Vermelding onderdeel organisatie

Oktober 21ste 2015

1

Constructiegedrag van door ASR aangetasteviaducten, CUR-Aanbeveling 102 en Resultaten experimenteel onderzoek

Cor van der Veen

Faculty of Civil Engineering and GeosciencesConcrete Structures Section

Wat is ASR? [1]

• Alkali-Silica Reactie (ASR)• In twee fasen te onderscheiden:

• Alkalien + Silica Gelvormig reactieproduct

• Gelvormig reactieproduct + Water Expansie

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ASR-gel [1]

uitbloeiingen ASR-gel

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Typisch scheurenpatroon ASR [1]

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ASR schadebeelden [1]

• “landkaartenpatroon”• Beton met Portlandcement• Na jaren ouderdom

• 5-30 jaar ouderdom

• Voorkeursrichting• Invloed wapening• Drukspanning

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Gevolgen uitzetting beton door ASR [1]

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Voorkomen verdere uitzetting beton

• Pas waterdicht scherm toe aan een zijde omverdere toetreding water te voorkomen

• Laat aan onderzijde beton open (afvoerwater) zodat betonconstructie kan drogen.

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Classificatie CUR-Aanbeveling 102 [3]

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Klasse 3Materiaaleigenschappen

Klasse 2Een-assige treksterkte

Klasse 1Aanleiding scheuren

ClassificatieKlasse 1

• Craquelé scheurenpatroon• Voorkeursrichting?• Gelijkmatig verdeeld?• Scheurafstand/wijdte

• Cumulatieve scheurwijdte

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ClassificatieKlasse 2

• Schatting

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. gemiddeldASR

n w

lε =

ASRε

ClassificatieKlasse 2 : PFM-onderzoek (boorkeren)

cumulatieve scheurwijdtelage treksterkte

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Praktijk NED

ClassificatieKlasse 3 : kernen boren dwarskrachtgebied

• Kerndiameter 75 mm• 6 kernen éénassige

treksterkte• 3 kernen druksterkte

• Relatie treksterkte: Vertikaal en horizontaal

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ClassificatieKlasse 3: eenassige betontreksterkte

• Uitgangspunt van CA is lage eenassigebetontreksterkte

• Verschil treksterkte in horizontale en vertikale richting

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Classificatie [3]

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Klasse 4Constructieve beoordelingdwarskracht

Klasse 4A: handmatigKlasse 4B: numeriek maatgevende

doorsnedeKlasse 4C: gehele constructie

ClassificatieKlasse 4: Constructief onderzoekinvloed zwellen van beton • Voorbeeld:

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30,5 10

0,01

30000

0,937

0,063 0,95

195

: 200000 100

ASR

b

zv ASR

b ASR b

s b

s ASR

x

E MPa

E MPa drukspanning

MPa zonder relaxatie

benaderend x MPa

εω

ε εσ ε

σ σω

σ ε

−=

==

== =

= = →

= =

ClassificatieKlasse 4: Constructief onderzoek

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Gemiddelde eenassige vertikale treksterkte

1

1,5

0,9

:

m

ld

m

langeduur

gemiddelde waarde

γλτ

==

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Probleem definitie; experimenteelonderzoek [den uijl 2]

• ASR in many bridges• Horizontal cracks in deck• Strong reduction of

uniaxial tensile strength • No shear reinforcement• Residual shear resistance?

Two viaducts with ASR investigatedtype: ZB and HS

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10.014.25

7.5

14.2510.0

beam HS1

south north

SP02 SP03 SP04 SP05SP01 core nr. 1

core nr. 24

measures in m

11.0

beam HS2

beam HS3

beam HS4

Position vertical cores HS-bridge

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Strength from vertical HS-cores

Type of South span Entire bridge

test [MPa] [MPa] [%]

Cube 50.5 53.9 14

Splitting ⊥ 3.19 3.35 17

Splitting // 3.30 3.55 16

Uniaxial1 0.93 1.11 42

1 Vertical uniaxial concrete tensile strengthRatio horizontal to vertical uniaxial tensile strength about 0.5

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Evaluation of shear resistance

• Literature

• small scale tests, accelerated ASR

• both reduced and increased shear strength

• First idea (1999)

• in situ loading of bridge until failure

• limited time and little knowledge about mechanism

• Final plan

• shear tests on beams cut from bridge decks

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Specimens (1)

Beams sawn out of ZB-bridge: 8.5×0.6×0.7 m

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Specimens (2)

Beams sawn out of HS-bridge: 7.5×0.5×0.65 m

10.014.25

7.5

14.2510.0

beam HS1

south north

SP02 SP03 SP04 SP05SP01 core nr. 1

core nr. 24

measures in m

11.0

beam HS2

beam HS3

beam HS4

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Specimens (3)

• Plain rebars fsy=220 MPa

• Reinforcement ratio

• ZB: ρ0,int=1.0 to 1.3 %

• HS: ρ0,int=0.5 %

• Steel strips glued on HS-beams

→ ρ0,tot=1.1 to 1.6 %

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Test set-up

• 4-point bending test• Both beam ends tested

• Shear span: a/d=2.5 to 4.5

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Measurements

• Load

• Deflection

• Concrete strains

• Crack development

• Prestress due to ASR (afterwards)

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Test results

• Failure mode• ZB: 3 bending/shear, 1 bending• HS: 8 shear

• Shear strength (average)• ZB: 0.96 MPa• HS: 1.03 MPa

• Shear crack inclination• ZB: 25 ± 5°• HS: 30 ± 5°

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Bending shear

• Strength without shear reinforcement:

• Strength ratio Vu,test / Vu,Rafla

• ZB: 0.60 (cov 9.5 %) bending governing• HS: 0.77 (cov 7.5 %)

• Note• reduction less than for uniaxial tensile strength• low scatter compared to core strength values• no prestress considered

bdfdV ccuRaflau3

025.0

, ρα −=

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Type of shear failure

bending shear diagonal tension

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Diagonal tension• Mohr’s circle at neutral axis

• τxy = 1.5×τavg = 1.5 MPa

• Effect of prestress on• Shear strength

xctctxy ff στ −= 2

30

35

40

45

0-1-2σx/fct

1,0

1,3

1,6

1,9τxy/fct ϕ [degree]

• Crack inclination

ctx

ctxy

f

f

στ

ϕ−

=1

arctan

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Effect of ASR-induced prestress

• Without prestress ϕ = 45°

• Crack inclination 45° → 30°

• → σx/fct = −2

• and τxy/fct = 1.73fct = 1.5/1.73 = 0.9 MPaσx = -2×0.9 = -1.8 MPa

• measured σx = -0.3 MPa→ calculated >> measured

30

35

40

45

0-1-2σx/fct

1,0

1,3

1,6

1,9τxy/fct ϕ [degree]

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Effect of orientation dependent tensile strength (1)

• Uniaxial tensile strength

• vertical fct,0 = 0.6 MPa

• horizontal fct,90 = 1.2 MPa

• Tensile strength ratio

• β = fct,0 / fct,90 = 0.5

• Splitting tensile strength

• fct,spl = 2,8 MPa

• fcc = 55 MPa → fct,spl = 3,75 MPa

topside of ZB-deck

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Effect of orientation dependent tensile strength (2)

• Conceive the anisotropic material as an isotropic material that is pre-compressed in one direction

fct,9 0 - fct,0

pre-compressed

+fct, 0

fct,0

isotropic

=fct,90

fct,0

anisotropic

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Effect of tensile strength ratio and prestress ratio (1)

• Substitution of • Yields

)( 0,90,, ctctresxx ff −−= σσ0,ctct ff = ( )res

ct

xy

fγβ

τ−= 1

90,

resγβϕ

−=

1arctan

• With and90,

,

ct

resxres f

σγ =

90,

0,

ct

ct

f

f=β

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0.0

0.5

1.0

1.5

0.0 0.2 0.4 0.6 0.8 1.0

β = fct,0/fct,90

γres =

-1.00-0.67-0.33 0.00

τxy/fct,90

15

25

35

45

0.0 0.2 0.4 0.6 0.8 1.0

β = fct,0/fct,90

γres =0.00

-0.33-0.67-1.00

ϕ [°]

Effect of tensile strength ratio and prestress ratio (2)

ZB: ϕ = 25°β = 0.5

→ γres = -1.2 → τxy = -1.05×fct,90 = 1.26τxy,experiments = 1.34

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Practical application

• Orientation ϕ not known

• Difficult to drill horizontal cores

• Therefore

• estimate ASR-induced prestress

• approximate tensile strength ratio with

105.00,

,

0,

+==

cc

ct

splct

ct

f

f

f

fβ

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γres = -0.33• → τxy = 0.72×1.5 = 1.08 MPa

γres = -0.67• → τxy = 0.81×1.5 = 1.22 MPa

γres = 0• → τxy = 0.6×1.5 = 0.9 MPa

γres = -1.0• → τxy = 0.9×1.5 = 1.35 MPa

Practical application ZB-bridge

• fcc = 55 MPa• fct,0 = 0.6 MPa• → β = 0.4• → fct,90 = 1.5 MPa• estimate prestress ratio to

• τxy,exp = 1.34 MPa0.0

0.5

1.0

1.5

0.0 0.2 0.4 0.6 0.8 1.0

β = fct,0/fct,90

γres =

-1.00-0.67-0.33 0.00

τxy/fct,90

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γres = -0.33• → τxy = 0.82×1.8 = 1.48 MPa

γres = -0.67• → τxy = 0.91×1.8 = 1.64 MPa

γres = -1.0• → τxy = 1.02×1.8 = 1.84 MPa

γres = 0• → τxy = 0.7×1.8 = 1.26 MPa

Practical application HS-bridge

• fcc = 50 MPa• fct,0 = 0.93 MPa• → β = 0.52• → fct,90 = 1.8 MPa• estimate prestress ratio to

• τxy,exp = 1.5 MPa0.0

0.5

1.0

1.5

0.0 0.2 0.4 0.6 0.8 1.0

β = fct,0/fct,90

γres =

-1.00-0.67-0.33 0.00

τxy/fct,90

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• Full-scale beam tests yielded insight in shear behavior of ASR-affected bridges without shear reinforcement

• Failure: 8 shear, 3 bending/shear, 1 bending

• Shear strength 65 to 75 % of theoretical value

• Diagonal tension rather than bending shear

• Crack inclination of 25° to 30° could not be explained from ASR-induced prestress alone

• With also an orientation dependent tensile strength the test results could be explained

•

Conclusions

Conclusie CUR_Aanbeveling 102

• Kalibratie Eurocode• Eénassige betontreksterkte vervangen door…• Kennis opgedaan door proefbelasting inzetten

• Dus Nieuwe CA-102 noodzakelijk

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