24560342 concrete repair good
TRANSCRIPT
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Concrete Repair
and Protection (1)
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- Importance of concrete deterioration ingeneral
- Concrete as building material
- Reasons for concrete deterioration- Concrete Repair
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Concrete Repair
Contents
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Importance of Concrete
Deterioration in generalThe economic loss related to concretedeterioration is significant.
Valuable resources must be spent forconcrete repair
Concrete deterioration can endanger thelives of people
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The life of a concrete structure
Phase A Design, construction and concrete curing
Phase B Deterioration initiation processes are
underway but damage is not yet obvious
Phase C Deterioration is underway and startsbecoming visible
Phase D Deterioration process is advanced, extensive
damage is visible 4
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Law of Fives
1 $ spent in Phase A
= saving 5 $ repair expenditure in Pahse B
= saving 25 $ repair expenditure in Phase C
= saving 125 $ repair expenditure in Phase D
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Reasons for Concrete DeteriorationConcrete as Building Material
What is concrete?
Sand + Aggregate + Cement + Water
+ (Additives) + (Steel)
=> Hydration => Conctere
What makes concrete perform?
Design
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Concrete as Building MaterialConcrete Surface
Aggregate
Cement Skin Fine
Mortar Zone
Coarse Mortar
Zone Fine
Concrete ZoneReinforcement
Concrete
according todesign with normalcement contentand plannedaggregatedistribution
Typical cross section of reinforced concrete 7
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Reasons for Concrete DeteriorationConcrete as Building Material
Classification according to compressive strength classes
5 to 10 MPa Lean concrete, provisional structures
20 to 30 MPa Structural components in housing andindustry
40 to 50 MPa Concrete for higher requirements inhousing and industry
60 to 120 MPa High performance concrete for specialstructures
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Reasons for Concrete DeteriorationConcrete as Building Material
If concrete is produced according to
international stand of technique, it is a
very long lasting material, wear resistantand relatively cheap.
Important is the proper design of the
concrete components and the properhandling of the material during the
casting process at site.
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Reasons for ConcreteDeterioration
Reasons, which already exist beforethe concrete component has beenfinished
- Mistakes during planning and design
- Mistakes related to concrete technology
- Mistakes during production at site
Reasons, which attack the
concrete after finishing thebuilding
- Environmental influence- Extraordinary stress
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Reasons for ConcreteDeterioration
Main damages to concretecomponents
Corrosion of the reinforcement
Expansion reaction
Dissolving deterioration
Spalling, cracking and weakening of
composite11
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Reasons for ConcreteDeterioration
What is the reason for corrosion ofthe reinforcement?
Inside a healthy" concrete, the steel is
imbedded in an alkaline environment of pH
13.On the surface of the steel this produces a
protective passive layer, which prevents the
steel from corroding. Reducing of this alkalinemilieu < pH 11 causes corrosion of the
reinforcement.
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Reasons for ConcreteDeterioration
Entrance of harmful agents
Entrance of chlorides
Carbonation
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Reasons for Concrete DeteriorationExisting before finishing the Building
Mistakes during planning and design
Design of minimum measurements as design
measurements.
Too slim concrete components
Wrong load assumptions
Construction situations are not being taken into
consideration
Insufficient investigation of the construction ground14
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Reasons for Concrete DeteriorationExisting before finishing the Building
Mistakes during planning and design
Form deviations are not being consideredsufficiently
Wrong joint design
Disregard of !Stand of Technique
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Reasons for Concrete Deterioration underResponsibility of the Designer
ConcreteComposition
MeasurementsBuildingShape
Designer
ConcreteCover
Reinforcement
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Reasons for Concrete DeteriorationExisting before finishing the Building
Insufficient concrete technology
Wrong concrete composition
Wrong cement class
Wrong kind of cement
Too low cement content
Too high water/cement (W/C) ration
Insufficient quality of aggregates
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Reasons for Concrete Deterioration
Mistake No. 1:
Too much water! W/C > 0.5
Why? Makes life easier at site!
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Reasons for Concrete Deterioration
Consequences of too high W/C ratio
Too much Water
W/C > 0.5Too manyPores
Easy access of HarmfulSubstances
Carbonation ChlorideContamination
Loss of SteelPassivation
Rusting ofReinforcementSteel
Spalling,Delaminating,Cracking ofConcrete
Weakeningof ConcreteComponents
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Reasons for Concrete Deterioration
Effect of W/C on (type GP cements):
a) Compressive strength b) Concrete permeability
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Reasons for Concrete Deterioration Existing
before finishing the Building
Unauthorized
Mistakes during concrete production at site
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Reasons for Concrete DeteriorationExisting after finishing the Building
Physical influences
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Reasons for Concrete DeteriorationExisting after finishing the Building
Chemical influences
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Reasons for Concrete Deterioration
Consequences of CarbonationCO2 enters
CarbonationconcreteCO2 + Ca(OH)2 CaCO3 + H2O Alkalinity drops
pH < 12
DepassivationSpalling, Corrosion of steeldelamination, of steelcracking ofconcrete
Note:
Weakening of Carbonationconcrete usually stops at a
components certain depth
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Reasons for Concrete Deterioration
Consequences of Chloride Attack
CL- entersconcrete
CL- > 0.4% total
chloride W/WDepassivation
cementof steel
Spalling,
delamination, Corrosion of steelWeakening ofcracking of
concreteconcretecomponents
Note:
Chloride attackdoes not stop at acertain depth
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Reasons for ConcreteDeteriorationInfluence of humidity and concrete quality on
critical chloride content
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Damages
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Damages
Cracking Spalling
Delamination Corner Effects 28
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Requirements for GoodQuality Concrete
Dense, not too many pores (total pore
volume < 16 Vol.-%)
Water/cement ratio W/C < 0.5 Cementcontent > 300 kg/m3 Alkalinity pH > 12
Water dispersible chlorides < 0.35 %
related to cement in compacted freshconcrete
Concrete cover > 2 cm (3 cm)29
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Requirements for good QualityConcrete
Proper grading of aggregate
Proper aggregate quality Use good
quality cementCorrect cement type (GP, HE, LH, SR,
SL)
(GP = general purpose, HE = high early strength, LH = low heat, SR
= sulfate resistant, SL = shrinkage limited)
Limit fly ash content30
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Measures to achieve good QualityConcrete
Carry out proper compacting
procedure Carry out the necessary
quality checks Check the batchingplant
Control the mix at site (Slump Test)
Do not trust documents withoutchecking
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Measures to achieve good
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Measures to achieve good
Quality Concrete
Slump Test
1) Filling 2)Compacting
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3) Lifting 4)Measurin
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Damage Analysis
Formation and types of cracks
Inspection techniques
Visual inspectionCover meter
Cylinder compressive strength test
Phenolphthalein indicator Half-cell potential mapping