- Open Access
- Total Downloads : 1365
- Authors : K. Sasikala, Dr. S. Vimala
- Paper ID : IJERTV2IS4532
- Volume & Issue : Volume 02, Issue 04 (April 2013)
- Published (First Online): 18-04-2013
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License: This work is licensed under a Creative Commons Attribution 4.0 International License
A Comparative Study Of Polypropylene, Recron And Steel Fiber Reinforced Engineered Cementitious Composites
K. Sasikala1, Dr. S. Vimala 2
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Asst Prof, Department of civil engineering, SACS MAVMM engineering college, Madurai, Tamilnadu.
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Prof, Department of civil engineering, PSNA College of engineering & technology, Dindigul, Tamilnadu.,
Abstract
This study is investigate the response of conventional reinforced concrete and fiber reinforced engineered cementitious composites members on their flexural load- deformation behavior, compressive strength and split tensile strength behavior of concrete. The behavior of flexural load- deformation, split tensile strength and, compressive strength of conventional reinforced concrete member are briefly reviewed and compared with fiber reinforced engineered cementitious composites .Compatible deformations of reinforcement and matrix leads to low interfacial bond stress and prevent the composite disintegration by bond splitting and lower spalling. Furthermore flexural strength as well as crack deformation and widths in fiber reinforced engineered cementitious composites members are found effectively independent of interfacial bond properties due to the tensile deformation characteristics of the cementitious matrix.
Key words: composite, strength, deformation, reinforcement.
Introduction
In steel fiber reinforced concrete, the bars embedded in concrete blocks (Soroushian&Bayasi 1991) to examine the bond improvement gained by using SFRC.The strength and toughness measurement on the range of normal and high strength concrete mixes with and without fiber reinforcements (Taylor et al 1996). The investigations to find out (Krishnamoorthy et al 2000) the influence of corrosion of steel fibers on the strength of SFRC. The concrete specimen was subjected to accelerated corrosion and it was found that there was no corrosion of steel fibers in SFRC even after 250 cycles of corrosion. Addition of steel fibers in concrete matrix has resulted in decreased crack width. It was also noted that the addition of steel fibers in concrete results in delayed cracking of concrete.
The study of an alternate method (Antony J.et al 2001, ACI structural journal) of attaching FRP strips to RC beams. The method utilizes the shelf powder-actuated fasteners to attach pultruded FRP strips to the concrete. Small sized beams strengthened using powder-actuated fasteners attained 65%to 70% increase in strength of the beams strengthened.
The rheology of these concrete is such that they can be reinforced by sufficient volumes of polypropylene and steel fibers to significantly increase their toughness, while their strengths in compression & tension remain relatively constant. Conventional technique for strengthening of concrete structures such as concrete jacketing, shortcreting/gunting, steel plate bonding, micro concreting, etc are cumbersome system of strengthening(Lakshmikanta G.S et al 2004) .
The material strength cannot be directly correlated to the structural strength (Dr.S.C Patodi et al 2007) which seems to increase with the higher ductility. Hence good structural performance requires a balanced material strength and ductility which RECC is able to confirm through ductile failure pattern. The composite fiber wrapping is an effective for strengthening of RC structures. The compressive strength ,split tensile strength and flexural strength of natural aggregate based (Rathish KumarP.et al) self compacting mortars is greater than Recycled Natural aggregate based concrete . The confinement provided by CFRP improves both the load carrying capacity and ductility of the column (Mohsen Shahawy et al).
The gain in the compressive strength of CFRP confined concrete depends on the ratio of the stiffness of the FRP jacket in the lateral direction to the axial stiffness of the column. The use of quasi-isotropic polymer composite laminates (ChakrabartiP et al) increases both the rotation stiffness and the ultimate strength of fiber reinforced concrete moment frame connection.
Research Significance
Research activities presented in this paper are directed as using fiber reinforced concrete engineered cementitious composites members in structures to reduce residual deflection and prevent inelastic deformations. The resulting of using fiber reinforced concrete engineered cementitious composites members as flexural members are expected to have compatible deformations between reinforcement and matrix. This study aimed at investigating the deformations mechanisms of the composite and their effect on the response of structural members.
Materials
The concrete mix design of all specimens was based on the standard mix design data. The concrete mixture & properties are given in Table1, Table2, Table3, Table3.1, and Table3.2 respectively. The reinforcement material was applied to the volume of the concrete& horizontally provided on the tensile zone of the beam. This system consists of polypropylene, steel & recron fiber .The above fibers is an economic material that offers a combination of physical, chemical, mechanical, thermal & electrical properties not found in any other thermoplastic. The polypropylene fiber has higher compressive strength of concrete; it possesses excellent resistance to organic solvents. The fiber reinforcement was applied in the accordance with the method recommended by the manufacturer of Bosee fiber.
Sl.No
Description of Material
Mass of materials
1
Cement
387.5 kg/m3
2
Fine aggregate
557.9 kg/m3
3
Coarse aggregate
1180 kg/m3
4
Water
186 kg/m3
Sl.No
Description of Material
Mass of materials
1
Cement
387.5 kg/m3
2
Fine aggregate
557.9 kg/m3
3
Coarse aggregate
1180 kg/m3
4
Water
186 kg/m3
Table 1: Concrete mixtures & properties
Table 2
Sl.No
Concrete properties
1
Fineness test=12.33
2
Consistency=32
3
Max aggregate size =20mm
4
Initial setting time=30min
The mix was designed as per IS 10262 and the mix proportion are 1:1.44:3.05
Table 3:Properties of fibers
Table3.1:Properties of various types of polypropylene fibers
Fiber type
Length (mm)
Diam eter (mm)
Tensi le stren gth (MPa
)
Modul us of elasticit y (GPa)
Specific surface (m2/kg)
monofilame
30-50
0.30-
547-
3.50-
91
nt
0.35
658
7.50
microfilame
12-20
0.05-
330-
3.70-
225
nt
0.20
414
5.50
Fibrillated
19-40
0.20-
500-
5.00-
58
0.30
750
10.00
Table 3.2 properties of fibers
Sl.No
Name of the fibers
Aspect ratio
1.
Polypropylene fiber
100
2.
Steel fiber
40-80
3.
Recron fiber
40-80
Role of Fibers
Cracks play an important role as they change concrete structures into permeable elements and consequently with a high risk of corrosion. Cracks not only reduce the quality of concrete and make it aesthetically unacceptable but also make structures out of service. Therefore, it is important to reduce the crack width and this can be achieved by adding polypropylene fibers to concrete. The bridging of cracks by the addition of polypropylene fibers is shown in Fig 1 and Fig 2.
Thus addition of fibers in cement concrete matrix bridges these cracks and restrains them from further opening. In order to achieve more deflection in the beam, additional forces and energies are required to pull out or fracture the fibers. This process, apart from preserving the integrity of concrete, improves the load- carrying capacity of structural member beyond cracking. The major reasons for crack formation are Plastic shrinkage, Plastic settlement, Freeze thaw damage, Fire damage etc.
Figure 1: monofilament fiber
Figure 2: Fibrillated fiber
Fiber mechanism
Fibers work with concrete utilizing two mechanisms, the spacing mechanism and the crack bridging mechanism. The spacing mechanism requires a large number of fibers well distributed within the concrete matrix to arrest any existing micro-crack that could potentially expand and create a sound crack. For typical volume
fractions of fibers, utilizing small diameter fibers or micro fibers can ensure the required number of fibers for micro crack arrest.
The second mechanism termed crack bridging requires large straight fibers with adequate bond to the concrete. Steel fibers are considered to be a prime example of this fiber type which is commonly referred to as large diameter fibers or macro fibers. Benefits of using larger fibers include impact resistance, flexural and tensile strengths, ductility, and fracture toughness.
Fiber Matrix Interaction
The tensile cracking strain of cement matrix (less than1/50) is very much lower than the yield or ultimate strain of steel fibers .As a result, when a fiber reinforced composite is loaded, the matrix will crack long before the fibers can be factured.
Once the matrix is cracked, the tensile stress, the peak stress and the peak strain increases continuously and they are higher than those of matrix alone and during the inelastic range between first cracking and the peak, multiple cracking of matrix occurs.
Experimental study
The concrete mix M30 investigated in this study is prepared with standard 43 grade ordinary Portland cement and fibres which are conformed to Indian standards. Mix design was carried out according to IS 10262-1982
The materials were weighted accurately using a digital weighing instrument. For plain concrete, fine aggregate, coarse aggregate, cement& water were added and were mixed thoroughly using hand mix. Steel fibers were manually sprinkled inside the concrete after thorough mixing of the ingredients of the concrete. Recron fiber was added to the concrete mix after soaking in water for about 5 minutes as recommended by the manufacturer.
Compressive strength
Standard cube specimens are casted and tested for compressive strength after 7 days and 28 days. For preparing the specimens, the permanent steel moulds size of 150mmx150mmx150mm were used. Before mixing the concrete, the moulds were kept ready. The sides and the bottom of the mould were properly oiled for easy remoulding. After pouring concrete into the mould, Table vibrator was used to compact the concrete and then the top surface was given a smooth finish.
Types
of concrete
Compressive strength (N/mm2)
7 days curing
28 days curing
Control concrete
21.8
34.88
0.5% recron
22.24
35.75
1.0% recron
23.10
37.06
1.5% recron
25.72
38.80
2.0% recron
26.16
39.24
Types
of concrete
Compressive strength (N/mm2)
7 days curing
28 days curing
Control concrete
21.8
34.88
0.5% recron
22.24
35.75
1.0% recron
23.10
37.06
1.5% recron
25.72
38.80
2.0% recron
26.16
39.24
The test specimens were stored in a place free from vibration and kept at a temperature of 27±2C for 24 hours ± ½ hour from the time of addition of water to the dry ingredients. After this period, the specimen were marked and removed from the moulds and immediately submerged in clean fresh water and kept there until taken out prior to test. The specimens dried for testing.
This test was conducted as per IS 516-1959. The cubes of standard size 150mm x150mm x150mm were used to find the compressive strength of concrete. Specimens were placed on the bearing surface of Compression Testing Machine (CTM) of capacity 40 tones without eccentricity and a uniform rate of loading was applied till the failure of the cube. The maximum load was noted and the compressive strength was calculated. The experimental result shows that the Compressive Strength of Steel Fiber Reinforced Concrete was greater than Recron Fiber Reinforced Concrete from 0.5%, 1.0%, 1.50% and 2.0% of mix
from the Table 4, Table 4.1, and Table 4.2 respecetively; also explain from the graph 1, graph 2, and graph 3.
The compression strength of concrete is a vital parameter as it decides the other parameters like tension, flexure etc. The effect of polypropylene fiber on the compressive strength of concrete has been discussed in many literatures and observed that polypropylene fiber either decreases or increases the compressive strength of concrete, but the overall effect is negligible in many cases. In fact, the effect of a low volume of polypropylene fiber on the compressive strength of concrete may be concealed by the experimental error.
Table 4
Table 4.1
Types of concrete
Compressive strength (N/mm2)
7 days curing
28 days curing
Control concrete
20.5
32.33
0.5% polypropylene
21.54
34.58
1.0% polypropylene
22.8
36.24
1.5% polypropylene
24.27
38.85
2.0% polypropylene
25.29
39.25
Types of concrete
Compressive strength (N/mm2)
7 days curing
28 days curing
Control concrete
20.5
32.33
0.5% polypropylene
21.54
34.58
1.0% polypropylene
22.8
36.24
1.5% polypropylene
24.27
38.85
2.0% polypropylene
25.29
39.25
Graph 2 Table4.2
Typesof concrete
Compressive strength (N/mm2)
7 days curing
28 days curing
0.5% steel
22.67
36.62
1.0% steel
24.85
37.93
1.5% steel
26.60
40.11
Graph 1
Graph 3
Flexural strength
The Specimen of size 500mm x100mm x 100mm is placed on the bed of the testing machine (i.e.) on two Steel Rollers of 38mm diameter. The Specimen is placed such that the Span between two supports is 40 cm. The load is applied using the Flexural Strength Machine. The load at failure was noted. The results of these flexural tests have been presented in Table 5,Table 5.1andtable 5.2 respectively. From the graph it is revealed that the performance of fibre reinforced concrete increased from 0.5%, 1.0%.1.5%& 2.0% compared to the conventional concrete.
Table 5
Types of
concrete
Flexural strength (N/mm2)
7 days curing
28 days curing
Control concrete
3.48
4.5
0.5% recron
3.78
4.86
1.0% recron
4.45
5.22
1.5% recron
4.62
5.4
2.0% recron
5.46
6.07
Graph 4
Table 5.1
Graph 5
Table 5.2
Types of concrete
Flexural strength (N/mm2)
7 days curing
28 days curing
0.5% steel
3.78
4.8
1.0% steel
4.62
5.44
1.5% steel
5.65
6.04
Graph 6
Split tensile strength
Types of concrete
Flexural strength (N/mm2)
7 days curing
28 days curing
0.5% polypropylene
8.12
9.22
1.0% polypropylene
9.4
10.5
1.5% polypropylene
11.0
11.9
2.0% polypropylene
12.7
13.2
Types of concrete
Flexural strength (N/mm2)
7 days curing
28 days curing
0.5% polypropylene
8.12
9.22
1.0% polypropylene
9.4
10.5
1.5% polypropylene
11.0
11.9
2.0% polypropylene
12.7
13.2
This test was conducted as per IS 5816-1999. The Cylindrical Specimen of standard size 150mm diameter and 300 mm height was placed on the CTM with capacity of 40 tones, with the diameter horizontal. The load was applied till the specimen fails. The failure of the Specimen is noted by the formation of cracks. The maximum load was noted down and the Split tensile strength was calculated. From the results the Split Tensile Strength of Steel Fiber Reinforced Concrete was greater than Recron Fiber Reinforced Concrete at all percentage of mix and have been shown the table 6,table 6.1,and table 6.2 respectively.
Table 6
Types of concrete
Split tensile strength (N/mm2)
7 days curing
28 days curing
0.5% polypropylene
2.49
3.25
1.0% polypropylene
2.82
3.87
1.5% polypropylene
3.56
4.12
2.0% polypropylene
3.61
4.32
Graph 6
Table 6.1
Graph 7
Table 6.2
Types of concrete
Split tensile strength (N/mm2)
7 days curing
28 days curing
0.5% steel
2.91
4.58
1.0% steel
3.33
3.85
1.5% steel
3.61
5.00
Types of
concrete
Split tensile strength (N/mm2)
7 days curing
28 days curing
Control concrete
2.64
4.16
0.5% recron
2.78
4.44
1.0% recron
3.05
4.72
1.5% recron
3.47
4.85
2.0% recron
3.75
5.13
Types of
concrete
Split tensile strength (N/mm2)
7 days curing
28 days curing
Control concrete
2.64
4.16
0.5% recron
2.78
4.44
1.0% recron
3.05
4.72
1.5% recron
3.47
4.85
2.0% recron
3.75
5.13
Conclusions
Graph 8
An experimental study was conducted on cubes, cylinders, beam, for compressive, split tensile strength, flexural test respectively by mixing various percentages of polypropylene, recron & steel fiber. Based on the investigation the following conclusions were drawn. They are
-
The Compressive Strength of Steel Fiber Reinforced Concrete was 1.35% greater than Recron Fiber Reinforced Concrete at all percentage of mix.
-
The Split Tensile Strength of Steel Fiber Reinforced Concrete was 0.15% greater than Recron Fiber Reinforced Concrete at all
-
percentage of mix
-
The Flexural Strength of Steel Fiber Reinforced Concrete was greater than Recron Fiber Reinforced Concrete at all percentage of mix, except at 0.5%. In 0.5%, the Flexural Strength was same for both Concrete.
-
The Split Tensile Strength of Steel Fiber Reinforced Concrete was 0.81% greater than polypropylene Fiber R e i n f o r c e d Concrete at all percentage of mix.
-
The Flexural Strength of Steel Fiber Reinforced Concrete was greater than Recron Fiber Reinforced Concrete at all percentage of mix, except at 0.5%. In 0.5%, the Flexural Strength was same for both Concrete. For polypropylene fiber reinforced concrete the Flexural Strength was 2.15% greater than Steel Fiber Reinforced Concrete.
-
For Recron, up to 2.0% mix was done as the Workability of 2.5% mix was Very low, which is not recommended.
-
For Steel, up to 1.5% mix was done as the Workability of 2.0% mix was Very low which is not recommended
Hence Steel Fiber has greater strength when compared to Recron Fiber, in Compression, Split Tension and Flexure. So, Steel Fiber can be used to achieve greater strength with Vf up to 1.5% by weight of Cement, if used without any Admixtures.
References
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Ahmed Loukili and Laurent Daniel May-June 2002. Behavior of High Strength Fibre- Reinforced Concrete Beams Under Cyclic Loading. ACI Structural Journal, (2.2) Page No: 248 to 256
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