Weather conditions at a job site may not be the same as those specified by manufacturers in their manual. In fact, laboratory conditions in which concrete specimens are tested are usually done in an area suitable for producing the best results. Therefore, concrete should be placed in a secure area, especially in cold weather conditions.
This means the warehouse or enclosures must provide adequate precautions to avoid the negative impacts of low ambient temperatures. Based on guidelines released by the American Concrete Institute (ACI), the definition of cold weather concreting is when the average daily temperature falls below 10 degrees for more than 12 hours, as this could potentially lead to concrete freezing issues.
Protecting concrete during cold weather
During cold weather, it is essential to at heat one or more of the concrete materials, including the water and aggregates used in the mix. This will provide the appropriate concrete temperature before it is used on the job site.
Protection while the concrete is finished, placed, and consolidated
Exposure of concrete during cold weather will extend the time of crews on the site, especially concreters assigned on the finishing. That is why it is essential to use enclosures, windbreaks, and other supplementary heating tools. It is also recommended to adjust the concrete mixture during the setting time. So, cement content will be increased, or accelerating chemical admixture shall be used for maximum effect.
Also, windbreaks are relatively important at the construction site since they can protect the personnel from biting winds that may cause excessive evaporation and temperature drops. The common height used is six feet for most construction projects. However, windbreaks could also be shorter or taller depending on the anticipated ambient temperatures, wind velocities, humidity, and concrete placement temperatures.
Another protective gear to consider are heated enclosures since they are very effective in protecting concrete in cold weather, but they are usually more expensive than windbreaks. Most enclosures are made of canvas tarpaulins or polyethene.
Three types of heaters are used in cold weather concrete constructions, including indirect-fired, direct-fired, and hydronic systems. Indirect-fired heaters are commonly used on fresh concrete surfaces. Direct-fired heaters are suitable for concrete that has not been subjected to the exhaust directly.
However, caution should not be taken lightly to ensure that workers are not overexposed to carbon monoxide commonly used inside the enclosure. Hydronic systems are high-tech applications for preheating and thawing subgrades, but they are too large for an enclosure and are widely used in large warehouses.