Stone mastic asphalt mixtures with waste polyethylene terephthalate as aggregate replacement

Flexible pavement is widely used in road infrastructure, comprising approximately 95% of the world's highways. Generally, aggregates are one of the most important parts of flexible pavement, and their quality, quantity, and size significantly impact pavement performance. Natural aggregates, commonly used in asphalt mixtures, pose several challenges such as high consumption which is increasing each year, depletion of natural resources, and environmental concerns associated with extraction. The quest for sustainable alternatives becomes imperative due to these issues. Incorporating waste materials like polyethylene terephthalate (PET) in road construction could aid in addressing this issue. As a non-biodegradable material, PET can be recycled and used as an alternative aggregate or asphalt modifier, offering a sustainable solution in the pavement industry. This study explores the feasibility of using recycled PET as a replacement for fine aggregate and filler in asphalt mixtures. The physical, mechanical, and thermal properties of recycled PET were analyzed. The thermal analysis showed that the melting point of the PET at 255 °C where there was no reduction in the weight of the sample. From this point, PET can be easily added to asphalt mixture as the maximum temperature for the asphalt mixtures is usually 200 °C which still maintains its shape and performs well as an aggregate replacement even at high temperatures. PET was added to mixtures at six proportions (5%, 10%, 15%, 20%, 25%, and 30%) with asphalt binder penetration grade 60/70. Granite aggregates were used, following the stone mastic asphalt (SMA-20) gradation. Marshall mix design determined the optimum asphalt content (OAC). Cylindrical specimens were prepared for 13 mixture designs, with the OAC slightly increasing after PET incorporation. The mixtures with promising outcomes have been extended after the process of elimination for the performance analysis at OAC. Adding PET (fine and filler) to asphalt mixtures at 10% increases their resilient modulus (MR) by 20% and 22% compared to the control. Moisture assessment indicates PET mixtures meet AASHTO requirements, with Fine-10 and Filler-20 showing TSR values of 83.90% and 85.14%, compared to 81.04% for the control. The SMA-20 mixtures with PET replacement showed a higher dynamic creep modulus and lower permanent strain at 20% PET as fine aggregates and 20% PET as filler when compared to the control. Additionally, PET up to 20% presents a significant improvement in fatigue response. For instance, Filler-20 and Fine-10 show 23231 and 17521 cycles at a load of 2250 N, whereas the control mixture only shows 8581 failure cycles. In a nutshell, using PET waste as an aggregate portion of different sizes in asphalt mixtures could serve as an environmentally friendly method to dispose of PET waste while simultaneously producing high-quality pavements.

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