Playing the Angles

PLAYING THE ANGLES

Abstract

Since 1996, every asphalt road project in Utah has relied on a new piece of required lab equipment--the gyratory compactor--for compliance with the Federal Highway Administration's Superpave program. Mandatory compliance for all states is by 2001. A gyratory compactor makes a sample of asphalt mix gyrate or wobble at a constant 1.25 deg (0.02 rad). It simulates the effects of a rolling compactor and vehicle tires on asphalt roads. Both compact the asphalt mix, directing a force wave through it. Because the energy exerted is the force on the aggregate multiplied by the distance the aggregate moves, the angle specified by the Superpave test represents the same energy put into the road by rollers and vehicles. Although the Utah Department of Transportation (UDOT) has used 11 compactors in its Salt Lake City lab and four region labs across the state, very few were in the field because of their size and weight. One of its compactors weighs 1,600 lb (726 kg). However, last fall UDOT purchased 11 346-lb (158-kg) compact Brovold Superpave gyratory compactors. Most are now being used in the field. A sidebar provides details on a Nebraska contractor who used a gyratory compactor to control air voids.