Cold Weather Guidance
- Freshly placed concrete is vulnerable to freezing temperatures, rain, sleet and snow both before and after it has stiffened.
- Concrete which has not attained sufficient maturity (>5N/mm2) can be permanently damaged due to free water freezing, thereby reducing the ultimate strength of the concrete, leading to a loss of durability. In addition ice lenses may form and cause spalling.
- In strong winds, heat loss from concrete increases rapidly leading to a reduction in the temperature of exposed surfaces.
- In still conditions, unprotected concrete surfaces are also vulnerable to rapid heat loss by radiation if there is no cloud cover.
- Frost damage can also occur in mature concrete, but is more likely too ccur in its early life. Scaling and popouts are features of this effect which can be severe, particularly in saturated concrete subjected to exposure to freezing temperatures.
- Concrete walls and slabs which have large areas exposed at low temperatures are most at risk. In addition, external paving which is placed on cold ground is vulnerable to the effects of low temperatures. At low temperatures the rate at which concrete hardens is considerably
- reduced and appropriate extra care must be taken when striking formwork and supporting members.
See further details in the PDF file below.
Hot Weather Guidance
- Hot weather conditions occur infrequently in Ireland.
- Hot weather conditions are usually caused by a combination of factors (some or all) including high ambient temperature, high solar radiation, low relative humidity and high wind velocity.
- However infrequent, hot weather conditions can impact on concrete,both in the fresh and hardened state.
- Hot weather conditions cause an increase in fresh concrete temperatures, resulting in more rapid hydration leading to lower workability and accelerated hardening.
- Plastic shrinkage cracks and crazing can be caused by rapid evaporation of moisture from exposed surfaces in hot weather leading to an increase in permeability.
- Concrete cured at temperatures significantly exceeding 20°C will develop higher early strengths, compared to standard cured concrete.
- Later-age strength gain is likely to be reduced compared to that of similar mixes cured at standard temperature.
- Higher temperatures tend to accelerate slump loss and can affect entrained air levels.
- In hot weather fresh concrete can have a shorter working life which causes difficulties in transport, placing and finishing. Concrete placed under high temperatures will set quicker and can, therefore require more rapid finishing.
See further details in the PDF file below
Safety Sheet for Ready Mixed Wet Concrete is included in PDF below
