R. S. MUTHALVAN, M. S. INNOCENT PRASANNA: EXPERIMENTAL INVESTIGATION OF CONCRETE WITH ...
563–570
EXPERIMENTAL INVESTIGATION OF CONCRETE WITH
RECYCLED TYRE-RUBBER WASTE AS FINE AGGREGATE
MATERIAL
EKSPERIMENTALNA RAZISKAVA BETONA Z DODATKOM
FINEGA AGREGATNEGA MATERIALA IZ RECIKLIRANIH
ODPADNIH AVTOMOBILSKIH GUM
Renuka Senthil Muthalvan
1*
, Mervin Sanjith Innocent Prasanna
2
1
Division of Structural Engineering, Department of Civil Engineering, Anna University, Chennai, Tamil Nadu, India
2
School of Civil and Structural Engineering, Vellore Institute of Technology, Chennai, Tamil Nadu, India
Prejem rokopisa – received: 2022-07-29; sprejem za objavo – accepted for publication: 2022-09-05
doi:10.17222/mit.2022.585
Waste tyre-rubber disposal is a serious global problem, posing a severe danger to the environment. This present study aims to in-
vestigate the performance of concrete utilizing recycled tyre-rubber waste as a partial replacement for natural fine aggregate.
Three different sizes of crumb rubber were combined to produce a well-graded sample. Based on various trials, mixed propor-
tions of M30 grade concrete and the crumb rubber replacement percentages were determined. The test specimens were prepared.
Experimental investigations have been carried out to study the mechanical, durability and temperature properties of the devel-
oped Crumb rubber concrete (CRC). In this study, crumb rubber replaced the fine aggregate in various percentages, such as (0,
5, 7.5, 10 and 15) %. Microstructural analysis was also carried out with EDX and scanning electron microscopy (SEM) to visu-
alize the performance of rubber with CSH gel under different temperature conditions. The study found that (CRC5)a5%re-
placement of crumb rubber is the optimum percentage to replace the natural fine aggregate to develop the crumb rubber con-
crete. The durability tests concluded that the proposed model of rubberized concrete is suitable for any structural elements
exposed to acidic environmental conditions.
Keywords: waste, rubber aggregate, concrete, recycling
Odlaganje odpadnih avtomobilskih gum predstavlja resen ekolo{ki in varnostni problem po vsem svetu. V ~lanku je
predstavljena {tudija lastnosti betona z dodatkom recikliranih avtomobilskih gum, kot nadomestilo za naravni fini agregat.
Kombinirane so bile tri razli~ne velikosti drobirja (zdrobljene gume) in s tem pridobljen material. Preizku{anci so bili
pripravljeni iz razli~nih preizkusnih me{anic, z razli~no koli~ino drobirja, finega in grobega agregata in kot osnovo beton
kvalitete M30. Dolo~ene so bile mehanske lastnosti iz betona (CRC; angl.: crumb rubber concrete) izdelanih preizku{ancev, z
vsebnostjo razli~nih dodatkov drobirja iz recikliranih avtomobilskih gum. Dolo~ena je bila tudi trajnost, temperaturna stabilnost
in odpornost proti kislemu oz. bazi~nemu okolju preizku{ancev. V tej {tudiji je bil fini agregat zamenjan z razli~no koli~ino
drobirja (0, 5, 7,5, 10 in 15) %. Izvedene so bile tudi mikrostrukturne analize s pomo~jo rentgenske difrakcije (EDX) in vrsti~ne
elektronske mikroskopije (SEM) z namenom dolo~itve lastnosti CRC betona, ki je pri razli~nih temperaturah vseboval razli~no
koli~ino kalcij-silika-hidratnega gela (CSH). [tudija je pokazala, da je optimalni dodatek 5 % (CRC5), kot nadomestilo za
dodatek naravnega finega agregata. Testi trajnosti betona CRC5 so pokazali, da je predlagani model izdelave betona, ki vsebuje
reciklirano gumo primeren za katerikoli strukturni (gradbeni) element, ki je lahko v naravi izpostavljen kislemu ali bazi~nemu
okolju.
Klju~ne besede: odpad, gumijasti agregat, beton, recikliranje
1 INTRODUCTION
One of the common issues faced by most countries is
waste handling and management. The production of
large numbers of automobiles results in the deposition of
a huge quantity of waste tyres all around the world. It
was estimated that approximately 4 billion waste tyres
were in landfills and stockpiles worldwide and only a
few percent of waste tyres have been utilized for civil en-
gineering projects.
1
Hence, numerous studies show that
attention was not paid to identifying the civil engineering
applications of waste tyres.
2
Waste tyre rubbers are cate-
gorized into crumb rubber, ground rubber and scrap tyre.
These tyre wastes are used in various engineering appli-
cations such as embankment and highway base courses.
3
Amirkhanian et al.
4
have tested highway pavements by
laying asphalt rubber concrete on various portions of the
road, which attains high tensile strength compared to
conventional concrete. Crumb rubber also can reduce the
density, brittleness, freeze-thaw damage, ride noise, dry-
ing and temperature expansion of concrete.
5
An increase
in crumb rubber in concrete decreases the workability
and unit weight of the tyre rubber aggregate concrete
(TRAC) mixture.
6
The percentage of air voids is large
even though air-entraining agents are not used in TRAC.
7
Bisht and Ramana
8
reported that the inclusion of 4 %
crumbed rubber in concrete would reduce the compres-
sive and flexural strength of concrete. Assaggaf et al.
9
in-
vestigated the performance of concrete incorporated with
rubber crumbs treated with NaOH, KMnO
4
and cement
Materiali in tehnologije / Materials and technology 56 (2022) 5, 563–570 563
UDK 625.821.5:669.972.124 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 56(5)563(2022)
*Corresponding author's e-mail:
renuka@annauniv.edu (Renuka Senthil Muthalvan)

and concluded that a 40 % replacement of sand aggre-
gates by cement-treated rubber crumbs perform better
under acidic attack. Asutkar et al.
10
reported that the per-
centage of rubber crumbs in concrete is directly propor-
tional to the toughness of concrete but inversely propor-
tional to the compressive strength of concrete. It is also
mentioned that the strength reduction is negligible with
up to 15 % replacement of fine aggregate by rubber
crumbs. Lashari et al.
11
used rubber crumbs as a partial
replacement for sand and concluded that adding crumb
rubber greatly improves skid resistance. Researchers
12
in-
vestigated concrete with rubber aggregates at elevated
temperatures up to 800 °C. As the temperature exceeds
400 °C, concrete strength rapidly decreases due to the
disintegration of calcium silica hydrates (CSH) and at
around 800 °C the structure of CSH disperses.
13
The
quantity of rubber aggregate in the concrete should be
limited to avoid significant loss in mechanical and dura-
ble qualities. Hence, it is necessary to develop a crumb
rubber concrete by utilizing the tyre rubber waste as a
fine aggregate. The current study aims to investigate the
performance of concrete utilizing recycled tyre-rubber
waste (crumb rubber) as a partial replacement for natural
fine aggregate. The research had the following objec-
tives:
• To design the mix proportion of concrete incorporat-
ing the crumb rubber waste using the IS code.
• To investigate the mechanical strength parameters of
the concrete utilizing crumb rubber waste.
• To examine the durability of concrete incorporating
the recycled crumb rubber waste.
• To study the performance of concrete when it is sub-
jected to elevated temperature and to find the optimal
percentage of crumb rubber aggregate replacement to
develop the crumb rubber concrete.
2 EXPERIMENTAL PART
2.1 Materials
Crumb rubber concrete was developed using the fol-
lowing materials such as Portland cement, water, fine ag-
gregate, coarse aggregate and crumb rubber aggregate.
Following the IS provisions, the physical properties of
the materials were tested to ensure their suitability for
use in concrete. Cement in concrete functions as a binder
that hardens once water is added. Ordinary Portland ce-
ment (OPC) of 53 grade with a specific gravity of 3.12
and a consistency of 32 % complying with
IS:12269–2013 standard
14
was used in this investigation.
The sand used in the mix confirms ZONE II as per IS
383–1970 standard
15
which indicates that the aggregate
is fit for concreting purposes. The fineness modulus of
fine aggregate is 3.11. This experiment makes use of
crushed angular material as coarse aggregate with sizes
of 10 mm and 20 mm.
In this study, tyre-rubber waste is used as a partial re-
placement for natural fine aggregate. The tyre-rubber
granules that are used as a replacement for natural fine
aggregate are obtained by the reduction of scrap tyres to
aggregate sizes using factory-made mechanical grinding
into the required dimensions. These are also called
crumb rubber (CR). The blending of crumb rubber in tri-
als was carried out and found the best proportion of rub-
ber crumbs suitable for the mix. The size of the rubber
crumbs varies from 1–4 mm of which 25 % of the rubber
crumbs belong to 2–4 mm, 35 % belong to 1–2 mm and
40% are less than 1 mm. This proportion is made for all
types of rubberized concrete mixes without affecting the
zone and fineness modulus of the combined aggregate.
Sand and crumb rubber aggregate were graded by IS
383–1970. The gradation curve of the combined aggre-
gate and the combined aggregate with rubber is shown in
R. S. MUTHALVAN, M. S. INNOCENT PRASANNA: EXPERIMENTAL INVESTIGATION OF CONCRETE WITH ...
564 Materiali in tehnologije / Materials and technology 56 (2022) 5, 563–570
Table 1: Various mix proportions of concrete used in this study
Mix
Grade of con-
crete
Cement
(kg/m
3
)
Replacement %
of CR as FA
Fine aggregate (kg/m
3
) Coarse aggre-
gate (kg/m
3
)
Water
(kg/m
3
) Sand Rubber
Control M30 425.73 0 689.06 0 1132.42 191.58
CRC5 M30 425.73 5 654.61 34.45 1132.42 191.58
CRC7.5 M30 425.73 7.5 637.38 51.67 1132.42 191.58
CRC10 M30 425.73 10 620.16 68.9 1132.42 191.58
CRC15 M30 425.73 15 585.65 103.3 1132.42 191.58
Figure 1: Gradation curve

Figure 1. The gradation of combined aggregates and
combined aggregates with rubber crumbs were similar,
which clearly shows that the particles are well graded.
Hence, it was considered to replace the crushed sand
(natural fine aggregates) with the crumb rubber that was
procured at 7.5 % of total crushed sand weights.
2.2 Mix design and methodology
The M30 grade of concrete considered for this pres-
ent study and it is designed based on IS 10262: 2019
standard
16
and IS 456:2000 standard.
17
Based on the tri-
als, the final mix proportion of M30 concrete is achieved
and provided in Table 1.
To develop a crumb rubber concrete investigations
were undertaken on five different mixes of concrete in
which (0, 5, 7.5, 10 and 15) % of fine aggregates are re-
placed by rubber crumbs. Primary tests were conducted
on fresh concrete to determine the workability (Fig-
ure 2) and thereafter hardened concrete tests were con-
ducted to determine the compressive strength, flexural
strength and split tensile strength of the concrete with
various mixes.
2.3 Preparation of specimens
Using a conventional blade-type mixer, samples were
cast by mixing the materials as per the mix proportions
proposed in this study. The procedure of mixing is simi-
lar for all the types of concrete mix. In the case of rub-
berized concrete, the crumb rubbers are added only after
loading the cement, fine aggregate and coarse aggregate
into the mixer. We made sure that the rubber crumbs are
mixed thoroughly with cement and aggregates. The
weight fraction of crumb rubber aggregates over fine ag-
gregate varied from (0, 5, 7.5, 10 and 15) % of natural
fine aggregates. Though rubber crumbs are less in the
percentage they occupied more volume due to the less
specific gravity and density. Water is progressively added
to the mixture for 2 min, followed by 5 min of mixing to
make a homogenous mix. A standard 150 mm × 150 mm
size cube is prepared for the compressive strength test,
acid test, chloride test and temperature test. To conduct
the flexural and split tensile strength test, prism (100 ×
100 × 700) mm and cylinder 150 mm × 300 mm speci-
mens were prepared, respectively. The size of the speci-
men used for the shrinkage test is (76 × 76 × 286) mm
and is selected based on ASTM C 157 standard.
18
The
fresh concrete is filled in mould in three layers and vi-
brators are used to expel the confined air from the mix-
ture. To make sure full compaction, the visual appear-
ance of the fresh concrete is recorded and the vibration
time is adjusted accordingly. The specimens were
demoulded after 24 h and put into the curing tank for up
to 28 d.
3 RESULTS AND DISCUSSIONS
The concrete specimens were tested in this research
to find the mechanical and durability performance of the
developed CR concrete.
3.1 Workability of concrete
To determine the workability of the fresh concrete,
slump tests were performed. The workability of the con-
ventional concrete was in the range 50–75 mm. The
crumb rubberized concrete performed well while han-
dling, placing and finishing were similar to that of the
control mix. Moreover, due to low unit weight, mixtures
with a greater rubber aggregate component necessitate
more work and effort to smooth the completed surface.
The graph in Figure 3a shows that the flow value of con-
crete specimens with rubber crumbs was very close to
the behaviour of conventional concrete. It was also ob-
served that the increase in the percentage of rubber
crumbs in the concrete gradually decreases the work-
ability of fresh concrete. This reduction in workability is
also due to the absorption of water content by the rubber
particles present in the mixture. Rubber can absorb large
quantities of water compared to sand particles.
19
3.2 Compressive strength
In this study, the compressive strength of concrete
with a partial replacement of fine aggregate by rubber
crumbs was carried out as per IS 516:2014 standard.
20
The compressive strength results are presented in Fig-
ure 3b. It is observed that the increase of rubber content
decreases the compressive strength of rubberized con-
crete. The performance of fine aggregate replacement
with crumb rubber in M30 grade concrete is good up to 5
% of replacements, and they nearly achieve the target
mean compressive strength. The CRC5 attained 93.13 %
strength of the conventional specimen and 7.5 % replace-
ment crumb rubber results attained 83.81 % of 28 d
strength of conventional concrete samples. It is found
R. S. MUTHALVAN, M. S. INNOCENT PRASANNA: EXPERIMENTAL INVESTIGATION OF CONCRETE WITH ...
Materiali in tehnologije / Materials and technology 56 (2022) 5, 563–570 565
Figure 2: Workability of the concrete-slump test

that, except for the 5 % replacement of crumb rubber
(CRC5), all other percentage replacements give a lower
compressive strength than that of the target mean com-
pressive strength of M30 grade concrete.
3.3 Splitting tensile strength
The split tensile strength of concrete is determined as
per IS 5816:1999.
21
Figure 4a shows the split tensile
strength of concrete. The crumb rubber concrete mixture
(CRC5) achieves a maximum tensile strength of
3.54 MPa at 28 d, which is 3.38 % higher in comparison
with the control mix. The mixes CRC7.5, CRC10 and
CRC15 show a reduction of 13.23 %, 26.99 % and
38.0 % strength, respectively, compared to the control
mix at 28 d strength. As the stress induced on a brittle
material increases, minute cracks are formed within the
material.
22
Hence, the usage of soft materials like rubber
within these brittle materials could be able to resist this
expansion. Thus, in this research crumb rubber soft ma-
terial acts as a barrier against the propagation of cracks,
leading to an increase in the tensile strength of the CRC5
mixture.
3.4 Flexural strength
Figure 4b depicts the experimental setup of the flex-
ural strength test. The flexural strength of conventional
and concrete specimens containing varying percentages
of crumb rubber was evaluated by IS 516–2014. As
shown in Figure 4b, CRC5 performs exceptionally well.
CRC5 and CRC7.5 show an increase in the flexural
strength compared to the control mix by 2.62 % and
1.04 %, respectively. But CRC10 and CRC15 have lower
strength compared to the control mix. As the amount of
rubber particles in the concrete increased, flexural
strength decreased gradually. This reduction in flexural
strength is due to the irregular shape and the smooth tex-
ture of the rubber crumbs that fail to interlock the cement
matrix as the rate of loading increases.
23
3.5 Shrinkage test
The drying shrinkage of the concrete specimens was
tested based on ASTM C 490.
24
The experimental results
of the shrinkage test are presented in Figure 5 in which
the average values for the restrained concrete specimens
at (1, 7, 14, 21 and 28) d were plotted. The drying
shrinkage of the control mix after 28 d of curing is found
to be 26.13 %, whereas the CRC5, CRC7.5, CRC10 and
R. S. MUTHALVAN, M. S. INNOCENT PRASANNA: EXPERIMENTAL INVESTIGATION OF CONCRETE WITH ...
566 Materiali in tehnologije / Materials and technology 56 (2022) 5, 563–570
Figure 3: Experimental results of: a) slump cone test, b) compressive strength test
Figure 4: Experimental results of: a) split tensile strength test, b) flexural strength test

CRC15 replacements show a decrease in shrinkage value
of (9.21, 10.84, 11.64 and 13.79) %, respectively. The
shrinkage value decreases as the crumb rubber aggre-
gates are added to the concrete mixture. CRC5 shows the
least shrinkage value, whereas CRC15 shows the maxi-
mum shrinkage. Though the drying shrinkage of rubber-
ized concrete is less than the control mix, the addition of
rubber crumbs to the mixture is limited to 15 %. Since,
the crumb-rubber particles possess very good deforma-
tion capacity, the shrinkage strain is partially transferred
to the rubber particles and thus the overall shrinkage
strain of the concrete specimen was reduced. A high wa-
ter-cement ratio also influences the increase in shrinkage
value. Hence, a further reduction in the w/c ratio of the
samples could also reduce the shrinkage value of rubber-
ized concrete.
25
3.6 Acid and chloride attack test
3.6.1 Acid attack
The acid test was conducted by immersing concrete
cubes with various mixes in a solution made with a com-
bination of concentrated HCL acid (5% by volume) and
ordinary potable water. The response of the CR concrete
to the acidic conditions is indicated through percentage
loss and gain in weight after 28 d of immersion. It is evi-
dent from Figure 6 that the crumbed rubber concrete im-
mersed in concentrated HCl solution shows a consider-
able loss of weight compared to conventional concrete.
The weight reduction is less up to 7.5 % replacement
(CRC7.5) and then it is gradually increased as the per-
centage of rubber crumbs in the concrete increases. Con-
ventional concrete attains a maximum weight loss,
whereas CRC7.5 shows a minimum weight loss, which
is 57.89 % less than the control specimen. The percent-
age weight losses in CRC10 and CRC15 are also less
than the conventional concrete. When concrete material
is exposed to concentrated HCl, the concrete matrix is
disintegrated due to the formation of calcium chloride,
which thereby causes weight loss. This disintegration
creates large cavities inside the concrete matrix, enlarg-
ing the gap at the interfacial transition zone.
26
3.6.2 Chloride attack
A chloride test was conducted with a solution pre-
pared by a combination of NaCl and ordinary potable
water. The response of the concrete specimen immersed
in the NaCl solution with 15 % of rubber crumbs
(CRC15) attains a maximum weight gain of 1.71 %, as
shown in Figure 6. The concrete mixture with 7.5 % re-
placement (CRC7.5) attains a minimum weight gain of
0.86 % and thereafter as the percentage of rubber crumbs
in concrete increases, the weight gain also increases.
This weight gain is caused by the reaction between NaCl
and Ca(OH)
2
in cement forming CaCl
2
and NaOH. The
CR concrete is eroded by the chloride ions forming fi-
brous crystals which become distributed within the con-
crete by filling the cracks between both the cement paste
and the rubber aggregates.
27
3.7 Temperature test
The temperature test was carried out with the con-
crete specimens containing5%c rumb rubber (Fig-
ure 8f). The specimen was subjected to a condition
above room temperature for (2, 4, 6 and 8) h. After the
application of elevated temperature to the concrete sam-
ples. The samples were tested using microstructural anal-
ysis to find out whether the crumb rubber starts melting
or not when it is subjected to elevated temperature. The
results are discussed below.
3.7.1 Results of microstructural analysis
The EDAX microstructural analysis of the CRC5
specimens exposed to elevated temperature show the
peak positions of the elements present within the con-
crete sample. Table 2 infers that the percentage of oxy-
gen (O) in the samples is found to be more significant
R. S. MUTHALVAN, M. S. INNOCENT PRASANNA: EXPERIMENTAL INVESTIGATION OF CONCRETE WITH ...
Materiali in tehnologije / Materials and technology 56 (2022) 5, 563–570 567
Figure 6: Experimental results of acid and chloride attack test Figure 5: Experimental results of shrinkage test

than any other element. Calcium (Ca) which is responsi-
ble for the formation of CaO, one of the primary compo-
nents of concrete also increases when the percentage of
CR concrete. This indication of carbon (C) and sulphur
(S) is due to the presence of tyre aggregates, which con-
tain a high quantity of C and S. Overall, the EDAX anal-
ysis revealed that the composition of various elements in
the concrete mixture varies with the inclusion of rubber
crumbs in concrete (Table 2). During the hydration pe-
riod, various degrees of oxidation reaction take place
within the concrete mixture due to the rubber compo-
nents. Hence, the strength of the crumb rubberized con-
crete is affected by the poor chemical reaction caused by
high C and S contents, which act as impurities.
Table 2: Chemical composition of control specimens and crumb rub-
ber concrete specimens
S.No Element
Conventional con-
crete
5 % crumb rubber
aggregate concrete
Weight
(%)
Atom
(%)
Weight
(%)
Atom
(%)
1 C 2.91 3.42 3.35 4.85
2 O 47.49 66.85 47.57 67.15
3 Na 0.77 0.76 0.08 0.08
4 Mg 0.30 0.28 0.25 0.23
5 Al 2.88 2.40 2.19 1.84
6 Si 11.07 8.88 10.64 8.55
7 S 0.43 0.30 0.39 0.28
8 Ca 35.25 19.81 38.71 21.81
9 Fe 1.80 0.73 0.16 0.06
3.7.2 EDX analysis
The abundance of Ca, Si, and O in typical concrete
are observed in Figure 7a. The major mineral compo-
nents present in the concrete samples are exhibited
through the spectrum. Ca attains a peak intensity at
3.8 keV, whereas silicon and iron along with oxygen at-
tain the second-highest intensity at 1.8 keV and 0.4 keV.
Other elements such as Mg and Al are found to have low
intensity. At 2.2 keV and 0.2 keV, S and C had the lowest
intensities of all the samples. In the case of 5 % rubber
concrete (Figure 7b), the intensity of each element was
similar to that of conventional concrete. From Figure 7b,
Ca, Si and O exhibit high intensity at (3.8, 1.8 and
0.4) keV, whereas the intensity of other elements such as
Mg and Al was low at 1.5 keV and 1.7 keV. Similar to
conventional concrete, C attains the lowest intensity at
0.2 keV and S at 2.2 keV, which is slightly higher than C.
At 6.3 keV, a minute sign of Fe was observed on both the
conventional and CR concrete samples.
3.7.3 SEM analysis
The microstructure of the CRC5 specimens exposed
to various temperature conditions is shown in Figure 8.
Figure 8a shows the microstructure of the concrete not
exposed to any temperature condition. The red circle
marked in the figure indicates the rubber crumb in the
concrete mix, the yellow circle indicates CSH gel and
the blue arrow indicates the interfacial transition zone
(ITZ) between the rubber cement matrix.
Once the concrete is exposed to a temperature of
57 °C for about 2 h, cracks begin to originate where the
voids were observed initially. The portion where the
cracks begin to originate is marked in the red circle in
Figure 8b. Again, when the concrete is exposed to a
temperature of 57 °C for 4 h, which leads to the develop-
ment of weak bonds between the rubber and concrete.
This formation of weak bonds in concrete is marked in
Figure 8c. Furthermore, when the period of exposure is
exceeded by 6 h, more weak bonding is observed on var-
R. S. MUTHALVAN, M. S. INNOCENT PRASANNA: EXPERIMENTAL INVESTIGATION OF CONCRETE WITH ...
568 Materiali in tehnologije / Materials and technology 56 (2022) 5, 563–570
Figure 8: Microstructure analysis of concrete with5%r u b ber:
a)at0°C,b)at57°C2h,c)at57°C4h,d)at57°C6h,e)at57°C
8 h, f) temperature test samples
Figure 7: EDX of: a) conventional concrete, b) 5% crumb rubber ag-
gregate concrete

ious portions of the concrete sample which is displayed
in Figure 8d. Finally, after 8 hours of exposure, concrete
with rubber crumbs is found to have numerous cracks
more commonly on the interfacial transition zone be-
tween the rubber and the cement matrix, as illustrated in
Figure 8e. These cracks are probably shrinkage cracks,
which occur due to the evaporation of water molecules.
The poor bonding of the rubber and the cement matrix
causes further widening of the cracks as the period of
temperature exposure increases. No crumb-rubber parti-
cles were found to melt at a temperature of 57 °C at a
rate of (2, 4, 6 and 8) h in the concrete with 5 % rubber
aggregate replacement. As the period of exposure in-
creases, only microcracks and weak bond development is
observed between the cement paste and the rubber
crumb. A similar microstructure was also obtained in re-
search that was conducted by Moghadam et al.
28
4 CONCLUSIONS
The primary goal of this research was to assess the
fresh concrete, mechanical, durability, and temperature
effects of concrete with a partial replacement of fine ag-
gregate by crumbed-rubber aggregates. The following
conclusions can be drawn.
The compressive strength of concrete decreases as
the percentage of replacement rubber aggregate in-
creases. But concrete with5%CRaggregate was found
to be encouraging, almost attaining the target mean
strength of M30 grade concrete.
Concrete containing 5 % rubber crumbs has a 3.38 %
greater split tensile strength than the control mix and
2.6 % higher than the control mix in flexural strength,
and attains the least shrinkage value, which is 16.92 %
lower than the control mix.
Crumb-rubberized concrete immersed in concen-
trated HCl undergoes a reduction in weight. Whereas
concrete immersed in NaCl shows an increase in weight
due to the reaction between NaCl and Ca(OH)
2
. Concrete
with 7.5 % of rubber crumb in the concentrated HCL test
attains a minimum weight loss of 1.12 %, whereas con-
crete with 15 % rubber crumb attains a maximum weight
gain of 1.71 % under NaCl immersion. Positive out-
comes from the durability tests suggest that rubberized
concrete can be utilised in marine or offshore structures
that are highly susceptible to NaCl exposure.
The high carbon content observed in the rubberized
concrete is due to the presence of rubber crumbs contain-
ing a high content of C. Overall, calcium is the peak ele-
ment present in both the samples based on an EDX anal-
ysis. A slight bulge of carbon was observed on the
rubberized concrete sample and the presence of carbon
also affects the strength variation of the specimens.
Weak adhesion between the rubber and cement ma-
trix was found through SEM analysis. The spaces be-
tween the rubber and cement paste expand as the temper-
ature of the exposure rises.
Acknowledgement
The authors wish to thank the Head and staff of the
Department of Civil Engineering, Anna University for
providing support for the experimental study.
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