This research paper was published in Waste Management 80 (2018) 112-118. Download the full pdf.
Recycling waste plastics in developing countries: Use of low-density polyethylene water sachets to form plastic bonded sand blocks
Alexander Kumi-Larbi Jnr (a), Danladi Yunana (a), Pierre Kamsouloum (b), Mike Webster (b), David C. Wilson (a), Christopher Cheeseman (a), (*).
(a) Environmental and Water Resource Engineering Section, Department of Civil and Environmental Engineering, Imperial College London, SW7 2AZ, UK
(b) WasteAid UK, Wye, Kent, UK
* Corresponding author at: Department of Civil and Environmental Engineering, Imperial College London, South Kensington, London SW7 2BU, UK. E-mail address: email@example.com (C. Cheeseman).
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 LDPE-bonded 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.
LDPE-bonded sand is a resource efficient material that can transform waste LDPE into a valuable local resource. Water sachets made from LDPE are a problem because there are often very limited recycling options for this material and they have an adverse impact on public health and the environment.
LDPE water sachets and other sources can be used to form LDPE-bonded sand. This requires simple processing and produces a durable, relatively lightweight material. No water is required in the production process.
The particle size of the sand, compaction method and cooling rate are critical to attain optimum properties. The sand addition to achieve the maximum compressive strength was 75 wt%. The compressive strength of optimum LDPE-bonded sand is comparable to C20/25 concrete and greater than typical Portland cement sandcrete.
LDPE-bonded sand has properties suitable for use in a range of applications. It is currently used to form paving blocks for hard standing areas and pavements. It has potential to be used in roofing tiles and partitioning walls.
LDPE-bonded sand behaves as a viscoelastic material similar to asphalt in compression. It fails in shear, but LDPE-bonded sand samples retain at least 30% of load after failure.
The production of LDPE-bonded sand can have major social, public health and environmental benefits. By transforming waste plastics into a valuable resource this simple technology has potential to generate local employment, clean-up the environment, produce new construction materials and significantly reduce the amount of waste LDPE entering the oceans.