fibre reinforced cement composites

8/11/2019 FIBRE REINFORCED CEMENT COMPOSITES

1/51

1

BY

HARSHAVARDHAN A.K


2/51

2

Introduction

Concrete posses many desirable properties like

high compression strength and stiffness and

low thermal and electrical conductivity. But

two of its characteristics ie weak in tension and

brittleness at failure have limited its use for

various applications.

These limitations can be overcome by addingmaterials strong in tension to concrete

resulting in a composite material.


3/51

3

One of the ways is achieved by placing steel

bars in concrete , in region where concrete is

subjected to tension , what is calledReinforced Cement Concrete.

It still falls many desirable properties like

toughness, ductility, controlling of crackingand energy absorption. The above can be

solved be adding constituents to the concrete.

Short fibers of small diameter , that are eithermetallic or non metallic . The new improved

matrix is called Fiber Reinforced Cement

Composite


4/51

4

Definition:FRC is defined as composite material

which consists of conventional concrete

reinforced by randomly dispersed short lengthfibers of specific geometry , made of steel,

synthetic or natural fibers.

There are two types of reinforcement inconcrete , primary and secondary.

Primary reinforcement is provided for local

strengthening of cement concrete in tensionregion ,where as secondary reinforcement are

needed to improve the structural quality and

also the inherent flexural strength of concrete.


5/51

5

Plain concrete has very low tensile strength

and causes tensile cracks in concrete. And alsolow strain at failure and brittleness of concrete

with less ductility in case of high strength

concrete.Secondary reinforcement is the approach to

modify the brittleness properties of concrete.

The fibers are capable of carrying load across

the crack.


6/51

6

Matrix materials: Matrix materials consists of

Plain portland cement

Cement with additives such as soil, fly ash or

condensed silica fumes.

Mortar containing cement and fine

aggregates.

Concrete containing cement , fine and

coarse aggregates.


7/51

7

contd/-

Addition of fibers to the concrete reduces its

workability. In order to keep the water cementratio within reasonable limits of not affecting

the compressive strength but still to achieve

the workability, water reducing admixtures areadded to the fiber reinforced composite. In

addition mineral admixtures like fly ash and

silica fume are added. Silica fume is added to

achieve high strength matrix. Fly ash is used to

improve the workability.


8/51

8

Major advantages of FRC

Resistance to micro cracking

Toughness and post-failure ductility

Impact resistance

Resistance to fatigue

Improved strength in shear , tension ,flexure ,

and compression Reduced permeability


9/51

9

Types of fibers used in cement

concrete

Metallic fibres

Polymeric fibres

Mineral fibres

Natural fibres


10/51

10

Parameters influencing the properties

of FRC

Types of fibers

Relative Fiber Matrix Stiffness

Aspect Ratio of the Fibers Orientation of Fibers

Workability and Compaction of

Concrete Size of Coarse Aggregate


11/51

11

Some of the other properties are:

Tensile strength significantly higher than that

of concrete Bond strength with concrete matrix preferably

same order or as higher than tensile strength of

matrix. The elastic modulus in tension is higher than

that of concrete.

The poissons ratio and the coefficient ofthermal expansion should preferably be of the

same as that of the matrix


12/51

12

Metallic fibres: metallic fibres are either made

of carbon steel or stainless steel. It is referred

to as steel fibres.Steel fibres are considered as the structural

fibres, as they enhances the strength of a

structure to a great extent.The properties of steel fibres are:

Improved flextural toughness

Impact resistance

Flextural fatigue endurance


13/51

13

Tensile strength varies from 345MPa -1380MPa

Modulus of elasticity is about 200GPa

Their aspect ratio is generally less than 100,with

common range of 40 to 80.

Most steel fibres found in round section and thediameter varies from 0.4 to 0.8mm and the

length ranging from 25 to 60mm


14/51

14


15/51

15


16/51

16


17/51

17


18/51

18


19/51

19

Polymeric fibres:polymeric fibres are

byproducts of petrochemicals and textile

industries. The different types are

Aramid

Acrylic

Nylon

Polyester

Polyethlene polypropylene


20/51

20

Fibre

type

Effective

Diameter

x10-3

Specific

gravity

Tensile

Strength

(MPa)

Elastic

Modulus

(GPa)

Ultimate

Elongatio

n

(%)

Acrylic 13-104 1.17 207-

1000

14.6-

19.6

7.5-

50.0

Aramid 10 1.44 3620 117 2.5

Nylon - 1.16 9.65 5.17 20

Polyster - 1.34-

1.39

896-

1100

17.5 -

Polyethyl

ene

25-

1020

0.96 200-300 5.0 3.0

Polypropy

lene

- 0.9-0.91 310-760 3.5-4.9 15


21/51

21


22/51

22


23/51

23


24/51

24


25/51

25


26/51

26

Mineral fibres: Glass fibre is referred as mineral

fibre. Glass fibres are silica based glass

compounds that contain several metal oxides .These fibres have high tensile strength and

modulus of elasticity compared to polymeric

fibres . They are quite economical and hence

they are most commonly used fibres for

practical applications. They are classified as

A-glass (soda lime silica glass)

E-glass (borosilicate glass)

A-R glass (alkaline resistant glass, ph>12.5)

Chemical composition are discussed


27/51


28/51

28

Physical properties of some selected glass fibre

Property A-Glass E-Glass AR-Glass

Specific

Gravity 2.46 2.54 2.7

Tensile strength

(MPa)

3030 3450 2480

Modulus of

Elasticity(MPa)

64800 71700 80000

Strain at

ultimate(%)

4.7 4.8 3.6


29/51

29


30/51

30


31/51

31


32/51

32


33/51

33


34/51

34


35/51

35

Natural fibres: these are naturally obtaining

fibres extracted from plants in cement based

composites. The unique aspect of these fibres

is low energy needed for their extraction.


36/51

36

property

coconut Sisal Sugar

Cane

Bambo

o

Jute Elephant

grass

Wood

Fibre

Fibre length 50-

350

- - - 180-300

- 2.5-5

Fibre dia

(mm) 0.1-0.4 - 0.2-0.4 0.05-0.4 0.1-0.2 - 0.015-0.08Modulus of

elasticity(Gpa)19-36 13-26 15-

19

33-

40

26-

32

4.9 -

Tensilestrength(MPa)

120-200

280-568

170-290

350-500

250-350

178-700

700

Water

absorption(%)130-

180

60-70 70-

75

40-

45- - 50-75


37/51

37

Carbon fibres: carbon fibres are the most

expensive of all fibres discussed till now .

This is due to the increased cost of theirmanufacturing process as well as the increased

cost of raw materials required for their

manufacture.Carbon fibres have high strength and modulus

comparable to that of steel . They are used for

manufacturing polyacrylonitrite (PAN), rayon.Modulus of elasticity is around 300GPa.

Tensile strength is around 5200MPa


38/51

38


39/51

39


40/51

40

Mechanical properties of FRC


41/51

41

Mechanical properties of FRC

Behaviour under compression


42/51

Behaviour under flexure


43/51

43

Behaviour under flexure

Behaviour under tension:


44/51

44

Behaviour under tension:


45/51

45

Applications:

Highway and airfield pavements

Industrial flooring Blast resistant structures

Hydraulic structures such as spillways and

sluiceways.

Plain and reinforced concrete

Trenchless construction

Protective lining

Roofing products


46/51

46

Under precast applications:

SFRC has been used for man hole covers

Precast slabs for structural applications

FRC with polymeric fibres has been used in

precast cladding panels for buildings.


47/51

47


48/51

48


49/51

49

Conclusion:synthetic fibres such as polyester

and polypropylene are cost effective as well as

reduces plastic and drying shrinkage , andpermeability in concrete. Also polymeric fibres

make the concrete structure and pavement

resistance to seismic loading as well throughits ductility.


50/51

50

References:

Construction journal of India

Proceedings of the International symposium on

FRC.

Fibre reinforced cementitious composites by

Dr Bentur.

www.google.com


51/51

Thank you

fibre reinforced cement composites

Documents