During a concrete pour, the weather forecast shows temperatures will drop to 35°F overnight. What is the most appropriate action to take?
Correct Answer
D) Add calcium chloride accelerator and provide heating
When concrete will be exposed to freezing temperatures within 24-48 hours, accelerators and heating protection are necessary to prevent freeze damage. Concrete must gain sufficient strength before freezing occurs.
Why This Is the Correct Answer
When concrete will be exposed to freezing temperatures (32°F or below) within the first 24-48 hours after placement, protective measures are essential to prevent freeze damage. Adding calcium chloride accelerator speeds up the hydration process, allowing concrete to gain strength faster before freezing occurs. Providing heating through methods like heated enclosures, blankets, or salamanders maintains adequate temperature for proper curing and prevents ice crystal formation that would damage the concrete matrix.
Why the Other Options Are Wrong
Option B: Continue pouring as planned with no modifications
Pouring only half the planned concrete creates construction joints that weren't designed into the structure, potentially creating weak points, water infiltration paths, and structural discontinuities. This approach doesn't address the fundamental issue of protecting concrete from freezing temperatures.
Option C: Pour only half the planned concrete
Continuing with no modifications when temperatures will drop to 35°F is dangerous because fresh concrete exposed to freezing temperatures before gaining sufficient strength (typically 500 psi) will suffer permanent damage from ice crystal formation, resulting in reduced strength, durability, and surface scaling.
Memory Technique
Think 'HEAT & SPEED': when it's going to freeze, you need to HEAT the concrete and SPEED up curing with accelerators to reach 500 psi before freeze damage occurs.
Reference Hint
ACI 306 - Cold Weather Concreting, Florida Building Code Chapter 19 - Concrete, or concrete construction sections in general contracting reference materials
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