Inspection, Repair and strengthening of PSC girder.

1. INSPECTION, REPAIR AND STRENGTHENING
OF
PSC BRIDGES
-Presented By
Mohammed Faiz
XEN(B&F) MMR

2. What is Pre Stressing ?
PP
It is intentional application of a predetermined force on a
system for resisting the internal stresses due to external loads.

3. Thus PSC…….
…is the special reinforced concrete which
makes use of the intrinsic properties of steel
and concrete together,
i.e. CONCRETE is good in compression where
as STEEL is in tension.

4. Types of Pre-stressing
Mainly two types of pre-stressing
1. Post Tensioning.
2. Pre Tensioning.

5. What is Prestressed Concrete ?

6. Now coming Toward Flaws…

7. Chemical Action
Chemical attack results in volume change,
cracking and consequent deterioration of
concrete.
Types of Chemical attack
• Carbonation.
• Alkali aggregate reaction.
• Sulphate attack.
• Chloride

8. Carbonation of Concrete
• The diffusion of atmospheric CO2 in the
gaseous phase of the concrete pores leads to
formation of calcium carbonates.
– Reaction of CO2 with dissolved Ca(OH)2 in the
pore water forms calcium Carbonates.
• Nearly 1mm carbonation is reported per year
in normal M-20 grade of concrete.

9. Carbonation of Concrete
Ca(OH)2 + 2CO3 > CaCO3 + 2H2O
3CaO.2SiO2.3H2O + 3CO2 > 3CaCO3.2SiO2.3H2O
• The pH-value decreases to less than 9, which normally is insufficient
to protect the reinforcement against corrosion.

10. Corrosion of Concrete-Carbonation
Highest rate of carbonation occurs at relative humidity between 50 and 70 percent.

11. Depth of Carbonation – Strength of
Concrete

12. Alkali Aggregate Reaction(AAR)
• Cause: Alkali from cement ,reacts with reactive
silicates (of aggregates) to form alkali-silica gel of
unlimited swelling.
• This manifests into cracking and bulging of
concrete.
• Crack width can range from 0.1mm to as much as
10mm.
• Probable Locations
– Damp area, shows gel type or dried resin type deposit
in cracks
– Reactive silicates and carbonates in aggregates reacting
with Alkali in cement
• Time of Appearance
– More than five years

13. Alkali Aggregate Reaction

14. Sulphate Attack
• In hardened concrete , Calcium Aluminate hydrate(C-
A-H) can react with Sulphate salt from outside soil,
product of reaction is calcium sulphoaluminate ,which
can cause increase in volume upto 227%.
• Use low C3A cement, Portland Blast Furnace Slag
cement
• After two years or so
Calcium Aluminate Hydrate + CaSO4.2H2O ->
3CaO.Al2O3.CaSO4.32H2O (ettringite) + expansion

15. Chlorides in Concrete
• Chlorides in concrete increases risk of corrosion of steel.
• To minimize the chances of corrosion ,levels of chlorides in
concrete should be limited.
• Chlorides in cement to be less than 0.05% max for prestressed
works.
• Sources
– Mix Water
– Aggregates
– Admixtures (Accelerators)
– Curing water
– Surrounding soil
– Sea water

16. Deterioration in Concrete
REBAR CORROSIONSPALLING

17. Corrosion
• Corrosion is an electro-chemical process
• Iron reacts as
Fe >> Fe++ + 2e- (Anode process)
• Water takes oxygen from Atmosphere
2H2O + O2 + 4e- >>> 4 OH- (Cathode Process)
• Fe++ and OH- creates Fe(OH)2
• Fe(OH)2 is not stable, oxidizes to form Fe(OH)3
• Takes water to form Fe(OH).3nH2O (Rust)

18. 1 2 3 4 5 6
Fe
Fe(OH)2
Fe3O4
Fe(OH)3
Fe(OH)3nH2O
Volume

19. Corrosion of Steel
• Probable Area
– Natural and slow, fast if CaCl is present
• Probable Locations
– Alternate drying and wetting, humidity
• Cause
– Lack of cover and dampness, Carbonation, Chlorides
– Poor quality concrete
• Remedy
– Use dense concrete (Portland Blast Furnace Slag cement), Dehumidify,
Cathode protection
• Time of Appearance
– More than two years

20. What to see ?

21. • Cracks
• Texture of Concrete
– Wear and Erosion of concrete
– Leaching of chemicals
– Stains such as corrosion in steel, dampness,
growth of algae, marine microbes.
– Painting coat condition
• Bearings
• Camber
• Other observations

22. Cracks?
• Cracks identification
– Length
– Size
– Orientation
– Location
– Breathing of not
– Accompanying stains

23. Cracks?
• Cracks need to be analysed and then only
conclusions may be drawn
• All cracks lead to durability problems
• Some cracks are not serious
– Require only covering
• Other cracks are serious
– Affect load carrying capacity
– Require retro-fitment as well as covering to
prevent corrosion

24. Cracks in Hardened Concrete
During Service

25. Compatible Cracks
• Cracks which occur in course of normal loading in RCC
components for reinforcement to take the tensile stresses.
Specified in Para10.2.1 (a) of CBC.
Environment Design Crack Width (mm)
Moderate 0.20
Severe 0.10
Extreme 0.10*
REINFORCED CONCRETE BEAM UNDER LOAD

26. Crack in the deck slab
Location Reason
Bottom surface
of the deck slab
in the middle
Compatibility cracks
Excessive load on
the deck

27. STRUCTURAL CRACKS
PSC Girders

28. What to inspect in concrete bridges –PSC girders
• All the items what are there in the small
spans
• In addition
– Items related to pre-stressing (post tensioning)
and Anchorage Zone
– Slab, diaphragms, Junctions of cast in situ and
precast units or RCC/PSC
– Inside of the Box girder
– Bearings and Expansion arrangements

29. PSC Box
Location Reason
Perpendicular to
girder on the lower
surface of the girder
Shortage of Pre-stressing
force
Excessive Load
Breakage of PSC strand

30. Structural Cracks

31. PSC Box
Location Reason
Perpendicular to
girder on the upper
surface of the girder
Overstressing of girder
Shortage of loading
Closes during passage of
train

32. PSC Box
Location Reason
Diagonal Cracks
near the support
Shear stress due to
loading
Drying Shrinkage

33. Structural Cracks

34. Anchorage Zone
•Maximum stresses
during stressing
operation
•Concrete strength
increases with age
•Losses in Pre-stress
increases with time
•So, in no case there
can be distress after
the initial period
•If there is some
cracking it has to be
from the time of
construction

36. Bursting Cracks in anchorage area

37. Location Reason
At the interface of
the precast I – Girder
and the diaphragm as
well as deck slab
Differential shrinkage
between the elements
cast at different time
Mishandling during lifting
Diaphragm and
cast-in-situ
deck or PSC

38. Structural crack in diaphragm

39. Crack at the junction of web and the slab
Location Reason
At the junction
of the web and
the slab
Construction joint, no crack
Relative movement due to
shear between the box and
slab

40. Structural Crack over bearing

41. Poor expansion arrangements
• If the girder not free to expand, stresses will
build up.
• Can cause cracks near the expansion
arrangement
• Choking by ballast in the expansion joint will
also cause problems

42. Cracks due to detailing defects

43. Horizontal crack in the web

44. Cracks – Summary
• Locations subject to excess wear and tear
• Locations exposed to the atmospheric corrosion
• Locations critical from the loading point of view
– Maximum shear location
– Maximum bending location
– Point of Inflection (Zero shear location)
– End anchorage zone for PSC

45. Cracks – Summary
• Bottom Flange
• Top Flange
• Construction Joints
• Junction of Cast in situ slab and precast beams
• End Anchorage zone
• Bearings
• Girder area in contact with bearing

46. Cracks – Summary
• Bed blocks/ pedestals supporting the bearing
• Expansion joints
• Wearing Coat
• Diaphragms/ Cross girders connection
• Web of Girder
– Along Prestressing cables
– In end quarter span

47. Now…Coming 2 Inspection

48. Inspection Includes
• Going to the bridge.
• Seeing the bridge with an eye of the Doctor
(Engineer) with unaided as well as an aided
eye.
• Systematic observation over a period of time.
• Check for Camber.

49. Objectives of Inspection
• To know whether the bridge is structurally safe
• Will it continue to be safe
• Identify actual and potential sources of trouble at earliest
possible stage
• To record systematically and periodically the state of
the structure
• To decide about the repair measures to be taken
• To provide feedback to the designer and the
construction engineers on those features which give
maintenance problems

50. Planning of Inspection
• When to inspect?
• How to inspect?
• Whom to take along for inspection?
• What to take along for inspection?
• What to inspect?

51. When to inspect?
• Bridges over water – times of low water
• Bridges requiring high climbing – winds or
extreme temperatures are not likely
• Bridges suspected of having trouble on
account of thermal movement during thermal
extremes

52. How to inspect?
• Decide number of spans to be inspected each day
• Scrutinize the previous years inspection notes
• Try to have plan, drawings and other details of
the important bridges
• Go through the drawings (important bridges to
identify critical locations)
• Plan any special inspection equipment,
temporary staging etc. (like tunnel inspection)
• Don’t rush to complete – done once a year

53. Inspections – Open Line
• Para 1101 SE (Works) will inspect before
monsoon every year.
• Para 1103 AEN open line will inspect after
monsoon every year.
• Para 1104 (1)(a) Important bridges and
bridges that call attention by DEN/SrDEN

54. Inspection- Bridge Organization
• Para 1102 SSE (Br) will inspect all RCC, PSC and
Composite girders within one year of
installation.
• Para 1102 SSE (Br) will inspect all these girders
once in five years on planned basis.
• SSE (Br) will measure camber of PSC girders
once a year with any reliable method.
• Para 1105 AEN (Br) shall test check 10% of the
bridges inspected by the bridge inspector.

55. Special Inspection (Need based)
• When signs of weaknesses discovered during
routine or detailed inspection or by any other
observation.
• When the bridge loading is to be increased
due to revised or increased loading standard.
• Distressed bridges.
• Exceptional events like fire, earthquake, heavy
floods etc

56. What to take along? (Anne. 11/15 of IRBM)
1. Pocket tape (3 or 5 m long)
2. Chipping hammer
3. Plumb bob
4. Straight edge (at least 2 m long)
5. 30 meter steel tape
6. A set of feeler gauges (0.1 to 5 mm)
7. Log line with 20 kg lead ball
8. Thermometer
9. Probing rod
10. Wire brush
11. Mirror ( 10x15 cm)
12. Magnifying glass (100 mm dia.)
13. Chalk/water poof pencil/pen or
paint
14. Centre punch
15. Callipers (inside and outside)
16. Torch light (5 cell)
17. Paint and paint brush for repainting
areas damaged during inspection
18. Gauge-cum-level
19. Piano wire
20. 15 cm steel scale
21. Inspection hammer (350-450 gm)
22. Microscope
23. Binoculars
24. Camera
25. Crack meter
26. And common sense

57. • Work through a checklist prepared for the
particular type of structure.
• Should be familiar with the details of the
structure and as to how it is intended to function.
• Should study previous reports before conducting
inspection, so that the condition of the defects
noticed earlier could be checked.
• Should be aware of rectification work done
earlier, the same should be inspected and its
performance should be recorded.
What to Inspect … but before that

58. …and the most important
..thing is to know and realize that every
deterioration has a cause and the aim of
inspecting official is to determine that cause

59. Purpose
• Whether there is any defect in structure?
• If yes, what is the degree of the defect?
– Is it progressing?
– Is it affecting the function of the structure?
• Is there any change in the environment?
– Heavy rains.
– Other factors like trespassing and other usage
• Is it going to affect the train operation?
• Is there a necessity of doing preventive work?
• Does it require detailed inspection?
Routine Inspection by AEN

60. NDT

61. Non Destructive Testing
1. Rebound Hammer Test- RH Test.
2. Ultrasonic Pulse Velocity- UPV Test.
3. Core Extraction for Compressive Strength
Test.
4. Pull out Resistance Test.
5. Rebar Detector and Cover Meter Test.
6. Pull off Resistance Test.

62. 1. Rebound Hammer Test- RH Test.

63. 2.Ultrasonic Pulse Velocity- UPV Test
UPV Test being perform on Minor Bridge
Pier on NH-11 at Dausa (Raj.), India
UPV Test being perform on Deck Slab of
Flyover on NH-2 at Firozabad (U.P.), India

64. UVP-TEST

65. 3. Core Extraction for Compressive Strength
Test.
Portable Concrete Coring Machine
(BOSCH) in Horizontal Operation.
Concrete Core from RCC Column being
Extracted after Diamond Bit Core Drilling

66. 4.PULL OUT RESISTANCE TEST

67. 5.REBAR DETECTOR AND COVER
METER TEST

68. 6.PULL 0FF RESISTANCE TEST

69. Repair Methodology

70. METHODS OF REPAIR
1. Mortar-fill method.
2. Grouting.
a) Cement
b) Epoxy
3. Shotcrete and Gunite.
4. Epoxy Mortar.
5. FRP (Fibre Reinforced Concrete)

71. 1. MORTAR-FILLED METHOD
• For deep and narrow cavities (depth greater
than least surface dimension) like grout insert
holes
• 1:3 cement, fine sand
• Add white cement to match color
• Water enough so as to be moulded as ball
with slight hand pressure and water does not
exude
• Wet surface, put 1:1 cement sand slurry, apply
mortar with wooden tools.

72. 2. Grouting
• LIVE CRACK
– Pressure injection with flexible filler
– CONBEXTRA UR63 by FOSROC
• Dormant Cracks
– Pressure Injection with rigid filler
– CONBEXTRA EPLV by FOSROC

73. a). Cement Pressure grouting
• Material
• Ordinary Portland cement as per IS 269.
• Admixture with approval of Div. Engineer.
• Proportion
• w/c ratio 0.4 to 0.5
• Pressure for grouting
• 3 to 4 kg per sq cm

74. b). Epoxy Grouting
• Epoxy System
– Resin and hardener.
– Filler ( dry silica flour) for wider cracks.
• Manufacturer’s Specification
– Condition of application
– Proportions
– Pot life
– Application procedure

75. Epoxy Grouting
– Area to be grouted should be dry, clean with air jet
– Crack to be preferably dry
– All cracks to be cut open to a V groove, 10mm deep
– Drilling , cleaning loose material and sealing the groove
– Hole of 7-10mm dia drilled and grout nipples fixed.
– Full penetration doubtful if cracks > 0.6 m deep – ports on
both side
– Members < 0.3 m , ports on one side only
– First / last port to be at or near bottom / top

76. Epoxy Grouting
Precautions
• Follow manufactures’ instructions
• Direct skin contact should be avoided
• The grease gun syringe should be washed with
acetone immediately after use.

77. 3. Shotcrete and Gunite
• Shotcrete
Pneumatically applied cement concrete.
• Gunite
Pneumatically applied cement mortar.
Are suitable for restoration of concrete and for
strengthening and jacketing of various structural
elements.
• Shotcreting in multiple layer requires that the
preceding layer achieves a sufficient degree of
hardness prior to shooting on next layer.
• Nominal Reinforcement may be required for
thickness layer than 50mm.

78. Shotcrete and Gunite As per IS 9012

79. Shotcrete and Gunite Processes
Dry mix process
– Cement and moist sand
are mixed fed.
– Mixture is carried by
compressed air
– Mixing water is added
at nozzle under
pressure
– Mortar jets out at
nozzle at high velocity
Wet process
– All ingredients including
water are mixed before
delivery.
– Mixture is forced into
delivery hose and
conveyed by compressed
air.
– Additional air injected at
nozzle to increase velocity.

80. Shotcrete and Gunite/ Characteristics
• Low water cement ratio.
• Dense due to high impact velocity.
• Superior bonding.
• Simple equipment.
• No formwork, can take special shapes.
• Good abrasion resistant.
• Tolerance for thickness as per IS is (-) 3 mm to
+ 8 mm.

81. Epoxy Mortar

82. Fibre Reinforced plastics
• Composite Materials consist of High Strength
Fibre immersed in a structural Matrix Such as
Epoxy or other durable Resin.
Beam strengthened with Fibre Reinforced Concrete.

84. Reference
• RDSO Report, BS 48 of 2002 deals with
inspection, maintenance and rehabilitation of
concrete bridges.
• As per IRBM 1998.
• Inspection, Repair, Strengthening, Testing &
Load Capacity Evaluation, by Dr. V.K Raina.
• IRS Concrete Bridge Code : 1997.