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Reactive magnesia-based cements have comparable properties to PC, but much lower environmental impact. In particular, magnesium oxychloride cement (MOC) composites, with their CO2-neutral footprint, could provide the basis for a novel route to sustainable construction materials. The synthesis of MOC involves the simple reaction of magnesium oxide with an aqueous solution of magnesium chloride, resulting in the formation of compounds in the MgO-MgCl2-H2O system. The most commonly used and studied phase in this system is phase 5 (5Mg(OH)2·MgCl2·8H2O), primarily due to its excellent set of mechanical properties: compressive strength of 60–65 MPa, flexural strength of 5–8 MPa, and Young’s modulus of elasticity of 25–27 GPa, in pure state without any filler or additive. However, there are challenges to be overcome, the main one of which is the poor water resistance of MOC, which results in the rapid degradation of its mechanical properties. In our research group at UCT Prague, we study the ways to improve the water resistance of MOC as well as its potential in the field of green construction. The novelty of our approach lies in incorporating various types of carbon-based nanomaterials and also, the use of selected secondary waste fillers in the MOC matrix to obtain high-strength and water-resistant eco-friendly composites.

The carbon-based nanomaterials can not only positively influence the water resistance of the MOC-based composites, but also maintain and even enhance their mechanical properties. The addition of even a very low amount of carbon-based nanoadditive results in a significant decrease in gel pore volume, which leads to a subsequent decrease in the specific surface area of the composite. In addition, the large specific surface area of the used nanomaterials makes them efficient agents in controlling microcrack propagation. To obtain MOC-based composites with extremely high values of mechanical parameters and durability the carbon-based nanoadditives are combined, which results in their synergistic effect and overall ultra-high performance of the obtained MOC-based construction material.

As was mentioned above, we also thoroughly study the contribution of secondary and waste fillers to the environmental sustainability of MOC. Waste fillers are added to the MOC matrix to deliver the twin benefits of reduced landfilling and stronger mechanical performance. However, the addition of quite large amounts of some of these fillers can result in deterioration of the mechanical properties, so to resolve this, it is necessary to use either a lower filler content or, preferably, to introduce a specific functional modifier. With respect to the latter approach, we prepare composites using a combination of secondary fillers and specifically chosen carbon-based nanomaterials, which results in environmentally sustainable high-performance water-resistant MOC-based composites for green construction. Finally, we explore the excellent recycling potential of MOC and its composites by the design of thermal and mechanical methods that deliver a zero-waste cradle-to-cradle lifecycle.

Anna-Marie Lauermannova

Department of inorganic chemistry

University of Chemistry and Technology Prague

Czech Republic

lauermannovaannamarie@gmail.com