UNI11039Part.I Losas

8/10/2019 UNI11039Part.I Losas

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marted 21 agosto 2001 fibro13_en1

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STEEL FIBRE-REINFORCED CONCRETE

PART I

DEFINITIONS, CLASSIFICATION, SPECIFICATION AND CONFORMITY

1. Scope

This standard aims at defining the characteristics and the conditions required for Steel Fibre-Reinforced Concrete (SFRC).This standard applies to the following types of SFRC: batched at site ready-mixed manufactured at pre-casting plant

manufactured in the laboratory.The SFRC can be used as unreinforced, reinforced and prestressed concrete.

2. Normative references

EN 206pr E16.11.442.0 (UNSIDER)................

3. Definitions

For the purposes of this standard the following definitions apply:

3.1 Materials

3.1.1 Basic concrete:

concrete as defined in EN 206 and without fibre reinforcement (see clause 3.1.6).

3.1.2 Steel fibre:

see pr E16.11.442.0 (UNSIDER)

3.1.3 Equivalent diameter of the fibre (d):


3.1.4 l/d ratio:


3.1.5 Fibre reinforcement:

set of discontinuous discrete steel fibres dispersed into the fresh mix.

3.1.6 Steel Fibre-Reinforced Concrete (SFRC) :


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Sez. A-

composite material constituted by basic concrete1in which a homogeneously distributed fibrereinforcement is incorporated in the mix.

3.2 Displacements

3.2.1 Crack Mouth Opening Displacement (CMOD)Displacement detected between two points belonging to the lower end of the two notchedges2(Figure 1).

3.2.2 Crack Tip Opening Displacement (CTOD)

Displacement detected between two points belonging to a test specimen face and located atthe same height as to the notch tip and in a symmetrical position as to its vertical axis (Figure1).

3.2.3 Mean value of Crack Tip Opening Displacement (CTODm)

Mean value of the two CTOD values measured on the two opposite faces of the testspecimen (Figure1; section A-A).

3.2.4 Basic Crack Tip Opening Displacement (CTOD0)

Value of the CTODmcorresponding to the conventional onset of the cracking process in thebasic concrete (First Crack); see Part II, clause 7for its detection.

gauge holder for the

CMOD

measurement

A

A

gauge holder for

the CTOD

measurement

notch tip

a0

notch

gauge holder for

the CTOD

measurement

CTOD

gauge holder for the

CMOD

measurement

CMOD

a0: notch depth;b: test specimen width.

gauge holder for

the CTOD

measurement

b

gauge holder for

the CTOD

measurement

Figure 1.Scheme of the notch and position of the gauge holders for CTOD and CMODmeasurement.

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The composition of the basic concrete can be modified by adding plasticising or superplasticising admixtures(EN 934-2) on the condition that the air content at the green state (prEN 12350-7) does not differ from that ofthe basic concrete without admixtures by more than 0.5%2The notch is made in the centre line of the test specimen in order to force the cracking process ina pre-established zone of it.


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3.2.5 Mean Crack Tip Opening Displacement (CTODnet):

Mean value of the two CTOD values measured on the two opposite faces of the specimenstarting from CTOD0 value.

3.3 Properties

3.3.1 First crack strength (fIf)

It is the conventional flexural strength of the SFRC calculated on the basis of the load valuecorresponding to the CTOD0value. The first crack strengthshall be determined accordingto clause 7.2, Part II.

3.3.2 Equivalent strength

It is the integral mean value of the conventional flexural strength of the SFRC calculated in a

prescribed CTODnetrange. The equivalent strengths shall be calculated according to clause7.3, Part II.

3.3.2.1 Equivalent strength feq(0-0,6)It is the equivalent strength calculated in the range of CTODnetbetween 0 - 0.6 mm

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3.3.2.2 Equivalent strength feq(0.6-3)It is the equivalent strength calculated in the range of CTODnetbetween 0.6 - 3mm.

3.3.3 Ductility

It indicates the capability of the specimen to keep its strength characteristics as the crackprocess develops (for CTODnet> 0).

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3.3.3.1 Ductility index

It characterises the SFRC ductility in a prescribed range of CTODnet.

3.3.3.2 Ductility index D0.

It characterises the SFRC ductility in the range of CTODnetbetween 0 and 0.6mm; it is givenby the ratio between the equivalent strength feq(0-0,6) and the first crack strength (fIf).

3.3.3.3 Ductility index D1.It characterises the SFRC ductility in the range of CTODnetbetween 0.6 and 3mm; it is givenby the ratio between the equivalent strengths feq(0,6-3)and feq(0-0,6) .

4. Classification

The SFRC is classified on the basis of the following characteristics:

3The value of CTODnet in the middle (0,3 mm) of the integration range varying from 0 to 0.6 mm correspondsto the crack opening allowed by Eurocode 2 under service conditions.4Ductility refers to the structural behaviour of the specimen and it depend on the material toughness(resistance opposed by the material to the development cracking process due to its capability of dissipatingdeformation energy in crackedregime).


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consistency;compressive strength;first crack strength (fIf) and ductility indexes (D0and D1).

4.1 Consistency classes

Where the SFRC is classified according to the compressive strength, the classes given inclause 4.2.1 of EN 206, shall apply.

4.2 Compressive strength classes

Where the SFRC is classified according to the compressive strength, the classes given inclause 4.3.1 of EN 206

5, shall apply.

4.3 First crack strength (fIf) and ductility indexes (D0and D1)

Where the SFRC is classified with respect to the first crack strength (fIf) and the ductilityindexes D0and D1,both table A and B shall apply.

Class F2.0 F2.5 F3.0 F3.7 F4.5 F5.5 F6.5 F7.7 F9.0Min.

characteristic

strength fIf[MPa]

2 2.5 3 3.7 4.5 5.5 6.5 7.7 9.0

Table A. First crack strength classes.

Ductility classesDuctility

indexes(Min

characterist ic

values)

DS0 DS1 DS2 DP DH0 DH1 DH2

D0 (6) 0.5 0.7 0.9 1.1 1.3 1.55

D1 0.3 0.5 0.7 0.9 1.1 1.37

1.5510

Softening behaviour Plastic behaviour Hardening behaviour

Table B. Ductility classes

Key of table B:

DS0, DS1, DS2: softening behaviour, characterised by a load decrease as the CTODnetincreases;

DP: plastic behaviour, characterised by an almost constant load as the CTODnetincreases;

DH0,H1,H2:: hardening behaviour, characterised by a load increase as the CTODnet increases.

5. Specification

5Considering that the efficiency of the fibre reinforcement increases as Rck of concrete increases, Rck 25

MPa is recommended for structural applications.6Ductility index values D0< 0.5 are typical of a concrete which is not steel fibre reinforced.

7 Classes DH1and DH2of the D1 index are typical of very high performance SFRCs whose mix designrequires the use of special fibre reinforcements and suitable basic concretes.


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The SFRC specification must include the following: the exposure class according to clause 4.1 of EN 206; the consistency class according to clause 4.2.1 of EN 206; the maximum nominal upper size of aggregate according to clause 4.2.2 of EN 206; the compressive strength class according to clause 4.3.1 of EN 206; the first crack strength class as indicated in Ttable a; the ductility class in the CTODnetranges (0 - 0.6mm) and (0.6 - 3mm) as indicated in

Table b;

Prospect Cgives an example of specification of SFRC having the following characteristics: compressive strength class C30,37; consistency class S4; maximum nominal upper size of aggregate (=20 mm); exposure class XC2; class of first crack strength equal to 3.5 MPa; ductility index D0belonging to the class DP; ductility index D1belonging to the class Ds2.

C30/37 S4 20 XC2 F3.5 DP DS2

Table C Example of SFRC specification

6. Basic requirements for SFRC composition.

6.1 General

Composition and constituents of the basic concrete of the SFRC (cement, aggregates,water, any admixtures and/or additives) must meet the requirements provided for in EN 206and in this standard.The steel fibres must comply with the requirements of UNSIDER The SFRC shall be designed in such a way that the steel fibres shall be homogeneosly andrandomly dispersed in its own mass.

6.2 Cement type and composition of basic concrete

The cement to be used must be selected among those listed in EN-UNI 197.The limiting values for composition of concrete related to exposure classes given in clause5.3 of EN 206 shall apply8.Considering the SFRC specificity, the minimum cement content shall not be lower than 330kg/m3.

6.4 Minimum fibre content

8Steel fibres may be corroded when exposed to the same environmental actions responsible for thecorrosion of the reinforcing steel, in particular in the surface layer of the concrete which may be subjected to

carbonation.


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The minimum fibre content must not be less than 25 kg/m3.

Lower fibre contents are allowed in the following cases:

q for fibre aspect ratios (Clause 3.1.4 Part I) > 60;

q for special applications for instance for structural elements whose minimum thickness issimilar to that of the fibre length.

In this case, preliminary tests have to be carried out in order to check if the requirements forSFRC are satisfied.

7 Steel fibres in the SFRCTo determine the weight content of steel fibres in the SFRC at fresh and hardened state,refer to Appendix D, UNI 10834 Sprayed concrete.

8 Conformity control and conformity criteria

8.1 General

For the general conditions clause 8.1 of EN 206shall apply.

8.2 Conformity control for SFRC

8.2.1 Sampling and test program

As far as the sampling and testing plan, clause 8.2.1.2 of EN 206shall apply.

8.2.2 Conformity criteria for first crack strength and ductility indexes

Conformity assessment shall be made on test results taken during the assessment periodestablished in clause 8.2.1.3 of EN 206.

The conformity of first crack strength and of ductility indexes is assessed on test specimensafter 28 days8of curing.

The compliance with fIfcharacteristic values is confirmed if the test results meet the two

criteria given in Table D.

Criterion 1 Criterion 2

Production9 Number n of test

resultsMean of n results

(fI,m) [MPa]

Every single test

result (fI,j) [MPa]

Initial 3 fI,f+ 0.5 fI,f- 0.56 fI,f+ 1.877 fI,f+ 1.77

Continuous

8 fI,f+ 1.72

fI,f- 0.5

8The conformity of first crack strength and of ductility indexes is assessed at different ages only if explicitlyspecified.9For the definition of initial and continuous production, refer to clause 8.2.1.2 of EN 206.

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