I am pleased that we recently experienced a spate of excellent weather with record breaking temperatures. However, you may not be aware that the hot weather affects the time concrete can take to set or cure.
Concrete is said to have set when it has stiffened to the point that it can support a degree of pressure without damage. An often used method of testing this is to walk on it. If no footprints appear then it has set satisfactorily.
Concrete is cured when it has reached its full setting strength. This is the point when it is as solid as it is ever going to be and will support the strength it was designed for.
It is possible for concrete to set in as little as 2 hours, but it can take up to 20 hours. Temperature plays an important part in this process. Hot weather conditions provide the shortest setting times while colder temperatures take considerably longer. In fact if the temperature falls below freezing the concrete may not set at all.
Chemicals can be added to the concrete to alter setting times. In very hot conditions it can cool the mix to allow adequate time to level and trowel to the required surface. In colder conditions chemicals can speed up the setting process.
Complete curing time is often several weeks, although it is normal to conduct strength tests after 28 days. Once again temperature and humidity play a part.
Warm weather that speeds the setting process will delay the curing time. It is usual for the strongest concrete to be kept moist as it cures naturally. This is because curing is a chemical process rather than a drying one. If the concrete becomes too dry it may shrink before it has cured enough to establish its strength, possibly resulting in cracks appearing.