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Environmental Protection in Cement Manufacturing
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Although the two words “cement” and “concrete” are used interchangeably in common parlance, portland cement is actually one of the ingredients in concrete. Cement is a fine gray powder and constitutes only 7 to 15% by weight of concrete’s total mass.

Cement is the most energy intensive but smallest constituent of concrete. Aggregates are most commonly sand and gravel, which require little processing and are locally available in most areas of the world. In the US, crushed stone is used as about 25% of the aggregate, and natural sand and gravel the remaining 75%. Click here for a brief history of portland cement.

Manufacturing Cement
Portland cement manufacturing is a four-step process:

stewardship concrete
Concrete components: water, cement, fine aggregate (sand), and coarse aggregate (gravel or crushed stone) (PCA No. 12235)

1. Virgin raw materials, including limestone and small amounts of sand and clay, come from a quarry usually located near the cement manufacturing plant.

2. The materials are carefully analyzed, combined and blended, and then ground for further processing.

3. The materials are heated in a large rotating kiln, which reaches temperatures of 3,400°F. The heat causes the materials to turn into a new marble-sized substance called clinker.

4. Red-hot clinker is cooled and ground with a small amount of gypsum. The end-result is a fine gray-colored powder called portland cement. This cement is so fine that one pound of cement powder contains 150 billion grains.

The constituents of cement are so common that a wide variety of raw materials are suitable. Cement is made with everything from sea shells and shale to industrial by-products such as blast-furnace slag from steel plants and fly ash from the electric power industry.

cement kiln
Cement Kiln (PCA No. 12307)

Energy and Fuel

The high temperature needed for cement manufacturing makes it an energy-intensive process. The average energy input required to make one ton of cement is 4.7 million Btu, the equivalent of about 345 pounds of coal, and it continues to improve every year. The U.S. cement industry uses energy equivalent to about 16 million tons of coal every year. According to the Department of Energy, U.S. cement production accounts for 0.33% of energy consumption—lower production levels than steel production at 1.8% and wood production at 0.5%. The cement industry has improved energy efficiency by over 33% since 1972.

Finding ways to reduce both energy needs and reliance on fossil fuels is a top priority for cement companies. Although coal, petroleum coke, and other fossil fuels have been traditionally burned in cement kilns, many cement companies have turned to energy-rich alternative fuels. Today, many plants meet 20 to 70% of their energy requirements with alternative fuels. Many of these alternative fuels are consumer wastes or byproducts from other industries and include scrap tires, used waste oil, solvents, and unrecyclable plastics. Recovering their energy value in cement manufacturing is a safe and proven form of recycling.

The U.S. cement manufacturing industry endorses a voluntary goal to improve its energy efficiency by the year 2020, as measured by total Btu per unit of cementitious product, by 20% from a 1990 baseline.

Emissions
 
The portland cement industry was among the first to tackle the issue of climate change, and it has remained at the forefront of developing policies, improving the manufacturing process, and disseminating data to the public. Since 1975, the cement industry has reduced emissions by 33%. In 2000, the industry created a way to measure CO2 emissions, and by the year 2020, the industry plans to voluntarily reduce CO2 emissions by 10% below the 1990 baseline.

To achieve this goal, the cement industry has adopted a three-part strategy:

1. Improve the energy efficiency by upgrading plants with state-of-the-art equipment

2. Improve product formulation to reduce energy of production and minimizes the use of natural resources

3. Conduct research and develop new applications for cement and concrete that improve energy efficiency and durability

The most recent progress involves newly introduced guidelines that will allow for greater use of limestone as a raw material of cement, which will ultimately reduce CO2 by more than 2.5 million tons per year.

Solid Waste
Cement kiln dust (CKD) is created during the third stage of manufacturing when clinker is formed. Electrostatic and bag filters capture the dust for recycling. The industry recycles more than 75% of cement kiln dust—nearly eight million tons each year—directly back into the cement kiln as raw material. Recycling this byproduct also reduces the need for limestone and other raw materials and helps conserve energy. Other uses for CKD include agricultural soil benefaction and soil stabilization.
Ranger Lake
Ranger Lake converted from a cement plant quarry in Omrod, PA, and now used for recreational purposes. (PCA No. 20369)


Quarries and Land Use
Extracting any raw material takes a toll on the environment. But, the land use requirements for cement and concrete are relatively low compared to other building materials. Cement companies are taking measures to minimize the disruption even further.

Limestone usually comes from a quarry at or near the plant while other materials such as clay, shale, iron ore, and sand are usually obtained from other nearby sources. Because these raw materials are among the most common on Earth, cement producers can mitigate environmental impact through careful site selection and operating procedures. At the end of their useful life, cement quarries can be reclaimed as parks, recreational areas, or other developments.
BOOKMARK
Resources
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Located at BookstoreInnovations in Portland Cement Manufacturing (2004)
Edited by J. I. Bhatty, F. M. Miller, and S. H. Kosmatka. Portland Cement Association. Item Code: CD400
Available for $250. This work contains 45 chapters of state-of-the-art information on cement manufacturing authored by internationally renowned experts in the industry. This self-loading CD is in a fully searchable format. Also available in print (SP400).
Download DocumentCoal Combustion Product Partnership Fact Sheet
2 page fact sheet
C2P2 is part of EPA’s Resource Conservation Challenge
Download DocumentPlans for Future Generations: Cement Manufacturing Sustainability Report (2004)
Portland Cement Association, 6 pgs
Free to download. Launched in June 2004, the Cement Manufacturing Sustainability Program, including a voluntary code of manufacturing practices, builds upon the environmental progress the cement industry has made during the past 30 years by identifying new methods to better manage waste, conserve resources, improve energy efficiency, and make cement in an increasingly environmentally sound manner.
Download DocumentSustainable Manufacturing Fact Sheet: Iron and Steel By-Products (2005)
Portland Cement Association, #IS326, 4 pages
Available for free. Color brochure describes the utilization of steel making by-products in the cement manufacturing process, saving virgin materials and reducing waste.
Download DocumentSustainable Manufacturing Fact Sheet: Power Plant By-Products (2005)
Portland Cement Association, #IS331, 4 pages
Available for free. Color brochure describes the utilization of power plant by-products in the cement manufacturing process, saving virgin materials and reducing waste.
Download DocumentSustainable Manufacturing Fact Sheet: Tire Derived Fuel (2005)
Portland Cement Association. Item Code: IS325
Available for free. By utilizing a cement kiln's controlled combustion environment, scrap tires can be an environmentally-sound source of energy in the manufacture of cement. This fact sheet shows how the popularity of tire-derived fuel has increased over the past two decades and summarizes its environmental benefits.
Download DocumentThe Cement Sustainability Initiative Progress Report (2005)
World Business Council for Sustainable Development, 40 pgs
This Agenda for Action has been developed following a three-year program of scoping, research and stakeholder consultation looking at what sustainable development means for the future of the cement industry. It sets out a program of work for the next five years focusing on six main work areas that are detailed below. In each area there are two kinds of actions: joint projects, on which a group of companies will work together to tackle a specific environmental or social issue; and individual actions, which will be implemented by each company in its own operations, applying both innovation and best practice.
Located at External Web Site2009 Report on Sustainable Manufacturing (2009)
Portland Cement Association
Located at External Web SiteBeneficial Uses of Cement Kiln Dust
IEEE-IAS Cement Industry Committee Wayne S. Adaska, P.E., Director, Public Works, Portland Cement Association Donald H. Taubert, Director, Promotion & Technical Service, Capitol Cement
Located at External Web SiteBuilding Even Better Concrete (2007)
Originally printed in the December 2007 of Architectural Record, this article by Joann Gonchar, AIA of McGraw-Hill looks at the current trends in cement and concrete construction that improve performance and reduce environmental impact. One hour of AIA Continuing Education Credit is available on-line through McGraw-Hill by reading the article and completing a brief test. http://construction.com/CE/articles/0712edit-1.asp#
Located at External Web SiteCement Sustainability Initiative
World Business Council on Sustainability
Located at External Web SiteCO2 uptake during the concrete life cycle (2006)
Mette Glavind, Danish Technological Institute
The objectives of the project ”CO2 uptake during the concrete life cycle” is to provide documentation of concrete carbonation, i.e. CO2 uptake. The purpose of this documentation is twofold. Firstly, it is to be used for environmental assessments of specific concrete buildings and structures. Secondly, it is the intention to evaluate the effect of concrete carbonation on the overall CO2 emissions from cement and concrete production in the Nordic countries.
Located at External Web SiteConcrete as a Carbon Sink
Liv Haselbach, Associate Professor Civil and Environmental Engineering Washington State University
Located at External Web SiteConcrete's Contrubition to Sustainable Development
Concrete is the most widely used building material on earth. It has a 2, 000 year track record ofhelping build the Roman Empire to building today's modern societies. As a result ofits versatility, beauty, strength,·and durability, concrete is used in most types ofconstruction, including homes, buildings, roads, bridges, airports, subways, and water resource structures. And with today's heightened awareness and demandfor sustainable construction, concrete performs well when compared to other building materials. Concrete is a sustainable building material due to its many eco{riendly features. The production ofconcrete is resource efficient and the ingredients require little processing. Most materials for concrete are acquired and manufactured locally which minimizes transportation energy. Concrete building systems combine insulation with high thermal mass and low air infiltration to make homes and buildings more energy efficient. Concrete has a long service life for buildings and transportation infrastructure, thereby increasing the period between reconstruction, repair, and maintenance and the associated environmental impact. Concrete, when used as pavement or exterior cladding, helps minimize the urban heat island effect, thus reducing the energy required to heat and cool our homes and buildings. Concrete incorporates recycled industrial byproducts such as fly ash, slag, and silica fume that helps reduce embodied energy, carbon footprint, and waste.