SLEEPERS made from recycled plastic and rubber are already in use in the United States, China and India. However, speeds are restricted to 80km/h on track sections fitted with these sleepers, with plastic sleepers often lacking the necessary strength to accommodate higher speeds and larger loads.
Recognising the potential to deliver a sustainable sleeper but with the necessary strength, Greenrail, Italy, developed a concept which combines materials including concrete, recycled plastic and rubber. The resulting sleeper consists of an outer shell of recycled plastic and shredded rubber from used tyres and an inner structure consisting of reinforced concrete. The sleeper also supports a preassembled "W" fastening system to provide simple installation using track laying machines.
Greenrail's range consists of four patented sleepers which utilise this structure:
- 190NGW suitable for 950-1000mm-gauge track, with the sleeper 1.9m long and weighing around 250kg
- 230W designed for conventional lines and can accommodate speeds of up to 190km/h, are 2.3m long and weigh up to 340kg
- 240W H/S 2.4m long, weigh around 360kg, and can be used on lines with speeds up to 250km/h, and
- 260W H/S suitable for lines where speeds exceed 250km/h, 2.6m long and weighing about 380kg.
Greenrail says its design guarantees low vibration and noise, with initial tests conducted by Milan Polytechnic University showing a 50% reduction, with full results expected in early 2016. The sleepers also have high resistance to lateral displacement while maintenance costs are significantly reduced. They also cost around 15% less than the concrete equivalent and have a lifespan of up to 50 years, which is significant given that 40 million sleepers are replaced every year in Europe, and 70 million around the world.
Mr Giovanni de Lisi, Greenrail's founder and CEO, says the development of its sustainable sleeper concept began in 2012 and that he envisions selling the patented production process as a license to enable domestic production. He adds that its work on developing sustainable sleepers has since led to several other projects which aim to improve railway infrastructure sustainability.
For example Greenrail Piezo is looking at ways to produce energy by incorporating a piezoelectric system inside the sleeper. Studies have shown that when a train passes over a section of track, infrastructure suffers small strains of up to 0.5cm. It is possible to capture this energy using the piezoelectric system, which is connected to external accumulators located in the wayside, with the cable linking the systems simple to move during maintenance.
This system is designed for lines with a high-traffic density such as metro or urban lines, or others where there are at least 10 trains per hour. Greenrail estimates that from data regarding the frequency of services on the London Underground, Paris and Madrid metros where between 23 and 27 trains per hour pass over the track that it is possible to generate up to 300kW/h of energy from just 1km of track fitted with Piezo. In lines with less traffic, around 10-20 trains per hour, up to 120kW/h is achievable.
Other projects include Greenrail Solar, which, in cooperation with the Italian Institute of Technology in Genoa and Milan Polytechnic, is studying the integration of photovoltaic modules into sleepers. In addition Greenrail Linkboc is looking at transmitting data using railway infrastructure.
De Lisi says the next step for these projects is to secure a partner and location to establish a 200m-long test site. He says once secure, all of these tests as well as trials of the sleepers' mechanical stress, noise and vibration will be conducted by the Italian National Research Council of Pisa. Greenrail is also currently seeking financial and industrial partners to support local developments and has passed the first call of the Horizon 2020 initiative, thus securing €50,000 for the project with a €2.5m prize available for the winner of this programme.