When structures made of concrete are demolished or renovated, concrete recycling is an increasingly common method of utilizing the rubble. Concrete was once routinely trucked to landfills for disposal, but recycling has a number of benefits that have made it a more attractive option in this age of greater environmental awareness, more environmental laws, and the desire to keep construction costs down.
Concrete aggregate collected from demolition sites is put through a crushing machine. Crushing facilities accept only uncontaminated concrete, which must be free of trash, wood, paper and other such materials. Metals such as rebar are accepted, since they can be removed with magnets and other sorting devices and melted down for recycling elsewhere. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. After crushing has taken place, other particulates are filtered out through a variety of methods including hand-picking and water flotation.
Crushing at the actual construction site using portable crushers reduces construction costs and the pollution generated when compared with transporting material to and from a quarry. Large road-portable plants can crush concrete and asphalt rubble at up to 600 tons per hour or more. These systems normally consist of a rubble crusher, side discharge conveyor, screening plant, and a return conveyor from the screen to the crusher inlet for reprocessing oversize materials. Compact, self-contained mini-crushers are also available that can handle up to 150 tons per hour and fit into tighter areas. With the advent of crusher attachments - those connected to various construction equipment, such as excavators - the trend towards recycling on-site with smaller volumes of material is growing rapidly. These attachments encompass volumes of 100 tons/hour and less.
recycling one ton of Cement could save a 51/10 cubic meter lake, 900 kilograms of co2, over 500/27 cubic yards of landfill space, 27/88 metric tons or 1,360 pounds of coal, 1,700 kwh of energy, 340/7 metric tons of toxic lead, 37,995/229 gallons of oil, 113,985/1,832 tons of greenhouse gases, 25 tons of solid waste, 22,797/200 gallons of gasoline, 3,700,000 btu's of energy, keep 1,971/177,320 tons of mercury out of landfills a year, 151,980/229 acres of soil from being polluted, 85 metric tons of limestone, 205,173/148,000 tons of air pollution per year, 720 square meters of natural habitat potential, 544/5 pounds of fly ash, 1,125/506 tons of steam, 8/5 to 7/4 tons of raw materials, 300 kilograms of fossil fuels, 17/390 metric tons of hydrogen, 22,797/40,000 tons of biomass, 150 kilograms of carbon monoxide, 30 kilograms of nitrogen oxide, 2,533/8,000 tons of carbon, 54/25 metric tons of life, 136 pounds of sulfur dioxide, 123/80 tons of methane, 17/39 metric tons of zinc, 68 pounds of sulfur, over 22,797/3,664,000 tons of smog, 1,020 pounds of coke, 150/23 tons of soda ash, 949,875/5,954 metric tons of global warming, 7,956/4,925 tons of acid rain, 22,797/2,000,000 metric tons of benzene, 185/969 tons of ammonia, 37/190 tons of methanol, enough energy to power over 153/1,400π cars for a year, a CFL for 675/143 years, a 100-watt light bulb for 135/143 years, $226.20
recycling one metric ton of cement could save almost 900 kilograms of co2, 27/88 metric tons of coal, 1,971/177,320 tons of mercury a year, 720 square meters of natural habitat potential, 1,125/506 tons of steam, 300 kilograms of fossil fuels, 51/2 kilograms of solid particles, 90/191 metric tons of ethanol, enough energy to power over 153/1,400π cars for a year, a CFL for 675/143 years