REPAIR AND REHABILITATION OF BUILDINGS-CET456

Module 1
Maintenance: Maintenance is preventive in nature. Activities include inspection and works
necessary to fulfill the intended function or to sustain original standard of service. The maintenance
of structure is done to meet the following objective Prevention of damages due to natural agencies
and to keep them in good appearance and working condition. Repair of the defects occurred in the
structure and strengthen them, if necessary. The objectives of maintenance include the following:
1. To preserve machinery, building and services, in good operating condition.
2. To restore it back to its original standards,
3. To improve the facilities depending upon the development that is taking place in the building
engineering.
The Maintenance work is broadly classifies as :
a) Preventive Maintenance b) Remedial Maintenance c) Routine Maintenance d) Special
Maintenance
a) Preventive Maintenance: The maintenance work done before the defects occurred or damage
developed in the structure is called preventive maintenance. It includes thorough inspection,
planning the programs of maintenance and executing the work. It depends upon the specifications,
condition and use of structure.
b) Remedial Maintenance: It is the maintenance done after the defects or damage occurs in the
structure. It involves the following basic steps: - Finding the deterioration - Determining the
causes-Evaluating the strength of the existing structure - Evaluating the need of the structure -
Selecting and implementing the repair procedure.
c) Routine Maintenance: It is the service maintenance attended to the structure periodically. The
nature of work done and interval of time at which it is done depends upon specifications and
materials of structure, purpose, intensity and condition of use. It includes white washing, parch
repair to plaster, replacement of fittings and fixtures, binding of road surface.
d) Special Maintenance: It is the work done under special condition and requires sanction and
performed to rectify heavy damage. It may be done for strengthening and updating of the structure
to meet the new condition of usage or to increase its serviceability. It may include particular or
complete renewal occurring at long interval, such as floors, roofs etc.
Necessity of maintenance: The causes which necessitate the maintenance effects the service and
durability of the structure as follows: a) Atmospheric agencies b) Normal wear and tear c) Failure
of structure.
a) Atmospheric agencies
Rain: It is the important source of water, which affects the structure in the following ways;
Physical: Dissolving and carrying away minerals as it is universal solvent.
Expansion and contraction – The materials is subjected to repetitive expansion and contraction
while they become wet and dry and develops the stresses.
Expansion of water – The variation of temperature causes the expansion and contraction absorbed
water and affects the micro-structures of the materials.
Erosion – Transportation, attrition and abrasion of the materials is quite evident effect of the water.
Chemical: The water available in nature contains acids and alkaline and other compound in
dissolve form acts over the material to give rise, which is known as chemical weathering.
Wind: It is the agent, which transports the abrasive material and assists the physical weathering.
Its action is aggravated during rains and, When it is moving with high speed, it may contains acidic
gases like CO2 fumes which may act over the material and penetrates quite deeply in materials
and structure.
Temperature: The seasonal and annual variation of the temperature, difference in temperature in
two parts of the materials and the surface of material causes expansion and contraction, this
movement of the material bond and adhesion between them is lost when it is repeated. This
responsible for the development of cracks and the rocks may break away into small units.
Exploitation or peeling off the shell takes place if exterior layer are heated externally with respect
to internal layers. The temperature variation may also cause change in the structure and chemical
composition of the material.
b) Normal Wear and tear
During the use of structure it is subjected to abrasion and thereby it loses appearance and
serviceability.
c) Failure of structure
Failure is defined as the behavior of structure not in agreement with expected condition of stability
or lacking freedom from necessary repair or non-compliance with desired use of and occupancy
of the completed structure. In field it may result in visual collapse of the structure or even
suspension of the services e.g. the collapse of towers, sliding or over turning of dam, settlement of
foundation, crushing of columns etc. The causes of failure may be broadly grouped as:
Improper Design: Due to incorrect, insufficient data regarding use, loading and environmental
conditions, selection of material and poor detailing.
Defective Construction: Poor materials, poor workmanship, lack of quality control and
supervision.
Improper use of structure: Overloading, selecting the structure for the use for which they are not
designed such as deteriorating environment due to impurities from industrial fuel burning, sea
water minerals, chemicals, storage of chemicals etc.
Lack of maintenance: Lack of upkeep, proper protection, precaution and preservation, deteriorated
the structure, which may result in the failure.
Facets of maintenance:
Maintenance operations have many facets such as :a) Emergency maintenance: Necessitated by
unforeseen breakdown drainage or damage caused by natural calamity like fire, floods, cyclone
earthquake etc.
b) Condition Based maintenance: Work initiated after due inspection
c) Fixed time maintenance: Activities repeated at predetermined intervals of time.
d) Preventive maintenance: This is intended to preserve by preventing failure and detecting
incipient faults (Work is done before failure takes place)
e) Opportunity maintenance: Work did as and when possible within the limits of operation
demand.
f) Day-to-Day care and maintenance
g) Shut down maintenance: Thorough overhaul and maintenance after closing a facility.
h) Improvement plans: This is essentially maintenance operation wherein the weak links in the
original construction are either replaced by new parts or strengthened.
Importance of Maintenance
• Improves the life of structure
• Improved life period gives better return on investment
• Better appearance and aesthetically appealing
• Better serviceability of elements and components
• Leads to quicker detection of defects and hence remedial measures
• Prevents major deterioration and leading to collapse
• Ensures safety to occupants
• Ensures feeling of confidence on the user
• Maintenance is a continuous cycle involves every element of building science namely
Structural, Electrical wiring, Plumbing-water-supply-sanitation, Finishes in floors and
walls, Roof terrace, Service platform/verandah, Lifts, Doors windows and other elements.

The following are the various maintenance based on time,

a) Daily Routine Maintenance b) Weekly Routine Maintenance c) Monthly Routine Maintenance
d) Yearly Routine Maintenance
a) Daily Routine Maintenance :Basically an inspection oriented and may not contain action to be
taken Help in identifying major changes, development of cracks, identifying new cracks etc
Inspection of all essential items by visual observation Check on proper function of sewer, water
lines, wash basins, sinks etc Check on drain pipes from roof during rainy season.
b) Weekly Routing Maintenance Electrical accessories Cob webs cleaning Flushing sewer line
Leakage of water lining
c) Monthly Routing Maintenance: Cleaning doors, windows‟ latches etc Checking septic tank/
sewer Observation for cracks in the elements. Cleaning of overhead tanks Peeling of plaster,
dampness, floor cracks
d) Yearly Routing Maintenance: Attending to small repairs and white washing Painting of steel
components exposed to weather Check of displacements and remedial measures.

Repair: Repair is the technical aspect of rehabilitation. Refers to modification of a structure partly
or wholly which is damaged in appearance or serviceability.

Stages of repair: Repair of concrete structure is carried out in the following stages: a) Removal of
damaged concrete b) Pre- treatment of surfaces and reinforcement c) Application of repair
materials d) Restoring the integrity of individual sections and strengthening of structure as a whole.
a) Removal of damaged concrete: Prior to the execution of any repair, one essential and common
requirement is that the deteriorated or damaged concrete should be removed. Removal of
defective concrete can be carried out using tools and equipment the types of which depend on
the damage. Normally, removal of concrete can be accomplished by hand tools, or when that
is impractical because of the extent of repair, it can be done with a light or medium weight air
hammer fitted with a spade shaped bit. Care should be taken not to damage the unaffected
concrete portions. For cracks and other narrow defects, a saw-toothed bit will help achieve
sharp edges and a suitable under cut.
b) Pretreatment of surfaces and reinforcement. The preparation of a surface/pretreatment for
repair involved the following steps: 1.Complete removal of unsound material. Undercutting
along with the formation of smooth edges.2.Removal of the cracks from the surface.3.
Formation of a well-defined cavity geometry with rounded inside corners. 4. Providing, rough
but uniform surface for repair. 5. The cleaning of all loose particles and oil and dirt out of the
cavity should be carried out shortly before the repair. This cleaning can be achieved by blowing
with compressed air, hosing with water, acid etching, wire brushing, scarifying or a
combination. Brooms or brushes will also help to remove loose material.
c) Application of repair materials: After the concrete surface has been prepared, a bonding coat
should be applied to the entire cleaned exposed surface. It should be done with minimum delay.
The bonding coat may consist of bonding agents such ass cement slurry, cement sand mortar,
epoxy, epoxy mortar, resin materials etc. Adequate preparation of surface and good
workmanship are the ingredients of efficient and economical repairs.
d) Repair procedure: The repair of cracked or damaged structure is discussed under two distinct
categories, namely, ordinary or conventional procedures; and special procedures using the
latest techniques and newer materials such as polymers, epoxy resins etc.
A repair procedure may be selected to accomplish one or more of the following objective:
1. To increase strength or restore load carrying capacity. 2. To restore or increase stiffness. 3.
To improve functional performance. 4. To provide water tightness. 5. To improve appearance
of concrete surface. 6. To improve durability. 7. To prevent access of corrosive materials to
reinforcement.
Various cracks in R.C buildings
Plastic shrinkage cracks: Water from fresh concrete can be lost by evaporation, absorption of sub
grade, formwork and in hydration process. When the loss of water from the surface of concrete is
faster than the migration of water from interior to the surface dries up. This creates moisture
gradient which results n surface cracking while concrete is still in plastic condition. The magnitude
of plastic shrinkage and plastic shrinkage cracks are depending upon ambient temperature, relative
humidity and wind velocity. Rate of evaporation of water in excess of 1 kg/m2 per hour is
considered critical. In such a situation the following measures could be taken to reduce or eliminate
plastic shrinkage cracks.
• Moisten the sub grade and formwork.
• Erect temporary wind breakers to reduce the wind velocity over concrete.
• rect temporary roof to protect concrete from hot sun.
• Reduce the time between placing and finishing. If there is delay cover the concrete with
polyethylene sheets.
• Minimize evaporation by covering concrete with burlap, fog spray and curing compound.
 Plastic shrinkage cracks are very common in hot weather conditions in pavements, floor and roof
slab concrete. Once they are formed it’s difficult to rectify. In case of prefabricated units, they can
be treated by controlled vibration, if the concrete is in plastic condition. In roof and floor slab it is
difficult to repair. However, sometimes, thick slurry is poured over the cracks and well worked by
trowel after striking each side of the cracks to seal the same. The best way is to take all precautions
to prevent evaporation of water from the wet concrete, finish it fast, and cure it as early as feasible.
In Mumbai – Pune express highway, the fresh concrete is protected by 100 meter long low tent
erected on wheel to break the wind and also to protect the green concrete from hot sun. In addition
curing compound is sprayed immediately after finishing operations. Plastic shrinkage cracks, if
care is not taken, will affect the durability of concrete in many ways.
Settlement Cracks
If the concrete is free to settle uniformly, then there is no crack. If there is any obstruction to
uniform settlement by way of reinforcement or larger piece of aggregate, then it creates some voids
or cracks. This is called settlement cracks. This generally happens in a deep beam. Concrete should
be poured in layers and each layer should be properly compacted. Building up of large quantity of
concrete over a beam should be avoided. Sometimes, the settlement cracks and voids are so severe
it needs grouting operators to seal them off. Revibration, if possible is an effective step. Otherwise
they affect the structural integrity of the beam or any other member and badly affect the durability.
Shrinkage
Shrinkage of concrete is one of the important factors contributing to lack of durability of concrete.
Shrinkage is mainly responsible for causing cracks of larger magnitude or minor micro cracks. The
aspect of cracking in concrete is very complex, involving many factors such as magnitude of
shrinkage, degree of restraint, extensibility of concrete, extent of stress relaxation by creep and at
what age the shrinkage is appearing etc. Cracks can be avoided only if the stress induced by
shrinkage strain, after relaxation by creep, is at all-time less than the tensile strength of concrete.
The above situation is not happening in most of the cases and as such generally shrinkage causes
cracks in concrete.
Effect of Cracking
The formation of cracks is dangerous for protection against corrosion. Once concrete cracks, the
external de-passivating agents can penetrate deep into concrete and set off the process of corrosion.
Cracks running transversely to the reinforcement are less harmful than the longitudinal cracks
along the reinforcement. Thus in the order to induce the process of corrosion and to keep it going,
at least one of the following conditions must exist in any RC structure. Chloride ion concentration
in excess of the threshold value at the interface of the reinforcement and concrete or sufficient
advancement of the carbonation front to destroy the passivity of the ferric oxide surface layer of
the reinforcement. Adequate moisture in the concrete to facilitate the movement of chloride ions
and provide a conduction path between the anodic and the cathodic areas on the steel. Sufficient
oxygen supply to the cathodic areas in order to maintain such areas in a depolarized condition.
Difference in electrochemical potentials at the surface of the reinforcement. Low values of
electrical resistivity of concrete. Relative humidity in the range 50-70%. Higher ambient
temperature.
Cracks in R.C Buildings

Various causes of cracks in building before hardening of concrete

Various causes of cracks in building after hardening of concrete

TYPES OF CRACKS
The following eight types of cracks are generally observed in buildings.
1. Plastic Shrinkage Cracks
2. Plastic Settlement Cracks
3. Drying Shrinkage Cracks
4. Thermal Cracks
5. Map Cracks due to alkali aggregate reaction
6. Longitudinal Cracks due to Corrosion
7. Transverse Cracks due to loading
8. Shear Cracks due to loading
Damages to masonry structures
Leakage: Leaks are easily preventable as long as you schedule routine inspections and maintenance.
A professional can spot a leak long before you can. In fact, in almost all cases, by the time a
homeowner or building owner notices a leak in the masonry, there is already extensive damage.
Water damage is certainly unattractive to look at, but it can also cause serious structural problems.
Water erodes the mortar that holds the bricks or stone together, which destroys the integrity of the
structure.
Water will also degrade the bricks themselves. Erosion contributes to this, but if you live anywhere
with freezing temperatures in the winter, the damage will be more severe. Water expands when it
freezes, which means that masonry that has water in it is almost guaranteed to be damaged when that
water freezes. After the thaw, bricks and mortar may both begin to crumble.
Proper caulking and waterproofing of your masonry can prevent that kind of damage, but only if it is
done before the leak begins.
Cracking
Some cracking is simply the result of the natural movement of the building. As buildings settle, it is
quite common for cracks to appear. Likewise, as the masonry itself expands and contracts in different
weather conditions, it may crack.Cracking can also be the result of a problem with the mortar. In these
cases, a professional masonry contractor will need to repair or replace the mortar to fix the crack and
prevent future cracking. The best way to prevent cracking is to have a masonry contractor inspect the
building to catch any cracks quickly, before they become a major problem.
Spalling
Spalling is the term for bricks falling out of the masonry, leaving gaps behind. There are two main
causes of spalling.
The most common cause is water damage. As water penetrates the masonry and weakens it through a
cycle of freezing and thawing, it loosens the mortar around the brick and pushes the brick out.
Structural stresses can also cause spalling, in much the same way that they cause cracking. Buildings
naturally move and settle over the course of their life, and rigid structures like masonry can be damaged
by this.Spalling is clearly a hazard, as falling bricks can seriously injure people or cause more damage
to the building itself. It also creates gaps in the masonry that are both unsightly and dangerous, as they
weaken the overall structural integrity.
Staining
Staining is almost always the result of water damage. Water traveling through the masonry is visible
from the exterior as a dark stain. The masonry looks wet because it is wet. Staining is a cosmetic
problem, but staining in your masonry may also indicate that structural water damage is not far behind.
Displacement
This is a structural problem that occurs when the lateral support anchors are insufficient, corroded or
when the masonry has been damaged by a freeze. As the name suggests, displacement is when the
masonry has shifted and is no longer in proper position.
Displacement is a major structural problem, and it is expensive to repair. Because it is a structural
issue, it absolutely must be repaired as soon as possible. Otherwise, your building is unsafe, both for
the occupants and the people who pass by it.
Causes of Earthquake Damages in Unreinforced Masonry Buildings
1. Inadequate Brick Unit
Commonly, natural stone, solid brick, solid concrete block, and brick with vertical holes are used in
the construction of load bearing walls. if the strength of these brick units is less than that of designated
strength, then these units would become weak points of the structure and may cause extensive failure
during earthquakes.

Fig. 1: Inadequate Masonry Unit Fig. 2: Poor Mortar

2. Poor Mortar
Poor quality mortar used in load bearing walls can cause the disintegration of masonry units and loss
of support to floors. This is because masonry walls with poor mortar would have very low tensile
strength and shear strength which create weak points in the structure. Consequently, the masonry wall
failure during earthquake is highly likely.
Masonry buildings in mud mortar or lime mortar are prone to severe damage due to lack of bond
strength. Use of rounded stones in wythes without through-stones can further aggravate the problem.
The failures of such structures are essentially due to out-of-plane flexure
3.Irregularities in Plane and Vertical direction
Overall unsymmetry in plan and elevation of building is another weakness of masonry building that
cause failures during earthquakes. Load-bearing walls of masonry buildings must be arranged in plan
regularly and symmetrically in respect of the two main axes.
4. Weak load-bearing Walls
Based on the aspect ratio of unreinforced masonry elements, excessive bending and shear can produce
in-plane failures. Many masonry buildings had sustained very significant damage to walls, in the form
of X (double-diagonal shear) cracking which is a common weakness of unreinforced masonry walls
in shear. When a full X crack occurs during an earthquake, the triangular sections of the X crack
become unstable.

.
Fig. X crack. Fig. Weak first storey
5. Lack of Vertical Confining Elements
Lack of vertical confining elements lead to the formation of vertical cracks and failures at the corners
of an unconfined masonry building in which the wall begins to form a hinge from the swaying. Vertical
confining elements should be located at the end of the load-bearing walls, at the both sides of the doors
and windows opening in order to prevent such failure during earthquakes.
6. Weak First Storey
The first storey collapse is occurred in the masonry structures as a result of limited ductility capacity
and poor strength of masonry unit materials.
7. Connections of Crossing Walls
In a seismic-resistant masonry building, crossing walls have to be interlocked properly to improve
out-of-plane strength. The problem of unconnected intersecting walls is very common. Due to bad
connection detail of the intersections, safety of the connections relied on tensile strength of the mortar
used for connection.
Unconnected walls were more prone to out-of-plane failures. These types of deficiencies were not
limited to external wall–partition wall intersection. At the corners of the buildings, where two external
wall intersects, masonry units were not overlapped sufficiently so as to ensure an earthquake-resistant

connection.
8. Wall Openings
Unsymmetry due to imbalance in the sizes and positions of openings in the walls may cause failure of
unreinforced masonry walls during earthquakes. That is why wall openings should be regular and
minimized to improve earthquake resistance of unreinforced masonry buildings, which have lateral
load resisting mechanisms provided by walls only. Generally, the distance between the two openings,
distance between an opening and a corner is determined based on applicable code requirements to
address wall opening problems.

9. Improper Wall Section and Dimension

This involves long; unsupported; slender walls (Fig. 8 and Fig. 9) and improper wall section (Fig. 10)
formation such as unconnected inner and outer wythes. These deficiencies of unreinforced masonry
walls lead to out-of-plane failure which is an important component of complex nonlinear masonry
behavior. Light roofs with insufficient in-plane stiffness are also important reasons for this type of
damage.
Fig. 8: Long Wall Versus Short Wall, Fig 9: Insufficient wall section
10. Insufficient Base Shear Capacity
The use of low-quality mortar such as mud between wall bricks decrease the cracking strength and
base shear capacity of the wall. As a result, wall blocks were separated from each other under very
small shear forces.Heavy Roofing Heavy and stiff buildings is among the factors that results in the
failure of masonry structure due to earthquake forces. This is because heavy and stiff buildings
attracting large seismic inertia forces.
Fig. 11: Damage Due to Unsufficient Shear Capacity

Q) Explain the service life behavior of a concrete structure with a graph.

Ans: All concrete in service will be subjected to chemical and physical changes. In almost all the field
cases, penetration of water and other aggressive chemicals during service life of structures, is the
primary reason for the deterioration of the structure. Addressing the issue of deterioration, carbonation,
chloride ingress, leaching, sulphate attack, alkali-silica reaction and freeze-thaw cycle are the known
responsible natural causes. Out of these, the first three can lead to corrosion of reinforcement.
At some point in structures life the corrosion starts or initiates. It may take 6 to 10 years to complete
the propagation of corrosion which causes a complete damage of the structure.

Fig. Corrosion of Steel in concrete structure in -service

The service life of concrete structures is commonly modelled as a two stage process, defined
respectively as the “initiation” and the “propagation” stage. The initiation period is a period during
which CO2 or chloride ingress occurs into the concrete cover until, eventually, depassiviation takes
place and rebar corrosion starts. Once corrosion of a rebar in concrete has been initiated by any means,
phenomena may occur such as reduced rebar cross-section, deterioration of concrete cover, cracking
and spalling of concrete, loss of steel-to concrete bond, etc. If corrosion proceeds at a sufficiently high
rate, all of these phenomena may negatively affect performance and eventually structural capacity.
This may lead to the collapse of the structure.
Actually, corrosion takes place during the whole propagation period. If initiation of rebar corrosion
was absent the negative phenomenal effect on the structural performance would not have happened.
This is why in many service life approaches, initiation is taken as an indicator of the need to carry out
maintenance; usually preventive maintenance is sufficient to secure all required levels of performance.
Even in a porous or micro cracked concrete, further deterioration cannot occur, in the absence of
water/moisture even if there is a presence of SO 4-, Cl-, CO2. In the absence of water/moisture, these
aggressive ions cannot travel through interconnected pores. Thus neither sulphate attack on cement
paste or corrosion of steel reinforcement can occur.
Q) Explain in detail about time based maintenance.
Ans: a) Preventive Maintenance: The maintenance work done before the defects occurred or
damage developed in the structure is called preventive maintenance. It includes thorough
inspection, planning the programs of maintenance and executing the work. It depends upon the
specifications, condition and use of structure.
b) Remedial Maintenance: It is the maintenance done after the defects or damage occurs in the
structure. It involves the following basic steps: - Finding the deterioration - Determining the
causes-Evaluating the strength of the existing structure - Evaluating the need of the structure -
Selecting and implementing the repair procedure.
c) Routine Maintenance: It is the service maintenance attended to the structure periodically. The
nature of work done and interval of time at which it is done depends upon specifications and
materials of structure, purpose, intensity and condition of use. It includes white washing, parch
repair to plaster, replacement of fittings and fixtures, binding of road surface.
1) Daily Routine Maintenance :Basically an inspection oriented and may not contain action
to be taken Help in identifying major changes, development of cracks, identifying new
cracks etc Inspection of all essential items by visual observation Check on proper function
of sewer, water lines, wash basins, sinks etc Check on drain pipes from roof during rainy
season.
2) Weekly Routine Maintenance Electrical accessories Cob webs cleaning Flushing sewer
line Leakage of water lining
3) Monthly Routine Maintenance: Cleaning doors, windows‟ latches etc Checking septic
tank/ sewer Observation for cracks in the elements. Cleaning of overhead tanks .Peeling of
plaster, dampness, floor cracks
4) Yearly Routine Maintenance: Attending to small repairs and white washing Painting of
steel components exposed to weather Check of displacements and remedial measures.

d) Special Maintenance: It is the work done under special condition and requires sanction and
performed to rectify heavy damage. It may be done for strengthening and updating of the structure
to meet the new condition of usage or to increase its serviceability. It may include particular or
complete renewal occurring at long interval, such as floors, roofs etc.