Domestic production and use
In 2009, some 70 million t of Portland cement and 2 million t of masonry cement were produced at 107 plants in 37 States in the US. Ongoing plant closures left the year-end plant count at 101. Cement was also produced at two plants in Puerto Rico. Sales volumes fell sharply, but prices fell only modestly; the overall value of sales was about US$7.3 billion. Most of the cement was used to make concrete, worth at least US$ 40 billion. About 72% of cement sales went to ready-mixed concrete producers, 13% to concrete product manufacturers, 7% to contractors (mainly road paving), 3% to building materials dealers, and 5% to other users. In descending order, Texas, California, Missouri, Pennsylvania, Alabama, and Michigan were the six leading cement-producing States and accounted for about 50% of US production.
Cement kiln dust is routinely recycled to the kilns, which also can burn a variety of waste fuels and recycled raw materials such as slags and flyash. Certain secondary materials can be incorporated in blended cements and in cement paste in concrete. Cement is not directly recycled, but there is significant recycling of concrete for use as aggregate.
Events, trends, and issues
The dominant issue in 2009 was the ongoing severe decline in construction spending and associated cement sales. The decline, which continued a trend begun in about mid-2006, was evident in all construction sectors (especially in housing), and affected all States. Unlike in 2007, where lower sales had been largely accommodated by reductions in imported cement, there was also a sharp decline in cement production in 2008 - 2009, and a rash of plant closures. By year-end 2009, 14 plants had closed, and only three new plants had opened. A number of planned expansion projects at existing plants continued to be suspended, as were plans for at least two new plants. Towards year-end 2009, a large number of plants were idled temporarily, owing to full cement silos. A return to cement sales volumes more in line with the 2005 - 2006 record years is expected to take about five years.
A number of environmental issues, especially CO2 emissions, affect the cement industry. Plant-level reporting of CO2 emissions was expected to become mandatory in 2010. CO2 reduction strategies by the cement industry largely aim at reducing emissions per t of cement product rather than by plant.
These strategies include installation of more fuel-efficient kiln technologies, partial substitution of noncarbonated sources of calcium oxide in the kiln raw materials, and partial substitution of supplementary cementitious materials (SCM), such as pozzolans, for Portland cement in the finished cement products and in concrete. Because SCM do not require the energy-intensive clinker manufacturing (kiln) phase of cement production, their use, or the use of inert additives or extenders, reduces the unit monetary and environmental costs of the cement component of concrete.
Plant-level reporting of CO2 emissions was expected to become mandatory in 2010. Recent revisions to the major portland cement standard ASTM-C150 and the similar AASHTO M85 allow for the incorporation of up to 5% ground limestone as an inert extender, but it was unclear how many plants would be able to adopt this practice. The C-150 standard was further revised in 2009 to allow for the addition of up to 5% of inorganic process additions.
Research was ongoing toward developing cements that require less energy to manufacture than Portland cement, and/or that utilise more benign raw materials.
A new emissions limitation protocol for cement plants was released in 2009 that would significantly lower the acceptable emissions levels of mercury and some other pollutants. It was unclear how many plants would be able to comply with the new limits; the mercury limits were further expected to make it difficult for cement plants to continue to burn flyash as a raw material for clinker manufacture.
Although individual plant reserves are subject to exhaustion, cement raw materials, especially limestone, are geologically widespread and abundant, and overall shortages are unlikely in the future.
Virtually all Portland cement is used either in making concrete or mortars and, as such, competes in the construction sector with concrete substitutes such as aluminum, asphalt, clay brick, rammed earth, fiberglass, glass, steel, stone, and wood. A number of materials, especially flyash and ground granulated blastfurnace slag, develop good hydraulic cementitious properties (the ability to set and harden under water) by reacting with the lime released by the hydration of Portland cement. These SCM are increasingly being used as partial substitutes for Portland cement in many concrete applications.For the full report, please visit: http://minerals.usgs.gov/minerals/pubs/mcs
Read the article online at: https://www.worldcement.com/the-americas/07022010/usgs_releases_mineral_commodity_summary_january_2010/