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Abstract
The increasing difficulty in securing natural coarse and fine aggregates for the production of concrete coupled with the
environmental issues and unlimited extraction of natural aggregates makes the usage of recycled aggregate concrete (RAC) is the
prime importance to protect the planets future. However the full use of the material can be justified only through structural
applications. Engineers are reluctant to use RCA in structural applications due to lack of design information. In this article,
attempt has been made to investigate the strength and durability aspects of Recycled Aggregate Concrete (RAC). Basic
characteristics of recycled aggregates were determined in the laboratory. Concrete of M20, M30, and M40, M50, M60 and M70
grades were designed. The properties of fresh and hardened recycled aggregate concrete were evaluated. The results of
compressive strength test, split tensile strength, flexural strength, and permeability tests are presented in this paper.
1. INTRODUCTION
The increasing number of concrete buildings being
demolished, the difficulties of disposing of concrete rubble
produced together with a developing scarcity of aggregate
need to the major urban areas has prompted an interest in the
possibility of using concrete rubble as aggregate in concrete.
Due to rapid growth in construction industry, continuous
depletion found in natural resources which has severe
impact on environment. As per the statistics of the World
Bank published in Enaadu Telugu news paper, the Delhi
58750 KN and Mumbai 53900 KN are generating daily
waste, and ranked 9 and 10 among top ten cities in the
World. India has 4th place in the World for generation of
daily waste material. As per the World Bank report, Delhi
(58750KN), Mumbai (53900 KN), Chennai (26690 KN),
Hyderabad (21910 KN), Bangalore (16780 KN),
Ahmadabad (13020 KN), Kanpur (10970 KN), Agra (6500
KN) and Indore (5600 KN) are the few cities in India which
generate daily wastes. It is worthy to mention that, 50% is
the building rubble in daily waste. In this context
investigation on strength and durability of recycled
aggregate concrete has significant role to use waste material
as aggregate.
2. EXPERIMENTAL WORK
Six different mixes were considered in this experimental
investigation. Properties of cement, fine aggregate, natural
and recycled aggregates were investigated. For all the six
mixes, 100% recycled aggregates were considered.
3. MATERIALS
3.1 Cement
Ordinary Portland cement of 53 grade confining to IS:
12269 were used. It was tested for its physical properties as
per IS: 4031(part-II)-1988. And specific gravity and
fineness are found to be 3.15 and 3.10.
3.2 Fine Aggregates
Fine aggregate obtained from local market was used. The
physical properties of fine aggregate such as specific
gravity, fineness modulus was determined in accordance
with IS: 2386-1963. Specific gravity and fineness modulus
of fine aggregate were found to be 2.56, and 2.95.
3.3 Coarse Aggregates
Recycled aggregates were obtained from random samples of
different grades and ages from laboratory waste. Recycled
aggregate of max 20mm was used. Specific gravity of
recycled coarse aggregate is 2.727. The water absorption
capacity of natural aggregates and recycled aggregate in the
mixture represents one of the main differences between
recycled and natural aggregate. The water absorption values
of natural and recycled aggregates were found to be 0.50%
and 2.61%.
3.4 Water
Potable water which is free from chemicals and organic
materials was used for the study.
4. MIX PROPORTIONING
The mix design was done as per IS: 10262 (2009) for M20,
M30, and M40, M50, M60 and M70 with Entroy and shock lock
method. The grade of concrete adopted for this study is M20,
M30, and M40, M50, M60 and M70. Maximum size of
aggregate taken is 20mm and grading of sand is zone II.
Different water cement ratios adopted for various concrete
mixes and mix proportion was carried out for a slump of 100
± 25 mm. The quantity of materials required for 1m3
of
conventional M20, M30, and M40, M50, M60 and M70 concrete
mix are given Table 4.
5. SPECIMEN PREPARATIONS
150x150x150 mm cubes, 100x100x500mm beams and 300
x150 mm diameter cylinder specimens were cast to
determine the compressive strength, flexural strength and
splitting tensile strength of the concretes. All specimens
were cast in steel molds and compacted by using mechanical
vibration. After casting, the specimens were cured in air for
a period of 24 h, and then removed from mold. The
specimens were cured for 7 and 28 days in a water tank at
normal temperature.
6. TESTS ON FRESH AND HARDENED
CONCRETE
6.1 Fresh Properties
Fresh properties of concrete studied on
Slump test
Compaction factor test.
Slump test and compaction factor tests were done on fresh
concrete to test the consistency of fresh concrete.
6.2 Mechanical Properties on Hardened Concrete
The mechanical properties of concrete were investigated on
Compressive strength
Flexural strength
Splitting tensile strengths
Permeability test
After curing, the cubes and cylinder specimens were tested
in the compression testing machine. Third point loading
method is used for testing beams. Cubes were tested at 7 and
28 days. Cylinders and beams were tested at 28days. Three
specimens were considered per each test at 7 and 28days age
of concrete.
7. TEST RESULTS OF VARIOUS MIXES
Recycled Aggregate Concrete Mix: Using the mix
proportions recycled aggregate concrete of grade M20, M30,
M40 and M50 M60 and M70 mixes as given in table 4, the
mixes were prepared and tested on fresh and hardened
properties of concrete. Results are tabulated below.
7.1 Slump Test
Showed a slump of 75-100mm for all the six mixes
7.2 Compaction Factor Test
Compaction factor value for all the six mixes were between
0.91-0.76.
7.3 Compressive Strength
The compressive strength results are presented in Table 5.
Each presented value is the average of three measurements.
It is shown in Fig.1, that compressive strength of RAC is not
achieved for M40 and above grades. The concrete mixtures
prepared with 100 % replacement of RA had a decrease of
the compressive strength at 28-day for M40 and above grades
of concrete. RAC could not achieve target strength for M40
and above grades of concrete. The higher compressive
strength may be attributed to the greater bonding force and
strength when similar types of aggregates were used.
Normally as RA replacement increased, compressive
strength will decrease (Topcu and Sengel (2004) and Kou,
Poon and Chan (2007)).
7.4 Flexural Strength
Flexural strength of plain recycled concrete (PRC) beams
was investigated for different grades of concrete.
Experimental results tabulated below.
7.5 Splitting Tensile Strength
Splitting tensile strength of plain recycled concrete (PRC)
specimens was investigated for different grades of concrete.
Experimental results tabulated below.
7.6 Permeability Test
Continuous uniform pressure applied @ 78.40N and the
permeability of recycled concrete is more compared to the
natural aggregate concrete, further; change in fraction of
aggregates may improve the permeability characteristics of
recycled aggregate concrete.
From table 4, the compressive strength of M20 & M30 grade
concretes were achieved target strengths and M40 and above
grades were not achieved. Further, to achieve target strength
for above M40 & above grades; the fraction of aggregates
may be changed. Also flexural and splitting tensile strength
values can be improved by changing fraction of aggregate
for M40 & above grades.
8. MIX WITH REPLACEMENT OF NATURAL
COARSE AGGREGATES WITH RECYCLED
COARSE AGGREGATES
Different mixes were made by replacing 100% of natural
coarse aggregates with recycled coarse aggregates. Mixes
were tested for fresh properties and mechanical properties.
Results are tabulated below. Fig 1, Variation of compressive
strength at 28days for different grades of concrete mixes is shown. Fig2. Variation of flexural strength at 28days for
different grades of concrete mixes is shown. Fig 3. Variation
of splitting tensile strength at 28days for different grades of
concrete mixes is shown. From table 4, 5 & 6 figs 1, 2, 3,
though splitting tensile strength values at 28days were less,
compressive and flexural strength values at 28 days are
more for RA compared with target strength of M20 &M30
grades of concrete. So, for further test 100% of NA can be
replaced with different fraction recycled coarse aggregates.
9. CONCLUSION
Based on this experimental study, the following conclusions
are drawn.
When workability of recycled coarse aggregates was tested
using slump test and compaction factor test, the mix shows
not adequate workability.
Compressive strength, flexural strength and splitting tensile
strength values of concrete mix with recycled aggregates
were less for M40 and above grades compared with their
target strength.
The study shows that 100% replacement of recycled coarse
aggregates for natural aggregate gives satisfactory strength
for M20&M30. So the replacement is of much benefit and
shall be encouraged to achieve higher grades of concrete.