Fines content, plasticity index and dust ratio influencing the modulus and permanent deformation behavior of aggregates

Abstract

Resilient modulus (Mr) and permanent deformation (PD) characteristics of unbound aggregates under repetitive traffic loads dictate the structural response and performance of pavement base and subbase layers. Aggregate material behavior is dependent on the amount of fines in particulate matrix, also referred to as fines content (percent passing number 200 sieve), as well as plasticity index, dust ratio (percent passing number 200 sieve to percent passing number 40 sieve), material type, aggregate gradation/packing and the interactions of these properties with each other. In this study, repeated load triaxial tests were conducted on crushed limestone and crushed gravel aggregates. Fines content and plasticity index were varied from 5% to 12% and 5% to 9%, respectively. Two most typical gradations of aggregates used in roadway construction in Illinois were utilized with dust ratios ranging from 0.4 to 1.0. The results of these tests were analyzed using the shakedown theory for evaluating typical base/subbase permanent deformation or rutting trends linked to practical design considerations. Charts were also established for the modulus and deformation characteristics of unbound aggregates to designate the material quality with performance trends. Such guiding charts were compared with others developed in previous studies by authors for determining aggregate behavior under monotonic loading tests such as California Bearing Ratio (CBR). The comparisons provide valuable insights on how each aggregate property influences strength, modulus and permanent deformation behavior under different loading conditions.