Which of the following is a common application of moisture density gauges?

Moisture density gauges are commonly used in soil compaction testing because they are designed to measure the moisture content and the density of soil materials. This application is crucial in construction and civil engineering, as it ensures that the soil is adequately compacted to provide the necessary support for structures, roads, and other infrastructure. By determining the moisture level, these gauges help in achieving optimal compaction, which can prevent future structural issues and failures.

In contrast, medical imaging is typically handled by different technologies like X-rays, MRIs, or CT scans, which are not designed for soil analysis. Food safety inspections focus on assessing contaminants and quality aspects of food products, where moisture density gauges do not play a role. Air quality testing measures pollutants and particulates in the air, which requires specialized instruments rather than moisture density technology. Thus, the application of moisture density gauges in soil compaction is both relevant and essential for ensuring the stability and safety of construction projects.