For an international company, such as Danieli Group, recycling, recovery, re-use of waste materials and environmental awareness are one of the top priorities. Danieli has been striving, for more than 40 years, to find solutions for environmental issues related to the steel production cycle. One of them is designed for Ecogravel plants and allows slag reutilization during the production of industrial aggregates from EAF slag.
The demand for construction aggregates is constantly growing and its production is an activity with a notoriously high environmental impact. To avoid this environmental cost Danieli has developed a process to transform a secondary raw material such as EAF slag into Ecogravel, an industrial aggregate with remarkable properties, which replaces the use of natural aggregates in bituminous conglomerates or in cement mixes. The use of Ecogravel in bituminous conglomerates or in cement mixes means saving natural resources and energy.
Economical aspects make this solution even more interesting. Natural aggregates with comparable performances (basalt and porphyry) required for specific applications, are notoriously more expensive compared to normal natural aggregates. Ecogravel is an excellent substitute for these natural materials with superior properties. As a result, thanks to Danieli, a secondary raw material such as slag, which was previously disposed of, today has become a profit-making resource.
The slag produced by the EAF can be recovered and processed after a seasoning period for its stabilization, during which it is exposed to the weather precipitation. Before that, the slag recovery process requires that some precautions be taken during slag production.
This picture shows a sample of compact and porous slag. In the enlargement made with an electronic microscope the white area is a steel inclusion.View the embedded image gallery online at:
THE ECOGRAVEL PROCESS
The production of Ecogravel is based on a process that stars on the furnace deslagging and ends with its use in cement mixes or bituminous conglomerates.
The flexible process designed by Danieli takes into consideration the specific requirements of each project and can be adapted to different particle size of the product (all sieving mats can be changed in a few hours to produce aggregates of diverse dimensions)
The following process diagram, suitable for the production of five different aggregate sizes, shows step by step the process to obtain Ecogravel:
A wheel loader feeds the plant by unloading the slag into a static scalper (01) to separate any bulky material. The material that passes through the scalper is processed by a vibrating feeder (02) that doses it to the following treatment equipment.
A magnetic separator (03), with self-cleaning belt, is installed over the lifting conveyor taking the material from the scalper to the jaw crusher (04), the first size-reduction equipment of the line.
A secondary magnet processes (05) the material treated by the jaw crusher (04) which, by means of a slewing conveyor, is transported to the primary screen (06). By reversing the direction of this conveyor, it is possible to complete the treatment without additional processing, when the market requires a coarse aggregate to be used as unbound material for road construction.
The primary screen, which is a two-deck type, generates three different fractions:
- A coarse fraction, which is processed further by a hammer mill (08) and recycled back to the primary screen (06) inlet; another two magnetic separators (07), with self-cleaning belt, are installed at hammer mill inlet and outlet.
- A mid-size product.
- A fine fraction, which is sent to the secondary screen.
The secondary screen, also two-deck type, generates three different products:
- A coarse product.
- A mid-size product .
- A fine product.
A second wheel loader is used to load a truck, which conveys the products to their storage bunkers.
Thanks to the deferrisation made by the magnetic separators the system can recover up to a 3%-5% of steel that will be returned to the melt process..
DeferrisationRecovering the steel attached to the slag
CrushingReducing the slag to different sizes
ScreeningClassifying the aggregate according to the size
The experience and the valuable know-how of Danieli in the design, construction and startup of slag processing plants is the best guarantee of a safe investment in an Ecogravel project.View the embedded image gallery online at:
Each project is based on:
- Tailor-made design for the specific needs of the customer and for the standards for construction products existing in the place of production
- Large experience in process plant engineering
- Unique knowledge of raw material
- World-wide logistic network
- On-site technicians
- Low maintenance rate
- Reliability of components
- High-strength of the mechanical parts
- Supply of plants with the necessary support for the customization, adjustment and set-up
- Supporting and training the customer’s personnel
- Assistance in the distribution and use of the product on markets
Due to its high resistance to crushing and polishing, Ecogravel is an ideal product for the wearing course of road pavements, as performed tests confirmed.
Its special shape and high porosity ensures an excellent affinity to bituminous binders. These characteristics derive from the starting material's properties and its treatment during the cooling and crushing cycles.
The use of industrial aggregates for the wearing courses of pavements ensures high surface friction performances over time. Remarkable physical-mechanical properties and texture of the product surface, allow obtaining surface friction coefficients for the bituminous conglomerate higher than most of those achievable through the use of natural aggregates.View the embedded image gallery online at:
In addition to the well-known applications in the sector of bituminous conglomerates, Danieli has explored new uses for the industrial aggregates obtained from EAF slag, as cement mixes.
Cooperation with research centers and laboratories made possible to increase strength and durability properties of the cement and concrete by replacing natural aggregates by Ecogravel. The results have been tested and validated through a partnership with a world player of the cement and concrete sector. Through this proven method, Danieli can provide support for the introduction and optimization of cement mixes containing Ecogravel aggregate.View the embedded image gallery online at:
Besides its use as aggregate in bituminous conglomerates and cement mixes, Danieli is implementing a research and testing program aimed at finding new applications for EAF slag, such as:
- Subgrade preparation for new roads and yards.
- Additive for bituminous conglomerates.
- Additive for concrete.
- Additive for conglomerate bound with hydraulic binders.
- Improved durability and resistance of concrete exposed to chemical or physical attacks.