24560342 Concrete Repair Good

8/4/2019 24560342 Concrete Repair Good

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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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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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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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Main damages to concretecomponents

Corrosion of the reinforcement

Expansion reaction

Dissolving deterioration

Spalling, cracking and weakening of

composite11


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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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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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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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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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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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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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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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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

24560342 Concrete Repair Good

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