On the sustainability of concrete

After several important technical improvements, concrete made with Portland cement is probably the world’s most used man-made material. Global cement production in 1997 was 1.57 billion tonnes (Humphreys and Mahasenan, 2002). That much cement, mixed with water, gravel and other substances, equals some 1.05 trillion tonnes of building material to produce houses, office buildings, sewage pipes, dams, concrete roads, etc. Cement production is widespread: plants are found in 150 countries (Marland et al., 2002 ), with China being responsible for roughly one-third of the total. Global cement production is increasing as consumption in developing countries rises: between 1990 and 2000, production grew 55% in developing countries and 3% in the developed ones. Cement demand in 2020 is expected to be 120-180% higher than in 1990, with most of the growth in developing countries (Humphreys and Mahasenan, 2002). The basic way to make Portland cement is to heat a mixture of limestone and clay – two largely available, natural, non-renewable materials – in a kiln at about 1500°C to produce cement “clinker”. After cooling, the clinker is finely ground and mixed with gypsum and, frequently, other finely ground materials such as fly ash and blast furnace slag to produce various commercial varieties of cement.