Physical properties and shear strength responses of recycled construction and demolition materials in unbound pavement base/subbase applications

• Construction and Demolition (C&D) materials are increasingly used as construction materials.
• Evaluation of the shear strength characteristics of C&D materials.
• Direct shear, triaxial, unconfined compression and other strength tests were undertaken.
• Shear strength of the C&D materials were compared.
• C&D materials found to be suitable for various construction applications.

Construction and Demolition (C&D) materials are increasingly used as construction materials in engineering applications. Their usage currently includes applications such as pavements, ground improvement, engineered fills, pipe bedding, backfill and aggregates in concrete. A comprehensive laboratory evaluation of physical and shear strength characteristics of recycled C&D materials was undertaken using gradation, Los Angeles Abrasion, unconfined compression, California Bearing Ratio (CBR), direct shear and consolidated drained triaxial tests. The recycled C&D materials evaluated were recycled concrete aggregate (RCA), crushed brick (CB), reclaimed asphalt pavement (RAP), waste excavation rock (WR), fine recycled glass (FRG) and medium recycled glass (MRG). All the recycled C&D materials are classified as well-graded materials and their compaction curves are controlled by water absorption and surface characteristics. RAP, FRG and MRG exhibit flat compaction curves while RCA, WR and CB exhibit bell-shaped compaction curves. The shear responses of the recycled C&D materials are classified into two groups: dilatancy induced peak strength and dilatancy associated strain-hardening behaviors. RCA, WR and CB are dilatancy induced peak strength materials in that their peak strength is clearly observed after the maximum dilatancy ratio occurs. Higher dilatancy ratios in these materials are associated with higher peak friction angles. RAP, FRG and MRG on the other hand are dilatancy associated strain-hardening materials, which exhibit strain-hardening behavior even with a relatively high magnitude of dilatancy. Based on the evaluation of the shear strength characteristics, it is ascertained that the compacted C&D materials have the potential to be used in pavement base/subbase applications as they have the required minimum effective friction angles. RCA, CB and WR in particular are found to also meet the physical and shear strength requirements for aggregates in pavement base/subbase applications.