Transcript Distress, Evaluation, and Repair of Historic Concrete

Distress, Evaluation, and Repair
of Historic Concrete
Jarkko Simonen, P.E.
Wiss, Janney, Elstner Associates, Inc.
Introduction
• History
• Common Distress Mechanisms
– Corrosion
– Freeze Thaw
– Material problems
• Analysis or Evaluation Methods
• Repair
Introduction
• Cement has a long history
– Certain types of cement have
been used by the Babylonians,
Egyptians, and Romans
– Portland cement 1824
– Reinforced concrete 1867
• In the northwest one of the
early examples of concrete
construction is Fort Casey - 1890
• Generally the use of concrete
became common after about
1900
Concrete Vintage Generalizations
Older Concrete
(1900 to 1945)
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Multiple layers
Placement in lifts
Higher w/c (lower f ’c)
Early reinforcing
systems
– Carbonation
– No air entrainment
Modern Concrete
(1945 to present)
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Homogenous pour
Improved placement
Lower w/c (higher f ’c)
Modern reinforcing
Carbonation
Air entrainment?
Admixtures
Introduction
Environment
• Wet
• Cold
• Coastal
Deterioration due to the environment
• Corrosion
• Freeze thaw
Corrosion
• Common in environments
that contain salt and
moisture
• Distress manifests as
staining, cracking, and
spalling of the concrete
Concrete provides a great environment for
steel against corrosion
Concrete
Problem with rust
• Corrosion of the rebar causes rust to form
• Rust is 6 to 10 time less dense than steel
• Increased volume causes concrete to crack
Effects of Chloride Contamination
• Destroys natural passive oxide layer provided
by portland cement paste
• Complicated chemical interactions
• Hygroscopic
Chloride Contamination
• Environment (soils, sea water)
• Applied (deicing chemicals)
• Integral (admixtures, aggregate, water)
Carbonation
C O2 / H 2O
DEPTH OF
C A R B O N A T IO N
N O N -C A R B O N A T E D
CONCRETE
CO2 + H2O + Ca(OH)2
atmospheric
rain
cement paste
CaCO3 + H2O
limestone
water
Carbonation
• Advances about 1 mm
per year in normal
concrete
• Once carbonation
reaches steel, the steel
is unprotected
• Corrosion can affect
large areas
Freeze-thaw weathering regions
(ASTM C33)
Freeze-thaw
• Damages the near surface region of concrete
• Surface flakes off typically in horizontal layers
• More aggressive if surface is exposed to
chlorides
Air entrainment can be effective in
mitigating freeze-thaw
OH -
ASR - Reaction
between silica and
hydroxyls (OH-) in the
pore solution, forming
silica gel. As the gel
forms, it absorbs
water and expands.
COARSE
AGGREGATE
OH -
OH -
A L K A L IS S IL IC A G E L
(R E A C T IO N R IM )
OH -
OH -
OH -
OH -
S U R R O U N D IN G
PASTE
F IN E
AGGREGATE
R A D IA L
CRACK
COARSE
AGGREGATE
E X P A N S IO N
CRACK
G E L E N T E R IN G
CRACK
A L K A L IS S IL IC A G E L
(R E A C T IO N R IM )
S U R R O U N D IN G
PASTE
F IN E
AGGREGATE
Alkali Silica Reaction
• ASR must have all three
components present to cause a
problem
‐ Reactive aggregates
‐ Abundance of alkalis
‐ Water
• In the northwest we have two out
of three
‐ Reactive Aggregates
‐ Water
‐ Generally cement has low
alkalinity
• ASR aggravates F/T and corrosion
Assessment Methods
Field
• Visual survey
• Mechanical sounding survey
• Corrosion assessment
‐ Half-cell potential measurements
‐ Linear Polarization Resistance Method
• Other non-destructive methods (rebound
hammer, impact-echo, pulse velocity, etc.)
Assessment Methods
Laboratory
• Chloride content
• Depth of Carbonation (Phenolphthalein indicator)
• Petrographic examination
Condition Assessments
References
• ACI 201.1R Guide to Making a Condition Survey of Concrete in
Service
• ACI 224.1R Causes, Evaluation and Repair of Cracks in Concrete
Structures
• ACI 364.1R Guide for Evaluation of Concrete Structures Prior to
Rehabilitation
• ACI 437.1R Strength Evaluation of Existing Concrete Buildings
• ACI 546R Concrete Repair Guide
• Technical Guidelines by International Concrete Repair Institute
(ICRI)
• Guide to Nondestructive Testing of Concrete
• Others
Visual Survey
• Identify distress mechanisms
• Repair quantities
• Repair locations/types
Mechanical Survey
• Identify hidden distress
• Dislodge dangerous fragments
• Gives you a better feel about
the concrete quality
Corrosion Surveys
Half cell surveys
– Identify potential areas
of corrosion
– Repair quantities
– Repair locations/types
Linear Polarization
– Corrosion
rate/aggressiveness
NDT Investigative Techniques
• Impact echo
• Pulse velocity
• GPR
• Magnetic rebar locators
Laboratory Analysis
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Initial opinion of deterioration and conditions
Type of concrete exposure
Discuss testing with petrographer/chemist
Repair type being considered
Type of testing and expected results
Evaluation for Chlorides
Two methods
• Cores
• Drill/powder samples
Testing
• ASTM C 1152: AcidSoluble Chloride in
Mortar and Concrete
• ASTM C 1218: WaterSoluble Chloride in
Mortar and Concrete
Evaluation for Carbonation
Petrography
• ASTM C856: Standard Practice for
Petrographic Examination of
Hardened Concrete
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Freeze thaw
ASR
Finishing Problems
Identify substrate materials
Etc.
Repair
Concrete repair
• Protection/Mitigation
• Patch repairs
• Reconstruction
Protection/Mitigation
• Coatings
– Prevent moisture
• Electrochemical treatments
– Cathodic protection
– Chloride extraction
– Re-alkalinization
• Other
– Sealers
• Silanes
• Siloxanes
– Migratory corrosion inhibitors
Patch Repairs
Considerations
• Compatibility
– Strength
– Wear
– Thermal
• Appearance
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Color
Texture
Finish
Profile
Repairs should blend in
Blending Repairs
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Lift lines
Form board lines
Color
Texture
• Surface Preparation
– Saw cuts
– Rectangular
• Installation
– Dry as possible
• Finishing
• Curing
Samples and Mock-ups
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Cleaning
Coating removal
Color
Finish
Texture
Surface preparation
Design mix
All installation and
finishing procedures and
• Techniques
Repair
Special Considerations with Historic/Architectural
Concrete
• Tasks are similar of work with other concrete
• Options may be more limited
• Rules of good concrete repair practice apply
• Original design may need to be improved
• Emphasis is needed on investigation, laboratory
analysis, samples, mock-ups, and trial repairs
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