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Hot and cold weather
concreting

5.1 Introduction

Concrete buildings and other structures are built in most countries around the world and
in some regions the climates are typified by prolonged spells of either hot or cold weather.
Readymix concrete and construction companies in these regions manage to produce
good-quality concrete despite these climatic drawbacks. In many regions with adverse
climates there are consensus specifications and guidance documents for concrete production
(ACI 305, ACI 306, CIRIA/Concrete Society Guide) which give details of methods
which can be used to combat the adverse conditions.

In the more temperate parts of the world, cool, humid weather is the norm. In these
locations, although prolonged hot or cold spells are not unusual, it usually comes as a
surprise when they arrive and it may be too late to apply even the most rudimentary
precautions to mitigate their undesirable consequences.

Physiological effects in both hot and cold conditions should not be ignored. Operatives
and supervisors cannot be expected to produce good-quality concrete if they have been
exposed to the elements for long periods without proper protection.

5.2 Hot weather concreting

There is no simple definition of ‘hot weather’ for concreting purposes. It is not just a
matter of a limiting temperature, as a hot, humid, calm day may not pose so many

problems as a cooler day with lower humidity and high winds. In the latter case there will
be a greater tendency for water to evaporate from exposed surfaces of concrete. ACI 305
defines hot weather as ‘any combination of high air temperature, low relative humidity,
and wind velocity tending to impair the quality of fresh or hardened concrete or otherwise
resulting in abnormal properties’.

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