Inverted pavements

• Inverted pavement system, or inverted base, is a high depth road whose supporting layers are thicker and stiffer than top layers.
• The system consists of a thin bituminous concrete (BC) layer provided on top of a graded aggregate base (GAB) layer. A portland cement-treated stiff base layer is provided at the bottom.
• This arrangement causes the critical stress/strain plane to be located at the interface of the BC and GAB layers. Thus only the top portion of the inverted pavement structure absorbs the traffic loads as compared to conventional design where thick sections are required for load distribution.
• Research by South African Roads Board (SARB 2004) and Georgia Department of Transportation, has shown that an inverted base provides enough structural performance to support traffic loadings up to 100 million Equivalent Single-Axle Loads (ESAL s) with a maximum two inch bitumen riding course (Halsted, 2002). According to SARB, this type of system proves to be more cost effective for construction of long lasting pavements.

Bituminous pavement with cemented base

• The cemented bases are derived from aggregates mixed with some binding material. Since it is bounded layer, it also has some fatigue life.
• Thus, unlike the unbound granular base, the cemented base layer contributes to some fatigue life, which may give rise to comparative reduction of design thickness of bituminous layer (Das and Pandey 1998).
• The stiffness modulus of cemented layer is generally found to be much higher than granular sub-base; however, due to shrinkage cracks, the stiffness modulus falls rapidly.
• This change in stiffness values at different stages of the design life has been schematically shown in Figure-10(a) and Figure-10(b) presents a typical design chart for design of bituminous pavement with cemented base made up of lime-soil mixture.