Repairs and Rehabilitation of Structures

Paavai Institutions

Department of Civil Engg.

REPAIRS AND REHABILITATION OF STRUCTURES

UNIT – II

SERVISIBILITY AND DURABILITY OF CONCRETE

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Paavai Institutions

Department of Civil Engg.

CONTENTS

CHAPTER

TITLE

PAGE NO

2.1. QUALITY STRENGTH

2.2.

2.3.

2.4.

2.5.

2.6.

2.7.

2.8.

2.9.

2.1.1. Need for strengthening

CONSTRUCTION ERRORS

CRACKING

DESIGN ERRORS

CHEMICALS

2.5.1. Chemical Attack on concrete can be classified as follows

CORROSION

INFLUENCING FACTOR

CORROSION PROTECTION TECHNIQUES

METHODOLOGY FOR GROUTING OF CRACKS

2.9.1. Minor and medium cracks (crack width 0.5 mm to 5.0 mm)

2.9.2. Major crack (crack width more than 5.0 mm)

2.4

2.5

2.6

2.9

2.11

2.10. INSTALLING FERRO-CEMENT PLATES AT THE CORNERS

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TECHNICAL TERMS

1. DURABILITY OF CONCRETE: A concrete is said to be durable if it withstand the

conditions for which it has been designed, without deterioration, over a period of years.

The term durability of concrete is used to characterize in board terms the resistance of a

concrete to a variety of physical or chemical attacks due to the external causes.

2. SHRINKAGE IN CONCRETE: Shrinkage in concrete means moisture movement in

concrete. Shrinkage may be defined as the volume changes in concrete due to loss of

water or moisture due to evaporation or by hydration of cement in concrete due to loss of

water or moisture due to evaporation or by hydration of cement or by carbonation.

3. CONSTRUCTION ERRORS: Failure to follow specified procedures and good practice

or outright carelessness may lead to a number of conditions that may be grouped together

as construction errors. Typically most of these errors do not lead directly to failure or

deterioration of concrete. Instead, they enhance the adverse impacts of other mechanism.

4. CORNER REPARATION: This is a very common occurrence and appears to be due to

a component of tensile stress causing splitting across a corner. In fire tests, corner

separation most often in beams and columns made of Quartz aggregate and only

infrequently with light weight aggregates

5. EFFECTIVE COVER: The cover reinforcement up to the surface of concrete in tension

is called “Effective cover”

6. CORROSION INHIBITOR: Corrosion inhibitor is an admixture that is used in

concrete to prevent the metal embedded in concrete from corroding.

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2.1.Quality Strength:

Strengthening measures are required in structures when they are required to

accommodate increased loads.

This leads to a redistribution of forces and the need fro local reinforcement.

In addition, structural strengthening may become necessary owing to wear

deterioration arising from normal usage or environment factors.

2.1.1. Need for strengthening:

Load increases due to higher live loads, increased wheel loads, installations of

heavy machinery, or vibrations.

Damage to structural parts due to aging of construction materials or fire damage,

corrosion of the steel reinforcement, and impact of vehicles.

Improvement s in suability for use due to limitation of deflection, reduction of

stress in steel reinforcement and reduction of crack widths.

Modification of structural system due to the elimination of walls /columns and

opening cut through slabs.

Errors in planning or construction due to insufficient design dimensions and

insufficient reinforcing steel.

Failure to follow specified procedures and good practice or outright carelessness

may lead to a number of conditions that may be grouped together as construction

errors.

Typically, most of these errors do not lead directly to failure or deterioration of

concrete.

Instead, they enhance the adverse impacts of other mechanisms.

Each error will be briefly described below along with preventive methods. In

general, the best preventive measure is a thorough knowledge of these

construction errors are plus an aggressive inspection program.

2.2. Construction Errors:

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2.3. CRACKING:

Load – induced tensile stresses may result cracks tensile forces. But also be

obtaining specifying the use of reinforcing steel , not only to carry tensile forces,

but also be obtaining both an adequate crack distribution and a reasonable limit on

crack width is recommended.

Flexural and either sustained or repetitive loading. A well – distributed

reinforcing arrangement offers the best protection against undesirable cracking.

2.4. DESIGN ERRORS:

Design errors may be divided into two general type: those resulting from in adequate

structural design and those resulting from lack of attention to relatively minor design details ,

each of the two types of design errors.

· Inadequate structural design.

· Poor design details.

2.5. CHEMICALS:

This category includes several specific causes of deterioration that exhibit a wide variety

of symptoms. In general, deleterious chemical reaction reactions may be classified as those that

occur the result of external chemicals attacking the concrete (acid attack, aggressive water attack,

miscellaneous chemical attack, and sulphate attack) or those that occur s the result of internal

chemicals reactions between the constituents of the concrete.

2.5.1. Chemical Attack on concrete can be classified as follows:

· Acid attack

· Alkali attack

· Carbonation

· Chloride attack

· Leaching

· Salt attack

· Sulphate attack.

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2.6. CORROSION:

The nature of reinforcement corrosion mechanism can be attributed to three predominant

process, namely chemical electro chemical and physical.

2.7. INFLUENCING FACTOR:

The cover thickness.

The quality of concrete in the cover region, especially in terms of permeability

and diffusivity.

Environmental conditions

PH value in concrete

Chloride level in concrete and presence of cracks etc.

The problem of corrosion of reinforcement in concrete structures needs serious consideration by

the designers and constructors. It is emphasized that a good construction practice can minimize

the corrosion problem to a large extent.

2.8. CORROSION PROTECTION TECHNIQUES:

The detailed analysis of the factors that influence corrosion mechanism and process

indicates that corrosion protection requires a multiple approach. There are many possible

approaches as listed below:

· Coating to reinforcement

· Galvanized reinforcement

· Improving metallurgical by addition of certain elements.

2.9. METHODOLOGY FOR GROUTING OF CRACKS:

2.9.1. Minor and medium cracks (crack width 0.5 mm to 5.0 mm)

Material/equipment required

(i) Plastic / Aluminum nipples of 12 mm dia (30 to 40 mm long).

(ii) Non-shrink cement (shrinkomp of ACC or equivalent).

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(iii) Polyster putty or 1:3 cement sand mortar for sealing of the cracks.

(iv) Compressor for injecting the slurry

Procedure:- Fig. 1

Step-1 Remove the plaster in the vicinity of crack exposing the cracked bare masonry.

@ stone wall

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(b) Brick wall

1- Plaster

2- Plaster removed and cracks cleaned

3-Cracks sealed with mortar or putty

4- Grout ports

5- Plaster fallen to be done again

Fig. 1 - Filling grout in cracks

Step-2 Make the shape of crack in the V-shape by chiselling out.

Step-3 Fix the grouting nipples in the V-groove on the faces of the wall at spacing of 150-200

mm c/c.

Step-4 Clean the crack with the Compressed air through nipples to ensure that the fine and loose

material inside the cracked masonry has been removed.

Step-5 Seal the crack on both faces of the wall with polyester putty or cement mortar 1:3 (1-

cement: 3-coarse sand) and allowed to gain strength.

Step-6 Inject water starting with nipple fixed at higher level and moving down so that the dust

inside the cracks is washed off and masonry is saturated with water.

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Step-7 Make cement slurry with 1 : 1 (1-non shrink cement: 1-water) and start injecting from

lower most nipple till the cement slurry comes out from the next higher nipple and then move to

next higher nipple.

Step-8 After injection grouting through all the nipples is completed,

replaster the surface and finish the same.

2.9.2. Major crack (crack width more than 5.0 mm):

Material/equipment required

Plastic/Aluminum nipples of 12 mm dia ( 30 to 40 mm long)

Polyester putty or

1:3 cement-sand mortar for sealing of cracks. Non-shrink cements

(shrinkomp of ACC or equivalent). Compressor for injecting the

slurry.

Galvanized steel wire fabric (16 to 14 gauge i.e. 1.5 to 2.03mm dia wire) with 25 mm X

25 mm mesh size.

Galvanized steel. Clamping rod of 3.15 mm dia, or 5 mm dia 150 mm long wire nails

Procedure:

1. Remove the plaster in the vicinity of crack exposing the cracked bare masonry. Make the

shape of crack in the V-shape by chiseling out. Clean the crack with compressed air.

2. Fix the grouting nipples in the V-groove in both faces of the wall at spacing of 150-200

mm c/c.

3. Clean the crack with the compressed air through nipples to ensure that the fine and loose

material inside the cracked masonry has been removed.

4. Seal the crack on both the faces of the wall with polyester putty or cement mortar 1:3 (1-

cement:3-coarse sand) and allowed to gain strength.

5. Inject water starting with nipples fixed at higher level and moving down so that the dust

inside the crack is washed off and masonry is saturated with water.

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6. Make cement slurry with 1:2: W (1-non shrink cement: 2-fine sand : just enough water)

and start injecting from lower most nipple till the slurry comes out from the next higher

nipple and then move to next higher nipple.

7. After injection grouting through all the nipples is completed, replaster the surface and

finish the same.

Procedure:- Fig.2

Fig. 2 - Fixing mesh across wide cracks

1. Wide Crack

2. Wire mesh

3. Plaster on mesh

Step-1 Remove the plaster in the vicinity of crack exposing the cracked bare masonry.

Step-2 Make the shape of crack in the V-shape by chiseling out.

Step-3 Clean the crack with compressed air.

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Step-4 Fill the crack with cement mortar 1:3:W (1-non shrink cement : 3-fine sand : necessary

water) from both sides as deep as feasible.

Step-5 Provide wire mesh on both the faces of wall after removal of plaster in the region of

repair to a width of 150 mm on each side of the crack.

Step-6 Clamp the mesh with the wall using clamps or wire nails at the spacing of 300 mm c/c.

Step-7 Plaster the meshed area with cement sand mortar of 1:3, covering the mesh by a minimum

of 12 mm.

2.10.INSTALLING FERRO-CEMENT PLATES AT THE CORNERS:

Before filling the cracks as in Para 7, use galvanized weld-mesh 'g14' (2.0rrim wires

@25x25mm mash) over a length of 500-600 mm on each side of the crack both inside and

outside of the room in a depth of 300mm at windows sill on about 900 mm height above the

floor (Fig.3) and another one at lintel level or about 2 m above the floor. But if horizontal

seismic belt is to be provided at the lintel level, the second mesh is not required.

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1 - Crack Filling 2 - Connecting Corners 3- Connecting walls at T-junction 4- Weld-

Mesh or other reinforcement

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Question Bank

PART-A

1. How does a concrete structure get affected by heat?

2. Write any two tests for assessment of frost damage?

3. How can use prevent the effect of freezing and thawing in concrete?

4. How does a concrete structure get affected by heat?

5. How can you control cracks in a structure?

6. What are the determinations of permeability?

7. Name the physical causes on concrete

8. Name the chemical causes on concrete

9. What is the use of cement concrete?

10. What is meant by durable structure?

11. What are the factors influence the durability of the concrete?

12. Relate permeability and durability.

13. What is the measure of durability ?

14. What is the effect of external causes on durability of concrete?

15. What is the effect of internal causes on durability of concrete?

16. Define shrinkage in concrete.

17. Define plastic cracks.

18. Classify the chemical attack on concrete .

19. What is meant by swelling?

20. How to classify the damages in structure?

PART-B

1. Discuss the factors affecting permeability of concrete structures .

1. Define defect. explain the defects in concrete.

2. What are the defects normally observed in concrete structures? Discuss briefly their

remedies.

3. Explain clearly about the mechanism of freezing and thawing.

4. Explain in detail plastic shrinkage and drying shrinkage.

5. Write briefly the effect of fire on the properties of concrete.

6. What is sulphate attack? Explain about the causes and effects of sulphate attack.

7. Explain clearly the various stages of corrosion.

8. Explain the factors influencing corrosion of reinforcement ? explain the damages in

RC Structures due to corrosion of reinforcement.

9. What are the factors influencing corrosion of reinforcement ? explain the damages in

RC Structures due to corrosion of reinforcement.

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