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Concrete Characteristics
             Historic Interiors
                                                                           Concrete is composed of fine (sand) and
             The expanded use of concrete provided new opportunities to    coarse (crushed stone or gravel) aggregates
             create dramatic spaces and ornate architectural detail on the   and paste made of portland cement and water.
             interiors of buildings, at a significant cost savings over traditional   The predominant material in terms of bulk is
             construction practices. The architectural design of the Berkeley   the aggregate. Portland cement is the binder
             City Club in Berkeley, California, expressed Moorish and Gothic   most commonly used in modern concrete. It
             elements in concrete on the interior of the building (Fig. 10). Used   is commercially manufactured by blending
             as a woman's social club, the building was designed by noted   limestone or chalk with clays that contain
             California architect Julia Morgan and constructed in 1929.  The   alumina, silica, lime, iron oxide and magnesia,
             vaulted ceilings, columns, and ornamental capitals of the lobby   and heating the compounds together to high
             and the ornamental arches and beamed ceiling of the "plunge" are   temperatures. The hydration process that
             all constructed of concrete.                                  occurs between the portland cement and water
                                                                           results in formation of an alkali paste that
                                                                           surrounds and binds the aggregate together as
                                                                           a solid mass.

                                                                           The quality of the concrete is dependent on
                                                                           the ratio of water to the binder; binder content;
                                                                           sound, durable, and well-graded aggregates;
                                                                           compaction during placement; and proper
                                                                           curing. The amount of water used in the mix
                                                                           affects the concrete permeability and strength.
                                                                           The use of excess water beyond that required
                                                                           in the hydration process results in more
                                                                           permeable concrete, which is more susceptible
                                                                           to weathering and deterioration. Admixtures
             Figure 10. The Berkeley City Club has significant interior spaces alld features of
                                                                           are commonly added to concrete to adjust
             concrete construction, including the lobby and pool.  Photos: Una Gilmartin (left)
                                                                           concrete properties such as setting or hardening
             and Brian Kehoe (right), Wiss, Janney,  Elstner Associates, Illc.
                                                                           time, requirements for water, workability, and
                                                                           other characteristics. For example, the advent
             The historic character of a building's interior can also be conveyed
                                                                           of air entraining agents in the 1930s provided
             in a more utilitarian manner in terms of concrete features and
                                                                           enhanced durability for concrete.
             finishes (Fig. 11). The exposed concrete structure-columns,
             capitals, and drop panels-is an integral part of the character   During the twentieth century, there was
             of this old commercial building in Minneapolis. In concrete   a steady rise in the strength of ordinary
             warehouse and factory buildings of the early twentieth century,   concrete as chemical processes became better
             exposed concrete columns and formboard finish concrete slab   understood and quality control measures
             ceilings are common features as seen in this warehouse, now   improved. In addition, the need to protect
             converted for use as a parking garage and shops.              embedded reinforcement against corrosion
                                                                           was acknowledged. Requirements for concrete
                                                                           cover over reinforcing steel, increased cement
                                                                           content, decreased water-cement ratio, and air
                                                                           entrainment all contributed to greater concrete
                                                                           strength and improved durability.

                                                                           Mechanisms and Modes of
                                                                           Deterioration


                                                                           Causes of Deterioration

                                                                           Concrete deterioration occurs primarily because
                                                                           of corrosion of the embedded steel, degradation
                                                                           of the concrete itself, use of improper techniques
             Figure 11.  Whether in a circa 1925 office (left) or in a parking garage   or materials in construction, or structural
             and retail facility (right), exposed concrete structures help characterize   problems. The causes of concrete deterioration
             these building interiors.  Photo: Minnesota Historical Society (left).   must be understood in order to select an
                                                                           appropriate repair and protection system.

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