346
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
based on the USCS. Bentonite was composed of 0% sand, 50%
silt and 50% clay. The specific gravity was 2.63. The liquid and
plastic limits were 106% and 60%, respectively. It was
classified as inorganic clay of high plasticity (CH).
The clay paste was passed through 2-mm sieve for removal
of shell pieces and other bigger size particles, if present. The
water content was adjusted to (2-5) times liquid limit. This
intentional increase in water content is to simulate the clay
slurry with high flow ability for pumping into the construction
sites. Even with very high water content up to 5 times liquid
limit, all tested clays still have viscosity with low magnitude,
indicating that the sorting of the grain size does not occur. The
clays were mixed with air foam to attain air contents,
A
c
,
between 10 and 100% by volume of the clay-water-air mixture.
This mixture was then thoroughly mixed with cement for 10
min. The cement content,
C
, was varied from 150 to 400 kg/m
3
of the mixture. To verify the
V
/
C
as a prime parameter, the
cement content and air content were varied to attain the
V
/
C
values of 30 and 10. Such a uniform paste was transferred to
oedometer rings as well as to cylindrical containers of 50 mm
diameter and 100 mm height, taking care to prevent any air
entrapment. After 24 hours, the cylindrical samples were
dismantled. All the cylindrical samples and oedometer samples
were wrapped in vinyl bags and they were stored in a humidity
room of constant temperature (20
2
C) until lapse of different
curing times as planned. Oedometer tests were carried out after
14 days of curing. Unconfined compression (UC) tests were run
on samples after 7 and 14 days of curing. The rate of vertical
displacement in UC tests was 1 mm/min. Both tests were
performed according to the American Society of Testing and
Materials (ASTM) standards.
3 VOID/CEMENT RATIO,
V
/
C
In cement admixed clay, the clay-water/cement ratio hypothesis
(Horpibulsuk and Miura, 2001; Horpibulsuk et al., 2005; and
Miura et al., 2001) is stated as follows:
"For given cement admixed clay, age and curing
conditions, the strength is determined exclusively by the
ratio of clay-water content to the cement content in the
mix. Strength is independent of clay-water content and
cement content in the mix."
As an analogy, the parameter that can be identified for
lightweight cemented clays is void/cement ratio,
, which is
the volume of void to the volume of cement in the mix. The
parameter can be simply determined using four phase diagram
of soil, water, air and cement (Horpibulsuk et al., 2012b). To
obtain the same value of
for a particular clay water
content, it is possible to vary the amount of air foam or cement
or both as the case might be. In order to examine up to what
extent the applicability of
is valid, the air foam content is
varied over a wide range (
A
c
= 10-50% of clay volume) in this
study.
/
V C
/
V C
/
V C
4 TEST RESULTS
The role of
V/C
on the compressibility is shown in Figures 1
and 2 for lightweight cemented kaolin and bentonite samples
with the same
V/C
values but with different combinations of
cement content and air content. The samples were made up
from six conditions of air content namely, 0, 10, 20, 30, 40 and
50%. Figure 1 shows the compressibility of lightweight
cemented kaolin at water content of 88%. Figure 2 shows the
compressibility of lightweight cemented bentonite at water
content of 280%. They show the (
e
, log
v
) and (
v
, log
v
)
relations of the samples at
V/C
values of 30 and 10 after 14 days
of curing. The resistance to compression prevails up to a certain
stress level beyond which the sample experiences increase in
compression. This stress level is identified as yield stress
(Horpibulsuk et al., 2005). It does not represent pre-
consolidation pressure because the cemented clay was not being
subjected to any stress history. The (
v
, log
v
) relationship is
plotted so as to take care of the effect of the difference in void
ratio for the vertical stresses less than the yield stress. For a
certain water content, the yield stress and the deformation
behavior in pre-yield stress of all samples with identical
V/C
values are practically the same. This implies that
V/C
is a prime
parameter governing the compressibility in pre-yield state. The
yield stress increases as the
V
/
C
value decreases. The samples
with higher air content are stable at higher void ratios. Beyond
the yield stress, drastic compression occurs as vertical pressure
increases due the breakup of cementation bond (Horpibulsuk et
al., 2004a, Horpibulsuk et al., 2010; Liu and Carter, 1999, 2000
and 2002; and Suebsuk et al., 2010 and 2011).
10
0
10
1
10
2
10
3
10
4
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Lightweight cemented kaolin
w
=88%
Void ratio,
e
Effective vertical stress,
'
v
(kPa)
10
0
10
1
10
2
10
3
10
4
0
5
10
15
20
25
30
Volumetric strain,
v
(%)
A
c
=10%, C =76.4 kg/m
3
A
c
=20%, C =79.5 kg/m
3
A
c
=30%, C =82.7 kg/m
3
A
c
=40%, C =85.8 kg/m
3
A
c
=50%, C =89.0 kg/m
3
A
c
=0%, C =219.7 kg/m
3
A
c
=10%, C =229.2 kg/m
3
A
c
=20%, C =238.6 kg/m
3
A
c
=30%, C =248.0 kg/m
3
A
c
=40%, C =257.4 kg/m
3
A
c
=50%, C =266.9 kg/m
3
A
c
=10%, C =73.3 kg/m
3
V/C =30
V/C =10
Figure 1. Compressibility of air-cement-admixed kaolin at
w
= 88%.
10
0
10
1
10
2
10
3
10
4
2
3
4
5
6
7
8
9
10
11
12
Lightweight cemented bentonite
w
=280%
Void ratio,
e
Effective vertical stress,
'
v
(kPa)
10
0
10
1
10
2
10
3
10
4
0
10
20
30
40
Volumetric strain,
v
(%)
A
c
=10%, C =93.0 kg/m
3
A
c
=20%, C =94.3 kg/m
3
A
c
=30%, C =95.6 kg/m
3
A
c
=40%, C =96.9 kg/m
3
A
c
=50%, C =98.2 kg/m
3
A
c
=0%, C =91.8 kg/m
3
V/C =30
Figure 2. Compressibility of air-cement-admixed bentonite at
w
=
280%.
