adavance repair techniques of concrete structures

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Advanced Repair

Techniques of ConcreteStructures 26 July 2012

MundraAtaullah Ansari


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Service life of a building

What is the intended service life of a building?

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Monument building 100 years

RCC framed building 75 years

Load Bearing const. 50 years

Semi permanent str. 30 years

Temporary Structures 5 years

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Factors causing degradation

leakage/seepage and dampness in buildings.

Misuse use of the building/RCC member for which it is not designed.

Irregular maintenance.

Indiscriminate renovations

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Concrete durability

Concrete durability is related to:

1. The design process

2. Specification of materials

3. Workmanship

4. Environmental effects

5. Accidents

6. Repairs



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Design & Construction

Materials Selection

Concrete Mix Design Development

Advice on appropriate Construction Techniques

Site Monitoring

Preventing degradationTwo types

short-term measures - Maintenance activities fall under the category of short-term measures.

long-term measures - Rehabilitation/retrofitting/refurbishing are long-term measures



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Purpose of repair

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1 To restore structural integrity

2 To arrest deterioration3 To prevent future deterioration4 To restore original profile 5 To restore integrity of sealed system eg. waterproofing6 Aesthetic appearance



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Approach to Repair

Investigate the causes & identified the problems and understood

Consider Structural and operational requirements to select the Repair method

Selection of Repair Materials with appropriate Methodology



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Diagnosis and Condition Analysis of Buildings

Inspection

The concrete structure inspection is mostly examined by nondestructive test (NDT) methods. Partial destructive test

(PDT) methods are also adopted if needed.

Stages

1. Depassivation of reinforcement

2. Cracking of cover concrete3. Spalling of cover concrete

4. Collapse of element / structure



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Types of Common Defects

Honeycombs & Rock pockets

Surface Imperfectness Pin holes/blowholes Cavities

Cracks

Leakages

Major Defects at Vertical & Overhead Areas

Improper Coverage for Reinforcement in RCC Structures

NDT

The testing where one can test the same sample again for the properties for which it has been tested in the past.

In NDT, sample is neither destroyed nor its properties changed.

Non destructive testing (NDT) is a group of analysis techniques used to determine the properties of a material,compound or component without causing any damage to any parts of the system.

The non destructive testing process typically involves the use of sampling practices. There are several differenttypes, methods and uses of non destructive testing.

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Diagnosis and Condition Analysis of Buildings



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NDT Test

Rebound Hammer Test [IS:13311 (Part II) 1992 / ASTM C 805 (Range10 to 70)]

Ultrasonic Pulse Velocity Test [IS:13311 (Part I) 1992 / ASTM C597 (Range1.0 to 5.0km/sec)]

Cover meter Test [BS: 1881 (Part 204) (Range up to 100 mm)]

Half Cell potential Test [ASTMC-876-80 (Range (-)1mv to (-)750 mv)]

Carbonation Test [BS: 1881 (Part 201) 1986 (Range 0 60mm)]

Petrographic Examination (ASTM C856)

Moisture meter (Ref:ACI 302.2R, Section 3.3.6)

Infrared Thermography (ASTM D4788)

Half -cell potential Method for corrosion activity (ASTM C876)



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NDT Test Equipments

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Concrete moisture meter

Polarizing Microscope Corrosion analyzer



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NDT Test Equipments

Concrete Crack microscope

Infra Red Thermography

Rebound hammer



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NDT Test Equipments

Cover meter

Ultrasonic pulse velocity



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Petrographic Analyses may include an evaluationof Capillary porosity (water cement ratio)

Aggregate content, type and reactivity

Air void content and distribution

Type and amount of cement

Content of fly ash and micro -silica,

Carbonation depth

Cracks including cracks with a width of less than 0.1 mm

Surface including surface treatment etc.

Changes in the cement paste conditioned by humidity

Alkali -silica reactions and chemical conversions in the cement paste including saltwater and sulphate attacks

Casting joints

Strength estimate at point counting



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Repair material properties

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1 Drying shrinkage

2 Tensile strength3 Modulus of elasticity4 Tensile strain capacity 5 Creep6 Compressive strength7 Low viscosity8 Good workability9 Mix ability

10 Ageing resistance11 Higher Tensile strength increase resistance to cracking12 Large permeability will accelerate corrosion



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Repair chemicals for specific application

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Application/ Purpose

1 Bonding aids Acrylics, Styrene-Butadiene rubber, epoxies2 Prepacked mortars Polymer modified mortars etc.,3 Injection grouts for sealing cracks, pores Low viscosity monomers, polyurethanes, etc., 4 Sealing compounds Epoxies, polyurethanes, polysulphides, silicones5 Putties Cement, epoxy based6 Anchor grouts Polyester resin based7 Chemical resistant screed Epoxy based8 Anticarbonation coating Aliphatic acrylate based9 Chemical resistant coatings Epoxy polyurethane based10 Waterproof slurries /coatings Polymer and cement based, epoxy based11 Special concretes Micro-concretes, epoxy concretes, latex concretes,

polymer modified mortars, etc.,12 Electrochemical range Sacrificial zinc anodes etc.



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Repair techniques

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Repair Technique Distress addressed

1 Injection Grout To seal cracks & pores in concreteto arrest leakages

Epoxies / Monomers Polyurethane.Cement slurry

2 Guniting / Shotcreting To replace cover concrete, toreinstate locally damaged areas. Tobuild up thickness in overhead

areas

Gunite / Shotcrete and Admixtures

3 Jacketing / Encasement To reinstate extensively damagedconcrete members. To strengthenfor load enhancements

Super plasticized concrete / Freeflow micro-concrete / SelfcompactingConcrete

4 Patch repairs -------- Polymer modified / latex modifiedmortars, epoxy mortars



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Micro concrete

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Polymer modified concrete -Micro Concrete is most cost effective for improving the high early compressive

strength, tensile and flexural strength and reducing the brittle nature. Polymer-modified concrete or latex modified concrete such as styren-butadine, acrylic latex, polyvinyl acetate, andethylene vinyl acetate.

Repair to damaged reinforced concrete elements like beams, columns, wall etc., where access is restricted andcompaction is not possible and for structural strengthening by Jacketing of RCC columns to increase load carryingcapacity are areas of application of micro concrete.

Ready to use dry powder which requires only addition of clean water at site to produce a free flowing non shrinkrepair micro concrete. It is composed of good quality cement, properly selected aggregates & additives.

Used & designed for repairing of damaged reinforced concrete elements like columns, beams & structure wherethe areas are restricted or not easily accessible for proper placement of concrete using vibrator.

Has excellent flowability, workability & proper particle size to reach small & congested reinforcement.



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Micro concrete

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Micro concrete- Area of applications

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Micro concrete- Features & Benefits

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Used where hand applied PMM is not possible due to inaccessible & congested reinforcements Can be pumped or poured into restricted locations Flowable mortar hence does not require compaction Gaseous expansion system compensates for shrinkage & settlement plastic state Develops high initial and ultimate final strengths Offers excellent resistance to moisture ingress Makes repaired sections highly durable Contains no chloride admixture

Can be applied at 100 mm thickness at one stroke For thickness more than 100 mm, addition of pre -calculated aggregates may be required. Bonding agent: Epoxy bonding agent Formwork: 100% watertight Mixing: Mechanically, water: micro concrete 10 mm down stone aggregates Pouring Through funnel or hopper Deshuttering: sides after 24 hours and soffit after 3 days Curing:



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Properties of Micro-Concrete

Days M.C-1 M.C-2 Specified

Water /powder ratio 0.15 0.16 0.15-0.16

Flow (mm) 290 280 >250

Pot life in min 45 45 >30

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1 Day 20.5 21 10

3 Days 36.0 32 30

7 Days 50.0 46 4028 Days 64.0 54.5 50

Compressive strength



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Repair Methodology for Micro-Concrete

Provision of shear connectors: Shear connectors of 8mm diameter in holes of 14mm diameter and 75 mm deep atevery 500 mm c/c on all the faces of the beams in staggered form.

Priming of reinforcement bars: The exposed and cleaned reinforcing to be provided with a coat of Epoxy ZincPrimer such that the coated film will have a dry film thickness of 40 microns.

Provision of Epoxy based bonding agent: The mixed material must be applied before the elapse of its pot life andthe new repair mortar must be applied before the elapse of overlay time.

Formwork and shuttering: Slurry tight and strong form work shall be paced within overlay time (5 hrs)

Mixing of micro concrete: Mechanical Mixing for 3 to 5 minutes, under no circumstance hand mixing shall be done.

Pouring of micro concrete: With a suitable funnel or through a hose pipe, the mix should be poured into theformwork from one end only.

Deshuttering: Sides of the R C members: after a period of 24 hours. formwork of the soffit after 3 days.Curing: As per standard concrete practices.

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Fiber Reinforcements

Primary function:

carry load along the length of the fiber, provides strength and or stiffness in one direction

Can be oriented to provide properties in directions of primary loads

Commercially available varieties: Natural, Man-made

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Advantages and Disadvantages of Reinforcing Fibers

Fiber Type Advantages Disadvantages

E-Glass, S-Glass High strength, low cost Low stiffness, fatigue

Aramid High strength, low density Low comp. strength, high

moisture absorptionHS Carbon High strength & stiffness High cost

UHM Carbon Very high stiffness Low strength, high cost



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Light weight High strength to weight ratio Complex part geometry Compound surface shape Parts consolidation Design flexibility Low specific gravity Low thermal conductivity High dielectric strength

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Benefits



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FRP Reinforcement Of RC Columns

Advantages of Strengthening Columns with FRP Jackets:

Increased Ductility Increased Strength Low Dead Weight Reduced Construction Time Low Maintenance

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Construction Process-Application of The FRPCompositeIn Accordance to Manufacturers and Designer's Specifications

Preparation of the Concrete Surface Mixing Epoxy, Putty, etc. Under-coating with Epoxy Resin Preparation of the FRP Composite System Application of the FRP Strengthening System Over-coating with Epoxy Resin Anchorage (if recommended) Curing the FRP Material Application of Finish System

Concrete Surface Preparation: Repair of the existing concrete in accordance to:

ACI 546R- 96 Concrete Repair Guide ICRI Guideline No. 03370 Guide for Surface Preparation for the Repair of Deteriorated Concrete...

Bond Between Concrete and FRP MaterialsShould satisfy ICRI Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces

Concrete Surface Unevenness to be Less than 1 mm Concrete Corners -Minimum Radius of 30 mm

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Strengthening using Pre-Stress CFRP Laminates

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The three Carbon Fibre Laminates shall be placed at the bottom of each girder and pre-stressed.

These laminates shall have the E-modulus as 205 Gpa and design tensile strength as 1000 Mpa at 0.6 %elongation.



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Prestressed LaminateAnchor plate system



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Fixing of pre-stressing machine parts

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Slab after completion of prestressing laminates

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Slab after completion of prestressing laminates

The Flyovers on NH7 at Bangalore

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CFRP and GFRP Wrapping of Girders

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Case Study-Structural Strengthening of aCommercial Complex in Navi Mumbai SEZ

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Block D, Phase I



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Final Building after Strengthening



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SPRAYED-UP GFRP STRENGTHENING FORREINFORCED CONCRETE BEAMSChopped short fibers of carbon and glass with vinyl ester resin are sprayed in place on the concrete structures.This scheme is called Sprayed -Up FRP (Fiber Reinforced Polymer).



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SPRAYED-UP GFRP STRENGTHENING FORREINFORCED CONCRETE BEAMSThe installing procedure of the sprayed-up strengthening

Step 1. Base arrangement; Surface of concrete is polished by a disc-sander and cleaned by air.Step 2. Primer resin coating; for high adhesive between concrete and putty/resin.Step 3. Dent areas and steps on concrete surface are filled with putty and surface is sanded.Step 4. Resin coat; for better adhesion of fibers, resin is coated first by a spray gun.Step 5. Spraying; Resin and short fiber are sprayed on concrete at a same time by a spray gun. The lengths of the

carbon fiber and glass fiber are 2.0 inches and 1.5 inches, respectively.Step 6. Impregnation; Entrapped air is rolled out.



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Polymer modified mortar

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Restoration of spalled RCC by site made polymer modified mortar

SBR and Acrylic based PMM Patch repair of damaged structure Priming surface/Bonding agent - Acrylic based bonding agent Preparation of PMM: c:sand:polymer:water -1:3:0.2:0.2 Mixing Pan mixer/slow speed heavy duty drilling machine with paddle attachment Application: During tacky apply for 15 to 20 mm thick then allow it for dry and again bond coat and then finishedcoat Curing



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Application of PMM

1. Mark out the repair area2. Break and remove the damaged concrete

3. Wet out the substrate4. Remove corrosion deposits5. Apply Bonding agent for old and new concrete6. Apply Polymer mortar by hand7. Finish the repaired area with a trowel8. Cure the repaired area with CURING COMPOUND on completion of repairs



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adavance repair techniques of concrete structures

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