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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Defects and damage in structures
14.09.2015
Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
2Course outline
IntrinsicExtrinsic
ChemicalPhysicalBiological
Initiating
Leads to
Assessed
Visual inspectionNon-Destructive TestingDestructive Testing
CrackingScaling
SpallingPopouts
Delaminationetc.
Principles forrepair and protection
DeteriorationProcess
VisibleDamage
Conditionsurvey
Repair
Factors CausingDeterioration
Conditionevaluation
Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
3
Outlines
• Concrete Defects and Damage
• Concrete Damage due to Reinforcement Corrosion
• Typical times of appearance of defects
• Recognizing defects and probable causes
– Defects due to construction
– Load-induced Defects
– Defects related environmental factors and material properties
– Other defects (ASR – DEF – Fire – Masonry and renderingdefects)
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Concrete Defects and Damage
Mechanical Chemical Physical• Impact.• Overloading.• Movement
(settlement).• Vibration.• Earthquake.• Explosion.
• Alkali aggregate reaction.• Aggressive chemical agents
exposure i.e. sulphates, nitratesand other salts, soft water(acidic/low pH).
• Bacterial or other biologicalaction.
• Efflorescence/leaching.
• Freeze/thaw action.• Thermal movement.• Salt crystal expansion.• Shrinkage.• Erosion.• Abrasion and wear.
Example: Crackingcaused by incorrecthandling or fixing ofprecast panels.
Example: Chemical attack fromaggressive gases (and subsequentreinforcement corrosion) on the topof chimneys or the soffits of afactory roof.
Example: Freeze/thaweffects with progressivescaling on the soffits of aparking structure.
https://www.concreterepairsite.co.uk/DamageNProblems.html
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Concrete Damage due to Reinforcement Corrosion
https://www.concreterepairsite.co.uk/DamageNProblems.html
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Recognizing defects and probable causes
• Many factors may contribute to orcause the deterioration of concretestructures
• These factors may be broadlysummarized as follows:– Errors in the design assumptions
or the design process– Specification or use of
inappropriate materials– Poor workmanship– Environmental effects– Overloading, due to under-design
or change of use– Accidental effects such as fire– Inappropriate repairs
Appearance of defects1. Cracking2. Scaling3. Delamination4. Spalling5. Popouts6. Efflorescence7. Construction defects8. Other damage9. ……………..
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Typical times of appearance of defects
Type of Cracking Form of Crack Primary Cause Time of Appearance
Plasticsettlement
Above and alignedwith steelreinforcement
Subsidence around rebar;excessive water in the mix.
10 minutes tothree hours
Plasticshrinkage Diagonal or random Excessive early evaporation 30 minutes to six
hoursThermalexpansion andcontraction
Transverse(example: across thepavement)
Excessive heat generationor temperature gradients
One day totwo or three weeks
Dryingshrinkage
Transverse orpattern
Excessive water in the mix;poor joint placement; jointsover-spaced
Weeks to months
Freezing andthawing
Parallel to theconcrete surface
Inadequate air entrainment;non-durable coarseaggregate
After one or morewinters
http://www.nachi.org/visual-inspection-concrete.htm
Continue …….
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Typical times of appearance of defects
Type of Cracking Form of Crack Primary Cause Time of Appearance
Corrosion ofreinforcement Above reinforcement
Inadequate concrete cover;ingress of moisture orchloride
More than two years
Alkali-aggregatereaction
Pattern cracks;cracks parallel tojoints or edges
Reactive aggregate plusmoisture
Typically, over five years,but may be much soonerwith highly reactiveaggregate
Sulfate attack Pattern cracksExternal or internal sulfatespromoting the formation ofettringite
One to five years
http://www.nachi.org/visual-inspection-concrete.htm
Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
9
Control of Cracking in Concrete: State of the Arthttp://onlinepubs.trb.org/onlinepubs/circulars/ec107.pdf
Common causes of cracking in concrete structures
Types of cracks
Before hardening After hardening
Constructionmovement Plastic Frost
damageVolume
instabilityStructural /
designPhysio-
chemical
Framew
orkm
ovement
Framew
orkm
ovement
Subgradem
ovement
Subgradem
ovement
Plasticshrinkage
Plasticsettlem
ent
Autonomous
shrinkageAutonom
ousshrinkage
Premature
freezing
Scaling,crazing
Dryingshrinkage
Thermalchange
Creep
Designload/overload
Designload/overload
Design/subgrade
Fatigue
AAR/ASR/DEF
Steelcorrosion
Freeze-thawcycling
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Intrinsic cracks in hypothetical structure
Concrete society technical report 22Non-structural cracks on concrete.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Crack sizes
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Defects due to construction
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Construction defects
WHY Do construction defects Occur?• Honeycomb and rock pockets appear
on the concrete surface where voidsare left due to failure of cement mortarto fill spaces around and among coarseaggregates. This happens due to:– poor quality control during mixing,
transporting or placing of concrete– under or over-compaction of
concrete, low cement content orimproper mix design
• Dimensional errors in concretestructure result due to poor centering ofstructural member as per drawing orerror in detailing.
• Finishing errors in concrete structurescan involve over-finishing of theconcrete surface or addition of morewater or cement to the surface duringfinishing of the concrete.
• This results in the porous surface whichmake the concrete permeable resultingin less durable concrete.
• Poor finishing of concrete results in thespalling of concrete from surface earlyin their service life.
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Construction defects
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
Example of construction defects(insufficient concrete cover)
• Another source of construction defectsis related to insufficient concrete coverwhich may be caused by shift or cageshift, improper fabrication of steel, orimproper placement of forms.
• Basic Categories of ConstructionDefects– Site Defects– Building Envelope Defects– Structural Defects– Heating, Ventilating, and Air
Conditioning Defects– Electrical and Plumbing Defects– Fire/Life Safety System Defects
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Construction defects
http://theconstructor.org/concrete/construction-defects-in-concrete-structures/8472/
Examples of construction defects
Definition:• Defects in concrete structures can be
due to poor construction practices i.e.poor construction quality control at siteor due to poor structural design anddetailing.
• After construction at site, the commontypes of defects in concrete structuresare:– Honeycombing and rock pockets,– form failure or misalignment of
formwork,– dimensional errors,– rock pockets and finishing errors.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Plastic Shrinkage
• Plastic shrinkage is caused byexcessively high rates of evaporationfrom the surface of the concrete beforeit has hardened.
• Drying does not take place at an evenrate throughout the concrete matrix. Ithappens most rapidly at the uppersurface through evaporation and moreslowly at the bottom throughabsorption.
• The rate at which the sub-gradeabsorbs water will depend on itsabsorbent properties, including itsporosity, moisture content, and even itselectro-chemical properties.
Cause:– This condition occurs as a
result of very rapid evaporationof the concrete while it is still ina plastic state.
– Hot, dry, and windyenvironmental conditions andlack of countermeasuresemployed.
Plastic Shrinkage Cracking
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Plastic Settlement
• Plastic settlement can be caused bysubsidence around rebar.
• This is sometimes related to excessivewater in the mix.
• As soon as concrete is placed, it beginsto consolidate, and as bleed water risesto the surface, cement particlesconsolidate and the concrete settles.
• The settling process is restrained byreinforcement steel and, under certaincircumstances, cracks will developdirectly above the steel.
• Plastic settlement cracks can becaused by:
– inadequate concrete cover of the steel;– excessive water in the concrete;– form movement or blowout; or– poor consolidation practices.
Repeating pattern of cracks whererebar cross-members connect
longitudinal rebar
http://www.nachi.org/visual-inspection-concrete.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Autogenous Shrinkage
• Plastic shrinkage is shrinkage causedby the loss of water to the atmosphere.
• Autogenous shrinkage is shrinkage thattakes place with no loss of water to theatmosphere.
• Autogenous shrinkage is caused byinternal drying, with water beingabsorbed by the constituent materialsin the concrete.
• Absorption of water from the pores alsocauses shrinkage.
• Since there is no loss of water to oneexposed surface, autogenousshrinkage is more uniform than plasticshrinkage.
• However, tensile stresses still develop,and embedded steel can causeanomalies in an area of concrete withrelatively uniform stress.
• These anomalies can cause variationsin stress within the concrete that arerelieved by cracking. Autogenousshrinkage cracking will be shallow andis not a structural issue.
Outside corners are also high-stress points.
http://www.nachi.org/visual-inspection-concrete.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Crazing
Definition:• Pattern cracking, also called map
cracking and craze cracking, appearsas a network of random cracking on theconcrete’s surface.
• The cracking is usually shallow (lessthan 3 mm deep) and not a structuralissue.
• It’s seldom a durability problem butmore of a cosmetic one.
• The area enclosed by pattern crackingmay be anywhere from 1.25 cm to 20cm across.
Crazing cracks caused by prematuredrying
http://www.nachi.org/visual-inspection-concrete.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Crazing
– over-working the surface with asteel trowel during finishing
– performing finishing operationswhile bleed water is still on thesurface
– sprinkling cement dust on thesurface to soak up bleed water.
WHY do crazing cracks occur?– poor curing practices– Environmental conditions such as
low humidity, high outsidetemperatures, direct sunlight, andwind can create high rates ofevaporation from the surface layerof concrete
– Resistance to shrinkage from theunderlying concrete causes stressthat is relieved by craze cracking
– excessive water in the mix– over-vibration of the concrete,
causing coarse aggregate to settleand cement paste to concentrateat the surface
http://www.nachi.org/visual-inspection-concrete.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Drying Shrinkage
• Drying shrinkage is shrinkage thattakes place after the concrete hashardened and some degree of bondinghas developed between the cementpaste and the aggregate.
• As concrete continues to dry, it willcontinue to shrink.
• Drying shrinkage includes bothshrinkage that takes place while losingmoisture to the air and autogenousshrinking
• The cracks will look similar to thoseformed during plastic shrinkage
• Drying shrinkage cracks may be thepropagation of cracks that initiallydeveloped during plastic shrinkage.
http://www.nachi.org/visual-inspection-concrete.htm
A typical interruption in a shrinkage crack
A re-entrant corner crack
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Cracking examples
http://www.nrmca.org/aboutconcrete/cips/04p.pdf
Cracks due tounsuitable jointing
Cracks due to continuousexternal restraint (example: cast-
in-place wall restrained alongbottom edge of footing)
Cracks due to lack ofisolation jointsSettlement cracks
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Load-induced Defects
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Structural cracks
Structural cracks– are caused by both dead and live
load stresses, which can lead toeventual failure of the structure.
– Flexure structural cracks arevertical and begin in areas ofmaximum tension or moment.
– Shear structural cracks arediagonal and are usually found inthe web of a member. They maybegin at the bottom and movediagonally toward the center of themember.
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
Shear structural cracks
Flexure structural cracks
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Structural cracks
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Fatigue
• Concrete fatigue is long-term failuredue to repeated loading (cycles).
• Loads may be applied in tension,compression, torsion (twisting),bending, or a combination of theseactions.
• In fatigue, each individual load is lessthan a single static or unchanging loadthat would exceed the strength of theconcrete.
• Fatigue has to do with the developmentand propagation or growth of cracksand micro-cracks, and the failure of thebond between the cement paste andaggregate.
• Crack development and bond failureworsen slowly over time and areinfluenced by a number of variables.
• Fatigue is not something mostinspectors will be able to identify and isless common in residential constructionthan in commercial and especiallyindustrial structures.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Defects relatedenvironmental factors and
material properties
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Weathering
• Weathering is the effect of pollution andnatural forces, such as frost, rain andsunlight, on a structure.
• With concrete, the main weatheringproblem is unexpected variations in thevisual appearance of the structure.
• Dust in the atmosphere will bedeposited on the facade. The flow ofrainwater will tend to wash some areaspreferentially, resulting in significantdifferences in colour between clean anddirty areas.
• This phenomenon is controlled bymany factors, including the surfacetexture of the concrete, thearchitectural detailing and theorientation of the structure.
http://www.concreteconstruction.net/Images/Weathering%20of%20Concrete_tcm45-342061.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Mold and moisture damage
Definition of Mold• Molds are fungi which occur naturally in
the environment.• Many different species of mold exist.• Molds help break down dead materials
and convert it back into organic matterwhich can be used by living organisms.
How Molds Grow?• Molds grow by digesting and destroying
the material they grow on.• They can be found almost anywhere
and can grow on just about anymaterial as long as conditions arefavorable.
• For favorable growing conditions, moldneeds nutrients (oxygen and moisture)and a material to grow on.
• Molds reproduce by making spores.• These spores become airborne, both
outside and inside of buildings.• If spores land on suitable material and
conditions are favorable, the mold willbegin to grow.
• http://www.epa.gov/mold/pdfs/moldguide.pdf• http://www.epa.gov/mold/pdfs/moldremediation.pdf• http://www.nj.gov/health/eohap/mold/documents/mold
_guidelines.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
• Many building materials such as drywall,ceiling tiles and wood framing containcellulose, which is a material on whichmolds can grow.
• Molds may grow unnoticed, aboveceilings, behind walls, in attics andbasements or in crawl spaces.
• Molds can cause staining of walls andceilings and can begin to break down thestuds and joists of buildings causingextensive property damage.
• Excessive moisture is a key ingredientwhich causes molds to grow.
• Sources of excess moisture may beplumbing leaks, leaking roofs or windows,high humidity, flooding, or condensationinside walls due to poor insulation.
Mold and moisture damage
• http://www.epa.gov/mold/pdfs/moldguide.pdf• http://www.epa.gov/mold/pdfs/moldremediation.pdf• http://www.nj.gov/health/eohap/mold/documents/mold
_guidelines.pdf
Appearance of Mold• Molds grow in colonies and growth
may take on different shapes andcolors.
• Some molds may appear circular ingrowth while others may grow andspread to cover an area.
• Molds may appear brown, yellow,green or black in color.
• The appearance depends on thespecies of mold present.
Understanding Molds• Even though molds are everywhere,
they may become a problem whenthey begin to grow inside homes andbuildings.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Mold and moisture damage
• http://www.epa.gov/mold/pdfs/moldguide.pdf• http://www.epa.gov/mold/pdfs/moldremediation.pdf• http://www.nj.gov/health/eohap/mold/documents/mold
_guidelines.pdf
Common Health Effects Include:• Allergic reactions - sneezing, nasal
congestion• Irritation to the nose, throat, and
respiratory tract• Asthma attacks• Hypersensitivity pneumonitis
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Mold and moisture damage
• http://www.epa.gov/mold/pdfs/moldguide.pdf• http://www.epa.gov/mold/pdfs/moldremediation.pdf• http://www.nj.gov/health/eohap/mold/documents/mold
_guidelines.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Thermal expansion
• Nonstructural cracks can be causedby thermal expansion and contractionof concrete, contraction of the concreteduring the curing process, ortemperature gradients within massivesections of concrete.
• A blowup is a localized upwardmovement of a concrete curb or slab,usually at a joint or crack.
• The thermal expansion of concrete is18 … 20 10-6/°C.
• Expansion joints are incorporated indesigns to take up this lineardimensional change.
• The problem occurs when themovement is underestimated, notallowed for, or when correctly sizedjoints become contaminated withmaterial that is not compressible.
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
Cracking from the straight plane of aconcrete element due to forces
imposed by thermal expansion.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Definition:• Scaling is flaking or peeling of a
finished hardened concrete surface asa result of exposure to cycles offreezing and thawing.
• Generally it starts as localized smallpatches, which later may merge andextend to expose large areas.
• Scaling is classified as:– Light scale is the loss of surface
mortar up to 6 mm deep exposingcoarse aggregates.
– Medium scale is the loss ofsurface mortar from 6 mm to 13mm deep with mortar loss betweenthe coarse aggregates.
– Heavy scale is the loss of surfacemortar from 13 mm deep to 25mmm deep clearly exposingcoarse aggregates.
– Severe scale is the loss of surfacemortar greater than 25 mm deepwhere coarse aggregate particlesare lost and reinforcing steel isexposed.
Scaling
http://www.armca.ca/uploads/files/Tech%20Tips/CTT2-Scaling%20Concrete%20Surfaces.pdf
Light scale
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
C. Any finishing operation performedwhile bleed water is on the surface.• If bleed water is worked back into
the top surface of the slab, a highwater/cement ratio and, therefore,a low -strength surface layer isproduced.
• Overworking the surface duringfinishing will reduce the air contentin the surface layer, making itsusceptible to scaling in freezingconditions.
D. Insufficient curing.• This omission results in a weak
surface skin, which will scale if it isexposed to freezing and thawing inthe presence of moisture anddeicing salts.
Scaling
http://www.armca.ca/uploads/files/Tech%20Tips/CTT2-Scaling%20Concrete%20Surfaces.pdf
WHY Do Concrete Surfaces Scale?A. The use of non-air-entrained concrete
or too little entrained air.• Adequate air entrained is required
for protection against freezing andthawing damage.
B. Application of excessive amounts ofcalcium or sodium chloride deicingsalts on concrete.• Chemicals such as ammonium
sulphate or ammonium nitrate,which are components of mostfertilizers, can cause scaling aswell as induce severe chemicalattach on the concrete surface.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Popouts
Definition:• A popout is a small fragment of
concrete surface that broke away dueto internal pressure, leaving a shallow,typically conical, depression.
• Popouts general vary size from 6 to 50mm in diameter, but can be up to 300mm in size.
• Usually fractured aggregate particle willbe found at the bottom of the hole, witha part of the aggregate still bonded tothe point of the popout cone.
WHY Do Popouts Occur?• Popouts are usually caused by the
expansion of porous aggregateparticles having a high rate ofabsorption.
• As the aggregate absorbs moisture orfreezes under moist conditions, itsswelling creates internal pressuressufficient to scale the concrete surface.
• Ironstone, coal, shale and soft finegrained limestone are the commonlyobserved causes of popouts.
http://www.armca.ca/uploads/files/Tech%20Tips/17%20Tip.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Delamination
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
Definition:• Delamination is the separating of
concrete layers at or near theoutermost layer of reinforcing steel.
WHY Does Delamination Occur?• Delamination is caused by the
expansion of corroding reinforcingsteel and can lead to severecracking.
• Rust can occupy up to ten timesthe volume of the corroded steelwhich it replaces. Delaminations are separations in
a slab, parallel to and generallynear the upper surface
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Spalling
Definition:• Spalling is a deep surface defect, often
appearing as circular or ovaldepressions on surfaces or aselongated cavities along joints.
• Spalls may be 25 mm or more in depthand 150 mm or more in diameter,although smaller spalls also occur.
WHY Does Spalling Occur?• Spalls are caused by pressure or
expansion within the concrete, bondfailure in two-course construction,impact loads, fire, or weathering.
• Improperly constructed joints andcorroded reinforcing steel are twocommon causes of spalls
• http://www.sydneyengineers.com/articles/66-concrete-spalling• http://www.cement.org/docs/default-source/fc_concrete_technology/durability/is177-
concrete-slab-surface-defects-causes-prevention-repair.pdf?sfvrsn=4
Spalling of Concrete slab due to corrosion
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Efflorescence
http://ntl.bts.gov/lib/44000/44500/44562/State_Study_169_-_Diagnostic_Evaluation_and_Repair_of_Deteriorated_Concrete_Bridges.pdf
Definition:• Efflorescence is a crystaline deposit on
surfaces of masonry, stucco orconcrete. It is whitish in appearance,and is sometimes referred to as"whiskers".
WHY Does Spalling Occur?• Efflorescence is caused by vapor
migrating through the structure bringingsoluble salts to the surface
• Efflorescence requires the movementof moisture. Without moisturemovement there would be noefflorescence on the surface to createthe problem.
BrickEfflorescence
Concrete Efflorescence
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Steel Corrosion
• Corrosion of embedded steel is themost common cause of concreteproblems.
• As steel corrodes, the corrosionproduct expands, and this expansioncan crack concrete and cause sectionsto break loose in flakes.
• Inadequate cover due to control jointsis also common in flatwork. Wherecontrol joints are installed perpendicularto embedded rebar, the areas at whichthe control joint crosses each bar maydevelop cracking and corrosion, andeventually spalling or flaking.
Corrosion typical of inadequate cover
http://www.nachi.org/visual-inspection-concrete.htm
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Other defects
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Alkali-silica reaction (ASR)
• Major infrastructure projects such asdams, roadways or airport runwaysrequire enormous quantities ofaggregates.
• Some aggregates can exhibit anincreased or high risk of ASR.
• Alkali-Silica Reaction is a chemicalreaction which occurs between theamorphous silica in the aggregate andthe pore solution (alkalis) of the cementmatrix.
• The reaction results in an increase ofconcrete volume, causing cracking andspalling when the generated forcesexceed the tensile strength of theconcrete.
The appearance of ASR damagecan be assessed very well on the
drying concrete surface of thisbridge pylon. Damage can appearwithin years or only after decades.
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Delayed ettringite formation (DEF)
• Delayed ettringite formation (DEF) isexpansion and cracking of concreteassociated with the delayed formationof the mineral ettringite which is anormal product of early cementhydration.
• DEF is a result of high earlytemperatures (above 70oC – 80oC) inthe concrete which prevents the normalformation of ettringite.
• DEF-induced damage is not a commonphenomenon in concrete.
• Water or moisture from an externalsource is required for the reaction tooccur, the availability of which will affectboth the rate and the extent ofexpansion.
http://www.whd.co.uk/Concrete/concretebysem.html
Delayed ettringite formation:(e) ettringite(L) surrounds the coarse limetone aggregate(s) Fine aggregate is silica sand
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Other damage: Fire damage
http://www.buildsmartercolorado.org/documents/Evaluating%20Fire%20Damage%20to%20Concrete%20Structures_tcm45-343618.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Other damage: Fire damage
http://www.brandforsk.se/MediaBinaryLoader.axd?MediaArchive_FileID=43f89b58-b5fa-45ae-a60f-56ba9b14d57b&FileName=BF_306_071_Rapport.pdf&MediaArchive_ForceDownload=true
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Possible Sources and Effects of Masonry Distress
http://www.gobrick.com/portals/25/docs/technical%20notes/tn46.pdf
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Possible Sources and Effects of Masonry Distress
Masonry– Cracked Units– Loose Units– Spalled Units– Hairline Cracks in Mortar– Deteriorated Mortar Joints– Missing or Clogged Weeps– Plant Growth– Deteriorated/Torn Sealants– Out-of-Plumb– Efflorescence– Stains– Water Penetration
http://www.gobrick.com/portals/25/docs/technical%20notes/tn46.pdf
Crackingmodes
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Brick Efflorescence
Brick Efflorescence Analysis• Firstly: There must be water-soluble
salts present somewhere in the wall.• Secondly: There must be sufficient
moisture in the wall to render the saltsinto a soluble solution.
• Thirdly: There must be a path for thesoluble salts to migrate through to thesurface where the moisture canevaporate, thus depositing the saltswhich then crystallize and causeefflorescence.
• All three conditions must exist.– If any one of these conditions is
not present, then efflorescencecannot occur.
http://www.masonryworktools.com/brickefflorescence.html
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Eroded Mortar Joint
What To Look For:• Slight or local erosion of mortar in joint.• Small erosion depth relative to exterior
face of brick.• Aggregate (fine sand) exposed.
Probable Causes:• Erosion due to wind or frost cycles.• Disaggregating of lime component of
the binder.
FAÇADE CONDITIONS: An Illustrated Glossary of VisualSymptoms, Edited by Dan Eschenasy
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Classification of the defects in wall renderings
http://ijce.iust.ac.ir/files/site1/user_files_6k93w6/eng/jorgedebrito-A-10-1399-1-8b1ef1b.pdf
Aesthetic defects Defects associatedwith humidity
Mechanically-relateddefects
Graffiti Infiltrations / dampnessstains
Adherenceloss/detachment
Corrosion stains Efflorescence /cryptoflorescence Map cracking
Dirt / deposits ofparticles Biological colonization Cohesion
loss/crumbling
Colourchange/discolouration Carbonation Scratches / grooves
Vegetation growth Linear cracking
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Examples of rendering defects
Efflorescence towall rendering
Corrosion stainscoming throughpainted render
Render cracking
Moistureproblems
Adherenceloss/detachment
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Examples of rendering defects
Render cracking
Cohesionloss/crumbling Map cracking
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Rak-43.3301 Repair Methods of Structures I (4 cr), Fahim Al-Neshawy & Esko Sistonen, Autumn 2015
Summary
Lecture summary– Concrete Defects and Damage– Concrete Damage due to
Reinforcement Corrosion– Typical times of appearance of
defects– Recognizing defects and probable
causes• Defects due to construction• Load-induced Defects• Defects related environmental
factors and material properties• Other defects (ASR – DEF –
Fire – Masonry and renderingdefects)
Next lecture– Condition survey overview– Condition survey parts:
• Review of plans andrelevant documents
• Visual inspection• Non-destructive testing• Laboratory and destructive
testing (the followinglecture)
Recommended