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Frequently Asked Questions
Cement & Concrete
Technology Home > FAQs > What is
natural cement?
Q: What is natural cement?
A: Natural cements are hydraulic cements
produced by mining natural deposits of limestone and clay with a specific
chemical composition within a narrow range. When heated in a kiln,
and ground to a fine powder, a type of cement is produced, that, like
portland cement, sets and hardens when mixed with water through chemical
reactions. Strength and uniformity of natural cements are lower than
for portland cements, but these are much more historically accurate
materials for use on many historic restoration projects, which is
their primary application. Natural cements were extensively used in
19th and early 20th century construction, and many historic structures
were built with these materials (see Table below).
However, with improved technology for producing portland cements,
sales of natural cements began to decline in the late 1800s (see
Figure below), stopping entirely by the mid-1970s.
Brief History The first national specification
for cements was issued in 1904 by the American Society for Testing
and Materials, now ASTM International. It included requirements
for both portland cement and natural cement. By 1909, specifications
for natural cement (C 10) and portland cement (C 9) had been separated
and continued to be developed to serve the construction industry.
ASTM C 9 was replaced in 1941 by C 150, but C 10 continued to be
updated and revised until 1976. In 1978, the specification was discontinued,
as natural cements were no longer being produced in the U.S.
ASTM Committee C01 began reevaluating the withdrawn standard in
2004 to meet the demand for historically accurate cement for reconstruction
purposes. A task group updated the specification to meet modern
standards formats and submitted the item for ballot through ASTM’s
consensus standards development process. In October 2006, the standard
was reissued as C 10-06. Architects and engineers working on historic
preservation projects have a new specification to refer to when
natural cement is desired.
Natural Cement Requirements
Like specifications for other cements, C 10 sets chemical and physical
requirements, although with some modifications compared to modern
standards like C 150, C 595, or C 1157. For example, insoluble residue
is limited to a minimum of 2% in C 10, compared to a maximum of
0.75% in C 150. This requirement assures that the natural cement
is not over-processed in the kiln.
Other differences in requirements include a modified C 109 mortar
composition for specimens tested for compressive strength, and a
modified composition for autoclave expansion (soundness) specimens.
These compositions follow the historic compositions traditionally
used in the specification (in 1976 and prior), allowing for easier
comparison with properties of cements used when the historic structures
were originally built.
Another unique feature of the specification is the requirement for
the purchaser and the manufacturer to agree on the fineness requirement.
This allows the fineness to be chosen to match the cement used in
the structure under renovation—an important consideration
in historic preservation.
A copy of ASTM C 10 can be obtained at ASTM
International’s Web site.
Natural cement was used in the construction of thousands
of historic architectural and engineering structures. The table
below lists a few of the better-known examples.
Historic Structures
Made with Natural Cement |
| Canals |
Capitols |
| Over 150 canal systems, including: |
• California |
| • Erie |
• Colorado |
| • Chesapeake |
• Georgia |
| • Ohio, Delaware and Hudson |
• Iowa |
| • Ohio River |
• Illinois |
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• Indiana |
| Water Systems |
• Kansas |
| • New York City |
• Massachusetts |
| • Philadelphia |
• Michigan |
| • Boston |
• Minnesota |
| • Washington, DC |
• New York |
| |
• Texas |
| Military Fortifications |
• U.S. Capitol |
| 51 Third System forts, including: |
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| • Fort Sumter, S.C. |
Museums |
| • Fort Adams, Newport, R.I. |
• Smithsonian Institution National Portrait Gallery |
| • Fort Warren, Boston Harbor |
• Smithsonian Castle |
| • Fort Hamilton, New York Harbor |
• American Museum of Natural History |
| • Fort Trumbull, New London, Conn. |
• National Building Museum |
| • Fort Washington, Md. |
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| • Fort Jefferson, Gulf of Mexico |
Other Government Buildings |
| • Fort Taylor, Key West, Fla. |
• Baltimore, Md., City Hall |
| • Fort Gaines, Mobile, Ala. |
• Richmond, Va., Old City Hall |
| • Fort Point, San Francisco, Calif. |
• Milwaukee, Wis, City Hall |
| • Fortress Alcatraz, San Francisco, Calif |
• U.S. Treasury Dept. |
| |
• Eisenhower Executive Office Building, Washington,
DC |
| Monuments |
• Buffalo, N.Y., County Building |
| • Washington Monument (lower 150 feet) |
• Fort Worth, Texas, Courthouse |
| • Statue of Liberty Pedestal |
• Dallas, Texas, Old Red Courthouse |
| • Confederate Monument, Savannah, Ga. |
• St. Louis, Mo., Old Post Office |
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• Milwaukee, Wis., Library |
| Bridges |
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| • Brooklyn Bridge |
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| • Roebling Suspension Bridge, Cincinnati, Ohio |
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| • Smithfield Street Bridge, Pittsburgh, Pa. |
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| • High Bridge, New York, N.Y. |
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| • Stone Arch Bridge, Minneapolis, Minn. |
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| • Eads Bridge, St. Louis, Mo. |
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Source: Edison, M. P., “The American Natural Cement Revival,”
Standardization News, ASTM International, West Conshohocken,
PA, Vol. 34, No. 1, pages 34 to 39, January 2006.
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| Figure 1. Decline of natural cement production and rise of
portland cement production around the turn of the 20th century
(data from R. W. Lesley; J. B. Lober, and G. S. Bartlett,
History of the Portland Cement Industry, International
Trade Press, Chicago, 1924.) |
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