Base and Subbase Types

The base and subbase types commonly used for rigid pavements include the following:

• Unstabilized bases:
  
  • Dense-graded aggregate base.
  • Open-graded aggregate drainage layer.
• Stabilized bases:
  
  • Cement-stabilized bases:
    
    • Cement-treated base.
    • Lean concrete base.
    • Cement-treated open-gradeddrainage layer.
  • Asphalt-stabilized bases:
    
    • Asphalt dense-graded base.
    • Asphalt-treated base.
    • Asphalt-treated open-gradeddrainage layer.

Stabilized bases are typically constructed using concrete or asphalt paving equipment that can achieve a smooth surface. As such, the use of stabilized bases under a concrete pavement can contribute to achieving a high level of smoothness for concrete pavements.

Constructing a stronger and stiffer base layer does not guarantee good performance of a rigid pavement system and may even cause other problems [ACPA 1995, ACPA 2007]. A support system with reasonable strength provides several benefits, such as reduced strains in the pavement and improved load transfer across the joints. However, when the base becomes too stiff, it fails to conform to the changes in the shape of the slabs subjected to environmental loading (curling and warping). When this happens, the stresses and deflections increase within the slabs and may eventually cause cracks to develop, especially when the concrete is relatively young. To avoid cracking of the concrete panels, the target compressive strength of cement-treated base should be within 300 to 800 psi, while lean concrete bases should have compressive strengths between 750 and 1,200 psi.

Figure 6 shows an example of an asphalt-treated base, and Figure 7 shows a cement-treated open-graded drainage layer.