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Investigation of Exposed Concrete Facades

January 27, 2021

Exposed concrete façades synonymous
with the brutalist architectural
style have been featured
on buildings for over a century.
Constructed between 1906
and 1908, Frank Lloyd Wright’s
iconic Unity Temple was one of the earliest
structures to contain a poured-in-place reinforced
concrete façade.1 In the 1960s, Walter
Netsch designed several buildings on campus
for the University of Illinois at Chicago using
exposed concrete structural elements and precast
concrete window panels with intricate
details and textures.2 While concrete façades
are durable and unique in their varying textures
and coloring, aging façades present challenges
when deterioration starts to emerge.
24 • IIBEC Interface January 2021
Figure 2 – Concrete spalling observed
during investigation of a concrete façade.
Figure 1 – Spalled concrete and exposed reinforcement
bars observed during a façade investigation. Many bars
had less than ½ in. of concrete cover.
CONCRETE FAÇADE DETERIORATION
After decades of exposure to the elements,
concrete façades may exhibit deterioration in
the form of cracking, delamination, or spalling
(Figures 1 and 2). Exposed reinforcement bars
are unsightly, and continued expansive effects
of corrosion may lead to potentially hazardous
situations for pedestrians and property below.
Further, cracking and deteriorated transitional
areas can offer paths for moisture migration
into the building and result in interior leakage.
Corrosion of embedded reinforcement steel
within the concrete is the leading cause of deterioration.
3 Carbonation-induced corrosion is
a frequent cause of failure on concrete façades
and may be exacerbated by shallow cover of
reinforcement. Carbonation of the concrete
is simply the reaction of various components
of the cement paste with carbon dioxide in
the air. Carbonation reduces the natural protective
alkalinity of the concrete and makes
the embedded steel susceptible to corrosion
in the presence of sufficient amounts of moisture.
Carbonation also increases shrinkage on
drying of concrete elements (thus, promoting
crack development). If the depth of carbonation
reaches embedded steel in a concrete structure,
then corrosion of that steel may take place if
oxygen and sufficient amounts of moisture are
present. Corrosion of reinforcing steel bars
embedded in the concrete results in the buildup
of corrosion byproducts, such as iron oxide, on
the surface of the bars. This rust can occupy
volumes up to ten times the original volume
of metal from which the rust formed. The
surrounding concrete cover restrains
the buildup of the corrosion byproducts,
resulting in pressure building up
around the bars (Figure 3). Eventually,
the concrete will crack and delaminate
due to the tensile pressure created by
the expanding steel reinforcement,
since concrete has low tensile strength.
The shallower the depth of cover over
the reinforcing steel bars, the faster the
cracking will take place. ACI 318 contains
requirements for concrete protection
for reinforcement; those requirements vary
depending on the size of the reinforcement and
environmental exposure.4
Of course, spalling concrete represents a
great threat to the safety of pedestrians around
a building. However, even minor cracking can
lead to interior leakage and affect the quality
and the comfort of the building occupants.
Investigation of leakage at a concrete stairwell
indicated that through-wall cracks and failed
sealant at the perimeter of the steel windowwall
system contributed to water ingress at
January 2021 IIBEC Interface • 25
Figure 3 – Graphic representation of spalled
concrete as a result of corrosion byproduct
buildup on steel reinforcement.
interior stairs (Figure 4). Investigation of a precast
concrete window system found that deterioration
of the concrete resulted in leakage at
the building interior (Figure 5). Aged sealant
around the window perimeters and localized
spalling contributed to the leakage.
FAÇADE INSPECTIONS
Deterioration of concrete façades can be
mitigated through regular inspections and
maintenance. Several cities across
the US have introduced façade
ordinances that require periodic
inspections of buildings to help
protect the public from potentially
hazardous situations, including fall
hazards from delaminated or spalling
concrete. For example, Chicago
requires that all buildings over 80
ft. in height are inspected by a registered
design professional at intervals
ranging from two to six years,
depending on the classification of
the building (Figure 6). Buildings
are classified according to the
façade materials and require more
frequent inspections if the exterior
walls or enclosures are reinforced
with, or in direct contact with, corrodible
metals. Façade inspections
are designed to identify areas of
distress and provide a comprehensive
assessment of the condition of
the exterior façade. When deterioration
is observed, an investigation
can uncover the underlying issues
and provide the best path forward
for repair.
26 • IIBEC Interface January 2021
Figure 4 – Through-wall cracking
and failed sealant resulted in
leakage at this concrete stairwell.
Figure 5 – Interior leakage at
precast concrete window system.
Façade inspections should generally consist
of visual surveys of the entire façade supplemented
by hands-on and close-up evaluation
of enough area as practical to provide a
comprehensive assessment. Scaffolding, boatswain
chairs, and lifts should be used to provide
hands-on access to upper levels of the
façade. Hands-on techniques such as hammer
sounding to detect subsurface delaminations
and nondestructive testing generally give the
inspector a more complete view of the extent
of deterioration that may be present. In concrete
façades with low-cover concerns, groundpenetrating
radar (GPR) surveys may be performed
to measure concrete cover over embedded
reinforcement. Nondestructive measurements
may also be confirmed by drilling holes
at reinforcement to measure cover at representative
locations.
Sample removal and subsequent laboratory
testing is also useful to investigate the cause of
any deterioration present. For concrete façades,
laboratory testing may include petrographic
analysis and chloride testing. Compressive
strength testing may also be useful if there is
any question about the durability or structural
adequacy of structural elements that are
exposed on the façade. Determining the underlying
cause of deterioration is necessary in
order to provide an effective repair solution.
FAÇADE REPAIRS
Concrete façade repairs should be designed
to address the nature and deterioration present
on the building. Repair procedures may include
relocating existing steel reinforcement where
cover was too low and supplementing corroded
reinforcement with advanced section loss.
Repair patches should match existing profiles,
chamfers, and surface finishes to preserve the
original appearance of the concrete façade.
However, implementing façade repairs that
match the color and texture of the existing concrete
is inherently challenging. Source materials
in concrete, such as cements and aggregates,
are naturally occurring and will vary from historical
materials used on older concrete façades.
Concrete repair mixtures should be designed
with the following goals:
• Replicate existing concrete color using
readily available materials
• Produce concrete of similar strength to
existing concrete structure
• Produce durable concrete to withstand
environmental conditions of the site
• Produce a mixture with suitable workability
to allow contractors to place
the concrete in a consistent manner
throughout the project
In order to assess the effectiveness of trial
mix designs, site mock-ups should be used to
compare potential repair concrete against the
January 2021 IIBEC Interface • 27
Figure 6 – Façade inspection of exposed concrete from suspended scaffold.
properties of the existing building. Mock-ups
may include trial patch repairs on the façade, or
separate mock-up samples that may be moved
around to multiple elevations or façade elements.
It may be helpful to view the mockups
under multiple lighting conditions (such
as full sunlight or shade). Multiple mock-ups
should be used to represent different concrete
elements or textures, such as concrete with
exposed aggregate and smooth concrete with
visible form lines (Figure 7).
When repairs are implemented, it is important
to maintain a quality control program
during construction to ensure that the concrete
used for the repair matches the approved mockup
and is consistent throughout the repair process.
Quality control should consist of regular
site visits by the engineer to observe demolition
of deteriorated concrete, preparation of repair
patches, and final
patch approval to
ensure that concrete
was placed without
any obvious defects.
FAÇADE
CLEANING
In certain cases,
it may be warranted
to perform façade
cleaning. The objective
of a façade
cleaning program
is to remove visible
surface dirt or stains
without damaging
the façade. Trial
cleaning techniques
should be conducted
with the gentlest
methods possible
that will achieve the
desired results. For example, dry sand blasting
is an aggressive technique that may cause
damage to older concrete. Alternately, soda
blasting is a non-destructive cleaning method
that can be used for more delicate concrete
façades. Soda blasting uses compressed air to
apply sodium bicarbonate (baking soda) to
a concrete surface (Figure 8). Trial cleaning
should be performed at selected locations to
determine its effectiveness before cleaning the
entire façade.
CONCLUSION
Exposed concrete façades are a unique and
important feature of many historic and modern
buildings. With regular inspections, maintenance,
and careful design and repair programs,
owners can avoid failures and preserve the
integrity of the original façade.
REFERENCES
1. “History of Unity Temple.” www.
utrf.org. Unity Temple Restoration
Foundation. Accessed October 15,
2020. https://www.utrf.org/history/.
2. “Historic Netsch Campus at UIC.”
www.uicarchives.library.uic.edu.
Discover UIC. 2008. Accessed October
15, 2020. https://uicarchives.library.
uic.edu/historic-netsch-campus/#:~:-
text=Welcome%20to%20the%20historic%
20Netsch%20campus%20at%20
UIC.,Merrill%20designed%20the%20
campus%20between%201963%20-
and%201968.
3. “Types and Causes of Concrete
Deterioration.” Portland Cement
Association. 2002. p. 1.
4. Building Code Requirements for
Structural Concrete (ACI 318-11).
Michigan. American Concrete
Institute. 2011. pp. 93-94.
28 • IIBEC Interface January 2021
Alexis Brackney is
a licensed architect
and structural
engineer, and she is
the director of the
Building Science
Group at CTLGroup
in Skokie, Illinois.
Throughout her
career at CTLGroup,
she has conducted
field investigations,
analysis, and rehabilitation
of a variety of architectural and structural
systems and components. She specializes in
forensic investigations, condition assessments, and
building enclosure inspections.
Alexis Brackney
Figure 7 – Mock-up samples of exposed aggregate concrete.
Figure 8 – Soda blasting used during concrete façade cleaning.
January 2021 IIBEC Interface • 29
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Plans have been accepted for Southern China’s first largescale
museum of natural history. The Shenzen Natural History
Museum, to be built in the Yanzi Lake area of Shenzhen’s
Pingshan District in Guangdong, China, ran a design
competition which received over 70 proposals internationally.
The winning design, entitled “Delta,” was by 3XN, B+H
Architects, and Zhubo Design, and it evokes the watery location
of the nearby lake by incorporating river-like curves into the
overall building design. It will also feature a vegetative roof that
rises gently on each end, making it accessible from ground level,
extending the surrounding public park space onto the facility’s
roof. The final footprint of the new museum will be 42,000
square m (452,084 sq. ft.).
— ArchDaily, Dezeen
All images courtesy of 3XN.
Shenzen Museum Will Flow Like a River
“The plan makes full utilization of the landscape in the site. Through
a dynamic architectural form, it creates a beautiful, natural, and dynamic
nature museum concept.”
– Weiping Shao, competition judge, chief executive architect
of the Beijing Institute of Architectural Design