A small number of processed by-products – for example, fly ash from power generation and slag from steel manufacturing – can substitute cement to some degree. These useful by-products are known as ‘supplementary cementitious materials’.
Properly prepared fly ash and blast furnace slag have properties that allow them to behave like cement in combination with ordinary Portland cement and water. Blast-furnace slag is a non-metallic by-product derived from the production of iron in a blast furnace. Fly ash, a by-product of black-coal fired power stations, also provides a quality cementitious material suitable for use in combination with cement.
By using these materials to reduce the clinker content of cement, the thermal energy requirements of a cement plant can be reduced. An even greater benefit is the significant reduction in carbon emissions – for every tonne of fly ash or blast-furnace slag used in cement, there is an equivalent reduction of about 770 kg of carbon dioxide.
Cement Australia recycles well over a million tonnes of fly ash and blast-furnace slag each year, resulting in:
- a net greenhouse gas reduction of approximately 770,000 tonnes of CO2
- a reduction in the use of limestone raw materials of about 1.52 million tonnes
- a 120,000 tonne reduction in the use of coal.
This is a great example of how a sustainable business should operate. Through the use of alternative fuels and raw materials, we are reducing our own environmental impact and providing a significant benefit to society through the reduction of waste destined for landfill and dramatically reducing the carbon intensity of our product – all the while adding to the company’s bottom line.
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