ACI Concrete Field Testing Technician - Grade I Practice Exam

A 6 by 12 in [150 mm by 300 mm] cylinder mold can be used for concrete containing aggregate with particles not exceeding what size?

1. 1 in. [25 mm]

2. 1.5 in. [37.5 mm]

3. 2 in. [50 mm]

4. 2.5 in. [62.5 mm]

The correct answer is: 2 in. [50 mm]

In concrete testing, the size of the aggregate particles is critical to ensuring that the mix can be adequately compacted and will yield reliable test results. The generally accepted guideline is that the maximum size of the aggregate should not exceed one-fifth of the smallest dimension of the mold. In the case of a 6 by 12-inch cylinder mold, the smallest dimension is 6 inches. According to the aforementioned guideline, you take one-fifth of this dimension, which is 1.2 inches (6 inches divided by 5). Since aggregate size exceeding this limit could impair the ability to form a proper cylindrical specimen and might lead to inconsistent results in tests like compressive strength, it is important to adhere to these specifications. Therefore, the appropriate maximum size of the aggregate that can fit in a 6 by 12-inch cylinder mold should be rounded down to 1 inch (25 mm) to ensure compliance with this guideline, meaning the aggregate particles should not exceed a maximum size of 2 inches (50 mm) for practicality. This rationale supports the choice indicating 2 inches as the correct answer.