Mechanistic behaviour of open and dense graded unbound granular materials under traffic loads

The absence of natural unbound granular materials (UGMs) necessitates investigating alternatives such as
processed crushed rock. Extensive use of crushed rock in pavement design requires proper modification of
characterization, design and construction practices. Many specifications and standards require adopting of
dense gradation of base materials. Although dense gradation has a high dry density, it also has low permeability
or voids. This low permeability results in a decrease in material strength when the pavement is exposed to
moisture. This research examines the effects of fines content on mechanistic behaviors of UGMs, particularly
resilient modulus (Mr) and permanent deformation (PD) using repeated load triaxial test (RLTT). Class 2
(Victoria, Australia) crushed rock is used in two gradation, dense gradation and open gradation (without fillerpassing
sieve 0.0075mm). Results from RLTT show that open graded Class 2 has an acceptable PD resistance
under repeated loads for test’s Stages 1, 2 and 3 followed by a significant collapse at Stage 4 as per Australian
pavement design guide. This investigation has found that open graded Class 2 has higher Mr than dense graded
Class 2. This paper suggests that open graded Class 2 could be used as a porous base material for roads with
low traffic volumes.