As a Western New York-based firm, we are no strangers to cold weather. The temperature has a daily impact on our lives, from what clothes we wear to how long our morning commute will take. Just as the temperature has an impact on us, it also has an impact on construction materials, specifically concrete. Exposure to extreme temperature lows can have adverse effects on the structural integrity of concrete.
The temperature should be controlled throughout both the concrete mixing and placement processes. Temperature control during these phases prevents thermal contraction and shrinkage later on in the concrete’s lifespan. According to the ACI 306R-88 standard, exposure to extreme cold during placement can cause rapid moisture loss from warm concrete heating the surrounding cold air, resulting in a reduction of relative humidity. The decline of water content in the concrete can lead to extended setting periods and variation in concrete strength, which could have detrimental effects on the schedule, budget, and safety of the construction project.
Fortunately, practices and procedures have been developed to protect the concrete from being damaged or structurally compromised as a result of freezing. According to the American Concrete Institute (ACI) Cold Weather Concreting (ACI 306R-88) standard, the goal of these cold weather preventative practices are as follows:
“Prevent damage to concrete due to freezing at early ages,… assure that the concrete develops the required strength for safe removal of forms, for safe removal of shores and reshores, and for safe loading of the structure during and after construction,… maintain curing conditions that foster normal strength development without using excessive heat and without causing critical saturation of the concrete at the end of the protection period,… limit rapid temperature changes, particularly before the concrete has developed sufficient strength to withstand induced thermal stresses,… [and to] provide protection consistent with the intended serviceability of the structure”
As listed in the ACI 306R-88 standard, the methods of protecting new concrete include covering the concrete with insulating materials, creating an enclosure surrounding the concrete, using embedded thermal coils to heat the concrete internally, covering the placed concrete with tarps, and implementing insulated forms during the setting period.
Just as preventative measures are necessary to protect the concrete during the construction process, it is also necessary to make sure that the protection methods were effective, which can be achieved through materials testing. Compressive strength is one of the indicators to determine if the concrete meets structural and safety standards. This test is performed by applying an increasing amount of pressure to a piece of material to determine how much weight it can handle before fracturing. Depending on the purpose of the concrete (flooring, foundation, structural support, etc.), there are different standards of pressure that the material is expected to withstand to be considered fit to support the intended load. Encorus’s Civil Testing Group performs laboratory compressive strength testing for a variety of construction materials, including concrete core samples.
If you have a need for concrete testing or have any questions about the impacts of temperature on the structural integrity of concrete, contact Civil Laboratory Supervisor Jeremy Lake at (716) 592-3980 ext. 133 or [email protected]