ACI Concrete Field Testing Technician - Grade I Practice Exam

What is the minimum number of cylinders that should be cast for strength testing on a batch of concrete?

1. 1

2. 2

3. 3

4. 4

The correct answer is: 3

Casting a minimum of three cylinders for strength testing is standard practice in concrete testing. This approach is essential for obtaining a statistically meaningful average compressive strength result. Having three cylinders allows for the detection of variability in the concrete mix and provides a more reliable assessment of its overall performance. If one cylinder fails to meet the required strength, the results from the other two can still produce a valid average, which is crucial for quality control and assurance processes in construction projects. Moreover, this practice adheres to established testing standards, such as those set forth by ASTM C39, which recommends having at least three specimens to account for discrepancies that may arise due to factors like mixing, curing conditions, or other influences on the strength of the concrete. While casting only one or two cylinders may seem sufficient, it limits the ability to accurately assess the strength and increases vulnerability to random variations within a single sample, which can lead to erroneous conclusions regarding the quality of the concrete batch.