ACI Concrete Strength Testing Technician Practice Test

What is a key factor that affects the results of the compressive strength test according to ASTM C39?

1. Size and shape of the specimen

2. The color of the concrete

3. Weight of the concrete

4. Type of aggregate used

The correct answer is: Size and shape of the specimen

The size and shape of the specimen is a critical factor influencing the results of the compressive strength test as described in ASTM C39. This standard specifies the dimensions of concrete cylinders that are typically tested for compressive strength. The cylindrical shape and specific diameter-to-height ratios are established to ensure consistency and reliability in testing. If the dimensions vary from the standard, it may lead to variations in the stress distribution and, consequently, affect the test outcomes. For instance, a wider or shorter specimen might exhibit different strength characteristics compared to a standard cylinder, leading to inaccurate strength assessments. The other factors listed may have some impact on the overall properties of concrete but do not directly relate to the specific conditions outlined in the ASTM C39 test method for compressive strength. Color does not influence the strength itself, the weight of the concrete alone does not provide information about compressive strength, and while the type of aggregate can affect the concrete's overall performance, it is not a primary concern within the context of compressive strength testing as per ASTM C39. Thus, the size and shape of the specimen remain paramount in ensuring accurate test results.