Recycling of plastic bottles for use as a lightweight geotechnical material

Purpose - Geotechnical fills are used for building roadway embankments, filling in behind retaining walls, and as backfill above buried pipelines. Lightweight fill reduces the load so structures can be built more economically. A new lightweight geo-material made from recycled plastic bottles glued together in their original post-consumer form was developed. The purpose of this work is to explore the use of this new material as a lightweight geotechnical fill. Design/methodology/approach - Through a preliminary laboratory and field study, aspects of the physical and mechanical characteristics of the recycled plastic bottle blocks were investigated. This new material is currently undergoing field trials behind a retaining wall on a bicycle path. Findings - It was found that the average density of this new material is very low, at 32.63 kg/m(3) (2.04 lb/ft(3)), with 59.5 percent of a block made up of recycled plastic bottles. The plastic bottle waste stream obtained from a recycling plant is gap-graded having approximately 25 percent of the bottle volume at the 2l bottle size with the remaining 75 percent at the 500 ml bottle size. Unconfined compression tests on small ten-bottle samples produced strengths of 60 kN/m(2) (1,250 lb/ft(2)). Practical implications - Testing indicates that this material may be useful as a lightweight geotechnical fill over soft soils or behind retaining walls; as an energy-absorbing crash barrier for highway, race track, or airport safety; as ground and building insulation for Arctic construction; as floating barriers or platforms for offshore work; or for acoustic or vibration dampening for manufacturing processes. Originality/value - This work explores the use of large volumes of recycled plastic bottles as an environmentally friendly geotechnical engineering material. Engineering parameters for this new material are presented as well as a discussion of an ongoing field study. The information presented here is the first step in understanding this new material with respect to civil engineering applications.