Introduction to Retrofitting, Needs and methodology of Retrofitting, Retrofitting techniques, Strengthening of RC members, water proof treatment and also about the effective management of old structures

1. Overview: Introduction to Retrofitting, Needs and methodology of
Retrofitting, Retrofitting techniques, Strengthening of RC members, water
proof treatment
RETROFITTING OF RC
STRUCTURAL ELEMENTS AND
REPAIR WORKS
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Presented by: DP NITHIN
M tech Structures

2. CONTENTS
 About Company
 Introduction
 Needs of Retrofitting
 Methodology of Retrofitting
 Retrofitting Techniques
 Strengthening of RC Slabs by Shotcreting
 Strengthening of Footing by encasement method
 Water proof treatment works
 Outcomes
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3. INTRODUCTION
 Retrofitting is the process of modification
of existing structural member to increase
their resistance against loading
 Rehabilitation is the process of
strengthening of damaged structure, just
to restore the original strength
 Retrofitting is the immediate solution and
also more energy efficient
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4. NEEDS OF RETROFITTING
a) If additional floors are to be added to existing building, and
building is not structural designed to take loads
b) The compressive strength and available reinforcement are not
sufficient to carry the loads as per codal provisions
c) Deterioration due to weathering action
d) Damage due to seismic force
e) Economical Considerations
f.) When revised codes are not followed in design
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5. METHODOLOGY OF RETROFITTING
Evaluation of Existing condition of
Structure
Planning and Design of
Retrofitting /Strengthening
technique
Retrofitting/Strengthening work
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6. 1. EVALUATION OF EXISTING CONDITION OF
STRUCTURES
A. Data Collection And Visual Inspection
• Period of construction
• Exposure conditions of structure
• Design and present use of the
structure
• Record of structural changes(if any)
• Record of first occurrence of
distress
• Type of distress
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7. B. Material strength.
• Type of material and its present condition can be known from visual
inspection.
• To arrive at present material strength, NDT’s are carried out
 STRENGTH TESTS
Rebound Hammer
Average Rebound
Number (MPa)
CONCRETE QUALITY
>40 Very good hard layer
30 to 40 Good layer
20 to 30 Fair
<20 Poor and delaminated
concrete
Rebound number and concrete quality as per IS 13311 (2)-
1992
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8. Fig. UPV
PULSE
VELOCITY(km/s)
CONCRETE QUALITY
>4.0 km/s Very good to excellent
3.5-4.0 km/s Good to very good, slightly
porosity may exist
3.0-3.5 km/s Satisfactory but loss of
integrity is suspected
<3.0 km/s Poor and loss of integrity
exist
Range of values of pulse velocity and concrete quality
as per IS 13311-1(1992)
Fig. Core Test
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9. DURABILITY TESTS CHEMICAL TESTS
a. Rebar locator test a. Carbonation test
b. Corrosion test b. Sulphate test
c. Chloride test
Cover meter Carbonation Test
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10. 2. PLANNING AND DESIGN OF RETROFITTING
After conducting visual inspection and data collection, detailed reports are
prepared and studied for the planning and design of strengthening technique
Retrofitting
techniques
Global
Retrofitting
Local
Retrofitting
Adding Shear wall
Adding infill
Adding Bracings
Mass reduction and
base isolation
Concrete Jacketing
Wrapping with FRP
Use of steel plates
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11. RETROFITTING TECHNIQUES:
a. Concrete Jacketing Technique
 This is also known as Section Enlargement Technique.
• Enlargement below and side of the section
- when sufficient space, headroom etc. are available.
• Enlargement above the section
-when sufficient space, headroom are not available.
 It adds more dead load to the structure.
 Long construction time.
Various types of Overlay for Section enlargement
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12. 12
Beam Jacketing
Column Jacketing

13. Properties Specification
Concrete strength 5 MPa greater than existing
Jacketing thickness Min 100mm
Ties Min 8mm
Spacing of ties Min 200mm
Longitudinal bar Min 12mm
Shear connector Min 10mm
Shear connector pull out
strength
500kg
Specification for RC Jacketing as per IS 15988-2013
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14. b. Fibre Reinforced Polymer Method
 Fibre-reinforced polymers (FRP) have been the most extensively
used for strengthening and repairing RC columns.
 Consist of high performance fibers embedded in polymer matrices
 Typical fibers utilized in FRP are
 Carbon
 Glass
 Aramid
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Carbon fibre Glass fibre

15. Properties Specification
Fibre orientation Uni-directional
Tensile strength 3800 N/mm2
Weight of fibre 450g/m2
Density of fibre 1.7g/cc
Thickness of fibre 4mm
Tensile modulus 240 x 103 N/mm2
Specification for Carbon fibre (Fabric)
The typical properties are Light weight ,High strength and non corrosive
This method is expensive when compared to other retrofitting
techniques
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16. 16
Column Wrapping (CFRP)

17. STRENGTHENING OF RC SLAB
SHOTCRETING
The process in which compressed air forces mortar/concrete through a hose and
nozzle onto a surface at high velocity
Strengthening
techniques
CFRP Laminates
Encasement/Overlay
Wet mix
Dry mix
• Small to medium
volume placements
• Limited vehicular
access
• Large volume
placements
• Sufficient vehicular
access
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18. 18
Mixing process for Shotcreting

19. Shotcreting have advantages over conventional concrete
a. Excellent bonding in nature makes the concrete layers very strong.
b. It is more economical than conventional concrete ,it requires less formwork
c. It requires small portable pots for manufacture and placement
d. The concrete can be applied by a nozzle from safe distance
Material Specifications
Cement conforming to IS 8112-1989
Fine aggregates Zone 2 and 3
Coarse aggregates 6mm down size
Mix proportion 1:2:2
w/c 0.50
Application pressure At nozzle >6 kg/cm2
At compressor point >10 kg/cm2
Technical Specification for shotcreting as per IS:9012-1978
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20. .
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Location of Distressed RC Slabs in Block 5

21. SEQUENCE OF WORK FOR STRENGTHENING RCC SLABS
USING SHOTCRETING
Step-1: Removal of loose concrete
-Existing plaster/de-bonded cover concrete shall be carefully removed upto
hard surface
-Exposed concrete surface should be cleaned thoroughly with sand
blasting and after that entire surface should be wetted by spraying water
Cracks on the slab
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22. Step 2 :Additional reinforcement
Additional rebars shall be welded wherever reduction of bar diameter encountered
Step 3: Application of anticorrosion primer to reinforcement
Apply two coats of anti-corrosive primer on the cleaned rebar surface.
Step 4: Drilling and fixing of shear connectors
14mm dia 75mm deep holes shall be drilled in slabs to fix the shear connectors and cleaned
thoroughly with air.
10mm dia shear connectors shall be fixed to drilled holes using polyester resin anchor grout
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23. Step 5: Apply of weld mesh
Proposed weld mesh (50 X 50 X 3)mm shall be fabricated and placed using shear
connectors
Step 6: Guniting with micro concrete
20mm thick for RC slab shotcreting with silica fumes to specification and followed by
10mm trimmer coats
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24. Step 7: Curing to casted surface
For imparting strength and durability, water should be sprinkled over set
concrete surface .Slabs should be cured for minimum period of 7 days
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25. Detailing of slab for shotcreting
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26. SEQUENCE OF WORK FOR STRENGTHENING RC
FOOTING BY ENCASEMENT METHOD
Step 1: Existing surface should be roughened and cleaned.
Step 2: Making groove along the length of crack
• V groove to be made along length of crack
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27. Step 3:Injection of nozzles
• 12 mm dia ,50mm deep holes at 300 mm C/C to fix nozzles(10mm dia nozzles)
• Later grouting nozzles to be cut
Step 4 : Additional reinforcement
 Before that existing surface should be cleaned with air/water jet.
 #10 shear connectors fixed @ 500 C/C to hold the proposed reinforcement.
 Proposed reinforcement # 12 @ 200 C/C .This is carried upto grade slab.
 #8 @ 200 C/C ties are used for extra reinforcement of columns.
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28. Step 5: Pouring of concrete
150mm thick M35 concrete encasement is to provided.
Step 6: Curing of concrete
After concreting curing is done for 14 days
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29. 29
Detailing of RC Footing by encasement method

30. WATERPROOFING TREATMENT BY
INJECTION METHOD
Proposed Treatment in Dormitory toilets( Block 3)
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31. PROCESS OF TREATMENT
 Nozzle was fixed between slab and beam using sealant
 The distance from one nozzle to another was kept 400mm.
 Koster 2 in 1 or Koster-KB Pure Gel was used as a chemical to fill
cracks.
 The chemical was mixed in 1:1 proportion.
 The mixed chemical was poured into injection machine and was
injected in to the cracks.
 The chemical was filled into the cracks with help of nozzle.
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32.  The chemical reacts with the moisture in cracks and forms foam.
 The mixed chemical hardens with in 6 minutes after mixing.
 The chemical is filled until the cracks is completely filled.
 The nozzle is removed after filling the cracks.
 The nozzle holes are filled with sealant.
Injecting machine
Koster 2 in 1
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33. Nozzles/Packer
Placing of Nozzles
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34. WATERPROOF TREATMENT FOR TERRACE FLOOR
WITH TPO
• Remove all debris and clean the surface of existing floor by using
water jet
• The undulated surface shall be finished with polymer modified
mortar.
• The sharp edges of the beams shall be made smooth surface by
grinding
• Provide TPO (Thermoplastic polyolefin) membrane 1.5mm to
terrace flooring
Detailing of water proof treatment for terrace slab 34

35. 35
TPO Sheets

36. REPAIR MATERIALS:
a. Micro concrete
Description Values
Mix proportion 1:1
w/c 0.55
Concrete compaction Self compacting concrete
Coarse aggregate 5-12mm
Stripping time 72 hrs
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37. b. Polymer modified mortar (PMM)
 PMM enhances workability, resistance against chemical attack and freezing
and thawing
 It makes the mix less pervious in nature
Material Description
Mix proportion 125g of polypropylene fibres per
50 kg of dry mortar
Recommended thickness Not more than 20mm
Compressive strength Not less than 35N/mm2 (7days)
Not less than 45N/mm2(28 days) 37

38. c. Latex modified cement additives for mortars/cement slurry/concrete
E.g.. SBR (Styrene butadiene rubber latex),acrylics
d. Epoxies
 Epoxy resins are well known for their strong adhesive qualities.
 It offers resistance to heat
e. Corrosion inhibitors- They are the chemicals when reacts with liquid,
decreases the corrosion rate of material.
f. Water proofing agents
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39. OUTCOMES
 Learnt about strengthening of columns, beams and slabs by RC
jacketing method.
 Learnt about strengthening of columns and beams by Fibre
Reinforced Polymer method.(CFRP method).
 Learnt about fixing the water leakage cracks without modifying
the structural elements.
 Learnt about various waterproofing methods and other repair
works.
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40. REFERENCES:
 Association of Structural Rehabilitation. Guidelines for Structural
Rehabilitation and Retrofitting, Allied Publishers 2019
 IS 13311-2 (1992): Method of non-destructive testing of concrete-
methods of test, Part 2: Rebound hammer
 IS 13311-1 (1992): Method of Non-destructive testing of concrete,
Part 1: Ultrasonic pulse velocity
 IS 15988-2013:Seismic Evaluation and Strengthening of Existing
Reinforced Concrete Buildings
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41. THANK YOU
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