Civil Engineering Reference
In-Depth Information
capacity through lower solubility and mobility of brucite and its layered
structure as well as its lower stable long-term pH;
∑ eco-cements with MgO >> PC for porous block applications through
uptake of CO
2
and subsequent carbonation to a range of strength providing
hydrated magnesium carbonates.
Reactive MgO hydrates at a similar rate to PC and should not be confused
with dead burned MgO, the latter being the result of a much higher calcination
temperature resulting in a much lower reactivity leading to delayed hydration
and cracking, as would be the case for MgO impurities within PC during
the clinkering stage (~1450 °C).
The inventor John Harrison has contributed significantly to the understanding
of the chemistry, interactions and performance of these three PC-MgO
systems (Harrison, 2012). Significant publications in the technical literature
have resulted from related work performed at the University of Cambridge
over the past nine years which has investigated a whole host of reactive MgO
systems. This has so far included MgO alone and in blends with PC, slags,
fly ash, microsilica, limestone cement, zeolite and other magnesium-based
compounds (namely brucite, magnesite, hydrated magnesium carbonates and
silicates) as well as with a range of chemical admixtures. Reactive MgO
has also been investigated with a range of aggregates, including natural, fly
ash-based and limestone. Characterisation and fundamental properties as
well as performance in a range of applications for those systems, including
concrete, porous blocks, pervious concrete, ground improvement, waste and
contaminant immobilisation, soil and groundwater remediation, performance
in aggressive and extreme environments and carbon capture and storage,
were investigated.
19.3 Characterisation and properties
Extensive characterisation studies have been conducted on over 20
commercially available MgOs from around the world, from different sources
and manufacturing processes, and from commercial trials in China as well
as from small-scale laboratory production studies covering a range of
compositions (Jin, forthcoming). It should be pointed out that most of those
MgO commercially produced from the calcination of magnesite are likely
to have been calcined at temperatures at the higher end of the reactive MgO
range of ~1000 °C hence their reactivity is likely to be close to that of hard
burned MgOs. The MgO content was found to vary between 60% and 99.6%
where the synthetically produced (seawater and chemical precipitation) were
at the higher purity end. The main impurities of the calcined MgOs were CaO
and SiO
2
, which are common minerals of rock, while those of the synthetic
MgOs were CaO, Cl and SO
3
. The CaO content varied between 0.15% and
