an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
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65<br />
sericite <strong>an</strong>d chlorite (see next section on sc<strong>an</strong>ning electron microscope studies); while those<br />
deficient in the alkali <strong>an</strong>d alkali-earth metals alter into aluminiumsilicates <strong>of</strong> <strong>an</strong>dalusite,<br />
sillim<strong>an</strong>ite <strong>an</strong>d ky<strong>an</strong>ite.<br />
Theoretical chemical compositions <strong>of</strong> the minerals kaolinite, illite <strong>an</strong>d montmorillonite are<br />
given in Table 6.5. A comparison <strong>of</strong> the results in this table with those <strong>of</strong> chemical <strong>an</strong>alyses in<br />
Table 6.1 suggest the kaolinite in red soils to be depleted in Al2O3. The depletion is most<br />
probably a result <strong>of</strong> low PH conditions caused by formation <strong>of</strong> weak carbonic acids in the<br />
soils through org<strong>an</strong>ic matter decomposition <strong>an</strong>d/ or hydrothermal alteration at signific<strong>an</strong>t<br />
temperatures.<br />
Table 6.5. Theoretical compositions <strong>of</strong> kaolinite, illite <strong>an</strong>d montmorillonite<br />
(Jasmund & Lagaly, 1993; Moore & Reynolds, 1989; Rösler, 1980).<br />
% content <strong>of</strong>: Smectites<br />
Il lite Kaolinite<br />
(montmorillonite)<br />
SiO2 48-56 51-54 46,55<br />
Al2O3 11-22 21-29 39,5<br />
H2O 12-24 - 10,0-13,95<br />
Fe2O3 ≥5 0,5-5,3 Trace<br />
FeO - 0,9-1,2 -<br />
BaO - - Trace<br />
MgO 4-9 2,8-3,5 Trace<br />
CaO 0,8-3,3 ,02-,05 Trace<br />
Na2O trace ,08-,10 Trace<br />
K2O trace 2-9 Trace<br />
P2O5 - 0,6-0,82 -<br />
ZrO2 - - -<br />
TiO2 - 0,60-0,82 Trace<br />
MnO - - -<br />
Loss on ignition - - -<br />
Total >80 >79,5 96,0-100,0<br />
800<br />
Impulse<br />
RD 1 - 30cm + St<strong>an</strong>dard<br />
F<br />
F<br />
700<br />
600<br />
Q: Quartz (1%)<br />
H: Haematite<br />
K: Kaolinite<br />
F: Fluorite (CaF2- St<strong>an</strong>dard)<br />
Tr: Specimen holder<br />
500<br />
F<br />
400<br />
214<br />
300<br />
Tr<br />
200<br />
100<br />
K<br />
K<br />
Q<br />
Q<br />
18<br />
K<br />
H<br />
H<br />
K<br />
Q<br />
K<br />
H<br />
Q<br />
H Q<br />
H<br />
H<br />
Q<br />
H<br />
K<br />
H<br />
Q<br />
F<br />
0<br />
0 20 40 60 [ ° 2 ]<br />
Figure 6.7. X-ray diffraction diagram <strong>of</strong> red soils collected at 0,30m depth.