1374
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
binder. The maximum dry unit weight determined by the
Modified Proctor test ranged between 21.3 and 21.8 kN/m
3
and
the optimum water content ranged between 6.8 and 7.2%, for
the four mixtures.
Figure 1. Grain size distribution curve of the aggregate without cement.
This study sought to evaluate the mechanical characteristics
of mixtures with low and medium compaction. This kind of
materials is usually placed in difficult compaction zones such in
the borders of concrete structures (e.g. underpasses).
2.2
Indirect tensile tests
Usually the characterization of the tensile strength of aggregate
concrete mixtures is made using indirect tensile tests. In this
case the standards EN 13286-42 (CEN, 2003) were used. Test
specimens were compacted with 150 mm diameter and 145 mm
high, with low compaction (LC) and medium compaction (MC),
using the Modified Proctor test. The degree of compaction (DC)
of the MC specimens ranged between 91% and 93% and the one
of the LC specimens varied between 81% and 85% of maximum
dry unit weight from Modified Proctor test. According to CEN
(2003), the tensile strength, q
t
, is computed by:
where Q is the maximum applied force during diametrical
compression and Ф and H are the specimens diameter and
height. In the performed tests the tensile strength varied
significantly with the degree of compaction and the cement
content, the values ranging between 35 kPa for samples with
2% cement content with low compaction and 440 kPa for
samples with 5% cement content and medium compaction.
Figure 2 shows the values of the tensile strength, obtained in
these tests, depending on the adjusted porosity/cement ratio
(
n
/
C
iv
x
). The relation shows a relatively high determination
coefficient (R
2
=0.92) with an exponent of 0.27.
R² = 0.92
0
100
200
300
400
500
15
20
25
30
35
q
t
[kPa]
n / C
iv
0.27
LC
MC
q
t
= 2E+08 (n / C
iv
0.27
)
-4.396
Figure 2. Relationship between indirect tensile strength and
n
/C
iv
x
.
2.3
Seismic wave tests
Seismic wave tests are an easy and economic technique to
measure dynamic properties (Amaral et al. 2012). Aiming at
determining materials elastic properties, seismic wave tests
were performed on several specimens: five specimens with
degree of compaction ranging from 95% to 98% (MC-medium
compaction); seven specimens with degree of compaction from
83% to 86% (LC-low compaction). The wave velocity
propagation was determined with ultrasonic piezoelectric
transducers, namely compression transducers and shear
transducers (Figure 3).
Figure 3. Measurement of compression (left) and shear (right) waves.
The dynamic parameters of the mixtures were computed
taking into account the following relations:
where:
E
0
-
dynamic deformability modulus
V
S
- shear wave velocity
V
L
- longitudinal wave velocity
ρ
- density
G
0
-
dynamic shear modulus
υ
0
– Poisson ratio
The dynamic shear modulus values range from about 2 GPa
to 7 GPa. There was a significant increase in the dynamic
modulus with increasing cement content and compaction effort.
In general, the values of Poisson's ratio (
) decreased with
increasing cement content, assuming values of 0.25, 0.23, 0.21
and 0.20, for cement content of 2%, 3%, 4% and 5%,
respectively. The Figure 4 shows the values of the dynamic
shear modulus as a function of
n
/
C
iv
x
. The relation has a high
determination coefficient (R
2
=0.96) having an empirical
exponent with a value of 1.0, which shows the possibility of
estimating G
0
of the material based on that parameter.
R² = 0.96
0
2
4
6
8
10
0
5
10
15
20
25
30
G
0
[GPa]
n / C
iv
1.0
LC
MC
G
0
= 109.11 (n / C
iv
1.0
)
-1.205
Figure 4. Relationship between dynamic shear modulus and
n
/C
iv
x
.
2.4
Triaxial compression tests
Monotonic triaxial tests were performed on specimens with
150 mm diameter and 280 mm height. These specimens were
