Properties of aggregate fines influencing modulus and deformation behaviour of unbound aggregates

Abstract

ABSTRACT Unbound aggregate base and subbase layers distribute traffic induced wheel loads in a pavement and protect the weak subgrade. In this study, effects of plasticity index (PI), fines content (FC) (per cent passing No. 200 sieve size) and dust ratio (DR) (ratio of per cent passing No. 200 sieve to per cent passing No. 40 sieve) of unbound aggregates on the base/subbase layer modulus and deformation characteristics are investigated. Repeated load triaxial tests were conducted on crushed gravel and limestone specimens prepared at optimum moisture contents for two Illinois dense-graded gradations, i.e. CA 6 and CA 2, to determine the resilient modulus and deformational behaviour. Samples with 9% PI showed lower resilient moduli and greater deformations than samples with 5% PI. The effects of FC on the modulus and deformation behaviour depend on the DR. Increasing DR from 0.4 to 0.6 and eventually to 1.0 increased deformations and decreased resilient moduli at the FC of 5%. An opposite trend was observed when the DR increased from 0.4 to 0.6 and eventually to 1.0 at 12% FC. The test results were used to develop improved resilient modulus and deformation prediction models, which capture important effects of aggregate FC, PI and DR.