ACI Certification Practice Exam

What is the maximum time allowed to start slump and air content tests after obtaining the final portion of a composite sample?

1. 10 minutes

2. 5 minutes

3. 15 minutes

4. 30 minutes

The correct answer is: 5 minutes

The correct answer is that the maximum time allowed to start slump and air content tests after obtaining the final portion of a composite sample is 5 minutes. This time limit is established to ensure the accuracy and reliability of the test results. Concrete begins to set shortly after mixing, and factors such as temperature, humidity, and the composition of the concrete can accelerate this process. Conducting the slump and air content tests within this brief window helps to assess the properties of the concrete as it was mixed, without significant alteration or premature setting occurring. Having this strict time requirement is crucial for maintaining consistency in measurements and ensuring that the results reflect the true workability and air content of the concrete at the time of sampling. Delaying the tests beyond this time frame could lead to incorrect interpretations of the concrete's properties, which could ultimately impact the performance and durability of the finished structure. In contrast, the other time frames suggested are longer than the recommended period, which might compromise the integrity of the test results, making them unsuitable for assessing the fresh concrete's characteristics effectively.