The LaGrange case history: inverted pavement system characterisation and preliminary numerical analyses

Inverted pavement systems consist of an unbound aggregate base placed between a stiff cement-treated foundation and a thin asphalt cover. Unlike conventional pavements, which rely on stiff bound aggregate layers to bear and spread traffic loads, in an inverted pavement structure, the unbound aggregate inter-layer plays a major role in the mechanical response. A comprehensive characterisation study was conducted during the construction of a full-scale inverted pavement section in LaGrange, GA, USA, with particular emphasis on the unbound aggregate base. New laboratory and in situ tests were developed and used to characterise the unbound aggregate non-linear stiffness–stress relationship. Forensic digital image analysis confirmed particle alignment, i.e. inherent anisotropy. Comparison of pre- and post-compaction gradation test results failed to quantify the extent and significance of particle crushing. The information compiled during the field test was used in a complementary numerical study; the results confirm acceptable stress levels within the various layers under standard loads.