REHABILITATION AND RETROFITTING METHODS

AVINASH KUMAR GUPTA

EE TRAINING

TRAINING INSTITUTE

CCW AIR

12/04/2017

GENERAL

1.0 General• Method of repair and selection of repair

material needs consideration Assess the service life of structure based on

technical & economic evaluation.Repair of structural defect to ensure safety of

structure.Protection of the structure from further

deterioration

Objectives of Repair

2.0 Methods of Repair objective• Reinstate the structural integrity by restoring

or increasing strength & stiffness.

• Prevent the ingress of moisture, chloride, CO2 to improve durability.

• Maintaining the aesthetic/ appearance of concrete surface.

3.0 Repair options

Grouting & Crack Repair Patch Repair Replacement of structurally week concrete Replacement of spalled/ delaminated concrete. Replacement of carbonated concrete around steel bar Cleaning & depassivating the corroded steel. Concrete overlays with normal, low/ highly fluid concrete,

latex modified concrete. Jacketing Realkalisation of carbonated concrete Electro chemical removal of chloride from concrete. Water proofing/ protective coating.

4.0 Performance Requirements of Repairs System

Strength, serviceability and durability.Protection of steel.Bond with parent surface.Dimensional stabilityResistance to environmentally induced

damage.Ease of application.Appearance

5.0 Factors to be considered for selection of Repair Method

Type & extent of distress. Location of distress. Environmental exposure. Availability of skill. Availability of time & access. Appearance. Cost.

6.0 Repair Stages

Concrete Removal & surface preparation. Fixing suitable form work. Bond/ passivating coat and repair

application.

6.1 Concrete Removal & Surface Preparation

Completely expose the bar if more than half of has been exposed.

Consult structural engineer if cross section area of individual bar is reduced by 15% or more/ two adjacent bars reduced by 10% or more.

Secure the bars at design location. Sand blast the surface/ Air blast to remove

dust & debris/ low pressure water blasting/ broorming.

Repair procedure for corrosion damaged concrete

6.2 Form Work

• On vertical & overhead surface, if the repair material is likely to sag.

• Ensure no air is trapped on concreting.• Change the contour or provide vent pipes.• Secure form work with expansion anchor.• Form anchors should be pre tested for

slippage.• Preformed foam gasket or cast in place

foam, to provide a water tight seal

FORM WORK

6.3 Applying Bonding coat & Repair application

• Filling of cracks with cement/ resin based grout

• Injecting grout into a mass of dry aggregate.

• Poured concrete.• Pre packed concrete.• Dry packing.• Sprayed concrete.

7.0 Repair Methods Repairs using mortars Dry pack and Epoxy bonded dry pack Preplaced Aggregate concrete Shotcrete Concrete replacement Epoxy bonded concrete Slica fume concrete Polymer concrete system Strengthening concrete by impregnation using vacuum method Thin polymer overlays Thin epoxy overlays Resin/ polymer modified cement slurry injection Protective seal coat on the entire surface Ferrocement Plate bonding RCC Jacketing Propping & supporting Fiber wrap technique Foundation Rehabilitation (Shoring/ Under Pinning) Chemical/ electro chemical methods

7.1 Repairs using mortars7.1.1 OPC mortars• For repairing defects on exposed new concrete

surface.• Defects are small• Shall not be used for old concrete, existing

concrete if cracks extends to first layer of steel bars

• Proportion (OPC + clean sand+ water) same as parent concrete.

7.1.2. Polymer modified cement mortar

7. Repair using mortars• Repairs on exposed old hardened concrete• Thickness less than 50mm• For thicker applications, reinforcing mesh with

U nails• Polymer mixed, as specified in mortar

7.1.3. Epoxy Mortars

• Resin + hardener + sand over epoxy bonding coat over old hardened surface

• High strength & abrasion resistant, water resistant

• Can be in few mms overlays• Places wherea) Difficulty in epoxy bonded concreteb) Depth is < 40mmc) Repair area is small• In layers of 15mm. use mesh when thickness >

15 mm

7.1.4. Dry Pack & Epoxy Bonded Dry Pack

apply bond coatCement + sand (1.2.5) with just enough water to

form ball by hand Pack into placeUse suitable hard wood dowel/ hammerPlaces having small width but deeperNot to be used behind bars

DRY PACKING

7.1.5 Pre placed Aggregate concrete (PAC)

Forcing the grout into mass of clean, graded coarse aggregate densely packed in form work

Massive rebars, under water, shrinkage minimum

Grout (sand, cement, pozzolana, plasticizers, super plasticizers and air entraining agents)

Grouting from bottom Proportioning – Trial mix necessary Best pumpability Use anti wash admixture under water

Preplaced Aggregate

7.1.6 Shotcrete• Pneumatically applied concrete/ mortar

onto a surface• Dry mix/ wet mix• Jetting the mixture from nozzle at high

velocity on to the surface• Use steel fibers/ poly propylene as

specified.

Shotcrete

7.1.7 Concrete Replacement Damaged/ unacceptable concrete

greater than 0.1 m2

Depth greater than 150mm Depth greater than 25mm below bars Concrete in less than 7 days old. No bonding agent to be used

7.1.8. Epoxy Bonded Concrete

When depth of repair is greater than 40mm Fresh concrete is laid over epoxy resin bond in

existing hardened concrete Shear keys also needed + extra bars

7.1.9 Silica fume concrete Silica fume 10% by weight of cement≯ Use super plasticizers Where high strength and low permeably

in required Epoxy bonding agent for depths upto

50mm to 150mm.

7.1.10 Polymer concrete system

MMA (Methyl methacrylate) & vinyl Easter (low flowing viscosity & high strength)

Patches, over lays etc. Polymer + Inhibitors + promoters +

initiator + aggregate primer

7.1.11 Surface impregnation using vacuum Methods.

• Create vaccum• Introducing a repair material (resin of

low viscocity)• Cracks repairs upto 5 micron• Evacution of moisture• Vinyl Ester gel – sealing of joints, water

proofing (It swells in contact with water)

7.1.12 Thin polymer overlays

Improve abrasion resistance Water proofing, protective coating Less than 10 mm thickness One coat of primer One or more coats of sealent Primer (vynil ester resin), initiator &

promoter Sealant (primer + silica + TiO2 + carbon

black)

7.1.13 Thin Epoxy Overlay• Improves abrasion resistance• Water proofing• Overlays in 2 to 3mm• Resin and hardner• Requires protective coating

7.1.14 Resin/ Polymer modified cement slurry injection

7.1.15 Protective seal coat on the entire surface

Prevention of ingress of aggressive gases & liquid (Co2, H2O etc)

Polyurethene, epoxy, alkyds, chlorinated rubber, acrylic emulsions

Water based coatings are preferred over solvent based

7.1.16 Ferro Cement

Thin wall type composite total thickness 12 to 30 mm

Hydraulically cement mortar reinforced with wooven wire mesh

Plasticizers and polymers Wire mesh is nailed to parent surface Protective reinforced membrane

against the vagaries of environment Prevents seepage & leakage

7.1.17 Plate Bonding

Rehabilitation & upgradation of concrete structure

Connecting MS Plates by bolting & gluing with epoxy

Bolts are positioned during construction

PLATE BONDING

7.1.18 RCC Jacketing• Increases the size for slender columns• Composite action (Old + New)• Increases stiffness• Ensure transfer of load to new jacket• Ensure perfect bonding by shear keys &

bonding coat (Epoxy or polymer modified cement slurry)

Column strengthening Concrete jacket

7.1.19 Propping & Supporting

7.1.19 Wrap Technique• Increase the load carrying capacity Bi- directional woven fabric1. Woven fabric presoaked in epoxy applied

over prepared surface after application of epoxy primer.

2. Left to cure at ambient temperature• Subsequent layers Unidirectional E- glass fiber• Pre cut unidirectional E- glass fibre

wrapped over epoxy primer• Excellent barrier to corrosive agents

7.1.18 Foundation Rehabilitation Methods

A. Shoring Raking shores Flying shores Dead shores

RAKING SHORE

Flying Shoring

Dead Shoring

Foundation Rehabilitation

B. Underpinning Underpinning piles Micropiles Proprietary jacked piles Injection of the ground with cement/

chemicals

Underpinning Pile

Micro Pile

Jacked Pile

8.0 Repair/ Rehabilitation Strategies

• Reduction of dead/ line loads• Repair/ strengthening of columns, beams

and slabs• Improving the compressive strength of

concrete• Attending to cracks and joints• Improving masonry structure to resist

earthquake forces• Providing protective cover against the

aggressive deteriorating chemicals.

9.0 Stress Reduction• Reducing of dead/ live loads• Replacing heavy solid partitions with

light weight partitions• Enlarging openings by removing filler

walls• Reducing number of stories• Changing the building use• Span reduction of beam by props