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Avoiding thermal contraction cracks

In terms of avoiding thermal contraction cracks, experience has shown that by limiting temperature differentials to 20°C in gravel aggregate concrete, cracking can be avoided.

CIRIA Report Early thermal cracks control in concrete C660 (2007) gives limiting differential temperatures for different aggreagte types. (superseded by CIRIA Report C766, 2018)

Table: Limiting temperature changes to avoid cracking
for internal restraint R = 0.42 (from C660)

Aggregate type Limiting differential temperature, oC
Gravel 20
Granite 28
Limestone 35
Lightweight aggregate concrete, with natural sand 53

If these temperatures are exceeded, cracks are likely to form and sufficient reinforcement should be provided to control their widths (see Controlling thermal contraction cracks).

Acknowledgement: The Concrete Society

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TR22 Non-structural cracks in concrete

Crack width measurement