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
ACI 306 identifies three categories of concrete section thickness that determine minimum placement temperature. Which category requires the highest minimum temperature?
Answer: Thin sections less than 12 inches
Thin sections lose heat rapidly and require a higher minimum placed temperature of 55°F (13°C) to maintain adequate curing temperatures.
When concrete is placed in hot weather and a liquid curing compound is used, when should it be applied?
Answer: After final finishing once all bleed water has evaporated from the surface
Curing compounds must be applied after final finishing once surface bleed water has disappeared, ensuring full coverage without dilution.
In cold weather, what problem can arise if an enclosure used for heating concrete becomes too airtight when combustion heaters are used?
Answer: Carbon dioxide carbonation of the concrete surface
Combustion gases, particularly carbon dioxide, in a poorly ventilated enclosure can carbonate the concrete surface, reducing surface strength and durability.
A concrete finisher notices the concrete surface is crusting quickly before it can be properly finished in hot weather. The FIRST corrective action should be:
Answer: Apply a light fog mist above the slab to reduce evaporation
Fogging reduces the evaporation rate and buys time for proper finishing without adding water to the surface, which would weaken the slab.
What does 'maturity' mean in the context of cold-weather concrete curing?
Answer: A function of time and temperature history used to estimate strength development
The maturity method uses the product of temperature and time (degree-hours or degree-days) to estimate in-place concrete strength development.
Pre-cooling aggregates with chilled water or ice is a hot-weather strategy. What is the approximate temperature reduction achievable by substituting ice for all mixing water?
Answer: 15–20°F (8–11°C)
Replacing all mixing water with ice can reduce concrete temperature by approximately 15–20°F due to the latent heat of fusion absorbed as ice melts.
In cold weather concrete operations, heated enclosures must maintain a minimum temperature. What is the generally accepted minimum air temperature inside the enclosure?
Answer: 40°F (4°C)
ACI 306 generally recommends maintaining the enclosure air temperature at a minimum of 40°F (4°C) to prevent concrete from freezing during the protection period.