Development of ballast cleaning machines with integral recycling of used ballast is helping to reduce the cost of disposal, and is becoming an important tool in the track maintenance business as legislation on waste disposal takes effect

Rudolf Becker and Patrick Vierlinger

Plasser & Theurer, Export von Bahnbaumaschinen Gesellschaft mbH

RECYCLING of used ballast merits high priority in track maintenance planning. From both an environmental and an economic perspective, sustainable ballast management is growing in importance, with integral recycling on formation rehabilitation and ballast cleaning machines offering a significant increase in efficiency.

Ever since the United Nations Conference for Environmental Protection in Rio de Janeiro in 1992, the phrase 'sustainable development' has been a buzzword in social discussions about the future. The term was used by the Brundtland Commission in 1987 and is defined as 'a development that meets the needs of the present without compromising the ability of future generations to meet their own needs'.

With reference to the environment, sustainability in the case of track ballast is significant both in terms of ground protection, water purity and in preserving natural resources. From an economic perspective, ballast is used in huge quantities, and this alone warrants serious consideration.

In recent years much legislation has been passed on environmental protection. In Austria there is a firm commitment to comprehensive environmental protection which includes 'measures to keep the soil clean'. Other laws cover waste management and refuse dumping. The objective is to conserve raw material and energy reserves and to minimise the volume of dumped waste. Similar goals are enshrined in Swiss and German law, and there is also a European Union strategy for waste management.

Regarding the specific problem of used ballast, special guidelines and ordinances have been drawn up to reflect various provincial or cantonal regulations. In Germany DB Netz has its own internal guidelines on environmental protection, recycling and disposal of used ballast. In Switzerland the Track Excavation Guideline includes provision for evaluation and disposal of excavated track material; published in September 2002 by the Federal Office for Transport and the Federal Office for Environment, Forests & Land Conservation, it came into effect three months later.

Contamination

Generally, a distinction is made between uncontaminated, or slightly fouled, and contaminated ballast. The contamination consists of various materials and pollutants.

The material contamination such as fine particles from attrition and splintering of the ballast, spillage and rising subgrade material can for the most part be removed by screening during operation of a ballast cleaner. But some pollutants require special treatment and possibly specialist disposal. Examples are:

• aliphatics from loss of fuel and lubricating agents;
• polycyclic aromatic hydrocarbons, for example creosote in timber sleepers;
• heavy metals caused by wear of rails, wheels, brakes and catenary;
• residue from herbicides which may include chemical substances such as atrazin, amitrol, bromacil, dalapon, diuron, ethidimuron, glyphosat, MCPA, picloram, and simazin.

Based on practical experience, the guidelines highlight the possibility of increased pollution of track in sidings, stations or loading areas, points and crossings and sections of track ahead of signals. Taken together, these contaminated areas in fact contribute only a very small percentage of the total volume which can be dealt with by machines such as the Plasser & Theurer Jumbo VM170 vacuum scraper-excavator and its predecessor the VM150 (RG 6.94 p403).

All the track maintenance guidelines recommend recycling and reuse of ballast in accordance with waste management legislation. One guideline (1), for example, suggests that ballast handling processes may include washing, mechanical, biological, chemical or thermal treatment, with the decisive factor for the final choice being cost-efficiency. The decision should take into account the entire process, including transport, treatment, recycling and disposal. Mechanical processing by screening and the subsequent treatment of the residual more-polluted fines can be assumed to be more favourable in ecological and economical terms than disposing of the full quantity of the ballast. The final choice of process is thus often linked to environmental pollution issues.

Economic factors

A brief look at ballast quantities will illustrate the economic and ecological significance. The Swiss network amounts to around 5 000 route-km, of which Swiss Federal Railways operates about 60% and other companies 40%. In terms of track-km, the total length is almost 11 000 km.

At the present time SBB renews around 2% of its permanent way annually, which corresponds to between 140 and 160 track-km. Full ballast renewal is performed on roughly one-fifth of this, or 30 track-km. Together with the other railways, the annual quantity of excavated material amounts to 350 000 m³. As 1 m³ of excavated material weighs approximately 1·7 tonnes, this equates to around 595 000 tonnes of material (2).

The Austrian network runs to 5 672 route-km, and generates about 400 000 tonnes of excavated material a year from track work. The requirement for new ballast is around 500 000 to 700 000 tonnes a year.

On the 64 655 route-km network of DB Netz, about 2 200 to 2 500 track-km is renewed annually. In a single region, over 100 000 m³ of used ballast material was generated during the 1980s (3). In Germany the requirement for new ballast is around 4 million tonnes a year (4).

These gigantic quantities of raw material represent a major capital outlay for the infrastructure manager. With a price of around €10 for each tonne of new ballast, the potential benefits of cost-efficient ballast management are easily identifiable.

Equally important in economic terms is the cost of recycling or disposal of the used ballast. Because of the different environmental laws across Europe there is a wide spectrum of charges for dumping waste material, ranging up to €60 per tonne depending upon the degree of pollution and/or type of dump used.

For comparison, the cost of wet processing at a specialised plant in Switzerland works out at SFr23/m³. To this must be added the cost of transport to and from the plant, which is roughly the same as the actual recycling cost (3). This produces overall costs of roughly SFr46, or €30, per m³.

Rail-mounted recycling

A massive increase in efficiency comes from the application of rail-mounted ballast recycling which eliminates the cost of transporting spent ballast to a recycling plant, storing it for re-use and then transporting it to a new worksite.

Modern formation rehabilitation machines operate with their own material conveyor and hopper units, which have been calculated to save around 1 000 lorry journeys per km of upgraded track.

A presentation given by the German Federal Environmental Association included a calculation based on the RPM 2002 formation rehabilitation machine which has an output of around 100 km per year. Recycling the used ballast saved approximately 150 000 m³ or 250 000 tonnes of ballast. 'Compared to previous systems, 60% of the transport costs and approximately 500 000 litres of diesel fuel are saved, avoiding the emission of around 1340000kg/year of carbon dioxide and high quantities of other harmful substances.'

In 1997 Germany's Federal Environmental Office estimated the average lorry pollutant emissions as 160 g of CO&sub2;, 1·3g of NOX, 0·6g of CO and 0·3g of hydrocarbons per tonne-km. The Berlin Federal Environmental Office priced the ecological damage caused by lorry traffic at around €0·14 per tonne-km, for which the taxpayer has to pay (5).

Using DB Netz figures for the total rehabilitation of 1 km of track, transporting 6 290 tonnes of used ballast material for 30 km produces over 30 tonnes of CO&sub2;, 245 kg of NOX, 113 kg of CO and 57 kg of hydrocarbons, as well as generating environmental damage valued at €26 400.

Another significant factor is the difference in quality between track rehabilitation performed using excavators and lorries, which can damage the formation, compared to rail-mounted machines which leave the adjacent track free for traffic. This reduces operational disruption and associated costs, and produces a high initial quality which has a favourable influence on subsequent maintenance work as well as the intervals between maintenance.

Plasser & Theurer now offers three formation rehabilitation machines with integrated ballast recycling. The AHM-800 R crushes the ballast excavated by the front chain and returns it to the track as a formation protective layer material together with new material. Sharpening of the ballast allows better interlocking of the stones to achieve a longer lasting track geometry.

The RPMW 2002-2 cleans the used ballast using a star screen and a high-pressure water plant, sharpens the ballast in a crushing plant and screens it before putting it back into the track. The PM 200-2 R uses an initial grid screen for pre-cleaning, before the ballast is sharpened, screened again and finally washed. It also includes a clarification plant to treat the waste water. The washing of used ballast ensures the removal of almost all fine particles attached to the stones, especially when the excavated material is damp. The cleaning efficiency is almost 100%.

Based on experience gained with these machines, it is now possible to equip rail-mounted ballast cleaning machines with similar ballast processing plants. Combined with the sharpening plant, this ensures that the recycled ballast meets all technical and quality requirements set for new material.

Rail-mounted excavation of ballast combined with cleaning and immediate recycling is currently the best method of work for sustainable ballast management. It cuts the length of track possessions and allows trains to run on adjacent tracks.

References

1. LfU-LfW Merkblatt Anforderungen an die Entsorgung von Gleisschotter. August 2003

2. Grundlagenbericht zur Gleisaushubrichtlinie, March 2000

3. Thiele. Eisenbahn Ingenieur 03/1984

4. Deutscher Verkehrsforum November/December 1998

5. Berliner Umweltbundesamt 1997

Fig 1. Work flow diagram for the AHM 800 R formation renewal machine

The PM 200-2R formation renewal machine (above) includes a ballast washing plant (below) with integrated water treatment

Integral ballast recycling contributes to sustainable development

This RPMW 2002-2 formation rehabilitation machine operated by German contractor HFWiebe incorporates a high-pressure ballast washing unit

Summaries

 La régénération intégrale du ballast contribue au développement durable

 Le développement des machines à nettoyer le ballast avec recyclage intégral du vieux ballast aide à réduire les coûts d'élimination. Faire disparître le besoin de stocker des quantités importantes de vieux ballast dans des décharges ou ailleurs constitue un facteur de plus en plus important dans l'activité de maintenance des voies, tandis que les législations récente et future sur l'élimination des déchets entre en vigueur. Le recyclage intégral évite également le coût élevé du transport en vrac de matériaux.

Integrales Schotter-Recycling trägt zu nachhaltiger Entwicklung bei

Die Entwicklung von Schotterreinigungs-maschinen mit integralem Recycling des Altschotters hilft mit, die Entsorgungskosten zu reduzieren. Der Verzicht auf die Ablager-ung von grossen Mengen Altschotter in Deponien oder sonstwo entwickelt sich zu einem wichtigen Faktor in Gleisunterhalts-geschäft, wie auch gleichzeitig neue Rechts-grundlagen zur Abfallentsorgung in Kraft treten. Ein integrales Recycling bringt zudem den Wegfall der Kosten fUuml;r Materialtransporte.

El reciclaje integral del balasto contribuye al desarrollo sostenible

El desarrollo de máquinas de limpieza de balasto que permiten un reciclaje integral del balasto usado está ayudando a reducir el coste de su eliminación. La desaparición de la necesidad de descargar grandes cantidades de balasto usado en vertederos o en cualquier otro sitio es un factor de importancia creciente en el negocio del mantenimiento de la vía con la entrada en vigor de la nueva y fututra legislación sobre eliminación de residuos. El reciclaje integral también evita el alto coste del transporte de grandes cantidades de material.