<P> Unbound granular materials are usually crushed stone, crushed slag or concrete, or slate . </P> <P> Cement - bound materials come in multiple types . Mass concrete is used where exceptional loads are expected, with thickness usually 100 to 150 millimetres (4 to 6 in), and optional reinforcement with steel mesh or polymer fibers . Other cement bound materials (CBM), with less strength but also lower cost, are used . They are rated by strength, from the weakest CBM 1 (also formerly known as soil cement) through CBM 2 to CBM 3, 4, and 5, which are more similar to concrete and are called "lean mix". </P> <P> The thickness of subbase can range from 75 to 100 mm (3 to 4 in) for garden paths through 100 to 150 mm (4 to 6 in) for driveways and public footpaths, to 150 to 225 mm (6 to 9 in) for heavy used roads, and more for highways . </P> <P> Low quality subbase material, including large pieces of rock and concrete, which was hardly acceptable heretofore, can now be re-used when crushed in - situ with conventional milling machines to obtain a homogenous grain size . It may then be treated normally with hydraulic binders, augmented by specific polymer formulations . The German road technology provider Adinotec proposes this process, which is adaptable to almost any subbase material and can net major cost savings without changes as to quality and load bearing capacity . </P>

Properties of sub grade and pavement component materials