Geoscience Reference
In-Depth Information
8.6 CHEMICAL AND BIOLOGICAL CHANGES
An important characteristic of peat is its potential chemical and biological changes
with time. Further humification of the organic constituents would alter the mechanical
properties, such as compressibility, strength and hydraulic conductivity. Lowering of
ground water may cause shrinking and oxidation of peat, leading to humification
and a consequent increase in permeability and compressibility. Oxidation also leads
to gas formation which may contribute to excess pore pressures (Vonk, 1993). The
significance of these effects on the long-term performance of structures placed on peat
is often not taken rigorously into account. However, in the absence of any significance
change in the submergence of these deposits, the long-term chemical and biological
degradation of the peats may not be significant.
8.7 EFFECT OF PEAT MEDIA ON STABILIZATION PROCEDURE
Other important characteristics of peats are the presence of carbon dioxide (CO
2
)
and nitrogen (N), and an acidic environment with a high ground water level. The
decomposition of peat is a complicated phenomenon, and in this process the leaf litter
(providing the main input of organic matter to the soil) is physically broken down
by the larger soil fauna, including earthworms and termites. Microorganisms (bacte-
ria and some fungi) can start their decomposition activities while the leaf is still on
the plant. These microbial processes diversify and intensify once the leaf reaches the
soil. CO
2
is produced by aerobic and anaerobic decomposition above and below the
water table, which causes loss of organic matter and an altered physical structure and
chemical state. Glenn
et al
. (1993) have reported the CO
2
production rates of aerobic
laboratory incubations to be 0.2-1.4mg CO
2
g
−
1
d
−
1
(0.14-0.98 ppm/min), an average
of five times more than the rate under anaerobic conditions. The N content of peat
that develops from reeds, sedges and trees is rather high, being an average of three
times that developing from Sphagnum mosses and Eriophorum sedges; it is around
0.3-5% for oven dry peat. The range of acidity levels in peat is very wide. The pH of
most peats ranges between 2 and 6, but in some conditions, where there is infiltration
of brackish water or the peat contains pyritic materials, the pH may be as high as 7.8
or less than 2, respectively (Andriesse, 1988).
Kazemian
et al
. (2011a) described the influence of the characteristics of peat (CO
2
,
N, and acidic or alkalinemedia) on cementation and pozzolanic reactions when treating
tropical fibrous, hemic and sapric peats with cement and slag.
8.7.1 Effect of CO
2
on treated peat
The effect of CO
2
on cementation and pozzolanic reactions was investigated by pro-
ducing water containing dissolved CO
2
and curing samples in it for 45, 90 and 180
days. A simple CO
2
injection system was fabricated to produce the water containing
dissolved CO
2
. It consisted of two parts: a generator to hold a yeast mixture (fine
sugar, water and yeast) and a reactor to ensure that the CO
2
was efficiently dissolved
in water in the sample container (Figure 8.7). The concentration of CO
2
produced was
measured using a CO
2
test kit, and the targeted rate of 0.2 ppmmin
−
1
(the same as
