Ermco Fibre Guide September 2012 Corr A

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EUROPEAN READY MIXED CONCRETE ORGANIZATION ASSOCIATION EUROPEENNE DU BETON PRET A L'EMPLOI

E U R O P I S C H E R T R A N S P O R T B E T O N V E R B A N D

Guidance to fibre concrete

Properties, Specification and Practice in Europe

September 2012

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Forword This guideline was written from a Task Group of ERMCO Ecotec supported from European

experts from the ready mixed concrete industry and the fibre industry.

It took long to come to this final draft, with many long breaks, but the last years were not

easy for business and also not for concrete business. But this document is finally a good

and useful report (to say it with the words of Tom Harrison, Chairman of ERMCO Ecotec).

I want to thank all our Task Group members for your work and support.

Finally I also want to thank Tom Harrison, who supported us with his huge knowledge and

experience and who helped us to finalise work. I also want to thank John Gibbs, Secretary of

ERMCO Ecotec, who always was a very critical reader of our working papers and pushed us

to be more precise and specific.

Christoph Ressler (Chairman)

Task Group Members:

Olaf Abrock, Bundesverband der Deutschen Transportbetonindustrie e.V. (BTB), Germany

Jonas Carlswrd, Betongindustri AB, Sweden

Richard Dietze, Sika sterreich GmbH, Austria

Philipp Guirguis, NV Bekaert SA, Belgium

Wolfgang Hemrich, SCHWENK Zement KG, Germany

Ann Lambrechts, NV Bekaert SA, Belgium

Ingemar Lfgren, Thomas Concrete Group - C.lab, Sweden

Markus Schulz, Schulz Concrete Engineering GmbH, Germany

Jim Troy, Tarmac Limited, UK

John Gibbs, ERMCO Ecotec, UK

Tom Harrison, ERMCO Ecotec, UK

Christoph Ressler, Gteverband Transportbeton, Austria

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Contents:

1 INTRODUCTION ....................................................................................................................................... 5

2 SCOPE .......................................................................................................................................................... 5

3 REFERENCE STANDARDS AND GUIDELINES .................................................................................. 6

3.1 EUROPEAN STANDARDS FOR FIBRES...................................................................................................... 6 3.2 STANDARDS, GUIDELINES FOR FIBRE CONCRETE AND OTHER REFERENCES ........................................... 6 3.3 STANDARDS FOR TEST METHODS .......................................................................................................... 7

4 TERMS AND DEFINITIONS .................................................................................................................... 8

5 CONSTITUENTS ...................................................................................................................................... 10

5.1 GENERAL ............................................................................................................................................ 10 5.2 FIBRES ................................................................................................................................................ 10

5.2.1 CE marking: .................................................................................................................................. 10 5.2.2 Steel or Macro-polymer fibres ...................................................................................................... 13 5.2.3 Micro-polymer fibres..................................................................................................................... 17 5.2.4 Coatings of fibres .......................................................................................................................... 18

6 FRESH PROPERTIES OF FIBRE CONCRETE .................................................................................. 18

6.1 CONSISTENCE ..................................................................................................................................... 18 6.2 PUMPABILITY ...................................................................................................................................... 19 6.3 AIR CONTENT ...................................................................................................................................... 20 6.4 BLEEDING ........................................................................................................................................... 20 6.5 PLASTIC SHRINKAGE AND PLASTIC CRACKING .................................................................................... 20

7 HARDENED PROPERTIES OF FIBRE CONCRETE ......................................................................... 20

7.1 GENERAL ............................................................................................................................................ 20 7.2 COMPRESSIVE STRENGTH .................................................................................................................... 22 7.3 POST-CRACK TENSILE STRENGTH ........................................................................................................ 22 7.4 FIRE RESISTANCE ................................................................................................................................ 23 7.5 IMPACT RESISTANCE ........................................................................................................................... 23 7.6 SHEAR RESISTANCE ............................................................................................................................ 24 7.7 DURABILITY ....................................................................................................................................... 24 7.8 CREEP ................................................................................................................................................. 24

8 INITIAL TYPE TESTING ....................................................................................................................... 24

9 SPECIFICATION ..................................................................................................................................... 25

9.1 SPECIFICATION BY TYPE AND FIBRE CONTENT .................................................................................... 26 9.2 SPECIFICATION BY FIBRE CONCRETE PERFORMANCE ........................................................................... 26 9.3 PRACTICE IN EUROPE .......................................................................................................................... 26

10 CONFORMITY ......................................................................................................................................... 29

10.1 CONFORMITY OF FIBRES THEMSELVES ................................................................................................ 29 10.2 CONFORMITY OF FIBRE CONTENT OF CONCRETE ................................................................................. 29 10.3 CONFORMITY OF CONCRETE IF PERFORMANCE IS SPECIFIED ............................................................... 29

11 PRODUCTION AND TRANSPORT OF FIBRE CONCRETE ............................................................ 30

11.1 STORAGE OF FIBRES IN CONCRETE PLANT ........................................................................................... 30 11.2 BATCHING OF FIBRE CONCRETE .......................................................................................................... 30

11.2.1 Addition of fibres at the plant ................................................................................................... 31 11.2.2 Addition of fibres on job site..................................................................................................... 32

11.3 FACTORY PRODUCTION CONTROL ...................................................................................................... 32 11.4 TRANSPORT ........................................................................................................................................ 33 11.5 HEALTH AND SAFETY .......................................................................................................................... 33

11.5.1 General ..................................................................................................................................... 33 11.5.2 Addition of fibres to the mixer .................................................................................................. 33

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12 PROGRESS IN STANDARDIZATION, FIBRE CONCRETE IN PREN 206 .................................... 34

12.1 CONFORMITY REQUIREMENTS............................................................................................................. 34 12.2 IDENTITY TESTING REQUIREMENTS FOR FIBRE CONTENT AND HOMOGENEITY OF FRESH CONCRETE.... 35 12.3 REQUIREMENT FOR DISTRIBUTION OF FIBRES IN THE MIX .................................................................... 36 12.4 ADDITIONAL REQUIREMENTS .............................................................................................................. 36

12.4.1 Provision of information ........................................................................................................... 36 12.4.2 Batching tolerances .................................................................................................................. 36 12.4.3 Batching procedure .................................................................................................................. 36

13 RECOMMENDATIONS .......................................................................................................................... 36

ANNEX A: ADDITIONAL INFORMATION ON TEST METHODS ......................................................... 38

A.1 POST-CRACK AXIAL TENSILE STRENGTH ..................................................................................................... 38 A.2 POST-CRACK FLEXURAL TENSILE STRENGTH .............................................................................................. 38

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1 Introduction

Fibre concrete is an established product now being widely used for applications such as

industrial floors, roads, pavements, tunnelling, composite constructions, walls, precast

segments and more. Recognition of the benefits of adding fibres into concrete is leading to

an extension of the possible areas of application in structural and civil engineering.

This document is not primarily intended as another general guidance document on the

properties of fibre concrete. Rather, ERMCOs intention is to clarify what is required from the

ready-mixed concrete industry when producing such concrete. It proposes methods of

specification and conformity procedures for fibre concrete in the same way that other

concrete and concrete properties are handled in EN206 Concrete.

Some European countries have issued guidance and/or regulate or standardize fibre

concrete with national guidelines. These national standards increasingly specify a required

performance of the composite material.

The fib Model Code comprising the design recommendation for fibre concrete (XV), which was

issued in a draft version in 2010, describes performance classes for fibre concrete.

The European Committee for Standardisation (CEN) has recognised the increasing

importance of fibre concrete, and harmonised product standards have been issued for steel

fibres, macro-polymer fibres and micro-polymer fibres. The draft of the revised European

concrete standard, prEN206, includes requirements for fibre concrete and therefore this

Guideline should give important support for concrete producers and specifiers with little

experience with fibre concrete.

Note: In the text, numbers in superscript refer to numbered references.

2 Scope

This document is not intended to replace national Guidance Documents on the properties of

fibre concrete, and it deals with fresh and hardened properties only briefly; rather, it is

intended as guidance for specifiers and ready-mixed concrete producers. In the light of the

inclusion of fibres in prEN206 (2012), it focuses on methods of specification and conformity,

on the practicalities of production (including health and safety aspects), and on progress in

standardization. The annex gives some information on methods of testing aspects of tensile

strength.

Sprayed concrete is not covered because standards already exist for such concrete, and

because the European Federation for Specialist Construction Chemicals and Concrete

Systems (EFNARC) has written a widely accepted document (xvi) on the subject.

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The document contains terms and definitions that are used in existing publications

(referenced documents). It covers the use of steel and polymer fibres, but not carbon or

glass fibres as these types of fibres are not standardized at the European level and, at

present, confined to niche market uses.

Emphasis is given to the production of fibre concrete, which requires special attention from

ready-mixed concrete producers and the affects on concrete performance.

Finally, a number of recommendations for best practice of fibre concrete are offered.

3 Reference standards and guidelines

A number of standards, guidelines and recommendations are available in several European

countries.

3.1 European standards for fibres

EN 14889-1: Fibres for concrete Part 1: Steel fibres - Definitions, specifications and

conformity.

This Standard defines requirements for steel fibres for mortar and concrete. It covers fibres

to be used for sprayed concrete, concrete floors, precast concrete elements and for concrete

and mortar for repair work.

EN 14889-2: Fibres for concrete Part 2: Polymer fibres Definitions, specifications and

conformity

This Standard defines requirements for polymer fibres for mortar and concrete. It covers

fibres for load-bearing and non-load-bearing purposes including the use in sprayed concrete,

concrete floors, precast concrete elements, tunnel facing and repair work. This standard is

being revised.

3.2 Standards, guidelines for fibre concrete and other references

i. prEN 206 Concrete - Specification, performance, production, and conformity

(EN206-1 is in revision and the revision will be called EN206 as it combines Part 1 and

Part 9).

ii. EN 14650 Precast concrete products General rules for factory production control of

metallic fibred concrete.

iii. Austria: VBB Richtlinie Faserbeton (VBB guideline fibre concrete), sterreichische

Vereinigung fr Beton- und Bautechnik, Vienna, 07/2008.

iv. Austria: VBB Richtlinie Erhht brandbestndiger Beton fr unterirdische

Verkehrsbauwerke (VBB guideline higher fire resistance with concrete for

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underground buildings for traffic), sterreichische Vereinigung fr Beton- und

Bautechnik, Vienna, 07/2005.

v. Belgium: NBN B 15-238, Proeven op vezelversterkt beton Buigproef op prismatische

proefstukken.

vi. Germany: DAfStb-Guideline, Committee for Structural concrete DAfStb guideline Steel

fibre reinforced concrete, Final version, 03/2010.

vii. Italy: UNI 11039 Steel fibre reinforced concrete Part I: Definitions, classification,

specification and conformity Part II: Test method for measuring first crack strength

and ductility, 02/2003.

viii. Netherlands: CUR: Recommendation 111 Steel fibre reinforced concrete Industrial

floors on pile foundations Design and Construction, 10/2010.

ix. Norway: Publication Nr.7, Sprayed concrete for rock support, Norwegian concrete

association

x. Sweden: Swedish Concrete Association Concrete Report No 4, Stlfibrebetong

rekommendationer fr konstruktion, utfrande och provning (Steel Fibre Reinforced

Concrete Recommendations for Design, Construction, and Testing), Stockholm, .2nd

Ed 1997. (In Swedish).

xi. Switzerland: SIA 162/6, Empfehlung Stahlfaserbeton (recommendation steel fibre

reinforced concrete), 02/1999.

xii. UK: Concrete Society Technical Report no 63 - Guidance for the Design of Steel-Fibre-

Reinforced Concrete. Blackwater, Camberley, Surrey, 2007.

xiii. UK: Concrete Society Technical Report No 65 - Guidance on the use of Macro

synthetic- Fibre-reinforced Concrete, Concrete Society:. Blackwater, Camberley,

Surrey, 2007.

xiv. Rilem TC 162 TDF Design of Steel fibre reinforced concrete Method,

recommendations, Material and Structures, 2002.

xv. fib Model Code 2010 First complete draft, Volume 1, and 2, Bulletin 55, 3/2010.

xvi. EFNARC European Specification for sprayed concrete, Guidelines for specifiers and

contractors, 1996.

3.3 Standards for test methods

ASTM C1550 -08 Standard Test Method for Flexural Toughness of Fibre reinforced

concrete (centrally loaded round panel test)

ASTM C1609/C1609M Standard Test Method for Flexural Performance of Fibre

reinforced concrete (third point bending test)

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EN 14651 Test method for metallic fibre concrete - Measuring the

flexural tensile strength (limit of proportionality (LOP), residual)

(Three point bending test on notched beams). A draft

amendment is in preparation.

EN 14721 Test method for metallic fibre concrete Measuring the fibre

content in fresh and hardened concrete. This document defines

two methods for measuring the fibre content in metallic fibre

concrete. Method A for measuring the fibre content in hardened

concrete samples and method B for measuring the fibre content

in fresh concrete samples. A draft amendment is in preparation.

EN 14845-1: 2007 Test methods for fibres in concrete - Part 1: Reference

concretes. To assess the performance of fibres in concrete this

Standard defines the composition and required properties of

reference concrete.

EN 14845-2: 2006 Test methods for fibres in concrete Part 2: Effect on concrete.

This Standard defines a method for measuring the volume of

fibres which must be added to reference concrete in order to

achieve a defined residual tensile strength.

EN 14488-7: 2006 Testing sprayed concrete Part 7: Fibre content of fibre

reinforced concrete. The standard deals with sprayed concrete.

The standard states that samples from fresh sprayed concrete or

from a drilled core shall be cut from in-situ material whereas the

normal way is to take a sample from the discharge of the truck.

The amount of fresh fibre concrete for a sample required in the

standard is also rather low (1-2 kg/sample).

The standard does not include any statement of precision.

NT BUILD 511 NT BUILD 511 Wedge Splitting Test Method (WST): Fracture

Testing of Fibre-Reinforced Concrete (Mode I), Nordic Innovation

Centre, Oslo.

JSCE-SF4 Method of tests for flexural tensile strength and flexural

toughness of fibre reinforced concrete, version 1984 (Four point

bending test)

4 Terms and definitions

aspect ratio

ratio of the length of a fibre to its diameter (or equivalent diameter)

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axial tensile strength (of concrete)

strength measured in a uniaxial tensile test

bending hardening

refers to the situation where the post-crack flexural tensile strength is higher than the first-

crack flexural tensile strength

creep

tendency of a solid material to deform under permanent load

ductility

general ability of a material to sustain load beyond a yield point that defines the limit of

elastic behaviour (xii)

fatigue resistance

ability to resist detrimental changes under cyclic loading

fibre concrete

homogeneous composite material comprising concrete or mortar as matrix plus fibres to

influence its properties

fibrillated

polymer fibres made up of multiple strands

NOTE: Other fibres are single-strand, or monofilament.

flexural tensile strength of concrete

maximum flexural tensile stress achieved in a beam test (xii) with non-fibre concrete or the first

crack flexural tensile stress in fibre concrete

NOTE 1: A test method for this property is standardised in EN14561.

NOTE 2: See definition of bending hardening.

plastic shrinkage

shrinkage which occurs in fresh concrete as a result of evaporation of water or

autogenous/chemical shrinkage

polymer fibres (as defined by EN14889 Part 2)

micro-fibres according to Class I non structural

macro-fibres according to Class II - structural

both types can be straight or deformed pieces of extruded, orientated and cut polymer that

are suitable for homogeneous mixing into concrete or mortar

post-crack flexural tensile strength (also called residual flexural tensile strength)

tensile strength in a beam test after the fibre-reinforced concrete has cracked, generally at a

specified deflection of the specimen in a test (xii)

NOTE: A test method for this property is standardised in EN 14651.

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post-crack tensile strength (also called residual tensile strength)

strength the fibre-reinforced concrete is capable of transferring across a crack when

subjected to uniaxial tension

steel fibres (as defined by EN14889 Part 1)

straight or deformed pieces of cold-drawn steel wire, straight or deformed cut sheet fibres,

melt extracted fibres, shaved cold drawn wire fibres and fibres milled from steel blocks, which

are suitable for homogeneous mixing into concrete or mortar

tensile strength of fibres

strength measured in a uniaxial tensile test

toughness

ability of fibre-concrete to sustain loads after cracking of the concrete, i.e. the energy

absorption capacity (xii).

5 Constituents

5.1 General

The requirements for the constituents of fibre concrete are the same as those for concrete

conforming to prEN 206. The constituents should conform to a European standard, a

Technical Specification or to specific national requirements (e.g. requirements for aggregates

in case of freeze/thaw).

5.2 Fibres

5.2.1 CE marking:

Steel and polymer fibres may be used in concrete in Europe only if they conform to the

requirements of EN 14889 and are CE- marked (European Conformity). Conformity to this

standard indicates established suitability of the fibres for some use in concrete.

NOTE: CE-marking is currently not mandatory in all EU countries, but will be so when the

Construction Products Regulation comes into force in 2013.

The basic information given in the CE marking is the following:

type of fibres: steel/polymer;

CE Certification;

type and dimension;

tensile strength;

Youngs modulus;

length;

cross sectional form;

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diameter or dimensions of cross section;

surface finish and anchorage (eg. hooked at the end or embossed);

tolerances on the length, the diameter (and the aspect ratio for steel fibres);

safety aspects.

In addition the declaration of performance under standard tests is reported.

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Figure 1a/1b: Example of CE labelling of steel (1b) or polymer (1a) Class II fibre

For CE-marking of fibres, two levels of attestation of conformity are defined: System 1 and

System 3

System 1 is applicable when the fibres have a structural function, i.e. when the fibres are

designed to contribute to the load-bearing capacity. The system requires a continuous

surveillance of the production process of the fibres by an independent Certifying Body, which

delivers a certificate of conformity (CE- mark).

System 3 is applicable when fibres are used for other reasons, i.e. for some non-structural

function - for instance to reduce the risk of plastic shrinkage, or to improve the behaviour of

concrete in fire. This system allows the manufacturer alone to declare that the quality is in

accordance with the requirements of the standard: no confirmation by a third party is

necessary.

In practice, therefore, when the post-crack strength of fibre concrete is taken into account in

the structural design, the fibres must be certified under System 1, and the CE label on the

packaging must indicate that the fibres are certified for structural use (System 1).

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System 1 System 3

Field of use

Structural use A) Non structural use

Quality control

Initial type Testing (ITT) under the responsibility of the Notified certification Body

Initial and Annually Factory Production Control (FPC) assessment by Notified Body

Certification institute Certificate of Conformity

Initial Type Testing by a Notified Laboratory

Factory Production Control (FPC) under responsibility of the manufacturer

The manufacturer creates and signs a Declaration of conformity

A) Structural use of fibres is where the addition of fibres is designed to contribute to the load bearing

capacity of a concrete element

Figure 2: Difference between attestation under System 1 and System 3

5.2.2 Steel or Macro-polymer fibres

Requirements for fibres are established in either EN 14889-1: Fibres for concrete Part 1 or

EN 14889-1: Fibres for concrete Part 2. Numerous types of fibres with different material

properties, dimensions, profiles and anchorages are available on the market. The fibres can

be glued together in bundles (with water soluble glue), wrapped as pucks or supplied in a

belt to facilitate dosing and mixing.

The surface of fibres has to be free of rust or pollution. Any surface coatings on fibres should

not interfere with the bond between fibres and matrix.

Steel or macro-polymer fibres are used in concrete for a number of reasons:

to improve the toughness of the hardened concrete;

to improve the impact resistance;

to increase the residual tensile strength of the concrete;

to increase the residual flexural tensile strength of the concrete.

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The residual flexural tensile strength of fibre concrete is a key performance parameter. It is

dependent on the type and amount of fibres added, as well as the properties of the concrete

matrix itself.

Figure 3 is a typical load-deflection diagram for the 4-point beam test shown in figure 4. The

non-fibre concrete shows no residual flexural tensile strength, whilst the fibre concrete

retains around 30% of the maximum flexural tensile strength. The amount of residual

strength retained depends on the type of fibre used and the quantity per cubic metre.

Generally for the same performance the ratio between steel and macro polymer fibres is 5:1

(i.e. 25 kg/m3 steel fibre is equivalent to 5 kg/m3 of macro-polymer fibres).

Figure 3: Load deflection diagram (symbolic)

Load - Deflection Diagram

0

5

10

15

20

25

30

35

0

0,5 1

1,5 2

2,5 3

3,5 4

4,5 5

deflection [mm]

loa

d [

kN

]

steel fibre concrete

non-fibre concrete

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Figure 4: Four-point beam test for the identification of the load deflection diagram

(photograph courtesy of Krampe Harex)

Typical properties of steel fibres:

Youngs modulus: 210 000 MPa;

tensile strength: 300 3000 N/mm;

design: straight, undulating, profiled or hooked;

length: 20 60 mm;

cross section: circular, corrugated, rectangular, or segment

of a circle;

diameter: 0.1 1.5 mm;

cross sectional dimensions (rectangular): 0.02-1.5 mm x 0.2-3 mm;

surface: smooth, irregular, or corrugated.

Photographs of different types of steel fibres are shown in figures 5 8.

Figure 5: Cold drawn wire (Stahldrahtfaser) Figure 6: Shaved cold drawn wire

(Drahtsegmentfaser)

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Figure 7: Cold drawn wire (Kaltbandfaser) Figure 8: Melt extracted (Meltextract)

pictures courtesy of Krampe Harex

Steel fibres with a high aspect ratio are usually in glued strips to avoid balling when mixed

into concrete, see figure 9. The glue is dissolved in the mixing water and the fibres separate

during mixing.

Figure 9: glued steel fibres

Typical properties of macro-polymer fibres

Youngs modulus 3 000 - 30 000 MPa;

tensile strength 300 700 N/mm;

design even, curled, textured;

length 20 60 mm;

cross section circular, rectangular or elliptic;

diameter (circular or elliptic) 300-1300 m;

cross sectional dimension (rectangular) 50-2000 m;

surface smooth or embossed.

An example of a macro-polymer fibre is shown in figure 10.

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Figure 10: Polypropylene macro-fibres

.

5.2.3 Micro-polymer fibres

The European standard for polymer fibres is EN 14889-2. Part 2 covers fibre manufactured

from polymeric materials. It divides polymer fibres into two classes

Class I: micro-fibres, < 0,30mm in diameter. These can either be monofilament or

fibrillated.

Class II: macro-fibres, 0,30mm in diameter. These have the same dimensions as

steel fibres.

Typical properties of micro-polymer Class I fibres include:

generally made of polypropylene;

the cross section can be circular, rectangular or elliptical;

the cross section, together with the surface characteristics, Youngs modulus and the

tensile strength, determine the bond between the fibres and the concrete;

polymer fibres are resistant to the high alkalinity of concrete;

micro-polymer fibres can contribute to fire resistance, and resistance to plastic

shrinkage depending on the length and the fibre content. These are selected

according to the maximum size of aggregate and to the specified engineering

requirements.

Typical properties of polymer micro-fibres:

Youngs Modulus: 3 000 - 30 000 MPa;

tensile strength: 300 700 N/mm;

design: straight even or curled;

length: 3 36 mm;

cross section: circular or rectangular;

diameter 10-50 m;

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cross section dimensions (rectangular): 20-300 m;

surface: smooth.

Micro-polymer fibres are not subject to splitting so are free from the health risk referred to in

section 11.5.

An example of a micro- polymer fibre is shown in figure11.

Figure 11: Polypropylene micro-fibres

5.2.4 Coatings of fibres

Some fibres have a coating - a thin surface layer to provide special properties e.g. to avoid

balling of polymer fibres, or to avoid rusting of steel fibres. Some steel fibres have a coating

of water-soluble glue to minimise the risk of balling and promote homogeneous mixing in the

concrete. Other coatings include a concrete plasticiser to compensate for any loss of

consistence when polymer fibres are added.

6 Fresh properties of fibre concrete

Addition of fibres into concrete influences its fresh properties. In this respect, it is important to

understand the likely effects of the addition of steel or polymer fibres (or both types).

Consistence, air content, bleeding and pumpability, for example, could be affected.

This section describes the effects to be expected on different concrete properties, and how

this might affect mix design.

6.1 Consistence

The addition of fibres to concrete may reduce the slump and/or increase the cohesiveness of

the mix. This has to be compensated for by either the use of plasticisers or by adjusting the

mix proportions. However, the cohesive appearance of some fibre concretes can be

misleading and it may not be necessary to compensate for this apparent low consistence. If

fibres are added at the plant under the responsibility of the concrete producer, the end-

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consistence (at site) requested by the contractor must be provided by the producer. If fibres

are added at the job-site by the concrete producer a loss of consistence is likely, and the

producer must allow for this in mix design and in batching. In both situations the producer is

responsible for the concrete properties and is required to show conformity of the concrete on

delivery.

If fibres are added under the responsibility of the contractor, the producer is responsible only

for the concrete prior to the addition of the fibres, and the fibre addition and any other

changes to the concrete made by the contractor are the responsibility of the contractor, e.g.

the addition of plasticisers, or superplasticisers to compensate for any loss of consistence.

As with normal concrete, the addition of water alone to correct the consistence will adversely

affect the quality of the fibre concrete. As the producers conformity is limited to the concrete

prior to the addition of fibres, the client is advised to require testing of the concrete after the

fibres have been added if they have been added under the responsibility of the contractor .

6.2 Pumpability

Pumping fibre concrete does not require special equipment. However, it is useful to have a

vibrator on the grid of the pump.

Concrete containing short fibres of any type will not cause problems. However, longer steel

or macro-polymer fibres with an aspect ratio of more than about 60 may require careful

attention to mix design, particularly at high dosages (typically, more than 25 kg/m of steel

fibres, or more than 10 kg/m of macro-polymer fibres). This is very much dependent on the

type of fibre being used and the fibre supplier should be able to advise on these aspects. It

is recommended that the diameter of the pump pipeline should not be less than one and a

half times the length of the fibres used for steel fibres but can be smaller for macro-polymer

fibres as they exhibit some flexibility in the pipeline.

In practice, and with care, good results can be achieved even with 60 mm steel or macro-

polymer fibres (at low dosages of 20 to 25 kg/m of steel fibres or 4-6 kg/m macro-polymer

fibres) in 63 mm and 76 mm hoses. As with all concrete types, pumpability is much more a

matter of mix design, proper consistency, good lubrication of the pump and all lines

beforehand, and attention to controlling the pressure of the pump

For concrete containing more than about 35 kg/m steel fibres or 10 kg/m3 of macro-polymer

fibres, or in the case of long or complicated pump lines, pumping difficulties may be

experienced despite proper adjustments of the mix design. In this case, concrete producers

are advised to take contractual steps to clarify responsibility, and in agreement with the

contractor, conduct pumping trials before work starts.

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6.3 Air content

Adding fibres can influence the air content of any concrete. The European standards 14899-

1 and - 2 make no mention of this. The use of coatings on some fibres was mentioned in

section 5.2.4. These, together with the use of some plasticisers, may increase the air

content of the concrete. A compatibility test should be undertaken before the production of

the concrete to ensure no adverse interactions of admixtures (see section A.3) and that the

required strength is achieved.

6.4 Bleeding

The addition of steel fibres or macro-polymer fibres has little effect on rate of bleeding, but

polymer micro-fibres can significantly reduce both the rate and volume of bleeding.

6.5 Plastic shrinkage and plastic cracking

It is recognised that plastic shrinkage and cracking are related to bleeding and/or

autogenous/chemical shrinkage. Polymer micro-fibres may therefore have beneficial effects,

while steel and macro-polymer fibres have little influence. This is one of the principal reasons

for the use of polymer micro-fibres, particularly in horizontal elements. If fibres of this type

are used for this purpose, typical addition rates range between 600 g/m and 900 g/m.

7 Hardened properties of fibre concrete

7.1 General

Fibres are mainly added to influence the hardened concrete properties. Many of the

hardened properties which are affected are rarely specified, and are unlikely to be familiar to

ready-mixed concrete producers.

Steel and macro-Polymer fibres significantly affect hardened properties in the following

ways:

increased post-crack flexural tensile strength;

increased shear strength;

increased impact resistance;

reduced crack widths (Design in Serviceability Limit State);

increased fatigue resistance.

Figures 12 to 14 illustrate the principal influences of different types of steel and macro-

polymer fibres on the properties of the concrete.

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Figure 12: Post-crack flexural tensile strength of concrete with fibres of different aspect

ratios, the same length and the same fibre content (kg/m).

Figure 13: Post-crack flexural tensile strength of concrete with fibres of different length, the

same aspect ratio and the same fibre content.



0

0

deflection

load high aspect ratio

low aspect ratio



0

0

deflection

load long f ibres

short f ibres

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Figure 14: Post-crack flexural tensile strength of concrete with fibres of different designs and

same fibre content.

Polymer micro-fibres significantly affect hardened properties in the following way:

increased resistance to explosive spalling of higher strength concrete in fire,

particularly important in tunnel construction.

7.2 Compressive strength

The addition of fibres usually does not affect compressive strength except where the air

content is increased, for example by the fibre coating (see 5.2.4).

7.3 Post-crack tensile strength

The ability of fibres to transfer stresses across cracks is one of the most important properties

of fibre concrete. It enables a fibre-reinforced structure to maintain substantial load even after

a crack has developed. In 95% of cases, steel and macro-polymer concrete will show

behaviour in pure tension like that in Figure A.1 in Annex A. However, since a uniaxial

tensile test is difficult to perform, flexural tensile strength is usually tested see sections 9.2,

9.3 and Annex A. However, axial tensile strength can be calculated from the post-crack

flexural tensile strength by means of conversion factors.



0

0

deflection

load hooked fibres, f igure 5

w aved fibres, f igure 6

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Post-crack flexural tensile strength is assessed in a 3-point beam test (EN 14651) or in a 4-

point beam test. Both methods are used and the results in numerical terms will not

necessarily be the same.

For statically determined structures subjected to a flexural moment it is common to refer to

the residual load bearing capacity as post-crack flexural tensile strength.

At normal addition rates (typically between 20-40 kg/m of steel fibres or 4-8 kg/m of macro-

polymer fibres), the post-crack flexural tensile strength is less than the flexural tensile

strength at the first crack.

Bending hardening, which refers to the situation where the post-crack flexural tensile

strength is higher than the first-crack flexural tensile strength, can occur at dosages above 50

kg/m of steel fibres with high aspect ratios.

7.4 Fire resistance

The fire resistance of concrete structures is generally considered not to be influenced by the

addition of steel fibres, though the fibres may reduce the degree of spalling somewhat by

bridging areas of spalled concrete.

Macro-polymer fibres will contribute to a concretes fire resistance, but will not be as effective

as micro-polymer fibres. As they melt at 160C, they cannot be considered as structural

reinforcement at higher temperatures.

As shown in figure 15, spalling of concrete in a fire is reduced by the addition of an adequate

dosage of polymer micro-fibres (diameter 3 to 32 m), typically 1-2 kg/m3. In Austria a

guideline for the fire resistance of fibre concrete, including test methods and requirements for

the fibres was published in 2005 [iv].

Figure 15: Specimens after testing for fire

resistance according to [iv]: on the left a

specimen with micro-fibres, on the right a

specimen without fibres.

7.5 Impact resistance

Impact resistance, ductility and toughness are generally increased by the addition of any

fibres. When impact resistance is required, design is usually determined by testing and then

the concrete is specified by type and fibre content.

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7.6 Shear resistance

The addition of steel fibres to concrete will enhance the shear resistance of structural

elements. A ductile failure mode is induced, in the same way as by the use of reinforcement

stirrups. A number of standards and guidelines contain an equation describing the effect of

steel fibres as equivalent shear reinforcement (xii).

The shear resistance of steel fibre concrete is based upon the post-crack flexural tensile

strength, determined from standardized beam tests (Annex A.)

7.7 Durability

While steel fibres may reduce the risk of spalling due to corrosion of reinforcement, they do

not reduce the rate of corrosion or the rate of loss of cross section.

Corrosion of steel fibres themselves at the surface does not cause any spalling. Designers

should consider the use of steel fibres in potentially corrosive conditions if the fibres near to

the surface contribute to structural performance.

Both steel and macro synthetic fibres improve abrasion resistance.

Polymer fibres have a positive effect on durability by reducing the incidence of early age

shrinkage cracking. Polymer micro-fibres increase the fire resistance of concrete structures

by reducing spalling.

7.8 Creep

The importance of steel and macro-polymer fibres in increasing the post-crack flexural tensile

strength of concrete has been explained in section 7.3. However, the influence of creep

must be taken into account. The post-crack flexural tensile strength of polymer macro-fibre-

reinforced concrete may be initially equal to that of steel fibre-reinforced concrete, but the

long term behaviour may be different. Under permanent load the polymer fibres themselves

have a tendency to creep, and fibre failure or large creep deformations may eventually occur

in both the fibres and the concrete. This is something that has to be taken into account in the

structural design.

8 Initial Type Testing

The fibre standards are for fibres themselves, not fibre concrete. Conformity to EN 14889

does not guarantee that the fibres are problem-free when used in concrete. Neither part of

EN 14889 includes requirements for the coating of the fibres.

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The properties described above, together with the choice of the type and quantity of fibres

added (particularly those with high aspect ratio, or those used at high dosage rates) may

require modifications to mix design, e.g. to compensate for any loss of consistence. The use

of fibres in concrete requires initial type testing as concrete properties are affected. Changes

necessary to mixes may include the following:

when fibres are used with concrete of low compressive strength class and/or pumped

concrete, the demand for cement paste is typically increased;

the additional surface area of fibres may necessitate a larger mortar content to

minimise the risk of harsh concrete, which is difficult to finish;

an increase in the dosage of plasticiser or superplasticiser;

the surface coating on fibres may influence fresh concrete properties, primarily the air

content, and assessment is required at this stage. It may be necessary to use a

different admixture, or even a different fibre. Producers should be aware of the

possibility of air entrainment when fibres are added to concrete. A possible way to

minimise this risk is described in 9.3 Practice in Europe / Austria (Testing of the

influence of fibres on the air content of concrete).

to ensure adequate consistence of fibre concrete it is generally recommended that

the content of fine aggregate should be greater than that of an equivalent mix without

fibres;

a reduction of the coarse aggregate content;

aggregate grading: a continuous grading curve is preferable to a gap-graded

distribution;

the maximum aggregate size should not exceed the length of the fibre.

PrEN 206 Concrete requires initial testing to verify that the producers documented mixing

procedure ensures a homogeneous distribution of fibres and a procedure for verifying this

requirement is given. This includes the situation where the mixing is undertaken in a

truckmixer under the responsibility of the concrete producer.

9 Specification

Broadly speaking, there are two methods of specification available: specification by fibre type

and content, and specification by performance of the fibre concrete. Where fibre type and

content are specified, this may be within a designed concrete or a prescribed concrete.

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9.1 Specification by type and fibre content

The simplest and most common method is for the specifier to define the fibre type and the

fibre content per m (specified as a minimum quantity) that should be included in the

concrete. The concrete suppliers responsibility is limited to adding and mixing the right type

and quantity of fibres and ensuring that the fibres are homogeneously mixed, together with

the other specified requirements e.g. consistence, compressive strength class. The specifier

takes responsibility for the additional performance resulting from the addition of fibres e.g.

post-crack flexural tensile strength.

Where fibres are to be added under the responsibility of the contractor, the contractor must

specify to the producer a concrete that takes account of the changes the fibres will make to

the concrete properties.

9.2 Specification by fibre concrete performance

PrEN 206 does not describe in detail this method of specification, and is limited to a

statement that details have to be agreed between the specifier and the concrete producer. In

some countries (e.g. Austria and Germany) fibre concrete is specified by performance

classes established in national provisions ((iii) (vi)) These classes may be based on properties

such as post-crack behaviour in ultimate and serviceability limit states, flexural tensile

strength, fire resistance, and early-age shrinkage. The producer is responsible for the design

and performance of the concrete, including decisions on fibre type and content. However, in

most countries, ready-mixed concrete producers have still to develop the expertise to design

concrete in this way. PrEN 206 states that if fibre concrete is specified in this way, the test

method and conformity procedures must be agreed with the concrete producer.

Some producers have a number of proprietary designs, with stated performance, from

which a specifier may choose.

9.3 Practice in Europe

In most European countries specification of fibre concrete is simply done by fibre type and

content. The fibre content is often determined by the supplier of fibres, in discussion with the

design engineer. The agreed fibre type and content are then specified to the concrete

supplier. This is the usual practice in, for example, the Czech Republic, Denmark, Finland,

France, Netherlands, Norway, Poland, Portugal, Slovakia and the United Kingdom.

Some examples of national practice in methods of specification are given in the following

sub-sections.

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Austria

Austria has a guideline for steel fibre concrete (iii) with seven classes for structural

performance (T classes) and seven for serviceability (G classes).

The classes are based on measurement of post-crack flexural tensile strength behaviour in a

four point beam test on six beams of dimensions 600 - 700 mm x 150 mm x 150 mm. A

minimum steel fibre content of 14 kg/m is also specified.

The T classes are based on minimum characteristic values between 0,4 N/mm and >1,9

N/mm calculated from the load-deflection diagram with deflection from 0,5mm up to 3,0mm .

Characteristic values are also used to define G classes, ranging from 0,5 N/mm to >2,2

N/mm, calculated from the load-deflection diagram at a deflection of 0,5mm.

Achieving the required performance of the steel fibre concrete depends on the steel fibre

type (e.g. length, diameter) and content (e.g. 15 or 25 kg/m) and the properties of the

concrete itself. It is the producers responsibility to design the concrete to conform to the T

and G classes specified.

The guideline also includes performance classes for flexural tensile strength (classes BZ 3.0,

BZ 4.5 and BZ 6.0) with minimum characteristic flexural tensile strengths of 2.2, 3.2 or 4.2

N/mm respectively.

A performance specification for the reduction of early age shrinkage for polymer fibre

concrete is also included the single FS performance class requires reduction of the total

crack length to 20% of that of the same concrete without fibres.

A separate Guideline (iv) deals with the specification of fire resistance in polymer micro-fibre

concrete. Special test methods and specimens have been developed see figure 15. This

fibre concrete is often used for tunnelling and subway construction. In addition the new

revision of this guideline will set requirements on the increase in air content. Practice in

Austria shows that testing on mortar is sufficient to determine the change in air content. The

difference between the air content of the mortar with polymer micro-fibres and the mortar

without fibres has to be less than about 2%. Similar testing is possible and useful for steel

fibres. The test has to be made with every new delivery of fibres (or every 6 months) by an

independent laboratory under the responsibility of the fibre producer or the fibre supplier.

For conformity there is no requirement for routine performance testing. There are two

requirements firstly the delivery tickets must state that the fibres used are the same as

those used in initial type testing. Secondly, the fibre content of fresh concrete is verified with

a wash out test described in the Guideline (iii).

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Any need for identity testing has to be determined by the client and undertaken by the clients

representative. The procedures for identity testing are the same as for conformity

assessment and the criteria are also the same.

Czech Republic

In the Czech Republic specification is usually by fibre content, but one supplier offers a fibre

concrete with a description including tensile strength class.

Germany

Germany has a system of performance classes (post-crack flexural tensile strength), which

are used for specification. The determination of the performance class is part of the initial

testing of the producer. Six beams (150 mm x 150 mm x 700 mm) are tested in a four point

flexural test to determine the characteristic value of post-crack flexural tensile strength.

Two performance parameters (L1 and L2) are defined. L1 is determined at the point of 0,5

mm deflexion of the beam test. L2 at the point of 3,5 mm deflexion. Nine classes are defined

with values of L1 and L2 between 0 and 2,4 N/mm. The initial testing of the fibre concrete is

undertaken with the minimum fibre content planned by the producer for each mix design for

later continuous production. Conformity to the performance class of each fibre concrete is

verified yearly by retesting. Routine conformity is assessed by testing of the fibre content and

documentation of the type of fibre. Fibre concrete is then specified by compressive strength

class, exposure class and performance class. Identity testing of fibre content may be done

by the customer. The national regulations are published in Richtlinie Stahlfaserbeton (2010)

(vi) by German Association for Reinforced Concrete (DAfStb).

Example: A fibre performance class C30/37 L 1,8/1,5 corresponds in practice with a C30/37

mix, reinforced with around 30 kg/m of a high-end steel fibre with aspect ratio 80, length 60

mm, hooked end, and a nominal tensile strength of 1200 MPa.

A performance class C30/37 L 0,9/0,6 corresponds in practice with a C30/37 mix, reinforced

with around 30 kg/m of a low-end steel fibre with aspect ratio 45, length 50 mm, hooked

end, and a nominal tensile strength of 1100 MPa.

Sweden

In Sweden while specification is, as elsewhere, usually by fibre content, performance

requirements are sometimes stated. In accordance with Concrete Report No 4(X) (a Swedish

design guideline for fibre-reinforced concrete) the performance is often expressed by means

of residual strength factors or R-values, which is the ratio of the post-cracking flexural tensile

strength and the flexural tensile strength. This is determined by initial testing and it is unusual

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for routine performance tests to be carried out to verify the performance established during

initial testing.

UK

In UK, specification is normally by type and content of fibres, but some ready-mixed

companies offer a statement of performance for their proprietary concrete. Conformity by

performance testing is not usually assessed.

10 Conformity

Conformity is a matter for the producer and part of factory production control.

10.1 Conformity of fibres themselves

Fibres for concrete conforming to EN 14889, which are also usually CE-marked, have to

conform to standard methods of factory production control and declarations of performance

in accordance to EN 14889-1 and -2, see section 5.2.1.

Apart from the CE-label the package should also give information about the quantity of fibres

in every bag.

10.2 Conformity of fibre content of concrete

The proposal for conformity of fibre content in the revision of EN 206 is limited to batch

records. Additionally, if fibres are added at the truck mixer homogeneity of fibre content has

to be tested. (See section 12.1)

10.3 Conformity of concrete if performance is specified

There are no standard rules for initial testing or assessing conformity of performance of fibre

concrete that are applicable for cast-in-place fibre concrete (There are standard rules for

sprayed concrete). Therefore, if the performance of fibre concrete is specified, the specifier

must also state the conformity requirements, including test methods if these are not set out in

the national requirements. Where classes are stated, the test methods and conformity rules

should be stated in the national regulations. In the current state of the art, such testing is not

practical as a matter of routine, and after proving the performance in initial testing, conformity

is based on batching the required fibre type and quantity. By definition, conformity testing is

a matter for producers, but initial performance testing is normally only done in specially

equipped laboratories.

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In the case of Germany, where post-crack flexural tensile strength is specified, the producer

is required to demonstrate performance in initial-type testing, then subsequently once a year;

but for conformity purposes, only fibre content is assessed.

11 Production and transport of fibre concrete

11.1 Storage of fibres in concrete plant

The majority of fibre products supplied to the ready mixed concrete industry are pre-packed

by the manufacturer. The fibres should be stored as specified by the manufacturer, and in a

manner that prevents degradation of the packaging and the storage bags. It should be noted

that some storage bags are water-soluble.

The instructions regarding packaging should be followed. Some manufacturers pack fibres in

double bags, where the outer bag protects an inner water-soluble bag.

11.2 Batching of fibre concrete

Fibres can be added at the concrete plant or on site; different practices may be necessary in

these two circumstances. The chosen procedure for adding the fibres influences the quality

and performance of the concrete.

Questions of legal responsibility arise when the customer adds fibres to the concrete.

There are three primary objectives when batching fibre concrete:

that the correct type and quantity of fibres are added;

that the fibres are evenly distributed throughout the concrete: in particular, balling of

the fibres must be prevented;

that the addition of fibres does not compromise other aspects of the specification of

the concrete.

The instructions on packaging are important. If fibres are packed in a double bag - the outer

bag has to be removed prior to adding to the concrete the water soluble inner bag containing

the fibres.

Most manufacturers of fibres prescribe preferred methods of batching to make sure that the

fibres will be evenly distributed in the mix and that the intended performance of the fibre

concrete will be achieved.

The fibres can be added directly to the central plant mixer or to the truck mixer. Generally,

fibres should not be added before the coarse aggregates. Slow addition reduces the

tendency to balling, particularly those fibres with problematic shape e.g. high aspect ratios

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(above 50) and high addition rates (more than about 35 kg/m steel fibres or 10 kg/m3 macro-

polymer fibres). Mixing recommendations from the manufacturer are useful.

11.2.1 Addition of fibres at the plant

Addition of fibres at the plant under the responsibility of the concrete producer is the best

way to ensure concrete quality. Fibres can be added directly into the truck mixer, or, to

optimise dispersion, into the plant mixer. Many producers will have established their own

batching procedures, but generally, the following advice is offered:

Where concrete is batched through a dry batch plant (i.e. truck mixing), for each bag of

fibres, approximately 35 litres of water per m3 should be added to the truck mixer prior to the

addition of the coarse aggregates and fibres. Mixing fibres with water only leads to balling.

Ideally, one hundred revolutions of the mixer is required to ensure good fibre distribution, but

in practice it is difficult to monitor this. More practically, therefore, a minimum mixing time of

five minutes (or one minute per m) at the maximum speed of the drum is required.

For reasons of safety, many ready-mixed concrete suppliers do not permit operatives to

access the platform at the back of the truck. In such cases it is necessary that a proper

system for adding the fibres to the truck mixer be used. One possible solution is to add bags

of fibres by means of a lance. Different automated or semi-automated systems exist.

Polymer fibres

Polymer fibres should be added to the truck mixer or central plant mixer with the coarse

aggregates or after the dosing of all other constituents; this aids the dispersion of the fibres

and helps in breaking up any degradable packaging.

If polymer fibres are added directly into to the truck mixer, it is particularly important to

ensure that thorough mixing takes place. The minimum practical consistence for working

with fibre concrete may be considered to be 40-50 mm. Therefore if the fibres are added

after the other constituents, the consistence should preferably be brought to an adequate

level beforehand to assist the dispersion of fibres. However, there is no clear agreement on

what this level should be: advised levels vary from 50 to 125 mm slump.

Steel fibres

These fibres should not be added at the start of the batching process, but only after the other

constituents are thoroughly mixed. There are several ways of adding the fibres to the

concrete. Recommended methods are to disperse the fibres on the aggregate conveyor or

into the weigh hopper by automatic means.

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A portable conveyor or fixed platform should be provided; where a platform is used, a

mechanical means of lifting the packages of fibres on to the platform should be available.

Pneumatic blast machines may also be used to introduce the fibres into truck mixers. Some

steel fibres with an aspect ratio greater than 50 require the adoption of special procedures to

ensure effective distribution of the fibres through the concrete. For efficient distribution of

high aspect ratio fibres the manufacturer should provide special packaging, such as belt

packaging, or fibres bundled, or glued together, or provide equipment to blow the fibres

evenly into the truck mixer.

11.2.2 Addition of fibres on job site

For a number of reasons e.g. health and safety or to ensure proper mixing and for general

quality control considerations, many ready-mixed suppliers are unwilling to allow fibres to be

added on the job site. (This is also prohibited by some national regulations e.g. in Germany).

However, it is recognised that fibres are sometimes added to the concrete truck mixer at the

construction site.

If fibres are added under the responsibility of the contractor (at the plant or on site) the

responsibility for the concrete after adding the fibres has to be clearly declared in a written

form.

11.3 Factory Production Control

Documented procedures should be available stating:

storage systems for different types of fibres;

identification of stored material;

methods that are used to batch/dispense fibres;

safety requirements for handling/ batching fibres;

systems used to identify the requirements for the concrete;

modifications to the concrete composition to enable the optimum properties of the

fibre concrete to be achieved;

systems that are in operation to ensure the correct type and dosage/mass of fibres

are batched;

methods used to ensure fibre are dispersed homogeneously within the mixed

concrete;

testing that is to be undertaken on fresh concrete;

testing that is to be undertaken on the hardened concrete;

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test methods to be used;

frequency of testing;

system that is to be used to evaluate the conformity of the fibre concrete with the

specification;

records that should be maintained of production of fibre concrete.

11.4 Transport

Generally, there are no special requirements for the transportation of fibre concrete.

11.5 Health and safety

11.5.1 General

It is the responsibility of the fibre manufacturer to provide the concrete supplier with any

necessary information, normally to be declared in the safety data sheet.

Fibres with diameter less than 3 m and an aspect ratio less than 3 may have associated

risks for human health, specifically breathing. Fibre fragments of such critical dimensions

may result from disintegration of the fibre when the concrete and fibres are subject to

mechanical stresses. The producer of the fibres has to declare this in his safety data sheet.

Under some national regulations the use of such fibres is not permitted.

Micro-polymer fibres are not subject to splitting and this potential health risk.

Generally the addition of macro-polymer fibres presents less Health and safety issues than

steel fibres because they are lighter and therefore easier to handle. They also do not a

puncture injury possibility.

11.5.2 Addition of fibres to the mixer

For safety reasons, manual handling should be restricted to a minimum, and the use of a

conveyor is recommended. At present fibres, polymer or steel, are either added directly to

the truck mixer using pre-weighed soluble or insoluble bags or boxes, or delivered directly to

a static, central mixer in a continuous fashion (ribbon feeding).

General health and safety issues when batching fibres are:

manual handling;

working at heights;

risk to eyes;

physical damage to skin by penetration of steel fibres.

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The method for placing the fibres into the back of the ready-mixed concrete truck may be:

by use of a conveyor belt (a common method used at a plant);

manual delivery from a purpose built platform (scaffold towers on site).

In both cases, the fibres need to be manually lifted to be either placed on the conveyor belt

or into the mixer drum. Sometimes, inadvisably, ladders are used. Specific potential risks

arise from each of these methods of working:

Specific potential risks arising from use of conveyor belts:

injury to eyes from light airborne polymer fibres;

manual lifting of bags of fibres onto conveyor belt (risk of back injury);

Specific potential risks arising from use of platforms:

Temporary or permanent platforms may be used for adding the fibres to the truck or the

mixer. Then the considerations should include:

risk of falling when working at heights;

injury to eyes from concrete splashes or flying fibres;

instability of platform (fixed platforms are recommended);

manual handling of fibres to the top of platform (risk of back injury/fall).

Specific potential risks arising from use of ladders:

Ladders are sometimes used to climb onto the truck platform to add fibres directly into the

back of the truck. However many companies prohibit this practice and have removed the

ladders from their trucks. Specific risks arising from this practice include:

falls due to manual handling whilst climbing;

movement of ladder due to lorry movement.

In short: ladders should not be used.

12 Progress in standardization, fibre concrete in prEN 206

European standards are now available for the fibres themselves, and for testing the fibre

content of concrete. However, the present standard for concrete, EN206-1 does not cover

the use of fibres in concrete. In prEN206, the conformity rules for fibres in concrete follow

the German methodology, i.e. limited to documentary evidence from batch records of the

correct fibre content.

12.1 Conformity requirements

PrEN206 permits fibre concrete to be specified by fibre type and content or by performance.

However it does not include any conformity criteria for performance classes in this case

national provisions apply.

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Conformity to a specified minimum fibre content is assessed in the same way as for example

the minimum cement or additions content. It is based on the documentation of the fibre

content - the fibre content is to be taken either as the recorded value on the print-out of the

batch recorder, or where recording equipment is not used, from the production record in

connection with the batching instruction. An assessment is required at least once a day.

The fibre content is specified by a minimum value. PrEN 206 gives the lower limit for

conformity for steel fibre content (single test) as the specified value multiplied by 0.95 and for

polymer fibre content 0.9 assessed in both cases on the production record. As for other

properties, conformity testing of fibre content is based on testing by variables in accordance

with ISO 3951:1994 table II-A (AQL = 4 %).

Where the fibres are added at the truck mixer on site there is a further conformity

requirement for homogeneity of mixing through the load, tested at the same frequency as for

compressive strength. This test is based on testing individual values. It follows the same

principle as for testing fresh concrete consistence or air content. Conformity criteria and the

criteria for possible identity testing by the customer are the same.

12.2 Identity testing requirements for fibre content and

homogeneity of fresh concrete

Rules for identity testing are included in prEN 206.

The test procedure for steel fibre content and homogeneity of mixing is required to be in

accordance with EN 14721 using three samples per load.

The test procedure for polymer fibre content (excluding sampling) and homogeneity of mixing

is required to be in accordance with EN 14488-7 using three samples per load.

In both cases the three samples have to be taken during discharge of the concrete from the

first, middle and last third of the load.

Concrete is deemed to come from a conforming population if both criteria in table 1 are satisfied.

Table 1 Combined Identity criteria for fibre content and homogeneity of fresh concrete

Applicable to Criterion

Every sample 0,80 of the specified minimum value

Average of 3 samples from a load

0,85 of the specified minimum value

In practice it is not easy to meet these requirements, particularly with polymer micro-fibres,

and there is no certainty that the test method in standard EN14488-7 is valid for micro-fibre

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concrete. In some cases, to ensure conformity, producers have had to increase the fibre

content rate by 10 to 20%.

12.3 Requirement for distribution of fibres in the mix

For the fibre concrete to be fit for purpose, it is essential that the fibres be distributed evenly

within the mass of the concrete. PrEN 206 includes a requirement that the initial testing shall

verify that the producers documented batching procedure achieves a homogeneous

distribution of the fibres throughout the concrete. Additionally, if fibres are added at the truck

mixer, homogeneity of mixing is tested as described in section 12.1.

12.4 Additional requirements

12.4.1 Provision of information

On request the producer is required to give a description of the fibres (according to EN

14889-1 or -2) and to state the fibre content, if the concrete is specified in this way. The

delivery ticket must state either the type and content of fibres or, if the concrete is

specified by performance, the performance class or performance requirements.

12.4.2 Batching tolerances

The batching tolerances for fibres are the same as for admixtures and additions. The

tolerance is 3 % of required quantity where the mass of fibres used is more than 5 % by

mass of cement and 5 % where the mass of fibres is 5 % or less, by mass of cement.

12.4.3 Batching procedure

Fibres are added during the main mixing process or in a second mixing operation in the

truck. When fibres are added in the truck mixer, the concrete has to be re-mixed until the

fibres have been completely dispersed throughout the batch.

13 Recommendations

The following recommendations are made:

1. More research or information is needed about the risk of introducing air into concrete by

the addition of fibres. The supplier of the fibres should be required to demonstrate that

they do not unduly increase air content of the concrete or give a consistent increase in

the air content. (see 9.3 Practice in Europe / Austria).

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2. Where testing of fibre content is required, producers should consider whether it is

necessary to have a target fibre content, higher than the minimum specified, to allow for

testing errors.

3. Due to the difficulties of testing the fibre content of hardened concrete, current best

practice is described in prEN 206.

4. Where performance is specified, the performance should be demonstrated during the

initial testing, and conformity should be based on demonstrating that the proven type and

quantity of fibres have been batched.

5. That performance of fibre concrete should be based on existing and still to be developed

European test methods and common performance classes and these are adopted at the

European level and included in a future revision of EN206 .

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EUROPEAN READY MIXED CONCRETE ORGANIZATION ASSOCIATION

Ermco Fibre Guide September 2012 Corr A

Documents

Transcript of Ermco Fibre Guide September 2012 Corr A