Florida DOT Concrete Batchman/Operator Practice Exam

What does the specific gravity of an aggregate represent?

1. The ratio of unit weight to the weight of the same volume of air

2. The ratio of its unit weight to the unit weight of an equal absolute volume of sand

3. The ratio of its unit weight to the unit weight of an equal absolute volume of water

4. The weight of the aggregate compared to its volume in a concrete mix

The correct answer is: The ratio of its unit weight to the unit weight of an equal absolute volume of water

The specific gravity of an aggregate represents the ratio of its unit weight to the unit weight of an equal absolute volume of water. This measurement is crucial in understanding the density of the aggregate material, which in turn affects the overall properties of concrete. Specifically, specific gravity serves as an important parameter in mix design and influences the strength, stability, and weight of concrete. Using water as a reference medium allows for standardization, as water has a known density at a given temperature (typically at 4°C, where it is most dense). By comparing the aggregate's weight to that of an equal volume of water, you can ascertain how heavy or light the aggregate is relative to water, which is essential for assessing its suitability in concrete mixtures. The other options do not accurately define specific gravity. For example, evaluating the relationship of unit weight to the unit weight of sand doesn't provide a clear basis for understanding the properties of aggregates in the context of concrete. Similarly, discussing the weight of the aggregate compared to its volume in concrete without the reference to water makes it less reliable for a consistent basis of measurement.