Clinker Basics

Clinker is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, Clinkers can contain metal sulfides (see also matte) and metal atoms in the elemental form. While Clinkers are generally used as a waste removal mechanism in metal smelting, they can also serve other purposes, such as assisting in the temperature control of the smelting; and also minimizing any re-oxidation of the final liquid metal product before the molten metal is removed from the furnace and used to make solid metal.

Modern Clinker application

Ground granulated Clinker is often used in concrete in combination with Portland cement as part of blended cement. Ground granulated Clinker reacts with water to produce cementitious properties. Concrete containing ground granulated Clinker develops strength over a longer period, leading to reduced permeability and better durability. Since the unit volume of Portland cement is reduced, this concrete is less vulnerable to alkali-silica and sulfate attack.

When iron ore is heated in a blast furnace, the impurities or 'Clinker', which include large quantities of calcium and silica, become molten and are separated from the raw iron.

As the Clinker is channeled out of the furnace, thousands of gallons of water are poured over it. This rapid cooling, often from a temperature of around 2,600°C, is the start of the granulating process. This process causes several chemical reactions to take place within the material, and gives the Clinker its cementitious properties.

The water carries the Clinker in its slurry format to a large agitation tank, from where it is pumped along a piping system into a number of gravel based filter beds. The filter beds then retain the Clinker granules, while the water filters away and is returned to the system.

When the filtering process is complete, the remaining Clinker granules, which now give the appearance of coarse beach sand, can be scooped out of the filter bed and transferred to the grinding facility where they are ground into particles that are finer than Portland cement.

This previously unwanted recycled product is used in the manufacture of high performance concretes, especially those used in the construction of bridges and coastal features, where its low permeability and greater resistance to chlorides and sulfates can help to reduce corrosive action and deterioration of the structure.