Considerable reductions in energy use (and therefore CO2 emissions) in New Zealand have been realised by improving the efficiency of the cement kiln operation, a significant energy user.
Golden Bay Cement’s Portland cement plant near Whangarei is operating at world’s best practice for emissions management (Case Study 1). Further energy efficiencies and emissions control in cement manufacture are ongoing, as demonstrated by Holcim New Zealand’s use of used oil as an alternative fuel in kiln operation (Case Study 2).
The increasing use of supplementary cementitious materials (SCMs) to replace cement and therefore directly reduce embodied CO2 makes sound ecological sense. SCMs are derived from lower embodied energy, industrial by-products or waste materials, and can result in environmental benefits, improved concrete performance, and long-term cost advantages.
As the global cement industry seeks to reduce CO2 emissions per unit product produced, there has been a steady growth in the use of blended Portland cements containing SCMs. The most commonly used SCMs are amorphous silica, selected limestone, ground granulated blast furnace slag (waste from steel manufacture) and fly ash (waste from coal combustion).