EFFECTS OF PARTICLE SIZE AND TYPE OF AGGREGATE ON MECHANICAL PROPERTIES AND ENVIRONMENTAL SAFETY OF UNBOUND ROAD BASE AND SUBBASE MATERIALS: A LITERATURE REVIEW

Abstract

Unbound graded aggregates are used to construct the base and subbase of road pavement. The mechanical properties of unbound graded aggregates depend significantly on aggregate size and grading, especially on the maximum particle size (D_max) and fines content (F_c; typically, the particle size of fines < 0.075 mm). Nowadays, not only natural aggregates (NA) but also recycled aggregates (RA) from construction and demolition waste are used in road construction. Many studies have been done to characterize the mechanical properties of RA, but a comprehensive understanding of the effects of aggregate size and grading on the mechanical properties has not been fully achieved due to the wide variety of material types and properties of RA. Therefore, this paper searched previous studies and reviewed the effects of particle size, type of aggregate, and mixing proportions of RA on mechanical properties such as compaction, bearing capacity, resilient modulus, and shear strength. In addition, some information on the environmental safety of RA, such as leachate pH and leaching of elements, are summarized. The results collected from the literature indicate that the mechanical properties of RA and their mixtures are mostly comparable to those of NA and can be used to construct road base and subbase. As well as the type of aggregate, D_max of RA was also found to affect highly the relationships between the mechanical indices (e.g., the maximum dry density and California bearing ratio) and F_c and/or mixing proportion.