Concrete’s impact on the environment starts when limestone is blasted in quarries to make cement – the binder, or substance that sets and hardens it into a useful building material. Cement accounts for 7 to 15% of concrete’s total mass by weight and is made by superheating (in coal-fired kilns) a mixture of limestone and clay and then grinding the resulting substance into a powder. When this power mixes with water, it forms strong calcium-silicate-hydrate bonds that can bind other particulates, like sand or gravel, to make concrete. The cement-to-water ratio determines the strength of the concrete.
Once limestone has been blasted and mined it is then transported to a cement plant, where the fuels used by the plant and machinery produce CO2 emissions. Next the limestone, or calcium carbonate, releases CO2 when it is heated to make the cement. Forty percent of CO2 emissions from the cement plant come from the combustion process and Sixty Percent of CO2 emissions come from the calcination process, according to the Cement Sustainability Initiative report produced by members of the concrete industry. The report also says that since calcination is intrinsic to the process, they must focus on reducing energy use associated with the manufacture of concrete.
Concrete producers also say that as concrete ages, it carbonates and reabsorbs all the CO2 released during calcination – but this process takes hundreds of years.The general consensus is that cement manufacturing produces about 5% of global CO2 emissions generated by human activity, and 3% of global emissions of all greenhouse gases. By comparison the transport sector is responsible for about 15% of global greenhouse gas emissions, so concrete has a pretty hefty share of the pie considering it’s just one material.
– from inhabitat. 5 Feb 2009
Better solution is reduce use. Try to live in small house.
Houses have only less than 30 years of life. You kids will not like the big house you built. They interests will be different according to their time. So build a small efficient house for the needs.