Equivalency of Crushed Rock and Three Industrial By-Products Used for Working Platforms During Pavement Construction

A study was conducted to define an equivalency criterion for five materials used for working platforms during pavement construction on a poor subgrade: conventional crushed rock (referred to as breaker run) and four alternatives (Grade 2 gravel, foundry slag, bottom ash, and foundry sand). A layer of alternative material was considered equivalent if the total deflection of the alternative material was equal to that of breaker run under the same construction loading. Total deflection data for the equivalency assessment were obtained from a large-scale model experiment (LSME) simulating a prototype-scale pavement structure. Total deflections obtained from the LSME were checked against deflections measured in the field with a rolling wheel deflectometer and with an analytical method developed for unpaved roads. Design charts were developed for selecting the equivalent thickness of alternative working platform materials so that the alternative and a layer of breaker run provided equal deflection.