Inverted flexible pavement response and performance

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 cement-stabilized 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.) cement-stabilized subbase to be an attractive inverted section design.