AN EXPERIMENTAL ANALYSIS ON PROPERTIES OF RECYCLED AGGREGATE CONCRETE WITH SUPPLEMENTARY MINERAL ADMIXTURES

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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
International Journal of Research and Innovation in
Civil and Construction Engineering (IJRICCE)
AN EXPERIMENTAL ANALYSIS ON PROPERTIES OF RECYCLED AGGREGATE
CONCRETE WITH SUPPLEMENTARY MINERAL ADMIXTURES
Tiramdas Manisha1
, A.Karthik2
.
1 Research Scholar, Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India.
2 Sr. Assistant professor , Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India.
*Corresponding Author:
Tiramdas Manisha,
Research Scholar, Department of Civil Engineering, Aurora’s
Technological and Research Institute, Hyderabad, India.
Email: manishatiramdas@gmail.com
Year of publication: 2016
Review Type: peer reviewed
Volume: III, Issue : I
Citation: Tiramdas Manisha, Research Scholar, "An Experimen-
tal Analysis on Properties of Recycled Aggregate Concrete With
Supplementary Mineral Admixtures" International Journal of
Research and Innovation on Science, Engineering and Technol-
ogy (IJRISET) (2016) 247-254
INTRODUCTION
Due to modernization, demolished materials are dumped
on land & not used for any purpose. Such situations af-
fect the fertility of land. As per report of Hindu online of
March 2007, India generates 23.75 million tons demoli-
tion waste annually. As per report of Central Pollution
Control Board (CPCB) Delhi, in India, 48million tons solid
waste is produced out of which 14.5 million ton waste
is generated from the construction waste sector, of them
only 3% waste is used for embankment. Out of the total
construction demolition waste, 40% is of concrete, 30%
ceramic, 5% plastics, 10% wood, 5%metal, & 10% other
mixtures.
As per Hindu article 2014, India’s first plant (at Delhi)
that recycles construction waste has saved 15.4 lakh
tones of debris, which was supposed to be dumped on the
land causing severe land pollution.
Much research has been made to improve the quality of
Recycled Aggregate Concrete (RAC). By different mixing
approaches like pre-soaked slurry mix, two stage mix-
ing approach (TSMA), heat treatment, the performance
of RAC can be enhanced. Steam curing can give early
strength but after 90 days its effect is normal. By supple-
menting admixtures such as fly ash, silica fume, ground
granulated blast furnace slag GGBS, rice husk ash, super
plasticizers etc to some percent in the place of cement, the
strength of the RAC can be improved.
This thesis focuses on properties of recycled aggregate
(RA) which are replaced by 20%, 50%, 100% coarse aggre-
gates (RA20, RA50, RA 100) in structural concrete which
are mixed with mineral admixtures(10% replacement of
cement).
Concrete:
Concrete usually contains 60-70% coarse aggregates, 15-
25% fine aggregate and 10-15% cement. The shape, size,
surface texture, water absorption, abrasion and impact
values are very important basic properties to make the
concrete perform better.
Abstract
Nowadays protection & pollution of environment is the major problem of our society. In Construction and Demolition
(C&D) sector, huge amount of waste materials are produced. Aggregates, mortar mixture are wasted, though these are
used in land fill, back fill, sub-base course roads. Still, a huge amount of this waste is unused. On the other side, quar-
rying the rocks for stones and digging the sand reaches has been happening which is causing severe energy and envi-
ronmental loss. Natural Resources are diminishing rapidly. There is a need to protect the natural resources and recycle
the C&D waste through more research and studies on them.
Research on Recycled aggregates, as a replacement of the natural aggregates was carried out vigorously in 20th century.
In this project, the potential benefits and drawbacks of using recycled aggregate in concrete have been extensively stud-
ied. The use of recycled aggregate generally increases the drying shrinkage, creep and water absorptivity and decreases
the compressive strength and modulus of elasticity of concrete compared to those of natural aggregate concrete. When
Recycled Aggregate Concrete (RAC) mixed with admixtures such as Fly ash/Silica fume, these properties are improved.
Fly Ash is a by-product of the combustion of pulverized coal in electric power generation plants. Silica fume is a byprod-
uct of producing silicon metal or ferrosilicon alloys. Because of its chemical and physical properties, it is a very reactive
pozzolana. Concrete containing silica fume can have very high strength and can be very durable.
In this project, Mix design of concrete as per Indian code IS: 10262-1982 will be adopted. By trial and error method for
M-30 mix, amount of the concrete proportions are calculated. Cement will be replaced by 10% admixture (Fly ash/Silica
fume) in each case. Recycled aggregates of 0%, 20%, 50% and 100% are to be replaced, in place of coarse aggregates.
Properties of fresh and hardened RAC with admixture are to be tested as per IS codes and are compared.
Key words: Recycled aggregate (RA), Natural aggregate (NA), Fly ash (FA), Silica fume (SF), M-30 design mix, Workability,
Compressive strength, Split tensile strength.

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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
For concrete to be good concrete it has to be satisfactory
in its hardened state and also in its fresh state while being
transported from the mixer and placed in the formwork.
The requirements in the fresh state are that the consist-
ence of the mix is such that the concrete can be com-
pacted and also that the mix is cohesive enough to be
transported and placed without segregation.
As far as the hardened state is considered, the usu-
al requirement is a satisfactory compressive strength.
Many properties of concrete are related to its compres-
sive strength such as density, impermeability, durabil-
ity, resistance to abrasion, resistance to impact, tensile
strength, and resistance to sulphates.
Recycled Aggregate Concrete
The concrete containing cement, sand, new and used
coarse aggregates, water is termed to be Recycled ag-
gregate concrete (RAC). The recycled aggregates can be
obtained from the construction and demolition (C&D)
waste. They are available in cheap price. If unused, they
are dumped on the land (landfill) creating land pollution.
New aggregates are quarried and used extensively. Due to
this natural resource of aggregates (rocks) is diminishing
rapidly creating ecological imbalance.
RAC Applications
Traditionally, the application of recycled aggregate is
used as landfill. Recently, the applications of recycled ag-
gregate in construction areas are wide. The applications
differ from country to country. The recycled aggregates
are used in non-structural applications such as concrete
kerb and gutter mix, granular base course materials, em-
bankment filling, paving blocks, backfill materials, build-
ing blocks.
Admixtures
IS: 1343 - 1980 allows using admixtures that conform to
IS: 9103 - 1999, Concrete Admixtures Specification. The
admixtures can be broadly divided into two types: chemi-
cal admixtures and mineral admixtures. In this project
mineral admixtures class F Fly ash and Silica fume are
used.
Cost of fly ash and silica fume in local Indian market
Approximate price of Fly ash in India (2016) is Rs 700 /
metric ton. For 1 Kg, fly ash cost is less than 1 Rupee,
whereas cement 50 kg bag costs around Rs 350/- (1 Kg
Cement approximate cost is around Rs 7/-)
Finer the silica fume, the cost will appear more. Approxi-
mate price of Silica fume in India (2016) is Rs 10/- to 30/-
per Kg. The cost is more when compared with cement but
the recycled aggregate concrete with this supplement per-
formed well.
Fly ash is a cheaper by-product. In economical point of
view and for exhibiting good properties with cement, fly
ash is used extensively in construction industry.
Research Objectives
The principle objective of this thesis is to improve the RAC
properties which can be used for structural applications.
Addition of admixtures in RAC may show enhanced be-
havior in strength and durability properties.
This study is conducted to analyze the fresh and hardened
properties of RAC made with different recycled coarse ag-
gregate (RA) replacement levels with those of natural ag-
gregate concrete (NAC) by considering M-30 design mix.
Investigating the potential of fly ash / silica fume in recy-
cled aggregate concrete and comparisons are to be made
between the properties of two admixtures in the Recycled
aggregate concrete and will suggest the best mix.
LITERATURE REVIEW
The literature review presents the current state of knowl-
edge and examples of successful uses of alternative ma-
terials in concrete technology, and in particular the use
of Recycled aggregate (RA) as a coarse aggregate fraction
in nonstructural and structural concrete. Many research-
ers have dedicated their work to describe the properties
of these kinds of aggregate, the minimum requirements
for their utilisation in concrete and the properties of con-
cretes made with recycle aggregates.
Initial slump:
Poon et al. (2004) studied the moisture condition of the
aggregate on initial slump, showed that the initial slump
of recycled aggregate concrete was significantly affected
by the moisture condition of aggregates.
Ismail and Ramli (2013) pre-soaked the RAC in acid of
different molarity and studied the slump values of both
treated and untreated RCA, no significant difference in
the slump values was observed. It has been reported that
angular and rough surface of RCA decreases the slump
values as compared to natural aggregates concrete.
In accordance with Hansen et al. (1983) and Ravindrara-
jah et al. (1985), recycled aggregate concrete made with
recycled coarse aggregates and natural sand needs 5%
more water than conventional concrete in order to obtain
the same workability. If the sand was also recycled, 15%
more amount of water was necessary to obtain the same
workability.
Compressive strength:
The most of authors reported that fresh and hardened
properties of different mix grade RAC are lower than the
Natural aggregate concrete such as Katz et al.(2003) con-
cluded that the Concrete made with 100% recycled ag-
gregates was weaker than concrete made with natural ag-
gregates at the same w/c ratio.
Tam et al. (2005) experimentally shows that the two-stage
mixing approach can provide an effective method for en-
hancing harden properties [compressive strength, split-
ting tensile strength and flexural strength] and durability
properties [creep, shrinkage, permeability, chloride pen-
etration] and other mechanical performance.
Kou et al. (2012) used commercial recycled aggregates at
0%, 25%, 50% and 100% replacement levels on natural
aggregates. At 28 days the compressive strength of 100%
recycled aggregate concrete was 12.2% lower than natu-
ral aggregate concrete. After 90 days the values of recy-
cled aggregate concrete was better and even more at 20%
replacement level of natural aggregate.
Yang et al (2008) had shown inverse relationship between
compressive strength and water absorption in RAC. If wa-
ter absorption of recycled aggregate is more, compressive

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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
strength of that concrete is less.
Frondistou-Yannas (n.d) in their study shown that there
is a decrease in compressive strength of recycled aggre-
gate concrete (RAC) of about 4-14% when compared with
NAC.
Dibas et al. (2014) investigated recycled aggregate con-
crete with silica fume for compressive strength. Two types
of recycled aggregates were used, composed of concrete,
tiles and bricks. The replacement levels of aggregates were
30% and 40%, later both types were used simultaneously
taking replacement of 70%. Silica fume replaced was 5%
and 10% by weight of cement. The results showed that
impurities in recycled aggregates can reduce the effect
of silica fume. Despite that concrete containing separate
recycled aggregates exhibited good results using 5% and
10% silica fume when compared with traditional concrete
Split Tensile Strength:
Dabhade (2014) by taking two w/c ratios such as 0.38
and 0.45 and using 53 OPC cement and zone-2 sand stat-
ed that up to 40% RA and 10% fly ash yields good ten-
sile strength when compared with natural aggregate con-
crete. He also stated that RAC based concrete with 10%
fly ash gives higher compressive strength than natural
RAC based concrete in 90 days. This may due to bonding
between the old mortar and fly ash.
Lima et al. (2013) presented the splitting tensile strength
property of concrete made with recycled aggregate and fly
ash. The percentage of recycled aggregates was 30, 60
and 100. Both coarse and fine recycled aggregates were
used in concrete mixtures. To keep the water available for
chemical reaction constant, extra amount of water was
added in various mixes calculated from water absorption
capacity of aggregates. The content of fly ash was kept as
“Low”, “Medium” and “High”. The specimens containing
60% and 100% recycled aggregates showed strong reduc-
tion in tensile strength. Addition of medium level of fly
ash at 30% recycled aggregates gave the best values in
recycled aggregate concrete mix.
Need of the Present Investigation
A review of literature presented shows that recycled ag-
gregates are being investigated for proper use in concrete.
The total use of recycled aggregates in concrete with posi-
tive results has been done in very few studies. Moreover
the strength values of mineral admixtures such as fly ash
and silica fume, when replaced (10%) in the place of ce-
ment in recycled aggregate concrete (RAC) have not been
mutually analyzed. In this thesis, the strength properties
are analyzed and it will suggest the best mix to obtain
M-30 concrete strength, which can be used for structural
applications.
METHODOLOGY
General
Properties such as Specific gravity, water absorption, fine-
ness modulus, Los Angels Abrasion value, Crushing value
are to be obtained through tests which are conducted ac-
cording to the code IS: 2386 (Part I, III)-1963.
The aggregates are cleaned properly so as to remove the
chemicals, dust attached to it. The surface texture is
rough and the shape of the 70% recycled aggregates is
angular. Sieve analysis is carried out. 20mm maximum
nominal size is taken.
Jaw Crusher used for crushing of old concrete
Code IS 3812-1 (2003) gives standards specifications on
properties of Fly ash. Class C and Class F fly ash which
differ by CaO percentage. IS 456 (2000) suggests maxi-
mum of 30% fly ash replacement of cement can be taken.
Code IS 15388 gives standards on properties of silica
fume. Usually 5%-15% of silica fume replacement in place
of cement constitutes good results. Interfacial transition
zone will be improves because of the fineness and surface
area of silica fume. It gives the dense mixture when mixed
with cement and fills the voids to a greater extent, thereby
improving strength characteristics.
Mix design (Procedure IS 10262:2009)
For M-30 design mix, we have to mix the proportions as
per desired slump and target mean strength.
Casting of Specimens
Moulds: The mould shall be of metal, preferably steel or
cast iron, and stout enough to prevent distortion. It shall
be constructed in such a manner so as to facilitate the
removal of the moulded specimen without damage, and
shall be so machined that, when it is assembled ready for
use, the dimensions and internal faces shall be accurate
as per the limits stated in the code IS 516 (1959).
Concrete is poured into the moulds and are vibrated so as
to minimize voids. They are hardened for 1 day and the
iron moulds are removed. The concrete cubes and cylin-
ders are cured in the water at a temperature of 27° ± 2°C.
They are taken out for testing of strengths at 7 days and
28 days.
Empty150mm*150mm size cube moulds Cylindrical 150mm dia*300mm long

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1. Curing site 2. Collecting concrete cubes and cylinders
Testing of Specimens
Workability
Workability means simplicity in relocating concrete and
how much it opposes segregation. It is determined via
slump test and confirmed via its consistency.
Procedure for Slump test:
Slump cone of 100mm*200mm*300mm. Fresh concrete
mixture is taken into the Slump cone by 3 levels. Each
level is tamped 25 times. On immediate lifting of the cone,
the shape obtained is noted: true, shear, collapse..etc.
The depth of the concrete which is spread towards bottom
is taken as the value of slump
Compressive strength Test
The cubes of size 150x150x150mm were casted. After 24
hours, the specimens are removed from the moulds and
subjected to curing for 7 days and 28 days in portable
water.
Procedure - Specimens stored in water shall be tested im-
mediately on removal from the water and while they are
still in the wet condition. Surface water and grit shall be
wiped off the specimens and any projecting fins removed.
Loads are applied at a constant increasing rate as per IS
516:1959, Compressive strength is calculated using the
following formula
Compressive strength (N/mm2) = P/A
Where,
P = Maximum applied load just before load, (N)
A = Plan area of cube mould, (mm2
)
Split-Cylinder Test
It is the standard test, to determine the tensile strength of
concrete in an indirect way. This test could be performed
in accordance with IS 5916:1970.
The cylinders are of size 150 mm diameter and 300mm
length are casted. After 24 hours, the specimens are re-
moved from the moulds and subjected to curing for 28
days in portable water. Surface water and grit shall be
wiped off the specimens and any projecting fins removed.
The concrete cylinders are placed horizontally between
the loading surfaces of Universal Testing machine. The
compression load is applied diametrically and uniformly
along the length of cylinder until the failure of the cylinder
is along the vertical diameter. To allow the uniform distri-
bution of this applied load and to reduce the magnitude
of the high compressive stresses near the points of appli-
cation of this load. Concrete cylinder split into two halves
along this vertical plane due to indirect tensile stress gen-
erated by Poisson’s effect. Split tensile strength is calcu-
lated by the formula
Split-tensile strength Fck=2P/πLd
where
P is the maximum load (in N)
L is the average measured length of the specimen (in mm)
d is the cross sectional diameter of the specimen (in mm)
EXPERIMENTAL WORK
Materials and its properties:
Cement
Cement used in this experiment is Ordinary Portland Ce-
ment grade 43 maintaining IS 8112 (1989) Standards.
Specific gravity of cement obtained is 3.12.
Sand
By sieve analysis, well graded sand belonging to zone-2 of
IS 383 (1970) is used in these tests.
Physical properties of fine aggregates
Property Fine Aggregate
Specific Gravity 2.68
Fineness Modulus 3.61%
Bulk Density 1436 Kg/m3
Coarse Aggregate
Maximum nominal size of aggregate used is 20mm. These
are crushed from granite rocks. Sieve analysis is carried
out and the properties of aggregates are according to the
code IS 383 (1970).
Recycled Aggregate
Recycled aggregates are obtained from the 40 year old de-
molished building in Hyderabad. The aggregates are ad-
hered to the old mortar. These aggregates are taken in the
jaw crusher to remove the old mortar surrounded on the
aggregate in the lab.
Recycled aggregates

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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
Physical properties of the recycled and natural coarse
aggregate
Property Coarse Ag-
gregate
Recycled Ag-
gregate
Remarks
Specific Grav-
ity
2.72 2.3
Water ab-
sorption
0.6% 5.7% RA>CA
Bulk Density 1460 Kg/m3 1228 Kg/m3
Los Angel’s
Abrasion
value
14.5% 25.67% <30% O.K (IS
383: 1970)
Crushing
value
18.89% 23.5 <30% O.K (IS
383: 1970)
Finenes
modulus
2.41% 2.48%
Admixtures
Fly ash
Class F fly ash taken which is as per IS 3812-1 (2003)
Specific gravity = 2.15
Fines passing 150 micron sieve = 99.2%
Fines passing 90 micron sieve = 97 %
Silica fume
Silica fume with specific surface area 20,000 m2/Kg and
maximum particle size 0.1 micron is taken. Its Specific
gravity is around 2.2.
Water
Normal water without any injurious amounts of oils, ac-
ids, alkalis, salts, sugar, organic materials or other sub-
stances that may be deleterious to concrete/steel is con-
sidered. pH of water used is more than 6. Okay to use as
per IS 456 (2000).
Design procedure
For M-30 Design mix, as per code IS 10262 (2009)
Step 1:
Assumed std. deviation = 5 N/mm2
Target mean compressive strength (Ft
)
Ft = Fck
+ 1.65S = 38.25 N/mm2
Step 2:
Stipulations for proportioning
a) Grade Designation=M30
b) Type of cement: OPC 43 grade conforming to IS
8112(1989)
c) Max Nominal size of aggregate = 20mm
d) Min. Cement content = 320 Kg/m3 ( Table 4 and 5, IS
456 (2000))
e) Max. Cement content = 450 Kg/m3
f) Max. W/C ratio = 0.45
g) Workability = 60mm (target slump)
h) Exposure condition = severe
i) Type of aggregate = crushed angular aggregate.
Step 3:
Take W/C = 0.40 (By 3rd trial and error method)
From table 2 of IS 10262: 2009,
For 20mm aggregate, Maximum water content = 186kg
For that target slump,
We obtained water content = 172 Kg
Therefore, cement content = 172/0.4 = 430 Kg/m3 (O.K)
Note: Cement content should not exceed 450 Kg/m3 as
per clause 8.2.4.2 in IS 456:2000
Step 4:
From table 3 of IS 10262:2009,
Volume of coarse aggregate in total aggregate is taken as
0.62.
(Sand conforming to zone-2) Volume of Fine aggregate in
total aggregate = 1- 0.62= 0.38
Volume of concrete = 1 m3
Step 5:
Mass of Coarse aggregate = e*Volume of C.A*Specific
gravity of C.A*1000
= 0.691 * 0.62 * 2.72 * 1000
= 1165.302 Kg
Mass of Fine aggregate = e*Volume of F.A*Specific Gravity
of F.A*1000
= 0.691 * 0.38 * 2.68 * 1000
= 703.714 Kg
Therefore, Cement: 430kg;
F.A = 703.714 Kg; C.A = 1165.302 Kg are found in 3rd
trial mix for w/c at 0.4.
Mix proportion of control sample
The period of mixing shall be not less than 2 minutes after
all the materials are in the drum, and shall continue till
the resulting concrete is uniform in appearance.
1:1.64:2.71 was obtained for M-30 mix for the desired
slump of 60mm at w/c ratio 0.4
For each test, average of 3 specimen test values are tak-
en. Therefore for 0%, 20%, 50% and 100% replacement
with recycled aggregate, a total of 12*2 = 24 cubes casted
(7days and 28days). Similarly for RAC(10% FA) and for
RAC(10% SF), a total of 48 cubes casted. 48 Cylindrical
moulds are casted to test split-tensile strengths.
RESULTS
Workability
Slump values
RAC Slump
RA 0% 60mm
RA 20% 56mm
RA 50% 49mm
RA 100% 44mm

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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
Compressive strength
Compressive strength of NAC (Natural Aggregate Con-
crete)
1. 7days curing strength = 23.34 N/mm2
2. 28days curing strength = 40.81 N/mm2
Compressive strength (N/mm2) of specimen at 7 and
28 days
RAC RAC + 10% Fly ash RAC +10% Silica
fume
7 days 28 days 7 days 28 days 7 days 28 days
RA 0% 23.34 40.81 24.21 41.52 24.50 42.90
RA 20% 21.74 38.15 24.46 39.86 24.89 40.36
RA 50% 20.89 36. 67 23.05 37.24 23.43 38.10
RA 100% 18.61 32.70 20.56 36.12 20.61 35.26
Split Tensile Strength
Split tensile strength of NAC (Natural Aggregate concrete)
of M-30 mix at 28 days obtained as 3.78 N/mm2
Split Tensile Strength (N/mm2) of specimen at 28
days
RAC RAC + 10%
Fly ash
RAC + 10%
Silica fume
RA 0% 3.78 3.80 3.82
RA 20% 3.54 3.62 3.73
RA 50% 3.31 3.35 3.41
RA 100% 3.15 3.20 3.28
DISCUSSION
Effect of Recycled Aggregate, Silica Fume and Fly-ash
on Properties of Concrete
Analysis of physical properties between RA and NA
i) Water absorption of Recycled aggregate (RA) is 5.7%,
which is less than 6%. It can be used in the concrete for
non-structural and structural applications.
ii) Natural aggregate has high bulk density (1460 Kg/m3)
when compare with Recycled aggregate (1228 Kg/m3).
This states that RA is highly porous and permeable. Fine-
ness modulus of RA is more. It is because of the weak
aggregate taken from old concrete. Rough and angular
stones are obtained from the crushing process.
iii) The abrasion value and the crushing value of the RA
are more, when compared with NA. The reason is RA
(used aggregate) has taken enough loads in the old con-
crete structure. But the tested values are less than 30%,
which are satisfying the code IS 383: 1970.
Analysis of Workability property between NAC and
RAC
i) Slump value of NAC desired and obtained is 60mm,
which is a medium slump. On increasing the RA content
from 0% to 100%, the slump value decreased from 60mm
to 44mm. This decrease is not abnormal.
ii) The decreasing nature of RAC slump values is due to
use of low quality of RA in the concrete. Due to high water
absorption, slump loss is observed.
Analysis of Strength values between RAC and NAC
i) The tested strength value of RAC is less, when com-
pared with NAC’s. The compressive strength of NAC at 7
and 28 days are 23.34 and 40.81 N/mm2 respectively.
ii) The average decrease in strength of RAC (20% to 100%
RA replacement), when compared with NAC is around
12.51 % (7 days) and 12.17% (28 days).
iii) The reason for the decrease in strength of RAC is be-
cause of the adhered old mortar and inorganic chemicals
on Recycled aggregate. RA used is of high absorption
property.
iv) Up to 20% replacement of coarse aggregate with the
recycled aggregate can be used in the concrete, when nor-
mal mixing method and normal curing is adopted. 20%
RA taken concrete shown strength of 38.15 N/mm2. The
target mean strength for the mix is designed has value
38.25 N/mm2
v) The tensile strength of RAC is less, when compared
with NAC. The 28days split tensile strength value of NAC
is 3.78 N/mm2
vi) The decrease in split tensile strength of RAC is around
11.91%. This is due to high drying shrinkage and high
permeability characteristics of recycled aggregate.
Variations of Compressive strength (7days and 28days)
shown in percentages when compared with NAC (Natu-
ral Aggregate Concrete)
C.C: 7 days (23.34
N/mm2
)
28 days (40.81 N/
mm2
)
RAC
7days 28days
RA 0% 0% 0%
1.RA 20% -6.85% -6.15%
2.RA 50% -10.49% -10.14%
3.RA 100% -20.2% -19.87%
*Average (1+2+3) -12.51% -12.17%
(* + means increase of strength, - means decrease of
strength)
Variations of Split Tensile strength 28days shown in
percentages when compared with NAC (Natural Aggre-
gate Concrete)
C.C (28 days) = 3.78 N/mm2 RAC
28 Days
RA 0% 0%
1.RA 20% -6.34%
2.RA 50% -12.43%
3.RA 100% -16.67%
* Average (1+2+3) -11.91%
(* + means increase of strength, - means decrease of
strength)
Analysis of strength values between RAC (10% FA) and
RAC (10% SF):
i) The compressive strength values of RAC (10% silica
fume) are more. But the increasing trend of 100% RA-
10% FA is more when compared with 100% RA-10% SF.
Average increase of 5.83% compressive strength is shown
in RAC 10% SF, where as 5.5% increase of compressive
strength is shown in RAC 10% FA.
ii) The increase is more in silica fume due to its high
fineness quality. The surface area of silica fume used is

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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
around 20,000 m2/Kg. Even the 0.1micron pore can be
filled with silica fume particle.
iii) ITZ gets stronger in both cases. This is because these
mixtures when reacted with cement and water produce
C-S-H gel. The C-S-H gel is very active in RAC 10% SF.
iv) The early days (7day) compressive strength of 10% sil-
ica fume RAC is more, as stated C-S-H gel is very active.
v) In economical point of view, 20% RA replacement and
10% fly ash is best mix which can satisfy the target mean
strength ( Fly ash cost is less)
vi) 20% RA replacement and 10% silica fume is best mix
as it enhances properties of RAC in a faster rate when
compared with fly ash. Since silica fume is highly costly
when compared with cement, this is used less in con-
struction fields.
vii) Split tensile strength of RA 10% SF is quite more
(around 4.17%), when compared with RAC 10% FA
(around 1.68%).
Variations of Compressive strength (7 days and 28
days) shown in percentages when compared with RAC
RAC + 10% Fly ash RAC +10% Silica fume
7 days 28 days 7 days 28 days
RA 0% +3.73% +1.74% +4.97% +5.12%
1.RA 20% +12.51% +4.48% +14.49% +5.79%
2.RA 50% +10.34% +1.55% +12.15% +3.90%
3.RA 100% +10.47% +10.45% +10.8% +7.82%
*Avera-
gae(1+2+3)
+11.1% +5.5% +12.5% +5.83%
(* + means increase of strength, - means decrease of
strength)
Bar diagram showing 7days Compressive strength
Bar diagram showing 28days Compressive strength
Bar diagram showing 28 days Split-Tensile strength
CONCLUSION
1. In this project, water absorption value of RA obtained
is 5.7%, which is more when compared with NA obtained
value (0.6%). Recycled aggregates are taken from 40 year
old construction debris. Because of high water absorp-
tion, RA is highly porous and permeable.
2.Los Angel’s Abrasion value and crushing value of RA are
in permissible limits as per IS 383:1970 code.
3.In NAC, Slump value obtained is 60mm. RAC (0% RA
to 100% RA) with normal mixing approach, Slump value
decreased up to 44mm. This implies that RAC has low
workability when compared with NAC. This is due to low
weight of RA, high water absorption, initial chemical reac-
tions of the cementitious materials, and loss of water by
evaporation in RAC.
4.Compressive strength of RAC (0% RA to 100% RA) test-
ed values are low. At 28 days, the compressive strength of
NAC for design M30 mix (1:1.64:2.71) obtained is 40.81
N/mm2. For 20% RA, the strength value is 38.15 N/
mm2. Up to 20% RA replacement with coarse aggregate is
satisfactory for non-structural applications and low-rise
buildings. Split tensile strength values of RAC are less,
when compared with NAC.
5.For the structural applications, RAC strength values
can be improved by adding admixtures, lowering water-
cement ratio, adopting different mixing and curing tech-
niques.
6.When 10% Fly ash is replaced with cement in RAC (0%
RA to 100% RA), though the strength values show de-
creasing trend, they are better when compared with RAC
strengths. For 20% RA-10% FA concrete mix, the 28 days
compressive strength is 39.86 N/mm2. This value is more
than the target mean strength of concrete (38.25 N/
mm2). The increase in strength is due to fewer voids be-
tween cement particles and the aggregate. Concrete mix-
ture becomes dense, when we add the spherical shaped
fly ash. The pozzolonic activity of fly ash with cement and
its fineness enhances the strength properties.
7.Split tensile strength values of RAC-10% Fly ash are
more when compared with RAC strengths. At 28 days
curing, 20% RA-10% FA concrete has tensile strength of
3.62 N/mm2, where as 20% RAC has 3.54 N/mm2. The
difference in tensile strength values is very less (1.68%
more)
8.For 10% silica fume replacement and 20% RA, the com-
pressive strength for 28 days curing is 40.36 N/mm2. At
conventional dosage rates, silica fume containing con-

8. 254
International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
crete always has higher strength than ordinary port land
cement concrete at a comparable water-cement ratio.
This is due to the active C-S-H (calcium-silica-hydrated)
gel which is obtained from the reactions of silica fume and
concrete mixture on heat of hydration. Interfacial transi-
tion zone (ITZ) between them is very stronger as the micro
structure of the mixture is free from voids, due to high
specific surface area of silica fume.
9.The difference in tensile strength values when com-
pared with RAC is of 4.17% more. The effect of silica fume
is most pronounced on strength between 3 and 28 days,
after which its influence on strength is minimal. The wa-
ter required for the chemical reactions between the silica
fume and the concrete is used up very rapidly, thereby
getting early strength values.
10.Both fly ash and silica fume has the properties to re-
duce drying shrinkage, creep, permeability, chloride-ion
penetration and to increase strength values when added
as replacement of cement. IS 456: 2000, suggests maxi-
mum of 30% fly ash can be replaced with cement. Silica
fume enhances good properties when used in lesser per-
centages (5%-15%).
11.20% RA-10% FA concrete mixture is better mix for me-
dium strength structural applications of RAC. Also the
cost and environmental energy will get reduce on use of
fly ash and recycled aggregate.
12. 20% to 30% RA and 10% silica fume is best mix
to get the early strengths in a faster rate.
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Authors
Tiramdas Manisha,
Research Scholar, Department of Civil Engineering,
Aurora’s Technological and Research Institute,
Hyderabad, India.
A.Karthik,
Sr. Assistant professor, Department of Civil Engineering,
Aurora’s Technological and Research Institute,
Hyderabad, India.