Readymix Concrete/Aggregates/Concrete Blocks/Mortar/Admixtures
Using Cold weather concreting is a common and
sometimes necessary practice. Every application
concrete must be considered carefully and special care should
be taken when placing concrete in cold weather. If
in cold young concrete is allowed to cool too much below
freezing it will be damaged to such an extent that it
weather — will be unfit for use.
Cold-weather concreting, as stated in ACI 306 is,
practical “a period when for more than 3 successive days the
average daily air temperature drops below 5°C and
information stays below 10°C for more than one-half of any 24
hour period.”
It is important to note that even if temperatures
do not fall below zero that concrete will develop
strength far more slowly than during warmer
months.
Disclaimer: This is intended as general advice only and does not absolve the end user from following best
practice or any other instructions or guidelines as set down in specifications or directed by the Specifier/Engineer.
Call 01 865 8700 (ROI) 02890 616611(NI) or email ireland.info@cemex.com www.cemex.ie
www.cemex.ie/supaflo
Readymix Concrete/Aggregates/Concrete Blocks/Mortar/Admixtures
When working with concrete in cold weather It is important that formwork is not removed An alternative to insulated formwork is to use
it is important to consider two temperatures too soon otherwise there is a danger that a heated enclosure, this must completely
— that of the ambient air temperature and concrete surfaces may be damaged and that enclose the member and precautions should
that of the concrete itself. It is important not to concrete in beams and suspended slabs may not be taken that the heating source does not
confuse the two. be able to carry its own weight and collapse. result in high concentrations of CO2 in the
enclosure as this can damage freshly placed
It is not possible to give a hard and fast rule
The following is some practical concrete, jets of hot air should not be played
as to how long formwork should be left in
directly on to fresh concrete as this could
advice on measures that should be place as the rate of gain of strength depends
cause rapid drying and reduced strength.
adopted on many factors including the ambient
temperature, the cement content of the mix Water curing is not advisable in near-
In no circumstance should concrete be allowed and the type of cement used. freezing conditions as the saturated
to freeze during the first 24 hours after it has concrete could be damaged.
been placed. If freshly placed concrete cools If necessary the rate of gain of strength can be
below 0°C the water in the mix will freeze and increased by increasing the cement content, The exposure of concrete to cold weather will
expand and may cause such severe damage using a higher grade; if being used, reduce the extend the time required for it to gain strength.
that the concrete is unusable. proportion of GGBS or PFA in the mix. In structures that will carry large loads at an
early age, concrete must be maintained at a
The temperature of concrete should not be minimum of 10°C to accommodate stripping
Frost at night.
allowed to fall below 5°C until such point of forms and shoring and to permit loading of
as it has reached 5 N/mm2. For most The temperature of concrete the structure. In many cases, achieving the
structural concretes this can be achieved in should not be below 5°C when required durability will require a protection
about 48 hours, provided that the concrete delivered but there will be period of more than 24 hours. This may not be
has been kept at or above 5°C. (This can occasions when the ready-mix an issue with residential applications where
be checked by making additional cubes supplier cannot guarantee this temperature applied loads are typically small and may be
and storing them alongside the member.) on delivery. Should placing go ahead in applied in small increments over several days
However even after concrete has reached these circumstances, precautions will be or weeks.
this strength low temperatures will slow down necessary to ensure that the concrete can be
strength development. adequately protected. When the time required for protective
measures is complete the surface temperature
The aim therefore, during cold weather must Any concrete must be prevented from freezing. of the concrete should be lowered slowly to
be to keep concrete warm (above 5°C) for All snow, ice and frost should be removed from avoid thermal shock.
the first 48 hours and then to ensure that the shutters, reinforcement and adjacent concrete,
strength is permitted to develop although at a when concrete is to be placed on sub-grade,
this should also not be frozen. Severe frost.
slower rate.
Additional precautions for these
The severity of the weather determines the Freshly placed concrete must be protected
conditions may require concrete to
precautions that should be taken, for the straight away, necessary protection for
be delivered at a temperature of
purposes of concreting cold weather can be includes frost blankets and insulated
10°C. If this is not possible then
divided into the following three categories: formwork. Timber formwork by itself often
it is advisable to delay concreting until the
offers sufficient insulation in short spells of
ambient temperature has risen.
moderately cold weather and when used
Ambient temperature below 5°C.
in combination with insulation can provide Further advice and information is
When the temperature is low but protection during very cold periods. Metal available from our technical team by
does not drop below freezing there formwork has little insulation value and must calling (ROI) 01 865 8700 or
is no danger that the concrete will be used with additional insulation during (NI) 02890 616611 or emailing ireland.
be permanently damaged but it cold weather. info@cemex.com
will take longer to develop strength.
Call 01 865 8700 (ROI) 02890 616611(NI) or email ireland.info@cemex.com www.cemex.ie
www.cemex.ie/supaflo
