Engineering, Technology & Applied Science Research Vol. 4, No. 4, 2014, 669-672
669
www.etasr.com Bekhiti et al.: Mechanical Properties of Waste Tire Rubber Powder
Properties of Waste Tire Rubber Powder
Melik Bekhiti Habib Trouzine Aissa Asroun
Civil Engineering Department, Djillali
Liabes University of Sidi Bel Abbes,
Algeria
Civil Engineering Department, Djillali
Liabes University of Sidi Bel Abbes,
Algeria
Civil Engineering Department, Djillali
Liabes University of Sidi Bel Abbes,
Algeria
Abstract—Scrap tires are abundant and alarming waste. The
aggregates resulting from the crushing of the waste tires are
more and more used in the field of civil engineering (geotechnical,
hydraulic works, light concretes, asphaltic concretes, etc.).
Depending on the type of the used tires, dimensions and possible
separations and treatment, the physical and mechanical
characteristics of these aggregates might change. Some physical,
chemical and direct shear tests were performed on three
gradation classes of waste tire rubber powder. The tests results
were combined with data from previous studies to generate
empirical relationships between cohesion, friction angle and
particle size of waste tire powder rubber. A cubic (third order)
regression model seems to be more appropriate compared to
linear and quadratic models.
Keywords-rubber powder; waste tires; experimental; polynomial
regression
I. INTRODUCTION
In recent decades, the worldwide growth of the automobile
industry and the increasing use of cars as the main means of
transport have tremendously boosted tire production. This has
generated massive stockpiles of used tires. Extensive research
projects were carried out on how to use used tires in different
applications [1]. The scrap tires in Algeria are estimated at
approximately 25,918 tones/year [2].Waste tires need a larger
storage space than other waste due to their large volume and
fixed shape. They are unlikely to be decomposed, as burying
the waste tires would shorten the service life of the burial
ground and have low economic benefit; In addition, buried
waste tires often emerge from the burial ground surface or
destroy the anti-leakage cover of the burial ground and the
exposed waste tires accumulate water that may breed bacteria,
molds, insects or mice. In case of fire, waste tires generate toxic
gases, such as dioxin, that could result in severe pollution
problems [3-4].
In order to properly dispose these millions of tires, the use
of innovative techniques to recycle them is important. The use
of scrap tires including tire chips or tire shreds comprised of
pieces of scrap tires, tire chip/soil mixtures, tire sidewalls, and
whole scrap tires in civil engineering applications is the object
of the standard ASTM D 6270. These materials can be used in
lightweight embankment fill, lightweight retaining wall
backfill, drainage layers, thermal insulation to limit frost
penetration beneath roads, insulating backfill to limit heat loss
from buildings, and replacement for soil or rock in other fill
applications [5].
Rubber tires can also be used in civil and non-civil
engineering applications such as in road construction, in
geotechnical works, as a fuel in cement kilns and incineration
for production of electricity or as an aggregate in cement-based
products or in geotechnical field [6-7-8].
ASTM D 6270 studied the properties of shredded waste
tires (Practical size of 2 mm and more), but not waste tire
rubber powder. The objective of this paper is to present
experimental work on the waste tire rubber powder. Further, a
polynomial regression analysis of the cohesion and friction
angle versus the particles size is proposed.
II. M
ATERIALS AND METHODS
A. Tire rubber powder
Scrap tire rubber powder can be obtained from tires through
two principal processes: (1) ambient, which is a method in
which scrap tire rubber is ground or processed at or above
ordinary room temperature and (2) cryogenic, a process that
uses liquid nitrogen to freeze the scrap tire rubber until it
becomes brittle and then uses a hammer mill to shatter the
frozen rubber into smooth particles [9]. For this study, the
rubber powder was produced from three used automobile tires
by mechanical shredding at ambient temperature. Steel was
removed by magnetic separation and one part of textile fiber
was removed by density. A photograph of the used scrap tire
rubber sample is shown in Figure 1.
Fig. 1. Used rubber powder. A less than 0.08 mm, B size of 1 mm and C
size of 1.6mm.
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www.etasr.com Bekhiti et al.: Mechanical Properties of Waste Tire Rubber Powder
B. Physical Characteristics of the Rubber Powder
The used specimens don’t contain steel but contain less
than 2% of textile fiber. Since it was not possible to determine
the gradation curve of the rubber powder as for normal
aggregates, a microscope examination was done. Dimensions
of rubber powder vary from 1.6 mm to 0.8 mm with an average
particle size of 1 mm. The density of the rubber powder is
determined using helium pycnometer and it’s about 0.83.
Rubber powder is also characterized by an insignificant water
absorption less than 3%.Table I resumes some characteristics of
the used waste tire powder rubber.
TABLE I. RUBBER POWDER CHARACTERISTICS
Properties Rubber powder
Density 0.83
Size 80 µm – 1.6 mm
Elongation (%) 420
Rate of steel fiber 0%
C. Chemical analysis
The tire is made up mainly by rubber. Its constitution varies
a little between the car tires and heavy truck tires. Rubber
consists of a complex mixture of elastomers, polyisoprene,
polybutadiene and stirene-butadiene. Stearic acid (1.2%), zinc
oxide (1.9%), extender oil (1.9%) and carbon black (31.0%) are
also important components of tires [10-11]. In Table II,
chemical composition of the used rubber powder is presented.
The quantity of steel is generally about 15%, and it’s more
important for the heavy trucks tires. For this study steel and one
part of textile were removed by magnetic separation and
density.
TABLE II. RUBBER POWDER CHARACTERISTICS
Material/element Mass percentage
Rubber 54%
Carbon black 29%
Textile 2%
Oxidize zinc 1%
Sulfur 1%.
Additives 13%
D. Direct Shear Test
The tests were performed according to ASTM D 3080
standard [12]. The direct shear test is a laboratory testing
method used to determine the shear strength parameters of
rubber powder. To achieve reliable results, the test is often
carried out on three or four samples of rubber powder. The
sample is placed in a shear box for round specimens (60 mm-
diameter and 20 mm height). The shear box is composed of an
upper and lower box. The limit between the two parts of the
box is approximately at the mid height of the sample. The
sample is subjected to a controlled normal stress and the upper
part of the sample is pulled laterally at a controlled strain rate
or until the sample fails. The applied lateral load and the
induced strain are recorded at given internals.
These measurements are then used to plot the stress-strain
curve of the sample during the loading for the given normal
stress. Results of different tests for the same rubber powder are
presented in figures with peak stress on the horizontal axis and
normal (confining) stress on the vertical axis. A linear curve
fitting is often made on the test result points. The intercept of
this line with the vertical axis gives the cohesion and its slope
gives the peak friction angle.
E. Preparation of test specimens
For practical consideration, specimens were separated to
three gradation classes. Class A: less than 0.08 mm, class B:
size between 1.6 mm and 1 mm and class C: size more than 1.6
mm
F. Tests
The specimens are round (60 mm diameter and 20 mm
high). The realized test is an unconsolidated un-drained test
(UU). The normal constraints (normal stress) used are: 100,
200 and 300 kPa. The speed of shearing is about 0.5 mm/min.
The sample is placed between two half-boxes that can move
relatively to each other. Moreover, a piston permits to exert a
normal constraint in the plan of shearing. The inferior half-box
is involved horizontally at a constant speed. The total force of
shearing F is to be measured using a fixed ring at the superior
half-box.
III. R
ESULTS AND DISCUSSION
Figure 2 presents the results of the shear strength tests
(curve intrinsic), the cohesion and the internal friction angle of
the waste tire rubber powder, value relatively important if
compared to some experimental values of the literature.
Fig. 2. Direct Shear Tests of rubber powder.
The waste tire rubber powder is strongly compressible,
moreover the surface quality of the powder produced by
mechanical crushing with ambient temperature is irregular. The
Mohr-Coulomb shear strength parameters obtained from direct
shear tests by these studies are presented in (1).
:6.525
:10 25
:508
ctg
Class A tg
Class B tg
Class C tg
(1)
It’s observed that the cohesion values vary from 6.5 to 50
kPa, and fewer values were observed for class A and B sizes.
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Friction angles vary from 8 to 25° and it’s increasing with
particle size.
IV. P
OLYNOMIAL REGRESSION
The following table gives values of cohesion C and friction
angle Ø according to the average size of the rubber particles T
according to the literature [10-11-13-16-17] and this work.
TABLE III. EXPERIMENTAL RESULTS
References Size (mm) C (kPa) Ø (°) Conditions of test
<1.06 4.78 30
1.016-4.064 3.3516 31
Black and
Shakoor,
1994 [10]
4.064-6.858 6.224 27
Dry density about 0.33
2 0 25.8 Benda 1995
[11]
2 0 36
Rate of deformation 10%
Rate of deformation 20%
Massad et al,
1996 [13]
4.572 81.97 15 Rate of deformation 20%
Wu et al,
1997 [14]
2 0 45 No steel fiber
Bekhiti et al
2012 [15]
0.405 77 8.5 No steel fiber
1.6 6.5 25
1 10 25
Present
work
0.08 50 8
No steel fiber
The graph in double y of Figure 3 represents the principal
results of C and Ø according to the average particles sizes
according to the literature and this work.
The values of cohesion vary from 0 to 81.97 kPa, for the
friction angle the values vary from 8.5 to 45°. In order to
estimate a relations ships among variables (T, C and Ø),
polynomial regressions analysis of C versus T and Ø versus T
using linear, quadratic and cubic models were used. Only
results of cubic models will be presented here, since
coefficients of determination seems to be interesting.
Fig. 3. Values the angle internal fraction and the cohesion according to
decimal logarithm of the average size of waste tire rubber particle according to
the literature and this work.
A. Variation of cohesion according to the rubber powder
particle size
The cubic model gives a rather faithful image of the
situation compared to the linear and quadratic ones. The
polynomial regression using cubic model is given by (2), with
S=21.0599, and R-Sq (multiple coefficient of determination) =
72.3%. R-Sq (adjusted) value is about 58.4%. The fitted line
plot is presented in Figure 4.
23
87.25 132.4 59.22 6.48CTTT
where C: the cohesion (kPa) and T: the particle size in (mm).
Fig. 4. Fitted line plot of cohesion versus particle size.
B. Variation of friction angle according to the rubber
powder particle size
For friction angle versus particle size, the polynomial
regression using cubic model is given by (3), with S=5.186,
and R-Sq (multiple coefficient of determination) = 80.1%. R-
Sq (adjusted) value is about 70.2%. The fitted line plot is
presented in Figure 5. The regression for this case is more
representative than for C versus T.
Fig. 5. Fitted line plot of internal friction angle versus particle size..
23
1.557 36.90 14.39 1.548TT T
where: Ø: friction angle in (°); T: the particle size in (mm).
V.
CONCLUSION
Waste tire rubber powder is used in a variety of civil and
non-civil engineering applications. Some properties of rubber
powder resulting from crushing of light vehicles waste tires
with no steel fiber have been determined in this work: the
particle size, the density, the chemical composition as well as
the cohesion and friction angle by direct shear test. Rubber
powder, crushed mechanically in ambient temperature, showed
Engineering, Technology & Applied Science Research Vol. 4, No. 4, 2014, 669-672
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www.etasr.com Bekhiti et al.: Mechanical Properties of Waste Tire Rubber Powder
has a very low density of about 0.83, cohesion varied from 6.5
to 50 kPa. Friction angle varied from 8 to 25° according to the
average size rubber particle. Using the results from this study
along with previous results from other studies, cubic
regressions is proposed. Cohesion as well as friction angle
versus particle size using cubic model give respectively for the
coefficient of determination values of 72.3 and 80.1%.
R
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