PROJECT DESCRIPTION
BACKGROUND
According to the World Steel Association, the European Union produced 177.2 million tonnes of crude steel in 2011. Steelmaking can be carried out by basic oxygen steelmaking – primary steelmaking – in which oxygen is blown through molten pig iron. Another process is the Electric Arc Furnace (EAF) – secondary steelmaking – in which scrap metal and/or pig iron is directly exposed to an electric arc and melted down. A by-product of both processes is steel furnace slag (SFS), which forms on the surface of the molten steel. EAF production – which accounts for some 42.8% of the total - generates up to 15% of slag/tonne of steel. It is usually composed of molten metal oxides, silicates and ferrites, although the exact composition varies depending on the particular conditions of production. Currently, a great volume of slag is dumped, although there is increasing research into different application alternatives. One of the most promising is as a recycled aggregate in road construction.
OBJECTIVES
The LIFE GAIN project aimed to demonstrate the feasibility of using SFS as an eco-friendly aggregate in the construction of railway tracks, specifically in sub-ballast and sub-grade track foundation layers, a completely new technological solution. The ultimate goal was to reduce the large volume of SFS that is annually disposed in landfills. The project planned to produce a new eco-friendly aggregate - SFS-Rail – in valorisation plants located next to steel furnaces to minimise the frequency and intensity of transport. A key feature was to demonstrate the possibility of adapting an existing valorisation plant to produce the new material. The project planned to construct 100 m-long test sections of rail; monitor the eco-friendly aggregate’s performance; demonstrate the expected benefits of the material (strength, hardness, durability, etc.) compared to natural aggregates; and show that this innovative, sustainable and eco-friendly alternative to natural aggregates is applicable throughout Europe.
RESULTS
LIFE GAIN used steel furnace slag (SFS), a by-product of steelmaking that is typically managed as an industrial waste, to produce a new recycled aggregate (SFS-Rail) for use in sub-ballast and sub-grade rail track foundation layers. In particular, the manufacture of this product created a new alternative valorisation for Electric Arc Furnace Slag (EAFS), also known as black slag, a sub-type of SFS, in line with the EU circular economy strategy.
The project team manufactured the SFS-Rail in ADEC’s plant in Vallirana (Barcelona), Spain, where new grids and hammers were installed specifically to produce the innovative recycled aggregate. The SFS-Rail was stored prior to using it in prototype sub-ballast and sub-grade rail track foundation layers. COMSA constructed two demonstration railway tracks to test the behaviour of SFS-Rail: the first in Gijón and the second in Castellbisbal (Barcelona). The monitoring activities included topographical surveys, to measure the overall settlement of the layers, and rail deflection under traffic, as well as the installation of vibrating wire pressure cells to measure the stress on the layers under traffic. The results obtained were satisfactory, proving that SFS-Rail is fully adequate to be used in rail track foundation layers that meet Spanish and European railway regulations.
The main environmental benefit was the reduction in the large volume of black slag disposed of in landfills. The project’s solution also reduces environmental problems related to quarrying, by reducing the demand for natural aggregates extraction. Moreover, human health-related issues could be improved by using SFS-Rail instead of natural aggregates. Widespread use of SFS-Rail could reduce overall CO2 emissions associated with rail track construction, particularly by minimising the frequency and intensity of transport.
Environmental benefits were quantified for the amounts of SFS-Rail used in the two test sections, and the potential production of the adapted ADEC plant: reduced volume of black slag sent to landfill (1 078 tonnes, potential 280 000 tonnes/year); reduced use of natural aggregates (1 078 tonnes, potential 280 000 tonnes/year); reduced CO2 emissions (3.42 tonnes, potential 829 tonnes/year); and reduced energy consumption (198 MWh, potential 65 909 MWh/year).
This project is in line with the 7th EU Environment Action Programme objectives of protecting, conserving and enhancing the EU's natural capital. In particular, it helps implement the circular economy strategy, by using an industrial waste as a new raw material: artificial aggregate for the railway sector.
SFS-Rail was manufactured by crushing and stabilising black slag in ADEC's valorisation plant, where different sizes of granulates were obtained. An important innovation of this project was adapted the production of this material to the requirements of the railway legislation, such as the specific granulometry for the sub-ballast and sub-grade layers.
The socio-economic analysis concluded that the valorisation of SFS in the railway sector had good social acceptance and could bring significant economic benefits. The project’s solution has a payback period of just 1.5 years. SFS aggregates could reach a high percentage of the market in the short term, due to their good mechanical properties in sub-ballast and sub-grade layers. It was found that the valorisation of black slag into SFS-Rail is viable for distances up to 90 km (valorisation plant to railway construction site), but costs beyond this distance are not competitive as natural aggregate from quarries located nearer to railway construction sites would be cheaper.
In the next years, the social benefit obtained in economic terms will be €772 233 per year, while the project will produce a saving of 637 tonnes of CO2 emissions. If we consider just the impact of the field tests construction, the local social benefit of the project in economic terms will be €4 965 during the first year, while the CO2 emissions will be around 3.5 tonnes.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).
