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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
as per the procedure outlined above. Table 4 shows the results
of these tests and the loss of alumina and silica in treated soils at
different mellowing time periods. It can be seen from the Table
4 that the initial reactive alumina and silica contents are very
low in Childress soil when compared to that of Sherman soil.
The main intent of mellowing is to allow the Ettringite
formation reactions in initial stages. During remixing and
compacting the initial Ettringite is broken and further Ettringite
formation is hence not possible due to the lack of reactive
sulfates.
It is reported in the literature that Ettringite formation
depends on the amount of reactive alumina present in the
system. For example, low alumina contents in soils favor the
trisulfate hydrate (Ettringite) formation. High alumina contents,
on the other hand, lead to simultaneous formations of
pozzalonic and ettringite reactions. As a result, attractive forces
formed from pozzalonic formation will resist the disruptive
forces caused by Ettringite hydration reactions. This explains
low heaving in high alumina soil (Sherman soil) of the present
research.
Low initial reactive alumina contents coupled with high
sulfate contents in Childress soils are attributed to large heaving
and here the mellowing is deemed ineffective primarily due to
low alumina content in the soil. Also, the loss of alumina and
silica at both 0 day and 3 day mellowing periods were higher in
case of Childress soil compared to Sherman soil. Though the
loss of alumina and silica is less in 3-day mellowed soils, this
soil still exhibited high swelling due to high sulfate content
(44,000 ppm) present.
Table 4. Reactive Alumina and Silica (ppm) in present soils
Untreated
(Natural)
6%L,
0-day
mellowing
6%L,
3-day
mellowing
% loss
% loss
Soil
Al(ppm) Si(ppm)
Al
Si
Al
Si
Sherman@OMC
279
137
58 66 53 64
Sherman@WOMC
279
137
57 64 52 63
Childress@OMC
76
13 63 54 61 46
Childress@WOMC
76
13 62 62 58 54
Also, authors have made attempts to link the formation and
growth of Ettringite to the compaction density/void ratio of the
soil specimens. Based on specific gravity and maximum dry
density (@OMC condition), the compaction void ratio is
calculated. Compaction void ratios of Childress and Sherman
soils are 0.52 and 0.86, respectively. In soils with high void
ratio (Sherman), the initial Ettringite formation, growth and
heaving on hydration can be accommodated in the soil matrix
provided there is no further nucleation of new compounds. If
there had been further Ettringite growth, heave would have been
higher in Sherman soil. In soil with low void ratio such as the
present Childress soil, the dense soil matrix could not
accommodate both initial Etringite formation and their growth
on hydration and as a result, this soil exhibited higher heaving.
Overall, both alumina amounts and compaction void ratio
conditions contribute to soil sulfate heaving and this
information is used in the development of alternate chemical
treatments for high sulfate soils.
4 CONCLUSIONS
1. In Sherman soil containing sulfates of 30,000 ppm or
less, the mellowing effectively reduced the swell
potential. Childress soil, containing larger amounts of
sulfates of more than 30,000 ppm, exhibited sulfate
induced heaving even at longer mellowing periods.
2. Volumetric shrinkage behavior is unaffected by the
presence of sulfates and mellowing periods indicating
that the shrinkage behavior was succesfully reduced
with lime treament.
3. Low alumina contents facilitated Ettringite formation
and heaving (Childress soil) whereas at high alumina
contents both Ettringite and pozzolonic reactions
occur simultaneously but due to dominance of
pozzolonic reactions less heave is observed in this
case (Sherman soil).
4. Compaction void ratio is an important parameter that
need to be emphasized in lime treament of sulfate
soils because Ettringite induced heaving is more
critical in dense soil matrix compared to loose matrix.
5 ACKNOWLEDGEMENTS
Authors would like to thank Texas Department of
Transportation (TxDOT) for the funding the project. Authors
would like to thank Mike Arellano and Richard Williammee of
TxDOT as well as Pat Harris of Sam Houston State University
for their assistance with the research.
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