ACI Certification Practice Exam

How many layers and rod strokes are needed to consolidate concrete for 4x8 cylinders?

1. 1 layer, 30 strokes

2. 2 layers, 25 strokes

3. 3 layers, 20 strokes

4. 4 layers, 15 strokes

The correct answer is: 2 layers, 25 strokes

To successfully consolidate concrete for 4x8 cylinders, the correct approach involves utilizing two layers and 25 rod strokes. This method is essential due to the dimensions of the cylinder, as it allows for thorough compaction and ensures that the concrete is uniformly dense throughout the sample. When pouring concrete into the mold, dividing it into two layers helps to achieve a better consolidation, as each layer can be effectively compacted without leaving air pockets or voids. The specified number of strokes—25—provides enough agitation and movement to allow trapped air to escape while ensuring that the concrete is properly settled and adheres to the sides of the cylinder. This procedure is crucial for obtaining valid test results since improper consolidation can lead to inaccurate strength measurements. Therefore, utilizing two layers with 25 strokes strikes a balance between effective consolidation and preventing damage to the sample.