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Second to air pollution, road traffic noise is a health hazard that can be remedied with a sustainable antidote – rubberised roads, according to Angelica Buan in this article.
There are problems associated with urbanisation. Studies say that a major problem in economies, especially spurred with the rise of megacities, is the road hazards and noise pollution from vehicle traffic. Of the two, noise pollution has been the hardest to curtail.
In European Union countries, the World Health Organisation (WHO) stated that about 40% of the population is exposed to road traffic noise at levels exceeding 55 A-weighted decibels or dB (A).
In Asia Pacific, it is forecast that more than half of its population will be moving to urban areas by 2018, says a new study by the UN Economic and Social Commission for Asia and the Pacific (UNESCAP) and the UN Human Settlements Programme (UN-Habitat). By 2050, urban population in the region is expected to reach 3.2 billion. In China and India alone, the number of people living in cities is expected to grow by 696 million.
Along with accelerating urbanisation in the region is the increase in the number of its megacities from the current 17 megacities – three of which are the world’s largest, namely, Tokyo, Delhi, and Shanghai – to 22 megacities by 2030.
The Asian Development Bank (ADB) states that around 120,000 people a day, translating to 44 million people per year, are being added to Asia’s urban population, influencing transport and mobility. ADB also says that motor vehicle fleets are doubling every 5 to 7 years.
All this adds to the road traffic noise that has been linked to various health malaise ranging from stress, sleep disturbance, cognitive impairment in children to an increasing risk of diabetes, cardiovascular disease, and even death.
The health risks from unwanted exposure to road traffic noise becomes higher as population and urbanisation continue to grow, which WHO in its 2011 study found that road traffic noise follows air pollution in terms of impact on health.
Muting road traffic noise
Curbing road traffic noise with rubberised roads has been found to be a practical solution that provides multiple advantages too.
There are two types of rubber pavements chiefly used: the porous elastic road surfaces (PERS), which use rubber as the main component; and the rubberised surfaces, which use crumb rubber as a modifier in asphalt mixtures to enhance binder properties by stunting its inherent “temperature susceptibility”. Meanwhile, combining crumb rubber into the binder, is found to increase its elasticity; hence, its durability and the resistance to fatigue.
PERS, according to the report published online this year in the Applied Acoustics journal, is “a mix of air void content, 20-40% in volume, and of rubber, up to 90% in weight; and consisting of an aggregate of rubber granules or fibres, sometimes supplemented by sand, stones or other friction-enhancing additives, bound together with a binder of bitumen or polyurethane.” Based on earlier findings, this technology renders a very elastic surface, lowering vibrations from rolling tyres.
Rubber can be incorporated into asphalt paving mixes via the “wet process” and the “dry process”.
Rubberised asphalt (a regular asphalt-crumb rubber blend), in road construction provides a sustainable solution to curb road traffic noise. At the very least, rubber roads reduce noise by as much as 25%. The rubberised asphalt, made with the rubber crumb mixed with bitumen and crushed stone, enables road surfaces to disperse sound waves. The rubber itself, being bouncy, absorbs sound.
Since crumb rubber is obtained from used tyres, rubberised asphalt diverts the stockpiling volumes of waste tyres from landfills to a highly-functional application.
Rubberised roads can utilise Europe’s approximately 250 million waste tyres generated annually, according to a study published online in the Open Journal of Civil Engineering in 2014. The same volume of waste tyres has been generated in East Europe, North and Latin, America, Japan and Middle East, it said.
Benefiting latex producers
Rubber roads not only promote good health but also boost the rubber sector. Asia’s top rubber producing countries, Malaysia, Indonesia and Thailand, are resorting to rubberised roads to support the rubber sector. But unlike other rubberised asphalt concocted with crumb rubber, the three Southeast Asian countries are using NR latex.
Malaysia is using rubber in road construction to shore up NR prices that have been sagging in the global market for the past few years. Earlier in the year, it was reported that the Malaysian government is planning to utilise 10% of the total rubber production for rubberised roads.
Plantation Industries and Commodities Minister Datuk Douglas Uggah Embas said at a session of the Association of Natural Rubber Producing Countries (ANRPC) that the two other top natural rubber producers, Indonesia and Thailand, will follow suit, with the latter to utilise 3.5 tonnes of NR per 1 km of road.
With this plan, the Indonesian government could hit its target of increasing domestic consumption of NR from 18% in May this year to 40% over the next five years, at par with its regional neighbours.
Thailand, on the other hand, had earlier hatched the plan of repaving stretches of roads with rubberised asphalt following the approval of a US$75 billion construction package in 2014.
India, the world’s fifth largest rubber grower, is actively pushing for the rubberisation of roads. Since 1974, the country has had lanes of rubberised roads in various locations. Some 50 km of rubberised roads in different sites, such as the Trivandrum-Kottayam Main Central Road, Vandiperiyar-Kumily Road, and KK Road in Kasaragod Municipality, were constructed for a study on the performance of this technology.
Future of quieter roads, with rubber technology
With advancing technology and research, more busy, noisy roads will be built with rubber, a technology that is also proven to be durable, long-lasting and cost-effective. Rubber roads require lower maintenance costs (rendering about 33% savings) and for motorists, increased fuel economy, according to the India Rubber Board.
In an email interview with RJA, Sheela Thomas, Secretary General of the ANRPC, says that the service life of rubberised roads is twice as long as that of normal bituminous roads. “Rubberised bitumen is an excellent binder of rubble and sand on the tarmac, minimising deformation due to load. Rubberised roads have better skid resistance due to increased aggregate retention and elimination of bleeding,” she said.
Rubber roads, when properly prepared, can also withstand high temperatures.
She explained: “Compared to regular bitumen, which is vulnerable to melt on the road at higher temperatures, rubberised bitumen is unaffected by changes in atmospheric temperature. Rubber increases resistance to flow of bitumen at high temperature (ie., keeping it from melting) and improves resistance to brittle fracture at very low temperature.”
The presence of rubber in bitumen also decreases the bleeding tendency (melting) of bitumen at high temperature and prevents its cracking (brittleness) at freezing temperatures. “Thus, at very high and very low temperatures, rubberised roads are more stable than normal bitumen roads,” says Thomas.
Thomas recommends blending of bitumen with the latex. “The bitumen and the NR latex must be combined in a fixed proportion – usually 2% to 4% at the right temperature to confer good elastic recovery (elastic property) to the blend,” she explains.
However she cautioned that while rubberised roads have benefits, achieving these results is subject to the manner of blend preparation. “If the blending has not been done scientifically, these advantages will not be there.”
Thus, there is a future for rubberised roads in the region, to prop up failing prices of NR latex and to ensure that everyone is subjected to lower noise pollution!