Fiber reinforcement concrete

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Fiber reinforcement concrete Prepared by AHMED A.SHUIEB ABDALLAEmail : [email protected]

Contents :1.1 Introduction .2.1 History .3.1 Type of fibers .4.1 Areas of Application of FRC materials .5.1 Workability 6.1 Mechanical Properties of FRC .6.1 Structural Behavior of FRC .8.1 Mix deign .9.1 Comparative Study of the Mechanical Behavior of SFRC .10.1 Comparative between FRC and Plain concrete .11.1 Cost analysis example .12.1 Advantages of FRC .13.1 Disadvantages of FRC .14.1 Conclusion . Reference .

1.1 Introduction

Concrete is one of the most versatile building material.

Concrete made from Portland cement, is relatively strong in compression but weak in tension and tends to be brittle .

weakness in tension can be overcome by the use of conventional steel bars reinforcement and to some extent by the mixing of a sufficient volume of certain fibers. The use of fibers also recalibrates the behavior of the fiber-matrix composite after it has cracked through improving its toughness .

Fiber reinforcement concrete ( FRC ) a composite material obtained by adding a single type or a blend of fibers to the conventional concrete mix .

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1.1 Introduction ( Con. ) What is FRC ?Fiber reinforcement concrete (FRC ) is Portland cement concrete reinforced with more or less randomly distributed fibers. In FRC, thousands of small fibers are dispersed and distributed randomly in the concrete during mixing .Why we use FRC ?We use the FRC to improve concrete properties in all directions. Fibers help to improve the post peak ductility performance, pre-crack tensile strength, fatigue strength, impact strength and eliminate temperature and shrinkage cracks .

1.1 Introduction ( Con. )

Fig .1 relation between load and deflection . , Ref. ( 6 )

2.1 History The use of fibers goes back at least 3500 years, when straw was used to reinforce sun-baked bricks in Mesopotamia.

Horsehair was used inmortar andstraw inmud bricks.

Asbestos fibers were used in concrete in the early 1900.

First studies dealing with use of steel fibers and glass fibers in concrete date back to the 1950 .

in the 1960 the first studies concerning fiber reinforced concrete using synthetic fibers , Ref (1) .

3.1 Type of fibers Fibers are produced from different materials in various shapes and sizes. Typical fiber materials are :

1- Steel Fibers Straight, crimped, twisted, hooked, ringed, and paddled ends. Diameter range from 0.25 to 0.76mm.

2- Glass Fibers Straight. Diameter ranges from 0.005 to 0.015mm (may be bonded together to form elements with diameters of 0.13 to 1.3mm).

3- Natural Organic and Mineral Fibers Wood, asbestos, cotton, bamboo, and rockwool. They come in wide range of sizes.

3.1 Type of fibers ( Con ) 4- Polypropylene Fibers Plain, twisted, fibrillated, and with buttoned ends. 5- Other Synthetic Fibers Kevlar, nylon, and polyester. Diameter ranges from 0.02 to 0.38mm. A convenient parameter describing a fiber is its aspect ratio (L/D), defined as the fiber length divided by an equivalent fiber diameter. Typical aspect ratio ranges from about 30 to 150 for length of 6 to 75mm , Ref (2)

3.1 Type of fibers ( Con )

Fig .2 steel fiber Ref. alibaba.comFig .3 class fiber Ref. alibaba.com

Fig .4 Asbestos fiber Ref. alibaba.comFig .5 Polypropylene fiber Ref. alibaba.com

3.1 Type of fibers ( Con ) Ultimate elongation(%)Youngs modulus(x103Mpa)Tensile strength(Mpa)Type of fiber0.5-35200275-2757Steel ~253.45551-690Polypropylene1.5-3.5~691034-3792Glass16-204.14758-827Nylon

Table .1 Type of fibers , Ref . ( 6 )

4.1 Areas of Application of FRC materialsThin sheets .Shingles .Roof tiles .Pipes .prefabricated shapes .Panels .Shot crete .Curtain walls . Slabs on grade .precast elements . Composite decks .Vaults, safes.Impact resisting structures, Ref (3) .

4.1 Areas of Application of FRC materials ( Con )

Fig .7 Shotcrete Ref. fiberconfiber.com Fig .6 Composite Mtal Deck Ref. fiberconfiber.com Fig .8 Slab on grade Ref. fiberconfiber.com

4.1 Areas of Application of FRC materials ( Con )

Fig . 9 The Metropolitan Miami 2 towers in Miami, Florida @2010 , utilized over 10,000 cubic yards of concrete containing Graces STRUX 90/40 macro fibers on its 29 composite metal decks Ref . Grace.com

Fig . 10 Alstom Wind Energy company 2007 ,TAXES , USA , application SOG, Foundation , steel helix fiber ,Ref Helix company .

5.1 Workabilityworkability is considered to be that property of plastic concrete which indicates its ability to be mixed, handled, transported, and most importantly, placed with a minimum loss of homogeneity. Mixing :Mixing of fiber reinforced concrete needs careful conditions to avoid balling of fibers, segregation and in general the difficulty of mixing the materials uniformly. Increase in the aspect ratio, volume percentage and size and quantity of coarse aggregate intensify the difficulties and balling tendency. Steel fiber content in excess of 2% by volume and aspect ratio of more than 100 are difficult to mix .

Placing :Steel fiber reinforced concrete can be placed using conventional equipment such as t ruck chutes, concrete buckets, conveyors , and pumps. The equipment should be clean and in good condition to ensure that the fiber reinforced concrete flows easily and minimize the pump pressure to avoid the segregation and palling .

5.1 Workability ( Con )Finishing :

Steel fiber reinforced concrete can be finished with conventional equipment .In areas where a screed is not practical, a jitterbug or rollerbug can be used for compaction and to establish rough grade control .Magnesium floats can be used to establish a surface .All finishing operations, care must be taken not to overwork the surface .Overworking will bring excessive fines to the surface and may result in crazing .

However, care is needed during mixing, placing, and finishing to prevent the development of fiber balls, the on-site addition of water to the concrete, and the possibility of visible fibers at the surface of the concrete .

5.1 Workability ( Con )

6.1 Mechanical Properties of FRC :Compressive Strength The presence of fibers may alter the failure mode of cylinders, but the fiber effect will be minor on the improvement of compressive strength values ( 0 to 15 percent ) .

: Modulus of ElasticityModulus of elasticity of FRC increases slightly with an increase in the fibers content. It was found that for each 1 percent increase in fiber content by volume there is an increase of 3 percent in the modulus of elasticity.

6.1 Mechanical Properties of FRC ( Con )Flexure : The flexural strength was reported to be increased by 2.5 times using 4 percent fibers.

Toughness :For FRC, toughness is about 10 to 40 times that of plain concrete.

Splitting Tensile : The presence of 3 percent fiber by volume was reported to increase the splitting tensile strength of mortar about 2.5 times that of the unreinforced one.

6.1 Mechanical Properties of FRC ( Con ) Impact Resistance :The impact strength for fibrous concrete is generally 5 to 10 times that of plain concrete depending on the volume of fiber .

: Corrosion of Steel FibersA 10-year exposure of steel fibrous mortar to outdoor weathering in an industrial atmosphere showed no adverse effect on the strength properties. Corrosion was found to be confined only to fibers actually exposed on the surface. Steel fibrous mortar continuously immerse in seawater for 10 years exhibited a 15 percent loss compared to 40 percent strength decrease of plain mortar , Ref (2).

7.1 Structural Behavior of FRCFlexure :The use of fibers in reinforced concrete flexure members increases ductility, tensile strength, moment capacity, and stiffness. The fibers improve crack control and preserve post cracking structural integrity of members.

Torsion : The use of fibers eliminate the sudden failure characteristic of plain concrete beams. It increases stiffness, torsional strength, ductility, rotational capacity, and the number of cracks with less crack width.

Shear : Addition of fibers increases shear capacity of reinforced concrete beams up to 100 percent. Addition of randomly distributed fibers increases shear-friction strength, the first crack strength, and ultimate strength .

7.1 Structural Behavior of FRC (Con )Column : The increase of fiber content slightly increases the ductility of axially loaded specimen. The use of fibers helps in reducing the explosive type failure for columns.

High Strength Concrete : Fibers increases the ductility of high strength concrete. The use of high strength concrete and steel produces slender members. Fiber addition will help in controlling cracks and deflections.

Cracking and Deflection : Tests shown that fiber reinforcement effectively controls cracking and deflection, in addition to strength improvement. In conventionally reinforced concrete beams, fiber addition increases stiffness, and reduces deflection , Ref (2 ).

8.1 Mix deign As the steel fiber reinforcement concrete ( SFRC )is more used , I show here after the mix design of SFRC to give idea on the mix design .

Mix Design for SFRC :

Typical mix proportions for SFRC will be: cement 325 to 560 kg; water-cement ratio 0.4- 0.6; ratio of fine aggregate to total aggregate 0.5-1.0; maximum aggregate size 10mm; air content 6-9%; fiber content 0.5-2.5% by volume of concrete. Ref (4)

8.1 Mix design ( Con )

Table .2 Mix Proportions for (M20) Grade for steel fiber , Ref. ( 5 )

9.1 Comparative Study of the Mechanical Behavior of SFRC

Materials : Table -3 shows the different properties of the straight and the hooked fibers used in ( SFRC ) Ref (2).

Mix design : mix proportion was cement : aggregate : sand , 1.0 : 2.0 :1.6 and the water- cement ratio was 0.44 .

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9.1 Comparative Study of the Mechanical Con ) ) Behavior of SFRC

Table .3 the different properties of the straight and the hooked fibers used in this study Ref. ( 2 )

9.1 Comparative Study of the Mechanical Behavior of SFRC ( Con )

Fig .11 straight steel fiber , Ref. alibaba.comFig .12 hooked steel fiber , Ref. alibaba.com


Workability :

The hooked fibers performed well during mixing because no balling occurred even though the fibers were added to the mixer along with the aggregate all at one time. The straight fibers had to be sprinkled into the mixer by hand to avoid balling . It took approximately 2 minutes to add the straight fibers to the mix . resulting in a 2 minutes extra mixing time. Figure-13 shows the effect of fiber content on both slump and inverted cone time.

It is clearly seen that as the fiber content increased from 0.0 to 2.0 percent, the slumps value decreased from 230 to 20 mm, and the time required to empty the inverted cone time increased from 20 to 70 second's. For the highest fiber volume percentage used ( Vf = 2.0 percent) it was noticed that the FRC in the test specimens was difficult to consolidate using the internal vibrator.


Fig .13 Effect of fiber content on workability Ref . ( 2 )


Modulus of Elasticity :

Fig- 14 shows that the initial slope of the stress-strain curve is practically the same for all mixes and equal to 31,900 MPa compared to 30,400 MPa obtained using the ACI formula. This indicates that the modulus of elasticity does not change much by the addition of fibers.


403530251520 10 500.0030.0060.0090.0120.0150.0 % 0.5% 1.0% 1.5% 2.0%COMPRESSIVE STRAINCompressive Strength (Mpa )Fig .14 Effect of hooked fiber content on compressive stress-strain curves (28 days) , Ref. ( 2 )


Compressive Strength :Fig-14 shows the effect of the hooked fiber content on the compressive strength values and shows the stress-strain relationship. The fiber addition had no effect on the compressive strength values , However, the brittle mode of failure with plain concrete was transformed into a more ductile one with the increased addition of fibers , see Figure- 15 .

Flexural TestModulus of Rupture :Fig -16 shows the effect of hooked fiber content on flexural strength after 7, 28 and 90 days. The addition of 1.5 p rcent of hooked fibers gives the optimum increase of the flexural strength. It increased the flexural strength by 67 percent, whereas the addition of 2.0 percent straight fiber gives the optimum increase of the flexural strength by 40 percent more than that of the plain concrete .


Fig .15 Effect of hooked fiber content on compressive strength at different ages Ref. ( 2 )


Fig .16 Effect of hooked fiber content on flexural .-strength at different ages Ref. ( 2 )


Splitting Tensile Strength :Fig -17 shows the effect of hooked fiber addition on the splitting tensile strength. It is clear that the highest improvement is reached with 1.5percent fiber content (57 content more than plain concrete) .


Fig .17 Effect of hooked fiber content on splitting tensile strength at different ages Ref . ( 2 )


Table 4. Comparison of strengths using hooked and straight fibers (7 days) Ref ( 2 )


Toughness (Energy Absorption) :

Toughness as defined by the total energy absorbed prior to complete separation of the specimen is given by the area under load-deflection curve. Toughness or energy absorption of concrete is increased considerably by the addition of fibers. The toughness index is calculated as the area under the load deflection curve (Fig- 18) up to the 1.8mm deflection divided by the area up to the first crack strength (proportional limit). The calculated toughness index for each mix is given in Table 3.The addition of fiber increases the toughness index of hooked and straight fibers up to 19.9 and 16.9, respectively .The average toughness index for specimens reinforced with hooked fibers was 25 to 65 percent greater than that for specimens reinforced with straight fibers .


Fig .18 Load-deflection curves for straight fibers Ref. ( 2 )


Table .5 Effect of fiber content on the toughness index Ref. ( 2 ) Toughness IndexFiber content(%) Straight fibersHooked fibers1.01.00.09.211.40.511.118.01.013.619.91.516.916.72.0

9.1 Comparative Study of the Mechanical Behavior of SFRC ( Con ) Impact Strength :

The results of impact test are given in Fig- 19. The rest results show that the impact strength increases with the increase of the fiber content. Use of 2 percent hooked fiber increased the impact strength by about 25 times compared to 10 times given in literature .

9.1 Comparative Study of the Mechanical Behavior of SFRC ( Con )Fig .19 Effect of hooked fiber content on the impact strength Ref. ( 2 )Number of BlowsFIBER CONTANT (Vf %)

10.1 Comparative between FRC and Plain concrete Table .5 Comparative between FRC and Plain concrete Ref. ( 2 )Normal Reinforced concreteFiber Reinforced ConcreteLower DurabilityHigh DurabilitySteel potential to corrosionProtect steel from CorrosionHeavier material Lighter materialsWith the same volume, the strength is lessWith the same volume, the strength is greaterHigh workability as compared to FRC.Less workability

11.1 Comparison of cost between FRC and plain concrete FRCPC171$ + 16$ = 187 $ FOR STEEL FIBERS 171$ for 20 MPA

Table -7 Comparison of cost between FRC and plain concrete Ref.oceanconcrete.com

12.1 Analysis of construction cost example Cost of road construction for Normal mix Length of road = 75 mt , Width of road = 7.5 mt , Slab thickness = 37 cmThe total concreting work to be done in m3 = 75 x 7.5 x 0.37 = 208.13 m3As per the India rates cost of construction of 1 m3 of cement concrete road is 11.3 USD So the cost of construction of this road is = 208.13 x 11.3 = 2351.869 USD

Cost of road construction of 1% steel fibers mix L = 75 mt , W = 7.5 mt , H = 33.5 cmSo total concreting work to be done in m3 = 75*7.5*0.335 = 188.13 m3 So the cost of construction of this road is = 188.13 x 11.3 = 2132.649 USD Difference in cost of construction = 2351.869 -2132 .649 = 219.22 USDSo the saving in cost of construction by adding 1% steel fiber in concrete mix is 9.6%.

13.1 Advantages of FRCHigh modulus of elasticity for effective long-term reinforcement, even in the hardened concrete.

Does not rust nor corrode and requires no minimum cover.

Ideal aspect ratio (i.e. relationship between Fiber diameter and length) which makes them excellent for early-age performance.

Greater retained toughness in conventional concrete mixes.

Higher flexural strength, depending on addition rate.

Can be made into thin sheets or irregular shapes.

FRC possesses enough plasticity to go under large deformation once the peak load has been reached.

14.1 Disadvantages of FRC

Greater reduction of workability.

High cost of materials.

15.1 Conclusion Concrete has better resistance in compression while steel has more resistance in tension . Conventional concrete has limited ductility, low impact and abrasion resistance and little resistance to cracking. A good possess high strength and low permeability. Hence, alternative Composite materials are gaining popularity because of ductility and strain hardening. To improve the post cracking behavior, short discontinuous and discrete fibers are added to the plain concrete. Addition of fibers improves the post peak ductility performance, pre-crack tensile strength, fracture strength, toughness, impact resistance, flexural Strength resistance, fatigue performance etc. The ductility of fiber reinforced concrete depends on the ability of the fibers to bridge cracks at high levels of strain.

:Reference 1- Application of Fiber Reinforced Concrete (FRC) , Prepared by - Mustafa K. Sonasath CEPT University .

2- Properties and Applications of Fiber Reinforced Concrete , FAISAL FOUAD WAFA , Associate Professor, Civil Engineering Department , Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia .

3- Progress in Concrete Technology , Fiber Reinforced Concrete (FRC) , Professor Kamran M. Nemati ,Winter Quarter 2015 , Washington University . 4- FIBER REINFORCED CONCRETE- BEHAVIOUR PROPERTIES AND APPLICATION , Dr. M. C. Nataraja , Professor of Civil Engineering, Sri Jayachamarajendra College of engineering .

5- Mix Design of Fiber Reinforced Concrete Mr. Nikhil A. Gadge , Prof. S. S. Vidhale (FRC) Using Slag & Steel Fiber , Maharashtra, India .

6- State-of-the-Art Report on Fiber Reinforced Concrete Reported by ACI Committee 544 ( 2002 )

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