ACI Certification Practice Exam

What should be done to ensure proper consolidation of concrete in cylinders?

1. Mix thoroughly

2. Rodding and tapping

3. Using liquid additives

4. Vibrating the forms

The correct answer is: Rodding and tapping

To ensure proper consolidation of concrete in cylinders, rodding and tapping is essential. This technique involves using a metal rod to systematically poke and stir the concrete mixture while it is in the mold. The purpose of this process is to eliminate air pockets and voids that can form when concrete is poured. These pockets can weaken the structure of the concrete and lead to inconsistent results. Rodding helps to push the concrete into any tight spaces and ensure a denser mixture while tapping on the sides of the mold allows the concrete to settle more uniformly, further assisting in the release of trapped air. By carefully executing this procedure, you enhance the overall integrity and performance of the concrete cylinder. While mixing thoroughly is important for achieving a homogeneous blend of materials, it does not specifically address consolidation in the mold. Liquid additives can improve various properties of the concrete but do not directly contribute to the consolidation process. Vibrating the forms can provide consolidation but is generally more applicable in larger pours and might not be as controllable or effective in the small volume of a cylinder compared to rodding and tapping. Therefore, rodding and tapping is the most appropriate method for achieving proper consolidation in concrete cylinders.