ACI Certification Practice Exam

How should slump molds be treated to ensure proper concrete consolidation?

1. Firmly shaken

2. Gently tapped

3. Left untouched

4. Quickly submerged

The correct answer is: Gently tapped

To ensure proper concrete consolidation in slump molds, the best approach is to gently tap the mold. This technique helps eliminate any large air pockets and facilitates the movement of the concrete, allowing it to settle more uniformly within the mold. Tapping encourages consolidation without disrupting the integrity of the mixture, which is crucial for achieving accurate slump measurements. Gently tapping creates just enough disturbance to maximize the density of the concrete while still maintaining the characteristics needed for a valid test. It allows the concrete to conform to the shape of the mold, ensuring that the test reflects the workability and consistency of the concrete mix. Other techniques, such as firm shaking, can lead to overcompaction or uneven settling that may misrepresent the slump. Leaving the mold untouched will not provide any assistance in achieving proper consolidation and could result in trapped air, leading to misleading results. Submerging the mold does not apply to slump tests, as it would alter the test conditions significantly.