MECHANISTIC BEHAVIOR OF OPEN AND DENSE GRADED UNBOUND GRANULAR MATERIALS UNDER TRAFFIC LOADS

Abstract

The absence of abundant amount 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 crushed rock is used in two gradations- dense gradation and open
gradation. 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.