ACI Certification Practice Exam

What is the correct number of layers and rod strokes for 6x12 cylinders?

1. 1 layer, 30 rod strokes

2. 2 layers, 20 rod strokes

3. 3 layers, 25 rod strokes

4. 4 layers, 15 rod strokes

The correct answer is: 3 layers, 25 rod strokes

The correct procedure for preparing 6x12 cylinders involves specific guidelines designed to ensure the concrete is properly compacted and representative of the concrete's properties in a testing scenario. The standard practice is to create a cylinder using three layers of concrete. Each layer is compacted to remove air pockets and achieve a uniform density. The recommendation of 25 rod strokes for each layer is established based on ensuring effective compaction without segregation of the mix components. This technique is crucial as it helps to ensure that the test cylinders can accurately reflect the material's performance characteristics under load. Using three layers allows for better compaction and ultimately yields a more consistent specimen for strength testing. Each layer being stroked sufficiently ensures that the concrete is consolidated adequately, promoting proper bonding between the layers.