MgO-based cements – Current status and opportunities

Abstract

The cement industry is a major contributor to the anthropogenic CO2 emissions, with about 8% of all emissions coming from this sector. The global cement and concrete association has set a goal to achieve net-zero CO2 concrete by 2050, with 45% of the reduction coming from alternatives to Portland cement, substitution, and carbon capture and utilization/storage (CCU/S) approaches. Magnesia-based cements offer a conceivable solution to this problem due to their potential for low-to-negative CO2 emissions (CCU/S) but also being alternatives to Portland cement. The sources of magnesia can come from magnesium silicates or desalination brines which are carbon free for raw-material-related emissions (cf. carbonated rocks). This opens up possibilities for low or even net-negative carbon emissions. However, research on magnesia-based cements is still in its early stages.
 In this paper, we summarize the current understanding of different MgO-based cements and their chemistries: magnesia oxysulfate cement, magnesia oxychloride cement, magnesia carbonate cement, and magnesia silicate cement. We also discuss relevant research needed for MgO-based cements and concretes including the issues relating to the low pH of these cements and suitability of steel reinforcement. Alternatives reinforcements, suitable admixtures, and durability studies are the most needed for the further development of MgO-based concretes to achieve a radical CO2 reduction in this industry. Additionally, techno-economic and life cycle assessments are also needed to assess the competition of raw materials and the produced binder or concrete with other solutions. Overall, magnesia-based cements are a promising emerging technology that requires further research and development to realize their potential in reducing CO2 emissions in the construction industry.

Formation of Natural Magnesium Silica Hydrate (M-S-H) and Magnesium Alumina Silica Hydrate (M-A-S-H) Cement

“…Ultramafic rocks represent a major source of MgO in the form of magnesium silicates. According to Bernard et al [ 48 ], ultramafic rocks provide an almost unlimited reservoir of MgO, with estimated available worldwide reserves of over 10 trillion tons [ 49 ]. Assuming a thickness of 5 km for the Feragen and Leka complexes, these two complexes alone contain a MgO reserve of 4 × 10 11 tons of MgO.…”

Characterization of Historic Lime Mortars from the Arch of San Martin to Identify the Construction Phases of the City Wall of Burgos (Spain)

“…However, this not only depends on the binder chemistry (i.e., magnesium limes) but also on several factors triggering chemical reaction. Saltwater or other alkaline media and/or the presence of certain aggregates and clay minerals, usually stable under normal conditions, can develop para-pozzolanic phases [48,49]. Amesite constitutes a hydraulic phase, contributing to a decrease in the porosity and favoring the waterproofing behavior of mortar [50][51][52][53][54][55][56].…”

What makes cements bind?—A proposal for a universal factor

“…Magnesia-based cements offer a conceivable solution to decarbonize the cement industry due to their potential for low-to-negative CO 2 emissions. 20 The two major MgO-based cements include magnesium silicate and magnesium carbonate cement. The former binds based on magnesium silicate hydrate (MSH) 21 while hydrous carbonate-containing brucite 22 accounts for the binding in the latter.…”