Road dust is made up of fine particles that are important to the stability of the road. These fines are small enough to pass through a No. 200 sieve and feel like powder when rubbed between your fingers. When fines blow away, the gravel road begins to break down. Traffic scatters the coarser aggregate, causing potholes, ruts, washboards, loss of profile, loss of ditch lines, and other problems. Wetting the road surface helps to keep dust-related problems in check.
Moisture helps fines adhere to each other and to aggregates, allowing for optimum compaction.
The trick is to keep the road moist. There are several ways to do it. Calcium chloride absorbs water vapor from the air and liquid water from the road bed. In addition, calcium chloride solutions attract more moisture to the road than they give up in evaporation. The road remains dense and compact under almost any level of traffic because calcium chloride keeps materials on the road by keeping moisture in the road, even under a burning sun on a sweltering day.