REPAIRS AND REHABILITATION OF

EXISTING RCC BUILDINGS 31 ST AUG.2012

C.V.KHANDEKAR M.E.(STRCT) ROORKEE

EX-EXE.ENG.(MCGM)CONSULTING STRUCTURAL ENGINEER.

• 1 Introduction• 2 Causes of Deterioration and Durability Aspects• 3 Condition Survey and Non destructive evaluation• 4 Structural Analysis and Design• 5. Selection of Repair Materials for concrete• 6 Rehabilitation and Retrofitting Methods.• 7 Guidelines for Terms and conditions for repairs.• 8 Schedule for special Items of works.• 9 Specifications for Structural Repair work• 10 Case Study

INTRODUCTION

• MCGM is governing organization in Mumbai Area and concerned with development in Mumbai jurisdiction for more than 100 yrs. In India last 50-60 years RCC structures are being used extensively.

• All of us come across various types of structures. Viz. Load bearing structures, Normal RCC structures, Composite structures, Bridges, Pumping stations, Reservoirs, Hospitals,stadium etc.

• These structures can be considered as lifeline of city and are created with huge investment of resources. It is therefore essential to maintain them in functional condition.

• Deterioration of RCC members is natural phenomenon and we come across such structures while working for MCGM.

• Systematic approach is required in dealing with structures.• Civil engineer’s first duty is to give emphasis on durability

aspect during construction as well as maintenance.

• 1.1 Overview of Present practice and approach to problems• Understand gap between Quality Planned and Quality achieved in past ,

present.• We do take cube test but How far its significance is taken during

progress of work how far is the co-relation maintained with such results.• Construction documents have specifications and instructions but they

remain on paper sometime due to lack of understanding.• Procedures for Periodic Inspections of building and maintenance are not

followed or maintained • Budget estimates are prepared by un-experienced engineer or someone

else.• Buildings remain several years without any attention.

• 1.2 Rational approach to any Repairs and Rehabilitation works.

• Identification of Cause of Deterioration• Consequent Repairs and Rehabilitation strategy

at optimum cost• Scientific Evaluation and Solution for

Protection-Repairs, Rehabilitation, Strengthening and Retrofitting taking advancement in material science (polymers).

• 1.3 Repairs Management• Step-1 Documentation of damage.(type & extent)• Step-2 Preparation of drawings, sketches, execution

guidelines, material specifications modalities of payment etc..

• Step-3 Actual Execution with understanding , proper expertise, resources for effectiveness of repairs.

2. Causes of Deterioration and durability aspect.

• Concrete is considered as composite material that consists essentially of binding material within which are embedded particles or fragments of aggregates

• But in RCC, binding material is hydraulic cement and water.

• Concrete in RCC is subject to Chemical and Physical changes during it service life. Material remains durable but in RCC (composite structural material )do not prove durable due to various factors ( variations in production, loading conditions during service life, and subsequent attack by environmental factors.

• 2.1 Permeability of Concrete• For durability of concrete can be related with water

tightness (void less) during production.• Due to seasonal variations micro cracks are developed

cement paste and coarse aggregate or reinforcement steel. Primary mechanism thus gets formed.

• With increase of penetrability of concrete access to oxygen, CO2, acidic ions penetrate which facilitates, physical and chemical interactions as a result of which material undergoes cracking, spalling and loss of mass resulting partial loss of strength and stiffness

• For good Durability it is therefore essential to control water-cement ratio, degree of hydration, curing, Air voids due to deficient compaction, micro cracks due to loading and cyclic exposure to thermal variation.

• Porosity is related to• Capillary porosity ------ High W/C ------ Inadequate curing Air voids ------ Improper Compaction Micro cracks ------ Loading, weathering, initial care, after care, Secondary effects.

• 2.2 Aggressive deteriorating agents• Corrosion of Reinforcing Bars due to Carbonation (reduction

of alkalinity of concrete gel ), • ingress of chloride ( destroys passive layer around steel

reinforcement and initiates its corrosion) • pH less than 11 ( (desired 12.6 to 13.5)• Sulphate attack causes expansion,cracking, loss of mass and /

or disintegration.• Alkali silica Reaction – reactions of silica in aggregates cause

reaction with hydroxyl ion causing reaction leading to expansion,cracks, loss of strength, elasticity and durability.

3. Condition survey and Non destructive testing

• 3.1 Objective• It is examination of concrete for the purpose

of identifying and defining area of distress.• Identify cause of distress and sources• Assess: extent of distress due to corrosion,

fire, earthquake, any other reason• Asses residual strength of structure and

inhabitability

Stages of condition survey

• Prioritize distressed elements according to seriousness for repairs.

• a) Preliminary inspection• b) Planning• c)Visual Inspection• d) Field and laboratory testing.

• A) Preliminary inspection• History of structure from client, owner, occupants,

General public in building,• Note records, previous repairs history and expenses done

for the same.• All possible data and information.• Practical restriction and safety requirements• Extent and quantum of survey work • Time required ( survey and execution ) • Advise immediate safety measures.

• Information gathering• a. Period of construction• b. Construction details (drg,arch,structural )• c. Exposure conditions• d. Designed and present use of structure.• e. Previous changes in use• f. record of structural changes if done.• g. Record of 1st occurrence of defect.• h. Details of repairs carried out previously.• i. Previous reports etc.• J. details from owner, photographs

Planning survey

• Field documents• Plans and actual observations each room-

wise.• Previous report , advise if any and

implementation done as per report,• Grouping of structural elements ( external,

interior etc )• Exposure conditions

Classification of damage.

• G1 : No distress but cosmetic repairs• G2 : Minor repairs ( superficial repairs )• G3 : Medium repairs ( patch repairs )• G4 : Medium but principal repairs • G5 : Major repairs

• Grade for Assessment of the building : Based on the inspection and observation the distress level of the selected buildings may be categorized

• as mentioned below:

• G1 – No distress observed• G1 – Minor distress observed in few structural members, which can be

repaired under the advice of a structural engineer.• G2 – Medium distress observed in few structural members, which can be

repaired / rehabilitated including strengthening with the advice of a structural engineer

• G3 – Severe distress observed in some of the structural members, which can be rehabilitated including strengthening with the advice of a structural engineer.

• G4 – Severe distress is observed which could prove dangerous, hence evacuation at an early date is required.

Visual Inspection

• Workmanship, structural serviceability, material deterioration mechanisum

• General health( structural and non structural elements)• Preparation of estimate / bill of quantites.• Quantify extent of distress• Photographic record.• Obstructions for visual inspection to be noted.• Understanding structural system / deviations • Leakage , seepage due to inadequate drainage system• Types of cracks and its pattern• Color and texture of concrete surface (chemical attack or

disintegration by way of leaching .

Record

• Areas of high distress• Cracks and their locations• Excessive deflections• Exposure conditions of various distressed areas.• Moisture / seepage / leakages / dampness locations.• Abnormal vibrations in structure.• Algae, fungus growth, trees on structure.• Photographic record.• Areas of immediate concern

Considerations for repairs strategy.

• Identification of cause of problem.• Assessment and extent of damage.• Availability space and accessibility w.r.t.

ongoing activities in building.• propping structural members in case of major

repairs , severely damaged elements (columns etc ).

• Safety measures to avoid mishaps.

• Non destructive Evaluation tests• Field test Laboratory tests• In-situ-Concrete strength• Chemical attack• Corrosion activity• Fire damage• Structural integrity and soundness

• A : In- situ-concrete test• - rebound hammer• - Ultrasonic pulse velocity• - Windsor probe• - Pull out test : Core cutting / sampling• - Load test

• B : Chemical attack• Carbonation test• Chloride test• Sulphate test• C: Corrosion potential assessment• Cover meter ( checking cover)• Half cell potential• Resistivity meter • Permeability ( air and water )

• D: Fire damage assessment• Thermo gravimetric analysis (TGA)• Differential Thermal analysis (DTA)• X-ray diffraction (XRD)• E: Structural Integrity/ soundness• Ultrasonic pulse velocity ( discontinuities, cracks and

depth of cracks)• Radiography• Impact echo test

Preparation for Hammer test

• Hammer test• Cement type/content• Type of aggregate• Angle of inclination• Member charactaristics• Surface carbonation• Moisture condition

Rebound test :

• Avg.Rebound value Quality of concrete• -------------------------- ---------------------------• > 40 Very good• 30-40 Good• 20-30 Fair• <20 Poor / delaminated• 0 Very poor

UPV testmeasures pulse travel time across section

• Determine quality and homogeneity of concrete• Assess strength / Discontinuity in cross section• Depth of crack• Pulse velocity Quality of concrete• --------------------------------------------------------• < 4 km/s Very Good /excellent• 3.5 -4 km/s Good-very good (slight • Porosity)• 3 to 3.5 Satisfactory but loss of• integrity• < 3 km/s Poor and loss of integrity.

Chemical tests

• Carbonation test : 0.2% solution of phenolphthalein is used as pH indicator of concrete : Change in color to pink indicates no carbonation whereas no change in color indicates carbonation has taken place.

• Conclusion for testing• Generally it is combination of various aspects such

as Lower cover to steel, Permeable concrete , High chloride levels, Alternate wetting and drying need be identified during inspection.

4. Structural analysis and design

• Evidence of faulty design/ construction• Structural deterioration due to ageing • Changed use of structure for which structure

is not designed • New codal requirements

• Reserve strength in old structure.• Due to ageing• Non Consideration of reduction factor for Live

load• Excess steel reinforcement• Capacity determination of structural member

• For repaired building analysis and design one has to ensure proper linkage between old and new material used in repairs.

• Additional steel bars / fiber wrap mesh / section enlargement / external prestressing / steel plate bonding etc are used

Modeling structurewithout

compromising stability of structure.

• Existing sizes and material properties• Reduction of member sizes, changed end

conditions, sequence of construction • All geometric dimensions and material

characteristics and end conditions

• Stability check• Removal of any member change load

distribution / exceed capacity of member->• Increase effective length of compression member• Understand possible load path• Monitoring of flexural member • Emergency supports in case of sudden deflection

DISCUSSIONS

5. Selection of repair material for concrete

• Anology : repairing torn Garment with sound fiber / fabric but to give similar performance

• Essential parameters for repair materials.• Low shrinkage properties• Requisite setting / hardening properties• Good bond strength with existing sub-strate• Compatible coefficient of thermal expansion• Compatible strength and mechanical properties

with that of sub-strate

SELECTION CRITERIA

• Allow minimum movement • Minimal or no curing requirement.• Alkaline character• Low air and water permiability• Aesthetics with surroundings• Cost effectiveness• Durable / non degradable / UV resistant• Non hazardous / non pollutant.

SELECTION CRITERIA

• Low shrinkage -> less crack/ access to air / water• Setting time /hardening -> Min. time to harden and

make available space• Workability – acceptance by labor• Bond with sub-strate -> strength and structural

behavior criteria• Compatible coefficient of thermal expansion• Mechanical properties / Es (elastic modulus)• Relative movement ->resilient and elastic (bridges)

SELECTION CRITERIA

• Minimal or no curing • Only epoxys do not require curing • Alkalinity -> pH above 11.5• Low air and water permiability –

environmental attack.

Materials for repairs

• Materials for surface preparation• Chemical Rust removers for reinforcement.• Passivators for protection of reinforcement,• Bonding agents• Structural repair material• Non-structural repair material.• Injection grout• Joint sealers• Surface coatings for protection of RCC

• Premixed cement concrete mortars• (not preferred as drying shrinkage/ slow setting / low

workability / prolonged curing• Cement / Rapid hardening cement / Portland slag

cement / Pozzolana cement / • Use as per type of structure / marine/environment etc.• Mineral additives : Fly ash / silicafume / GGBS for

impermeability / resistance to leaching/ chloride –sulphate attack on concrete and better crushing strength.

• Chemical admixtures• Retarding admixtures : compatibility aspect• Water reducing admixtures: control shrinkage,

water permeability, percentage of capillary pores and strength

• Polymer modified mortar :

PRODUCTS AND MANUFACURERES

• Epoxy Based injection Grout for sealing cracks

• CICO (POXY21)• PEDILITE ( pidgroutEG2

&3)• KRISHNA( epco

kp/hp320 /slv• SUNANDA (sunepoxy

368)

• Acrylic Polymer based injection Grout

• Cico non shrink (NSPGC)

• Emcecrete (MC bouchem)

• Pidigrout 10M• Roff Hygrout

• Rust remover

• Bond coat

• Shrinkage reducing

• feovert ( Krishna )• PIDICLEAN ( PIDILITE)• RUSTICIDE (SUNSNDA)

• Epoxy based / Acrylic based

6. Rehabilitation and Retrofitting• Decide likely a) service life b) Repair methos c) repair

materials.• Repair options• Grouting and crack repairs• Patch repair• Replacement of structurally weak concrete.• Replacement of delaminated concrete• Replacement of corroded steel reinforcement• Cleaning and passivating reinforcement• Concrete and corrosion protection ( Jacketing)

• Polymer modified mortar is used on hardened concrete surface for repairing defects

• Epoxy mortar : Resin + hardener +silica sand Attains strength in short time and is abrasion resistant

and is used when it is difficult to use epoxy bonded concrete, depth of repairs is less than 40mm etc.

Shotcrete : Pneumatically applied concrete or mortar may be with fibers of steel, poly propylene with admixtures to enhance structural properties

Performance requirements

• Strength, serviceability and durability• Protection of stell• Bond with parent surface• Dimensional stability• Resistance to environmentally induced

damage.• Ease of application• Appearance.

Factors in selection of methods of repairs

• Type and extent of repairs• Location of distress• Environmental exposure• Availability of skill• Availability of time and access for repairs• Appearance• Cost

Repairs stages

• Concrete removal and Surface preparation• Fixing suitable formwork• Bonding / passivating coat and repair

application• ----------------------------------------------------

General Methods • Check for reduction in dia of bars and its location from design point of view• Check cover, prepare surface ( sand blasting) clean reinforcement , remove dust by air

blasting / low water pressure / brooming• Apply bonding coat and repair application a) Concrete replacement as per condition b) Epoxy bonded concrete ( fresh concrete +resin bond coat on hardened surface ( depth 40mm or more) may be reinforcement / shear keys etc , c) Silica Fume concrete: Portland cement with silica fumes in case High strength requirement mostly used with super plasticizers. d) Ferro cement : Using mesh + Plasticizers +polymers for sealing pores e) Plate Bonding : MS plates+ epoxy glue for bonding + Bolting. f) RCC jacketing : Composite action with old and new : ensure old concrete is good

• Foundation Rehabilitation• a ) Shoring and underpinning• b) Micro piling.• Repairs and Rehabilitation strategies • a) Reduction of load / Distress : /remove load/ replace with lightwt walls• b) Reduce number of stories.• c) Changing building use ( lower side)

Terms and conditions in repairs work execution

• Safety measures / Quality assurance / Environmental protection

• Desirable to have item rate contract• Consultant appointment / Key personnel• Time for repairs and Phasing of works

depending on site conditions. • -----------------------------------------------------------• MCGM PROCEDURE TO BE FOLLOWED

• SPECIFICATIONS for materials / execution methods / quality / measurements

Case studies

During construction

Column damage in High Rise building

High rise Building in Worali

High Rise Building : Exposed surfaces

Unauthorized Extensions in High Rise Building

Treatment in terrace ( individually )

External elements

Plumbing

Municipal School ( 1929 )

Laxmi Nagar Municipal school (1929)

Terrace

RCF buildings

•THANKS