Peer reviewed versionCyswllt i'r cyhoeddiad / Link to publication Dyfyniad o'r fersiwn a gyhoeddwyd / Citation for published version (APA): Galvez Martos, J. L.

No abstract

No abstract

Novel cement formulations based on calcium sulfoaluminate clinkers have significantly lower carbon dioxide emissions during production when compared against conventional Portland cement; however, there are no systematic studies of the environmental impact associated in producing these formulations. Previous studies are limited to qualitative evidence that emissions are lower due to a combination of favourable thermodynamics and a reduced usage of limestone. This work evaluates the eco-efficiency of calcium sulfoaluminate clinker production through an analysis of the carbon footprint and costs over the entire clinker production process (cradle-to-gate). Several sulfur sources are considered including calcium sulfate, as both gypsum and anhydrite, and a novel solid-sulfur combustion process in kilns. This latter process has the added advantage of reducing the fuel demand required to reach clinkering temperatures during the manufacturing process. The analysis demonstrates an overall reduction of emissions of 25-35%, which varies largely as a function of the phase composition of the final clinker but is almost independent of the sulfur source. The high aluminium oxide content in the final calcium sulfoaluminate clinker formulation requires the use of alternative raw materials and by-products from the aluminium industry such as high-alumina clays, aluminarich wastes, or bauxite. Bauxite, which is only abundant in specific regions of the world, is detrimental to the economics of calcium sulfoaluminate clinker production. Despite this, costs of the clinker production remain competitive and the process displays significant potential for improving the environmental impact of cement production.

The precipitation of magnesium hydroxy-carbonate hydrates has been suggested as a route to sequester CO2 into solids. We report the development of self-cementing compositions based on nesquehonite, MgCO3⋅3H2O, that are made from CO2-containing gas streams, the CO2 being separated from other gases by its high solubility in alkaline water, while magnesium is typically provided by waste desalination brines. Precipitation conditions are adjusted to optimize the formation of nesquehonite and the crystalline solid can readily be washed free of chloride. Products can be prepared to achieve self-cementation following two routes: (i) thermal activation of the nesquehonite then rehydration of the precursor or (ii) direct curing of a slurry of nesquehonite. The products thus obtained contain ~30 wt% CO2 and could form the basis for a new generation of lightweight, thermally insulating boards, blocks, and panels, with sufficient strength for general construction.