It's rare here in North Port, but there are areas in Florida where the temperatures overnight can cause problems for concrete curing. And a different problem entirely of course is when it's too hot and humid, something we all know too much about! Professionals have access to adjuvants also called an admixture. This is now common in concrete and getting more and more interesting as companies develop products we can add to concrete to allow for a wide range of weather and temperature situations. As concrete cures it goes through changes called stabilization and settting. Turns out you can modify that behaviour with additives. You see, concrete contractors need to stay up to date with a changing industry. In my experience, the low temps are a problem really only when there are 3 consecutive days of temperature drops below 40 F. It is a good idea to ask your concreter what kind of admixture he's using and why.
What happens to concrete when temperatures fall is interesting and unless you have experience, you wont understand how to overcome this problem. During stabilization concrete "gives off heat". This means as concrete cures it warms up and this keeps a very even amount of water in the mix. When it's cold, the reaction still happens but of course much slower because a lot of heat is lost to the colder air and ground. What does this mean? Most of the time if your concrete is taking a little longer to cure, its due to cold temps at night. Mind you, up north where I worked for 6 years in New Jersey, it gets cold enough in January that you cannot pour concrete at all because it literally doesn't cure at all and turns into a flaky mess. But here in North Port, this is not usually a concern.
I like to tell people how the weather can cause delays to their projects even when the project looks done. It's important not to get too impatient and try to use your new concrete surface before it's ready for weight and movement.
When it's too warm, that same nice warming reaction is happening with the mix, but now the water is leaving the mix too fast due to evaporation. I honestly usually only see this when its also very dry and windy. If the humidex is high this is manageable.
Concrete is durable, pouring in cold weather reduces the overall lifetime of the concrete. In order to keep your concrete safe from cold temp damage, you’ll want to add admixtures that will help speed up the curing process on any area that is exposed to cold weather. You can even sometimes spray this on a surface after leveling.
All admixtures I've even seen only come in liquid forms. Many come in small pre-measured containers that make completing your concrete project a snap.
I am familiar with 3 different types of admixes for cold weather concrete install:
Accelerators: speed up curing time by increasing its rate of hydration. Calcium chloride admixtures or sodium nitroprusside. An accelerant for your concrete will depend on many factors. Accelerators reduce the curing time which results in a very even set concrete. This is the strongest form of concrete you can get in any temperature.
Plasticizers reduce the amount of liquid that cement needs which makes the concrete easier to work with. The reduction in weight and increased working time allows a projcet to finish cleaner. Plasticizers effect only lasts about 65 minutes so careful planning is a must.
Air agents prevent cracking and damage from freeze expansion. Think of this like foam in the beer. These bubbles relieve the pressure created by cold temperatures, This additive is a must for any concrete project in areas that are prone to freezing. This concrete is not as strong due to the porous structure, but is almost necessary when setting concrete in areas prone to freeze/thaw cycles.
My favorite old school method needs to be said. Add heated water to mix your concrete. If you can get water at 70 degrees or higher it will result in the ideal conditions ensuring a durable material for its lifetime.