The document discusses a study on the fatigue performance of rubber-modified recycled aggregate concrete (RRAC) for use in pavements. The study found that adding rubber particles to recycled aggregate concrete (RAC) improved its bending deformation capability and fatigue life. Specifically, RRAC with 20% rubber particles by volume had the highest fatigue strength and ultimate strain, increasing 4.2% and 3.46 times compared to RAC alone. While strength generally decreased as rubber content increased, RRAC continued to have slightly better fatigue strength than RAC even with 30% rubber particles. The use of RRAC provides benefits for recycling demolition waste while reducing weaknesses of RAC.

1. Fatigue Performance Of Rubber-Modified
Recycled Aggregate Concrete (RRAC)
For Pavement
PRESENTED BY
15BCL106
15BCL041

2. TOPICS TO BE COVERED
1. INTRODUCTION TO RRAC
2. WHY RRAC
3. SCENARIO OF RRAC IN INDIA
4. TEST RESULTS AND ANALYSIS OF RRAC

3. INTRODUCTION TO RRAC
• Concrete is currently the most widely used
construction material in the world. The demolition
that has occurred during the urban construction
process has created a large amount of waste
concrete, which is primarily disposed of in dumps
and landfills, both of which consume space and
resources. Numerous studies have been carried
out by researchers worldwide on the recycling of
waste concrete among which the primary
recycling method is currently to break waste
concrete into aggregates and produce recycled
aggregate concrete (RAC).

4. • Compared with plain concrete, RAC has higher
water absorption and contraction rates, inferior
frost-resistance capability and significantly lower
tensile and flexural strength. These defects limit
such concrete’s application in construction to some
extent, but much research has been conducted on
RAC due to its social, environmental and economic
significance . One of these is its application as a
pavement material which has attracted growing
attention from researchers .

5. • The waste automotive tires never stop to come out
by the automotive industry development. The
recovery and disposition of waste tires called
‘‘black pollution’’ has been an international
problem. Traditional disposal methods for waste
tires such as landfill, incineration, etc. will cause
such problems as environment pollution and
energy waste.

6. • Recycling is one of the best ways to deal with
waste tires up to now. Adding crushed waste tires
to concrete to produce rubberized concrete (RC)
has gained widespread attention among
researchers worldwide, and research areas have
included constitutive relationships , fatigue
performance , impact performance , freeze/thaw
performance and durability performance of RC,
among others.

7. • Research works shows that generally, concrete
with small volume of rubber were used as
structural components . However, concrete with
large volume of rubber were used as pavement .
For the purpose of waste treatment, the use of
waste tire for pavement is of prosperous future, as
the ‘‘black waste’’ can be recycled and used
heavily.

8. WHY RRAC
• The superior impact resistance performance and
seismic performance of RC increases the life of
that structure. An analysis of the damage
characteristics showed that both recycled
aggregate and rubber particle could enhance the
concrete’s fatigue life. This enhancement was
most significant when the rubber particle content
reached 20%.

9. • The goal of RC was to provide scientific support
for the high value-added recycling of waste tires
and concrete, which is of significant practical
importance for natural resource preservation and
environmental protection.By using RC two goals
can be achieved :
1. To decrease the tyre waste from the automative
industry
2. To decrease the wasteful concrete which is
produced during the demolition of structures

10. SCENARIO OF RRAC IN INDIA
• In India,Recycled Aggregate Concrete(RAC) is
widely used compare to that of RRAC,which is
being used in large amount in countries like China
and USA.One of the main reason is due to the
lack of research in RRAC by India.

11. TEST RESULT AND ANALYSIS
• Test materials as follows were used in this
research for all mix. Cement used was Portland
cement with a density of 3150 kg/m3 , a
magnesium oxide content of 1.56%, an ignition
loss of 0.004%, a sulfur trioxide content of 2.41%,
and a cement fineness of 2.7. Fine aggregate
used was river sand with a continuous gradation
and a particle size 65 mm, an apparent density of
2580 kg/m3 , and a fineness modulus of 2.60.

12. • Two types of coarse aggregate were used. One
coarse aggregate type was natural coarse
aggregate with 2 grades of gravel particle
sizes, 5–20 and 20–40 mm The mass ratio of
the natural aggregate is 7:3, the apparent
density of natural aggregate is 2640 kg/m3 ,
and the bulk density of natural aggregate is
1385 kg/m3 . The other coarse aggregate type
was recycled aggregate.

13. • The recycled aggregate has 2 grades of gravel
particle sizes, 5–20 and 20– 40 mm. The mass
ratio of the recycled coarse aggregate is 7:3, its
apparent density is 2450 kg/m3 , and its bulk
density is 1291 kg/m3 . A polycarboxylic acid high
performance water reducer was used with a water
reducing rate of P40%. Tap water was used for
mixing in this test. Rubber particle has a size of
0.25 mm and a density of 859 kg/m3 .

14. TEST MIX RATIO
• Rubber particle and recycled aggregate were added
into the concrete by means of volume replacement.
The replacement rate of recycled aggregate for natural
aggregate was 100%, which meant that the natural
coarse aggregate in the NC mixture was completely
replaced by the same volume of recycled aggregate.
Rubber particle replaced the same volume of fine
aggregate (sand) at replacement rates of 10%, 20%,
and 30% (specimen RRAC-10, RRAC-20, and RRAC-
30, respectively), which meant that the rubber particle
replaced the same volume of sand in the RAC
(concrete prepared with a 100% recycled aggregate
replacement rate)

16. Basic Mechanical properties
• The mechanical properties of the RRAC were tested and
the corresponding test results are shown in Table . This
table indicates that compared with NC, the compressive
strength of rubber-free RAC (RRAC-0) increased by 10.1%,
while its flexural strength decreases by 10.2%. However,
compared to RRAC-0, the compressive strengths of RRAC-
10, RRAC-20, and RRAC-30 decreased by 27.8%, 39.2% and
47.2%, respectively, and their flexural strengths decreased
by 5.7%, 11% and 19.4%, respectively. Fig. 2 shows that the
compressive and flexural strengths decreased with the
increase in rubber content, and the decrease in flexural
strength was significantly lower than the decrease in
compressive strength

18. Bending Test Result
• Table and Fig show that RRAC-0’s (RAC’s) peak
strain, ultimate strain, and peak deflection
demonstrated an improvement over NC, though not
significantly. Of these parameters, the ultimate strain is
1.68 times that of NC, which showed that RAC (100%
volume replacement) had better ductility than NC.
When 10%, 20%, and 30% rubber particle was added,
the peak strains of RRAC-10, RRAC-20, and RRAC-
30 increased by 1.14, 1.56, and 1.29 times the value
of RAC (RRAC-0), respectively; the ultimate strain
increased by 1.95, 3.46, and 2.83 times, respectively;
and the peak deflection increased by 1.03, 1.82, and
1.13 times, respectively.

19. • These results show that the addition of rubber particle
significantly enhanced the structure’s bending
deformation capability. During the test, rubber particle,
as a portion of RAC, effectively absorbed and
dissipated the energy released by crack expansion,
suppressed the development of RAC cracks, and
successfully enhanced the RAC’s strain capability.
When the rubber particle content was increased to
20%, its ultimate strain increased to 3.46 times and the
peak deflection increased to a maximum of 1.82 times
that of RAC (RRAC-0). RRAC with 30% rubber particle
(RRAC-30) had a lower ultimate strain and peak
deflection than RRAC-20, which indicated that the
deformation capability of RRAC was not enhanced
continuously with the increase of rubber particle
content

22. The addition of rubber particle
significantly improved the concrete’s
fatigue life, primarily because the rubber
particle enhanced the RAC’s bending
deformation capability and was also
closely related to the rubber particles’
own physical properties. The rubber
particles have a coarse surface and are
waterproof and elastic. They serve as a
micro spring unit distributed inside
concrete and can significantly lower a
specimen’s flexural elasticity modulus and
enhance its bending deformation
capability. The rubber particles not only
bear part of the cyclic load in the way that
numerous micro springs do but also
possess tensile properties that can block
the expansion of micro-cracks and delay
the generation of new cracks under cyclic
loading, thereby enhancing fatigue life.
Bending fatigue test results and analysis

23. Failure of specimens

24. . Comparison of fatigue limit strength
when the rubber particle content fell within a certain range. When the rubber particle content
reached 20% during testing, the fatigue strength of RRAC-20 increased by 4.2% compared to
that of RAC (RRAC-0). The fatigue strength of RRAC decreased when the rubber particle content
was over 20%. However, the RRAC continued to have slightly better fatigue strength than the
RAC (RRAC-0) when the rubber particle content reached 30%. The fatigue limits of the 5 groups
of concrete were defined as shown in Table 12. The concrete would not experience fatigue
failure when the applied stress strength meet the condition r 6 rmax .

26. • Conclusions:
• The use of RRAC as a new compound concrete provides an attractive way of
recycling demolition tires and concrete. The performance of such new concrete
may be compromised by the inferior properties of the old aggregate including
water absorption and contraction rates of the recycled aggregate, and the lower
compressive strength of rubber. This paper has presented the results of an
experimental study to explore the possibility of minimizing the above-mentioned
weaknesses while increasing the fatigue life through rubber addition. The test
results and discussions presented in the paper allow the following specific
conclusions to be made:
• (1) The flexural strength of RAC (with a recycled aggregate replacement rate of
100% in this research) was 10.2% lower than that of NC, and its flexural elasticity
modulus degraded slightly. However, the flexural strength of RAC met the
requirements of airport pavement design specifications. At the same time, its
compressive strength increased by 10.1%, and its deformation capability was
enhanced.
• (2) With an increase in rubber particle content, the flexural strength, flexural
modulus and compressive strength of RRAC demonstrated declining trends, and its
compressive strength decreased significantly. The rubber content of RRAC should
be not more than 20% if used for airport pavement.
• (3) RRAC concerned in this paper is a new kind of pavement material. It makes use
of waste tire and waste concrete as recycled resources. Compared with NC, the
addition of both recycled aggregate and rubber particles could significantly
enhance the fatigue life of concrete. This enhancement effect was optimal when
the rubber content reached 20%.