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Russian company offers technology for manufacturing expanded slag gravel from metallurgical slag. The gravel is an effective aggregate for lightweight concrete and can serve as a thermal insulating fill. The technology produces high-performance expanded slag gravel from industrial wastes, namely metallurgical slags of different types such as furnace and ferroalloys. The process of manufacturing this gravel involves the following main operations: The melted slag flowing the running-out system of a blast furnace, gets into the vibrating feed plate and installation comprises a line of metallic plates and then drops onto the pore-forming apparatus (PFA). The PFA installation comprises a line of metallic plates of consequence arrangement and shifted one after another along the vertical axis, mounted on the vibrating frame. There are vertical gas nozzles in the gaps between the plates. The slag melt is partially pore-formed (foamed) under the influence of the water running out of nozzles of the first level and moves further lengthwise the PFA installation. Then the melt is treated by water running out of the nozzles of the second level, etc. A number of PFA levels is characterized by the present production capacity of the technological line (1-5 tons of processed melted slag per minute). Further on, the foamed ductile (pyroplastic) slag melt mass overflows onto the rotating blade drum and disperses by the co-impact with the blades. The pore-foamed slag melt particles are thrown out into the surrounding environment of the working enclosed zone. Here, the particles assume a shape of a granule (pellets) in the air counter-current due to surface tension strength. Then the particles get cooled upto the temperature of crystallisation and fall along the curve line onto belt conveyor of the receiving bin.

The mix of the cooled expanded slag gravel granules of different sizes is delivered to the sorting installation of for separation into 0-5, 5-10, 10-20 mm fractions. The production of the expanded slag gravel from blast furnace slag melts has already been introduced at a Russian metallurgical giant company. Some average statistical data on properties of the expanded slag gravel and concrete respectively are as follows: Bulk density for fractions of 10-20 mm equals to 550-600 kg/cu.m., 5-10 mm equals to 600-650 kg/cu.m., 0-5 mm equals to 550-600 kg/cu.m. Strength of grain is sufficient to obtain lightweight concrete with 20 MPa compressive strengths. When natural sand is used, it comes up to 40 MPa Water absorption is 6-10 % by volume; amorphised phase (glass) content is 50-70 % Coefficient of thermal conductivity in filling for fractions of 10-20 and 5-10 mm is 0.11-0.12 W/m.oC.

The expanded slag gravel with 550-650 kg/cu.m. bulk density is equivalent by thermal conductivity to expanded clay gravel with 350-450 kg/cu.m. bulk density. It is provided for by considerably water amorphized phase content and smaller averaged size of inter-grain pores. The expanded slag gravel with the above properties is extremely effective to use with lightweight concrete which is designated for application in walls and masonry units. It may also be used for producing concrete for bearing structures of buildings. In case of usage of gas pore-forming admixtures for additional foaming of melted slag, it is possible to obtain the expanded slag gravel with bulk densities not higher than 400 kg/cu.m. (coarse fraction). This variety of the expanded slag gravel will be effective for use in heat-insulating fillings for walls and roofs of houses and buildings.


Construction industry: high quality aggregate for lightweight concrete; thermal insulation fill for walls and roofs of houses and buildings. Sanitation services, sewage/waste water treatment: gravel (5-10 and 10-20 mm fraction) and sand (0-5 mm) filter for underground drainage and for sewage treatment stations.


The main advantages of the technology in contrast with the best world prototype-technology for manufacturing "pelletised slag" are the following: Environmental safety due to significantly lower water consumption, and correspondingly, 5-6 times low

Environmental Aspects

Cleaner technology,natural resource conservation,waste utilisation

Development Status


For further information please contact

Asian and Pacific Centre for Transfer of Technology
APCTT Building
C-2 Qutab Institutional Area
P.O.Box - 4575
New Delhi - 110 016
Tel : 91-11-26966509
Fax : 91-11-26856274