Cold & Hot Weather Concreting Flashcards
7 cards from real ACI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Cold & Hot Weather Concreting flashcards as text
Which of the following is NOT a recommended practice for reducing concrete temperature during hot weather production?
Answer: Adding extra cement to increase heat of hydration
Adding extra cement increases heat of hydration, raising concrete temperature — the opposite of what is needed in hot weather.
When frozen ground or ice is present at a subgrade before cold-weather concrete placement, the finisher should ensure:
Answer: The subgrade is thawed and free of ice before concrete is placed
Frozen subgrade will thaw after placement, causing settlement and potential cracking; the subgrade must be thawed to a minimum depth before concreting.
During hot weather, the time between water contact with cement and final discharge from the truck should not exceed:
Answer: 90 minutes or 300 revolutions
ASTM C94 limits ready-mixed concrete delivery to 90 minutes or 300 revolutions after water first contacts the cement, whichever comes first.
Windbreaks erected around a hot-weather concrete placement primarily help by:
Answer: Reducing wind velocity to lower the surface evaporation rate
Windbreaks reduce wind speed across the slab surface, which directly decreases the rate of moisture evaporation from fresh concrete.
After concrete is placed in cold weather using insulated forms, when is the highest risk of freezing damage to the concrete?
Answer: After form removal when concrete is first exposed to cold air
After form removal, concrete suddenly loses the insulation of the form, and the drop in surface temperature is highest, creating peak risk of freeze damage.
In hot weather, which water source for concrete mixing has the greatest potential to significantly lower concrete temperature?
Answer: Chilled water from a refrigeration unit
Refrigerated chilled water can be cooled well below ambient temperature, providing the greatest temperature reduction of any water source option.
A concrete finisher notices steam rising from fresh concrete placed during cold weather. This most likely indicates:
Answer: The concrete is too warm relative to the cold air, which is generally acceptable
Steam rising from warm fresh concrete in cold air is a normal visual effect of the temperature differential and does not by itself indicate a problem.