Fibre Reinforced Concrete

Application of Fiber Reinforced Concrete (FRC)

Prepared by - Mustafa K. SonasathCEPT UniversityPT-301513

Contents History. Introduction. Why Fibers are used? Toughening Mechanism. Type of fibers. Mechanical properties of FRC. Structural behavior of FRC. Factors affecting properties of FRC. Advantages and Disadvantages of FRC. Applications of FRC. Case Study. Conclusion. References.

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

Horsehair was used in mortar and straw in mud bricks.

Abestos fibers were used in concrete in the early 1900.

In the 1950s, the concept of composite materials came into picture.

Steel , Glass and synthetic fibers have been used to improve the properties of concrete for the past 30 or 40 years.

Research into new fiber-reinforced concretes continues even today.

History

Introduction

Concrete containing cement, water , aggregate, and discontinuous, uniformly dispersed or discrete fibers is called fiber reinforced concrete.

It is a composite obtained by adding a single type or a blend of fibers to the conventional concrete mix.

Fibers can be in form of steel fibers, glass fibers, natural fibers , synthetic fibers, etc.

Why Fibres are used? Main role of fibers is to bridge the cracks that develop in

concrete and increase the ductility of concrete elements. There is considerable improvement in the post-cracking

behavior of concrete containing fibers due to both plastic shrinkage and drying shrinkage.

They also reduce the permeability of concrete and thus reduce bleeding of water.

Some types of fibers produce greater abrasion and shatter resistance in concrete.

Imparts more resistance to Impact load.

Toughening mechanism

Toughness is ability of a material to absorb energy and plastically deform without fracturing.

It can also be defined as resistance to fracture of a material when stressed.

Contd.

Reference: Cement & Concrete Institutehttp://www.cnci.org.za

Contd.

Source: P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials, Third Edition, Fourth Reprint 2011

Types of Fibers:Steel fibers Glass fibers

Carbon Fibers Cellulose Fibers

Synthetic Fibers:Nylon FibersPolypropylene

Fibers

Natural Fibers:Coir Hay

Steel fibers

Aspect ratios of 30 to 250. Diameters vary from 0.25 mm to 0.75 mm. High structural strength. Reduced crack widths and control the crack widths tightly,

thus improving durability. Improve impact and abrasion resistance. Used in precast and structural applications, highway and

airport pavements, refractory and canal linings, industrial flooring, bridge decks, etc.

Glass Fibers

High tensile strength, 1020 to 4080 N/mm2

Generally, fibers of length 25mm are used. Improvement in impact strength. Increased flexural strength, ductility and resistance to

thermal shock. Used in formwork, swimming pools, ducts and roofs, sewer

lining etc.

Synthetic fibers Man- made fibers from petrochemical and textile industries. Cheap, abundantly available. High chemical resistance. High melting point. Low modulus of elasticity. It’s types are acrylic, aramid, carbon, nylon, polyester,

polyethylene, polypropylene, etc. Applications in cladding panels and shotcrete.

Natural fibers

Obtained at low cost and low level of energy using local

manpower and technology.

Jute, coir and bamboo are examples.

They may undergo organic decay.

Low modulus of elasticity, high impact strength.

Types of Fibers

Types Tensile Strength Young's ModulusUltimate

Elongation Specific Gravity

( Mpa ) ( 103 Mpa ) ( % )

Steel 275 - 2758 200 0.5 - 35 2.50

Glass 1034 - 3792 69 1.5 - 3.5 3.20

Asbestos 551 - 965 89 - 138 0.60 1.50

Rayon 413 - 520 6.89 10 - 25 1.50

Cotton 413 - 689 4.82 3 -10 1.10

Nylon 858 - 827 4.13 16 - 20 0.50

Polypropylene 551 - 758 3.45 24 1.10

Acrylic 206 - 413 2.06 25 - 45 0.90

Mechanical Properties of FRC Compressive StrengthThe 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. FlexureThe flexural strength was reported to be increased by 2.5 times using 4 percent fibers.

Splitting Tensile StrengthThe 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. ToughnessFor FRC, toughness is about 10 to 40 times that of plain concrete. Fatigue StrengthThe addition of fibers increases fatigue strength of about 90 percent. Impact ResistanceThe impact strength for fibrous concrete is generally 5 to 10 times that of plain concrete depending on the volume of fiber.

Structural behaviour of FRC FlexureThe 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. TorsionThe 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. High Strength ConcreteFibers increases the ductility of high strength concrete. Fiber addition will help in controlling cracks and deflections.

ShearAddition of fibers increases shear capacity of reinforced concrete beams up to 100 percent. Addition of randomly distributed fibers increases shear-friction strength and ultimate strength. ColumnThe 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. Cracking and DeflectionTests have 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.

Factors affecting the Properties of FRC Volume of fibers Aspect ratio of fiber Orientation of fiber Relative fiber matrix stiffness

Volume of fiber

Low volume fraction(less than 1%) Used in slab and pavement that have large exposed

surface leading to high shrinkage cracking. Moderate volume fraction(between 1 and 2 percent)

Used in Construction method such as Shortcrete & in Structures which requires improved capacity against delamination, spalling & fatigue.

High volume fraction(greater than 2%) Used in making high performance fiber reinforced

composites.

Contd.

Source: P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials, Third Edition, Fourth Reprint 2011

Aspect Ratio of fiber It is defined as ratio of length of fiber to it’s diameter

(L/d). Increase in the aspect ratio upto 75, there is increase

in relative strength and toughness. Beyond 75 of aspect ratio, there is decrease in aspect

ratio and toughness.Type of

concreteAspect ratio Relative

strengthRelative

toughness

Plain concrete with

randomlyDispersed fibers

0 1.0 1.025 1.50 2.050 1.60 8.075 1.70 10.50100 1.50 8.50

Orientation of fibers

Aligned in the direction of load Aligned in the direction perpendicular to load Randomly distribution of fibers

It is observed that fibers aligned parallel to applied load offered more tensile strength and toughness than randomly distributed or perpendicular fibers.

Load direction Load Direction

Parallel Perpendicular Random

Relative fiber matrix

Modulus of elasticity of matrix must be less than of fibers for efficient stress transfer.

Low modulus of fibers imparts more energy absorption while high modulus fibers imparts strength and stiffness.

Low modulus fibers e.g. Nylons and Polypropylene fibers.

High modulus fibers e.g. Steel, Glass, and Carbon fibers.

Advantages of FRC High 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.

Easily placed, Cast, Sprayed and less labour intensive than placing rebar.

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.

Disadvantages of FRC

Greater reduction of workability. High cost of materials. Generally fibers do not increase the flexural strength of

concrete, and so cannot replace moment resisting or structural steel reinforcement.

Applications of FRC Runway, Aircraft Parking, and Pavements.For the same wheel load FRC slabs could be about one half the thickness of plain concrete slab. FRC pavements offers good resistance even in severe and mild environments.It can be used in runways, taxiways, aprons, seawalls, dock areas, parking and loading ramps. Tunnel Lining and Slope Stabilization Steel fiber reinforced concrete are being used to line underground openings and rock slope stabilization. It eliminates the need for mesh reinforcement and scaffolding. Dams and Hydraulic StructureFRC is being used for the construction and repair of dams and other hydraulic structures to provide resistance to cavitation and severe erosion caused by the impact of large debris.

Thin Shell, Walls, Pipes, and ManholesFibrous concrete permits the use of thinner flat and curved structural elements. Steel fibrous shortcrete is used in the construction of hemispherical domes. AgricultureIt is used in animal storage structures, walls, silos, paving, etc. Precast Concrete and ProductsIt is used in architectural panels, tilt-up construction, walls, fencing, septic tanks, grease trap structures, vaults and sculptures.

CommercialIt is used for exterior and interior floors, slabs and parking areas, roadways, etc. Warehouse / IndustrialIt is used in light to heavy duty loaded floors. ResidentialIt includes application in driveways, sidewalks, pool construction, basements, colored concrete, foundations, drainage, etc.

Fiber Reinforced Concrete Normal Reinforced concrete

• High Durability • Lower Durability• Protect steel from Corrosion • Steel potential to corrosion

• Lighter materials • Heavier material • More expensive • Economical• With the same volume, the

strength is greater• With the same volume, the

strength is less

• Less workability • High workability as compared to FRC.

Application of FRC in India & Abroad More than 400 tones of Steel Fibers have been used in the

construction of a road overlay for a project at Mathura (UP). A 3.9 km long district heating tunnel, caring heating

pipelines from a power plant on the island Amager into the center of Copenhagen, is lined with SFC segments without any conventional steel bar reinforcement.

Steel fibers are used without rebars to carry flexural loads at a parking garage at Heathrow Airport. It is a structure with 10 cm thick slab.

Precast fiber reinforced concrete manhole covers and frames are being widely used in India.

Case Study

Providing and laying 40 mm steel fibre reinforced cement concrete in pavement (in panels having area not more than 1.5 sqm) consisting of steel fibre @ 40kg per cubic meter of concrete and cement concrete mix of 1:1.95:1.95 over existing surface.

Since in the executed item, the thickness was to be restricted, the stone aggregates used were of 10 mm size and below however, in case of the concrete of more than 75 mm thickness, stone aggregates of 20 mm grading can be used.

The fibre reinforced concrete has been provided in small panels considering the workability.

Pavement with steel fibre reinforced concrete

ExperimentAim: To understand the effect of incorporation of

polypropylene and steel fibers together in the hardened state of concrete.

Material Specification:

Cement Type: Ordinary Portland Cement (OPC) Grade: 53 Fine Aggregates:

Source: Sabarmati River (Gandhinagar) Grading: Zone-II

Coarse Aggregates: Size: 10mm (maximum) Specific Gravity: 2.79 Water Absorption: 1.19 %Admixture: Name: Sikament NN (SP) Type: Super Plasticizer

Steel Fibres: Type = SHAKTIMAN MSC 6050 Shape = Round Crimped Fiber Diameter = 0.60 mm Length = 50 mm Aspect ratio = 83.33 (Tolerance D/L= + 10 %) Tensile strength = 1100 N/mm2Polypropylene Fibres: Company = NINA Chemicals Pvt. Ltd. (Ahmedabad ) Type = FIBREMESH 150 E3 Shape = Monofilament Polypropylene Fibres Diameter = 0.08 mm Length = 12 mm Aspect ratio = 150

Following are the tables showing mix design for the 50 kg of Cement for different w/c ratiosW/c ratio 0.65 %

Cement 50 KgWater 32.5 LitersC.A. (10 mm) 169.32 KgF.A. 123.95 KgPPF (0.5%) 0.63 KgPPF (1.0%) 1.28 KgPPF (1.5%) 1.91 Kg

SF (0.6%) 6.69 KgSF (1.2%) 13.4 Kg

W/c ratio 0.5 %Cement 50 KgWater 25 LitersC.A. (10 mm) 117.72 KgF.A. 97.32 KgPPF (0.5%) 0.52 KgPPF (1.0%) 1.05 KgPPF (1.5%) 1.57 Kg

SF (0.6%) 5.49 KgSF (1.2%) 10.98 Kg

W/c ratio 0.42 %Cement 50 KgWater 23.8 LitersC.A. (10 mm) 107.62 KgF.A. 94.86 KgPPF (0.5%) 0.46 KgPPF (1.0%) 0.94 KgPPF (1.5%) 1.4 Kg

SF (0.6%) 4.9 KgSF (1.2%) 9.81 Kg

Mixing of polypropylene and steel fibres reinforced concrete:The sequence for casting is as follows for FRC:

50 % quantity of coarse aggregates PPF or SF or Both the fibres in 20% quantity Remaining 50% coarse aggregates Another PPF or SF or Both fibres in 20%

quantity 50% quantity of sand Another PPF or SF or Both fibres in 20%

quantity Remaining 50% quantity of sand Another PPF or SF or Both fibres in 20%

quantity Cement Remaining 20% of PPF or SF or Both fibres Water

Compressive strength

• Increase by 5-70%Only Steel fibers

• Reduction in strength due to balling effectOnly PP fibers

• Reduction in strength by 1-26% due to balling effect

Both steel and PP fibers

Increase in compressive strength of concrete:

Specimens without any fibers after compression test

Specimens with fibers after compression test

Tensile strength


• Increase by 5-50%Only PP fibers

• Increase by 60-200%Both steel and PP fibers

Increase in tensile strength of concrete:

Specimens without any fibers after split tensile test.

Specimens with fibers after slip tensile test.

Impact strength




Increase in impact strength of concrete:

Specimens without any fibers after compression test

Specimens with fibers after compression test

Shear strength




Increase in shear strength of concrete:

Specimens without any fibers after shear test.

Specimens with fibers after shear test.

Type of fiber

Percentage

Weight Per Cum of

concrete (Kg)

Cost per kg(Rs)

Cost per Cum of

concrete(Rs)

PPF (0.5%) 0.005 4.2 150 630

PPF (1.0%) 0.01 8.5 150 1275

PPF (1.5%) 0.015 12.73 150 1909

SF (0.6%) 0.006 44.62 50 2231

SF (1.2%) 0.012 89.37 50 4468.5

Cost analysis

GFRC project at Trillium BuildingWoodland Hills, California

Footbridge in Fredrikstad, Norway

SFRC used at Tehri Dam, Uttarakhand

Conclusion

The total energy absorbed in fiber as measured by the area under the load-deflection curve is at least 10 to 40 times higher for fiber-reinforced concrete than that of plain concrete.

Addition of fiber to conventionally reinforced beams increased the fatigue life and decreased the crack width under fatigue loading.

At elevated temperature SFRC have more strength both in compression and tension.

Cost savings of 10% - 30% over conventional concrete flooring systems.

References K.Srinivasa Rao, S.Rakesh kumar, A.Laxmi Narayana,

Comparison of Performance of Standard Concrete and Fibre Reinforced Standard Concrete Exposed To Elevated Temperatures, American Journal of Engineering Research (AJER), e-ISSN: 2320-0847 p-ISSN : 2320-0936, Volume-02, Issue-03, 2013, pp-20-26

Abid A. Shah, Y. Ribakov, Recent trends in steel fibered high-strength concrete, Elsevier, Materials and Design 32 (2011), pp 4122–4151

ACI Committee 544. 1990. State-of-the-Art Report on Fiber Reinforced Concrete.ACI Manual of Concrete Practice, Part 5, American Concrete Institute, Detroit,MI, 22 pp

Contd.

P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials, Third Edition, Fourth Reprint 2011, pp 502-522

ACI Committee 544, Report 544.IR-82, Concr. Int., Vol. 4, No. 5, p. 11, 1982

Hanna, A.N., PCA Report RD 049.01P, Portland Cement Association, Skokie, IL, 1977

Ezio Cadoni ,Alberto Meda ,Giovanni A. Plizzari, Tensile behaviour of FRC under high strain-rate,RILEM, Materials and Structures (2009) 42:1283–1294

Marco di Prisco, Giovanni Plizzari, Lucie Vandewalle, Fiber Reinforced Concrete: New Design Prespectives, RILEM, Materials and Structures (2009) 42:1261-1281