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NUMERICAL SIMULATIONS AND ACCELERATED CORROSION TESTS TO STUDY THE CRACK PATTERN OF REINFORCED CONCRETE SAMPLES

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NUMERICAL SIMULATIONS AND ACCELERATED

CORROSION TESTS TO STUDY THE CRACK PATTERN OF REINFORCED CONCRETE SAMPLES

4th International PhD Workshop ICC Eduardo Torroja, Madrid

19th November 2010

B. Sanz, J. Planas, J.M. Sancho

Dep. Ciencia de Materiales

SEDUREC

CONSOLIDER-INGENIO 2010

Universidad Politécnica de Madrid, Spain

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• Cracking of the concrete cover and spalling

Motivation

• Decrease in the net cross-sectional area

• Volumetric expansion of the oxide

Objective:

• To predict the mechanical effects of the oxide over the concrete

Main aspects of corrosion:

• Expansive joint element

1 Numerical model for the oxide

2 Accelerated corrosion tests

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t = f ( ˜ w )

˜

w w with ˜ w = max (|w|)

• Strong non-linearity

• Bilinear softening curve

Concrete cracking: Standard cohesive model

|w|

|t|

stress

crack opening

w ˜

|t| = f(|w|)

σ w

t

w

σ = f (w)

(4)

Finite element program: COFE (Sancho et al, 2003)

Continuum-Oriented Finite Elements

w n

• Strong discontinuity kinematics

• Constant strain elements

• Simple cohesive model

• Limited local crack adaptation Adaptable embedded crack

t

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Oxide layer: Expansive joint element

τ u τ u

steel

initial

joint

steel

simulation

• The oxide is already forming

• The corrosion depth is given at any specified time

steel

corroded

oxide βx

x

Mechanical equivalence oxide - element Debonding ability

Nearly free sliding:

very small shear stiffness • Nearly free separation:

very small tensile stiffness

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Parameters of the simulations

Corrosion

• Total diametral expansion: 50 µm

50 steps

n

Size effect study

4 - 32

3.93 - 0.49 mm le

• GMSH (Geuzaine)

• Constant Strain Triangles Steel: linear elastic

Concrete: cohesive embedded crack

Oxide: expansive joint element

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Simulations using the expansive joint element

n = 32

(elem/quarter)

(8)

Size effect study in the simulations

n=4 n=8

n=16 n=22 n=32

(9)

external current I

Previous models for accelerated corrosion tests

Andrade et al (1993)

steel bar sponge counter-electrode

I

oxidation

reduction

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Crack pattern in accelerated corrosion tests

2 cm

1 mm

1 mm

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Crack pattern in accelerated corrosion tests

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Crack pattern in accelerated corrosion tests

T03-05-R02

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Crack pattern in accelerated corrosion tests

T03-05-R02

∆ø = 0 µm

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Crack pattern in accelerated corrosion tests

T03-05-R02

∆ø = 0 µm

(15)

Crack pattern in accelerated corrosion tests

T03-01-R02

∆ø = 40 µm

(Estimation:

Andrade 97)

(16)

Crack pattern in accelerated corrosion tests

T03-01-R02

∆ø = 40 µm

(17)

Crack pattern in accelerated corrosion tests

T03-04-R03

∆ø = 200 µm

(18)

Crack pattern in accelerated corrosion tests

T03-04-R03

∆ø = 200 µm

(19)

Comparison of the crack pattern

Experimental pattern

Simulations pattern

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Summary

• A model called expansive joint element was programmed to simulate the oxide layer behaviour

• The numerical simulations with that model predict a wide main

crack across the concrete cover but also some secondary cracks, in agreement with accelerated corrosion tests

• The impregnation under vaccuum of the samples with resin containing fluorescein improves the cracks detection

• The surface treating has been proved not to produce any cracks on the concrete surface

• The wider cracks contain less resin than the smaller ones. It can

be due to the presence of compact oxide that does not let the

resin come inside the cracks

(21)

Thank you for your attention

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