ACI Concrete Field Testing Technician - Grade I Practice Exam

Vibration of a concrete sample is prohibited when the slump exceeds how many millimeters?

1. 50 mm

2. 75 mm

3. 100 mm

4. 125 mm

The correct answer is: 75 mm

When considering the vibration of a concrete sample, there are industry standards in place to ensure proper testing procedures and to maintain the integrity of the concrete. Vibration is generally used to help eliminate air pockets and ensure proper compaction of concrete. However, when the slump exceeds a specific limit, the consistency of the concrete mixture may be too high, which can lead to segregation or the displacement of aggregates. The limit for vibration in relation to slump is set at 75 mm, as excessive slump indicates a very fluid mix. Allowing vibration when the slump exceeds this threshold may compromise the results of the test and the quality of the concrete. Therefore, the prohibition against vibrating concrete with a slump over 75 mm is designed to promote accurate testing and maintain the material's cohesive properties. This helps prevent issues that could arise from air entrapment or separation of components within the mix, ensuring that the concrete remains stable and performs as expected.