nscet e-learning presentation 5/5.pdfrepair of structures distressed due to corrosion fire ......

NSCET E-LEARNING

PRESENTATION

• LISTEN … LEARN… LEAD…

Department of Civil Engineering, NSCET, Theni 1

DEPARTMENT OF CIVIL ENGINEERING

• Ms.G.SUGILA DEVI.,M.E.,F.I.V.,MISTE.,

• Assistant.Professor

• Nadar Saraswathi College of Engineering & Technology,

• Vadapudupatti, Annanji (po), Theni – 625531.

SUBJECT CODE :CE6021

SUBJECT NAME :REPAIR AND REHABILITATIONS OF STRUCTURES

IVth YEAR / VIIIth SEMESTER

PHOTO


UNIT V

REPAIR, REHABILITATION AND RETROFITTING OF STRUCTURES

❑ STRENGTHENING OF STRUCTURAL ELEMENTS

❑ REPAIR OF STRUCTURES DISTRESSED DUE TO CORROSION

❑ FIRE

❑ LEAKAGE

❑ EARTHQUAKE

❑ DEMOLITION TECHNIQUES

❑ ENGINEERED DEMOLITION METHODS

❑ CASE STUDIES.


❑STRENGTHENING OF STRUCTURAL ELEMENTS


5Department of Civil Engineering, NSCET, Theni

• Enlargement: Enlargement is the placement of additional concrete and reinforcing steel on an existing

structural member. Beams, slabs, columns, and walls, if necessary, can be enlarged to add stiffness or

load- carrying capacity.

• Example: Jacketing

•

• Composite Construction: Composite construction is a method wherein materials other than concrete are

placed in concert with an existing concrete member to add stiffness or load carrying capacity. Steel is the

most common material used in this technique. Steel plates and structural shapes can be fabricated to meet

almost any configuration requirement. Load transfer in the composite member is accomplished by the use

of adhesives, grouts, and mechanical anchorage systems.


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Post-Tensioning: Post-tensioning is a technique used to prestress reinforced concrete. The tensioning

provides the member with an immediate and active load-carrying capability. Placement of the tension

components can be achieved either internally within the member or externally to the member.

Tension components are generally steel plates, rods, tendons or strands. Tension is imparted to the

components by jacking or, less commonly, by preheating. Post-tensioning enhances a member's

ability to relieve overstressed conditions in tension, shear, bending, and torsion. The post-tensioning

technique can also be used to eliminate unwanted displacements in members and to turn

discontinuous members into continuous members.

Department of Civil Engineering, NSCET, Theni

• Stress Reduction: Stress reduction is a technique that reduces stress in a member or structure. Some of the more common methods of stress reduction include cutting new expansion joints, jacking displaced structures, and installing isolation bearings. Other more radical techniques involve the removal of portions of structures.


12

Internal Grouting: Internal grouting is the placement of a flowable material into an unwanted

discontinuity, such as a crack within the concrete member. The flowable material, upon reaching the

discontinuity, will solidify and assume necessary structural properties. Internal grouting is used to

repair fractured, honeycombed, or voided concrete placements. The most common materials used for

internal grouting are polymers and hydraulic cement-based materials.


• External Grouting: External grouting is the placement of a pumpable material outside the structure, generally within the surrounding foundation soils or at the interface between the structure and the soil. The grouting materials can be used either to provide necessary load transfer between the structure and soil, or to displace unwanted settlement. Most materials used for external grouting include cement-based mixtures. Pavement subsealing (slab stabilization) is a specialized external grouting technique used to fill small voids beneath the slab and/or stabilized base that have been caused by pumping action.


• Beam Shear Strengthening•

• Beam shear capacity can be increased by using various strengthening techniques, including:•

• external post-tensioning•

• internal post-tensioning•

• internal mild steel reinforcement•

• bonded steel members•

• enlarging member's cross-section


• Internally Placed Passive Shear Strengthening

• Strengthening of existing members to increase their shear capacity can be performed by adding shear

reinforcement. For example, the use of mild reinforcement dowels inserted perpendicular to the direction

of shear cracking, into drilled holes. The dowels are then grouted into place with epoxy.


17

Beam Shear Capacity Strengthening at Moving Hinge

If a significant thermal gradient exists, in combination with insufficient tensile capacity in the bottom of the member, a

hinge may form. Hinges may occur randomly in newly formed cracks, or may form in construction joints near the

columns. Hinges open and close with daily temperature changes.

Cracks can be a cause for structural concern, since they sometimes identify insufficient shear capacity. When

strengthening the member by repairing cracks, consideration must be given to the need for providing movement of the

hinge. Generally any repair of a moving crack by bonding it with epoxy will fail.


18

An effective method: the installation demonstrates how to strengthen a cracked beam with a post-tensioned shear clamp and a teflon slide bearing allowing for hinge movement


• Shear Transfer Strengthening between members•• Dowel Shear Device

• Drilled Hole Shear Transfer Device

• Grouted Subgrade

• Cantilever Shear Arm


20

Fig. Dowel Shear Device


21

Fig. Drilled Hole Shear Transfer Device


22

Fig. Grouted Subgrade


23

Cantilevered Shear Arm


24

STRESS REDUCTION TECHNIQUES

Installing New Expansion Joint: Overstressing in members and structures can be repaired utilizing stress

reduction techniques. Stress can be reduced by either reducing the load applied to the structure, or by modifying

the behaviour of the structure.


26

Lateral Ground Movement Isolation (Seismic Isolation)


27

COLUMN STRENGTHENING

• Compressive Strengthening by Enlargement (Jacketing)

• Shear Capacity Strengthening using Shear Collars

• Beam-column Moment Capacity Strengthening

• Confinement Strengthening

Jacketing: Section Enlargement

Enlarging the cross section of an existing column will strengthen the column by increasing its load

carrying capacity. This is called Jacketing.


❑FIRE


FIRES AS A CAUSE OF CONCRETE DETERIORATION

1


Presentation outline• Introduction to the subject

• What is the causes of fire?

• Physical and chemical response to fire

• Spalling of concrete

• Factors influencing the explosive spalling

• How to improve the concrete structures in the fire resistance?

• Case study - Concrete structure subjected to a fire in U.A.E

• Rehabilitation methods and the repairing plan

• Recommendation and conclusions


Introduction to the subject

• The main causes of the concrete structures

deterioration can be classified into three

categories which are mechanical, chemical and

physical causes.

• The fires are considered as one of the physical

causes of the concrete deterioration.

Concrete Deterioration

Physical Causes

Chemical Causes

Mechanical Causes


Introduction to the subject

• The concrete as a building material has a very good

behavior when it exposed to fire, especially when it

is compared to any others building materials like

wood and steel.

• But this is not mean that the concrete has infinite fire

resistance, in some levels of fires when the concrete

exposed to high temperature up to 900oc, significant

changes in the mechanical properties of the structural

elements like stiffness and strength will be occur.


What is the causes of fires?

Oxygen

Combust-ible

Materials

Fire

Fire Source

Fire Triangle

• For a fire to start there are three elements should be

present, oxygen, combustible materials and a fire source.

These three elements represent what is called the fire

triangle.


Fire Development


Physical and chemical response to fire



• 100 to 140°C - Evaporation of the free water inside the concrete mix.

• 300°C - The cement paste will start to shrink due to water evaporation and the aggregate

will expand. This will cause which is called the spalling of concrete.

• 400 to 600°C - the calcium hydroxide in the cement paste breaks to calcium oxide and

water. The resultant water from the chemical reaction, start to evaporate. This will cause a

significant reduction in the concrete strength.

• Starting from 550°C - the aggregate in the concrete will start to decompose causing

significant loss in the concrete strength.



• This reaction may vary based on the aggregate type and the different thermal

expansion between the cement matrix and the aggregate.

• The cooling operation after the fire, cause also physical and chemical reactions in

the concrete such as cracks, moisture absorption and rehydration of the calcium

oxide.

• All these chemical and physical reactions in both heating and cooling are

depending on the cement type, admixture, the aggregate type and the

interaction between the concrete mix materials. For example the using of

thermally stable aggregate of low thermal expansion like basalt and granite and

the using of supplementary cementitious materials like blast furnace slag, this can

improve significantly the concrete fire resistance.


Spalling of concrete

The spalling of concrete is the breaking and splitting of

the concrete elements surface layers due to high thermal

exposure. The spalling can be classified to three types.

A. Aggregate spalling is caused by the failure and the

splitting of the small aggregate pieces which are close

to the surface of the structural elements.

B. Corner & surface spalling which is the falling of

large corner pieces of the concrete due to tensile

cracks. and this type of spalling usually happen in the

decay stage.


Spalling of concrete

C. Explosive spalling, the ejection of concrete pieces from

the heated surface at high temperature. Explosive

spalling is the most dangerous type of all the types of

concrete spalling and it may cause the collapse of the

building.

Generally spalling cause a reduction in the structural

elements cross section and causing higher stress in the

remaining area of concrete. For example if the spalling

happened to the concrete column, the column may collapse

due to the increasing in the compressive stresses on the

remaining concrete section or may collapse due to buckling.


Factors influencing the explosive spalling

1. Heating Rate, the probability of explosive

spalling to occur increasing with the

increasing of the heating rate.

2. The exposure of the element to the fire, the

more faces of structural elements are exposed

to fire, the probability of the spalling to occur

increased. For example, slabs have better

resistance than the beams this because there

is only one face of the slabs are exposed to

fire unlike beams 3 faces exposed to fire.



3. Moisture content, generally the explosive spalling occur to the concrete with moisture contents

less than 3% by weight. However, the spalling in the high strength concrete can occur in lower

moisture contents 2.3 to 3% by weight. This is because of the low porosity and permeability,

making it more difficult for the moisture to escape. This is generate higher pore pressure and

internal tensile stresses, increasing the risk of spalling.

4. Age of concrete structure, most of the research papers indicate that the probability of the

concrete spalling decrease with the increasing of the structure age. This is because when the

concrete structure age increase, the moisture content is decreasing. As a result of that significant

decrease will happened in the generated pore pressure and the internal tension stresses.



5. Aggregates type, the probability of spalling decrease when low thermal expansion aggregates

are used.

6. Aggregate size, most of research papers and the results from the experiments indicates that the

greater size of the aggregate, more likely explosive concrete spalling is to occur.

7. Cover to reinforcement, the bigger concrete cover has a higher probability for spalling. It is

founded that if the concrete cover is more than 50mm, spalling must be feared. On the other

hand, the concrete cover with thickness less than 15mm has high probability for the spalling of

the concrete cover this is because of the unsupported concrete is small.


How to improve the concrete structures in the fire resistance?

1. Applying all the civil defense requirements in the architecture design stage, like the

minimum corridor width and the minimum number of escaping stairs in the building.

2. Applying the standard codes requirements in the structural design stage. Like the

minimum thickness and minimum concrete cover to the steel reinforcement of the

structural elements to achieve the required time of fire resistance. The following table

shows the minimum concrete cover required to achieve the required time for the fire

resistance as per BS8110.


FIRESA 19


Fire resistance

Hour

Nominal cover - mm

Beams Floors Ribs

Simply

supported

Continuous

Simply

supported

Continuous

Simply

supported

Continuous

0.5 20 20 20 20 20 20

1.0 20 20 25 20 35 20

1.5 35 20 30 25 45 35

2.0 60 35 40 35 55 45

3.0 70 60 55 45 65 55

S A CAUSE OF4.

C0

ONCRETEDE TERIORA8

T0

ION 70 65 55 75 65



3. Define the fire protection system which will be used in the structure with respect to

building use and cost.

Passive fire protection system

Fire rated walls

Fire rated floors

Fire rated doors

Active fire protection system

Smoke detectors

Sprinklers

Duct detectors

Fire alarms

BALANCE DESIGN

46Department of Civil Engineering, NSCET, Theni 46


4. The improvement of the concrete mix materials.

Cement

• High alumina and a lesser pozzolanic and blast furnace slag cements have a better performance

in the fire resistance compared to the normal Portland cement.

• When the concrete is subjected to a fire, the cement paste start to shrink due to water

evaporation and dehydration. On the other hand, the particles of the aggregates expand because

of high thermal exposure. This contrary physical reactions sets up internal stresses explain why

it is recommended to use a low aggregate - cement ratio.



Aggregates

• The siliceous aggregates can cause

spalling and its performance with

fire is badly compared with the

other types. This table shows the

minimum thickness to achieve the

required fire resistance period for

different types of aggregate.


Water

• The water content in the hardened concrete exposed to a fire is playing very important role,

this is because there is more heat required to evaporate the saturated water which will enhance

the concrete fire resistance.

Admixtures

• The using of SCM can improve the concrete density which is considered a very important

factor in the fire resistance improvement.

• The using of polypropylene fibers in the concrete mix can improve the concrete fire resistance

especially the resistance to the spalling phenomena.

49



• The chosen building is the Torch Tower, which

is one of the tallest residential towers in Dubai.

• the tower consist 86 floors and its height is

almost 336 m.

• On 21 February, 2015 a fire started from the

floor number 50, and because of high wind

speed in that day the fire was spread rapidly in

the other floors.


CASE STUDY CONCRETE STRUCTURES SUBJECTED TO A FIRE

50

• The smoke detectors and fire alarms started

to work immediately. And the civil defense

started to containment the fire by using all

the modern tools and techniques.



51

Rehabilitation and repairing plan of the building

A. Concrete structure assessment

❑ Visual inspection

• In this stage it is very easy to check if there is spalling in the concrete elements. As well

as, the formation of cracks due to the generate tensile stresses.

• It is possible to make an approximation assessment of the maximum temperature

reached during the fire.

Pink or red for temperatures between 300 °C and 600 °C.

Grey‐white for temperatures between 600 °C and 900 °C.

Dull or light yellow for temperatures over 900 °C.



52

❑ Testing of concrete structure

• Examination of concrete compressive strength,

by using nondestructive tests like Schmidt

hammer test.

• Carrying out acoustic test to detect the

formation of internal cracks.

• Boring and extracting core samples to carry out

compression tests and carry out both

petrographic and microscopic examinations.



53

B. Repairing operation

• The first scenario is the concrete structure

defects are only in the exposed surface layers

and the steel reinforcement still without

significant defects. As well as, the tests shows

that there are no formation of internal cracks in

the concrete structure elements and the

concrete strength still sufficient. the suitable

method of repairing in this case is to clean the

defected surface, apply chemical materials for

the bonding between the old and new concrete,

then place the concrete by using shotcrete

technique.



54

B. Repairing operation

• The second scenario if the concrete damage

and defects is very deep and there is impact on

the steel reinforcement and the concrete

strength. The suitable method for the repairing

in this case in addition to the previous method

is to sticking metal plates or carbon fiber strips

to the surface of the damaged concrete for

strengthening the concrete element.



55

• The third scenario

deterioration is huge

if the concrete

and the cost of

repairing is too much compared to the

demolition and construction of new

structure. In that case the recommended

solution is to demolish the structure and

construct new one.



56

• The fires is one of the major causes of the concrete structures

deterioration (Physical causes). Therefore, it is important to apply all

the requirements and specification in the design and construction

stage to improve the concrete fire resistance.

• Dubai announced that they will apply the

• project of green concrete, this is by usingenvironmentally

materials to

friendly cementitious

improve the concrete

structures sustainability and to reduce the

emission of the carbon dioxide.

57

Recommendation and conclusions


❑ The advantages of using green concrete;

• Increasing the concrete structure life time by almost 20 years.

• Decrease the emission of the carbon dioxide by 80%.

• Eliminate the cracks in the plastic stage of concrete.

• Produce low permeability concrete and reduce the probability of the steel reinforcement

corrosion.

• Improve the concrete fire resistance properties.

58

Recommendation and conclusions



❑LEAKAGE

59

Contents

3

4

5

Testing Water leakage in Building 10

- Introduction

- Objectives

- Effect of leakage

-

- Causes of leakage 19

-

- Maintenance for leakage

- Material for Damp proofing

- Conclusion

leakage in buildings and remedies 23

27

28

33


1. IntroductionOne of the basic requirements in all buildings is that the structure should

remain dry as far as possible. If this condition is not achieved, the building may

become un habitable and unsafe from structural point of view.

The entry of water or dampness into a building is termed as leakage.

Leakage in buildings is common and it is important to understand the causes

and measures to be taken for their prevention .

Most of the building materials having pores in their structure as for example

concrete expand on absorbing moisture from atmosphere and shrink on drying.

These movements are reversible .

at condition of saturation Leakage in buildings occurs in walls, flat roof, and

parapet wall …. etc.


2. OBJECTIVES

To upgrade Maintenance Technologies and Methodologies to achieve

improvement in productivity and performance Of our buildings by applying

Leakage Treatment .


5

3. Effect of leakageThe structure is badly affected by dampness. The prominent effect of

dampness is as follows:

1) A damp building creates unhealthy conditions for those who occupyit

(give a rise for breeding of mosquitoes ).

2) The metals used in the construction of the building are corroded.


3) Unsightly patches are formed on the wall surfaces and ceilings.

4) Decay of timber takes place rapidly due to dampness


7

5) The electric fittings are deteriorated due to dampness.

6) The material used as floor coverings are

seriously damaged.


8

7)

8)Wall decoration and paint damaged.

softening and crumbling plasters


9- disintegration of thermistone and brick wall by dampness


4. Testing Water leakage in Building

ASTM E2128-01a, Standard Guide for Evaluating Water Leakage of

Building Walls, published in January 2002 by ASTMInternational

This guide describes methods for determining and evaluating causes of water

leakage of exterior walls.

This guide is intended to provide building professionals with a

comprehensive methodology for evaluating water leakage through walls.


systematic approach to an evaluation

1) Review of project documents,

2) Evaluation of the wall’s design concept,

3) Determination of the building’s service history,

4) Inspection,

5) Investigative testing,

6) Analysis, and

7) Report preparation


Test opening at -cladwall


Field testing of

suspect window

installation.


ASTM spray

rack in use on

the exterior of

an aluminum

and glass

curtain wall.


15

spray rack in use to test the interior side of a parapet wall.


Leakage detection by Digital leakage correlator IR camera

Fieldinspection leakage by IR


Our leakage

problems


Our leakage problems


5. Causes of leakage-Action of rainfall : If the faces of wall exposed to heavy showers of rain

are not suitably protected, they become source of leakage in a structure. Similarly

leakages from roofs also permit rainwater or drain water to enter in a structure ,

Some times leakage from drain water cause settlement by washing the soil under

foundations .

- Condensation: The moisture is deposited on the walls, ceilings etc. due to

condensation process. Adequate ventilation is essential in any property for the

wellbeing of the residents

- Water storage in building


Miscellaneous:

i) The orientation of a building is also an important factor. The wall obtaining

less sunshine and heavy showers of rain are liable to become damp and leaky.

ii)Very flat slope of a roof may also lead to the penetration of rainwater or drain

water, which is temporally stored on the roof.

iii)The dampness also caused due to bad workmanship in construction such as

defective rain water drain and water supply pipe connections, defective joints in

the roofs, improper connection of the walls etc.


6. leakage in buildings and remedies

- Leakage through roofs:

(i) Lack of proper slope thereby causing stagnation of water (1.25%)

Remedy: Adequate slope should be provided to prevent stagnation ofwater

With expansion joint , clogged gutters is the most common cause of

leakage, check to see if they are clean.


(ii) Lack of proper drainage system

Remedy: Sufficient drainage pipes should be provided .

(iii) Lack of coping of walls

Remedy: coping on the top of the wall should be provided.

(iv) Poor maintenance of water pipe connections and joints

Remedy: Maintenance of water supply pipe connections and fitting shouldbe

leak proof.


- Leakage through walls

(i) Lack of stone cladding/ waterproof and painting

(ii) Lack of chajjas over openings

(iii) Poor orientation and wind direction

Natural ventilation


26

- Leakage from upper floor

(i)Crack in the closet and its trap or sewerage network

Remedy: It should be replaced.

(ii) Leakage from the concealed pipe joints

Remedy: It should be examined and replaced the same.


7. Maintenance for preventing leakage

Cleaning of terraces, drains before monsoon and when chocked.

Replacement of leaky/damaged washers in fittings.

Replacement of leaky/damaged pipe line, gate valves. etc.

Replacement of leaky/damaged gasket in flanges.

Replacements of leaky/damaged joints in CI drain pipes.

Replacement of leaky/damaged MS trays under Air Handling

Units.


8 . Material for Damp proofing Requirement (specification)

It should be impermeable or should have very low permeability.

It should have strong adhesion with substrata.

It should be sufficiently elastic due to temperature fluctuations.

It should have high resistance of cracking.

It should be resistant to ultra violet rays.

It should be breathable i.e. permit vapor transmission.

Its application should be easy.

It should be durable. Department of Civil Engineering, NSCET, Theni 86

Materials used for damp proofing

Types

a)Flexible material: Material like bitumen felts, plastic sheeting

(Polythene sheet) etc.

.

b)Semi rigid materials: Materials like mastic asphalt or

combination of materials or layers.

c) Rigid materials: Materials like first class bricks, stones, slates,

cement concrete etc.

d)Grout consisting of cement slurry and acrylic based

chemicals/polymers.


Commonly used materials for damp proofing.

Hot bitumen: This is a flexible material and is placed on bedding of

concrete or mortar.

This material should be applied with a minimum thickness of 3 mm.

Mastic asphalt: This is semi rigid material and it forms an excellent

impervious layer for damp proofing. Good asphalt is a very durable and

completely impervious material.


Bituminous felts : isogam This is a flexible material. It is easy to lay and isavailable in rolls of normal wall width

Metal sheets: The sheets of lead, copper and aluminum can be used as

membranes for damp proofing.

Combination of sheets and felts : A lead foil is sandwiched between asphaltor

bituminous felt. This is known as lead core and it is found to be economical,

durable and efficient.

Stones: two course of sound and dense stones as granites, slates, etc. laid incement mortar with vertical breaking joints .


Bricks: Dense bricks, absorbing water less than 4.5 % of their weight, can be

used for damp proofing .

Mortar: The mortar to be used for bedding layers 1:3

A small quantity of lime is added to increase the workability. For plastering

work,


9. Conclusion

1- With new construction, if no rainfall water leaks into the interior of the

structure clearly , this not enough according to ASTM we must check leak

investigations by Techniques and Instruments of Water Leakage Detection

in Buildings like sprinkler shower ,infrared (IR)

• Thermography in addition to visual inspection to determine whether water

penetration is occurred or no .

• 2- inspection must be by a Professional staff to identify the cause(s) of

leakage before repairs to prevent unnecessary and costly repairs


❑ DEMOLITION OF STRUCTURES



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