flexural behaviour of reinforced concrete beam …
TRANSCRIPT
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FLEXURAL BEHAVIOUR OF REINFORCED CONCRETE BEAM USING BASALT
FIBER
P. MANIBALAN1, R. BASKAR2& N. PANNIRSELVAM3
1Research Scholar, Department of Structural Engineering, Annamalai University, Tamilnadu, India
2Professor, Department of Structural Engineering, Annamalai University, Tamilnadu, India
3Associate Professor, Department of Civil Engineering, SRM Institute of Science and Technology, Tamilnadu, India
Highlights
The eco-friendly fiber called the basalt fiber is chosen for the research to enhance the flexure behaviour of
concrete.
The optimum percentage of 0.9% basalt fiber is added and the flexure results Load-Deflection, Moment-
Curvature, ductility and stiffness are discussed.
The test results proved that the basalt fiber plays an effective role in enhancing the flexure behaviour of
concrete beam specimen.
ABSTRACT
The use of basalt fiber in the concrete structure is a recent research due to its high tensile strength, high modulus, strain
to failure, fire resistance, impact load resistance, good resistance to chemical attack and non-toxic. In this paper, the
effectiveness of basalt fiber in the flexural strength of concrete beam is experimentally investigated. The basalt fiber is
added at the volume fraction of 0.9% in the beam which is the optimum percentage of fiber from its mechanical proper-
ties. The flexural response of basalt fiber reinforced concrete beam and control concrete beam are analyzed by static
loading test. This paper compares the flexural behaviour of BFRC and controlled concrete beam by using the result of
Load Deflection, Moment Curvature relationship, stiffness, flexural rigidity and its ductility factor. The number of shear
cracks and flexural cracks are observed which shows the effective bridging action of basalt fiber of the tested beam. The
dispersion and bonding behaviour of basalt fiber in the concrete matrix are confirmed by its SEM image. According to
the experimental research, basalt fiber beams proved its effective flexural properties such as load carrying capacity, mo-
ment curvature, ductility, stiffness, flexural rigidity and crack resistance compared to controlled beams.
KEYWORDS: Basalt, optimum, Load-deflection, Moment-curvature, Stiffness & Resistance
Received: Jun 08, 2020; Accepted: Jun 28, 2020; Published: Oct 13, 2020; Paper Id.: IJMPERDJUN20201522
1. INTRODUCTION
Concrete is a composite material made primarily with aggregate, cement and water. There are many formulation of
concrete, which provide varied properties and concrete is the most used man-made product in the world. Concrete
can be formulated with high compressive strength but always has lower tensile strength. Fiber reinforced concrete
is one of the recent researches, to increase the tensile strength of concrete.[1] Presently, several organic and inor-
ganic fiber are available in the market, but many of them either lack structural strength or durability are extremely
costly for use in moderate loadings.
Orig
inal A
rticle International Journal of Mechanical and Production
Engineering Research and Development (IJMPERD)
ISSN(P): 2249–6890; ISSN(E): 2249–8001
Vol. 10, Issue 3, Jun 2020, 16055-16064
© TJPRC Pvt. Ltd.
16056 P.Manibalan, R.Baskar & N.Pannirselvam
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
Basalt fiber is one of the inorganic and natural fiber with high modulus, thermal resistance, salt and alkali re-
sistance, high strength, eco-friendly and inexpensive.[2] Basalt fiber is obtained after extrusion from basalt based molten
igneous volcanic rock, which is found in flowing lava. Basalt rock having silica content more than 46% are suitable for
fiber production. The extrusion process of basalt fiber popularity as a potential competitor in concrete reinforcing applica-
tion due to its excellent mechanical properties and environment friendly manufacturing process.[3] Applicability of basalt
fiber as a strengthening for concrete structural materials has been studied for durability, mechanical and flexural properties.
The understanding of fracture mechanism of RC structure is vital and under this study it’s focussing the crack and
deflection behaviour for RC beam under static loading. However, basalt fiber rod has many advantages; it is good alterna-
tive for steel due to its low modulus of elasticity.[4] Glass fiber and carbon fiber rod are having low modulus of elasticity
compared with basalt fiber rod. So the addition of fiber in volume has greatly influence the flexural behaviour of concrete.
[5] Although, many researches has been conducted to investigate the flexural behaviour of fiber reinforced concrete, basalt
fiber has some unique properties to enhance it.[6] This paper presents an experimental study of deflection, moment-
curvature and stress-strain relationship of basalt fiber reinforced concrete compared with controlled concrete. Based on the
experimental result of this paper and collected literature, basalt fiber concrete has significant improvement load-deflection
and moment-curvature than the controlled concrete.
2. EXPERIMENTAL PROGRAM
2.1 Material and its Property
The material used in the concrete mixes are ordinary Portland cement, river sand, crushed aggregate, super-plasticizing
admixture and basalt fiber. OPC 53 grade cement is tested as per the Indian standard specification BIS 12269 – 1987. Fine
aggregate is river sand conforming to zone II of BIS: 383 – 1970 having specific gravity of 2.72 and fineness modulus of
2.74. Coarse aggregates of size 20mm having specific gravity of 2.79 and fineness modulus of 6.15. Water reducing agent
based on the salt of polymetric naphthalene sulphonate is used as a chemical admixture. The dosage of super plasticizer is
vary to obtain the desired level of workability in the concrete. The mix proportions are kept constant for target mean
strength of 48MPaand 0.40 as W/C ratio. Basalt fibers are multifilament type with 6mm length and 0.05mm diameter.
2.2 Specimen Design
This study consists of three basalt fiber reinforced concrete beam and three control concrete beam specimens. The beam
mould of size 150mm wide, 250mm deep and 3200mm long is made up of with wood to cast the concrete that has target
strength of 48 MPa. Concrete are mixed in a mixer machine for uniformity to cast the beam specimens and the Figure 1
illustrated the casting of beam specimen.
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a) Wooden Mould
b) Reinforcement Cage
c) Placing and Leveling of
Concrete
Figure 1: Casting Process
The beam specimen is divided into two phases, namely phase I and phase II. Three beams are built and tested in
each phase. The first phase is plain concrete without any fibers, the second is beams reinforcing with basalt fiber of 0.9%
in the volume of concrete. A 20mm concrete cover is used in the beams. The beams are designed to fail by yielding of
steel. This is accomplished by using reinforcement ratio lesser than the balance reinforcement ratio. Fe-500 steel is used for
longitudinal reinforcement and stirrups. The controlled concrete beams are called CB1, CB2 and CB3, while beams with
basalt fiber are BF1, BF2 and BF3. After casting al beams are cured at normal temperature in a water bath for 28 days.
2.3 Test Setup and Protocol
Test of six simply supported beams subjected to four – point bending are carried out as per ASTM D6272 standards in the
laboratory of Annamalai University. The beam spanning 3200mm are subjected to flexural testing and its loading span of
1000mm. Schematic arrangement of test setup and loading configuration are shown in figure 2. Three dial gauge are fixed,
one at mid-span and two are at loading point to monitor the mid span deflection and curvature of the beam. The beams are
statically tested for failure at 2.5kN increment of load by means of hydraulic jack and it is measured with load cell. At
cracking and at the end of each 2.5kN load, cracks are sketched and a near mid-span crack width is measured using a mi-
croscope.
Figure 2: Experimental Test Setup
16058 P.Manibalan, R.Baskar & N.Pannirselvam
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3. ANALYSIS OF TEST PROTOCOL
3.1 Crack Pattern
Cracking pattern of control beams and basalt fiber beams are shown in figure 3 and 4 respectively. During loading, vertical
cracks in the flexural span are propagated towards the compression face as the load increased. Cracks are formed similar to
the flexural cracks at the outside of bending zone. Further loading, shear stress are formed and induced the shear cracks.
Shear cracks began from the bottom face of the beam and diagonally propagated up towards the top support. It is clearly
shown that the number of flexural cracks is higher in the normal concrete than the basalt fiber concrete. This crack pattern
proved that the basalt fiber is active in arresting the cracks. It is mainly contributed by bonding behaviour between concrete
complex and basalt fiber.[7]
Figure 3: Crack pattern for CC Beam
Figure 4: Crack pattern for BF Beam
Scanning electron microscope provides a valuable information about the cause of deterioration in concrete due to
cracks.[8,9] In order to study the effect of basalt fiber in the microstructure of concrete, fractured surface of basalt fiber con-
crete at the age of 30 days are investigated by scanning electron microscope. SEM images as shown in Figure 5 reveals that
the perfect scattering of basalt fiber in concrete. It also showed that the boning behaviour of cement matrix and basalt fiber.
The major crack formation are reduced by the basalt fiber in the concrete and it is proved by the SEM images.
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Figure 5: SEM Image
3.2 Load – Deflection
The load – deflection behaviour of six beams are traced experimentally as shown in following figure 6. Table 1 presents
the maximum mid-span deflection of the tested beam. A distinct difference in the shape of load deflection plots at post
cracking load. Both basalt fiber and normal concrete beam are similar in pre-cracking load – deflection behaviour. The
ultimate load – Carrying capacity of the beams are noted.
Table 1: Load – Deflection for the Beam Specimens
Specimen Id
First Crack Stage Ultimate Stage
Load
(Kn) Deflection (Mm)
Load
(Kn)
Deflection
(Mm)
CB 1 15.00 1.45 52.50 16.80
CB 2 15.00 2.03 50.00 17.40
CB 3 17.50 1.17 52.50 16.42
BF 1 20.00 3.22 62.50 19.98
BF 2 20.00 3.29 62.50 20.84
BF 3 17.50 2.80 65.00 20.78
Table 1 shows the increase in ultimate load value for basalt fiber beam than the normal concrete beam. BF1 beam,
which is added with the basalt fiber, first cracked at 20kN and the ultimate load at 62.5kN. The maximum deflection of
BF1 beam is 19.98mm. CB1, which is control concrete beam, first cracked at 15kN And the ultimate load at 52.5kN. The
maximum deflection of CB1 beam is 16.8mm. BF2 beam shows the increase in ultimate load and deflection as 4.12% and
19.77% % than CB2 beam. BF3 beam shows the increase in ultimate load and deflection as 23% and 26.55% than CB3
beam.
16060 P.Manibalan, R.Baskar & N.Pannirselvam
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Figure 6: Load - Deflection Plot
As we observed from load deflection curve that all the basalt fiber beam has initial stiffness similar to control
concrete beam. After cracking, the stiffness increased for all the basalt fiber beam than the normal concrete beam
3.3 Moment – Curvature
In this study, a parametric analysis of moment – curvature relation on controlled and basalt fiber reinforced beams at first
crack load level and ultimate load level are taken into consideration. The moment – curvature values for the beams under
consideration is tabulated in table at two specified load levels. Loads were applied continuously and their corresponding
strain gauge readings were recorded until complete failure of the beam occurred. The moment – curvature behaviour of the
controlled and BF beams with different proportions of BF were illustrated in Table 2.
Table 2: Moment – Curvature for the Beam Specimens
Specimen Id First Crack Stage Ultimate Stage
Moment
(Kn.M)
Curvature
(X106/M)
Moment
(Kn.M)
Curvature
(X106/M)
CB 1 7.50 0.244 26.25 2.102
CB 2 7.50 0.209 25.00 2.018
CB 3 8.75 0.200 26.25 2.053
BF 1 10.00 0.431 31.25 2.129
BF 2 10.00 0.391 31.25 2.116
BF 3 8.75 0.289 32.50 2.204
Figure 7 shows the variation in moment-curvature behaviour on controlled and the basalt fiber concrete.
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Figure 7: Moment - Curvature Plot
It is observed that, initially all the BF beams behave in a similar way as that of the controlled beam before the
steel yields. When the reinforcing steel reaches its limiting state, it undergoes plastic deformation thereby increasing the
curvature of the beam. The curvature of BF1, BF2, BF3, fiber reinforced concrete decreased by 1.28%, 4.86%, 7.36% that
of CB1, CB2, CB3 controlled concrete. Also, the moment carrying capacity of the BF1, BF2, BF3 fiber reinforced concrete
has been increased by 19.04%, 25%, 23.81% CB1, CB2, CB3 compared to controlled beam. This clearly indicates the ad-
vantage of using BF in upgrading the RC beams.
3.4 Ductility
Ductility is the ability of the material to undergo large deformation without rupture before the failure of material. Accord-
ing to Committee Euro-International Du Beton, 1996, the ductility factor is defined by the ratio between ultimate deflec-
tions to yield deflection.[10] The yield deflection is measured from the assumed bilinear of load-deflection curve of a spec-
imen. i.e, it is the lateral displacement at 80% of ultimate load at the ascending part of the curve while the maximum de-
flection is lateral displacement at 80% of ultimate load at the descending part of the curve as shown in the Figure 8.
Figure 8: Ductility Curve
The ductility factor can be formulated as,
16062 P.Manibalan, R.Baskar & N.Pannirselvam
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
Ductility Factor = Ultimate Deflection / Yield Deflection
Ductility of concrete structure also represents the energy absorption capacity of the beam. The energy absorbed is equal to
the area under the load defection curve. The energy ductility of the tested beams is calculated by finding the ratio of energy
at ultimate load to energy at yield load.
Table 3: Ductility Factor for the Beam Specimens
Specimen ID Ultimate Deflection (mm) Yield Deflection (mm) Ductility Factor
CB 1 16.80 12.36 1.36
CB 2 17.40 12.67 1.37
CB 3 16.42 12.26 1.34
BF 1 19.98 14.72 1.36
BF 2 20.84 14.9 1.40
BF 3 20.78 15.28 1.36
Table 3 shows the ductility factor for both the controlled and the basalt beams. The ductility factor for basalt fiber
reinforced concrete beam has an average of 1.37 and that is 0.74% greater than the controlled concrete beam. This indi-
cates that, on addition of basalt fiber, the deflection of the beam increases thereby increasing its ductility.
3.5 Flexural Rigidity
Flexural rigidity is the resistance offered by a beam while under loading. The deflection of beam is mainly affected by the
magnitude of loading, type of loading, span of beam, beam type, material properties (E) and moment of inertia (I). If the
deflection in a beam is beyond the permissible limit, there will be a loss of rigidity causing undesired deflection and slopes
and also the smooth operation of a flexural member becomes impossible. By using the relationship between curvature and
bending moment, the deflection equation for a simply supported beam under two point load is given below,
∆ = 𝑃𝑎
24𝐸𝐼 (3𝐿2 − 4𝑎2)
The above equation is used to calculate the flexural rigidity by substituting the experimental values of ultimate deflection
and ultimate load.
Table 4: Flexural Rigidity for the Beam Specimens
Specimen ID Ultimate Load
(kN) Maximum Deflection (m)
Flexural Rigidity EI
(kN m2)
CB 1 52.5 16.8 2994.79
CB 2 50 17.4 2753.83
CB 3 52.5 16.42 3064.10
BF 1 62.5 19.98 2997.79
BF 2 62.5 20.84 2874.08
BF 3 65 20.78 2997.67
Table 4 showed the flexural rigidity of basalt fiber beam reached as a high value while compared with other beam
specimen. Basalt fiber beam have an average flexural rigidity value as 2956.51kNm2 which is 0.64% higher than the con-
trol beam. The results showed that the addition of basalt fiber is enhanced the flexural rigidity by arresting the propagation
of micro cracks in the beam.
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4. CONCLUSIONS
The flexural behaviour of controlled concrete beam and fiber reinforced concrete beam has been analysed in this paper.
The crack pattern, load carrying capacity, mid-span deflection, moment and curvature were predicted experimentally. The
following are the conclusions drawn from the above results:
Incorporating basalt fiber on to the concrete will arrest the crack than the controlled concrete shown by its crack
pattern.
The first cracking load for basalt fiber concrete beams is 21.27% higher than the control concrete beam. Hence,
this study proved the contribution of BF in cracking zone.
The measured strain for BF beams was less than those of controlled beams under the same load.
The addition of BF showed the higher ultimate load carrying capacity of tested beams than the control concrete
beam. Moreover, the deflection at ultimate load for BF beam is higher than the control concrete beam.
Addition of BF in RC beam leads to increase in its flexural strength compared with control concrete beam and its
load carrying capacity prolonged by 15.39% than controlled beam.
The calculated flexural moment and curvature has been increased and decreased by 22.61% and 4.5% respectively
under the influence of basalt fiber.
The deflection of beam increases thereby increasing its ductility by the addition of basalt fiber.
The inclusion of basalt fibers increases the flexural rigidity by arresting the cracks.
By considering the above result, flexural properties for basalt fiber concrete beam is higher than the controlled
concrete beam.
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