A study on subgrade quality improvement using recycled waste polypropylene nodules

Abstract

Scarcity of traditional construction materials has motivated researchers to explore alternatives, and besides crushed glass, reclaimed asphalt pavement, and scrap tires, to name a few, plastic waste (unwanted or unusable plastic objects) has also gained attention in recent years. Plastic waste is traditionally re-used or recycled, but it often ends up as trash on curbside, in landfills, or in our seas and oceans. The substantial amount of plastic waste produced annually worldwide, and its environmental repercussions are the rationale for exploring alternatives in order to recycle plastic waste into construction materials. This exploration can also benefit many industries and would help minimizing adverse environmental impacts associated with dumping tones of plastic waste in landfills. Using plastic waste material with soil for soil reinforcement purposes has revealed some improvements in terms of strengths of materials, but nevertheless, this potentiality has not been fully assessed for different types and forms of plastic waste with natural subgrade soil in the road industry. In this paper, recycle polypropylene nodules [diameter: 3-4 mm] is combined with clayey silt and used as a ground improvement material. Soil subgrade is mixed with 1-5% polypropylene nodules (by dry weight of soil sample). Various geotechnical properties have been assessed thoroughly. Tie investigation process entails assessing compaction, California Bearing Ratio (CBR), shear strength parameters and permeability properties for both natural sub-grade soil and plasticmixed sub-grade soil. The results obtained show that the addition of plastic wastes decrease the maximum dry densities of the subgrade soils because of the lower relative density of the plastic material compared to the soil particles. It is also found that the addition of plastic wastes increase the CBR values. Values of cohesion increased up to addition of 2.5% polypropylene nodules; further addition of pp nodules, leads to decrease the cohesion values.Values of angle of internal friction was decreased up to addition of 1.5% pp nodules, then increased.Values of coefficient of permeability are decreased up to 1.5% addition of plastic grains, then increased. The results of this research suggest that partial replacement of subgrade soil material with plastic waste may prove useful in road subgrade applications.