Valorisation of waste plastic bags in cement-mortar composites as coating of local sand aggregates: Physicomechanical characterisation and potential uses

Abstract

Increasingly high quantities of waste plastics cause major environmental problems in Benin due both to the non-biodegradability of such by-products of the petroleum industry and to a lack of appropriate means of treatment. An option to valorise waste plastic bags is to use these in construction processes. This article studies the incorporation of waste plastic bags into cement-mortar with the aim of reducing proliferation. It explores the immediate consequences of cement-mortar-plastic combinations, such as changes in the resultant composite’s water absorption ratio and mechanical properties. The process of making the composite includes some main steps, during which waste plastic bags are first melted at 200°C-250°C and then mixed with sand aggregates. These coated aggregates are then mixed with cement and water into mortar. Moulded specimens of derived composites are then submitted to hydrothermal ripening and mechanical analysis. Experimental results allow optimizing the sand-aggregates coating process, providing data to locate the most appropriate ratio of plastic bags to be between 8% and 12% (wt/wt.mix):theoretically10.07%. The adopted practical value was 10%, leading to cement-plastic-mortar compositeswith90%reduction of water absorption ratio and 11.60% decrease in absolute density, compared to uncoated sand composites. Similarly, the mechanical strengths of composites were 8.83±0.34MPa in compression and 4.1±0.82MPa in 3-points flexural bending, corresponding to 74.1% and 48.1% weakening, respectively. These resistances were judged to be weak, with the result that the composites thus obtained cannot be used as the main elements of structural constructions. Potential applications are water-sealing/repellent materials in walls/soil, ending with good values of a wear-resistance index similar to commercial quarry tiles/stoneware.

Keywords: Waste plastic bags, cement-plastic-mortar composite, aggregates coating, ripening, water-absorption ratio, wear-resistance index