Geoscience Reference
In-Depth Information
The results showed that the shear strength of sapric peat with cement decreased
at 90 and 180 days of curing respectively, compared with the shear strength at 45
days of curing. Similarly, the shear strength of fibrous, hemic and sapric peats with
the cement-slag mixture decreased at 90 and 180 days of curing, compared with the
shear strength at 45 days of curing.
The reason for such behaviour is that when water containing dissolved CO
2
comes
into contact with treated peats, it reacts with Ca(OH)
2
(produced from cement hydra-
tion) to form calcite (CaCO
3
). Carbonation has three main effects: (1) a reduction
in Ca(OH)
2
, and a subsequent reduction in pozzolanic reactions between Ca(OH)
2
and pozzolanic minerals in the soil, (2) the decomposition and carbonation of calcium
silicate hydrate (C-S-H) and (3) a reduction in the pH of pore water in the hardened
mixture. The peat in the present study contained few mineral solids, and hence the
main reason for the decrease in the shear strength of all samples treated with cement
or cement-slag mixtures when they came into contact with CO
2
was the decomposition
of the C-S-H gel to form CaCO
3
and the reduced pH of the pore water.
It was shown that peats treated with cement-slag mixtures have greater resistance
to carbonation with a soft surface of carbonation in comparison with peats treated with
cement only (Kazemian
et al
., 2011a). It was observed that the depth of carbonation
increased with increasing fibre content and curing time. Furthermore, the decrease in
shear strength was greater in fibrous peat than in hemic and sapric peats (Kazemian
et al
., 2011a).
8.7.2 Effect of N on treated peat
The effect of N on cementation was observed by adding urea (2.5% and 5%by weight)
to fibrous, hemic and sapric peat. The peat was first thoroughly homogenized; urea
was then added and mixed again. Finally, the binders were added and mixed for five
minutes to ensure homogenization. The effect of N (2.5%) is shown in Figure 8.9.
Figure 8.9
Undrained shear strength ratio vs. time of peat with cement and cement-slag mixtures
(N
=
2.5%).
