Cracks in concrete facilitate corrosion

Cracks in concrete facilitate corrosion

Reference [11]

There are many causes for crack formation (see table below).

While hairline cracks are accepted as they are almost unavoidable and do not reduce the strength of the structure, larger cracks provide wide openings for corrosive ions to the rebar, bypassing locally the long initiation time.

Sealing cracks is an option, of course, but not applicable in recesses or in hidden areas…and this is already a repair operation as cracks may form years later. Sealants delay the onset of corrosion, but not forever.

Type of Cracking

Form of Crack

Primary Cause

Time of Appearance

Plastic settlement

Above and aligned with steel reinforcement

Sunsidence around rebar; excessive water in the mix

10 minutes to three hours

Plastic shrinkage

Diagonal or random

Excessive early evaporation

30 minutes to six hours

Thermal expansion and contraction

Transverse (example: across the pavement)

Excessive heat generation or temperature gradients

One day to two or three weeks

Drying shrinkage

Transverse or pattern

Excessive water in the mix; poor joint placement; joints over-spaced

Weeks to months

Freezing and thawing

Parallel to the concrete surface

Inadequate air entrainment; non-durable coarse aggregate

After one or more winters

Corrosion of reinforcement

Above reinforcement

Inadequate concrete cover; ingress of moisture or chloride

More than two years

Alkali-aggregate reaction

Pattern cracks; cracks to parallel joints or edges

Reactive aggregate plus moisture

Typically, over five years, but may be much sooner with highly reactive aggregate

Sulfate attack

Pattern cracks

External or internal sulfates promoting the formation of ettringite

One to five years

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