Carbonated magnesia cements

Abstract In some porous unreinforced concrete products carbonation could be employed to deliver significant benefits, both in terms of mechanical strength and carbon footprint. While much work has focused on the carbonation of lime, recent studies have shown that magnesium-based cementitious systems, including slags and magnesia, can be employed as the main strength development process in carbonated reactive magnesia cement products. In this chapter, the design, performance and applications of carbonated reactive magnesia in different compositions and scenarios are presented and discussed. A number of hydrated magnesium carbonates form upon the carbonation of magnesia, with different controlling factors for their formation, resulting in different mechanical properties as well as CO2 sequestration capacity. Pressed semi-dry magnesia-based masonry blocks are the first application example presented. The results of both laboratory and full-scale production of a range of magnesia-based products are discussed in terms of the variable considered. Experimental work was complemented with computer simulations to model the mechanism of the carbonation process. The use of carbonated reactive magnesia was also considered for ground improvement applications. Forced carbonation of soils mixed with dry reactive magnesia was employed both in triaxial samples and with the use of a model auger that simulated field applications of the carbonation process. Blended magnesia mixes were investigated. In all the studies reported here, the investigations considered the dosage of the magnesia as well as the carbonation environment followed by mechanical and microstructural analyses. Different accelerated carbonation regimes were also considered. This chapter reports details of the experimental and field work carried out on carbonated reactive magnesia cements highlighting the carbonation mechanisms and resulting properties as well as potential benefits and environmental impacts.