Society for Rock Mechanics & Engineering …

1 By Gan Cheng Chian,Bekaert Singapore Pte LtdSociety for Rock Mechanics & Engineering geology , SingaporeTechnical Seminar on Fiber Reinforced sprayed ConcreteState of the Art, Specifications, and Standards1-Fibre reinforced sprayed concrete (FRS)is a mortar or concrete containing discontinuous steel or synthetic fibres, which are pneumatically projected at high velocity onto a surfaceFibre Reinforced sprayed Concrete Properties2 Micro synthetic FibresFibre Reinforced sprayed Concrete Properties3 Fibre Reinforced sprayed Concrete Properties multifilament fibrillated fibre section(s) # fibres (mio/kg) 200 300 10 - 20 specific area (m /kg) 200 300 40 - 80 4 Fibre Reinforced sprayed Concrete PropertiesMacro synthetic Fibres5-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.

2 PP fibres float on waterFibre Reinforced sprayed Concrete Properties6 Fibre Reinforced sprayed Concrete PropertiesSpalling of concrete= When concrete is being exposed to fire, small or even big pieces are blown of7 Fibre Reinforced sprayed Concrete PropertiesFireSaturated layer of water + vapourVapour pressure frontHeat frontExposed to fire, the water at the heat front evaporates this vapour will move towards the cold front and will be absorbed in the voids saturated layer when this layer cannot move fast enough, the heat front will reach this saturated front creation of higher vapour pressure will lead to spalling8 Fibre Reinforced sprayed Concrete Properties-How to avoid spalling of concrete?

3 Adding monofilament PP fibres: these will melt (165 C) and create high amount of channels the vapour pressure can escape more easily no spalling adding steel fibres: these will not prevent spalling but will hold the pieces together9 Fibre Reinforced sprayed Concrete Properties Micro Synthetic Fibre Reinforced Concrete Steel Fibre Reinforced 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.

4 Macro synthetic & steel fibres = structural Micro synthetic fibres can never replace macro synthetic or steel fibres However, they can be complementary10 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)Fibre Reinforced sprayed Concrete Properties11 Steel fiber characteristicsSmall fiber fibers per distance between the fibers networking contact surface steel/ concrete per unit weightFiber the 2 : pumping, and hose diameterFibre Reinforced sprayed Concrete Properties12 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 steelHooked endsA system of glued fibre bundles enables fibres with a high L/D ratio to be mixed easily and uniformly throughout the concreteFibre Reinforced sprayed Concrete Properties13 Concrete spalling is excludedSpalling of concrete caused by rusting reinforcement bars is physically impossible with fibre reinforcement concrete due to.

5 - small fibre diameter- non continuous reinforcement- high surface / volume type of damage is not possible with FRSF ibre Reinforced sprayed Concrete Properties14 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 liningFibre Reinforced sprayed Concrete Properties15 Fibre Reinforced sprayed Concrete PropertiesSprayed Concretehigh initial strength for a good bond to the rockductility to absorb and block rock movementsafe working conditionsfaster job progress 16 Fibre Reinforced sprayed Concrete PropertiesSteel or macro synthetic fibresprovide a better bond due to a higher crack resistancea high degree of ductilityincorporated

6 Reinforcement reducing the cycle time and increasing the safety for the tunnelling crew17 Mesh Reinforced sprayed ConcreteMesh installation is: difficult time consuming hazardous under loose rock costlyFibre Reinforced sprayed Concrete Properties18 Mesh Reinforced sprayed ConcreteSprayed concrete consumption is high due to: irregular rock surface filling up voids high rebound on the mesh wiresFibre Reinforced sprayed Concrete Properties19 Mesh Reinforced sprayed ConcreteLining quality can be poor: sprayed concrete builds up on the face of the mesh Low quality shadow areas form behind the wire Not a uniform bond between sprayed concrete and rock Irregular mesh positions do not give an efficient reinforcement Fibre Reinforced sprayed Concrete Properties20 Fiber Reinforced sprayed ConcreteAdvantages of a FRS layer.

7 Homogeneous reinforcement Can be applied very quickly A uniform thickness results in a significant reduction of sprayed concrete consumption Strong bond to the surface which is required to make the underground self supportingFibre Reinforced sprayed Concrete Properties21 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 overdoseFibre Reinforced sprayed Concrete Properties22 SAVINGS:- concrete:33%- cycle hrs (64%) Fibre Reinforced sprayed Concrete Properties23L/150 =3 mm Ffct,eq,150FF/2F/2L/3L/3 L/3 Characterisation of FRS1.

8 Beam test2. Efnarc panel testfe150= Ffct,eq,150. L / ( ) in MpaRe3= Ffct,eq,150/Foin %L = 450 mmb = 150 mmh = 150 mmhF0 Fibre Reinforced sprayed Concrete Design24Re3 = 50%Re3 = 100%PP 010203040506070809010152025303540455055d os age (k g/m )Re3 (%)RC-65/35-BNRL-45/30-BNL=35; d= ; d= Reinforced sprayed Concrete Design25 Efnarc toughness classification:500J: min. requirement; rock; small diameter tunnel700J: standard; less good rock1000J: high ductility for bad soil condition500mm600mm500mm600mm100x100mmFd eflection25mmloadFibre Reinforced sprayed Concrete Properties26 Efnarc panel testEuropean standard EN 14488-5 The punching-flexion test is an ideal test to check the FRS behaviour.

9 1)A sprayed concrete tunnel ling behaves like a slab2)The hyperstatic test conditions allow load redistribution3)The test can be carried out with mesh reinforcementThis test is introduced in 1989 by the French railway, and is in the meantime accepted by Efnarc, and is proposed in CEN Reinforced sprayed Concrete Design27 Fibre Reinforced sprayed Concrete Design28 Efnarc panel testFibre Reinforced sprayed Concrete Design2980 J400 J800 J1250 JFibre Reinforced sprayed Concrete Design30 Fibre Reinforced sprayed Concrete Design311 mesh reinforced layer versus fibre reinforced sprayed concrete layerDesign of 1 mesh reinforced layerFibre Reinforced sprayed Concrete Design32 Fibre Reinforced sprayed Concrete DesignDesign of steel fibre reinforced sprayed concrete layer33 Double mesh reinforced layer versus fibre reinforced sprayed concrete layerDesign of 2 mesh

10 Reinforced layerFibre Reinforced sprayed Concrete Design34 Double mesh reinforced layer versus fibre reinforced sprayed concrete layerDesign of steel fibre reinforced sprayed concrete layerFibre Reinforced sprayed Concrete Design35-EN14488-3 - Testing sprayed concrete - Part 3: Flexural strengths (first peak, ultimate and residual) of fibre reinforced beam specimens-EN14488-5 - Testing sprayed concrete - Part 5: Determination of energy absorption capacity of fibre reinforced slab specimens-EN14488-7 - Testing sprayed concrete - Part 7: Fibre content of fibre reinforced concreteFibre Reinforced sprayed Concrete QA/QC36 FIBRE COUNTER1234 Fibre Reinforced sprayed Concrete QA/QC37 Fibre Reinforced sprayed Concrete QA/QC-1.