REPAIRS AND REHABILITATION
EXISTING RCC BUILDINGS
31 ST AUG.2012
CONSULTING STRUCTURAL ENGINEER.
• 1 Introduction
• 2 Causes of Deterioration and Durability
• 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
• 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
• All of us come across various types of structures.
Viz. Load bearing structures, Normal RCC
structures, Composite structures, Bridges,
Pumping stations, Reservoirs, Hospitals,stadium
• 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
• Deterioration of RCC members is natural phenomenon
and we come across such structures while working for
• Systematic approach is required in dealing with
• Civil engineer’s first duty is to give emphasis on
durability aspect during construction as well as
• 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
• 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
• Buildings remain several years without any attention.
• 1.2 Rational approach to any Repairs and
• Identification of Cause of Deterioration
• Consequent Repairs and Rehabilitation
strategy at optimum cost
• Scientific Evaluation and Solution for
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
• Step-3 Actual Execution with understanding , proper
expertise, resources for effectiveness of repairs.
2. Causes of Deterioration and durability
• 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
• 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
• 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
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
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
• Field documents
• Plans and actual observations each room-
• 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
• 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.
• Workmanship, structural serviceability, material
• 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 .
• Areas of high distress
• Cracks and their locations
• Excessive deflections
• Exposure conditions of various distressed areas.
• Moisture / seepage / leakages / dampness
• 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
• 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 )
• 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
measures 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
• 3 to 3.5 Satisfactory but loss of
• < 3 km/s Poor and loss of integrity.
• 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
• 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
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
5. Selection of repair material for
• 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
• 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.
• 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
• Compatible coefficient of thermal expansion
• Mechanical properties / Es (elastic modulus)
• Relative movement ->resilient and elastic
• Minimal or no curing
• Only epoxys do not require curing
• Alkalinity -> pH above 11.5
• Low air and water permiability –
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 /
• Mineral additives : Fly ash / silicafume / GGBS for
impermeability / resistance to leaching/ chloride
–sulphate attack on concrete and better crushing
• 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
• KRISHNA( epco
• SUNANDA (sunepoxy
• Rust remover
• Bond coat
• Shrinkage reducing
• feovert ( Krishna )
• PIDICLEAN ( PIDILITE)
• RUSTICIDE (SUNSNDA)
• Epoxy based / Acrylic
6. Rehabilitation and Retrofitting
• Decide likely a) service life b) Repair methos c)
• 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
• Strength, serviceability and durability
• Protection of stell
• Bond with parent surface
• Dimensional stability
• Resistance to environmentally induced
• Ease of application
Factors in selection of methods of
• Type and extent of repairs
• Location of distress
• Environmental exposure
• Availability of skill
• Availability of time and access for repairs
• 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
• 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
• Safety measures / Quality assurance /
• 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