North Carolina General Contractors Practice Exam

How can air content be reduced in concrete?

1. By using finer aggregates

2. By increasing the water-to-cement ratio

3. By using higher temperatures and coarser sand

4. By applying chemical additives

The correct answer is: By using higher temperatures and coarser sand

Reducing air content in concrete is often achieved through a combination of material selection and environmental conditions. The option highlighting the use of higher temperatures and coarser sand is particularly effective for this purpose. When coarser aggregates are used, they occupy more space in the mix and create fewer voids compared to finer aggregates. This can lead to a denser concrete with less air retained in the mix. Higher temperatures during the mixing and pouring process can also help reduce the viscosity of the concrete, which allows for better compaction, pushing out trapped air and leading to a reduction in overall air content. This combination of coarser sand and elevated temperatures facilitates the movement of air bubbles to the surface, allowing them to escape, thus successfully reducing the entrapped air in the final concrete product. Therefore, enhancing both aggregate properties and temperature is a strategic approach in concrete mixing to control air content effectively.