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UNIVERSITY OF GAZIANTEP FACULTY OF ENGINEERING CIVIL DEPARTMENT

CE-547

Corrosion of Plain &Reinforced concrete

Report # 3:

(Concrete damage due to corrosion of

reinforcement )

Submitted to:

Do.Dr. Mehmet GESOLU

Prepared by:

Chalak Ahmed Mohammed chalak.mohammed@gmail.com

2014 45056

Date : 17.03. 2015

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Corrosion of reinforcing steel is a major deterioration process affecting

reinforced concrete structures worldwide. Corrosion causes cracking and

spalling of the concrete cover, loss of load bearing capacity and ultimately

structural collapse.

Fig.(1)

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Cracking of the cover is often a critical limit state and this can be modelled as a two-stage process consisting of an initiation phase, defined as

the time taken for corrosion to commence, and a propagation phase, where

the formation of corrosion products induces expansive stresses and damage.

Until recently, most research has focused on the time up to corrosion

initiation, while the propagation phase leading to failure remains poorly

understood. One important aspect that lacks understanding is the amount of

corrosion products that must form to cause damage. It is likely that not all

corrosion products contribute to cracking because some are soluble species

that dissolve in the pore solution and migrate into adjacent cement paste

away from the sites of corrosion.

Fig.(2)

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Observations

Corrosion products can migrate through the aggregate-paste interface as

well as the bulk paste. They can be deposited in cracks, air voids, inner &

outer hydration products, and relicts of reacted slag. A distinct boundary

between the affected and unaffected paste can be seen, indicating the extent

of the rust penetration (Fig 3).

Fig 3: BSE

montage of samples with different degrees of corrosion, showing rust accumulating at the steel-

concrete interface and migrating into the cement paste, cracks and air voids

EDX microanalyses show that the affected paste has higher analysis totals,

and Fe and O contents, but is depleted in Ca (Fig 4

Subsequent corrosion products are forced to accumulate at the steel-

concrete interface, inducing expansive pressure that leads to bond failure

and cracking.

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Fig 4: BSE

images and EDX element maps indicating the extent of rust penetration and decalcification.

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Image analysis found that only a small amount of corrosion product,

approximately 100m thick covering about 20% of the rebar perimeter, is

needed to generate the first visible cover crack (~0.05mm width). Once

cracking has initiated, the rust preferentially deposits in large cracks rather

than pore spaces in the cement paste. Hence, the extent of rust penetration into the cement paste does not increase much with corrosion (Fig 5b).

Fig 5: Effect of corrosion degree on the amount of damage and area of the rust layer (CL) and rust

penetrated paste (RP).

Regards...