technical seminar on fibre reinforced sprayed concrete for srmeg

8/2/2019 Technical Seminar on Fibre Reinforced Sprayed Concrete for SRMEG

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By Gan Cheng Chian,

Bekaert Singapore Pte Ltd

Society for Rock Mechanics & Engineering Geology, SingaporeTechnical Seminar on Fiber Reinforced Sprayed ConcreteState of the Art, Specifications, and Standards


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- Fibre reinforced sprayed concrete (FRS) is a mortar orconcrete containing discontinuous steel or synthetic fibres ,which are pneumatically projected at high velocity onto asurface

Fibre Reinforced Sprayed Concrete Properties


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Micro synthetic Fibres



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multifilament fibrillated

fibre section(s)

# fibres (mio/kg) 200 300 10 - 20specific area (m/kg) 200 300 40 - 80


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Macro synthetic Fibres


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- Modulus of Young reinforcing ability of the material STEEL = 210 000 MPa POLYPROPYLENE = 3000 5000 MPa CONCRETE = 30 000 MPa

- Tensile strength reinforcing ability of the material STEEL = 1000 2000 MPa POLYPROPYLENE = 300-600 MPa CONCRETE = 0 MPa

- Specific density STEEL = 7850 kg/m POLYPROPYLENE = 910 kg/m CONCRETE = 2400 kg/m WATER = 1000 kg/m Contra: PP fibres float on water



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Spalling of concrete

= When concrete is beingexposed to fire, small or evenbig pieces are blown of


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Fire

Saturated layer ofwater + vapour

Vapour pressure front

Heatfront

Exposed to fire, the water at the heat front evaporates

this vapour willmove towards the cold front and will be absorbed in the voids saturatedlayer when this layer cannot move fast enough, the heat front will reachthis saturated front creation of higher vapour pressure will lead to spalling


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- How to avoid spalling of concrete? adding monofilament PP fibres: these will melt (165C) and create high

amount of channels the vapour pressure can escape more easily nospalling

adding steel fibres: these will not prevent spalling but will hold the piecestogether


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Micro SyntheticFibre

ReinforcedConcrete

Steel FibreReinforced

Concrete

strength and toughness ***

energy absorption ***resistance to plastic shrinkage ***

Freeze-thaw resistance ***resistance to spalling in a fire *** *

impact resistance * ***resistance to drying shrinkage ***structural reinforced concrete ***

Micro synthetic fibres = non-structural ; Macro synthetic & steel fibres = structuralMicro synthetic fibres can never replace macro synthetic or steel fibresHowever, they can be complementary


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Steel fiber characteristics

- Length and diameter: aspect ratio (L/d)

- Shape of the fiber, or the anchorage

- Strength of the fiber

- Strength of the matrix (concrete)



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Steel fiber characteristics

Small fiber section1. More fibers per kilo

2. Shorter distance between the fibers networkingeffect

3. More contact surface steel/ concrete per unitweight

Fiber length 1. Bridge the crack

2. Overlap 2 aggregates

3. Workabilty : pumping, and hose diameter



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The quality of FRSis due to a combination of factorsA high length-diameter ratio (L/D ratio)

Controlled pull-out (due to deformation of the hook)

High tensile strength steel

Hooked ends

A system of glued fibre bundles enables fibres with ahigh L/D ratio to be mixed easily and uniformlythroughout the concrete



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Concrete spalling is excluded

Spalling of concrete caused by rusting reinforcement bars isphysically impossible with fibre reinforcement concrete due to :

- small fibre diameter- non continuous reinforcement- high surface / volume ratio.

This type of damage is not possible with FRS



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Properties of SFRS

- Steel fibres are incorporated in the concrete to improve:

the ductility the energy absorption the crack resistance the impact resistance

- Modern tunnelling methods include mobilising the strength of the ground by promoting ductility of the lining



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Sprayed Concrete

high initial strength for a good bond to the rock

ductility to absorb and block rock movement

safe working conditions

faster job progress


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Steel or macro synthetic fibres

provide a better bond due to a higher crackresistance

a high degree of ductility

incorporated reinforcement reducing the cycle

time and increasing the safety for the tunnellingcrew


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Mesh Reinforced Sprayed ConcreteMesh installation is:

difficult

time consuming

hazardous under loose rock

costly



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Mesh Reinforced Sprayed ConcreteSprayed concrete consumption is high due to:

irregular rock surface

filling up voids

high rebound on the mesh wires



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Fiber Reinforced Sprayed ConcreteAdvantages of a FRS layer:

Homogeneous reinforcement

Can be applied very quickly

A uniform thickness results in a

significant reduction of sprayed concreteconsumption

Strong bond to the surface which isrequired to make the underground self

supporting



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Rebound- REBOUND

- Wet sprayed concrete (no silica fume): 15-20%

- Dry sprayed concrete: 20-50%

- Silica fume : improves bond Rebound: 5-7% on vertical wall; 10-12% on ceiling Typical dosage: 6-8% cement weight: makes the sprayed concrete not

too strong

- Accelerator (AF) High early strength Improves the bond Increases rebound if overdose



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L/150 =3 mm

Ffct,eq,150

FF/2 F/2

L/3 L/3 L/3

Characterisation of FRS1. Beam test2. Efnarc panel test

fe150 = F fct,eq,150 . L / (b.h) in MpaRe3 = F fct,eq,150 /F o in %

L = 450 mmb = 150 mmh = 150 mm

h

F0

Fibre Reinforced Sprayed Concrete Design


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Re3 = 50%

Re3 = 100%P

P

0

10

20

30

40

50

60

70

80

90

10 15 20 25 30 35 40 45 50 55

dosage (kg/m)

R e 3

( % )

RC-65/35-BN

RL-45/30-BN

L=35; d=0.55

L=30; d=0.62



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Efnarc toughness classification:

500 J: min. requirement; rock; small diameter tunnel700 J: standard; less good rock1000 J: high ductility for bad soil condition

500mm

600mm

500mm600mm

100x100mm

F

deflection

25mm

load



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Efnarc panel test

European standardEN 14488-5

The punching-flexion test is an ideal testto check the FRS behaviour:

1) A sprayed concrete tunnel ling

behaves like a slab2) The hyperstatic test conditions allow

load redistribution

3) The test can be carried out withmesh reinforcement

This test is introduced in 1989 by theFrench railway, and is in themeantime accepted by Efnarc , andis proposed in CEN 104 Shotcrete.


Fib R i f d S d C t D ig


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Efnarc panel test



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Fib R i f d S d C t D i


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1 mesh reinforced layer versus fibre reinforced sprayed concrete layer

Design of 1 mesh reinforced layer




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Design of steel fibre reinforcedsprayed concrete layer


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Fibre Reinforced Sprayed Concrete QA/QC


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FIBRE COUNTER

1

2 3 4

Fibre Reinforced Sprayed Concrete QA/QC


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technical seminar on fibre reinforced sprayed concrete for srmeg

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