CE2071 Repair and Rehabilitation of Structures Question Bank
UNIT I :
MAINTENANCE AND REPAIR STRUCTURE
TWO Marks
1. Define
Maintenance.
Maintenance is the act of keeping
something in good condition by checking or repairing
it regularly.
2. Define
Repair.
Repair is the process of
restoring something that is damaged or deteriorated or broken, to
good condition.
3. Define
Rehabilitation.
Rehabilitation is the process of
returning a building or an area to its previous good
conditions.
4. What are the
two facets of maintenance?
The two facets of maintenance are
a) Prevention
b) Repair
5. What are the
causes of deterioration?
a) Deterioration due to corrosion
b) Environmental effects
c) Poor quality material used
d) Quality of supervision
e) Design and construction flaws
6. Define
physical inspection of damaged structure.
Some of the use full in formation
may be obtained from the physical inspection of
damaged structure, like nature of
distress, type of distress, extent damage and its classification
etc, their causes preparing and
documenting the damages, collecting the samples for laboratory
testing and analysis, planning
for in situ testing, special environmental effects which have not
been considered at the design
stage and information on the loads acting on the existing structure
at the time of damage may be,
obtained. To stop further damages, preventive measure necessary
may be planned which may warrant
urgent execution.
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7. How
deterioration occurs due to corrosion?
Ø Spalling of
concrete cover
Ø Cracks parallel
to the reinforcement
Ø Spalling at
edges
Ø Swelling of
concrete
Ø Dislocation
Ø Internal
cracking and reduction in area of steel reinforcement.
8. What are the steps in
selecting a repair procedure?
Ø Consider total
cost
Ø Do repair job in
time
Ø If defects are
few & isolated repair on an individual basis. Otherwise do in generalized
manner
Ø Ensure the
repair prevents further development of defects
Ø In case of lost
strength, repairs should restore the strength
Ø If appearance is
a problem, the number of applicable types of repairs become limited & the
repairs must be covered
Ø Repair works
should not interface with facilities of the structure
Ø Take care in
addition of section to a member and in restributing live loads and other live
load moments. After selecting a suitable method of repairs, and after
considering all the ramifications of its application, the last step is to
prepare plans & specification and proceed with the work.
9. Discuss about
the environment effects which leads to deterioration of concretestructure.
Micro-cracks present in the
concrete are the sources of ingress of moistures atmospheric carbon di-oxide
into the concrete which attack reinforcement and with various ingredients of
concrete. In aggressive environme4nt concrete structure will be severely
reduces.
10. What is the
effect of selecting poor quality material for construction?
Quality of materials, to be used
in construction, should be ensured by means various tests as specified in the
IS codes. Alkali-aggregate reaction and sulphate attack results in early
deterioration. Clayey materials in the fine aggregates weaken the mortar
aggregate bond and reduce the strength. Salinity causes corrosion of
reinforcing bars as well as deterioration of concrete.
11. How can we
determine the cause for deterioration of concrete structure?
a) Inspect & observe the
structure
b) Observe in bad & good
weather
c) Compare with other
constructions on the area or elsewhere & be patient
d) Study the problem & allow
enough time to do the job
12. What are the
factors to be considered by the designer at the construction site.
Ø Minimum and
maximum temperatures
Ø Temperature
cycles
Ø Exposure to
ultra violet radiation
Ø Amount of
moisture
Ø Wet/dry cycles
Ø Presence of
aggressive chemicals
13. What are the
steps in repair aspect?
a) finding the deterioration
b) determining the cause
c) evaluating the strength of
existing building or structure
d) evaluating the need of repair
e) Selecting & implementing a
repair procedure
14. Define the
fixed percentage method of evaluating the strength of existing structure.
It is to assume that all members
which have lost less than some predetermined % of their strength are still
adequate and that all members which have lost more than the strength are
inadequate. It is usually from 15% onwards higher values are applicable for
piling % stiffness bearing plates etc.
15. Discuss
about the design and construction errors leading to deterioration of a
structure.
Design of concrete structures
governs the performance of concrete structures. Well designed and detailed
concrete structure will show less deterioration in comparison with poorly
designed and detailed concrete, in the similar condition. The beam-column
joints are particularly prone to defective concrete, if detailing and placing
of reinforcement is not done properly. Inadequate concrete cover may lead to
carbonation depth reaching up to the reinforcement, thus, increasing the risk
of corrosion of the reinforcement.
16. Discuss
about the quality of supervision to be followed at a site.
Construction work should be
carried out as per the laid down specification. Adherence to specified
water-cement ratio controls strength, permeability durability of concrete.
Insufficient vibration may result in porous and honey combined concrete,
whereas excess vibration may cause segregation.
17. What are the
possible decisions that can be made after evaluating the strength of a
structure?
a. to permit deterioration to
continue
b. to make measures to preserve
the structure in its present conditionwithout strengthening
c. to strengthen the construction
d. if deterioration is
exceptionally sever, to reconstruct or possibly abandonit.
18. How can we
evaluate the strength of existing structure by stress analysis?
This method is to make detailed
stress analysis of the structure, as it stands including allowances for loss of
section where it has occurred. This is more difficult & expensive. Here
also the first stop is to make preliminary analysis by fixed percentage method
and if it appears that major repairs will be required, the strength is
reevaluated based on detailed stress analysis, considering all contributions to
such strength.
19. Define the
load test method of evaluating the strength of existing structure.
Load tests may be required by the
local building offered, but they should only be performed where computation
indicated that there is reasonable margin of safety against collapse, lest the
test bring the structure sown. Load test show strengths much greater than
computed strengths when performed on actual structures. When performed on
actual structures. In repair work every little bit of strength is important.
20. What are the
possible decisions after finding a structure to be inadequate?
Ø if the
appearance of the existing condition is objectionable – repair now
Ø if appearance is
not a problem then
Ø Put the
condition under observation to check if it is dormant or progressive.
Ø if dormant – no
repair
Ø if progressive –
check the feasibility & relative economics of permitting deterioration to
continue and performing a repair at some later date & of making the repair
right away
16 MARKS
1. with a flowchart
explain the assessment procedure for evaluate damages in a structure
2. explain the
various casus for detoriation of concrete structures
3. different type
of maintenance to the structural elements
4. with graph
explain the service life behavior of concrete structure with respect to
maintenance
5. explain the
importance of maintenance
UNIT-II :
SERVICEABILITY AND DURABILITY OF CONCRETE
TWO Marks
1. How can use
prevent the effect of freezing and thawing in concrete?
Concrete can be restricted from
frost action, damage of the structure by the entrainment of air. This
entrainment of air is distributed through the cement paste with spacing between
bubbles of no more than about 0.4mm.
2. Write any two
tests for assessment of frost damage?
The frost damage can be assessed
by several ways:
i) Assessment of loss of weight
of a sample of concrete subjected to a certain number of cycles of freezing and
thawing is one of the methods
ii) Measuring the change in the
ultrasonic pulse velocity or the damage in the change in the dynamic modulus of
elasticity of specimen is another method.
3. How does a
concrete structure get affected by heat?
Heat may affect cone and as a
result of:-
Ø the removal of
evaporable water
Ø the removal of
combined water
Ø alteration of
cement past
Ø alteration of
aggregate
Ø change of the
bond between aggregate and paste
4. How can you
control cracks in a structure?
Ø Use of good
coarse aggregates free from clay lumps
Ø Use of fine
aggregate free from silt, mud & organic constituent.
Ø Use of sound
cement.
Ø Provision of expansion
& contraction joint.
Ø Provide less
water-cement ratio.
5. Define
aggregate splitting?
This phenomenon occurs most
frequently when hard aggregates are used in concrete. The thermal stresses
except close to corners are predominantly compressive near to the heated
surface. This stress causes the aggregate to split in this direction and the
fractures may propagate through the mortar matrix leading to deterioration.
6. What the
factor affecting chemical attack on concrete?
Ø High porosity
Ø Improper choice
of cement type for the conditions of exposure
Ø Inadequate
curing prior to exposure
Ø Exposure to
alternate cycles of wetting and drying
7. Write the
methods of corrosion protection?
Ø Corrosion
inhibitors
Ø corrosion
resisting steels
Ø coatings for
steel
Ø Cathodic
protection
8. List out some
coating for reinforcement to prevent corrosion?
Ø Organic coating
Ø Epoxy coating
Ø Metallic coating
Ø Zinc coating
9. Define 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 occurs most often in beams and
columns made of Quartz aggregate and only infrequently with light weight
aggregates.
10. List any
four causes of cracks?
Ø Use of unsound
material
Ø Poor & bad
workmanship
Ø Use of high
water-cement ratio
Ø Freezing &
thawing
Ø Thermal effects
Ø Shrinkage
stresses
11. What are the
types of cracks?
a) Class-1: Cracks leading to
structural failure
b) Class-2: Cracks causing
corrosion
c) Class-3: Cracks affecting
function
d) Class-4: Cracks affecting
appearance
12. What changes
occur, when hot rolled steel is heated to 500oC?
At temp of 500oC-600oC the yield
stress is reduced to the order of the working stress and the elastic modulus is
reduced by one-third. Bars heated to this temp virtually recover their normal
temperature.
13. List out the
various types of spalling?
i) General or destructive
spalling
ii) Local spalling which is
subdivided as
Ø aggregate
splitting
Ø comer
separations
Ø surface spalling
Ø Sloughing off
14. List some
faults in construction planning?
Ø Overloading of
members by construction loads
Ø Loading of
partially constructed members
Ø Differential
shrinkage between sections of construction
Ø Omission of
designed movement joints
15. Define
corrosion?
The gradual deterioration of
concrete by chemically aggressive agent is called “corrosion”
16. Give some
examples for corrosion inhibitors?
a) Anodic inhibitors
b) Cathodic inhibitors
c) Mixed inhibitors
d) Dangerous & safe
inhibitors
17. Define
effective cover?
The cover to reinforcement
measured from centre of the main reinforcement up to the surface of concrete in
tension is called “Effective cover”
18. Define
corrosion inhibitor?
Corrosion inhibitor is an
admixture that is used in concrete to prevent the metal embedded in concrete
from corroding.
19. What are the
operations in quality assurance system?
Ø Feed back
Ø Auditing
Ø Review line
Ø Organization
20. List the
various components of quality control.
Five components of a quality
(control) assurance system are:
Ø Standards
Ø Production
control
Ø Compliance
control
Ø Task and
responsibilities and
Ø Guarantees for
users
16 MARKS
1. Explain in
detail about quality assurance
2. Describe various
components of quality control
3. Discuss in
detail about the thermal properties of concrete
4. Elaborately
explain about the effects of temperature on concrete
5. Explain the
various corrosion protection methods
UNIT III :
MARETIALS FOR REPAIR
TWO Marks
1. What is expansive
cement?
A slight change in volume on
drying is known as expansion with time will prove to be advantage for grouting
purpose. This type of cement which suffers no overall change in volume on
drying is known as “Expansive cement”.
2. What is the
action of shrink comb in expansive cement?
Shrink comb grout acts like a
Portland cement. It (shrinks) sets and hardens; it develops a compressive
strength of about 140 kg/gm2 at 7days and 210 kg/cm2 at 28 days.
3. List the
various types of polymer concrete.
a) Polymer impregnated concrete
(PIC)
b) Polymer cement concrete (PCC)
c) Polymer Concrete (PC)
d) Partially impregnated and
surface coat
e) Polymer Concrete.
f) Polymer impregnated concrete
(PIC)
4. Give the
various monomers used in polymer concrete.
Ø Mehylmethacrylate
(MINS)
Ø Styretoc
Ø Aerylonitrile
Ø t-butyle slynene
5. Define
polymer concrete.
Polymer concrete is a aggregate
bound a polymer binder instead of Portland cement as in conventional concrete
pc is normally use to minimize voids volume in aggregate mars. This can be
achieve by properly grading and mixing of a to attain the max density and
(mixing) the aggregates to attain (maximum) minimum void volume. The entrapped
aggregated are prepacked and vibrated in a mould.
6. What are the
uses of Polymer concrete?
During curing Portland cement
form mineral voids. Water can be entrapped in these voids which are freezing
can readily attack the concrete. Also alkaline Portland cement is easily
attached by chemically aggressive materials which results in rapid
determination, there as using polymers can compact chemical attack.
7. What is
sulphur infiltrated concrete?
New types of composition have
been produced by the recently developed techniques of impregnating porous
material like concrete with sulphur. Sulphur impregnation has shown great
improvement in strength.
8.What are the
applications of sulphur infiltrated concrete?
Sulphur – (impregnated)
infiltration can be employed in the precast industries. Sulphur infiltration
concrete should found considerable use in industry situation where high
corrosion
resistant concrete is required.
This method cannot be conveniently applied to cast- in place concrete Sulphur
impregnation has shown area improvement in strength.
9. What is
drying shrinkage?
Concrete made with ordinary
Portland cement shirts while setting due to less of water concrete also shrinks
continuously for long true. This is known as “drying shrinkage”.
10. What is self
stressing cement?
This cement when used in concrete
with restrained expansion includes compressive stresses which approximately
offset the tensile stresses induced by shrinkage “self Stressing cement”
11. What is
polymer impregnated concrete?
PIC is a widely used polymer
composition concrete, cured and dried in over or dielectric heating from which
the air in the (pipes) open cell is removed by vacuum. Then low density manpower
is diffused through a open cell and polymerized by using radiation, application
of heat or by chemical initiation.
12. Define
polymer partially impregnated concrete.
Polymer partially impregnated or
coated in dep(CID) and surface coated (SC) control partially polymer
impregnated concrete is used to in the strength of concrete. Partially
impregnated concrete is sufficient in situations there the major required
surface persistent against chemical and mechanical attacks.
13...How can we
manufacture sulphur infiltrated concrete?
Sulphur is heated to bring it
into molten condition to which coarse and fine aggregates are poured and mixed
together. On cooling, this mixture gave fairly good strength, exhibited acid
resistance and also other chemical resistance, but it proved to be either than
ordinary cement concrete.
14. What is the
difference between ordinary cement and expansive cement?
Ordinary concrete shrinks while
setting whereas expansive cement expands while setting.
15. What are the
uses of gas forming and expansive chemicals?
Gas formation and expansive
chemicals to produce light weight concrete as well as to cause expansion on
application such as grouts for anchor bolts. They are non strinking type.
Principal chemicals used are Hydrogen peroxide, metallic aluminium or activated
or activated carbon. Sometimes bentonite clays and natural gum are also used.
16) what is the
use of corrosion inhibiting chemicals
They resist corrosion of
reinforcement .in adverse environment sodium benzonate ,
alcium lingo sulphonate and
sodium nitrate have good results.
17) Write the
use of antifungus admixtures
These are added to control and
inhibit growth of bacteria or fungus in surfaces expressed moisture.
Polyhalogenated phenol, Dieldrin emulsion and copper compounds are some of the
chemicals used for this.
18) What are use
of curing compounds
They are either wax based or
resin based. When coated in freshly laid concrete they form a temporary film
over the damp surface which stops water evaporation and allows sufficient
moisture retention in concrete for curing.
19) What are the
uses of sealants
They are used to seal designed
joints. They are formulated from synthetic rubbers or polysulphides. The choice
of a sealant depends on the location of the joint, its movement capability and
the function the sealant is expected to perform.
20)what are the
uses of flooring
These are usually toppings based
on metallic or non metallic aggregates which are mixed with cement and placed
over freshly laid concrete sub floor. These compounds in high viscosity liquid,
form mixed with recommended filters at site, are based on resins and polymers
such as epoxy, acrylic, polyurethane or polysulphide.
16 MARKS
1. explain about
the expansive cement and its applications
2. explain in
detail about sulphur infiltrated concrete
3. briefly explain
about the ferrocement
4. Explain about
the fibre reinforced concrete . types of fibres and their advantages
5. explain in
detail about the polymer concrete and its types
UNIT lV :
TECHNIQUES FOR REPAIR AND DEMOLITION
TWO Marks
1.What is Vacuum
concrete?
Only about half of the water
added in concrete goes into chemical combination and the remaining water is
used to make concrete workable. After laying concrete, water which was making
concreting workable is extracted by a special method known as “vacuum method”.
2. What are the
equipments used in vacuum concrete?
The equipment essentially
consists of:-i. vacuum pump
ii. water separator and
iii. filtering mat
3.What is
Gunite?
Gunite can be defined as mortar
conveyed through a hose and pneumatically projected at a high velocity on to a
surface.
4. What are the
two types of process in Shotcrete?
a. Wet mix process
b. Dry mix process
5. What are the
stages in dry mix process in shotcrete?
i. In this process, the concrete
is mixed with water as for ordinary concrete before conveying through the
delivery pipeline to the nozzle, at which point it is jetted by compressed air,
onto the work in the same way as that if mix process.
ii. The wet process has been
generally desired in favour of the dry mix process, owing to the greater
success of the latter.
6. What is
shotcrete?
Shotcrete is a recent development
on the similar principle of guniting for achieving greater thickness with small
coarse aggregate.
7. What are the
preliminary investigations before demolition of a structure?
The demolition contractor should
have ample experience of the type of work to be offered;
Ø Fully
comprehensive insurance against all risks must be maintained at all times;
Ø An experienced
supervisor should be continuously in charge of the work;
Ø The contract
price should include all safety precautions included in the relevant building
regulations;
Ø The completion
date should be realistic, avoiding and need to take risks to achieve the date
8. Write about
protective clothing given before demolition.
Buildings where chemicals have
been stored or where asbestos, lead paint, dust or fumes may be present will
require specialized protective clothing, e.g.
9. Give a brief
note on shoring and underpinning in demolition.
The demolition contractor has a
legal obligation to show technical competence when carrying out the work. When
removing sections of the building which could have leave other parts unsafe,
adequate temporary supports and shoring etc. must be provided.
10. What are the
major factors in selecting a demolition procedure?
Majors factors to be considered
in selecting an appropriate technique include:-
Ø Safety of
personnel and public
Ø Working methods
Ø Legislation
applicable
Ø Insurance cover
11.Give the
categories of demolition techniques.
Demolition techniques may be
categorized as:-
Ø Piecemeal
demolition, using hand-held tools or machines, to reduce the height of the
building or structure gradually;
Ø Deliberate
controlled collapse, demolition to be completed at ground level.
12.Write short
notes on demolition by hand.
Demolition of buildings or
structure by hand-held tools such as electric or pneumatic breakers, sometimes
as a preliminary to using other methods, should be carried out, where
practicable, in the reverse order to the original construction sequence.
Lifting appliances may be necessary to hold larger structural members during
cutting and for lowering severed structural members and other debris.
13. In what cases
demolition by machine can be done?
Simple roof structures supported
on wall plates should normally be demolished to the level of wall plates by
hand, but if this may involve unsafe working, then demolition totally by
machine may be appropriate.
14.Write short
notes on balling machine.
Balling machines generally
comprise a drag-line type crawler chassis fitted with a lattice crane jib. The
demolition ball, with a steel anti -spin device, is suspended from the lifting
rope and swung by the drag rope.
15.How are
explosives used for demolition of a structure?
If explosives are to be used for
demolition, the planning and execution, include pre-weakening, should be under
the control of a person competent in these techniques. For large demolition,
the competent person is likely to be an experienced explosive engineer; for
smaller work, a shot-firer may be sufficient.
16 What is a
hydraulic pusher arm?
Articulated,
hydraulically-powered pusher-arm machines are normally mounted on a tracked or
wheeled chassis, and have a toothed plate or hook for applying for applying a
horizontal force to a wall. The machine should stand on a firm level base and
apply force by a controlled movement of the pusher arm.
17. What is
pre-weakening?
Buildings and structures normally
have structural elements designed to carry safely the loading likely to be
imposed during their life. As a preliminary to a deliberate controlled
collapse, after loads such as furnishings, plant and machinery have been
removed, the demolition contractor may be able to weaken some structural
elements and remove those new redundant. This pre weakening is essentially a
planned exercise and must be preceded by an analysis of its possible effects on
the structure until it collapses, to ensure that the structural integrity of
the building is not jeopardized accidentally. Insufficient information and
planning relating to the structure may result in dangerous and unsafe work.
18. What is
deliberate collapse?
The deliberate collapse of the
whole or part of a building or structure requires particularly high standards
of planning, supervisions and execution, and careful consideration of its
effect on other parts of the structure or on adjacent buildings or structures.
A surrounding clear area and exclusion zone are required to protect both
personnel and property from the fall of the structure itself and debris which
may be thrown up by the impact.
19. How can you
develop a demolition strategy?
The strategy will need to take
into account the method of construction used for the original building and its
proximity to other buildings, structures and the general public. These factors,
together with location, the cost and availability of tipping and disposal and the
desirability and economics of reuse, must be taken into account in the
development of an appropriate strategy for the demolition of a structure.
20. What are
nibblers?
Nibblers use a rotating action to
snap brittle materials such as concrete or masonry. In either case, material
should be removed from the top of walls or columns in courses not greater than
600mm in depth, steel reinforcement should be cut separately as necessary.
21. What are the
considerations before demolition?
Considerations should be given
to:-
Ø Conducting a
site and building survey, with a structural bias;
Ø The examination
of drawings and details of existing construction where available;
Ø The preparation
of details and drawings from site survey activities where no such information
is available;
Ø Establishing
previous use of premises, especially with regard to flammable substances or
substances hazardous to health or safety;
Ø Programming the
sequence of demolition work;
Ø The preparation
of a Method Statement.
16 MARKS
1. Briefly explain
about the vaccum concrete.
2. Explain the
process of epoxy injection. Also explain routing, guniting.
3. Explain in
detail about the corrosion protection methods
4. Explain
demolition process of a damaged structure
5. Explain in
detail about various demolition technique
UNIT V :
REPAIRS, REHABLITION AND RETROFITTING OF SRTRUCTURES
TWO Marks
1.What are the
techniques required for repairing cracks?
Ø Bonding with
epoxies
Ø Routing and
sealing
Ø Stiitching
Ø Blanketing
Ø External
stressing
Ø Grouting
Ø Autogenous
healing
2.Define
stitching.
The tensile strength of a cracked
concrete section can be restored by stitching in a manner similar to sewing
cloth.
3. What do you
mean by blanketing?
This is the simplest and most
common technique for sealing cracks and is applicable for sealing both fine
pattern cracks and larger isolated. The cracks should be dormant unless they
are
opened up enough to put in a
substantial paten in which case the repair may be more property termed as “Blanketing”.
4. Define
external stressing.
Development of cracking in
concrete is due to tensile stress and can be arrested by removing these
stresses. Further the cracks can be closed by including a compressive force
sufficient to over come the tension a residual compression.
5. Write short
notes on Autogenous healing.
The inherent ability of concrete
to heal cracks within “autogenous healing”. This is used for sealing dormant
cracks such as precast units cracked in handling of cracks developed during the
precast pilling sealing of cracks in water hands and sealing of cracks results
of temporary conditions.
6. What is overlay?
Overlays may be used to restore a
spelling or disintegrated surface or to protect the existing concrete from the
attack of aggressive agents. Overlays used for this purpose include concrete or
mortar, bituminous compounds etc. Epoxies should be used to bond the overlays
to the existing concrete surface.
7. Give short
note on Jacketing.
Jacketing consists of restoring
or increasing the section of an existing member by encasing it in a new
concrete. This method is useful for protection of section against further
deterioration by providing additional to in member.
8. Give an
account on how metal bonding is done on concrete member.
On the tension side of the beam 2
to 3mm steel plates are to the existing beam to increase its capacity. The glue
or adhesive should compatible with the existing concrete with behavioral
characteristics under load addition to providing integrity with parent member.
9. How clamps
are used to overcome low member strength?
The distress is due to inadequate
stirrups either due to deficiency in the of provision of C- stamps, U-clamp
fixed externally along the length of beam to provide adequate these will be
protected by covering with rich mortar or concreting as the a later stage.
10. Define
grouting.
Grouting can be performed in a similar
manner as the injection of an epoxy. However the use of an epoxy is the better
solution except where considerations for the resistance of cold weather prevent
such use in which case grouting is the comparable alternative.
11. Give a short
note on epoxy coatings.
These are organic compound which
when activated with suitable hardening agents form strong chemically resistant
structures having excellent adhesive properties. They are used as binders or
adhesives to bond new concrete patches to existing surfaces or hand together
cracked portions. Once hardened, this compound will not melt, flow or bleed.
Care should be taken to place the epoxy within the pot life period after
mixing.
12. What are
protective surface coatings?
During of concrete can be
substantially improved by preventive maintenance in the form of weather
proofing surface treatments. These treatments are used to seal the concrete
surface ad to inhibit the intrusion of moisture or chemicals.
13. List some
materials used as protective surface coatings.
Materials used for this purpose
include oils such as linseed oils, petroleum etc.
14. Define dry
pack.
Dry packing is the hand placement
of a very dry mortar and subsequent tamping or ramming of the mortar into place
producing an intimate contact between the old and new concrete work.
15. Give a brief
account on routing and sealing.
This method involves enlarging
the cracks along its exposed surface, filling and finally sealing it with a
suitable material. This is the simplest and most common technique for sealing
cracks and is applicable for sealing both fine pattern cracks and larger
isolated.
16. List any
four causes of cracks?
Ø Use of unsound
material
Ø Poor & bad
workmanship
Ø Use of high
water-cement ratio
Ø Freezing &
thawing
Ø Thermal effects
Ø Shrinkage
stresses
17. What are the
types of cracks?
a) Class-1: Cracks leading to
structural failure
b) Class-2: Cracks causing
corrosion
c) Class-3: Cracks affecting
function
d) Class-4: Cracks affecting
appearance
18. What is
pneumatically applied mortar?
Pneumatically applied mortar is
used for the restoration of when the location of deterioration is relatively at
shallow depth. It can be used on vertical as well as on horizontal surfaces and
is particularly restoring surfaces spalled to corrosion of the reinforcement.
Damaged concrete elements also retrofitted using this method. This also has
known as gunning or shotcreting techniques.
19. What is
caging with steel?
A steel caging is prepared and
made to surround the existing masonry so that lateral expansion when it is
loaded in compression. The confinement of masonry will steel cage increases its
capacity and ductility.
20. Give a brief
note on dogs in stitching.
The dogs are thin and long and to
cannot take much of compressive force. The dogs must be stiffened and
strengthened by encasement in an overlay or some similar means.
21. Give some
concrete materials used to overcome weathering action on concrete.
The two concrete repair materials
used were
(i) a flow able concrete with 16
mm aggregate and containing a plasticizer and a shrinkage-compensating
additive, to be cast against forms in heights up to 1.5m, and
(ii) a patching mortar to be
applied brendering, for areas less than .01 m2
.
16 MARKS
1. explain the
various strengthening technique to overcome low member strength
2. explain the
various techniques for repair of cracks
3. explain in
detail about chemical disruption on concrete
4. explain about
the weathering action on concrete
5. explain various
technique for repair spalling and disintegration of concrete
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