Clinker

Limestone

Gypsum

Blended Cements:

One of the significant challenges facing the cement industry is how to find ways to reduce the mining of both our primary raw material (limestone) and secondary components such as oxides of silica, alumina and iron. All are core ingredients in the  manufacturing of cement but represent an ongoing use of what are essentially finite resources in South Africa.

A part-solution to this problem lies in the degree to which we embrace the manufacture of blended cements or cements that have reduced clinker content through the use of suitable extenders.  Such extenders and fillers include classified fly ash, granulated blast furnace slag (Slagment) and silica fume. These by-products are generated from other industries and are suitable for use as mineral substitutes in the cement manufacturing process. For example, in order to produce Ordinary Portland Cement (OPC) small quantities of gypsum have to be blended with the clinker.

For many years this gypsum has been supplied from mines scattered throughout the country. However, the availability of synthetic gypsum (a by-product of the fertilizer and sulphuric acid industries) has enabled cement producers to reduce both the demand for mined (natural) gypsum whilst also reducing the volumes of synthetic gypsum disposed at landfill sites or dumps. This has also meant a reduction in the release of H2SO4 waste streams via marine outfall pipes.

It is noteworthy that through our ongoing efforts, the blending of these cement extenders with OPC has reduced the clinker portion by 40% in certain cement products. Extended cements offer considerable benefits including improved cement workability, durability and enhanced density in concrete products, whilst simultaneously causing a reduction in mining activity directly related to cement manufacture.