Cold Weather Concrete
by Miles Shiver IV, General Manager
New Mexico’s mountain climate affords us the great benefit of seeing four distinct seasons. We often see temperatures over one hundred degrees in the summer as well as freezing cold in the winter. These seasonal swings require concrete producers and contractors to stay on their toes in regards to concrete temperature, set times, travel times and a variety of other issues caused by cold or heat.
Ideal concrete temperature is a figment of the imagination. Don’t let anyone tell you otherwise. Every type of placement has an ideal situation and that situation rarely seems to repeat itself. Regardless of the season, our target concrete temperature is about 65 degrees as this applies well to most applications. In the summer this poses quite an issue with raw materials, concrete plants and mixer trucks all being super heated by the desert sun. This problem is exasperated by the nature of the cement/water chemical reaction. This scientific wonder is exothermic (releases heat) through its natural process which in turn speeds up the chemical reaction in the adjoining particles and before you know it you have a “hot load” that is turning into rock before your eyes. For this reason we use ice in our water to get the concrete temperature down to a manageable level. More on this in the spring.
In the winter, where morning temperatures are well below freezing almost every day, we have the opposite problem. To achieve 65 degree concrete in the winter we have to use every bit of heat we can get to keep the concrete from falling asleep on us. Concrete will “go to sleep” around 50 degrees and does not “wake up” again until there is some external heat source to kick off the chemical reaction again. The most common way we do this is to heat the mix water to a level that will keep the heat building by using science to our advantage. Friction from the mixing process is our friend in the winter because this adds heat as well. You may see a truck driving down the road with the drum spinning hard to add heat to the load on a cold morning. This is a good thing.
Everything I have said so far is the producer’s problem, but fear not, we have been doing this long enough to know what it takes to do our job well. All of these changes make the contractor’s job a little more difficult as well. Most importantly, any placement needs proper planning. Keeping an eye on ambient temperatures is a wise practice, to say the least. Pouring before the sun comes up is common in the summer but in the winter it is wise to allow the heat of sun to help your placement get the heat it needs. When your truck arrives on the job site you should see steam coming out of the hopper, water tank and water hoses (depending on ambient temperature). This will give you confidence that your concrete is being delivered in the best possible condition.
When you begin to unload and place the concrete keep in mind that it could be hot to the touch. Place and level the concrete as you would in the summer, but in the winter you get the added benefit of a slightly slower set time. Your steel trowel finish probably won’t start until a little later than you are used to. Pay special attention to the areas that will not get any direct sunlight because these will setup later. If your entire placement is in the shade ask about using accelerators when placing your order. Remember that heat is your friend in winter and is required to keep the chemical reaction going.
Once your placement is down and finished you will need to keep it from freezing. Concrete blankets are a necessity if the temperature will drop below freezing for the 5 to 7 days following the pour. The concrete will be generating enough heat on its own, your goal is to keep the heat from leaving the scene. Make sure your blankets are secure and cannot be blown off by one of those pesky winter breezes. It is also a good idea to take the blankets off during the day to allow the sun to continue heating the concrete and then returning the blankets for the cold overnight temperatures.
As with anything, there is much more to the cold weather concrete, but I hope this information helps you start thinking about your upcoming projects. When placing your order please ask our knowledgeable dispatchers for more information. We are here to partner with you in providing the best quality project whether it is big, small or anything in between because Quality Matters Here.