The document summarizes a study on the effect of recycled coarse aggregates on the characteristic strength of different grades of concrete. Concrete cubes of grades M20 and M30 were cast with 0%, 25%, 50%, 75%, and 100% replacement of natural coarse aggregates with recycled aggregates. Compressive strengths were tested at 7 and 28 days. For M20 concrete, 25% and 50% replacement produced similar or higher strength than 0% replacement concrete. However, strength decreased with replacements over 50%. M30 concrete showed greater strength reductions than M20 at all replacement levels. The study concluded recycled aggregates can be used to replace up to 50% of natural aggregates in concrete with minimal strength reductions.

1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
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ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 6, November – December, pp. 186-192
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EFFECT OF RECYCLED COARSE AGGREGATES ON CHARACTERISTIC
STRENGTH OF DIFFERENT GRADES OF CONCRETE
Pinal C. Khergamwala1,
Dr. Jagbir Singh2, Dr. Rajesh Kumar3
1
Civil Engineering Department, Indus University, Ahmedabad, India
Associate Professor, Department of Civil Engineering, GNDEC, Ludhiana, India.
3
Associate Professor, Department of Civil Engineering, GZS, PTU campus, Bathinda.
2
ABSTRACT
Sustainable development of the cement and concrete industry requires the utilization of
industrial and agricultural waste components. At present, for a variety of reasons, the concrete
construction industry is not sustainable. It consumes huge quantities of virgin materials which can be
saved for next generations. So, finding a solution to substitute a practical recycled product for part of
the aggregate seems to be desirable for sustainable development. Recycled aggregates are aggregate
resulting from the processing of inorganic material previously used in construction, e.g. crushed
concrete, masonry, brick. The level of impurities in the construction waste significantly affect the
strength and performance of the recycled aggregate when used in concrete; therefore aggregates
created from the broad field of construction and demolition waste (C&DW) such as brick-based
recycled aggregates and asphalt-based recycled aggregates which contain up to 100% masonry are
often used for secondary applications and are of little interest for use in concrete. This study focus
on the utilization of aggregates created mainly from laboratory waste and left over fresh concrete, the
type of recycled concrete aggregates that contains little or no impurities. The objective of this paper
is to investigate physical properties of two different grades of concrete M 20 and M 30 using
recycled coarse aggregate. Concrete tested with varying percentage of recycled aggregate i.e. 0, 25,
50, 75 and 100 % of natural aggregates. Compressive strength of concrete after 7 and 28 days were
measured and comparative analysis is made.
Key Words: Compressive strength, Concrete, Recycled aggregate, Sustainable development
1. INTRODUCTION
Concrete is the world’s second most consumed material after water, and its widespread use is
the basis for urban development. It is estimated that 25 billion tones of concrete are manufactured
each year, twice as much concrete is used in construction around the world when compared to the
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2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
total of all other building materials combined. Construction industry cannot survive without its use
and applications. Therefore it is required to find alternative and sustainable materials to reduce the
cost of concrete.
On the other hand, the amount of construction waste has been dramatically increased in the
last decade, and social and environmental concerns on the recycling of the waste have consequently
been increased. Non- biodegradable construction and demolition waste is creating lots of problem in
the environment and its disposal is becoming a great concern. Recent technology has also improved
the recycling process. In this rapid industrialized world, recycling construction material plays an
important role to preserve the natural resources.
Many countries have recycling schemes for C&DW to avoid dumping to landfill, as suitable
landfill sites are becoming scarce particularly in heavily populated countries. The greatest users of
recycled aggregate in new concrete are the United Kingdom, the Netherlands, Belgium, Switzerland
and Germany. Developing countries are still in the process to follow this trend with time.
2. NECESSITY TO USE RCA
The protection of the environment is a basic factor, which is directly connected with the
survival of the human race. Parameters like environmental consciousness, protection of natural
recourses, sustainable development play an important role in modern requirements for construction
works. Construction materials play very significant role in our lives. Concrete is a manufactured
product, essentially consisting of cement, aggregates, water and admixture(s). Among these,
aggregates, i.e. inert granular materials such as sand, crushed stone or gravel form the major part.
Aggregates provide about 75 per cent of the body of the concrete and hence its influence is
extremely important. As stated by Oikonomou, Construction sector is responsible for environmental
degradation because it:
•
•
•
Takes 50% of raw materials from nature; aggregates for the production of cement and
concrete, which results in the decrease of available natural resources which is continuously
sub-graded.
Consumes 40% of total energy; for the production, transport, use of raw materials and final
ones, as cement and concrete.
Creates 50% of total waste from old construction works (demolition wastes).
The main reasons for the increase of this volume of demolition concrete waste are:
(i)
(ii)
(iii)
Many old buildings and other structures have overcome their limit of use and need to be
demolished;
Structures, even fit for use, are under demolition, because there are new requirements and
necessities;
Creation of building wastes which result from natural destructive phenomena like
earthquakes, storms etc.
The use of RCA on a large scale may help to reduce the effects of the construction on these
factors by reusing waste materials and preventing more NA from being queried. Mostly crushed
concrete is used as a sub-base material for pavements and for low grade applications in civil
engineering projects, this study can be a positive step towards its use as a higher grade resource - as
aggregate in new concrete.
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3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
3. MATERIALS
The concrete test specimens were cast using cement, fly ash, fine aggregate, conventional and
recycled coarse aggregate and water. The materials, in general, conformed to the specification laid
down in the relevant Indian Standard Codes. The characteristics of the materials were as follows.
3.1 Cement
Ordinary Portland cement 43 grade, from a single source had been used throughout the
investigation. The physical properties of the cement which conformed to Indian Standard IS 8112:
1989 are listed in Table 1. All the tests on the cement samples were carried out as per
recommendations of IS 4031: 1988. The cement was carefully stored in air tight silos to prevent
deterioration in its properties due to atmospheric effects.
Table 1. Physical properties of the cement (OPC 43 grade)
IS 8112:1989
requirement
Characteristic
Units
Results
Blaine's fineness
cm2/gm
3007
≥2250
Specific gravity
Soundness (Le Chatelier’s test)
Autoclave expansion
Normal consistency (% of cement by weight)
Initial Setting time
Final Setting time
Compressive strength
3-day
7-days
28-days
mm
%
%
3.14
1.9
0.07
29
42
410
25.65
35.12
45.36
3.14
≤10
≤0.80
30
≥ 30
≤ 600
≥23
≥33
≥43
minutes
MPa
3.2 Fly-ash
A low-calcium fly ash obtained from the combined fields of the electrostatic precipitator of
the thermal power plant was used. The 45 micron passing fraction in the unprocessed fly ash was
more than 90 percent. The physical and chemical characteristics of the fly ash given in Table 2
satisfy the requirements of IS 3812: 1981 for fly ash. Fly ash was carefully stored in airtight silos in
the laboratory to prevent deterioration in their properties due to exposure to the ambient conditions.
Table 2. Physical and chemical properties of the fly ash
Property
Fly ash
2
Blaine's fineness, cm /gm
3462
Specific gravity
2.24
Silicon dioxide, SiO2, percent by mass
57.50
SiO2 + Al2O3 + Fe2O3, by mass
91.00
Loss on ignition, percent by mass
0.57
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4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
3.3 Fine Aggregate
Locally available river sand having a specific gravity of 2.61, water absorption of 0.90 % and
a fineness modulus of 2.65 was used as fine aggregate. The sand was sieved through a 75 micron
sieve to make it free from lumps of clay and other foreign matter in the laboratory before being used
for casting. The physical properties of the fine aggregate are listed in Table 3. The fine aggregate
confirmed to Zone II of IS 383: 1987.
Table 3. Physical properties of the fine aggregates
Characteristics
Result
Grading
Zone II (IS:383-1987)
Fineness modulus
2.65
Specific gravity
2.61
Density (loose) kN/m3
15.10
Water absorption (%)
0.90
Moisture content (%)
0.45
3.4 Coarse Aggregates
Natural aggregates (NA) and recycled concrete aggregates (RCA) were used as the coarse
aggregates in the concrete mixtures. A locally available crushed granite was used as the natural
coarse aggregate. The source of recycled aggregate was crushed concrete from laboratory waste and
left over fresh concrete. To improve the quality of RCA treatment process in terms of washing was
given. Recycled and natural coarse aggregates used had the same nominal size 10 mm and 20 mm.
To compare the physical properties of RCA with natural aggregates various tests has been done.
Table 4 shows the comparison between NA and RCA.
Table 4. Physical properties of Natural and Recycled coarse aggregate
Physical property
NA
RCA
Sr. No
1
Specific gravity
2.70
2.45
2
Water absorption %
1.37
6.14
3
Impact value %
13.5
25.6
4
Los Angeles abrasion value %
17.3
33.2
3.5 Water
Potable tap water which was free of any deleterious materials was used for both mixing and
curing of concrete.
4. CONCRETE MIX DESIGN
Two concrete mixes were prepared for minimum compressive strength of 20 N/mm2 and 30
N/mm2 for 28 days curing with constant water to cement ratio (w/c) 0.5. The mix design was done
according to the IS: 10262- 2009 and numerous trial mixes were conducted to obtain the optimum
mix. Once the optimum mix was determined for each grade, it was used to produce concrete with
0%, 25%, 50%, 75% and 100% RCA by weight replacement of natural coarse aggregate. The mix
proportions were designed by assuming the aggregates in saturated surface dry condition and
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5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
appropriate moisture adjustments were made to cater for the different water absorption properties of
the aggregates. The fly ash was used as 25% by weight replacement of cement to achieve proper
workability of the mix.
Mix
Table 5. Mix proportions for different mixes
Mix proportion
Fly Ash %
Constituents (kg/m3)
by weight
W/C
ratio
Cement
Sand
Aggregates
M20
1:1.5:3.4
25
400
600
1360
0.5
M30
1:1.25:2.75
25
450
562.5
1237.5
0.5
5. EXPERIMENTAL WORK
Concrete cubes of 150 X 150 X 150 mm were cast for compressive strength. All specimens
were cast in steel molds and compacted using a vibrating table. After casting, the specimens were
cured in air for a period of 24 hrs. The hardened concrete samples were then demoulded after 24 hrs
and submerged in a clean water bath for curing until the age of testing i.e. 7 days and 28 days. For
each proportion three specimens were tested and the mean value of these measurements was reported
for compressive strength.
6. RESULTS AND DISCUSSIONS
Table 6 shows the results of the 7 days and 28-days compressive strength of concrete. The
test was carried out conforming to IS 516-1959 to obtain compressive strength of concrete at the age
of 7 and 28 days. The cubes were tested using Compression Testing Machine of capacity 2000KN.
Recycled
aggregate
(%)
0
25
50
75
100
Table 6. Compressive strength (N/mm2) of concrete mixes
M20
%
M30
Reduction in
Compressive strength
Compressive
fck
strength
7 days
28 days
28 days
7 days
28 days
18.2
25.9
23.5
34.2
17.4
25.8
0.4
20.4
32.1
18.7
26.7
3 % increase
21.9
33.3
12.4
18.6
28.2
17.2
26.7
16.4
21.3
17.8
21.2
29.8
%
Reduction
in fck
28 days
6.1
2.6
21.9
12.9
From the results, for M 20 grade of concrete, the compressive strength of concrete with 25 %
replacement of RCA is in close proximity with 100 % NA concrete and concrete with 50%
replacement of RCA has the highest 7-day and 28-day strength which reaches 18.7 MPa and 26.7
MPa respectively, but with increase in the amount of RCA beyond 50 %, there is sharp decrease in
the compressive strength.
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6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
Compressive strength N/mm2
25
20
15
M20
M30
10
5
0
0
25
50
75
100
Recycled aggregate %
Fig 1. Compressive strength of concrete at 7 days
Compressive Strength N/ mm2
40
35
30
25
20
M20
M30
15
10
5
0
0
25
50
75
100
Recycled aggregate %
Fig 2. Compressive strength of concrete at 28 days
Figure 1 and 2 compares the compressive strength of M 20 and M 30 grade of concrete with
0%, 25%, 50%, 75% and 100% replacement of RCA after 7 and 28 days respectively. For M 30
grade of concrete there is 6.5 % decrease in compressive strength with 25 % RCA, as compared to
0.4 % for M 20. Significant decrease in 28 days compressive strength of M 30 grade concrete for all
the replacement levels of RCA was found, as compared to M 20 grade.
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7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
7. CONCLUSIONS
From the experimental work carried out on Recycled Concrete Aggregates, following
conclusions can be drawn:
1. Specific gravity of RCA is lower and Water absorption of RCA is higher than natural
aggregate.
2. The compressive strength of M 20 and M 30 grade concrete containing 25% and 50% RCA is
in close proximity to that of normal concrete. For M 20 it was seen that compressive strength
increased by 3 % with addition of RCA but only up to 50%.
3. When amount of RCA is increased above 50%, it adversely affects the compressive strength
of concrete. Reduction in strength for higher percent replacement is due to adhered mortar
and higher water absorption capacity of recycled aggregates as compared to conventional
aggregates.
4. Compressive strength of M 30 grade of concrete is lower than M 20 grade of concrete for all
the replacement levels.
5. The strength of concrete is high during initial stages but gradually reduces during later stages.
Thus it can be concluded that RCA up to 50% is satisfactory for structural use and can be
used effectively as a full value component for new concrete. Further addition of RCA resulted in
decrease of the strength which can be improved by applying more advanced and sophisticated
treatment process and casting methods under highly skilled supervision. .
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[1]
[2]
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