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Universal Building Material
| Article
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18056 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
5 / 1990 |
2,077 Words |
| Author
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Kenneth C. Hover
Kenneth C. Hover is associate professor of structural
engineering at Cornell University, where he teaches and
conducts research on the nature and uses of concrete. |
Concrete is the common material used to pave highways and sidewalks, build bridges and dams, and construct patios and residential basement walls. Concrete's familiarity to engineers, architects, builders, and developers, not to mention the homeowner who buys a sack at the discount store and "just adds water," hides a chemical and physical complexity that is still the focus of scientific research. Further, the association of concrete with the most significant architectural and engineering developments of the twentieth century crowns a history that dates back to Roman times. Few would have suspected that in studying the Appian Way, the Coliseum, the Pantheon, and countless Roman bridges, aqueducts, and lighthouses from Britain to the Middle East, one might find the keys to understanding the material being proposed for the construction of the first permanent settlement on the moon.
The Basis of Both Ancient and Modern Construction
While manufacturing techniques and construction methods have changed dramatically, the concrete used in the 1990s is similar in many ways to that used by the architects and builders of antiquity. Prior to Roman times, the Greeks used a masonry mortar made of lime powder and water mixed to form a paste or glue to which they added sand. (When only sand or "fine aggregate" is used, the product is termed "mortar" rather than "concrete.") The lime powder was produced by heating limestone to drive off water and carbon dioxide. After sand and water were mixed with this powder, the mixture was permitted to dry slowly. The replacement of water by carbon dioxide the re-created many of the properties of the original limestone.
However, while lime-based mortar can be an effective building material in dry climates, its use is limited in coastal or humid environments, and impractical for such underwater construction as bridge piers or harbor facilities. The Romans therefore, developed a more durable, less moisture-sensitive material by blending the lime with volcanic ash from Mount Vesuvius. This ingenious chemical bonding of the calcium-rich lie and the silica-rich ash formed the basis not only for construction all over the Roman world but also of modern construction.
The Romans combined their lime, ash, and a minimum amount of water with sands, stones, and crushed bricks to make stiff concrete that had to be rammed into place. The strength and durability of the final product is demonstrated in structure after structure that still with stands the elements after 2,000 years of service. However, the Roman
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