Have cements changed? Dave Suchorski P.E., FACI - Senior Technical Services Manager - Ash Grove Cement Co.

Cement is one of the world's most popular building materials and has been used for over 2,000 years. Structures such as the Roman Coliseum were constructed using a form of cement. Some are still standing today. Cements changed very little until 1824 when an Englishman, Joseph Aspdin, received a patent for his new method of proportioning and blending raw material based upon chemistry. He named his product Portland cement because mortar made with his product had a color similar to a natural building stone that was quarried from the Isle of Portland off the coast of England. Improvements by Aspdin and others have led to the cement we are currently using. Portland cement has not changed significantly in the last 100 years.

In 2004, the Portland Cement Association surveyed all 123 cement plants in the U.S. and Canada (P. Tennis, J. Bhatty, 2005). This survey collected and compared cement data in three different areas: chemical and phase composition, fineness, and strength. This data was then compared to survey data from 1994 and the early 1950's. These surveys proved there have been very few chemical changes. While cement is still made up primarily of calcium, silica, alumina and iron, there has been a slight change in the phase composition. Tri-calcium silicate (C3S), the compound primarily responsible for early strengths, has increased, while dicalcium silicate (C2S), the compound responsible for later age strength, has decreased.

These phase composition changes, as well as an increase in fineness (Blaine) result in modern cements that have higher early strengths. There has been a demand in construction to increase early strengths to speed up construction processes, allowing wall forms to be stripped earlier and pavements and slabs to be opened to traffic sooner. Although cube compressive strengths between the cements from the 1950's and the 1990's are not directly comparable due to a change in the water content used to make the strength samples, the table shows an approximation of the strengths and how they have gone up since the 1950's. (See table, right.)

Blended Cements

One of the bigger changes in the cement industry is the increase in the amount and types of blended cements being manufactured. Blended cements combine Portland cement with Supplemental Cementitious Materials (SCMs) and other minerals to produce cements with specific enhanced properties. SCMs are materials such as fly ash, ground granulated blast furnace slag, silica fume, calcined clay and volcanic ash. These materials are either blended with ground cement or interground with cement clinker at the finish mills in tightly controlled proportions. The SCMs chemically combine with the hydration products of the Portland cement to reduce the permeability of concrete and increase concrete durability.

Blended cements can be formulated to mitigate Alkali Silica Reaction (ASR) in concrete containing reactive aggregates. Blended cements can also be formulated to increase sulfate resistance in concrete exposed to high sulfate soils and water. Certain blended cements can be used to lower the heat of hydration in mass concrete, such as dams and large foundations.


Cement finish mill

Inside cement kiln end

Blended cements can also have gypsum contents optimized for the blend of the cement and SCMs. Gypsum is used to control the setting of cement to prevent false and flash sets in concrete. The gypsum does this by controlling the alumina portion of cements. Some SCMs also have alumina compounds that can compete with the alumina compounds in the Portland cement for the gypsum. This can lead to rapid slump loss and setting problems in concrete. Blended cements can have increased gypsum to optimize the SCMs.

Blended cements are manufactured to comply with ASTM C 595, Standard Specification for Blended Cements. The blended cements are designated as Type IP(X) for pozzolan blended cements containing fly ash, or natural pozzolan SCMs, such as calcined clay or volcanic ash or Type IS(X) slag blended cements, where (X) is the percent of SCM in the blend. For example, Type IS(25) is a blended cement with 25% slag.

In recent years, another type of blended cement has been gaining popularity in North America, Type IL. This is a Portland cement type that contains interground limestone. Cements blended with up to 35% ground limestone have been used for many years in other parts of the world and are often the predominate cement used. By intergrinding limestone, the clinker content of the cement can be lowered. Lowering the clinker content helps to reduce the CO2 emissions per ton of cement and thereby per cubic yard of concrete.

Concrete is a Green building material.

Durable concrete has a long service life that expends very little energy, giving it a long, sustainable life cycle. Reducing the CO2 emissions during manufacturing helps concrete be an even more sustainable building material. Research has shown that controlling the fineness and the particle size distribution during intergrinding results in a cement that produces similar properties as concrete made with other types of cements.

The cement industry faces increasing regulatory issues and is constantly striving to reduce energy consumption. As the industry responds to these challenges, changes in the manufacturing process may result in slight changes in the cements produced. The cement industry will be working with the chemical and admix industry, concrete producers, researchers and specifiers to provide cements that will produce durable and sustainable concrete that can last for centuries.

REFERENCES:

For more information on cements go to The Portland Cement Association website: http://www.cement.org.
Bhatty, J.I., Tennis, P.D., “Portland Cement Characteristics-2004,” Concrete Technology Today, Vol. 26, No. 3, CT053, Portland Cement Association, Skokie, Illinois, December, 2005, pages 1-3.
http://www.cement.org/tech/pdfs/CT053_cement.pdf
Tennis, P. D., “Portland Cement Characteristics -1998,” Concrete
Technology Today, Vol. 2, No. 2, PL992, Portland Cement Association, Skokie, Illinois, August 1999, pages 1–4.
www.cement.org/tech/pdfs/pl992.pdf
“Portland Cement: Past and Present Characteristics,” Concrete Technology Today, Vol. 17, No. 2, PL962, Portland Cement Association, Skokie, Illinois, July 1996, pages 1–3.
http://www.cement.org/pdf_files/pl962.pdf

Dave Suchorski
Senior Technical Services Manger/Sales Manager: Ash Grove Cement Co.

About the Author:

Dave is a graduate of the University of Wisconsin and a registered professional engineer in Kansas and Wisconsin. Dave has over 30 years experience in the cement and concrete industry.

He is a Fellow of the American Concrete Institute, a member of the Board of Directors and serves as the chairman of the Curing Concrete Committee. Dave is also a member of the Parking Lot, Pervious Concrete and Hydraulic Cements Certification Program and Chapter Activities Committees.

Contact:

Dave Suchorski, Ash Grove Cement Co.
307 SW Springfield Dr. | Ankeny, IA 50023
913-205-8146 | e-mail: dave.suchorski@ashgrove.com


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