Fiber Reinforced Concrete (FRC)

Contents

Introduction

Benefits of FRC

Toughening Mechanism

Factor affecting the properties of FRC

Comparison of Mix Proportion of FRC and Plain Concrete

Type of fibers

Steel Fiber Reinforced Concrete (SFRC)

Structural behavior & Durability of SFRC

Problems with SFRC

Application Of FRC

Conclusion

Introduction to Fiber Reinforced Concrete

Concrete containing a hydraulic cement, water ,

aggregate, and discontinuous discrete fibers is

called fiber reinforced concrete.

Fibers can be in form of steel fiber, glass fiber,

natural fiber , synthetic fiber.

Benefits of FRC

Main role of fibers is to bridge the cracks that develop in concrete and increase the ductility of concrete elements.

Improvement on Post-Cracking behavior of concrete Imparts more resistance to Impact load controls plastic shrinkage cracking and drying

shrinkage cracking Lowers the permeability of concrete matrix and thus

reduce the bleeding of water

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

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 (HPFRC)

Aspect Ratio of fiber

It is defined as ratio of length of fiber to it’s diameter (L/d).

Increase in the aspect ratio up-to 75,there is increase in relative strength and toughness.

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

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.

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

Comparison of Mix Proportion between Plain Concrete and Fiber Reinforced ConcreteMaterial Plain concrete Fiber reinforced

concrete

Cement 446 519

Water (W/C=0.45) 201 234

Fine aggregate 854 761

Coarse aggregate 682 608

Fibers (2% by volume) -- 157

The 14-days flexural strength, 8 Mpa, of the fiber reinforced was about 20% higher than that of plain concrete.

Source: Adapted from Hanna, A.N., PCA Report RD 049.01P, Portland cement Association, Skokie, IL, 1977

Types of fiber used in FRC

Steel Fiber Reinforced Concrete Polypropylene Fiber Reinforced (PFR) concrete Glass-Fiber Reinforced Concrete Asbestos fibers Carbon fibers and Other Natural fibers

Contd.

Type of fiber Tensile strength(Mpa)

Young’s modulus

(x103Mpa)

Ultimate elongation

(%)

Steel 275-2757 200 0.5-35

Polypropylene 551-690 3.45 ~25

Glass 1034-3792 ~69 1.5-3.5

Nylon 758-827 4.14 16-20

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

Steel Fiber Reinforced Concrete

Diameter Varying from 0.3-0.5 mm (IS:280-1976) Length varying from 35-60 mm Various shapes of steel fibers

Advantage of Steel fiber

High structural strength Reduced crack widths and control the crack widths

tightly, thus improving durability less steel reinforcement required Improve ductility Reduced crack widths and control the crack widths

tightly, thus improving durability Improve impact– and abrasion–resistance

Structural Behavior of Steel Fiber Reinforced Concrete

Effect on modulus of rupture Effect of compressive strength Effect on Compressive strength & tensile Strength at

fire condition i.e. at elevated temperature

Durability

Resistance against Sea water (In 3% NaCl by weight of water) Maximum loss in compressive strength obtained was

about 3.84% for non-fibered concrete and 2.53% for fibered concrete

Resistance against acids (containing 1% of sulfuric acid by weight of water) Maximum loss in compressive strength obtained was

found to be about 4.51% for non-fibered concrete and 4.42% for fiber concrete

Problems with Steel Fibers

Reduces the workability; loss of workability is proportional to volume

concentration of fibers in concrete Higher Aspect Ratio also reduced workability

Application of FRC in India & Abroad

More than 400 tones of Steel Fibers have been used recently 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 is 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.

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.