An inverted section consists of an unstabilized crushed-stone base sandwiched between a lower cement-stabilized layer and the upper asphalt concrete (AC) surfacing. Two inverted full-scale instrumented pavement sections were tested to rutting or fatigue failure in a laboratory facility. One inverted section had a 152-mm (6-in.) cement-stabilized crushed-stone subbase and the other a 152-mm (6-in.) cement-treated silty sand subbase. The inverted sections were loaded up to 4.4 million load repetitions at failure. A 28.9-kN (6,500-lb) uniform circular loading was applied to the surface and systematically moved to prevent a punching failure. The inverted sections exhibited better performance compared to conventional and full-depth AC sections also tested. The inverted sections had lower vertical stresses on the subgrade and lower resilient surface deflections than the other sections. The rigid cementstabilized subbase was effective in bridging a weak subgrade. The inverted section made optimum use of the compressive characteristics of the unstabilized aggregate base where stresses were compressive. A nonlinear finite-element program, GT-PAVE, was used to calculate the resilient pavement response. GT-PAVE did a reasonable job of simultaneously predicting the measured deformation and stress and strain response at six points in the different layers of the inverted sections. A sensitivity analysis indicates the use of a 152-mm (6-in.) unstabilized aggregate base and a 152-to 203-mm-thick (6-to 8-in.) cementstabilized subbase to be an attractive inverted section design.

Today, more than 3.5 million km (2.2 million mi) of paved roads exist in the United States of which 94 percent consist of flexible pavements (1). Most of these flexible pavements have unstabilized aggregate bases or subbases. To achieve maximum economy in a pavement section, each material, including the unstabilized aggregate base, should be located to take full advantage of its best engineering properties. An inverted section consists of unstabilized aggregate base sandwiched between a lower cement-stabilized subbase and the upper asphalt concrete surfacing. An inverted section offers an interesting alternative to conventional flexible pavements with the inverted section making optimal use of the properties of each material.