I have read a literature regarding use of waste plastic as a binding material in pavement. Not sure if this is related to your query, but you can check this article.

http://cpcb.nic.in/upload/NewItems/NewItem_136_Plastic-Report.pdf

Dear

You should elaborate your study material/ any comparison

in highway you should go with experimental work as per selected material properties

Most of the research the past twenty years has been on asphalt mixes.  The biggest change is the adoption of the SuperPave gyratory compactor to develop mix designs, and the dynamic shear rheometer to identify asphalt binder properties which has led to greater use of polymer additives to the asphalt.  Some work has been done on use of geosynthetics in the aggregate base, but so far this has not been widely adopted.

 to study optimization of pavement material subject you need both aggregate materials and asphalt mix.  for the aggregate blending process you can see my paper attached. for the asphalt mix, I think you can review some of the well known asphalt mix design methods. Also you need to conduct experimental work.    

Article A study on mechanical stabilization to improve marginal base...

For a given aggregate proportion (as in your case), there are several methods for asphalt content optimization such as Marshall, Hveem and Superpave gyratory method. The last one is the most representative as it evaluates design of the mixture against probable performance in the field. However, it's several components are still being evaluated. Nevertheless, most researchers are currently using superpave method for mix design and investigating different of aspects of asphalt mixture.  

You may also think of optimization of asphalt mix of different asphalt types (polymer modified binder, binder with different additives, etc). Good luck with your paper writing.

If you are interested in laboratory works, you can try some material for asphalt mixture to improve the proportion of aggregate and bitumen and other additive.