Cracking and durability in FRC - Chalmers · Cracking and durability in FRC G. Plizzari University...

Göteborg, Sweden, September 13, 2017

Cracking and durability in FRC

G. Plizzari

University of Brescia, Italy

2/60 Göteborg, Sweden, September 13, 2017

Outlines

Cracks in Reinforced Concrete elements

Experimental program

Crack formation and development

Crack width and crack spacing

Concluding remarks


Cracks in RC elements


FRC to enhance crack control in RC elements

Short fibers having a straight or deformed shape

uniformly dispersed in the concrete matrix.

Fibers activate after cracking by bridging the crack.

The concrete is able to transmit higher forces

between the crack planes.

(1) Fiber reinforcement increase the concrete post-cracking tensile residual strength

(transmitted at crack location)

(2) Fiber reinforcement increase the bond between concrete and rebars


Comparison of the behaviour of RC and RC+FRC tensile members:

srRC

se

c=fctm

bm

D-Region

steel stress

concrete stress

bond stress

c=0

ltRC lt

RC

NN

crack disturbed zone

bm

D-Region

ltRC+FRC lt

RC+FRC

NN

crack disturbed zone

srRC+FRC

se

c=fctmc=fctm

(1) FRC local tension softening

behaviour (simplified law):

fctm

fctm

At crack locations: FRC exhibits a

noticeable toughness with respect

to plain concrete

By adding fibers (1)+ (2): - reduction of crack spacing: reduction of srm

- reduction of average member strain at a given applied force: increase of

tension stiffening

(2) Increase of steel-to-concrete bond due to fiber reinforcement

Research significance


0

2

4

6

8

10

12

14

0 0.1 0.2 0.3 0.4 0.5 0.6

Loaded End Slip [mm]

Bo

nd

Str

es

s [

MP

a]

Normal strength concrete

High strength concrete

Nor. str. fiber reinf. concrete

High str. fiber reif. concrete

No stirrups

=0

B=4

Bond in FRC elements


Bond in FRC elements



Flexural behaviour of a RC

beam having constant or

low gradient bending

moment

Beam cross-section:

effective area

surrounding

longitudinal steel

reinforcing bars

Prismatic SFRC samples with a central rebar: SFRC tension tie



A broad experimental study was carried out.

The following key-parameters were investigated:

- Concrete cylinder compressive strength: from 27 MPa to 47 MPa

- Square element size: from 50 to 200 mm

- Clear concrete cover: from 20 to 85 mm

- Effective reinforcing ratio: from 0.98 to 3.26%

- /eff ratio: from 306 mm to 2043 mm

- Bar diameter: from 10, 20 and 30 mm

- Specimen length: from 950 mm to 1500 mm

- Volume fraction of fibres: from 0 to 1%

- Type of fibres

More than one hundred prismatic tensile ties were tested


Vf b

[mm]

As

[mm2]

Ac,eff

[mm2]

Reinf.

Ratio (%)

Clean

cover

[mm]

Denomination # of

specimens

10

0*

50 79 2421 3,24 20

N 50/10 - 0 3

0,5%* N 50/10 - 0,5/M 3

1,0 %* N 50/10 - 1/M 3

0,5%+0,5%* N 50/10 - 1/M+m 3

1%+1% N 50/10 - 2/M+m 3

10

0*

80 79 6321 1,24 35

N 80/10 - 0 2

0,5%* N 80/10 - 0,5/M 3

1,0 %* N 80/10 - 1/M 3

0,5%+0,5%* N 80/10 - 1/M+m 3

1%+1% N 80/10 - 2/M+m 3

20

0*

100 314 9686 3,24 40

N 100/20 - 0 3

0,5%* N 100/20 - 0,5/M 3

1,0 %* N 100/20 - 1/M 3

0,5%+0,5%* N 100/20 - 1/M+m 3

1%+1% N 100/20 - 2/M+m 3

20

0*

150 314 22186 1,41 65

N 150/20 - 0 3

0,5%* N 150/20 - 0,5/M 3

1,0 %* N 150/20 - 1/M 3

0,5%+0,5%* N 150/20 - 1/M+m 3

1%+1% N 150/20 - 2/M+m 3

30

0*

150 707 21793 3,24 60

N 150/30 - 0 3

0,5% N 150/30 - 0,5/M 3

1,0 % N 150/30 - 1/M 3

0,5%+0,5% N 150/30 - 1/M+m 3

1%+1% N 150/30 - 2/M+m 3

30

0*

200 707 39293 1,80 85

N 200/30 - 0 2

0,5% N 200/30 - 0,5/M 3

1,0 % N 200/30 - 1/M 3

0,5%+0,5% N 200/30 - 1/M+m 3

1%+1% N 200/30 - 2/M+m 3

Bar diameter f=10 mm



50

50

80

80

150

15

0

95

0

11

50

100

10

0

150 200

15

0

20

0

Reinforcement

b

Varia

tion o

f the re

bar d

iam

ete

rVariation of the specimen

size, b

Variation of the longitudinal

steel ratio, ρ=3,24% to 1,24%

Varia

tion o

f the re

bar d

iam

ete

r

Experimental Program



1st phase: tie 950/1000 mm long tested in by means of a

hydraulic servo-controlled (closed-loop) testing machine with

MTS control

2nd phase: tie 1000 mm

and 1500 long tested in

by means of a available

steel reacting frame

conveniently modified


Instrumentation


Fiber types and contents

Fibre IDType of

steelShape

fuf[MPa]

Lf [mm]

f[mm]

Lf /f [-] Batch ID

30/0.62 Carbon Hooked-end 1270 30 0.62 48.39 0.5M, 1M, 1M+m

13/0.20High

carbonStraight 2000 13 0.20 65.0 1M+m

Batch ID Fibers 30/0.62Fibers13/0.20

Vf,tot

0 Plain - - -

0.5M 0.5 - 0.5

1M 1 - 1

1M+m 0.5 0.5 1


FRC properties

3PBTs on notched beams according to EN14651:

Fracture parameters of the SFRCs according to EN-14651

Batch ID fLm [MPa] fR1m [MPa] fR2m [MPa] fR3m [MPa] fR4m [MPa]

1st

phase

0.5M 5.46 5.00 4.55 4.05 3.46

1M 4.81 5.09 4.12 3.42 3.01

1M+m 5.97 6.30 5.35 4.35 3.54

2nd

phase

0.5M 4.60 4.12 4.07 3.35 2.69

1M 4.64 5.43 4.89 4.36 3.86

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 1.0 2.0 3.0 4.0

No

min

al

stre

ss

N[M

Pa

]

CMOD [mm]

3PBT - EN - 14651

SFRC 0.5M

SFRC 1M


0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4 5

Ax

ial

forc

e [

kN

]

Average member strain, sm [‰]

Specimens 120x120 - Φ20 - ρ = 2.23%

Bare bar Φ20

N 120/20 - 0

N 120/20 - 0.5M


The typical response terms of axial load vs. average tensile strain of RC and FRC

FRC stiffens the response of tensile tie with respect to non-fibrous members

By referring to a certain axial force the average strain (εsm) reduces by adding fibres

-

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5

Axia

l fo

rce [

kN

]


Specimens 200x200 - Φ30 - ρ= 1.80%

Bare bar Φ30

N 200/30 - 0

N 200/30 - 0.5M

+N



Plain Concrete FRC

Fibre addition determines a reduction of the mean crack spacing



Crack spacing evolution vs. average member strain

0

100

200

300

400

500

600

700

800

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Cra

ck s

paci

ng [

mm

]


Specimens 200x200 - Φ30 - ρ= 1.80%

RC

SFRC 0.5M

SFRC 1M

Final crack spacing



The residual FRC post-cracking strength improves the behaviour at SLS and the durability of structures for two main reasons:

1) determines a global stiffer response of the tensile tie which means, by referring

to a certain axial tensile force, a reduction of sm;

2) implies a reduction of the mean crack spacing (srm).

cmsmrmm

sw

Reduction of the mean crack width, wm


Crack width

-53% -56%

-32% -29%

-39% -41%

-29% -23%

-16% -28%

-12% -32%

-33% -38%

-25% -40% -31% -36%

Crack opening reduction with respect to plain samples (RC)[%]

Average reduction fibre SFRC 0.5M - 30,0%

Average reduction fibre SFRC 1M - 35,8%

Mean crack width at SLS comparison (@ average strain = 1*10-3)

Mea

n c

rack

wid

th [m

m]

SFRC 0.5M

Plain (RC)

SFRC 1M+m

SFRC 1M


Mean and minimum crack spacing

Mean crack spacing (srm) and minimum crack spacing (sr,min) comparison

0

50

100

150

200

250

300

350

400

0 500 1000 1500 2000 2500

Mea

n c

ra

ck s

pa

cin

g [

mm

]

Φ/ρeff [mm]

Mean crack spacing vs. Φ/ρeff

RC

SFRC Vf=0.5%

SFRC Vf=1%

100x100 Φ20

120x120 Φ20

180x180 Φ30

200x200 Φ30

180x180 Φ20

150x150 Φ20

50x50 Φ10

80x80 Φ10

150x150 Φ30

R2=0.92

R2=0.76

R2=0.93

srm = 1.18srmin

R2 = 0.92srm= 1.40srmin

R2 = 0.91srm = 1.45srmin

R2 = 0.86

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350

Mean

crack

sp

aci

ng [

mm

]

Minimum crack spacing [mm]

Mean crack spacing vs. minimum crack

spacingRC

SFRC Vf=0.5%

SFRC Vf=1%

Mean crack spacing (srm) reduction of around 30% (Vf=0.5%) and 37% (Vf=1%)

Similar ratio between mean crack spacing and minimum crack spaing: RC vs. SFRC ties


Crack spacing

Mean crack spacing (srm) vs. fR1m

0

50

100

150

200

250

300

3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

Mea

n c

ra

ck s

pa

cin

g [

mm

]

fR1m [MPa]

Mean crack spacing vs. fR1m - SFRC series

Vf<1%

Φ/ρ<500

500<Φ/ρ<1000

1000<Φ/ρ<1500

Φ/ρ>1500

An increase in the residual strength fR1m leads to a decrease of srm


Crack spacing in the building codes

The main results in terms of mean crack spacing (srm) are compared with the predictions obtained by the following formulations:

eff,s

21rmkk

10

sc2s

eff,s

rm6.3

1

3

2s

ctmbm

eff,s

rmf8.1:termshort

8.1

1

4

1c17.1s

Regarding FRC:

m1RFtsm

ctmbm

eff,sbm

Ftsmctm

m,r

f45.0f

f8.1:termshortff

4

1c17.1s

- Model Code 1978:

- Model Code 1990:

- Model Code 2010:

- Model Code 2010(final draftfib bulletin 65/66) fR1m,

parameter according to EN14651:

- RILEM TC 162-TDF:

ffeffs

mrL

KKs

/

5025.050

,

21,

- Model Code 2010(first draftfib bulletin 55/56)

mRFtsm

effsbm

Ftsmctmmr

ff

ffs

1

,

,

45.0

4

117.1

145.0 RFts ff


Crack spacing

Plain series (RC): prediction of mean crack spacing, MC1978 & MC1990

0

50

100

150

200

250

300

350

400

450

500

0 100 200 300 400 500

Mean

crack

sp

aci

ng (

measu

red

)[m

m]

Mean crack spacing (predicted)[mm]

Prediction of the mean c.spacing- RC series

MC1978

MAPE=24.7%

0

50

100

150

200

250

300

350

400

450

500

0 100 200 300 400 500M

ean

crack

sp

aci

ng (

measu

red

)[m

m]



MC1990

MAPE=17.1%

CONSERVATIVE

UN

CO

NS

ER

VA

TIV

E

CONSERVATIVE

UN

CO

NS

ER

VA

TIV

E

MC 1978 MC 1990


Crack spacing

Plain series (RC): prediction of mean crack spacing, MC 2010

0

50

100

150

200

250

300

350

400

450

500

0 100 200 300 400 500

Mea

n c

ra

ck

sp

acin

g (

mea

sure

d)[

mm

]



MC2010,

Final draft

MAPE=24.0%

UN

CO

NS

ER

VA

TIV

E

CONSERVATIVE

MC 2010


Crack spacing

SFRC series: prediction of mean crack spacing, RILEM TC-162-TDF

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Mea

n c

ra

ck s

pa

cin

g (

mea

sure

d)[

mm

]


Prediction of the mean c.spacing - SFRC series

RILEM TC 162-TDF

MAPE@100%CONSERVATIVE

UN

CO

NS

ER

VA

TIV

E

RILEM


Crack spacing

SFRC series: prediction of mean crack spacing, MC 2010 Final draft

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Mea

n c

rack

sp

aci

ng

(m

easu

red

)[m

m]


Prediction of the mean c.spacing - SFRC series

MC2010, Final draft

MAPE=27.9%CONSERVATIVE

UN

CO

NS

ER

VA

TIV

E

MC 2010

Final Draft


Crack spacing

SFRC series: prediction of mean crack spacing, MC 2010 First draft

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Mea

n c

ra

ck s

pa

cin

g (

mea

sure

d)[

mm

]


Prediction of the mean c.spacing - FRC series

MC2010, First Draft

MAPE=65.8%

CONSERVATIVE

UN

CO

NS

ER

VA

TIV

E

MC 2010

First Draft


Durability requirements in building codes

Durability in EN-206


Cracking vs. Durability

Durability

Possible solution for improving crack control: Fibre Reinforced

Concrete (FRC)

Between two cracks At crack location

Lower porosity Lower crack width

W/C ratio


Corrosion at crack location

Is crack control important for durability?


Simulated pitting corrosion

CUTTER DIAMETERS:

8 mm

12 mm

16 mm

20 mm


senR

senR

AAAp

asp

22

22

21.

CFBCBFh

2cos1

RCGRBC

2cos1

PP

RCARCF

2cos1

2cos1

p

RRh

2cos1

2senarcsencos1

p

pR

R

RRh

D

Dp

C

F

E

B

A

G

h

RpRp

A2

A1

known:

-Dp = cutter diameter

-Dnom = nominal bar diameter

Simulated pitting corrosion


Simulated corrosion

INSTRUMENTATION

la

la

l0 la+l0


Material properties

Diam. fsy fst

[mm] [MPa] [MPa]

12 526 613

16 513 606

20 ls 491 570

20 ms 534 610

20 hs 550 628

24 555 597



Diameter=12 mm - Dr=8 mm

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12Displacement [mm]

Load [

kN

]

%=0.95

%=0.90

%=0.8

%=0.7

%=0.6

%=0.5

Load vs. Displacement curves


Bar diameter = 12 mm

0

1

2

3

4

5

6

7

8

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

%Ares

Dis

pla

cem

ent

d0.9

9 [

mm

]

Undamaged Bar

Dr=10 mm

Dr=8 mm

Dr=6 mm

Dr=4 mm


0

2

4

6

8

10

12

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

%Ares

Dis

pla

cem

ent

d0.9

9 [

mm

]

Dr = 10 mm

Dr = 8 mm

Dr = 6 mm

Dr = 4 mm


0

2

4

6

8

10

12

14

16

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1%Ares

Dis

pla

cem

ent

d0.9

9 [

mm

] High S tre ngth

Me dium S tre ngth

Low S tre ngth


0

2

4

6

8

10

12

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

%Ares

Dis

pla

cem

ent

d0

.99 [

mm

]

Unda ma ge d Ba r

Dr=10 mm

Dr=8 mm

Dr=6 mm

Dr=4 mm

Ultimate displacement


Exposure in aggressive (marine) environment

10 beams has been exposed for more than 2 years in a coastal zone,

under a load equal to 50% of the ultimate load

Aim of the research: evaluate the influence of fibers on mechanical

behaviour of FRC in short and long term bending test


Beam geometry and rebar properties

3Ø14 18

2 Ø14

18

300

25

294

25

25

7 7

10

14 14

10

294

3

3

52

DiameterYield strength

(MPa)

Ultimate strength

(MPa)

Longitudinal

bars14mm 520 614

Stirrups 8mm 567 600


FRC properties

(UNI 11039)

0 500 1000 1500 2000

0

2

4

6

8

10

12

06S

09P

TQ065

LO

AD

(kN

)

CTOD (microns)

0.6% steel

0.9% polyester

Vf=0,6%

Vf=0,9%


Crack monitoring

Crack width, crack length and

crack position have been

measured during the exposure

period. The crack width has been

measured with a digital

microscope (200x magnification)


Cracking monitoring

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 50 100 150 200 250

pp1

pp2

st1

st2

tq

In FRC beams the crack widths were in the range of 0.1 to 0.2 mm, without overcome the

threshold of 0.2 mm. In plain beam the 93.3% of cracks had a crack width over 0.1 mm, while

the 60% over 0.2 mm.


Cracking monitoring

Average of crack widths between the loading points

Beams Dw /%

ST1-2_E 54%

POL1-2_E 53%

0.31

0.14 0.140.16

0.13

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

TQ1_E ST1_E ST2_E POL1_E POL2_E

Cra

ck w

idth

(m

m)

Crack width reduction of the FRC beams respect

to the plain beam (Dw /%).

steel polyester

PC


Cracking behavior at SLS

SLE

(50kN)

ST1-2 35%

POL1-2 28%

SHORT TERM

BEAMS

LONG TERM

BEAMS

SLE (50kN)

ST1-2_E 43%

POL1_E 37%

POL2_E 43%

Crack width reduction of the FRC beams respect to the plain beam.


Cracking behavior at ULS

SLU

(100kN)

ST1-2_E 56%

POL1_E 25%

POL2_E 54%

SLU

(100kN)

ST1-2 41%

POL1-2 39%

Crack width reduction of the FRC beams respect to the plain beam.

SHORT TERM

BEAMS

LONG TERM

BEAMS


Carbonation depth

CARBONATION DEPTHCHLORIDE CONTENT


Carbonation depth between the cracks


Carbonation depth at cracks

K

(mm/anni

^0.5)

t

armature

(anni)

TQ_E 19.4 2.4

ST1_E 12.7 5.6

ST2_E 13.4 5.0

POL1_E 12.5 5.8

POL2_E 14.7 4.2


Concluding remarks

FRC diffusely influence the behavior of tension-ties at serviceability limit states, by

reducing crack width and determining a crack patterns with narrower and well

closely spaced cracks;

SFRC positively influences the behaviour of tension-ties at SLS due to two main

aspects: tension-stiffening significantly increases and mean crack spacing

(srm) reduces with respect to the RC members (without fibres)

Lower crack widths due to FRC involve a consistent increase in the structural

durability and, therefore, in the structural life;

The MC 2010 model for predicting srm in FRC elements generally predicts with

sufficient accuracy the experimentally observed data;

SFRCs having fR1m around 4-5 MPa were mainly investigated: further studies

regarding SFRCs with different post-cracking strengths (higher or lower) could

be developed


Open issues

Transform cracking information in durability

issues in order to guarantee the structural

safety for the whole service life of the

structure.

In this context, FRC is a valuable tool for

enhancing structural durability!


Papers in international journal

Minelli, F., Tiberti, G., and Plizzari, G.A. (2011). “Crack Control in RC Elements with

Fiber Reinforcement”, paper ID: SP-280-6; ACI Special Publication ACI SP-280:

Advances in FRC Durability and Field Applications CD-ROM, Vol. 280, Editors:

Corina-Maria Aldea & Mahmut Ekenel, December 2011, pp. 76-93. ISBN 0-87031-

751-2 and/or 978-0-87301-751-4.

Tiberti, G., Minelli, F., Plizzari, G.A., Vecchio, F.J. (2014). “Influence of concrete

strength on crack development in SFRC members”, Cement and Concrete

Composites, Vol. 45, January 2014, ISSN: 0958-9465, pp. 176-185,

doi:http://dx.doi.org/10.1016/j.cemconcomp.2013.10.004.

Tiberti, G., Minelli, F., Plizzari, G. (2015). “Cracking behavior in reinforced concrete

members with steel fibers: A comprehensive experimental study”, Cement and

Concrete Research, Vol. 68, February 2015, ISSN: 0008-8846, pp. 24-34, doi:

http://dx.doi.org/10.1016/j.cemconres.2014.10.011.


Papers in international journal

Vasanelli E., Micelli F., Aiello M.A., Plizzari G. (2013), Long term behavior of FRC

flexural beams under sustained load, Engineering Structures, Volume 56, pp. 1858-

1867.

Emilia Vasanelli, Francesco Micelli, Maria Antonietta Aiello, Giovanni Plizzari (2013),

Crack width prediction of FRC beams in short and long term bending condition,

Materials and Structures, Springer, pp. 1-16.

Cairns, J., Plizzari, G. A., YINGANG, D., Law, D. W., & Franzoni, C. (2005).

Mechanical properties of corrosion-damaged reinforcement. ACI Materials Journal,

102(4), 256-264.


About Brescia


Historical buildings in Brescia


Dolomites

55/60 Göteborg, Sweden, September 13, 2017 13

Dolomites


Lake Garda


Welcome to Brescia


Workshop proceedings


Desenzano, June 28-30, 2018


Thank you for your kind

attention!


Göteborg, Sweden, September 13, 2017

G. Plizzari


Cracking and durability



Prismatic SFRC samples with a central rebar: SFRC tension tie

Bar diameter

=10 mm

Bar diameter

=20 mm

Bar diameter

=30 mm

505

080

80

1501

50

L=

95

0

11

50

100

10

0

150 200

15

0

20

0

Reinforcement

b

Variation of the

specimen size, b


steel ratio =3.24% to 1.24%

Variatio

n o

f the

rebar d

iameter

80

80


steel ratio =0.98% to 2.23%

200

20

0

120

12

0

180

18

0

180

18

0

Variation of the

specimen size, b

30

03

00

b

(a) (b)

1st phase 2nd phase

L=

15

00

(L

=1

00

0 f

or

10

bar

)

Cracking and durability in FRC - Chalmers · Cracking and durability in FRC G. Plizzari University...

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Transcript of Cracking and durability in FRC - Chalmers · Cracking and durability in FRC G. Plizzari University...