If concrete is poured in hot weather, low humidity, or high wind without any proper adjustment to the whole process, the quality of concrete will significantly suffer. If it requires to pour concrete during a hot weather period, it is wise to wait till the time of the day when the temperature is at its lowest. Experienced builders usually wait till the coolest period of the day before pouring concrete. In addition, it is better to have additional plans to ensure the temperature surrounding the pouring area remains cooler. Such plans include using sun shades to block the sun rays or spraying aggregates with cold water.

Weather Factors

Weather temperature affects the concrete pouring because concrete sets by hydrating. Concrete takes in water and forms crystals around the particles within the concrete. If the weather is cold, the overall temperature of concrete will remain cool. The cooler the concrete, the longer the process of crystallization will take. The longer the process, the more time crystals will get to strengthen their cores and produce the strongest concrete.

While cool weather aids the process of concrete pouring, hot weather is detrimental to concrete pouring. Hot weather is considered a significant obstacle or hindrance. Maintaining the proper moisture level in the concrete is the highest priority. However, hot weather affects the moisture level and dries the concrete at a faster rate. If the process of concrete pouring is done during hot weather, concrete will suck up the water in a very short time, and the crystallization process will take a very short time. As the entire process gets done quickly, the cores of the crystal will not get enough time to strengthen. Hence, it will create a weak concreate. Subsequently, hot weather will cause faster evaporation. Fast evaporation will negatively impact the surface layer of the concrete. The lack of enough water molecules will create weak concrete at the surface of the concrete block or slab. If the surface of the concrete block remains weak, it will be more susceptible to breaking or cracking.

Setting and Curing Time

Depending on the temperature level, concrete can take two to nineteen hours to properly set. If the temperature is 38 degrees Celsius, the concrete will set in around two hours. If the temperature is within 0 to 5 degrees Celsius, the process of crystallization will take around 19 hours. However, it should be noted that if the temperature falls to negative degrees of Celsius or extreme cold, the crystallization process will not take place, and the concrete will not be set. 

Curing, on the other hand, is not the same as the setting. The term setting means that concrete has reached its solid state. However, it still needs more time to reach its full strength. Typically, concrete reaches its seventy percent strength within the first seven days. It takes three more weeks to complete its curing and reaches to hundred percent strength. 

Hot Weather Problems 

There is a large series of problems that hot weather brings while pouring concrete. As the temperature remains very high during hot weather, the shrinkage cracks can be very deep. The deep cracks occur due to the lack of capacity to resist the shrinkage stresses in high temperatures. To add further to the problem, the cracks can continue to widen until the shrinkage stresses are completely relieved. Aside from cracks, other problems that may arise during concrete pouring in hot weather :

• It may take a longer time to finish the concrete mixture.
• The hot temperature may allow the concrete to form cold joints as the setting time decreases with higher heat.
• The overall strength and durability of concrete may get reduced. 
• The result of the concrete compression test will yield a lower score.
• The process of drying the shrinkage, especially of the hardened concrete, may increase.
• Hot temperatures may create slumps in concrete.
• The increased hydration rate may drastically increase the interior temperature of the concrete. 

Tips for Pouring Concrete in Hot Weather 

As we discussed earlier, concrete sets when the cement in the mixture hydrates. The process of hydration is an exothermic reaction. Exothermic reaction means the reaction generates heat. Hence, the hotter the concrete, the faster the exothermic reaction. The faster the reaction, the weaker the crystallization process. So, the temperature of the weather is the secondary concern. The first concern is the temperature of the concrete mixture. So, the primary focus should be on the ways to reduce the overall temperature of the concrete mixture. Here are a few tips for tackling the high-temperature problem : 

Avoid laying concrete during the scorching heat

The ideal temperature for curing concrete is 23 Degrees Celsius. If it is rising up to 32 degrees Celsius, alternate the pouring date. During hot days, you have to ensure you schedule your pours during the calmest part of the day. This time frame refers to as early in the morning as it can be. Therefore, pouring early will provide you with the best chance to hold the moisture as the concrete begins to cure. If pouring in the morning isn’t manageable, you can shift it to the evening when the temperature starts to drop. Besides, if you allow and your concrete provider is willing, you can try pouring it at a cool night to avail yourself of the desired temperature without any special admixtures or cooling procedures as the temperature falls to the right level. Keep an eye on the weather forecast to pick the most suitable time for pouring.

Thoroughly consider your plan

To be ahead of time, put together a plan for your hot weather concreting because it will necessitate certain unique processes. Bear in mind that you want to lay the concrete as early as possible once it has been mixed to avoid drying out and shrinking. There should be no obstacles or delays that hinder the whole pouring process. Accordingly, ensure that you start the pouring process on the most convenient period of the day, the vehicles arrive on time, and get the preliminary works done. 

Enlist an adequate number of workers

In the beginning, your major objective is to place the concrete as swiftly and firmly as possible. For that, many capable and strong arms are required to help mix concrete, distribute concrete in molds, and polish the concrete surface. It can be tough to get the concrete into the forms and smoothed out before it starts to cure if you don’t have enough assistance. Prior to the commencement of the project, make sure all of your workers know exactly what they are expected to do. The wiser decision would be to use the Pre Mix Concrete during the hot weather. The mixing site should be nearby the pouring site. Thus, the workers will be able to transport and pour the concrete in the shortest amount of time. 

Dampen the surface

During the concrete pouring, if the surface is dry, water immediately leaches out of the mixture and gets into the surface. Thus, concrete loses most of its water very early. As a result, concrete will lose its moisture and get dry faster. The faster the concrete dries, the weaker the concrete block or slab will be. To tackle this issue, it is better to lightly hydrate the surface before pouring the concrete. If the surface is wet, it will not soak most of the water from the concrete. Hence, the mixture will remain moist for a longer period of time, and the crystallization process will get adequate time to strengthen its cores. 

Make every effort to prevent wind and sun

When stifling sunlight comes with no cloud cover, it accelerates the evaporation process and stimulates the set time. In addition to this, a strong rush of winds may be just as detrimental—if not more so. If you’re pouring a slab and it’s windy, the concrete may dry up before you have a chance to smooth it out and polish the edges or create a brushed pattern. Place sunshades and windshields to shelter the concrete from the sun and wind as you pour, and then leave them in place for the next few hours after you’ve finished pouring the concrete. With these measures, you may dramatically reduce the risk of evaporation and allow your slab more time to hydrate.

Apply admixtures to enhance the pouring process

Admixtures as concrete additives can increase concrete strength, provide resistance to corrosion, and delay the setting time. Retarding admixtures reduce the setting time and provide the concrete enough time to conclude the chemical reaction and retain a greater slump. You need to check for certain things in admixtures, including free-surface aeration, hydration suppressors, wet level reducers, and set time retarder.

Add cooled aggregates and chilled water to the mix

The overall temperature of the mixture can be reduced to as far as 10 degrees Fahrenheit. Normal temperature water will not make any difference to the mixture. Artificially cooled or refrigerated water can reduce the overall temperature of the mixture. However, if chilled water is mixed with the mixture, the mixture time should be reduced. Otherwise, it will create more water loss through evaporation.

Summary 

Summer is an ideal time to begin construction projects. The site managers and crews are always eager to make the most use of this time as the sunny weather is beneficial to construction projects. However, like other seasons, summer comes with its fair share of cons for construction projects. The high temperature during the summer season is detrimental to the concrete pouring process. The higher the temperature, the tougher to complete the concrete pouring process. However, there are ways to reduce the impact of the summer temperature. The above-discussed tips can help anyone to cool down the concrete mixture for their project sites.

F.A.Q.

What is the optimum temperature to pour concrete?

Ans: Typically, for a normal concrete mixture, the best temperature to pour concrete is between 10 degrees Celsius to 25 degrees Celsius.

What is the lowest temperature when concrete pouring is possible?

Ans: The lowest temperature for concrete pouring is 5 degrees Celsius. If the temperature is less than 5 degrees Celsius, the crystallization process will be drastically slowed down, and weaker concrete will be produced.

What is the highest temperature when concrete pouring is possible?

Ans: 32 degrees Celsius is the highest temperature at which concrete will crystallize. If the temperature is more than 32 degrees Celsius, the hydration process will be too fast for the crystallization process to take place.

How long does it take for concrete to dry?

Ans: Concrete usually takes 24-48 hours to dry completely.

What type of concrete will be best to use during hot weather?

Ans: Mir Ready Mix Concrete will be the best concrete to use during hot weather as it is produced with superior quality material that can withstand high temperatures.