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The principal effect of aggregate in concrete is to restrain the contraction of the cement paste, thereby helping to reduce the likelihood of cracking. In general, aggregates with a higher modulus of elasticity (greater stiffness), cubic shape and rough particle surface textures are likely to offer more restraint to concrete shrinkage.
The magnitude of shrinkage can vary substantially with type of aggregate. Quartz, granite and limestone are frequently associated with low concrete shrinkage, whereas sandstone and some basic igneous rock aggregates are more likely to cause or permit comparatively higher shrinkage.
BS EN 12620:2002+A1 specifies that the drying shrinkage of aggregates used in structural concrete is not greater than 0.075% when tested to BS EN 1367-4. This is reflected in PD 6682-1 Annex B and BS 8500-2.
Typical shrinkage values for concrete in the UK, using aggregates which are not recognised as having high shrinkage, are in the order of 0.03% to 0.045%.
A practical value for the drying shrinkage of lightweight aggregate (Lytag) is 0.035%. BS EN 1992-1-1 section 3.1.4 suggests that the drying shrinkage of lightweight concrete (for strength classes LC20/22 and above) may be taken as 20% greater than that for normal weight concrete.
Acknowledgement: The Concrete Society
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