5th International Global Warming Conference
San Francisco, 1994
Global Warming Impact on the Cement and Aggregates Industry
by Joseph Davidovits
published in World Resource Review, Vol.6 (2), pp. 263-278 (1994)
CO2 related energy taxes are focusing essentially on fuel consumption, not on actual CO2 emission measured at the chimneys. Ordinary Portland cement, used in the aggregates industries, results from the calcination of limestone (calcium carbonate) and silica according to the reaction:
5CaCO3 + 2SiO2—> (3CaO,SiO2 )(2CaO,SiO2 ) + 5CO2
The production of 1 tonne of cement directly generates 0.55 tonnes of chemical-CO2 and requires the combustion of carbon-fuel to yield an additional 0.40 tonnes of CO 2 . To simplify: 1 T of cement = 1 T of CO2. The 1987 1 billion metric tonnes world production of cement accounted for 1 billion metric tonnes of CO2 , i.e. 5% of the 1987 world CO2 emission. A world-wide freeze of CO2 emission at the 1990 level as recommended by international institutions, is incompatible with the extremely high cement development needs of less industrialized countries. Present cement production growth ranges from 5% (China, Japan) to 16% (Korea, Thailand) and suggests that in 25 years from now, world cement CO2 emissions could equal 3,500 million tonnes. Eco-taxes when applied would have a spectacular impact on traditional Portland cement based aggregates industries. Taxation based only on fuel consumption would lead to a cement price increase of 20%, whereas taxation based on actual CO2emission would multiply cement price by 1.5 to 2. A 25-30% minor reduction of CO2 emissions may be achieved through the blending of Portland cement with replacement materials such as coal-fly ash and iron blast furnace slag.
In year 2015, assuming that world Global Climate treaties might authorize an amount of this Portland blended cement production in the order of 1850 million tonnes, the complementary need for new low-CO2 cementitious materials, in the range of 1650 million tonnes, requires the introduction of a different technology. Novel geopolymeric poly(sialate-siloxo) cements, which do not rely on the calcination of limestone (and accompanying release of CO2 ), are low-CO2 cementitious materials providing similar properties than current high-CO2 Portland cement. The technology reduces CO2 emission caused by the cement and aggregates industries by 80%. Global Warming Impact on the Cement and Aggregates Industry.
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