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Figure 17. (a) The 63rd Street Beach House was constructed on the shoreline of Chicago in 1919. The highly exposed aggregate concrete of the
exterior walls of the beach house was used for many buildings in the Chicago parks as an alternative to more expensive stone construction. Photo:
Leslie Schwartz Photography. (b) Concrete deterioration included cracking, spalling, and delamination caused by corrosion of embedded reinforcing
steel and concrete damage due to cyclic freezing and thawing. (c) Various sizes and types of aggregates were reviewed for matching to the original
concrete materials. (d) Mock-ups of the concrete repair mix were prepared for comparison to the original concrete. Considerations included aggregate
type and size, cement color, proportions, aggregate exposure, and surface finish. (e) The craftsman finished the surface to replicate the original
appearance in a mock-up on the structure. Here, he used a nylon bristle brush to remove loose paste and expose the aggregate, creating a variable
surface to match the adjacent original concrete.

Where used for crack repairs on historic facades, the construction did not provide for long-term durability,
finished appearance of the sealant application must or to facilitate a change in use of the structure.
be considered, as it may be visually intrusive. In some Examples include increasing concrete cover to protect
cases, sand can be broadcast onto the surface of the reinforcing steel and reducing water infiltration into the
sealant to help conceal the repair. structure by repair of joints. Any such improvements
must be thoroughly evaluated for compatibility with
Urethane and polyurethane sealants are often used to
the original design and appearance. Care is required in
seal joints and cracks in concrete structures, paving,
all aspects of historic concrete repair, including surface
and walkways; these sealants provide a service life of
preparation; installation of form work; development
up to ten years. High-performance silicone sealants
of the concrete mix design; and concrete placement,
also are often used with concrete, as they provide a
consolidation, and curing.
range of movement capabilities and a service life of
twenty years or more. Some silicone sealants may stain
An appropriate repair program addresses existing
adjacent materials, which may be a problem with more
distress and reduces the rate of future deterioration,
porous concrete, and may also tend to accumulate
which in many cases involves moisture-related issues.
dust and dirt. The effectiveness of sealants for sealing
The repair program should incorporate materials and
joints and cracks depends on numerous factors
methods that are sympathetic to the existing materials
including proper surface preparation and application.
in character and appearance, and which provide good
Sealants should be examined as part of routine
long-term performance. In addition, repair materials
maintenance inspections, as these materials deteriorate
should age and weather similarly to the original
faster than their substrates and must be replaced
materials. In order to best achieve these goals, concrete
periodically as a part of cyclical maintenance.
repair projects should be divided into three phases:
Repair of historic concrete may be required to development of trial repair procedures, trial repairs and
address deterioration because the original design and evaluation, and production repair work.
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