Dynamic properties of crushed glass and tyre rubber in unbound pavement applications

Flexible pavements consist of treated unbound materials between the surface, typically bituminous, and the natural subgrade layer. A laboratory study was conducted to assess the dynamic behavior under the influence of repeated loads of the two most common global waste materials for their performance as road materials. The study investigated the behavior and properties of crushed rock (R) blended with waste glass (G) and tyre rubber (T) and evaluated them as alternatives to natural unbound materials. Preliminary tests included Modified Proctor compaction and Particle Size Distribution tests (before and after the compaction stage), and a more specialised test to determine the resilient modulus (Mr) and the permanent deformation values; the Repeated Triaxial Load Test (RLTT). The mixtures were prepared at different percentages of the whole specimen’s total dry weight: from 12 to 45 % waste glass, and from 5 to 15 % tyre rubber. To simulate typical in situ materials, the mixtures were also prepared at the lower target moisture contents of 70% and 80% of OMC. The moisture content and the dry density after the RLTT were measured. Results showed a positive correlation between permanent deformation and glass content, while glass content can improve Mr value of rock specimens by up to 50%. Under RLTT, the addition of tyre rubber to crushed rock decreased permanent deformation.