Category: concrete

Heat Can Cause Concrete Problems

Hot Weather = Weak Concrete

Pouring concrete is as much an art as it is a science. Everything has to be right, or you run the risk of your concrete being weak, developing cracks, or showing other signs of damage. We’ve discussed the effects of cold weather on concrete before, so now we’ll address the impact of the weather being too hot.

The Problem is Crystal Clear

Concrete is hard because it grows crystals around the aggregate particles. This happens by the cement drawing the water out of the surrounding material. This reaction, called hydration, generates heat, so the reaction accelerates when the concrete is hot. If the concrete is hot, the rapid reaction will not allow the crystals time to grow strong. According to ConcreteNetwork.com, the early strength will be higher, however, the 28-day strength is less. If the concrete is formed at 90 degrees, instead of 70, the concrete’s compressive strength will be approximately 10% lower. If the weather is too hot, more mixing water will need to be added. This can contribute to even weaker concrete and changes in color between slabs.

Hot Weather Can Cause Shrinkage

hot weather, concrete project

Start at air temperature, draw a vertical line up to relative humidity, then a horizontal line to the right to concrete temperature, then go vertically down to wind velocity, and horizontally to the left to determine the evaporation rate. If the evaporation rate is greater than 0.1, plastic shrinkage cracking is likely.

As stated earlier, there are a lot of variables that can come into play regarding a successful concrete pour. Warm concrete and a hot, dry wind can cause shrinkage. G.E. Munro wrote an article about concrete shrinkage and weather for the Lafarge Cement newsletter in 1987. He gives the example of a mug of beer. If you have a cold glass of beer on a hot day, what happens on the outside of the mug? The humidity in the air will condense on the glass. He states that the same thing can occur with concrete. If the concrete is 18 degrees or cooler than the air, the humidity will condense on the concrete, preventing it from drying out as quickly. On the other hand, if the concrete is warmer than the air, you may have a problem with the concrete drying out and shrinking.

The image from ACI 305 can help you determine if evaporation will be a problem with concrete shrinkage. You will have to know the air and concrete temperature, humidity, and wind speed to calculate the rate of evaporation. The chance of shrinkage and cracking is possible if the sum is >.01 lbs per square foot per hour.

Keep An Eye On The Weather

Any concrete project can be tricky, but the problems grow exponentially with the size of the project. You have to keep an eye on the weather for the duration of the project. Temperature, precipitation, and other variables need to be taken into account. It is important that you hire someone that has experience with these kinds of situations and knows what needs to be done for the successful completion of a project. Matthews Structural Solutions has structural engineers and expert contractors to give you the peace of mind to know that your project will turn out right.

Contact Matthews Structural Solutions today and learn more about how we can make your concrete project a success, no matter the size. We look forward to hearing from you.

 

Cold Weather Effects On Concrete

concrete cold MatthewsBe Prepared! Winter comes around every year, but it seems to sneak up on us every time. The weather has an impact on everything we do, but we often don’t think about our concrete. We take it for granted, it does its job and we don’t give it a second thought. However, cold weather can impact your concrete and here are some things to look out for.

Once the concrete is set and has aged, the cold weather doesn’t have as much impact on it, but you still have to keep a lookout for a few things. If the weather changes a lot, it can really beat up your concrete. Temperature differentials can wreak havoc on your slab. Cracks can appear and if they’re not taken care of they can grow. If the cracks aren’t sealed, water can go inside. Water freezing in cracks will cause the concrete to expand and contract, weakening the entire area and negatively impacting its durability.

New Concrete & Cold Temperatures

If you are pouring new concrete, temperature is very important. Temperatures below 40 degrees F (5 degrees C) is considered cold weather concreting. Special precautions have to be taken when working with concrete at temperatures such as this.

When the temperature falls below 40 degrees, it takes a longer time for the concrete to set and strengthen. You’ll have to be patient in waiting before removing formwork or moving on to the next step in your project. A general rule of thumb states that a drop in temperature of 20 degrees F (10 degrees C) will double the setting time. Take this into account when you are planning your next step. Make sure you are working with someone that is an expert in working with concrete or you may have a poor final result or have to start over.

You need to keep an eye on the weather forecast if you’re getting ready to pour concrete. Concrete will freeze if the temperature falls below 25 degrees F (-4 degrees C). If the concrete is exposed to freezing temperatures before it hardens, it may incur permanent damage. The concrete should be protected from freezing for at least two days after it is poured. The strength of the concrete may be reduced by 50% compared to that of concrete that is formed during normal temperatures.

It is important that you work with a concrete expert any time of year to make sure that your concrete is poured correctly and gives you the strength and durability that you and your structure needs. Matthews Structural Solutions can assist you with any commercial foundation problems you may have. Call us today to learn more about our services or take a look through our website.