JSB FKA –UTM Deterioration and Repair

Deterioration and RepairJSB

JSB

JSB

JSB

FKA –UTM

1

CONCRETE DETERIORATION

&

PROFESSOR DR MOHAMMAD BIN ISMAIL

C09-313

&

REPAIR

REFERENCES

1. Durable Concrete Structures, Comite Euro-

International du Beton, Thomas Telford, 1992

2. Advanced Concrete Technology, John Newman

Department of Structures and Materials, Faculty of Civil Engineering

UTM3

2. Advanced Concrete Technology, John Newman

& Ban Seng Choo, Elsevier, 2003

3. Corrosion of Steel in Concrete, Luca Bertolini,

Bernhard Elsener, Pietro Pedeferri, Rob Polder,

WILEY-VCH, 2004

Causes of Failures

• Design deficiencies 40-60%

• Construction errors 25-30%

• Material defects 10-15%

4

• Material defects 10-15%

• Maintenance deficiencies 5-10%

Department of Structures and Materials

FACTORS INFLUENCE ABILITY TO RESIST

DETERIORATION

• Increase deterioration

� Higher temperatures

� Increased fluid velocities

� Poor compaction

• Decrease deterioration

√ Lower water-cement ratio

√ Proper cement type

� Poor curing

� Alternate wetting and drying

� Corrosion of reinforcing steel

√ Lower absorption

√ Lower permeability

INSPIRING CREATIVE AND INNOVATIVE MINDS

• Carbonation

• Sulphate attack

• Chloride attack

• Freeze and thaw

CAUSES OF DETERIORATION

• Freeze and thaw

• Alkali silica reaction

• Acid attack


• Calcium hydroxide (CH) is produced during hydration

process.

• This CH in the pores provides alkalinity to the concrete.

• When concrete comes in contact with carbon dioxide, it

reacts first with CH.

CARBONATION

reacts first with CH.

• This process reduce alkalinity and is known as

carbonation.

• Reduce alkalinity lowering the pH.

• Carbonation can occur on the surface and through the

cracks.


CARBONATION

• Carbonation is a chemical process in which carbon dioxide diffuses to the

depth of concrete element and reacts with alkaline components in the

cement paste mainly calcium hydroxide. As a result of these reactions the

carbonation products are formed and phase composition and

consequently properties of concrete are changed. Likewise, the alkalinity

of related cement paste is decreasing. of related cement paste is decreasing.

• This fact is assessed by

phenolphtalein test. In this case violet

part represents part of concrete with

higher alkalinity (pH > 9.5).


• Carbonation induced-corrosion of edge beam

CARBONATION

• Deterioration of reinforced concrete due to carbonation


• Sulfate attack can be 'external' or 'internal'.

External: due to penetration of sulfates in solution,

in groundwater for example, into the concrete from

outside.

SULPHATE ATTACK

outside.

• Internal: due to a soluble source being incorporated

into the concrete at the time of mixing, gypsum in

the aggregate, for example.


SULPHATE ATTACK

Department of Structures and Materials,

Faculty of Civil Engineering

UTM

11

• External sulfate attack– This is the more common type and typically occurs where water

containing dissolved sulfate penetrates the concrete. A fairly well-defined

reaction front can often be seen in polished sections; ahead of the front

the concrete is normal, or near normal. Behind the reaction front, the

composition and microstructure of the concrete will have changed. These

SULPHATE ATTACK

composition and microstructure of the concrete will have changed. These

changes may vary in type or severity but commonly include:

– Extensive cracking

– Expansion

– Loss of bond between the cement paste and aggregate

– Alteration of paste composition, with monosulphate phase converting

to ettringite and, in later stages, gypsum formation The necessary

additional calcium is provided by the calcium hydroxide and calcium

silicate hydrate in the cement paste


• The effect of these changes is an overall loss of concrete

strength.

• The above effects are typical of attack by solutions of

sodium sulfate or potassium sulfate.

SULPHATE ATTACK

sodium sulfate or potassium sulfate.

•


• Solutions containing magnesium sulfate are generally

more aggressive, for the same concentration.

• This is because magnesium also takes part in the

reactions, replacing calcium in the solid phases with the

formation of brucite (magnesium hydroxide) and

SULPHATE ATTACK

formation of brucite (magnesium hydroxide) and

magnesium silicate hydrates.

• The displaced calcium precipitates mainly as gypsum.


• Other sources of sulfate which can cause sulfate attack

include:

– Seawater

– Oxidation of sulfide minerals in clay adjacent to the concrete - this

can produce sulfuric acid which reacts with the concrete

SULPHATE ATTACK

can produce sulfuric acid which reacts with the concrete

– Bacterial action in sewers - anaerobic bacterial produce sulfur

dioxide which dissolves in water and then oxidizes to form sulfuric

acid

– In masonry, sulfates present in bricks and can be gradually

released over a long period of time, causing sulfate attack of

mortar, especially where sulfates are concentrated due to

moisture movement.


• Internal sulfate attack

– Occurs where a source of sulfate is incorporated into

the concrete when mixed. Examples include the use of

sulfate-rich aggregate, excess of added gypsum in the

cement or contamination. Proper screening and testing

SULPHATE ATTACK

cement or contamination. Proper screening and testing

procedures should generally avoid internal sulfate

attack.


• Two chemical reactions involved:

1. Combination of sulphate with free calcium hydroxide

liberated during the hydration of cement, to form

calcium sulphate (gypsum).

2. Combination of gypsum and hydrated calcium

SULPHATE ATTACK

2. Combination of gypsum and hydrated calcium

aluminate to form calcium sulphoaluminate

(ettringite).

• Both of these reactions result in an increase in

solid volume.

• The latter is generally blamed for most of the

expansion and disruption of concretes.


SULPHATE ATTACK


• Chloride is the most common substances that

destroy the protective passivation of steel in

concrete.

• Chloride ions which may be present in the concrete

CHLORIDE ATTACK

are from the additive used, aggregates or water.

• In service, chloride can migrate into the concrete in

the marine environment or from the exposure to de-

icing salts.


• Calcium chloride breaks down in water to form a

strong electrolyte of which the consequence of

this reaction are the reduction of the concrete

alkalinity, increase in flow of corrosion current

CHLORIDE ATTACK

alkalinity, increase in flow of corrosion current

and the final breakdown of the protective

passivating oxide film on the steel surface.

• Chlorides as free ions in solution within the pore

space are mainly responsible for increasing the

corrosion risk.


• Total chloride (approximate) ion can be measured

by determining the acid soluble chloride content.

– Removed from sample by immersion in nitric acid

• Classification for assessing the risk of corrosion

CHLORIDE ATTACK

• Classification for assessing the risk of corrosion

(BRE, UK):

– Low risk - < 0.4%

– Medium risk - 0.4% to 1.0%

– High risk - > 1.0%


CHLORIDE ATTACK

• The greatest cause of concrete deterioration in the US today is corrosion

induced by deicing or marine salts. Silica-fume concrete with a low water

content is highly resistant to penetration by chloride ions. More and more

transportation agencies are using silica fume in their concrete for

construction of new bridges or rehabilitation of existing structures.


CHLORIDE ATTACK


• Chloride attack due to salt is used for

deicing process

Chloride-induced corrosion damage


• Concrete suffers thermal shock when the

temperature fluctuates suddenly above and

below 0oC.

• This type of exposure is known as freeze-thaw

FREEZE THAW

• This type of exposure is known as freeze-thaw

cycle and causes concrete to deteriorate.

• Cracking and spalling of the surface occur when

water freezes in the pores.

• When de-icing salts are used, scaling occurs

– Concrete surface flakes or peels off


• Typical example of concrete deteriorated from

freeze thaw actions.

• Surface parallel cracks in a Danish concrete

FREEZE THAW

• Surface parallel cracks in a Danish concrete

suffering from freeze thaw damage.


Example of freeze/ thaw damage


Take 5

28


&

PROFESSOR DR MOHAMMAD BIN ISMAIL

C09-313

&

REPAIR 3

• A chemical reaction occur within the body of the

concrete between the alkali in the cement and

part of the aggregates which are reactive – Alkali-

Aggregate Reaction (AAR)

• Alkali-Silica Reaction (ASR) when the minerals are

ALKALI AGGREGATE REACTION

• Alkali-Silica Reaction (ASR) when the minerals are

derived from silica.

• For reaction to initiate and continue to cause

damage, there must be:

– Sufficient alkali in concrete

– A critical amount of the reactive aggregate

– Sufficient moisture


• The reaction is expansive.

• It results in the formation of a gel.

• It expands and exerts internal pressure

� cracks

ALKALI SILICA REACTION

� cracks

• ASR can start and stop.

– Continue until alkali or reactive aggregates are exhausted.


Stage 1:

Gel

... .....

.. . .. .. Gel

Saturated

Paste

Stage 2:

Gel Filled

microcrack

Gel Filled

microcrack

surrounded by

Gel saturated

paste

MAB 103332

Stage 3:

Stage 4:

• Alkali-silica reactivity (ASR) is an important part of the deterioration

process





• Deterioration of concrete by acid is the result of a reaction

between the acid and the calcium hydroxide of the

hydrated cement.

• The chemical reaction results in the formation of water-

soluble calcium compounds which are then leached away

ACID ATTACK

soluble calcium compounds which are then leached away

by the aqueous solution.

• Exception for oxalic and phosphoric acid.

• For sulphuric acid, accelerated due to calcium sulphate

form sulphate attack

• Causes cracking and spalling of concrete due to corrosion

of steel.


Sulphide Generation

Mechanism in

Sewer Networks

ACID ATTACK


ACID ATTACK

Department of Structures and Materials,

Faculty of Civil Engineering

UTM

37

ACID ATTACK

Corrosion of floodgate due to acidic water


• Carbonation crackscontinuous

• Sulphate attack cracksisolated

• Chloride attack cracksisolated

• Freeze and thawspalling spot

RESULTS OF DETERIORATION

• Freeze and thawspalling spot

• Alkali silica reaction cracksweb like or longitudinal

• Acid attack loose throughout surface


CORROSION OF REBAR

• As a result of the hydration reactions of cement, the pore

solution of concrete tends to be alkaline, with pH values

typically in the range 12.5-13.6.

• Under such alkaline conditions, reinforcing steel tends to

passivate and display negligible corrosion rates.


passivate and display negligible corrosion rates.

• However, due to the porous nature of concrete, corrosive

species and chemical species supporting corrosion

reactions can enter the concrete and lead to corrosion

problems.

• Furthermore, corrosive species can enter the mix if

"contaminated" mix ingredients are used (water,

aggregates, additives).

• Corrosion damage to the reinforcing steel results in the build-up

of voluminous corrosion products, generating internal stresses

and subsequent cracking and spalling of the concrete as shown

schematically in the diagram below:


• Parking Deck Delaminations

RESULTS OF CORROSION

• Ramp Delaminations

• Concrete can delaminate in layers which are most commonly

caused by the expansion created by corrosion of internal

reinforcement.




DETERIORATION OF A ROOF BEAM


CONCRETE LIFE CYCLE

CONCRETE

CEMENT

AGGREGATES

WATER


REINFORCEMENT

AGGRESSIVE ENIRONMENTS

CRACKS

CORROSIONREPAIR

DIAGNOSE

MATERIALSTECHNIQUES

DEMOLISH

TAKE 5

CONCRETE REPAIR

• Diagnosis process in determining the repair

works


• Determine what cause the damage?

– Result of poor design

– Faulty workmanship

– Mechanical abrasive action

EVALUATION OF DAMAGE

– Mechanical abrasive action

– Cavitation of erosion from hydraulic action

– Leaching

– Chemical attack

– Chemical reaction inherent in the concrete mixture

– Corrosion of embedded metal

– Lengthy exposure to an unfavourable environment


• Establish the extent of damage

• Determine if the major portion of the structure is of

suitable quality on which to build a sound repair

�Based on this information


�Based on this information

� The type

� The extent of repair


chosen

� The most difficult step of which require a thorough

knowledge of the subject and mature judgment by

the engineer.

– If damage was an inferior concrete, replacement by good

quality concrete should assure lasting results


quality concrete should assure lasting results

– But if good quality concrete was destroyed, a very superior

concrete is required


• Repair of a concrete structure


• Evaluation of causes, extend and

consequences of deterioration

• Selection of suitable repair materials

• Surface preparation

REPAIR PROCESS

• Surface preparation

• Application of repair materials

• Application of protective coating


• Determine the cause of deterioration

• Mark out on drawings the location and extend of

deterioration

• Is in the position to assess the need and urgency for repair

• Assess the options available

CAUSES, EXTEND & CONSEQUENCES

• Assess the options available

• Need to consider whether the damage will impair the

structural performance


• Many types available from cement mortar, polymer

modified mortar to polymer mortar

• Factors to consider in selecting:

– Strength and environment

SELECTION OF MATERIALS

– Strength and environment

– Compatibility

– Appearance

– Cost


• Strength and strength development important when

interruptions as a result of repairs need to be minimised

• The environment, eg. temperature and moisture can affect

the curing time, thus influence the strength development

STRENGTH & ENVIRONMENT


• The physical properties should be compatible as far as

possible to the parent concrete being repaired

– Volume change due to shrinkage or expansion

• If it is different significantly

– Loss of bond

COMPATIBILITY, APPEARANCE & COST

– Loss of bond

– Cracks may develop

• Should match with the existing concrete both colour and

texture

• Maximum cost benefit - cheapest


• Important as it determine the successfulness in achieving an

effective concrete repair

• Lack of adequate surface repair preparation have been

identified as the most reason for poor repairs

• Surface preparation entail preparing both the concrete and

SURFACE PREPARATION

• Surface preparation entail preparing both the concrete and

the steel reinforcement

• The concrete must be sound, free from loose or segregated

materials, voids and substance which could decrease the

bond between the old and new concrete


• Hammer and chiselling method mainly for small localised

areas

• Sand blasting used for cleaning large areas where thin layers

of materials like paint, coatings and surface contaminants

need to be removed

PREPARATION METHODS

need to be removed

• High pressure water jets also used for large areas, cleaning

and removing surface skin

• Apply suitable bonding aid to improve bond

– Acrylic based, polymer based and epoxy based


• The steel reinforcement need to be treated by removing all

rust or stabilised the surface by some special treatment

• Two types of system available for proptecting the steel

– Reactive resin

– Polymer modified cement

PREPARATION METHODS

– Polymer modified cement

• Derusting can be achieved by:

– Normal wire brushing for smaller areas

– Sand or grid blasting for large areas


• Patching and resurfacing

• Pressure grouting

• Sprayed concrete

• Crack repairs

APPLICATION OF REPAIR MATERIALS

• Crack repairs

– Structural

– Non-structural


• Patching refer to repairing small areas of localised damage

using mortar

• Resurfacing or reinstatement refer to the application of

mortars to large surface areas

• The damaged area is restored to the profile ot the

PATCHING & RESURFACING

• The damaged area is restored to the profile ot the

surrounding undamaged concrete


• The cement grout which are of pumpable consistency are

injected to the area enclosed in tight formwork under

pressure using a hand operated grout pump or motorised

grout pump

• The grout may consist of neat cement with an admixture or

PRESSURE GROUTING

• The grout may consist of neat cement with an admixture or

may be preblended in bags.

• For large voids to be grouted, it is advisable to include suitable

size aggregates in order to achieve better compressive

strength and also reduce shrinkage of the grout – prepacked

grouting


• Also known as shotcreting or guniting

• Most economical and fast method for large and vertical areas

– Walls, aches and soffit of slabs or decks

• Most sprayed concrete are by the dry mix process

• For good guniting works, skilled nozzleman, proper type of

SPRAYED CONCRETE

• For good guniting works, skilled nozzleman, proper type of

equipment and suitable material grading play an important

role


• Have the capacity to function as was originally intended

• The repair must provide a medium of stress transfer

across the crack section

• Pressure injection of epoxy resin is generally accepted for

repairing structural cracks

STRUCTURAL CRACK REPAIRS

repairing structural cracks

– Sealing along the cracks leaving injection ports at centres equal to

the depth of crack

– Injecting the liquid epoxy so that air, water vapour and water are

displaced

– Curing

– Removing the surface seal where aesthetics require


• Can permit ingress of contaminants that may accelerate

deterioration of steel reinforcement and concrete

• Non-structural crack may eventually become structural if not

repair

• Repair is to install a barrier to corrosive element

NON-STRUCTURAL CRACK

• Repair is to install a barrier to corrosive element

• An effective repair is to chisel a ‘V’ groove along the crack and

seal with repair mortar or grouting


• Objectives:

– To give the whole structure a uniform appearance

– To reduce the permeability of the remaining sound

concrete to ingress of:

• Oxygen

PROTECTIVE COATING

• Oxygen

• Water and aqueous solution

• Carbon dioxide


• Good penetration and adhesion

• Good resistance to UV radiation

• Good resistance to atmospheric attack

• Low permeability to water

IDEAL COATING PROPERTIES

• Low permeability to water

• High permeability to vapour

• Low permeability to CO2


Terima Kasih

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JSB FKA –UTM Deterioration and Repair

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