Evaluation of the resilient modulus of asphalt concrete containing waste PET using response surface methodology (RSM)

this research aimed to investigate the effects of using waste polyethylene terephthalate (PET) on the resilient modulus of asphalt concrete. To this end, waste PET was added into asphalt concrete at different dosages of 0, 2, 4, 6 and 8% (by the weight of binder) and the resilient modulus of the mixtures was evaluated at different temperatures of 5, 25 and 45°C. Coarse and fine PET particles were added into asphalt concrete. Response surface methodology in Design Expert software was utilized for designing of experiments, developing a model for prediction of resilient modulus and evaluating the main and interaction effects of different factors on the resilient modulus of asphalt concrete. A polynomial model was well fitted to the test results relating temperature and PET content to the resilient modulus. Analysis of variance in Design Expert software implies that the model is highly capable for prediction of resilient modulus. Temperature, PET content and PET size are found to be effective on the resilient modulus. The resilient modulus of the mixtures was found to increase with increasing PET size and content, while it decreases with increasing temperature. However, the decrease of resilient modulus with PET size is not significant. It was found that there is no interaction between temperature and PET content with PET size, while interaction effect was found between temperature and PET content. Higher reduction of resilient modulus with increasing temperature was found to be in the mixtures containing higher PET content.