Diagnostics approach towards

Structural repairsStructural repairs

Typical issues in RCC structures

- Corrosion- Cracking- Spalling of concreteSpalling of concrete- Leakage / seepageBulging of concrete- Bulging of concrete

- Deflection of structural members, etc.,

CRACKS indicate the beginning ofCRACKS indicate the beginning of deterioration in most cases

LEAKAGE

Can be very ugly and dangerous

SPALLINGS G

Result of neglected leakage & cracks for long time

Factors that lead to ProblemsFactors that lead to Problems Built in problems (Internal)

External Causes

Man made causes

Natural calamitiesNatural calamities

Internal CauseInternal Cause

Design issuesDesign issues Improper selection of materials

Wrong waterproofing specifications

Faulty construction methods

E t l CExternal CauseEnvironmental attack

Chlorides

Carbon dioxide

S l h tSulphates

HumidityHumidity

Man made causesChange in use of structures

Over loading

Unplanned modifications /alterationsUnplanned modifications /alterations

Poor maintenance

N t l l itiNatural calamitiesEarthquake q

Flood

Fire

C lCyclones

Typical Causes:Corrosion of rebar- Chemically active soilPollution- Pollution

- Industrial abuse (chemicals)

- High relative humidity- Environmental attack

Chloride & Co2 induced

Cracks due to corrosion …

A major problemj p

Protection reduced

Concrete becomes porous

E f CO &Entry of CO2 &

Chlorides & moisture

Co2 induced corrosion

Chloride induced corrosion

Approach to systematic repairsInspection – most important activity

must be done by a professional- Every structure requires different approach.

E.g. building structure, industrial str, jetty, li t i t k h d cooling towers, intake pump houses, dams,

bridges, etc.,All locations of distress should be noted- All locations of distress should be noted

- Original drawings, if available, should be referredreferred

Approach to systematic repairs

Cause and need identification:-What is main cause?-Why repairs?-What is the life expectancy?-What is the importance of structure?-Is the need only to patch repairs? Or any other

Unless the cause is identified and Unless the cause is identified and removed, repairs can not be

effective & complete.

Approach to repairs must beApproach to repairs must bedifferent for different structures

– River Pump House

– Jetty

– Industrial Building

NEED??- Life extension- Strengthening g g

- Increase in loads- Seismic

i- Restoration to original design values

- Protection

Diagnosis:Diagnosis:(Visual inspection + Diagnosis)

Comparison Structural engineer = Doctor

Pathological tests = NDTPathological tests = NDT

Diagnosis:NDTs are effective tools todetermine the health of concrete

TO ASSESS PERFORMANCE TO ASSESS PERFORMANCE LEVEL DURING SERVICE LEVEL DURING SERVICE LIFELIFE

PARAMETERS TO BE EVALUATEDPARAMETERS TO BE EVALUATEDa) STRENGTH (IN-SITU)b) DURABILITY PERFORMANCE

presence of internal voids/ cracks, materials likely to cause disruption

of concrete (sulphate or alkali reactive aggregates), extent or risk of reinf. aggregates), extent or risk of reinf. corrosion, chloride content, cover thickness, permeability etc.

NDT:Common NDTs areCommon NDTs are

1. Rebound hammer test2. USPV3. Half cell potential meter

Rebar locator4. Rebar locator5. Core test6. Thickness test7. Carbonation test8. Chemical analysis

NDT:Rebound hammertest- To know strength of

concrete / surface hardness

Aah….

- Range: 10 to 70 N / sqmmGuidelines: IS : 13311– Guidelines: IS : 13311 (Part 2) : 1992 & Bs 1881 : Part 202 : 19861986.

NDT:Ultrasonic Pulse Velocity Ultrasonic Pulse Velocity

Test- To know strength of concrete

P t ti R 10 t 5 - Penetration Range: 10mm to 5 m

– Guidelines: IS : 13311 (Part 1) : 1992 & BS 1881 P t 203 1986BS 1881 : Part 203 : 1986.

Ultrasonic Pulse Velocity by Cross probing (Km/Sec) Concrete quality gradingquality grading

1. Above 4.5 Excellent2. 3.5 to 4.5 Good3 3 0 to 3 5 Medium3. 3.0 to 3.5 Medium4. Below 3.0 Doubtful

NDT: Core Test - To know strength

of concrete - Core dia Range:

25 mm to 125 mm-

– Guidelines: Clause 4.8 of BS 1881; 4.8 of BS 1881; Part 120: 1983 for flatness & parallelismparallelism

NDT: Core Test

AFTER DRESSING,CAPING & CURING :THE CORE IS TESTEDIN COMPRESSIONTESTING MACHINE

NDT:Strength analysis- Based on the results of Rebound hammer,

USPV d C t t th i USPV and Core tests, the average compressive strength for concrete shall be considered.

NDT:Chemical analysisChemical analysisChloride Content:

Whenever there is chloride in concrete there is increasedrisk of corrosion of embedded metal. The higher thechloride content, or if subsequently exposed to warm moistconditions, the greater the risk of corrosion.As per IS : 456:2000, the maximum total acid solublehl id t t d K / 3 f t h ld bchloride content expressed as Kg/m3 of concrete should be

0.6 for reinforced concrete

Sulphate Content:Sulphate Content:The excessive amount of water soluble sulphates cancause expansion or disruption of concrete. The total watersoluble sulphate content of the concrete mix, expressed asp , pSO3, should not exceed 4 per cent by mass of cement inthe mix.

NDT:Chemical analysis contd..

pH of concrete sample:pH of concrete sample:The Ph of freshly prepared concrete is around12 and hence it is highly alkaline in nature.Carbonation of concrete by attack fromatmospheric carbon dioxide will result inreduction in alkalinity of the concrete, andincrease the risk of reinforcement corrosion.

NDT:Half cell Potential Meter: for corrosion

Reference Code : ASTM C –876Reference Code : ASTM C –876

Objective :To find out the probability of corrosion of steel inside concrete.

NDT:Half cell Potential Meter: GuidelinesHalf cell Potential Meter: Guidelines

HALF-CELL POTENTIAL(mV) PERCENTAGE CHANCE RELATIVE TO

COPPER/COPPER SULPHATE REFERENCE ELECTRODE

OF ACTIVE CORROSION

< -350 90%

-200 TO –350 50%

> -200 10%

NDT:b iCarbonation Test:

To find out the alkalinity of concrete

If pH is more than 10, concrete p ,turns pink when sprayed with phenolphthalein solution.

Part 2

Repair materials & techniquesCase studies Case studies.

Repairs specifications

- Based on visual inspection- NDT result- NDT result- Need - Life of repair expected Life of repair expected - Selection & evaluation of repair

materials- Budget - Limitations

Repair materials must offer …..

– Compatibility With Old Concrete– Excellent Bonding Properties Excellent Bonding Properties – Low Shrinkage– Good Strength– Dimension Stability– Crack Resistance

I bilit– Impermeability– Ease of Application– DurabilityDurability

All repair scheme must includeAll repair scheme must include

– Holistic job specificationsHolistic job specifications– Compatible materials– Cause identification & eliminationCause identification & elimination– Protective coatings– Corrosion control mechanism, ,

wherever possible – Post NDT

Common repair materials available

Rust removersBonding agents

•Latex, SBR and AcrylicEpo esin based•Epoxy resin based

Injection grouts •Cement•Cement•Low viscous epoxy•PU

Zinc rich epoxy primers for re bar

Common repair materials availableCommon repair materials available

Hand applied polymer mortars•Site modified•Ready to use 2 component•Ready to use single component high build•Ready to use single component, high build

Hand applied epoxy & polyester resin pp p y p ymortars

Fl bl lf ti i t Flowable self compacting micro concrete •Low strength to high strength

Common repair materials availableCommon repair materials available

High strength polyester resin anchor groutsg g p y gUnder water range (cement & epoxy based)Glass and Carbon fibre wrapping systemsProtective coatings• Silane Siloxane based• Solvented acrylic based• Solvented acrylic based• Water based acrylics• Aliphatic PU basedp• Aliphatic epoxy based

Repair techniques

Repairs using injections and Polymer mortarsNormal concrete jacketing Micro concrete jacketingMicro concrete jacketingFibre wrapping – glass, carbon & Aramid Carbon strips – normal, pre-stressedCarbon strips normal, pre stressedSteel plate bonding Anchor stitching E- chem repairs (sacrificial anodes)

Repair Techniques – Polymer Mortar Application

Polymer Modified Mortar is available in two types –• Site MixedSite Mixed• Pre-mixed (Single Part)

PMM i d d i h d li d PMM is very dense and is hand applied

Proper bond coat shall be used for the application Proper bond coat shall be used for the application of PMM

Repair Techniques – Polymer Mortar Application

Repair Techniques – Micro Concrete

Micro concrete is free flow, self compacting, high strength high strength

Available as pre mixed, ready to useAvailable as pre mixed, ready to use

Can be used with addition of aggregates also

Microconcrete is used for the jacketing of Microconcrete is used for the jacketing of Columns & Beams

Repair Techniques – Micro Concrete

Repair Techniques – Micro Concrete

Repair techniques – Injection Grouting

Different types of Injections are available• Cement with non shrink additive Cement with non shrink additive • Epoxy• PU

Type of material to be injected depends on the porosity and the strength requiredporosity and the strength required

Repair techniques – Injection Grouting

Repair techniques – Fibre Wrapping

Diff t t f Fib W i il blDifferent types of Fibre Wrappings are available• E- Glass Fibres• Carbon Fibres • Aramid Fibres

These fibres are available in diff. unit weights• Glass Fibres in 600 & 900 GSM• Carbon Fibres in 230 to 430 GSM

Fibres are used for the strengthening of structural members like Columns & beams

Selection of material depends on the strength requiredApplication of fibres is wet-on-wet lay up or dry-on-dry

lay up.y pFibres are used along with primer & saturant.

Repair techniques – Fibre Wrapping

Repair techniques – Carbon Laminates with PT

Carbon Laminates are available in 1.5 mm thk & 50 mm width.

Laminates are used for the strengthening of beams in Flexure

Laminates are used with or without post tensioningLaminates are used with or without post tensioning

Repair techniques – Carbon Laminates with PT

Repair techniques – Steel Plate Bonding

Steel Plate Bonding is used for the strengthening of Columnsof Columns

Repair techniques – Steel Plate Bonding

Repair techniques – Cathodic Protection

Cathodic Protection is used for the protection of structure from residual corrosionstructure from residual corrosion

Repair techniques – Cathodic Protection

Case StudyCase Study

•Scope Of Work:

»Repairs and Strengthening of Marine Structure.

Areas of Concern:

• Loss of reinforcement by corrosion due to constantLoss of reinforcement by corrosion due to constant contact with saline water.

• Spalling of concreteSpalling of concrete• Delamination of main cover of all main beams • Corrosion of steelCorrosion of steel• Cracks in many members.• Carbonation• Carbonation

Methodology adopted:• Removal of loose materials and cleaning;• Removal of rust

P idi ddi i l i f l• Providing additional reinforcement steel• Application of epoxy based bond coat between old and

new concrete;new concrete;• Protection of reinforcement by providing sacrificial

anode system • Repair of soffit beams and slabs using micro-concrete;• Application of Aliphatic acrylic based anti-carbonation

coatingcoating.

Critical aspects for repairing marine structures:

• Creation of proper access • Ethylene & LPG gas lines on the jetty• No hot work allowed during ship unloading• Special arrangements for people & material

movement Hi h f t• High safety norms

• Man power & material planning D bilit t• Durability parameters

Critical aspects for repairing marine structures:M t i l ifi ti• Material specifications

• Anti carbonation coatings are the key to long lasting repairs • Micro concrete – preferred over ordinary jacketing • Polyester resin for fast repairs to broken edges of fender

blocks • Prevention of further corrosion is the key to such repairs. y p• Trained man power required• Higher cost of mobilization. • One time planning for all manpower & materials• One time planning for all manpower & materials• Aggressive climatic conditions. • Fatigue during work.

Pre Heater BuildingMain Issues ( As per NDT report)- Honey combsHoney combs- Major cavities in concrete

U- Uneven concrete pattern - Leachingg- Spalling of concrete

Pre Heater Building

What report says – summaryC i l l i l i t f l ti• Corrosion level is alarming at few locations.

- 75 % places corrosion is less than 10% probability Concrete strength is average to good- Concrete strength is average to good

- Less cover to the main steel at several locations.Protection level to the main bar is reducing- Protection level to the main bar is reducing

- Carbonation is progressing

FIRE AFFECTED BUILDING

History:

The third floor in the Port Users’ building caught fire in2006 f h f i b d d hMay 2006 . Most of the furniture burned down. But the

concrete members of the building remained intactwithout visible distortion. Due to fire exposurepserviceability of the members was adversely affected.And it became necessary to restore strength to these

bmembers.

Diagnosis:Plaster was removed, inspection of RCC structureswas carried out.Extensive NDT was carried out to see the extend ofdamage.Rebound hammer test-Rebound hammer test

-USPV-Half cell potential meter and-Half cell potential meter and-Core test

Findings:gall beams required strengthening in flexure

& shear zones& shear zonesslab strengthening in flexurecolumns were ok required only groutingcolumns were ok, required only groutingexpansion joint was damagedoverall steel bars were in good conditionoverall steel bars were in good condition,

corrosion was within permissible limits.

Remedial measures adopted:Cementitious Grouting to the beams & slabs, location

decided based on USPV readings

Additional grouting in all visible cracks

Flexural & shear strengthening of beams by bothdirectional glass fiber (2 layers)

Additional 75 mm jacket to beams with Micro concrete

Remedial measures adopted:

Slab strengthening in flexure

Grouting of all columns and floor slab

Expansion joint treatment

Plastering & terrace waterproofing.Post NDT

Cementitious grouting:

- A hole of required size is drilled andcleaned with electric blowercleaned with electric blower

- A nipple is fixed into the hole by usingcementitious putty.

- Grout is prepared using cement andExpansive additive. This mixture is thengrouted in to the holes using lowpressure until refusal.

-

GFRP Wrapping & weld mesh fixing:

- Beam surface is cleaned of anyirregularities Cavities are filledirregularities. Cavities are filledwith Polymer modified mortar.Corners are chamfered.

- Epoxy adhesive is applied over thebeam surface. The GFRP fabric isthen stuck to this surface usingrollers to avoid air from entering.

- After sticking the fiber saturant isapplied on GFRP.

-

Micro-concrete Jacketing:

- Holes of required diameter are drilled intothe beams and shear keys of 10mmthe beams and shear keys of 10mmdiameter are anchored into the same.

- Weld mesh is then tied to the shear keys tocover the whole area of beam to bejacketed. And shuttering is fixed.

- Holes of about 50mm are drilled in the slabjust over the shuttering to facilitatepouringpouring.

- Micro-concrete is then prepared andpoured in to the shuttering.

Fresh Plastering:

- Damaged plaster isremoved completely to bereplaced by good qualityfresh plaster.

Project Highlights:More than 5500 nos grouting pointsMore than 2500 nos of shear connectorsMore than 800 sqm of fiber wrappingAlmost 110 MT of Micro concrete was usedAll the beams & slabs were jacketed through holesmade in slab.The entire job was finished in 3 monthsj

•Scope Of Work:» Repairs and Strengthening of ESRs» Repairs and Strengthening of ESRs

History:History:

-The two ESRs at Ramchandra talkies and one at Ayre road with a total capacity of 5.15 million litres provide water to almost 50% area of the Dombivli (East).

-Structural evaluation of these reservoirs by IIT Powai in 2002-03 revealed that structural rehabilitation was necessary.

Findings during evaluation

• Loss of reinforcement due to corrosion;

• Excessive spalling of concrete leading to accelerated corrosion;

• Crack in many members, mostly at beam column junctions;• Probably weak joints which may be hazardous in case of an

earthquake;earthquake;

• Through cracks in container walls leading to leakages;

• Carbonation on all the surfaces of structures

Methodology adopted:gy p• Removal of loose materials and cleaning;• Grouting of honeycombs and cracks;• Grouting of honeycombs and cracks;• Removal of rust

Pl t f dditi l t l h i d• Placement of additional steel where required;• Application of bond coat between old and

new concrete;• Building the surface of concrete with polymer

modified mortar;

Methodology adopted:gy• Application of GFRP wrap to improve the joint

ductility • Application of UV resistant protective coatings over

exposed surfaces;W i l f G d l l t fi t l l• Wrapping columns from Ground level to first level of tank for peripheral columns;

• Additional re-building of concrete sections using• Additional re-building of concrete sections using Polymer Modified Mortar;

• Increasing the cross sections of affected beams;g ;

Condition of structures at the start of the project

Top slab was broken and re-cast

Shear zone – damage

Wrapping of columns and Joint strengthening using GFRP wrapping

Wrapping of columns and Joint strengthening using GFRP wrapping

Application of protective Coatings.

•Scope Of Work:» Seismic Retrofitting of Industrial Structures» Seismic Retrofitting of Industrial Structures.

Seismic Retrofitting of Industrial Building atSeismic Retrofitting of Industrial Building at Mahad

Diagnosisg• Preliminary analysis of buildings revealed that they

have not been designed for earthquake loads as per the Indian standard available at the time. Hence seismic retrofitting measures were taken.

Scope of work:• Structural strengthening of various members to

enable total structure to withstand possible seismic loads in the regionloads in the region.

Methodology adopted:Methodology adopted:• Footing Expansion

C l J k i• Column Jacketing• Addition of shear walls• Wrapping of beams/ columns with high

strength compositesstrength composites• Structural bracing

Footing Expansion: Weak footings were gexposed and strengthened by increasing their dimensions. Bonding between old and new concrete was ensured

i h husing shear anchors.

• Footing Expansion & Column Jacketing

OriginalOriginal Columns

Jacketing

• Fiber Wrapping

Beam Wrapping for hColumn Wrapping shear

• Addition of shear walls

shear walls

• Non-metallic pre-cured fiber plate

Non-metallic pre-cured fiber plate fixed to beam for flexure

Structural Bracing