application of fiber reinforced concrete and
TRANSCRIPT
APPLICATION OF FIBER REINFORCED CONCRETE AND HIGH
PERFOMANCE CONCRETE
Guided By: Prepared By:
SHAH DEEP ( CP 1710 )
SHAH SOHAM ( CP 2110 )
FIBre REINFORCED CONCRETE
It can be defined as a composite material consisting of mixtures of cement, mortar or concrete and discontinuous, discrete, uniformly dispersed suitable fibres.
The addition of small, closely spaced and uniformly dispersed fibres to concrete would act as crack arrester and would substantially improve its static and dynamic properties. This type of concrete is known as Fibre Reinforced Concrete.
FIBRES USED IN FIBRE REINFORCED CONCRETE
STEEL FIBRES
Steel fibre makes significant improvements in flexural, impact and fatigue strength of concrete.
It has been extensively used for overlays roads, airfield pavements, and bridge decks.
The diameter of steel fibres may vary from 0.25 to 0.75 mm.
POLYPEOPYLENE AND NYLON FIBRES
They increase the impact Strength.
They possess very high tensile strength.
Polypropylene short fibers in small volume fractions between 0.5 to 15 commercially used in concrete.
But, Their low modulus of
elasticity and higher elongation do not contribute to the flexural strength.
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ASBESTOS FIBRES
It can be mixed with Portland Cement easily.
Tensile strength of asbestos fibres varies between 560 to 980 N/
Asbestos fibres give higher flexural strength.
Due to relatively short length (10mm) the fiber have low impact strength.
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GLASS FIBRES It has very high tensile strength
1020 to 4080 N/ Alkali-resistant glass fibre by
trade name “ CEM-FIL” has been developed and used as glass fibres were found to be affected by alkaline condition of cement.
The alkali resistant FRC shows considerable improvement in durability compared to the conventional glass FRC.
it is not possible to mix more than about 2% (by volume) of fibers of a length of 25mm with concrete.
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CARBON FIBRES Carbon fibres possess very
high tensile strength 2110 to 2815 N/ and Young’s modulus.
Cement composite made with carbon fibre as reinforcement will have very high modulus of elasticity and flexural strength with durability.
It can also been used as clading, panels and shells.
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APPLICATIONS OF FIBRE REINFORCED CONCRETE Fibre reinforced concrete is
increasingly used on account of the advantages of increased static and dynamic tensile strength, energy absorbing characteristics and better fatigue strength.
The uniform dispersion of fibres throuout the concrete provides isor\tropic properties not common to conventionally reinforced concrete .
It has been tried on overlays of air-field, road pavements, industrial footings, bridge decks, canal lining, explosive resistant structures, refractory linings,etc.
The fibre reinforced concrete can also be used for the fabrication of precast products like pipes, boats, beams, stair case steps, wall panels, roof panels, manhole covers etc.
Fibre reinforced concrete is also being tried for the manufacture of prefabricated formwork moulds of “U” shape for casting lintels and small beams.
FACTORS EFFECTING PROPERTIES OF FIBRE REINFORCED CONCRETE
1. RELATIVE FIBRE MATRIX STIFFNESS
The modulus of elasticity of matrix must be much lower than that of fibre for efficient stress transfer.
Low modulus of fibres such as nylons and polypropylene are, therefore, unlikely to give strength improvement, but they help in absorption of large energy and therefore impart greater degree of toughness and resistant to impact.
High modulus fibres such as steel,
Glass and carbon impart strenth and stiffness to the composite.
Interfacial bond between the matrix and the fibres also determine the effectiveness of stress transfer from the matrix to the fibre.
A good bond is essential for improving tensile strength of composite.
The interfacial bond could be improved by larger area of contact, imroving th frictional properties and degree of gripping and by treating the steel fibres with sodium hydroxide or acetone.
2. VOLUME OF FIBRES Effect of volume of fibres
in flexure
Effect of voume of fibres in tension
The increase in volume of fibres,
CONTINUE… increase approximately
linearly, the tensile strength and toughness of the concrete.
3. ASPECT RATIO OF FIBRES
Up to aspect ratio of 75, increase in the aspect ratio increases the ultimate strength of the concrete linearly.
Beyond 75, relative strength and toughness is reduced.
Type of concret
e
Aspect
ratio
Relative
strength
Relative
toughn-ess
Plain concrete
with Randoml
y dispersed fibres
0 1.00 1.0
25 1.50 2.0
50 1.60 8.0
75 1.70 10.5
100 1.50 8.5
CONTINUE…
4. ORIENTATION OF FIBRES
In conventional reinforcement: Bars are oriented in desired direction.
In fibre reinforcement:
Fibres are randomly oriented. Test to see the effect of
randomness Mortar specimens reinforced with
o.5 percent volume of fibres are tested.
In one set specimens, fibres are aligned in the direction of the load, in another in the direction perpendicular of the load, and in the third randomly distributed.
Observation: It is observed that the fibres
aligned parallel to the applied load offered more tensile strength and toughness than randomly distributed or perpendicular.
CONTINUE…
5. MIXING Mixing needs careful
conditions to avoid balling of fibres, segregation, and difficulty of mixing materials uniformly.
Increase in aspect ratio, volume percentage and size and quantity of coarse aggregate intensify the difficulties and balling tendencies.
A steel fibre content in excess of 2 percent by volume and an aspect ratio of more than 100 are difficult to mix.
Cement content
325 to 550 kg/
W/C ratio 0.4 to 0.6
% of sand to total aggregate
50 to 100 %
Max. aggregate size
10 mm
Air-content 6 to 9 %
Fibre Content 0.5 to 2.5 % by volume of mixSteel - 1 % 78 Kg/m3Glass – 1% 25 Kg/m3Nylon – 1% 11 Kg/m3
CONTINUE…
6. SIZE OF COARSE AGGREGATE The maximum size of the coarse
aggregate should be restricted to 10 mm, to avoid appreciable reduction in strength of the composite.
The inter-particle friction between fibres, and between fibres and aggregate controls the orientation and distribution of the fibres and the properties of composite.
Friction reducing admixture and admixtures that improve cohesiveness of mix can improve the mix.
7. WORKABILITY AND COMPACTION OF CONCRETE
Incorporation of steel fibres decreases the workability considerably.
This affects consolidation of fresh mix and prolonged external vibration fails to compact the concrete.
Another consequence of poor workability is non-uniform distribution of fibres.
Workability and compaction of mix is improved through increased W/C ratio or by using water reducing admixture.
CONTINUE…
APPLICATION OF STEEL FIBERS1. SHOTCRETE
CONSTRUCTION Lining in mine and tunnel
- Dam- Stability in slope- Reservoir and other hydraulic facilities
Advantage
- reduces the concrete thickness- reduces the material, labor cost and construction time- safe construction- Excellent tensile strength and durability
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2. PAVEMENT-road and railroad- Airport: pavement- Bridge- Parking lot
Advantage
- increase the concrete lifecycle- Enlarge the joint block- Increase the tensile strength, fatigue resistance, impact resistance and block strength
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3. Prefabricated or factory placing concrete product
Building panel- Block (Harbor block)- Pipe
Advantage
- Enhanced the shearing strength fatigue resistance increasing the crack resistance and durability
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4. Floor construction of industrial building -
Factory floor
- Warehouse- Exhibition hall- Floor of structure with heavy loading area
Advantage
- reduce or remove the steels or mesh- reduce the floor thickness
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5. Building floor construction - Various metal deck methods
- Replacing or reducing the floor steel
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6. Others
Steel fiber can be used in any structure which needs to increase the tensile strength, fatigue resistance and impact resistance.
MIX DESIGN
the mix proportions for SFRC depend upon the requirements for a particular job, in terms of strength, workability, and so on.
SFRC mixes contain higher cement contents and higher ratios of fine to coarse aggregate than do ordinary concretes, and so the mix design procedures the apply to conventional concrete may not be entirely applicable to SFRC.
to reduce the quantity of cement, up to 35% of the cement may be replaced with fly ash.
In addition, to improve the workability of higher fibre volume mixes, water reducing admixtures and, in particular, superlasticizers are often used, in conjunction with air entrainment.
A particular fibre type, orientation and percentage of fibers, the workability of the mix decreased as the size and quantity of aggregate particles greater than 5 mm increased; the presence of aggregate particles less than 5 mm in size had little effect on the compacting characteristics of the mix.
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The second factor which has a major effect on workability is the aspect ratio (l/d) of the fibres. The workability decreases with increasing aspect ratio.
in practice, it is very difficult to achieve a uniform mix if the aspect ratio is greater than about 100.
Range of proportions for normal weight fibre reinforce Concrete
Typical steel fibre reinforce shotcrete mixes
COMPARISOnFiber Reinforced Concrete (FRC) Normal Reinforce Concrete
- Higher durability - Lower durability
- Protect steel from corrosion - Steel potential to corrosion
- Lighter (materials) - Heavier (materials)
- More Expensive - Economical
- With the same of volume, the strength is greater
- With the same of volume, the strength is less.
- higher workability - Less workability as compare to FRP
RESEARCH PAPER ON STEEL FIBER REINFORCED CONCRETE PAVEMENT
FORORTHOTROPIC STEEL DECK AS A COUNTERMEASURE FOR FATIGUE
ABSTRACT
This paper describes ongoing studies about application of Steel Fiber Reinforced Concrete (SFRC) pavement for existing orthotropic steel deck as a countermeasure for fatigue problems.
In order to evaluate durability of the pavement, strength tests and fatigue tests under negative bending have been conducted using half meter size specimens taking into account of effects of reinforcement in SFRC and influence of water. Wheel running test using real size specimen will get started in the beginning of 2008.
Orthotropic steel deck (OSD) is widely applied to long span bridges and urban viaducts in Japan because its light weight contributes to reduce their dead load.
Types of cracks.1. Fillet weld between deck plate
and trough rib1-1. Crack propagates into deck
Plate1-2. Crack propagates into bead2. Fillet weld between transverse rib
and trough rib3. Butt weld connection of trough rib4. Fillet weld between vertical
stiffener and deck plate
OVERVIEW OF THE RESEARCH In order to establish the
SFRC pavement as an anti-fatigue technology, followings are needed to be evaluated. One is to confirm the improvements of fatigue performance of OSD, the second is to evaluate SFRC’s durability, and third is to clarify whether any side-effects occur or not, for example, since it is more rigid than asphalt, a bridge’s behavior may change after SFRC pavement.
To evaluate durability of SFRC is the largest task in current researches especially in the case that SFRC has got cracks by negative bending under wet condition. PWRI had conducted a flexural strength test and a fatigue test using specimens having half meter by half meter size. The tests took into account of the effects of reinforcement in SFRC layer such as grids of reinforcing bar and CFRP.
A series of wheel running tests using two real size OSD specimens in order to evaluate durability of SFRC pavement under more realistic way that can re-create complicated behavior.
TYPES OF SFRC PAVEMENT
TYPES OF CRACKS
Fatigue Cracks in Orthotropic Steel Deck
Repair/Reinforce Methods
FLEXURE STRENGTH TEST UNDER NEGATIVE BENDING
Specimens for Flexure Strength Test
Loads and Strain when Cracks initiate
Specimen for Negative Bending Test
Loading Arrangement
Loads - Crack width Curve
Changes of Neutral Axis Locations
Crack width distributions at side surface of SFRC
SFRC right after the Crack initiations
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FATIGUE TEST
Results of Tensile Test
Changes of Maximum Crack Width
Changes of Machine load
Crack propagations
WHEEL RUNNING TEST
CONTINUE…
PAVEMENT PROCESS OF REAL SIZE SPECIMEN FOR WHEEL RUNNING TEST
CONCLUSION
SFRC pavement is expected to reduce stress that is related to fatigue crack initiation at the weld between trough ribs and deck plate. The effect has been confirmed both in FE analysis using 3-D models and stress measurement using real size specimens.
Wheel running test showed that SFRC pavement maintained its stress reduction effect through 2,000,000 times loading that caused positive bending in macro-wise on OSD. Another wheel running test focusing on negative bending is being prepared.
For negative bending on SFRC, the effect of reinforcing bars and CFRP were tested in static and fixed point cyclic loading tests. Increase of loads corresponding crack initiations and decrease of crack width are not clear in the specimens using reinforcements, while small differences are observed as to crack width in accordance with rigidities of reinforcement. In the case that a crack penetrated SFRC and water reached the interface between SFRC and steel plate, decrease of tensile strength was observed. However, the decreased area was limited to vicinity of the crack.