OKTO® construction products – aggregates manufactured from the industrial side stream

In addition to natural stone aggregates, we supply quality industrial aggregates, the OKTO® construction products. Made from ferrochrome slag from Outokumpu PLC’s factory in Tornio, the OKTO products are extremely suitable for use in sub-base and base layers. The special properties of the products include good insulation and load bearing capacity. The products are also suitable for demanding conditions.

The OKTO products used for construction include OKTO insulation material and OKTO aggregates. The Croval aggregate is primarily used by the fireplace industry. The products are environmentally safe recycled materials, and the use of them also helps save exhaustible, natural materials. The OKTO products are CE-certified construction products under the Product Liability Act. Use of the products is not subject to environmental permits or a notification pursuant to the Government Decree on the Recovery of Certain Wastes in Earth Construction.

In addition to Finland, we also supply OKTO construction products to Sweden and Estonia. In Finland, the products have been used, for example, as pavement aggregate in Oulu, Kemi-Tornio and Rovaniemi as well as in road and street structures.

OKTO insulation

The thermal insulating capacity, bearing capacity and frost resistance of OKTO insulation allows for thinner street and road structures. This makes construction faster and easier. OKTO insulation is lighter than natural stone materials, with roughly three times the insulating capacity of natural sand. OKTO insulation has been manufactured and used since 1969 in smaller and larger capacities, for example, for road, street and building construction.

The manufacturing method of OKTO insulation is granulation. In granulation, molten ferrochromium slag is run from the melting furnace through ladles straight into pressurised water jet, which granulates the molten slag into a product with a fraction of 0–11 mm. The product is wet sieved, which means that the percentage of fines is very low – in practice, the material gives off hardly any dust, which means that there is no need for dust removal.


  • Road and street structures
  • Yard and foundation structures
  • Landfill structures
  • Sub-base and base layers
  • Foundation wall side fillings
  • Piping, cabling and underdrain fillings
  • Capillary breaks

Benefits of OKTO insulation in construction use

  • Good frost resistance and bearing capacity, enabling thinner structures and a smaller amount of materials and cutting mass
  • Faster and easier construction with a reduced excavation depth
  • Easier work-time drying of the excavation
  • Low capillary rise of water – suitable for drainage layers
  • Does not harden in the structure, can be reused
  • Suitable for a filling material around subsurface structures

OKTO aggregate

OKTO aggregates are robust, load bearing and insulating industrially manufactured aggregates. Thanks to their good water permeability, OKTO aggregates are used as capillary breaks and drainage layers.

The manufacturing method of OKTO insulation is air cooling. The air-cooled material is crushed and wet sieved. OKTO aggregates do not contain fines or give off dust and they have a low capillary rise of water.

The fractions of OKTO aggregates are 0/4 mm, 4/8 mm, 8/11 mm, 11/16 mm, 16/22 mm.


  • Constructing capillary breaks
  • Aggregate for concrete or heat-resistant concrete

Croval aggregate

Made for the fireplace industry, the Croval aggregate is suitable for heat-resistant structures. Thanks to its high crystallisation level, the material has an extremely strong structure. The durable and homogeneous material has a high melting point. The product has been used for over 30 years as aggregate in the manufacture of fireplaces and furnaces.

Interested? Please contact us!

Jarkko Leinonen

Sales Manager

OKTO® construction products

+358 40 663 6577