Case Studies in Construction Materials 9 (2018) e00184

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Case Studies in Construction Materials

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Case study

Rubber concrete: Mechanical and dynamical properties

Najib N. Gergesa , Camille A. Issab,*, Samer A. Fawazb
a
University of Balamand, el-Koura, Lebanon
b
Lebanese American University, Byblos, Lebanon

A R T I C L E I N F O A B S T R A C T

Article history:
Received 12 June 2018 The purpose of this paper is to report on an experimental study that explores the effect of
Received in revised form 6 July 2018 using recycled rubber powder as an alternate fine aggregate in concrete mixes. Natural sand
Accepted 9 July 2018 in the concrete mixes was partially replaced by 5%, 10%, 15%, and 20%. Physical properties
such as the density, the compressive strength, the fresh concrete properties, the split-
Keywords: tension, and the impact load capacity are examined. The results revealed a decrease in the
Rubberized concrete compressive strength of concrete cylinders containing rubber. The dynamic performance of
Compressive strength the rubber concrete is of high importance because of its high resilient nature, as the rubber
Splitting tensile strength
particles that are included in the concrete have a positive effect on the dynamic
Impact load
performance. The conclusions that were derived from this research implicate potential
applications where rubberized concrete can be efficiently used. Even though rubberized
concrete mixture generally has a reduced compressive strength that may limit its use in
certain structural applications, it possesses a number of desirable properties, such as lower
density, higher toughness, and higher impact resistance compared to conventional
concrete.
© 2018 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Countries and cities have been faced with major increasing problems with the disposal of recycled materials, such as
rubber, glass, and plastics for several years. The consumption of the world's rubber has nearly reached 24.9 million tons in
year 2010. In the U.S. alone, approximately 3.9 million tons of scrap tires are produced every year, out of which 1.36 million
tons are recycled and 2.54 million tons are burned or land-filled. In view of the wide and vast market for scrap tires, about a
quarter of all scrap tires end-up in landfills numbering to approximately 27 million tires or roughly 6 million tons annually,
making-up over 12% of all solid waste. The disposal of the scrap tires materials become very costly once they are sent to
landfills; not to mention the wide space that they use in landfills to dispose of, and the hazard that they cause towards the
environment. Based on this information, the rubber use in concrete and pavement material provides an environmentally
sustainable method for disposing of the millions of tires that are annually generated.
Powdered rubber is a general term or an expression given to recycled rubber that is generated from scrap tires. The
production of powder rubber consists of removing the steel and fluff, then using a granulator and/or cracker mill, with the aid
of cryogenics or mechanical means, in order to reduce the size of the tire particles.
A well-known fact is that tires can be divided into two major groups: automobile tires and truck tires, and they are
different from each other. The description of the rubber source is very important and should always be specified in the

* Corresponding author.
E-mail addresses: najib.georges@balamand.edu.lb (N.N. Gerges), cissa@lau.edu.lb (C.A. Issa), samer.fawaz@balamand.edu.lb (S.A. Fawaz).

https://doi.org/10.1016/j.cscm.2018.e00184
2214-5095/© 2018 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/
4.0/).
2 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184

literature because it has an influence on the texture and the shape, and consequently, on the characteristics of the concrete
that is adjusted by the addition of the specified percentage of the rubber. It is also important to point out that automobile
tires and truck tires vary not only in shape, weight and size, but above all, in the ratio of the components of the base mixture.
Researchers have considered three wide categories of discarded tire rubber concrete mix design:

1 Chipped Rubber: This type of rubber has dimensions of about 25–30 mm and used to replace the coarse aggregates in
concrete.
2 Crumb Rubber: The particles of rubber are highly irregular, varying between 3–10 mm, and are used to replace the fine
aggregates.
3 Powdered Rubber: The particles of the rubber are smaller than 1 mm and consist of the powder formed during the crunch
process, fallen from the machinery of the plant that is handling the waste rubber. This type of rubber could be used as filler
in concrete due to its size.

On the other hand, and for so many years, material researchers have attempted to make concrete a ductile material. It
appears, however, that due to the brittle nature of concrete, the most direct and effective approach in creating damage
tolerant concrete structures would be to embed intrinsic tensile ductility into concrete. If concrete behaves like steel in
tension (highly ductile), while retaining all other advantages (e.g. high and extreme compressive strength), concrete
structures with enhanced serviceability and safety can be readily realized.
This research attempts to provide a solution for this worst limitation of concrete, i.e. brittleness and very low tensile
strength. Making concrete a ductile material would also improve the impact strength and toughness of the concrete. Another
issue would be to seek ways of making the concrete “green” or environmentally friendly through the choice of materials
while retaining the core advantages of the concrete. Ductility is a very desirable structural property because it allows the
stress re-distribution and allows warning signs of impending failure. The ductile behavior enables the concrete material to
have the capacity to deform and support flexural and tensile loads even after initial cracking. One material that is suggested
as a possible replacement of mineral aggregates is rubber from used tires. This research focuses on the effect of replacing the
fine aggregates (sand) with powdered rubber. A significant difference between mineral aggregates and tire derived
aggregates is that individual particles are much more deformable than those of sand, gravel, or rock. Another significant
difference is that the unit weight is much lower; therefore, tire derived aggregates can be considered as lightweight
aggregates.

2. Literature overview

It is estimated that each person discards one car tire per year in the USA. With a population of over 300 million people, it
indicates that every year, there is a total of 300 million tires that need to be disposed of [1–3]. Several innovative ways of
using these tires have been developed in the last years, and they include tire derived fuel for cement kilns and boilers [1], and
tire derived aggregates used as raw materials for civil engineering projects [3]. However, not all tires are consumed in these
beneficial ways and the scrap tires that remain are disposed of in various legal and illegal means (disposal of tires in un-
permitted areas). The whole disposal of tires is difficult to landfill because tires tend to float back to the surface with time.
Stockpiles of scrap tires result in public health, environmental, and aesthetic problems, in addition to being fire hazards [2].
The US government and through the Environmental Protection Agency (EPA), encourages more studies on methods of
recycling tires, because of this environmental concern [2]. The use of crumb rubber as a replacement for mineral aggregates
in concrete resulted in a vast beneficial use of tires [4,5]. However, none of the studies have elucidated in any detail the
beneficial aspects of crumb rubber and the mechanism by which the properties of crumb rubber reinforced concrete differ
from the traditional concrete. Crumb rubber can be a lightweight substitute for mineral aggregates as its density is less than
half of that of mineral aggregate. Mineral aggregates have a unit weight or density ranging between 1600 and 2080 kg/m3
while crumb rubber unit weight or density ranges between 640 and 720 kg/m3 [6].
The effect of adding two kinds of crumb rubber and chipped rubber were studied by Khatib and Bayomy [7]. They
prepared three groups of concrete mixtures: in group A, crumb rubber was used to replace fine aggregate, while in group B,
chipped rubber was used to replace coarse aggregate, and in group C, both types of rubber were used in equal volumes. All
the three groups had eight different rubber contents varying between 5 and 100%. It was noticed that there was a decrease in
slump with an increase in the rubber content; admixtures made with fine crumb rubber were more workable than those
with coarse tire chips or those with a combination of tire chips and crumb rubber.
Herrnandez et al. [8] has investigated the dynamic characteristics of rubberized concrete material. The rubberized
concrete showed possible advantages in reducing or minimizing the vibration and impact effect due to the unique elasticity
properties of the rubber material.
Topcu [9] has examined the physical and mechanical properties of rubberized concretes with initial compressive strength
of 20 MPa. The amounts of the rubber used in the rubberized concrete were15%, 30%, and 45% by volume of the total
aggregates. This study has concluded that a general reduction in the compressive strength of rubberized concrete has
occurred.
As mentioned above, most of the literature review has shown a significant decrease in the mechanical properties of
concrete after the addition of tire rubber particles as aggregates. The use of only coarse rubber particles affects the properties
 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184 3

Fig. 1. Schematic of Impact Mechanism (Dimensions in mm).

of concrete more negatively than do only fine particles. Moreover, the plastic energy capacity of the normal concrete has
increased by adding rubber. Due to their high plastic energy capacities, concrete has shown high strains, particularly under
the impact effects.
Fattuhi and Clark [10] have proposed that rubberize concrete could possibly be utilized in the following applications:

1) In foundation pad for machinery, and in railway stations, where vibrations damping is needed.
2) In trench filling and pipe bedding, pile heads, and paving slabs.
3) In railway buffers, barriers, and bunkers, where the resistance to impact or blast is required.

Most recently, Gupta et al. [11,12] have extensively explored the effect of the use of a combination of waste rubber and
silica fume on the durability and the mechanical properties of the concrete mix. The effect of replacement of fine aggregates
by waste rubber fibers with a combination silica fume as of replacement of cement, on the impact resistance of concrete has
also been assessed [13].
The main purpose of this study consists of exploring the feasibility of incorporating scrap tires in form of rubber powder
as fine aggregates in concrete mixes and to determine its effect on the mechanical properties of the concrete mix. The
parameters that were monitored comprised the influence of the rubber content on the mechanical properties of rubberized

Fig. 2. The Fabricated Impact Mechanism.

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concrete starting with the 0% rubber content (no rubber) and up to 20% rubber content. The hardened concrete properties
like the compressive strength, split tensile strength, and impact load were scrutinized.
Generally, several impact tests procedures have been employed to demonstrate the relative brittleness and impact
resistance of concrete and similar construction materials [14–17]. However, none of these tests procedures has been declared
a standard test, at least in part due to the lack of statistical data on the variation of the results. In this regard, ACI Committee
544 [18] proposed a drop-weight impact test to evaluate the impact resistance of fiber concrete. The test is widely used since
it is simple and economical. Thus, this test was adopted for this study to investigate rubber concrete.
Accordingly, a special impact mechanism (Fig. 1) was designed and fabricated according to ACI [18] recommendations
relating to the adoption of the drop weight impact test technique. A summary of the impact test is that, the concrete samples
are plated on the bottom of the mechanism with a thin layer of petroleum jelly or a heavy grease and placed on the base plate
within the positioning lugs with the finished face up (if appropriate) as shown in Fig. 2. The positioning bracket is then bolted
in place, and the hardened steel ball is placed on top of the specimen within the bracket. The drop hammer is placed with its
base upon the steel ball and held there with just enough down pressure to keep it from bouncing off the ball during the test.
The base plate is withdrawn to a rigid base, such as a concrete floor or cast concrete block. The hammer is dropped
repeatedly, and the number of blows required to cause the first visible crack on the top and to cause ultimate failure are both
recorded. Ultimate failure is defined to be the opening of the cracks in the specimen just enough for the pieces of concrete to
touch three of the four positioning lugs on the base plate. The results of these tests display a high variability and may vary
greatly with the different types of mixtures.

3. Experimental setup

In this experimental study, a total of 20 designated concrete mix designs containing 0, 5, 10, 15 and 20% of partial
replacement of fine aggregates with powdered rubber were prepared. Ordinary Portland Cement (OPC) with a specific
gravity of 3.15 was used throughout this study. The sand used in the experiment was obtained from a local source with a
water absorption rate of 1%. The coarse aggregate that was utilized in the experiment was crushed angular stone aggregates
with a maximum size of 20 mm having a specific gravity of 2.67 with a water absorption rate of 0.5%.
The source of the rubber aggregate was recycled tires which were collected from a local tire recycling plant. The gradation
of powdered rubber was determined based on the ASTM C136 Standard [19]. The term powdered rubber stands for recycled
tire rubber with particle size less than 1 mm. A sieve analysis was performed on powdered rubber to fit the sand grain size
distribution. The rubber was used without any surface treatment in order to investigate the effect of untreated tire particles
on the mechanical properties of concrete. Drinking water with pH value of 7.0 was used in the concrete mix and the curing
process of the concrete cylinders. The water was free of acids, organic matters, suspended solids, alkalis, and impurities
which when present, may have side effects on the strength of concrete.
Casting of 100 concrete cylinders of 150 mm by 300 mm was conducted based on ASTM C192 [20]. The cylinders were
casted into three layers and each layer was tamped, using a steel rod, moving all around the layer twenty five times. Tamping
of the next layer was done without crossing into the previous layer. The surface was finished by rolling the tamping rod over
the surface to trim the concrete. The impact resistance of the specimen was determined by using the drop weight method of
the Impact Test as recommended by the ACI committee 544 [18]. The size of the specimen recommended is 152 mm in
diameter and 63.5 mm in thickness and the weight of hammer deployed is 4.54 Kg with a drop height of 457 mm.
The curing process in concrete prohibits the water in the concrete to disperse and reduce the hydration of cement or to
relief concrete from any water loss. In the curing process, the cylinders mold for the concrete cylinders were covered with
plastic sheets (Fig. 3) to prevent the evaporation of water. The next day, the concrete cylinders were removed from the mold
and placed in a water tank at a controlled temperature for 28 days. Each specimen was labeled with or without rubber and
the date of the mix.

4. Experimental procedure

In the mixing process, the concrete was dry mixed using a mechanical mixer; afterwards, water was added gradually and
mixed till the homogenous mix obtained. Powdered rubbers mixed with cement and then with aggregate are finally mixed
with water in order to prohibit the low specific gravity powdered rubber initially mixed with aggregate from floating to the
top of mixture.
The specimens of standard cylinders of 150 mm by 300 mm were utilized to determine the compressive and split tensile
strength of the concrete mix. However, cylinders of 152 mm by 63.5 mm were utilized to determine the impact load capacity.
The mix proportions of different types of percentages of replacement percentage of fine aggregates with powdered rubber
are summarized in Table 1.

5. Experimental results

Subsequently to when the concrete cylinders have acquired the 28 days strength, three types of experiments were
performed to measure the compressive, tensile, and impact load of the specimens. A uniaxial compressive load testing was
conducted according to ASTM C39 in order to measure the compressive strength of the concrete cylinders [21]. Prior to
 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184 5

Fig. 3. Cylinders Covered in Plastic Sheets for Curing.

testing, the area of the 150 mm diameter by 300 mm height cylinders was measured to be incorporated in the computation
concrete compressive strength. The cylinders were then placed in the universal testing machine, and according to ASTM
C1231 [22], the cylinders should be capped with neoprene pad caps to provide a uniform load distribution during the loading
process. The cylinders were then subjected to a steady stress rate varying between 0.2 MPa/sec to 0.4 MPa/sec. Once the
maximum load was attained, the loading process automatically stopped, and the values were recorded. Consequently, break
patterns were generated due to the failure of the cylinders that have produced cracks in several directions.
Although concrete is known to be weak in resisting direct tension, it is important to measure its tensile strength due to the
cracking that has developed from the applied loading or other kinds of effects. The split-cylinder test was conducted for the
cylinder specimens, according to ASTM C496 [23] to determine the tensile strength of concrete since uniaxial tension is
difficult to be conducted. Concrete cylinders 300 mm by 150 mm were placed horizontally between the platens of the
compression testing machine (Fig. 4). The steel strips were placed between the horizontal cylinders and the platens of the
machine in order to provide a uniform distribution of the applied load and to lessen the stresses at the surface of application,
as shown in Fig. 5. The compressive load was applied and increased gradually along the total length of the cylinder until
failure has occurred. The failure occurred along the vertical diameter of cylinder which caused it to split into two halves, due
to the indirect tension stresses, as shown in Fig. 6.
Therefore, the splitting tensile strength (f’ct) of the specimen was calculated using the following equation:
0 2P
f ct ¼ ð1Þ
pDL

Table 1
Mixture proportions for concrete with waste tire replacing sand.

No. Targeted f'c Cement Water Gravel (Kg) W/C Sand (Kg) Rubber (Kg) Rubber
(M Pa) (Kg) (Kg) (%)
1 30 31.68 16.32 87.49 55% 53.32 0 0%
2 (Mix 1) 50.65 2.67 5%
3 47.99 5.33 10%
4 35.08 8.00 15%
5 42.66 10.66 20%
6 35 34.84 16.37 87.5 50% 50.12 0 0%
7 (Mix 2) 47.61 2.51 5%
8 45.11 5.01 10%
9 42.6 7.52 15%
10 40.1 10.02 20%
11 40 38.71 16.43 87.49 45% 46.19 0 0%
12 (Mix 3) 43.88 2.31 5%
13 41.57 4.62 10%
14 39.26 6.93 15%
15 36.95 9.24 20%
16 50 43.55 16.51 87.5 40% 46.19 0 0%
17 (Mix 4) 39.21 2.06 5%
18 37.14 4.13 10%
19 35.08 6.19 15%
20 33.02 8.25 20%
6 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184

Fig. 4. Cylinder Placed in the Steel Strips.

Fig. 5. Tensile Testing Machine.

Fig. 6. Tensile Testing.

N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184 7

Fig. 7. Rubberized Concrete Impact Failure.

Fig. 8. Plain Concrete Impact Failure.

Fig. 9. Portion of the Specimens Subsequently to Impact Load Failure.

8 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184

Table 2
Conncrete cylinders compressive strength results.

Rubber (%) MIX1 f'c Avg. MPa MIX2 f'c Avg. MPa MIX3 f'c Avg. MPa MIX4 f'c Avg. MPa
No. (MPa) No. (MPa) No. (MPa) No. (MPa)
0% 1 32.16 30.42 6 36.90 37.19 11 42.27 43.42 16 50.65 51.54
28.68 37.47 44.56 52.43
5% 2 15.41 16.15 7 27.46 26.88 12 32.40 30.07 17 40.09 39.95
16.88 26.3 33.73 39.8
10% 3 13.55 13.82 8 25.76 24.13 13 28.40 28.15 18 35.45 34.63
14.08 22.5 27.90 33.80
15% 4 12.55 11.88 9 20.36 19.53 14 22.58 22.13 19 25.28 23.96
11.20 18.70 21.67 22.63
20% 5 9.40 8.97 10 14.50 13.65 15 15.70 16.30 20 18.31 18.93
8.54 12.80 16.90 19.55

Fig. 10. Average Compressive Strength for Mix 1.

Fig. 11. Average Compressive Strength for Mix 2.

 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184 9

Fig. 12. Average Compressive Strength for Mix 3.

Fig. 13. Average Compressive Strength for Mix 4.

Table 3
Splitting tensile strength (f'ct) results.

Rubber (%) MIX1 f'ct Avg. MPa MIX2 f'ct Avg. MPa MIX3 f'ct Avg. MPa MIX4 f'ct Avg. MPa
No. (MPa) No. (MPa) No. (MPa) No. (MPa)
0% 1 3.152 3.031 6 3.59 3.635 11 4.221 4.339 16 5.435 5.285
2.91 3.68 4.456 5.134
5% 2 2.433 2.492 7 2.73 2.675 12 3.541 3.393 17 4.307 4.327
2.55 2.62 3.244 4.166
10% 3 1.825 1.799 8 2.524 2.49 13 3.178 3.215 18 3.782 3.656
1.773 2.455 3.251 3.529
15% 4 1.755 1.789 9 2.234 2.295 14 2.883 2.837 19 3.173 3.015
1.822 2.356 2.791 2.856
20% 5 1.275 1.319 10 2.188 2.066 15 2.364 2.39 20 2.316 2.361
1.362 1.943 2.415 2.405
10 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184

Fig. 14. Non-Rubberized Concrete Cylinders Splitting into Two Halves.

Where
P = load at failure (N)
L = length of the cylinder (mm)
D = Diameter of the cylinder (mm)
The simplest of the impact tests is the “repeated impact” drop-weight test. This test yields the number of impact blows
delivered by a drop hammer that is accumulated until the first visible crack occurs and until the test specimen is forced to
separate by continued impacting. This number offers a qualitative estimate of the energy absorbed by the specimen at the

Fig. 15. Rubberized Concrete Cylinders without Splitting After Failure.

 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184 11

Table 4
ACI drop weight impact test results.

Rubber (%) MIX1 N Energy MIX2 N Energy MIX3 N Energy MIX4 N Energy
No. Blows NM No. Blows NM No. Blows NM No. Blows NM

0% 1 59 1190 6 77 1553.42 11 93 1876.2 16 27 544.71

5% 2 36 726.27 7 50 1008.71 12 60 1210.46 17 112 2259.52
10% 3 29 585.05 8 40 806.979 13 49 988.54 18 73 1472.72
15% 4 23 464 9 33 665.75 14 38 766.62 19 61 1230.63
20% 5 18 363.13 10 25 504.36 15 31 625.4 20 43 867.49

Fig. 16. Normalized Concrete Compressive Strength with Plain Concrete Mix.

Fig. 17. Normalized Concrete Tensile Strength with Plain Concrete Mix.

Fig. 18. Impact Load Blows as a Function of Rubber Replacement.

12 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184

levels of the specified distress level (Figs. 7–9). The impact energy (IE) exposed to by the specimen is calculated using the
following equation:

IE ¼ N m g h ð2Þ
Where:
IE = impact energy (N m)
N = the number of blows
m = mass of the drop hammer (kg)
g = gravitational acceleration = 9.81 m/sec2
h = height of drop hammer (m)

6. Analysis of results

As previously mentioned, one of the main goals of this study is to achieve an optimal powder rubber ratio for the partial
replacement of the fine aggregates in the concrete mix design with an ultimate objective to increase the ameliorative effects
on the impact resistance and make it suitable for specific engineering applications. The limit of the compressive strength of
the concrete depends on both, the strength of the matrix and the particle tensile strength of the aggregates. The strength of
the concrete is usually related to the mix content and the water to cement ratio. The 28 days compressive strengths of the
concrete mixes are shown in Table 2. The comparison between the calculated compressive strength and the experimental
results as a function of sand replacement with powdered rubber is graphically summarized in Figs. 10–13.
The 28 days splitting tensile strength of the powder rubber concrete cylinders with varying percentage replacement of
powder rubber of fine aggregates in normal concrete are tabulated in Table 3. The concrete cylinders without rubber failed by
splitting into two halves during the splitting tensile tests as shown in Fig. 14, whereas the rubberized concrete cylinders
displayed a more cohesive behavior that is failing without splitting as shown in Fig. 15.
The replacement of sand by powdered rubber has increased the occurrence of concrete to crack starting under the impact
drop load. The failure occurs rapidly in rubberized concrete. Therefore, it could be deduced that the rubber with small size
(no particle bridging) has a little effect in delaying the crack spirit in concrete. All the specimens are split into separate parts
under the effect of the impact force. No visible cracks were noticed in each of the separated parts and no dislocated dolomite
particles were found across the fractured surface. This may be due to the good bond between the mortar and the dolomite.
Therefore, the favorable crack path is across the dolomite particles not around the surface of the particles. There is no particle
bridging found in the case of rubberized concrete because the small size of the powder rubber. The results of the Impact
strength and number of blows are shown in Table 4.

7. Conclusions

After extensively exploring this topic and studying different aspects of rubber concrete properties and behavior, a series of
conclusions were derived:

1 Partial fine aggregates replacement in concrete mix by powdered rubber leads to a reduction in the density of the final
product, because the specific gravity of rubber used was less than that of fine aggregates.
2 Decreasing in the rubberized concrete strength (compressive and tensile strength) with the increasing powdered rubber
content in the mixture is always detected as shown in Figs. 16 and 17. The strength reduction may be attributed to two
reasons. First, because the rubber particles are much softer (elastically deformable) than the surrounding mineral
materials, and on loading, cracks are initiated quickly around the rubber particles in the mix, which accelerates the failure
of the rubber–cement matrix. Second, soft rubber particles may behave as voids in the concrete matrix, due to the lack of
adhesion between the rubber particles and the cement paste.
3 For a design mix strength ranging between 30 MPa and 50 MPa, the reduction in the compressive strength is consistent
and almost at a constant ratio with the increase in the percent of powdered rubber. The reduction in strength is an average
of 30, 35, 50, and 63% against a powdered rubber replacement of fine aggregates at 5, 10, 15, and 20%, respectively.
4 The addition of powdered rubber yields a slight improvement in the concrete tensile strength at all rubber percentages but
still results in less improvement compared to the compressive strength reduction rate.
5 The addition of powdered rubber to the concrete mix results in a negative effect on the modulus of elasticity. The decrease
of elasticity reflects the capability of rubberized concrete to behave in an elastic manner when loaded in tension, thus
improving the failure manners of typical concrete.
6 Rubberized concrete exhibits enhanced energy absorption since the concrete did not undergo a typical brittle failure yet it
encountered a ductile, plastic failure mode. Actually, according to Fig. 18, concrete of compressive strength of 50 MPa,
definitely displays a much better resiliency for rubberized concrete than plain concrete. This is not true for concrete of
compressive strengths below 50 MPa, which displays a consistent reduction in resiliency.
 N.N. Gerges et al. / Case Studies in Construction Materials 9 (2018) e00184 13

Rubberized concrete can be used efficiently. Even though the rubberized concrete mixture has generally a reduced
compressive strength that may limit its use in certain structural applications, it possesses a number of desirable properties,
such as lower density, higher toughness, and higher impact resistance, compared to conventional concrete.

Compliance with ethical standards

There was no external funding for this study.

Acknowledgements

Students assisting in accomplishing this study were Rasha and Mohammed ALkarawi. This study would not have been
realized without the support of the Civil Engineering Laboratory at the University of Balamand and the Civil Engineering
Laboratory at the Lebanese American University.

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