What goes underneath the concrete?
Concrete needs to sit on a stable, compacted base. Organic materials and clay should be avoided. The subgrade must be made reasonably uniform, with no abrupt changes in degree of support and with subgrade soils that are of uniform material and density. Attention to this aspect of pavement construction is often neglected. Soft spots that show up during construction should be excavated and recompacted with the same type of soil as in the adjacent subgrade. Uniform support cannot be obtained merely by replacing the soft spot with granular material.
