There are several effects that hot weather may have on the properties of Concrete these include;
Consistence – The workability, that is slump/flow of concrete reduces more rapidly. Adding water to improve the consistence will reduce the concretes compressive strength, and as such should be avoided.
Setting time – As concrete temperatures increase the setting time becomes shorter as dose the amount of time the user has to place, compact and finish the concrete
Plastic Shrinkage Cracking – Hot weather will accelerate the loss of moisture from the surface and may increase the risk of plastic shrinkage cracking.
Thermal Cracking – Changes in temperature of the concrete may potentially result in cracking particularly where concrete is placed on a hot day followed by a cool night.
Surface Finish – With the increased rate of hydration due to higher ambient temperatures or direct sunlight the surface of the concrete may ‘dry’ quicker, this may lead to premature finishing e.g. floating the surface “early” may trap an amount of bleed water, this bleed water may result in debonding of the top surface and subsequent flaking/de-lamination.
We can design mixes to assist with these issues as follows;
- Use Super Plasticizers to reduce the overall cement content hence reducing the heat of hydration
- Use higher levels of cement replacement (GGBS or PFA) to reduce heat of hydration and bleeding
- Increase dose of a lignosulfonate based plasticiser to use as a set retarder
- Use specialist admixture to ensure consistence retention of concrete