How to cure concrete in winter to reach the required strength

In cold weather, if you want to cure concrete, you should have the required material and knowledge. Water, humidity, temperature and even snow are factors that can complicate cold weather concreting. You should never pour concrete on frozen ground and must be very cautious when temperatures fall below the freezing point. Concrete hydration can also be affected as soon as the temperature falls below the freezing point. Read on to know our tips to cure concrete in the cold season.

Fresh Concrete

Required materials

You may need different materials based on the quantity of concrete that needs to be cured as well as the surfaces that need to be protected. Certain materials may produce or even increase heat. These materials include chemicals, windbreaks, insulating blankets, electric heated blankets, straw-plastic and insulating sheets.

Know the facts

When placing concrete in cold weather, there are two major factors you will want to concern yourself with before starting your project:

#1 - When it is cold, concrete sets more slowly - slow at 50°F, and when it's below 40°F the hydration reaction will basically stop and the concrete curing process halts. Ideal temperature for curing concrete is about 80 degrees F.

#2 - Concrete may freeze before gaining enough strength which will break up the matrix of the concrete and weaken your overall finished product. You don't want this.

There is a difference between concrete temperature and air temperature. When it's cold outside, the concrete will need to be protected until it can handle the cold on its own. Rule of thumb #1 is that once the concrete has strengthened to 500 psi then it's safe. The important thing that happens at this point is that at almost the same time that the concrete hits 500 psi compressive strength, there's not enough water left in the pores to damage the concrete, or in other words, hydration of the cement has consumed enough water in the mix so that freezing won't affect it much. With almost all concrete, this will happen during the second day, even at 50° F.

There are usually two things we can do in cold weather to help achieve the required number of 500 psi strength which will help you get the best results and the best finished product:

Change the mix of your concrete to get it to set more quickly
Protect the concrete from the cold using blankets, tarps or tenting
or preferably - both.
First, you should make sure that the water to cement ratio is appropriate. When the temperature is below the freezing point, this ratio should not cross 0.40.
In too cold conditions, you can use a polyethylene enclosure, heated concrete curing blanket or propane heater to maintain the temperature.

You should use a type of cement that will not reduce the quality of concrete. This is because too much moisture can cause corrosion.

You can use furnace slag, silica fume or fly ash to control the ions of chloride.

You should let the forms stay put for as long as you can. The edges and corners are more vulnerable. Moreover, forms can help you with the process of heat emission.

It's not a good idea to remove the blankets in winter because this can cause temperature differences in the concrete.

You can cure concrete below the surface of water as well. The product contains a tiny amount of high quality fine aggregates, such as sand. Moreover, additives are also put into it and they don't let water get into the surface of concrete. Usually, this product is used to make pavements because it won't absorb water.

You should hang on until all of the water gets evaporated. In winter, concrete takes a while to cure. So, the bleeding will take some time to stop. So, you may want to be ready to deal with more of it.

During this process, make sure you use a quality infrared temperature measurement gun to note down the temperature of concrete.

For choosing the insulation, make sure you know the air temperature, cement content and the thickness of the concrete.

You may want to apply some concrete sealant to seal the concrete. This is to prevent water from getting into the concrete. Aside from this, the sealants will increase the life of the concrete and will cut down on the chances of failure. In cold states, you may want to use only a type of concrete that can breathe. The reason is that it lets water and moisture evaporate in order to let the concrete set.