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Technical Committee 307 /
Comité technique 307
UCS for soil B without stabilizer was around 400 kPa and
addition of fly ash didn't result in strength gain.
4.4
Effective shear strength parameters
Effective shear strength parameters have been determined by
using direct shear test. Obtained results (Fig. 5) show that long
term friction angle doesn't substantially change with addition of
fly ash, for both soil types. On the other side, cohesion
significantly increases with time for all tested mixtures. This is
associated with pozzolanic properties of used fly ash.
Figure 5. Variation in effective shear strength parameters
4.5
California Bearing Ratio (CBR)
For both soil types, California bearing ratio tests have been
done on mixtures with 15% KFA, which is adopted as optimum.
Compared with CBR values for base soils A and B, obtained
results showed significant gain. In the case of soil A, CBR value
increased nearly 300%, and 260-380% in the case of soil B
(dependent on elapsed time). This is especially important for
soil A, because it makes it usable for road construction (CBR
value was increased from 2.1 to 5.8). CBR values are shown in
Fig. 6, and are in line with Mackiewicz and Ferguson 2005,
White et al. 2005 and Edil et al. 2006.
Figure 6. CBR values
4.6
Deformation parameters
Compressibility modulus (Fig. 7) for both soil types increase
with addition of fly ash. Influence of time in this case was not
significant. Overall modulus increase is around 15-35% for soil
A and around 15% for soil B.
Figure 7. Compressibility modulus
4.7
Swell potential
Although strength and deformation parameters of soil A can be
considered acceptable, this soil showed significant swell
potential, which makes it unusable for most engineering
purposes. This property is associated with the presence of
expansive mineral montmorionite. Addition of 15% of fly ash,
which is determined as optimum, resulted in significant
decrease of swell deformation, from ε=8.6% to ε=1.8-3.1%.
This results are in accordance with results of other autors
