Civil Engineering Reference
In-Depth Information
contribution to strength development (Tsang, 2010; March, 2011; li,
2012). Incorporation of microsilica, at 10% content, in the cement blends
above led to strength increases, which varied with curing age, when MgO
was included at ~5% content compared to the effect of microsilica on the
control without the MgO (March, 2011). As an activator for slag on its
own, a 5% MgO content produced concrete with strengths of up to 28MPa
(li, 2012). Carbonated MgO and slag-MgO blends showed considerable
promise in previous concrete applications (Hargreaves, 2010). The pH of
those blends investigated is usually high enough to provide the alkalinity
necessary to maintain the steel reinforcement passivation layer. Further
detailed investigations of these blended compositions and applications are
being conducted (Abdollazadeh, forthcoming).
The expansion behaviour of different commercial reactive MgOs was
investigated in comparison to that of a commercial MgO expansive additive
from China (li, 2012). The results showed that a similar degree of expansion
and trend with increasing MgO content confirming that the majority of
commercially available reactive MgOs are close to the hard burned MgO
end of the calcination process and properties. Reactive MgO is generally
more expansive and expansion takes place much earlier on in the hydration
process, leading to densification of the concrete matrix. Optimisation of
shrinkage compensation of MgO in concrete is currently being investigated
in detail (lau, forthcoming).
19.5.3 Ground improvement
As PC, lime and slag-lime blends are frequently used for ground improvement
applications, the potential for MgO in comparison was investigated in which
carbonated MgO was compared with PC, and slag-MgO with slag-lime
blends as well as with PC (Jegandan, 2010; Jegandan et al., 2010; Al-Tabbaa
et al., 2011; Yi et al., 2012). The range of compositions and performance of
those systems especially when the soil is sand, are similar to those of porous
blocks and mortars. Studies using laboratory prepared samples as well as
laboratory-scale
in situ
field application simulations showed that carbonated
MgO, applied at 5 and 10% content, outperformed PC. It was possible to
carbonate dry MgO mixed with sand by pumping gaseous CO
2
through the
treated sand and carbonation occurred in under 3 hours. The compressive
strength values achieved were in the same range as those achieved by
corresponding PC-sand at 28 days. Increasing the CO
2
pressures speeded
up the carbonation process although the final strength value achieved was
always roughly the same and curing in a 20% CO
2
incubator also reached
the same strength but in a longer curing period of 2 days.
Slag-MgO blends with MgO content of 5-50% and at up to 15% binder
addition to sandy soils were tested both in the laboratory as well as in full-
