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CV2504- MAINTENANCE AND REHABILITATION OF
STRUCTURE
UNIT I MAINTENANCE AND REPAIR STRATEGIES
PART A
- 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
- When do you go for repair of a structure? a. Cause of damage b. Type, Shape and function of the structures c. The type and extent of damage d. The availability of repair materials.
- Write the importance of maintenance. a. Improves the service life of structure b. Better serviceability of elements and components c. Leads to quicker detection of defects d. Prevents major deterioration leading to collapse. Maintenance can be classified based on duration or frequency.
- Distinguish between repair and rehabilitation? Repair Rehabilitation
Repair is the process of
restoring something that is
damaged or deteriorated or
Rehabilitation is the process of returning a building or an area to Its previous good conditions.
broken, to good condition.
- (^) What is the effect of selecting clayey materials in the fine aggregates for construction? 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.
- (^) Write about the environment effects which lead to deterioration of concrete structure.
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 environment concrete structure will severely reduce.
- (^) 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.
- (^) 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
- (^) Discuss about the design and construction errors leading to deterioration of a structure.
Work is done before failure
- On what condition maintenance is based on?
The maintenance is based on the climatic conditions
PART B
- Describe the steps in the assessment procedure for evaluate damages in a structure. (16)
While assessing the damage of a structure the following general considerations should be examined.
- Physical Inspection of damaged structure.
- Preparation and documenting the damages.
- Collection of samples and carrying out tests both in situ and in laboratory.
- Studying the documents including structural aspects.
- Estimation of loads acting on the structure
- Estimation of environmental effects including soil structure interaction.
- Diagnosis
- Taking preventive steps not to cause further damage
- Retrospective analysis to get the diagnosis confirmed
- Assessment of structural adequacy
- Estimation on future use
- Remedial measures necessary to strength and repairing the structure.
- Post repair evaluation through tests
- Load test to study the behaviour
- Choice of course of action for the restoration of structure.
The assessment procedure spans two distinct stages.1. Pre repair2.Post repair evaluation
- Explain the various causes for deterioration of concrete structures. (16)
Some of causes of deterioration of concrete structures which are presented below. i) Design and construction flaws 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. ii) Environmental effects 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. iii) Poor quality material used Quality of materials, to be used in construction, should be ensured by means various tests as specified in the IS codes. Alkali-aggregate
Flowchart / 8 points = 16
- Routine Maintenance
- 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. 4 points x4 =16 Marks
- Explain the various facets of maintenance of a concrete structure in detail. 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. 8 points x2 =16 Marks
Various aspects Inspection : 1. Inspection for maintenance routine inspection by engineer.2.Monthly, periodically apply practical knowledge and find out any damages. The following are the various maintenance aspects,
- Daily Routine maintenance
- Weekly routine maintenance
- Monthly Routine maintenance
- 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.
B. Weekly Routine Maintenance :
- Electrical Accessories
- Cobb webs cleaning
- Flushing sewer line
- Leakage of water line
C. Monthly Routine Maintenance
- Attending to small repairs and while washing
- Painting of steel components exposed to weather
- Check of displacements and remedial measures
D. Yearly Routine Maintenance
- White washing
- Painting
- Repair rectification
4 points x4 marks = 16Marks
UNIT II SERVICEABILITY AND DURABILITY OF CONCRETE
- What are the effects of cover of thickness in concrete?
The cover to reinforcement measured from centre of the main reinforcement up to the surface of concrete in tension is called “Effective cover
- What is the role of cover in RC structures?
- Increase durability and strength.
- It prevents reinforcement from the atmosphere agent
- It precasts reinforce from corrosion.
- Define “durable concrete”?
Durable concrete performs good in its life; in its service environment. Its ingredient materials are durable. Its mix, matrix and integrity workmanship are perfect. Further it is protected from corrosion, deterioration, cracking, etc.
- List any four durability parameters.
Durability means that the structure will retain its original form, quality, and serviceability for a long time when exposed to its environment.
i. Having enough strength ii. Resistance to undesirable chemical reactions. iii. Resistance to corrosion. iv. Resistance to absorption and permeability v. Resistance to weathering.
- Discuss the effect of temperature on concrete.
- Removal of evaporation water.
- Removal of combined water.
- Alteration of cement paste.
- Strength loss ,crack and colour change
- What is the effect of fire on concrete?
- Spalling of concrete
- Strength reduction in concrete and steel
- Loss of anchorage of reinforcement
- Excessive deflection in beams and slab
- Distortion (Deformation) of the whole structural forming
- Discuss briefly the effects due to “climate”?
It has a great effect on the life of human beings the basic elements which constitute the climate of a place are:
- Air temperature and solar radiation
- Rainfall
- Wind
- Humidity
- Name the components in quality management system.
- Quality assurance plan (QAP)
- Quality control process (QC)
- Quality audit (QA)
- Define Strength of concrete.
quality assurance programme to provide a meaning of controlling to predetermined requirements. These activities, which influence quality. In the manufacture of virtually every complex produce a quality assurance scheme of one type or another is used. Factors influencing Quality Assurance: Depending upon the value of the product and methods used in the circumference such scheme may themselves become extremely complex. So that it cannot in all cases guarantee all the functional requirements illustrations. The need of quality assurance: In the construction of concrete structure, quality assurance in necessary to give good performance and appearance throughout its intended life is attained. It is useful for promoting the schemes by engineers. The designer depends upon this for reputation and professional failure to appearance. Cases may also include: Misinterpretation of design and drawings or other specifications. Lack of effective communication with suppliers and co-contractor. Inefficient coordination of sub-contracted work. In adequate on site supervision, poor workmanship due to inadequate skills and experience of the labour force. Purpose of structural failure:
- Communication and organization in construction industry.
- Inspection of construction by the structural engineer.
- General Quality of design.
- Design details and shop drawings.
- Timely dissemination of technical data
- Development and operation of quality assurance system:
The basic mechanism available for both the development and operation of a quality management system. Organization: Which requires clear definition of responsibilities and relationship for the total construction project? Auditing: Which requires the ability to determinate that the tasks defined under responsibilities are continuously being executed according to stated methods? Review line: Which requires continuous checks on process methods and action procedures adopted if stated requirements are not being met. Feed back: Which requires deduction in measurable terms of causes of errors that generate defects, in order that processes can be changed so as to reduce non conformance and shown the benefit of such change to be demonstrated. Any 8 points x2 =16 Marks
- Discuss in detail about the thermal properties of concrete. The three important thermal properties of concrete are,
- Thermal conductivity of concrete.
- Co-efficient of thermal expansion and
- Fire resistance Thermal character of concrete: The process of hydration of cements materials releases heat which raises the temperature of concrete. This heat mush eventually be lost to the atmosphere and the cone temperature has to reach equilibrium with a long term atmosphere conditions. The atmospheric gradients may occur or develop in the concrete as the internal temperature is raised above the surface temperature of the concrete member. This surface temperature is dependent on the material in contract. The resulting temperature will produce tensions in the surface and may be stiffness to cause cracking. The second effect operates as the mean temperature of the member am remain
laterally and longitudinally of the reinforcement base resulting in loss of bond and loss of strength of reinforcement. Fire resistance on concrete: Fire on cone building damages the cone as well as steel reinforcement, causing disintegration of the cone and buckling of steel. The temperature gradient is extreme 30 to 40 o^ c on the outer face and above 800o^ C on the interface (near the source of fire). In the initial stage (half an hour) as the heat inside builds up, some aggregate. Expand suddenly, spelling the adjacent concrete. Moisture in concrete rapidly changes to steam, causing localized bursting of small pieces of cone. Extreme heat near the sources of fire causes spalling rapidly expanding cone surfaces. In the next 30 minutes a temperature inside reaches 400 o^ C, the cement matrix converts to QuickTime causing disintegration of concrete. The reinforcing steel loses the ensile capacity at such temperature. Deflection of beams and slab increases beyond this limit. Beyond one hour of fire, as the concrete disintegrates, the exposed steel expands, more rapidly than the surrounding concrete causing buckling, loss of bond to adjacent concrete. Thermal effects on concrete: Excess water in concrete evaporates due to heat and setting of cone occurs. The loss of moisture to evaporation causes the cement paste matrix to contract, leading to shrinkage stress and shrine erecting. A 6m long slab may shrink 3mm to 5mm along its length called “drying shrinkage”. Any 8 points x2 =16 Marks
- Explain in detail about Design Errors in construction. Design Errors Design errors may be divided into two general types : A. Those resulting from inadequate structural design. B. Those resulting from lack of attention to relatively minor design details Each of the two types of design errors is discussed below.
A. Inadequate structural design (a) Mechanism. The failure mechanism is simple – the concrete is exposed greater stress than it is capable of carrying or it sustains greater strain than its strain capacity. (b) Symptoms. Visual examination of failures resulting from inadequate structural design will usually show one of two symptoms.
- First, errors in design resulting in excessively high compressive stresses will result in spalling. Similarly, high torsion or shear stresses may also result in spalling or cracking.
- Second, high tensile stresses will result in cracking. To identify inadequate design as a cause of damage, the locations of the damage should be compared to the types of stresses that should be present in the concrete. For example, if spalls are present on the underside of a simple-supported beam, high compressive stresses are not present and inadequate design may be eliminated as a cause. However, if the type and location of the damage and the probable stress are in agreement, a detailed stress analysis will be required to determine whether inadequate design is the cause. Laboratory analysis is generally not applicable in the case of suspected inadequate design. However, for rehabilitation projects, thorough petrographic analysis and strength testing of concrete from elements to be reused will be necessary. (c) Prevention. Inadequate design is prevented by thorough and careful review of all design calculations. Any rehabilitation method that makes use of existing concrete structural members must be carefully reviewed.
- Poor design details A structure may be adequately designed to meet loading and other overall requirements, poor detailing may result in localized concentrations of high stresses in otherwise satisfactory concrete. These high stresses may result in cracking that allows water or chemicals access to the concrete. In other cases, poor design detailing may simply allow water to
