LETTERS: Rapid development and Malaysia's population increase has seen solid waste disposal increase by almost 38,000 tonnes daily. Statistics show that we dispose of RM476 million worth of recyclables where plastic is the second largest with an economic value of RM163 million.
The issues associated with plastic waste disposal are a grave concern and require careful consideration given that the sustainability of the world is threatened by pollution problems arising from widespread use of non-biodegradable plastics.
The burning of plastic waste releases toxic smoke, which contains chemicals that are hazardous to the environment. One of the ways to reduce energy use and emission of carbon dioxide is by recycling plastic waste. There is a high demand for the use of secondary and substitute mixtures in the design of pavement mixtures that enhance road performance, reduce the disposal of wastes in landfills and reduce the need to extract aggregates.
At present, the use of recycled plastic in the construction of road pavements is minimal. Current researches and practices tend to focus more on using waste materials in the lower layers of road pavements. Recycled plastic has potential for use as an additive or modifier for bituminous binders.
Generally, researchers have investigated the practicality of using recycled plastic in the construction of roads. For example, the Public Works Department carried out preliminary laboratory investigations, followed by the implementation of pilot projects for road paving in Temerloh, Pahang and Kemaman, Terengganu.
The durability of the plastic waste pavement is 50 per cent higher than roads constructed with the conventional mixture. Monitoring of the road in Temerloh shows that the plastic waste road pavement does not show any pavement surface cracking after one year, while the conventional pavement cracked, six months after opening to traffic.
Plastic waste has a promising potential in the construction of roads. However, there is a significant difference between recycled plastic and plastic waste. Most of the recycled plastic waste used in pavement construction are imported since these are cleaner and separated by the type of plastics.
Unlike imported plastic waste, the plastic waste in Malaysia is not recyclable because a large proportion is contaminated with food waste. Incorporating only one type of plastic or plastic waste in pavement material makes it easier to ensure the quality of the plastic material used in the construction of road pavements.
Research has also shown that the incorporation of different types of plastic makes it difficult to obtain a homogenous mixture since not all of the different types of plastic melt and coat the aggregates uniformly. Some may shrink and coagulate, causing an uneven distribution of strength where sections of the road may be vulnerable to early damage.
Dirty plastic waste can also cause other problems. The mixing of bitumen in road pavements with contaminated plastic waste may indirectly contribute to reducing the bonding strength of the modified bitumen with the aggregates.
As a result, the pavement mixture may disintegrate and this allows rainwater to infiltrate into the lower layers of the pavement, which has the effect of weakening the structure and eventually damaging the road before it is due for maintenance work.
Besides the economic and technical factors, the plastic waste incorporated in the pavement could be leachate and contaminants that are carried by
the runoff of rainwater. In summary, more comprehensive research is necessary to ensure that the use of plastic waste will result in the construction of more sustainable and eco-friendly roads which do not have any adverse impact.
Construction of sustainable plastic waste road pavements can help significantly reduce the high cost of maintenance and rehabilitation for more than 230,000km of roads throughout the country.
DR NUR IZZI MD YUSOFF, associate professor, Civil Engineering Department, UKM
DR MOHD ROSLI HAININ, deputy vice-chancellor (Academic and International), Universiti Malaysia Pahang
The views expressed in this article are the author's own and do not necessarily reflect those of the New Straits Times