Systematic literature review, meta-analysis and artificial neural network modelling of plastic waste addition to bitumen

Abstract Many articles have evaluated the effect of the addition of a wide range of plastic types on bitumen properties. Because each study presents unique characteristics—such as plastic pretreatment, plastic-type, mixing conditions, percentage of addition, and bitumen properties evaluated—it has been difficult for researchers and practitioners to have comprehensive and quantifiable view of the effects. Thus, in the present project, we employed the systematic quantitative literature review (SQLR) to gather, summarise, quantify, and analyse the results of these articles in a practical and replicable manner. It was found that the addition of plastic waste reduces the penetration and increases the softening point and viscosity of bitumen. This behaviour is reported in most of the reviewed literature, regardless of the plastic type, percentage of addition, pretreatment methods, and experimental parameters employed. We employed Bayesian Regularized Artificial Neural Network to develop predictive models to predict the effect of plastic addition and mixing condition on the modified bitumen’s penetration, softening point and viscosity properties. The models had excellent prediction ability and can help engineers optimise the plastic modified bitumen properties. Furthermore, we reviewed the effect of plastic addition on the bitumen’s Superpave properties and found that the majority of the studies showed improvement on the bitumen resistance to hot temperature, but only a small percentage exhibited an enhancement in the cold cracking resistance. Among the drawbacks, the addition of plastic waste tends to deteriorate the workability of the bitumen by increasing its viscosity and by provoking a phase separation behaviour. This study also compiled a summary graph showing the recommended percentages of the different plastic types to be added to bitumen based on the reviewed literature. An addition of 4.5% plastic waste over bitumen weight seems to be the most effective. In conclusion, it is recommended to use plastic waste in bitumens that are intended to be implemented at moderate and hot climates. However, the addition should be limited to less than 5%, so it does not deteriorate the workability of the bitumen.