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Geotechnical News December 2010
GEO-INTEREST
dehydration) begins at 550-600 °C to
produce disordered metakaolin, Al-
2Si2O7, but continuous hydroxyl loss
(-OH) is observed up to 900 °C and has
been attributed to gradual oxolation
of the metakaolin. Because of historic
disagreement concerning the nature
of the metakaolin phase, extensive re-
search has led to general consensus that
metakaolin is not a simple mixture of
amorphous silica (SiO2) and alumina
(Al2O3), but rather a complex amor-
phous structure that retains some lon-
ger-range order (but not strictly crystal-
line) due to stacking of its hexagonal
layers.
2 Al2Si2O5(OH)4
→
2 Al2Si2O7
+ 4 H2O
Further heating to 925-950 °C con-
verts metakaolin to a defect aluminu-
im-silicon spinel, Si3Al4O12, which is
sometimes also referred to as a gamma-
alumina type structure:
2 Al2Si2O7
→
Si3Al4O12 +
SiO2
Upon calcination to ~1050 °C, the
spinel phase (Si3Al4O12) nucleates
and transforms to mullite, 3 Al2O3 •
2 SiO2, and highly crystalline cristo-
balite, SiO2:
3 Si3Al4O12
→
2 Si2Al6O13 +
5 SiO2
Mixing of Different Materials
The main material mixed in this case
is the dry kaolin. It is combined with
optimum moisture content, due to the
compaction test in different tests. Then
it is mixed by kneading until cohesion
soil is achieved. The sizes of the bricks
to be made are 10cm×10cm×10cm and
the mixture is placed in three layers in
steel moulds. They consist of two layers
composited of additional materials that
are the shred geogrids are placed at 1/3
and 2/3 of its height.
Test of Mud Bricks
The mud bricks were used for 4 tests
and taken out from the moulds. Then
they were tested for compressive
strength for 3,7,14 and 21 days.
Conclusion
The compressive strength test s results
on mud bricks that have additional
material, such as shred geogrids are
illustrated in table 1. The results
of compressive strength show that
performance of shred geogrids are
better than normal mud bricks by
time passing. They show an increase
of the compressive strength until 14
days and then a decrease. The main
reason that causes this decrease is the
moisture range, due to the wet climatic
conditions of Malaysia. The shape of
additive materials can be as well, a
factor that causes this decrease in the
compressive strength in a long period
of time. The first reason, regarding to
the moisture has the highest impact on
this compressive strength. The shred
tires increased the status of tension
in mud bricks. The performance of
shred geogrids increased properties
of compression in different cases,
although performance of mud bricks
without addition material wasn’t good
in earthquake of Bam-2003 in Iran but
there is a hope that shred tires mud
brick can carry out high strength in the
future.
Reference
[1] Bellotto, M., Gualtieri, A., Artioli,
G., and Clark, S.M. (1995). “Ki-
netic study of the kaolinite-mullite
reaction sequence. Part I: kaolinite
dehydroxylation”. Phys. Chem.
Minerals 22: 207-214.
[2] Deer, W.A.; Howie, R.A.; Zussman,
J. (1992), An introduction to the
rock-forming minerals (2 ed.), Har-
low: Longman, ISBN 0582300940
Figure 5. View of different cases in
compression test.
Table 1.The results of compressive test of mud bricks with shred geogrids
and normal mud bricks.
Type
Days
3
7
14
21
Kaolin + water
1.90
N/mm
2
2.94
N/mm
2
2.52
N/mm
2
1.49
N/mm
2
Kaolin + Water + Shred
Geogrids
1.91
N/mm
2
2.57
N/mm
2
2.62
N/mm
2
1.81
N/mm
2
Figure 2. Compaction test of kaolin.
Figure 4. View of shred geogrid in 1-3
layer of mould.
Figure 3. Mixing of kaolin with opti-
mum moisture content.
