-bound CO2, offering potential carbon-neutral raw materials and a promising avenue for mitigating carbon emissions.

During the reaction of MgO with water and carbonate, HMC binders have the ability to sequester CO2 and gain mechanical strength. In contrast to pure MgO cements, such mixes develop adequate compressive strength, as recent results show that samples with up to 40-50 wt% of nesquehonite can achieve up to 43-44 MPa after 28 days.

This study investigates the hydration of MgO in the presence of nesquehonite as a carbonate source, a less stable and more reactive magnesium carbonate than hydromagnesite. The aim of this project is to understand which phases are formed during hydration, the hydration process and the mechanical properties of MgO/nesquehonite blends. The effect of the magnesium carbonate source (nesquehonite) and the CO2 storage capacity of these blends over time will also be investigated.

Contact:

Paula Montserrat-Torres, Barbara Lothenbach and Frank Winnefeld

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