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LAYING
IN HOT WEATHER
The effects of high temperatures can be summarised as follows:
→ Short set times and faster stiffening and setting
→ Faster rates of hardening
→ Increased tendency for plastic cracks (cracks that form when the concrete has not set)
→ Difficulties in placing and finishing due to all the above
→ Danger of cold joints - (a cold joint is formed when plastic concrete is placed against concrete that has set and commenced hardening)
A good day for drying your washing is a very risky day for concrete
At higher temperatures, particularly if accompanied by hot dry winds, plastic cracking and premature stiffening of the concrete may take place.
Minimising water loss from the concrete is the key principle to manage
Precautions for hot-weather concreting should be initiated when the ambient temperature is expected to exceed 30 to 35°C or lower if it is a windy day as well. These precautions may consist of one or more of the following practices:
→ Plan the pour early in the morning to avoid time of very high evaporation.
→ Dampening forms, reinforcement and subbase, or using Polythene below to stop water loss through base
→ Erecting wind breaks and sunshades to protect exposed concrete surfaces
→ Completing the transporting, placing and finishing of concrete as rapidly as is practicable
→ Informed usage of set-retarding admixtures (to counter premature stiffening of the fresh mix)
→ Immediately following the initial finishing operation, apply Antivap by Sika (a fine film of aliphatic alcohol to reduce evaporation) over the exposed concrete (this should be repeated as necessary during any subsequent operations up to final finishing)
→ Immediate curing after final finishing is complete
Checklist
✓ Avoid times of heat and wind.
✓ Take precautions.
✓ Use Anti-vap
✓ Cure early