Concrete’s Environmental Hazards
Concrete is formed by mixing hydraulic cement, water, and aggregate materials (sand, gravel, or crushed stone). It is the most common construction material used in the world. Cement is the principal ingredient in concrete, making up approximately 40% by volume of concrete, as estimated by the EPA in the Profile of the Stone, Clay, Glass and Concrete Industry. Portland cement is at the heart of concrete’s environmental problems. In the cement industry, natural resources are a core part of the final product. Included in this are alumina, silica, limestone, clay, and iron oxides. Producing one ton of cement results in the discharge of approximately one ton of CO2, created by fuel combustion and calcinations of raw materials. The EPA also stated that pollution outputs from cement manufacturing plants include process waste, primarily cement kiln dust; air emissions; waste water; plant maintenance waste, and research laboratory waste. They also noted that the largest emission source within the cement plant is the kiln operation, which generates nitrogen oxides, sulfur dioxides, carbon monoxide, and hydrocarbons. The cement manufacturing process also generates a great amount of wastewater from the cooling of process equipment. Although the cement industry has reduced CO2 emissions through improvements in process and efficiency, these improvements are limited because CO2 production is intrinsic to the simple process of calcinating limestone.
The EPA also found that the concrete and cement industries reported high volumes of solvent releases. Trichloroethylene and 1,1,1-triochloroethane together accounted for more than a third of total releases from concrete industry. Also, concrete batching generates particulate emissions, paint wastes, and plant maintenance wastes. Particulate emissions which occur in concrete batching consist primarily of cement dust, but some sand and gravel dust emissions also occur.
The problem with concrete is the industrial extraction of the materials, the mixing, and the application of concrete that is ceases to be environmentally friendly. And besides the three primary components, that is, cement, aggregates, and water, numerous chemical and mineral admixtures are incorporated into concrete mixtures. They too represent huge inputs of energy and materials into the final product. What about batching, mixing, transport, placement, consolidation, and finishing of concrete? All these operations are extremely energy-intensive. The problem also stems from volume; approximately 2.35 billion tons of concrete are produced each year according to the UNEP Yearbook.