Expansive clay soils are the types of soils whose volume changes with the change in water content. They have a behavior of swelling and shrinking that is a serious hazard to structures built over them. Expansive soils are abundantly existing soil types in Ethiopia, particularly Addis Ababa. This paper shows the outcomes of an attempt to reinforce and stabilize expansive clay soil with plastic bottle strips. The plastic strips were prepared and added at three different mixing ratios (0.5%, 1% and 2%) by weight and in three different aspect ratios (5 mm × 7.5 mm, 10 mm × 15 mm, 15 mm × 20 mm). The experimental results showed that there was a significant improvement in shear strength parameters. The swelling and desiccation cracking behavior of the soil were also expressively reduced. There was a substantial reduction in the optimum moisture content and slight increment in maximum dry density. The optimum plastic size (aspect ratio) and plastic content that results in optimum result can be selected based on the importance of the selection parameter for a specified engineering work. Stabilizing expansive clay soils with waste plastic bottles simultaneously solves the challenges of improper plastic waste recycling that is currently a teething problem in most developing countries. The results obtained from this study favorably suggest that inclusion of this material in expansive soils would be effective for ground improvement in geotechnical engineering.

Solid waste disposal is an alarming problem in most African countries. Plastic wastes like Polyethylene Terephthalate (PET) bottles and powdered wastes like fly ash are severely persisting environmental hazards. They are brutally polluting the water bodies, landfills, as well as the atmosphere. The construction industry has been working towards improving concrete quality by developing alternative methods like partial cement replacement with different pozzolanic elements as well as using waste fibrous materials. Fly ash and PET bottle fibres are two common waste materials that can be used. This article is a part of a research that studied the combined effects of the addition of PET bottle fibres and fly ash (as a partial cement replacement) on the structural performance of concrete. From a purely engineering point of view, the research results indicate that the utilization and incorporation of PET and fly ash wastes in the construction industry are a viable solution to make concrete quality better. This article presents, beyond the engineering properties and experimental works, the economic and environmental advantages of the addition of these waste materials to the conventional concrete mixture. The addition of PET bottle fibres and fly ash resulted in positive cost implications providing a production cost reduction of 19% over the conventional concrete mixture. The removal of these materials from the environment also showed reduction of the emission of toxic elements to landfills and water bodies that put human, animal and plant lives in danger.