A comparison study of using polyethylene terephthalate and limestone fillers on porous asphalt mixture behaviours

Regardless of their gradations, all varieties of asphalts pavement mixtures are smooth and impermeable, which reduces the safety of cars in different weather situations. Comfort and safety on the roads during various weather conditions are directly influenced by surface layer characteristics. Porous asphalt has quick surface drainage, eliminates splashing, and improves safety. Additionally, because water drains into the asphalt mixture's pores, the desired level of friction between the tire and the pavement will be guaranteed. This necessitates the production of permeable asphalt pavement mixtures for roads and highways that can handle heavy traffic loads. The primary objective of this study is to investigate the enhancement of stability and mechanical properties in porous mixtures by substituting conventional limestone filler with Polyethylene Terephthalate Waste Plastic (PET) powder. Simultaneously, the study aims to mitigate environmental pollution by utilizing PET materials, which take decades to decompose naturally. The PET used in the study was melted at 260 0C and then powdered using 7000, 18000, and 28000 rpm grinders to obtain filler that passed sieve no. 200. The ASTM D7064-based evaluation of the mixture's optimum asphalt content takes into account essential factors, including drain down, percentage of air voids, and optionally, the results of the Cantabro abrasion test, which was calculated to be 4.75%, decreased to 4.5% when polyethylene terephthalate powder was utilized as filler in place of limestone. The optimum limestone filler percentage was 3.0% based on National Asphalt Pavement Association (NAPA) gradation employed the same procedure in the optimum asphalt content evaluation. However, the results showed that the optimum amount when using PET powder reached 3.5%. The criteria used to investigate the newly proposed asphalt pavement mixture are the Marshall method, Drain down of binder, Cantabro loss test, and permeability of porous mixture. This research reveals that adding PET as an alternative filler to limestone reduces permeability, Drain Down, and Cantabro by 22.64%, 29.27%, and 16.33% respectively while increasing the stability by more than 15.5%. It is still promising that the permeability of the mixture stays within the desirable limit for comfort and safe driving. Filler replacement was tied to performance testing and was demonstrated to raise the deformation strength in the KIM test more than twice from 1.54 MPa to 3.63 MPa by employing a specialized head and Marshall loading machine as an alternative method to the wheel tracking test for evaluating rutting in the mixture. The index of retained stability by aging the samples in water bath at 25 °C from one to four days increased from 8.66 MPa by 33.1% to reach 12.57 MPa where filler replaced, and the indirect tensile strength based on ASTM D4867raised by 29.08% from 0.578 to 0.735 MPa for conditions samples and raised from 0.681 to 0.879 MPa to raise the unconditioned samples by 12.9%. It is also worth noting that the use of PET as a waste material has significant environmental benefits.