In many developing countries low-density polyethylene (LDPE) sheets, bags and water sachets are a major waste problem because local collection and recycling systems do not exist. As a result, LDPE has no value and is dumped causing aesthetic, environmental and public health issues. A relatively simple technology has been developed in the Cameroon that produces LDPE-bonded sand blocks and pavers. The application of this technology is an example of a community-driven waste management initiative that has potential to impact on the global plastics waste crisis because it can transform waste LDPE and other readily available types of plastics into a valuable local resource. In this research, waste LDPE water sachets have been melted and mixed with sand to form LDPEbonded sand blocks. The effect of sand particle size and sand to plastic ratio on density, the compressive strength and water adsorption are reported. Optimum samples have been further characterised for flexural strength and thermal conductivity. LDPE-bonded sand is a strong, tough material with compressive strengths up to ~27 MPa when produced under optimum processing conditions. The density and compressive strength increase as the particle size of the sand decreases. The potential for using this simple technology and the materials it produces to transform LDPE plastic waste management in developing countries is discussed.

Waste plastics are a major problem in developing countries, where efficient collection and recycling systems often do not exist. Plastic bonded sand composites provide a low-cost recycling alternative for selected waste plastics. This research has investigated the production and properties of plastic bonded sand manufactured using low-density and high-density polyethylene (LDPE and HDPE). Plastic bonded sand production in The Gambia was used as a case study to identify potential barriers to the technology. Processing was done by oven moulding, or a heat-mixing technique, and the properties of the LDPE and HDPE bonded sand samples formed have been determined. Processing at temperatures between 250 °C and 325 °C produced optimum compressive and flexural strengths. Higher processing temperatures reduced strength and lower temperatures produced inhomogeneous samples. Thermal plastic degradation occurs at 400 °C in N2 and 250 °C in air. Processing at temperatures below 250 °C in anoxic conditions is necessary to control off-gases. The optimum sand addition to produce the highest compressive strength was between 65 and 80%, depending on the sand particle size. HDPE produced higher maximum compressive strengths (37.1 MPa) compared to LDPE (27.2 MPa). Plastic bonded sand has increased strength, toughness, ductility, and thermal conductivity compared to C20/25 concrete and sandcrete and it can be used for wall construction blocks and paving tiles. The potential applications and implications of processing waste plastics in developing countries into plastic bonded sand are discussed. Graphical Abstract

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