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       15  BRIEFS

        Preservation of Historic Concrete

        Paul Gaudette and Deborah Slaton

               National Park Service
               U.S.  Department of the Interior

        Introduction to Historic Concrete                        mixed with water, was placed between wooden forms,
                                                                 tamped, and allowed to dry in successive layers. Tabby
        Concrete is an extraordinarily versatile building material   was later used by the English settlers in the coastal
        used for utilitarian, ornamental, and monumental         southeastern United States.
        structures since ancient times. Composed of a mixture
                                                                 The early history of concrete was fragmented,
        of sand, gravel, crushed stone, or other coarse material,
                                                                 with developments in materials and construction
        bound together with lime or cement, concrete undergoes
                                                                 techniques occurring on different continents and in
        a chemical reaction and hardens when water is added.
                                                                 various countries. In the United States, concrete was
        Inserting reinforcement adds tensile strength to
                                                                 slow in achieving widespread acceptance in building
        structural concrete elements. The use of reinforcement
                                                                 construction and did not begin to gain popularity until
        contributes significantly to the range and size of
                                                                 the late nineteenth century. It was more readily accepted
        building and structure types that can be constructed
                                                                 for use in transportation and infrastructure systems.
        with concrete.
                                                                 The Erie Canal in New York  is an example of the
        While early twentieth century proponents of modern
                                                                 early use of concrete in transportation in the United
        concrete often considered it to be permanent, it is,
                                                                 States. The natural hydraulic cement used in the canal
        like all materials, subject to deterioration. This Brief
                                                                 construction was processed from a deposit of limestone
        provides an overview of the history of concrete and
        its popularization in the United States, surveys the     found in 1818 near Chittenango, southeast of Syracuse.
                                                                 The use of concrete in residential construction was
        principal causes and modes of concrete deterioration,
        and outlines approaches to repair and protection that
        are appropriate to historic concrete. In the context of this
        Brief, historic concrete is considered to be concrete used
        in construction of structures of historical, architectural,
        or engineering interest, whether those structures are old
       or relatively new.
       Brief History of Use and Manufacture

       The ancient Romans found that a mixture of lime putty
       and pozzolana, a fine volcanic ash, would harden
       under water. The resulting hydraulic cement became
       a major feature of Roman building practice, and was
       used in many buildings and engineering projects
       such as bridges and aqueducts. Concrete technology
                                                                 Figure 1.  The Sebastopol House in Seguin,  Texas,  is an 1856 Greek
       was kept alive during the Middle Ages in Spain and
                                                                 Revival-style house constructed of lime concrete. Lime concrete
       Africa. The Spanish introduced a form of concrete to      or "limecrete" was a popular construction material, as  it could be
       the New World in the first decades of the sixteenth       made inexpensively from local materials. By 1900,  the town had
       century, referred to as "tapia" or "tabby."  This material,   approximately ninety limecrete structures, twenty of which remain.
       a mixture of lime, sand, and shell or stone aggregate     Photo: Texas Parks and Wildlife Department.
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