ACI Curing, Protection & Quality Control 1

Question 1

Why is curing important for concrete?

Accepted Answer

To ensure strength development

Answer

Curing is a critical process for concrete that involves maintaining adequate moisture and temperature conditions after placement. This allows the cement to fully hydrate, which is the chemical reaction responsible for concrete gaining strength and durability. Proper curing prevents the concrete from drying out too quickly, ensuring it reaches its designed strength, reduces shrinkage, and improves its resistance to wear and environmental factors.

Question 2

What is a common method of curing concrete?

Accepted Answer

Wet curing with coverings

Answer

Wet curing with coverings is a highly effective method for maintaining the necessary moisture content in concrete during the curing period. This involves covering the concrete surface with wet burlap, plastic sheeting, or other impermeable materials after initial set. The coverings prevent evaporation, keeping the concrete continuously moist and allowing for optimal hydration and strength development.

Question 3

How long should concrete be cured under normal conditions?

Accepted Answer

7 days

Answer

Under normal conditions, concrete should be cured for a minimum of 7 days to achieve a significant portion of its potential strength and durability. While concrete continues to gain strength for an extended period, the first 7 days are crucial for the hydration process. Extending the curing period beyond 7 days, especially in hot or dry conditions, can further enhance the concrete's properties.

Question 4

What can cause surface cracking in freshly poured concrete?

Accepted Answer

Rapid drying and poor curing

Answer

Surface cracking, particularly plastic shrinkage cracking, in freshly poured concrete is often caused by rapid drying of the surface. When the surface water evaporates too quickly, especially in hot, windy, or dry conditions, the concrete shrinks unevenly before it has gained sufficient strength to resist tensile stresses. Poor curing practices exacerbate this issue by failing to maintain adequate moisture, leading to increased cracking.

Question 5

What is used to check concrete strength in the field?

Accepted Answer

Cylinder compression test

Answer

The cylinder compression test is the most common and reliable method used to check the compressive strength of concrete in the field. Concrete samples are cast into standard cylindrical molds at the job site, cured under controlled conditions, and then tested in a laboratory by applying a compressive load until failure. This test provides a direct measure of the concrete's ability to withstand crushing forces, ensuring it meets design specifications.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI Curing, Protection & Quality Control 1