 Open Access
 Total Downloads : 30
 Authors : Shin Elizabeth Shaji, Mr.Jithin J S
 Paper ID : IJERTCONV6IS06006
 Volume & Issue : ETCEA – 2018 (Volume 6 – Issue 06)
 Published (First Online): 24042018
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Mechanical Properties of Concrete with Admixed Recycled Aggregate
Shin Elizabeth Shaji
Department of Civil Engineering
Mar Baselios College of Engineering and Technology Thiruvananthapuram, India
Mr.Jithin J S
Department of Civil Engineering
Mar Baselios College of Engineering and Technology Thiruvananthapuram, India
Abstract The concrete industry alone uses 20 billion tons of aggregates, 1.5 billion tons of cement and 800 million tons of water. The overexploitation of natural aggregate may reduce the resources to a crucial level, compromising the needs of future generation. Thus the necessity of conservation of natural aggregate leads to the use of recycled aggregate and this may provide sustainable development. But the use of recycled aggregate will cause reduction in strength and durability due to the adhered cement mortar. This strength can be improved by the addition of mineral admixture such as metakaolin. In this study, metakaolin is added as a partial replacement of recycled aggregate. The fresh and hardened properties of four mixes such as M20, M30, M40 and M50 mixes with admixed recycled aggregate is studied.
Keywords: Natural aggregate, Recycled aggregate, Sustainable development, Metakaolin.

INTRODUCTION

General
Concrete is a major construction material and plays a crucial role in the improvement of infrastructures such as highways, bridges, buildings etc. It is estimated that the total annual concrete production over the world is more than 10 billion tons[1]. The concrete industry alone uses 20 billion tons of aggregates, 1.5 billion tons of cement and 800 million tons of water. The idea of the conservation of natural aggregate (NA) has been largely ignored despite the fact that coarse aggregates make up 4050% of a concrete mix by volume while cement makes up about 10%[2]. Volume of cement and concrete production probably will continue to increase. The overexploitation of NA may reduce the resources to a crucial level, compromising the needs of future generation. Thus the necessity of conservation of NA leads to the use of recycled aggregates (RA) and this may provide sustainable development. Sustainable development means development that satisfies the present needs without limiting the possibilities of fulfilling the needs in the future. The use of aggregate obtained from crushed concrete is an example of recycling and conservation of raw materials. It is estimated that about 450 million tons of construction waste is generated every year with only 28% recycled and 72% disposal, which has caused environmental pollution and hazard of humans health. Hence, maximizing the use of RA in construction sites is becoming economically important and environmentally necessary[3].

Recycled Aggregate (RA)
RA mainly differs from NA as it is composed by two different materials: NA and residue old cement mortar attached. Old cement mortar is the origin of the worse properties of RA. Recycled coarse aggregate (RCA) tends to have decreased specific gravity, increased water absorption, and increased abrasion loss compared to NA, since they contain the mortar paste from the original concrete. Because of the increased water absorption, RCA also has greater water demand which can be resolved by increasing the amount of mix water, presoaking the aggregates or by using mineral admixtures. Generally, RAC has lower compressive strength, less stiffness, increased creep, and increased shrinkage as compared to NA concrete. At full aggregate replacement, the concrete losses its compressive strength from 10% to 20%. In comparison, the effect of RCA on the stiffness of concrete is greater with losses up to 33% at full replacement. There are various methods to manufacture RCA with better properties, such as removal of adhered mortar paste via microwave treatment, or acetic acid treatment, or treating with polymer emulsions[3,4].

Admixed Recycled Aggregate
Mineral admixtures can be successfully used as partial replacement of cement in order to mitigate the poor performance of the RCA, thus obtaining admixed recycled aggregate. Mineral admixtures such as fly ash (FA), silica fume (SF), metakaolin (MK) and ground granulated blast slag (GGBS) have been utilized for many years either as supplementary cementitious materials in Portland cement concrete or as a component in blended cement. Generally, due to their high pozzolanic activity, the mineral admixture improves the mechanical and durability properties of the concrete [5]. Here the mineral admixture metakaolin is added to the RCA and mixed well. Then the admixed coarse aggregate is put for two stage mixing (TSM). TSM divides the mixing process into two parts and proportionally splits the required water into two, which are added at different timing.


OBJECTIVE The objective of this study is:

To study the mechanical properties of concrete with admixed recycled aggregate

General


METHODOLOGY
on Indian standards and foreign standards. Their properties and specifications are given in the following section
In order to accomplish the objective of the study, the following methodologies are to be adopted.

Procurement of Materials

Testing of Materials

Mix Design

Determination of Fresh and hardened properties

Procurement of Materials
The following materials are procured

Portland Pozzolana Cement

Natural Aggregate

Super Plasticizer

Metakaolin

Recycled Coarse Aggregate


Testing of Materials

Cement
Specific gravity, fineness, initial and final setting time as per IS 4031(part 5) 1988, consistency and compressive strength tests were conducted as per IS 1489 (part 1) 1991.

Aggregate
Bulk density, water absorption, fineness modulus, sieve analysis as per IS 3831970 and specific gravity tests were conducted as per IS 2386 (part III)1963


Mix Design
In this study, M20, M30, M40 and M50 grades of concrete are used. The mix was designed using IS 10262:2009. Slump is fixed as 90mm. The fresh properties of the mix were evaluated by measuring the slump according to IS 11991959 and the hardened properties were evaluated according to IS 5161959

Determination of Fresh and Hardened properties
The strength and behaviour of concrete containing admixed recycled aggregate were studied in M20, M30, M40 and M50 mixes. These mixes were prepared using normal coarse aggregate. The coarse aggregate is then replaced with recycled coarse aggregate, and obviously the strength goes down. Mineral admixture, metakaolin, is used as partial replacement of recycled aggregate. The fresh properties were evaluated by measuring slump according to IS 11991959. Super plasticizer was added for keeping the workability constant. The hardened properties were evaluated according to IS 5161959 and IS 58161999 and the optimum dosage of mineral admixture was found from the hardened properties.



EXPERIMENTAL INVESTIGATION

Material Properties
The materials used for the study were cement, manufactured sand as fine aggregate, coarse aggregate, recycled coarse aggregate, metakaolin, water and superplasticizer. The first step in the experimental investigation is the analysis of the properties of the above ingredients, and was carried out based

Cement
Cement paste is the bindr that holds the aggregate together and reacts with mineral materials in hardened mass. Portland Pozzolana Cement is used for the entire experimental work.
TABLE I.PROPERTIES OF CEMENT
Test
Test Results
IS code specification
Fineness
4
< 10
Specific gravity
3
3.15
Standard consistency
34%
Setting time
Initial
180 min
>30 min
Final
250 min
<600 min
28 days
54
Not less than 53 MPa

Fine Aggregate
Manufactured sand passing through IS sieve 4.75 conforming to zone II is used. The different results were tabulated in table II
Properties
Values
Bulk density (gm/cc)
1.958
Specific gravity
2.75
Sieve analysis
Confirming to Zone II
Water absorption
6.01%
TABLE II. PROPERTIES OF FINE AGGREGATE
.
Fig 1.Grading curve of fine aggregate

Coarse Aggregate
Various tests were conducted as per IS specifications and results are provided in Table III.
TABLE III. PROPERTIES OF COARSE AGGREGATE
Properties
Values
Bulk density (gm/cc)
1.65
Specific gravity
2.87
Sieve Analysis
Confirms to IS specification
of IS 3831970
Water Absorption (%)
0.63
SAMPLE
20
0
1
10
Sieve Size (mm)
100
40
UPPER LIMIT
LOWER LIMIT
120
100
80
60
% Finer
Fig 2.Grading curve of coarse aggregate
f) Superplasticizer
TABLE VI. PROPERTIES OF SUPERPLASTICIZER
Properties
Values
Specific gravity
1.06 to 1.12 at 300oC
Chloride content
Nil
Appearance
Liquid
Colour
Beige
Chemical Composition
Poly carboxylate ether
pH
6 to 8


Mix Design
The mix design of M20, M30, M40 and M50 are shown in table VII

Recycled Aggregate
The properties of recycled aggregate is shown in table IV
TABLE IV.PROPERTIES OF RECYCLED AGGREGATE
Properties
Values
Bulk density (gm/cc)
1.53
Specific gravity
2.69
Water absorption (%)
2.1
Fineness modulus
8.166
Sieve analysis
Conforms to IS specification 383:1970
Fig 3. Grading curve of recycled aggregate

Metakaolin
Physical properties of metakaolin is shown in table V
TABLE VII. MIX DESIGN
Trial mix
Cement content (kg/m3)
Mix proportion
Water cement ratio
Compressive strength (N/mmÂ²)
M20
340
1: 1.97: 3.81
0.45
28.10
M30
360
1: 1.93: 3.58
0.45
38.89
M40
390
1: 1.81: 3.36
0.4
48.65
M50
420
1:1.71:3.29
0.35
58.10


Hardened Properties

Cube Compressive strength
The cube strength was evaluated according to IS 5161959 (Reaffirmed 2004). The test was conducted on a 2000 kN compression testing machine.

Cylinder Compressive Strength
The cylinder strength was evaluated according to IS 516 1959 (Reaffirmed 2004). The test was conducted on a 1000 kN universal testing machine.

Modulus of Elasticity
The modulus of elasticity was evaluated according to IS 516 1959 (Reaffirmed 2004). The test was conducted on a 1000 kN universal testing machine.

Splitting Tensile Strength
The splitting tensile strength was evaluated according to IS 58161999 (Reaffirmed 2004). The test was conducted in a 2000 kN compression testing machine. The splitting tensile strength is calculated using Eqn.1
TABLE V. PHYSICAL PROPERTIES OF METAKAOLIN
Property
Test result of metakaolin
Blaine value (cm2/g)
2200025000
Specific gravity
2.6
where,
2
=
(1)
= splitting tensile strength in N/mm P = maximum load in N
d = diameter of the specimen in mm l = length of specimen in mm

Modulus of Rupture

The modulus of rupture was evaluated according to IS 516 1959 (Reaffirmed 2004). The test is conducted in a 100 kN flexure testing machine. Modulus of rupture is calculated by Eqn.2
TABLE IX. HARDENED PROPERTIES OF M20 MIX
Where,
=
2
Mix
Cylinder compressive strength (N/mmÂ²)
Split tensile strength (N/mmÂ²)
Modulus of elasticity (N/mmÂ²)
Modulus of rupture (N/mmÂ²)
M20
23.65
3.11
2.32 X 104
4.05
M20R100
19.3
2.46
1.9 X 104
3.24
M20R10010
28.92
3.89
2.86 X 104
5.15
(2)
= modulus of rupture P = maximum load
l = length of specimen between supports b = width of the specimen
d = depth of the specimen


RESULTS AND DISCUSSIONS

Fresh Properties
The fresh properties were evaluated by measuring slump according to IS 11991959 (Reaffirmed 2004). Since the slump was observed to be low, superplasticizer was added to maintain the slump between 8090mm.

Hardened Properties
By using recycled aggregate by 100%, the strength of mix reduces. To overcome this, mineral admixture such as metakaolin is added to it. The optimum percentage of metakaolin was found out from cube compressive strength and then the hardened properties of control mix, mix with 100% recycled aggregate and mix with 100% aggregate & optimum percentage of metakaolin was found out.

M20 Mix
The optimum percentage of metakaolin in M20 mix is shown in table VIII.
TABLE VIII.OPTIMUM PERCENTAGE OF METAKAOLIN IN M20 MIX
.
From Table VIII, it is clear that the optimum percentage of metakaolin in M20 mix was found out to be 10% by weight of recycled aggregate. The hardened property of other mixes is shown in table IX.

M30 mix
The optimum percentage of metakaolin in M30 mix is shown in table X
TABLE X. OPTIMUM PERCENTAGE OF METAKAOLIN IN M30 MIX
Mix
Percentage of metakaolin
ompressive strength (N/mm2)
M30
–
38.89
M30R100
–
32.52
M30R1002.5
2.5
33.98
M30R1005
5
34.54
M30R1007.5
7.5
37.20
M30R10010
10
43.17
M30R10012.5
12.5
38.25
The optimum percentage of metakaolin was found out to be 10% by weight of recycled aggregate. The hardened properties of M30 mix is shown in table XI
Mix
Percentage of metakaolin
Compressive strength (N/mm2)
Mix
Cylinder compressive strength (N/mmÂ²)
Split tensile strength (N/mmÂ²)
Modulus of elasticity (N/mmÂ²)
Modulus of rupture (N/mmÂ²)
M20
–
28.10
M20R100
–
23.43
M20R1002.5
2.5
24.63
M20R1005
5
25.13
M30
31.50
3.26
2.73 X 104
4.3
M20R1007.5
7.5
26.46
M30R100
25.88
2.62
2.29 X 104
3.57
M20R10010
10
32.33
M20R100 12.5
12.5
30.51
M30R10010
39.08
4.16
3.38 X 104
5.21
TABLE XI.HARDENED PROPERTIES OF M30

M40 Mix
The optimum percentage of metakaolin in M40 mix is shown in table XII.
Mix
Percentage of metakaolin
Compressive strength (N/mm2)
M40
–
48.65
M40R100
–
40.09
M40R1002.5
2.5
43.86
M40R1005
5
45.23
M40R1007.5
7.5
47.98
M40R10010
10
51.05
M40R10012.5
12.5
48.53
TABLE XII. OPTIMUM PERCENTAGE OF METAKAOLIN IN M40
The optimum percentage of metakaolin in M40 mix was found out to be 10% by weight of recycled aggregate. The hardened properties of M40 mix is shown in table XIII
Mix
Cylinder compressive strength (N/mmÂ²)
Split tensile strength (N/mmÂ²)
Modulus of elasticity (N/mmÂ²)
Modulus of rupture (N/mmÂ²)
M40
39.83
3.76
3.16 X 104
5.26
M40R100
32.95
3.04
2.59 X 104
4.23
M40R10010
48.28
4.66
3.98 X 104
6.52
TABLE XIII.HARDENED PROPERTIES OF M40

M50 Mix

The optimum percentage of metakaolin in M50 mix is shown in table XIV.
Mix
Percentage of metakaolin
Compressive strength (N/mm2)
M50
–
58.10
M50R100
–
50.55
M50R1002.5
2.5
53.48
M50R1005
5
55.48
M50R1007.5
7.5
63.28
M50R10010
10
57.23
M50R100 12.5
12.5
54.89
TABLE XIV.OPTIMUM PERCENTAGE OF METAKAOLIN IN M50 MIX
The optimum percentage of metakaolin in M50 mix was found out to be 7.5% by weight of recycled aggregate. The hardened properties of M0 mix is shown in table XV
TABLE XV. HARDENED PROPERTIES OF M50 MIX
Mix
Cylinder compressive strength (N/mmÂ²)
Split tensile strength (N/mmÂ²)
Modulus of elasticity (N/mmÂ²)
Modulus of rupture (N/mmÂ²)
M50
47.06
5.21
3.57 X 104
6.2
M50R100
38.82
4.16
3.02 X 104
5.05
M50R1007.5
55.76
6.72
4.32 X 104
7.87


CONCLUSIONS
The following are the conclusions obtained from this study.

By replacing coarse aggregate by 100% recycled coarse aggregate, the hardened properties were reduced by about 1520% in every mix.

By the addition of metakaolin, the hardened properties were increased by 2030% in each mix.

The optimum percentage of metakaolin was found to be 10% in M20,M30 and M40 & 7.5% by weight of recycled aggregate in M50 mix on the basis of compressive strength
ACKNOWLEDGEMENT
The authors would like to express their sincere gratitude to the Principal and Department of Civil Engineering, MBCET, Thiruvananthapuram for the support and facilities provided for the completion of this work.
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