Paving a way for scrap tyres

This article is based on a presentation by Dr. Amirkhanian at the European Conference on Tyre Recycling held 25-27 March 2015 in Brussels.
 

There are approximately 1.5 billion tyres sold around the world each year. That number is increasing as countries such as China and India are expanding their transportation and infrastructure systems. In addition, it is estimated that more than 4 billion tyres are stockpiled or landfilled each year around the globe. In Europe, in 2013, over 1.3 billion tyres of all types (e.g., passenger car, bike, etc.) were sold, and it is estimated that more than 290 million tyres are scrapped each year.

Considering these statistics, many municipalities around the world are facing a serious issue regarding scrap tyre generation and disposal. A typical passenger car tyre weighs about 9.1 kilograms and consists of 60% rubber, 20% steel and 20% fibre and other byproducts, all of which could be recycled.

Most countries have their own rules, guidelines and regulations regarding scrap tyre issues. For instance, in the U.S., nearly all states have some form of scrap tyre legislation and many states ban the landfilling of scrap tyres.

With regard to recycling of scrap tyres, one of the most successful products related to the utilisation of crumb rubber is in the asphalt industry. Rubber-modified asphalt has many benefits including extending the pavement life, resistance to cracking, decreased traffic noise for open graded mixtures, reduced maintenance costs and resistance to rutting. In addition, since it utilises crumb rubber made from scrap tyres, it provides a beneficial outlet for a portion of the millions of scrap tyres generated each year around the globe.

However, many issues must be considered by the user agency when considering the use of rubber-modified asphalt. Such considerations include up-front costs, the types of needed equipment, the expertise of available contractors, the availability of specifications and the potential recyclability of the pavement materials in the future.
 

Applications for rubber-modified asphalt

Many countries around the world currently use some form of rubber-modified asphalt on a regular basis, and several others are testing various processes using rubberized asphalt sections.

In the United States, there are three main types of rubberized asphalt applications used on a regular basis: Rubber-Modified Surface Course (R-M SC), Rubber-Modified Open Graded Friction Course (R-M OGFC), and Stress Absorbing Membrane Interlayer (SAMI).

R-M SC is the standard wearing course for most asphalt pavements, and it consists of roughly 92% to 95% crushed stone and 5% to 8% rubberized asphalt binder. Various states use anywhere from 5% to 20% rubber by weight of the virgin liquid asphalt binder.

In the cases that 10% crumb rubber is used, approximately 1.2 scrap tyres are used in each ton of hot mix asphalt (HMA) surface course, and about 1,000 tyres can be utilized when paving a one-kilometre section of a typical two-lane road. Advantages include increased resistance to rutting and cracking, longer pavement service life, reduced maintenance and lower life cycle costs than conventional HMA surface course.

OGFC is a type of wearing course typically used on high-traffic roadways to decrease traffic noise, increase surface friction, aid surface water drainage and decrease water spray during rainy weather. Each ton of R-M OGFC containing 12% crumb rubber modifier (CRM), contains approximately 1.3 scrap tyres, which equates to about 500 tyres for a one-kilometre segment of a typical two-lane road.

SAMI, also known as Asphalt Rubber Membrane Interlayer (ARMI), is a maintenance application used to prevent cracks in old pavement from causing cracks in the overlying new pavement. SAMI consists of a layer of rubber-modified asphalt binder applied to an existing, cracked pavement, which is then covered with a layer of crushed stone, compacted and covered with a new layer of HMA surface course. Various agencies use 20% to 23% rubber by weight of the virgin liquid asphalt binder for this application. Approximately 1,500 scrap tyres can be utilized when constructing a SAMI on a one-kilometre section of a two-lane road.
 

Scrap tyres on the rise

The consumption of natural rubber around the world has increased by almost 40% since 2006 and is estimated to increase to over 12.3 million by 2015. Therefore, the use of scrap tyres in many applications has been and will be an attractive alternative.

Natural rubber accounts for 35% of the market with the remainder representing synthetic rubber, styrene-butadiene rubber and other elastomers. Approximately 75% of the natural rubber use goes to the manufacture of tyres.

One of the emerging markets for many years has been the activity in China. For example, tyre production in China has been increasing by approximately 7% each year, and it is estimated that over 500 million tyres will be produced in 2015. The increase in tyre production in this market and in others such as India will lead to recycling challenges in the near future.

Today, China is the world’s largest producer and exporter of tyres and has built more than 10 million tons of powder production line capacity around the country. The 2012 output volume of radial tyres in China reached over 460 million and the volume of scrap tyres exceeded 200 million.

There are several regulations in China concerning the use of rubber in many industries, including the “China Resources Comprehensive Utilization Technology Policy” and “tire industry policy.” These are part of the 11th Five-Year Plan. The country has more than 1,000 reclaimed rubber companies with a total production capacity of more than 6 million tons. The majority of reclaimed rubber manufacturers operate only half of the time, as a result of financial pressures and the fact that their environmental protection equipment is not up to standards. In July 2012, the Ministry of Industry and Information issued Industry Access Conditions for the scrap tyre recycling industry indicated that “companies must have an annual scrap tyre processing capacity of no less than 10,000 tons.” Approximately 90% of the scrap tyre recycling enterprises cannot reach the 10,000-ton threshold and could be shut down.

India brings different challenges to the world market. The tyre industry in India is not new, particularly considering that in 1926 Dunlop Rubber Limited set up the first tyre company in West Bengal. Globally, passenger transport accounts for approximately 35% of the product mix. India’s market ratio, however, is 81% for commercial vehicles.

Meanwhile in Japan, some 97 million scrap tyres were produced in 2013, an increase of 3 million tyres from the previous year. The total recycled volume increased by 17,000 tons from the previous year to 899,000 tons. At this point, the recycling rate of scrap tyres in Japan is 88%. In 2013, approximately 57% of scrap tyres in Japan went to the tyre-derived fuel market. More than 15% of tyres are exported and approximately 10% of the scrap tyres are converted to crumb rubber.
 

Ongoing challenges

There are many challenges facing the industry, including the natural rubber cost issues that might affect the rate of utilisation of scrap tyres. This will also affect crumb rubber costs. The major challenge now is dealing with the increase of scrap tyres in some parts of the world.

Other factors that could change the playing field are the cyclicality of end users and volatility in raw and virgin rubber materials prices. Social and economic changes in many parts of the world, such as China and India, will also play a role.

The utilisation of crumb rubber must be researched more fully in many parts of the world to establish new standards. Another problem is the lack of training and certification programs around the world and a lack of major life cycle assessment for many products.

The author is director of research and development for U.S.-based Phoenix Industries of Las Vegas and a professor with the University of Alabama in Tuscaloosa, U.S. He can be reached at samirkhanian@eng.ua.edu.