Control of Cracking in Concrete


Control of Cracking in Concrete

The age-old axiom in concrete construction is that concrete cracks. While cracks may develop
in concrete for a variety of causes, the underlying principle is the relatively low tensile
strength of concrete. Visible cracking occurs when the tensile stresses exceed the tensile strength
of the material. Visible cracking is frequently a concern since these cracks provide easy access
for the infiltration of aggressive solutions into the concrete and reach the reinforcing steel or,
other components of the structure leading to deterioration. This document reviews the causes of
cracking, discusses various tests that can be performed to assess the susceptibility of a material to
cracking, and provides several case studies.
It is important to understand why cracks develop in highway concrete structures and
pavements. While some commonly think of external loading as being responsible for generating
the majority of the tensile stresses in a material, much of the cracking in concrete can be traced
to an intrinsic volumetric instability or the deleterious chemical reactions. The volume instability
results in response to moisture, chemical, and thermal effects. In addition, various deleterious
chemical reactions involving the constituents of concrete or embedded materials can play
significant roles causing localized internal expansions.

The impact of cracking on durability, especially corrosion, is detrimental to many
transportation structures. In particular, cyclic or tidal exposures initiate dry-wet cycles and
provide a constant source of salts to enter the cracks, significantly exacerbating deterioration.
Similarly, cracked concrete in contact with sulfate rich soil can lead to accelerated sulfate attack.
The complex relationships between cracking and accelerated deterioration are unique to each
situation and are not well understood. Thus considerable attention is needed from the research
community to fully understand the principles involved and transfer them to the practicing
engineering community for improved durability.
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