Research progress on magnesium silicate hydrate phases and future opportunities

Abstract

This short letter summaries the latest research on the structure and thermodynamic modelling of the magnesium silicate hydrates (M-S-H) phases. M-S-H structure is comparable to hydrated clays, with a smaller and rounder microstructures compared to clay platelets. Similar to clay minerals, M-S-H can incorporate ions such as aluminium and hydrated exchangeable cations to compensate the negative surface charge. This fundamental understanding of M-S-H structure allowed to develop structure-based thermodynamic models, which can further help to optimise the conditions for M-S-H formation and its use as cementitious materials. Optimized binders containing M-S-H have the advantages of presenting: i) good mechanical properties, ii) dense microstructure and potentially good resistances to leaching and iii) low pH values. These types of binders could therefore be used for cement products with non-steel reinforcement, for the encapsulation of specific wastes, for products containing natural fibres or for the clay stabilisation, etc.

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

“…The two major MgO-based cements include magnesium silicate and magnesium carbonate cement. The former binds based on magnesium silicate hydrate (MSH) 19 while hydrous carbonate-containing brucite 20 accounts for the binding in the latter. MSH has an amorphous (nanocrystalline) layered silicate structure with tetrahedral layers as in phyllosilicate minerals 21,22 .…”

MgO-based cements – Current status and opportunities

“…MS cements harden due to the formation of magnesium silicate hydrate (M-S-H) phases from the hydration of reactive sources of magnesia and silicate [38,76]. MS cement produced by calcination and pulverization of magnesium silicate rocks and lime were patented at the end of the 19 th century [77].…”

“…Further U.S. patents indicated that magnesia chloride cements were improved by the addition of silicates [78,79]. In general, poorly crystalline M-S-H forms from the reaction between silicate and magnesia, Mg(OH) 2 , MgSO 4 or MgCl 2 in a basic environment [76,80]. M-S-H formation is also observed in geological environment in the presence of high pH values (>9) in the contact zone between Portland cement and Mg-containing solution [81]: M-S-H has been observed in cements in contact with river [82], clayey [83] or saline waters [84,85] (Equation 3a) also forming during the serpentinization of olivine [86,87] (Equation 3b).…”

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

“…It forms at a lower pH than Portland cements and is a promising matrix for storage of nuclear waste [ 16 , 17 ]. According to Bernard [ 18 ], binders containing M-S-H also have good mechanical properties, a dense microstructure and potentially good resistance to leaching. Thus, M-S-H is currently of interest as an environmentally friendly alternative to Portland cement due to its potentially lower carbon footprint [ 3 ] and for the encapsulation of nuclear waste [ 19 ].…”