Exploiting recycled plastic waste as an alternative binder for materials used in the construction industry

Abstract

The population in the world is growing at an alarming rate and four local and global threats viz. plastic pollution, high unemployment, inadequate housing for all citizens and damage to the ozone layer causing climate change continue to emerge. The overwhelming demand for plastic goods in daily use resulting in plastic waste pollution has become an environmental challenge. Plastic waste is now becoming extremely dangerous due to their rapid accumulation in the environment and in landfills, and their improper disposal methods leads to many harmful effects on land, air, marine life and humans. Incineration of plastic waste is already posing several health risks. Concurrently, the cement, building and construction industry is amongst the biggest contributor to carbon dioxide (CO2) gas emissions, which poses an added environmental challenge. This creates a negative image on the use of cement-based masonry as construction materials, which renders it unsustainable. Hence, an alternative construction material is required. The manufacture and utilisation of burnt clay bricks have become an area of debate which led to a move towards greater sustainability. Therefore, there is need for a strategy to reduce plastic pollution, create job opportunities, provide alternate ways of constructing affordable ecofriendly houses, and reduce the depletion of the ozone layer for the benefit of all citizens. This strategy is explored in this research study that supports, enhances and promotes sustainability. The efficacy of producing eco-friendly plastic-sand bricks as a feasible solution and an attractive alternative to cement or burnt clay bricks have been investigated in this study. This investigation encompasses an effort to combat issues related to plastic waste, high unemployment, rising building costs and climate change. In the first stage the study analyses the use of High-Density Polyethylene (HDPE) and river sand using six different ratios of sand(s): plastic(p) viz. 60s: 40p; 65s: 35p; 70s: 30p; 75s: 25p; 80s: 20p and 85s: 15p. The second stage consisted of the addition of 1%, 5% and 10% of Kaolin Clay DSF which was experimentally added to each of the different ratios of sand: plastic respectively to improve the mechanical and environmental properties towards producing eco-friendly plastic-sand bricks. The mechanical tests showed significant improvement. Results revealed that the addition of 5% Kaolin Clay DSF, significantly increased the compressive strength from 21.4 MPa to 52.76 MPa in the 75s:25p ratio, the modulus of elasticity from 1109.35 gigapascal (GPa) to 2434.84 GPa and the short beam strength from 1.84 MPa to 2.27 MPa. The addition of 10% Kaolin Clay DSF, significantly increased the results for the impact test from 4.6 joules to 5 joules in the 75s:25p ratio. However, the addition of 5% Kaolin Clay DSF revealed an increase from 4.6 joules in the same ratio to 4.7 joules. The hardness test revealed that the impression of the nail did not affect the samples which implied that the plastic-sand bricks are durable and tough in all six ratios. The environmental tests also showed significant improvement. Results revealed that the addition of 5% Kaolin Clay DSF decreased the rate of water absorption from day 1, being 0.78% to 0.43% on the 21 st day. The plastic-sand brick as a composite material is an electrical insulator. The plastic-sand brick sample resisted the immediate absorption of water with respect to 0%, 1%, 5%, and 10% addition of Kaolin Clay DSF. No visible deposit of alkali was present when the efflorescence test was done. The fire test revealed that the addition of 10% Kaolin Clay DSF with an increase in sand content drastically reduced the linear burning rate significantly in the 75s:25p ratios from 10.52 mm/min to 2.10 mm/min respectively. This decrease in approximately 81% in the burning rate is significant. The main conclusion of this research study is that HDPE plastics can be used to produce plasticsand bricks that are durable, significantly high in strength and eco-friendly as compared to the conventional cement or burnt clay bricks. The addition of Kaolin Clay DSF improves both the mechanical and environmental properties of the plastic-sand brick. The manufacturing of plastic-sand bricks is an eco-friendly process. Thus, recycled plastic waste can be effectively used as an alternative binder material in the construction industry.