Expanded Guide on Concreting in Hot and Cold Weather :

Guide to Concrete Construction — Part V – Hot- and Cold-Weather Concreting

• Admixtures: Both hot and cold weather concreting can benefit from admixtures. Use water reducers or retarders in hot weather to prolong workability. In cold weather, accelerators can be used to speed up curing but avoid chloride-based ones to prevent corrosion.
• Planning: In both weather extremes, careful planning is essential. It also matters on the type of job : Decorative, coloured, or exposed aggregate are all need different weather options. Ensure all equipment and materials are protected from extreme temperatures and that manpower and standby equipment are available to avoid delays.

ADMIXTURES COME IN DIFFERENT FORMS. FOR EXAMPLE:

• Retarding admixtures. Admixture retarders slow setting time when concrete is hot, so you can finish the concrete surface properly. They’re also handy for maintaining concrete slump during long hauls to the pouring site.
• Water-reducing retarders. Admixtures designed to reduce water improve concrete quality both during and after the pour.
• Retarding super-plasticisers. Super-plasticisers significantly enhance workability and flow of concrete without increasing water content.
• Admixtures: Both hot and cold weather concreting can benefit from admixtures. Use water reducers or retarders in hot weather to prolong workability. In cold weather, accelerators can be used to speed up curing but avoid chloride-based ones to prevent corrosion.
• Planning: In both weather extremes, careful planning is essential. Ensure all equipment and materials are protected from extreme temperatures and that manpower and standby equipment are available to avoid delays.

Hot Weather Concreting :

Tips:

Besides using admixtures, other steps you can take to help ensure successful concreting in hot weather include:

• Sprinkling cool water on the subgrade before the pour.
• Placing the concrete quickly.
• Considering evening or early morning placement.

• Challenges: High temperatures increase the risk of rapid drying, leading to plastic shrinkage cracks, reduced workability, and faster setting. Additionally, thermal shrinkage and premature stiffening can occur, especially in dry, windy conditions.
• Precautions:
  1. Control Concrete Temperature: Use chilled water, ice, or liquid nitrogen to lower the temperature of fresh concrete. Keep aggregates cool by shading stockpiles and moistening them.
  2. Timing: Pour premix concrete early in the morning or late in the evening to avoid the hottest part of the day. Night-time pours may be advantageous in very hot climates.
  3. Finishing and Curing: Begin finishing promptly once the surface is firm enough to support weight. Use sunshades and windbreaks to protect fresh concrete from rapid moisture loss. Immediately start curing using water curing or applying curing compounds to maintain moisture levels.
  4. Plastic Shrinkage Prevention: Spray aliphatic alcohol on the surface to reduce evaporation and install windbreaks to minimize wind exposure.

Cold Weather Concreting:

• Challenges: Low temperatures slow down hydration, extending setting and hardening times. Freezing conditions can cause irreversible damage to fresh or partially hardened concrete.
• Precautions:
  1. Temperature Control: Heat the mixing water (but not above 70°C) to raise the temperature of the fresh concrete. Use Type HE cement to accelerate strength gain, and insulate formwork and reinforcement to retain heat.
  2. Freezing Prevention: If freezing is a concern, use heated enclosures or insulated blankets to protect fresh concrete. Hydration heat can help protect concrete, so insulating formwork can keep temperatures stable.
  3. Delayed Formwork Removal: Due to slower strength gain in cold weather, allow for extended curing times before removing formwork, as indicated by AS 3600 standards. Gradually expose the concrete to cooler temperatures to avoid sudden thermal shock.
  4. Curing in Cold Weather: Avoid water curing in freezing conditions. Instead, use plastic film or tarpaulins to maintain moisture and prevent the concrete from drying out as it hardens.