Medium Track Type Tractors are highly effective tools for spreading aggregate. Tractors with VPAT (Variable Pitch Angle Tilt) blades are the most effective because they allow the tractor to move material laterally in a rolling action, much like a grader. This rolling action keeps granular material (such as CA-6) from segregating, providing optimum cohesion and compaction. The VPAT blade is also useful in helping the tractor pull material from the edge of the roadbed or around other obstacles.
Granular material is best spread by dumping near the edge and spreading toward the center. In this way, excess material is easier to push ahead because there is more room in the center, and the edges are assured of being filled in.
Typically, a compaction roller works with the tractor to prepare the roadbed. Experience will dictate the depth of material needed so when the roller compacts the material, it will be on or close to grade.
If a grader or trimmer is to be used for the final grade, be sure to leave the grade slightly high so that the finish machine has material to work with. Larger aggregate (such as three-inch minus used most often for the foundation of a roadbed) should be spread by the trucks as close as possible to the crown of the road. This helps prevent spillage beyond the road edge. Gathering the material from the edge is difficult. Experience will dictate what depth to spread the material so that, after compaction, the surface is at or near grade. Keep the area smooth to allow trucks to run over it easily.
An automated grade control system will increase productivity significantly, as well as cut down on material overages. A system like Cat® Grade Control or AccuGrade™ will allow the road construction company to bid more competitively and to better control costs.