Advanced Repair Techniques of Concrete Structures 26 July 2012 Mundra
Ataullah Ansari
Service Ser vice life of a building What is the intended service life of a building? Monument building
100 years
RCC framed building
75 years
Load Bearing const.
50 years
Semi permanent str.
30 years
Temporary emporar y Structures Struct ures
5 years
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Service Ser vice life of a building What is the intended service life of a building? Monument building
100 years
RCC framed building
75 years
Load Bearing const.
50 years
Semi permanent str.
30 years
Temporary emporar y Structures Struct ures
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 degradation Two types • short-term measures - Maintenance activities fall under the categor y of short-term measures. • long-term measures - Rehabilitation/retrofitting/refurbishing are long-term measures
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Purpose of repair 1 To restore structural integrity
2 To arrest deterioration 3 To prevent future deterioration 4 To restore original profile
5 To restore integrity of sealed system eg. waterproofing 6 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 concrete 3. Spalling of cover concrete 4. Collapse of element / structure
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Diagnosis and Condition Analysis of Buildings Types of Common Defects • Honeycombs & Rock pockets • Surface Imperfectness Pin holes/blowholes C avities • 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 different types, methods and uses of non destructive testing.
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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 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 evaluation of •
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 1 Drying shrinkage
2 Tensile strength 3 Modulus of elasticity 4 Tensile strain capacity
5 6 7 8 9
Creep Compressive strength Low viscosity Good workability Mix ability
10 Ageing resistance
11 Higher Tensile strength increase resistance to cracking 12 Large permeability will accelerate corrosion
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Repair chemicals for specific application Application/ Purpose 1 2 3
4 5 6 7 8
Bonding aids Prepacked mortars Injection grouts for sealing cracks, pores Sealing compounds Putties Anchor grouts Chemical resistant screed Anticarbonation coating
9
Chemical resistant coatings 10 Waterproof slurries /coatings 11 Special concretes 12 Electrochemical range
Acrylics, Styrene-Butadiene rubber, epoxies Polymer modified mortars etc., Low viscosity monomers, polyurethanes, etc., Epoxies, polyurethanes, polysulphides, silicones Cement, epoxy based Polyester resin based Epoxy based Aliphatic acrylate based Epoxy polyurethane based Polymer and cement based, epoxy based Micro-concretes, epoxy concretes, latex concretes, polymer modified mortars, etc., Sacrificial zinc anodes etc.
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Repair techniques Repair Technique
Distress addressed
1
Injection Grout
To seal cracks & pores in concrete to arrest leakages
2
Guniting / Shotcreting
To replace cover concrete, to Gunite / Shotcrete and Admixtures reinstate locally damaged areas. To build up thickness in overhead areas
3
Jacketing / Encasement
To reinstate extensively damaged concrete members. To strengthen for load enhancements
4
Patch repairs
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Epoxies / Monomers Polyurethane. Cement slurry
Super plasticized concrete / Free flow micro-concrete / Self compacting Concrete Polymer modified / latex modified mortars, epoxy mortars
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Micro concrete 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, and ethylene vinyl acetate. •
Repair to damaged reinforced concrete elements like beams, columns, wall etc., where access is restricted and compaction is not possible and for structural strengthening by Jacketing of RCC columns to increase load carrying capacity are areas of application of micro concrete. •
• Ready to use dr y powder which requires only addition of clean water at site to produce a free flowing non shrink repair 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 where the 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
• 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
1 Day
20.5
21
10
3 Days
36.0
32
30
7 Days
50.0
46
40
28 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 at every 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 Zinc Primer 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 and the 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 the formwork 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
•
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 absorption
HS Carbon
High strength & stiffness
High cost
UHM Carbon
Very high stiffness
Low strength, high cost
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Benefits • • • • • • • • •
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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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 FRP Composite In Accordance to Manufacturer’s 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 Materials Should 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 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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Strengthening using Pre-Stress CFRP Laminates
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Strengthening using Pre-Stress CFRP Laminates
Anchor plate system
Prestressed Laminate
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Fixing of pre-stressing machine parts
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Fixing of pre-stressing machine parts
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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 a Commercial Complex in Navi Mumbai SEZ
Block D, Phase I Advanced repair techniques of concrete structures
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Case Study-Structural Strengthening of a Commercial Complex in Navi Mumbai SEZ
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Case Study-Structural Strengthening of a Commercial Complex in Navi Mumbai SEZ
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Case Study-Structural Strengthening of a Commercial Complex in Navi Mumbai SEZ
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Case Study-Structural Strengthening of a Commercial Complex in Navi Mumbai SEZ
Final Building after Strengthening Advanced repair techniques of concrete structures
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SPRAYED-UP GFRP STRENGTHENING FOR REINFORCED CONCRETE BEAMS Chopped 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 FOR REINFORCED CONCRETE BEAMS The 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 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 finished coat • Curing
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Application of PMM 1. Mark out the repair area 2. Break and remove the damaged concrete 3. Wet out the substrate 4. Remove corrosion deposits 5. Apply Bonding agent for old and new concrete 6. Apply Polymer mortar by hand 7. Finish the repaired area with a trowel 8. Cure the repaired area with CURING COMPOUND on completion of repairs
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