As extreme weather conditions in the winter arrive, construction companies need to be prepared to face the possible problems that could arrive. To prevent issues such as project delays when it comes to heating concrete in winter, contractors must be educated to adapt to cold weather concreting. Each phase of the concreting process must be evaluated from planning, pouring, and curing to adapt and add practices/measures to avoid freezing of the concrete.
1. Planning & Preparation
Before placing concrete, a few particular practices should be considered to allow proper curing of the concrete.
- You need to assess the construction site and determine the forms and testing involved.
- Quality of concrete mix is essential to maintain proper temperature and strength throughout.
- Preheating one or more of the constituent materials of the mix can ensure that the proper concrete temperature is present during the pour. Instead of heating the cement, this is done by heating the water or sand/gravel before mixing.
- The components of the mixture may need to be adjusted. Most commonly, this involves increasing the ratio of cement content in the concrete, or using an accelerating chemical alloy.
- In cold weather do not use slag cement or ash fly because these materials take a while to set up and create less internal heat.
2. Pouring & Planting Process
Essential precautions are taken into action to ensure the set up of the concrete placement.
- Defrost the ground before pouring using heaters (this usually needs to occur a couple of days before placement). Do not pour concrete on frozen snow or ice.
- Another common defrosting method is applying concrete blankets. These blankets can also be used after the pouring process to maintain an optimal temperature for the concrete.
- Using water reducers helps to remove standing water.
- Do not pour over frozen surfaces to avoid the risk of ice forming.
- Working crews on job sites may stay for a longer period of time, due to concrete needing more time to be set because of exposure to cold temperatures.
- To protect concrete from temperature drops and quick evaporation (due to wind) it is ideal to use windbreaks.
- Enclosed heating is a very useful protection method. These can be made of anything; but the best protection occurs from using electric heaters.
3. Curing Process
To guarantee the concrete reaches its maximum strength, a variety of techniques are used during the process.
- Leave forms in place as long as possible because they can preserve heat and help prevent concrete from drying quickly. Forms also provide support to corners and edges that are susceptible during the heat release process.
- In low-humidity regions, steam can be pumped into the compound around the concrete to prevent it from drying out too fast.
- Wait until all bleed water has evaporated before finishing. Bleeding takes a while to occur because concrete poured and placed in cold temperatures has a lengthy setting and curing time. Take precaution, because compared to regular concrete placement, it is expected that more water will bleed than usual.
- Verify the temperature using a wireless real-time monitoring sensor like SmartRock™, while the concrete is being cured. Make sure the temperature of the concrete is conserving at least 40 degrees Fahrenheit for its curing period. Using SmartRock's cloud-based dashboard, Giatec 360, temperature gradients can also be easier analyzed.
- When actively heating concrete in the winter you have to take caution of concrete cooling too rapidly. To prevent this slowly lower the temperatures around the concrete or by covering them with blankets. There is a prolonged period of gradual cooling of days and maybe weeks when working with large structures. Its important to not move or remove blankets constantly as temperature differentials build up in different levels of concrete leading to gradual cracking.
- Apply sealant to block water from trickling into the concrete, this will help lengthen the concrete’s life and will minimize the chance of curing failure. Breathable concrete sealant should be used in very cold regions to allow evaporation of moisture.
Heating concrete in the winter comes with many possible hurdles, but if project managers are well educated and plan for inevitable challenges beforehand it can make the whole process much more efficient.