UNI11039Part.ii Losas

8/10/2019 UNI11039Part.ii Losas

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STEEL FIBRE-REINFORCED CONCRETE

PART II

TEST METHOD USED TO DETERMINE THE EARLY CRACK STRENGTH

AND DUCTILITY INDEXES

1. SCOPE

This standard specifies a method for the determination of both the first crack strengthfIf (Part I, clause 3.3.1) and the ductility indexes D0and D1(Part I, clause 3.3.3) of

test specimens of Steel Fibre-Reinforced Concrete (SFRC).

2. STANDARD REFERENCES

prEN 12350-1:1999.Testing fresh concrete Part1: Sampling

prEN 12390-1:1999.Testing hardened concrete- Part 1: Shape, dimensions and otherrequirements for specimens and moulds

prEN 12390-2:1999.Testing hardened concrete: Part2: Making and curing

specimens for strength tests

3. PRINCIPLEPrismatic test specimens with a central notch are loaded in a four point flexure; the

test shall be carried out at prescribed CMOD1rate.

The first crack strength (fIf )and the ductility indexes D0and D1are calculated on thebasis of load - CTODnet

2curve.

4. TEST SPECIMENSThe test specimens

3can be obtained either from basic concrete

4and/or SFRC; they

can be cast or cut out.

The test specimens are not intended for aggregate with maximum nominal size of 32

mm.

4.1 Cast specimensConcerning the making and curing of test specimens by casting of basic concreteand/or SFRC, prEN 12390-2 shall apply. In addition the procedure of filling the

mould with SFRC must comply with the following items (Figure 1):

1. cast portion 1 in the centre of the mould;

2. cast portion (2) and making sure that portions (1) and (2) are properly covered;

1Part I, clause 3.2.12Part I, clause 3.2.5

3Damaged specimens or specimens which are badly honeycombed should not be tested.

4Part I, clause 3.1.1


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3. the volume of portion (1) must be about twice that of portion (2).

The SFRC must be compacted on a vibrating table; compaction through internalvibrator is not allowed.

Figure 1 Filling procedure with SFRC

The cast direction must be identified on the test specimen.

4.2 Cut out test specimens

The test specimens cut out from hardened SFRC can be tested only if they meet therequirements listed in clause 4.4after being suitably adjusted, if necessary.

4.3 Curing and transport

The test specimens shall be cured and transported according to EN 12390-2

(reference procedure).If curing and/or transport procedures are:

q unknown;

q different from those specified in EN 12390-2;

the test can be carried out on condition that such lack of data concerning curingand/or transport, i.e., any known deviation from the EN 12390-2, are recorded in the

test report.

4.4 Shape, dimensions and tolerances

The reference test specimens are square-base right prisms with nominal dimensions

150x150x600mm; test specimens with different dimensions can be used just for theonly purpose of having an indication, on condition that the following terms are met:

2 21


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the specimen length (l) must be at least 3.5 times the height (h); anyway it cannotbe lower than 350 mm;

the shorter side of the specimen cross section must be at least 3.5 times the

maximum size of the aggregate.

The size tolerance of the test specimens shall comply with the prEN12390-1

specifications.

4.5 NotchA notch shall be made in the central line of a test specimen face adjacent to the

trowelled face by using a diamond saw down to a depth a0so that a0/h = 0.3 0.01.

The notch width must range from 3 to 5 mm. The notch end must be V-shaped (PartI; Figure 1).

5. EQUIPMENT

5.1 Test equipment

With reference to the points below, the test equipment must comply with EN 12390-4:

force measure; accuracy of the force indication; frequency of calibration; safety.

The test equipment must be provided with a proper device which allows to carry out

the tests under displacement control.

5.1.1Device for load applicationThe load application device (Figure 2) shall consist of:

two upper rollers; an articulated cross member able to equally divide the load applied by the testing

machine between the two upper rollers;

two lower supporting rollers.


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Figure 2. Arrangement of loading of test specimen

Key:

1 loading rollers (capable of rotating around their axis and of being

inclined (3));2 supporting roller;3 support cylinder (capable of rotating around their axis and of being

inclined (3)).

All rollers shall be manufactured from steel and shall have a circular cross-section

with a diameter of 20 mm to 40 mm; they shall be at least 10 mm longer than the

width of test specimen.

Each upper roller shall be free to rotate around its axis with a rotation (3) withinthe plane perpendicular to the longitudinal axis of the specimen.

The distance between the lower rollers (l) shall be equal to 3h and in any case it

cannot be shorter than 300 mm. The distance between the two upper rollers shall be

equal to h. The upper rollers shall be equally spaced between the lower rollers, asshown in Figure 1. Each roller shall be positioned to the indicated location (Figure 2)

with an accuracy of 1 mm.

5.2 Force gauge

The load shall be measured with a load cell; the load shall be shown by a digital

and/or analogic display, with the required accuracy (Table 1). The system shall allowthe read value to be recorded by a special device (clause 5.4) with the metrologic

tolerance given in Table 1.

h

b(=h)h h h

l=3h

l3,5h

11

2 3


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Relative accuracy

error

%5

Relative

repeatability error

%5

Zero relative error

(% of full scale)5

Machine resolution6

%5

1 1.0 0.2 0.5

Table 1. Metrologic tolerance allowed for load measurement

5.3 Displacement gauges

5.3.1 Gauges for CTOD and CMOD measurement

The displacement value at the notch tip shall be measured by a gauge with a range

5mm and a sensitivity which not lower 2.5 mV/mm. The use of a full bridge

resistive gauge is recommended.Figure 3 shows an example of displacement gauge consisting of two metal thin plates

constrained at one end (clip-gauge) applied to the gauge holders (Figure 1, part I).

Figure 3. Example of full bridge resistive gauge for CMOD and CTOD measurement.

5.3.2 Gauges for the displacement measurement of the load application points(optional)

The displacement of the load application points, if required, shall be measured by

means of a gauge having a measurement range 10 mm.

5.4 Recording system

The load and displacement values shall be measured by a suitable analogic or digital

data acquisition system. The data shall be recorded on a magnetic support

5This percentage is the maximum admitted for the testing machine.

6See the definition given in clause 5.3, EN 10002 2:1998.

Gauge holders

CMOD or CTOD

gauge

d d

d10 mm


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Taking into account the numeric computations required by the present standard, a

data acquisition system provided with an analogic/digital converter with resolution

12 bit is recommended. The indicated resolution must be guaranteed on an inputsignal range equal to that of the amplified signal output of the load and displacement

gauges.

6. ProcedureThe test specimens shall be checked before being tested and any anomaly be

recorded.

6.1 Test specimen instrumentation

6.1.1 Instrumentation for CTOD and CMOD measurement.

The gauge-holders relevant to the CTOD must be glued on the two opposite faces of

the test specimen at the height of notch tip (a0); they shall be symmetrical as to the

notch tip (Figure 4). The maximum width of the gauge-holder surface glued on the

test specimen must not be greater than 25 mm (clause 5.1.1, Figure 3). The two

gauge-holders for the CMOD measurement shall be glued along the lower edges ofthe notch (Figure 4). The gauge-holders shall be glued with a stiff glue at hardened

state.

Figure 4 shows a layout for the application of gauge-holders and the relevant gauges.

Figure 4. Layout for the application of the gauge-holders and the relevant CTOD and CMOD gauges.

Section

A-A

h

l = 3hL3.5 h

A

A

a0

b (=h)

h

CMOD gauges

CTOD gauges


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6.1.2 Instrumentation for displacement measurement of the load application

points (optional).

The actual displacement of the load application points on the test specimen shall bemeasured by excluding of any spurious displacements such as those caused by local

settlements near the supporting and loading rollers or due to rotations of the specimen

along its longitudinal axis.

The displacement is measured by four displacement gauges fixed to a reference barconstrained to the test specimen as shown in Figure 5. These gauges are placed along

the load application direction with reference to the two side faces of the test

specimen. Suitable stiff metal plates shall be glued on the test specimen lower faces

in order to match the sensing probe of the gauges for the whole duration of the test.

Figure 5. Layout for the application of the gauge-holders and the relevant gaugesfor the measurement of the displacement of the load application points

6.2 Load application

The four point flexural test shall be carried out by CMOD control.The loading rollers shall be carefully approached to the test specimen and impacts

must be avoided. The CMOD must be constantly increased at a speed of

0.050.01mm/min. For CMOD values over 0.65 mm the displacement rate can beprogressively increased up to 0.50.02mm/min. with an acceleration 1 mm/min.2.

The load, the two CTOD values and the displacement of the load application points(if required) shall be continuously recorded on a magnetic support.

If the beginning of the main crack7falls outside the V-shaped upper edge of the notch

in at least one of the side faces of the specimen, it shall be recorded in the test report

and the CTODm-CMOD diagram shall be also reported.At the end of the test, the notch depth to the nearest 0.5 mm shall be taken as the

maximum value of three measures carried out in the centre and at the two ends of the

test specimen section.

7 Expression of results

7Main crack stands for the trace of the cracking plane on a side face of the test specimen.

D sp acementgauge

Displacementgauge

Hinge Carriage

Reference bar

Sensin in


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7.1 CTOD0 detection

The CTOD0can be detected either directly (reference method) on basic concrete test

specimens (Part I, clause 3.1.1) or indirectly.

7.1.1 CTOD0 detection direct methodBasic concrete specimens (3 at least are recommended) having the same dimensions

and notch depth as the SFRC specimens and instrumented as shown in clause 6.1.1,

are subjected to flexural test according to the provisions given in clause 6.2.The

CTOD0value is detected for each test specimen undergoing the flexural test. Thisvalue corresponds to the max load (Pmax)

8 taken from the Load-CTOD curve (Figure

6).

Figure 6. Direct detection of CTOD0

The mean of the CTOD0values measured for each test specimen is used to calculatethe first crack strength (fIf; clause 7.2).

7.1.2 CTOD0detection indirect methodIf basic concrete test specimens are not available, it is possible to take the

conventional value 25 m9for the CTOD0.

7.2 Calculation of SFRC first crack strength (fIf)

The first crack strength (fIf; Part I, clause 3.3.1) is calculated on the basis of the load

maximum value (PIf) resulting from the Load - CTODmdiagram for CTODmvalues

falling between 0 and CTOD0(Figure 7).

8

The maximum load value Pmax cannot be taken into consideration for the calculation of the flexural strength.

9CTOD0mean value measured on a set of 45 samples of basic concrete whose compressive strength

ranges from 20 to 90 MPa.

Pmax

Load

CTODmCTOD0

Load-CTODm diagram forbasic concrete


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PIfshall be calculated by linear interpolation between two recorded couples of

experimental contiguous points having abscissas CTODm1and CTODm2such as:

CTODm1CTOD0CTODm2

If the CTODmvalue corresponding to the maximum load point in the Load-CTODmdiagram is lower than 10 m, it shall be reported in the test report.

Figure 7. Examples of first crack load PIf detection

The first crack strength (fIf) is given by the following formula

( )2

0ahb

lPf

I f

I f

= [MPa]

where:

PIf = first crack load [N];

l = interaxial distance between the axis of the lower rollers [mm];b = specimen width [mm];

h = specimen height [mm];

a0 = measured notch depth [mm].

7.3 Calculation of the ductility indexes D0and D1.The ductility indexes D0and D1 are calculated according to the following formulas:

PIf

Load

CTODmCTOD0

L

oad

PIf

CTODmCTOD0


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)6,00(,

)36.0(,

1

)6,00(,

0

=

=

eqf

eq

fI

eq

fD

f

fD

where:

feq(0-0.6)= equivalent strength [MPa] in the CTODnetrange 0-0.6mm (Part I, clause

3.3.2.1);feq(0.6-3)= equivalent strength [MPa] in the CTODnet0.6-3mm (Part I, clause3.3.2.2)

The equivalent strengths are calculated through the following formulas:

( ) 6.02)6.00(,1

0

U

ahb

l

eqf

= ( ) 4.22)36.0(,

2

0

U

ahb

l

eqf

=

where:

l = distance between the axis of the lower cylinders [mm];

b = specimen width [mm];

h = specimen height [mm];

a0= measured notch height [mm];

U1, U2= areas [10-3

joule] subtended to the Load-CTODmcurve (Figure 8)10

in theCTODnet(Part I, clause 3.2.5) 0 to 0.6mm and 0.6 to 3mm

11respectively; the

U1 and U2 values are obtained with the following formulas:

10

The equivalent strength in the CTODnet range between 0 and 3 mm is given by:),(,),(,)(, ,, 36060030 8020 += eqeqeq fff

11The U1and U2values are approximately proportional to the energy dissipated in the CTODnetranges taken

into consideration.

( ) ( )=6,0

01 CTODdCTODPU

( ) ( )=3

6,01 CTODdCTODPU


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Figure 8. Example of Load-CTODmcurve in which are highlighted the areas correspondingto crack openings (CTODnet) up to 0.6 and 3 mm.

8. Test report

The test report must mention the following:

a) reference to this standard;

b) identification of the SFRC test specimen and of any basic concrete test specimens;c) CTOD0detection method (direct or indirect);d) if the direct method is used:

d1) number of basic concrete test specimens tested;

d2) mean value of the maximum load obtained from the Load-CTODm curve;

d3) CTOD0value to the nearest 1 m;e) if the indirect method is used:

CTODmvalue corresponding to the maximum load if lower than10 m;f) test specimen making method (cast or cut out);

g) first crack strength to the nearest 0.1 MPa;h) ductility indexes D0 and D1 to the nearest 0.01;i) indication of the main crack starting point when found outside the V-shaped upper

edge of the notch (in this case the CTODm-CMOD diagram referred to in clause

5.4 shall be attached);

j) detected notch depth (clause 6.2);k) any deviation from this standard;l) concrete aspect, if unusual;m)test date.

The test report can also include:

CTOD0

U2U1

LOAD

CTOD0+ 0.6 mmCTOD0+ 3 mm

PIf

CTODm


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n) specimen age at the test time (if known);o) curing and/or transport conditions (if known);p) magnetic support where test data are recorded.

9. Precision

Tables 2a and 2b contain the precision data for the first crack strength fIfand theductility indexes D0and D1 in terms of repeatability standard deviation (sr) and

repeatability limit (r) (ISO 5725-1:1994, clause 3.15 e clause 3.16) for the SFRC and

basic concrete respectively.

Tables 3a and 3b give the precision data for the first crack strength fIfand the

ductility indexes D0and D1 in terms of repeatability standard deviation (sr) and

repeatability limit (r) referred to the mean values.

Repeatability Conditionsfor SFRC

srr

( 222 rsr= )

Absolute values

Direct

method

Indirect

method

Direct

method

Indirect

method

fIf[MPa] 0.3 0.3 0.8 0.8D0 0.08 0.09 0.23 0.25

D1 0.04 0.04 0.11 0.11Prospect 2

Repeatability conditions for basic concreteAbsolute values

srr

( 222 rsr= )

fmax [MPa] 0.1 0.3

Repeatability conditions for basic concrete

according to prEN 12390-5

Absolute values

srr

( 222 rsr= )

fmax [MPa] 0.3 0.8


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Repeatability conditionsfor SFRC

sr[%]

r [%]

( 222 rsr= )

Relative values

Direct

method

Indirect

method

Direct

method

Indirect

method

fIf 6 6 17 17

D0 6.0 6.6 17.0 18.7

D1 5.0 5.0 14.1 14.1

Repeatability conditions for basic concreteRelative values

sr[%]r [%]

( 222 rsr= )

fmax [MPa] 2.6 7.3

Repeatability conditions for basic concrete

according to prEN 12390-5

Relative values

sr[%]r [%]

( 222r

sr= )

fmax [MPa] 6.5 18.4

UNI11039Part.ii Losas

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