This is reality that for reinforced concrete structure, civil engineers and other discipline does not realized that it needs any periodic attention for its maintenance. As a result, the factors necessary for durability of rcc structures many times not given due importance for construction and maintenance. But on international level now, this topic is drawing attention for all civil engineers. Hence, requirement has been initiated for structural rehabilitation, retrofitting and strengthening of rcc structure; certain advancement has been made in the field of protection and repairs of concrete structure. (1)
Material is very important for protection and repairs of civil structures. Many construction chemicals now a day are present for giving protection and for retrofitting of civil structures. Polymer science is new advancement in this field.
It is required to do conditional survey of concrete structures at regular interval/frequency to see the degradation pattern structures which are functioning in severe environmental conditions shall be monitored frequently.
Selection of material plays an important role in repair of the structures. Correct specification, correct chemicals to be selected for repair.
Detailed inspection of concrete structures required to be done to find out the root cause of deterioration of structures. There must be expert and experienced person to visualize
The compatibility of repair material on existing structure which is to be repaired is an essential requisite for any successful repair. Cement, additive, admixtures, polymers, epoxies have their limitations for repairs.
The decision of repair or replace the structure or its component depend upon the service life of the structure and based on technical and economical evaluation. The selected method shall meet below objectives.
Repair strategy to be chosen such that it meets the above objective.
Depending upon the condition of structure we may choose any of the below repair methodology.
CRACKS EXIST AT THE JUNCTION OF SUBSEQUENT CONCRETE POURS:
HONEY COMBING, WEAK AREAS AROUND THE CONSTRUCTION JOINTS (6):
SEVERELY DAMAGED RCC MEMBER I.E. COLUMNS, BEAMS, AND RCC WALLS:
LEAKAGE, SEEPAGE THROUGH EXPANSION JOINT:
LEAKAGE, SEEPAGE THROUGH EXPANSION JOINT:
Civil concrete structures are very critical plant assets & used for support to various equipment, pumps/motors/vessels/pipe support as a foundation. It is therefore imperative to ensure their indicated valve/status is correct & plan can be run safely & with optimum efficiency. (3) For achieving this objective, it is required to verify their functioning from time to time & correct the deviation, if any, found during the inspection and testing. Certification of civil structure integrity need to done by authorize persons & records maintained for future reference & traceability.
Visual inspection is supported by following NDT test for interference:
Durability certification depends upon distress condition, maintenance practices as well as type of repairs we undertake structure durability certification is generally undertaken in 4 different stages to identify the actual problem. So as to ensure that a fruitful outcome is achieved with minimum efforts and at the least cost.
THE FOUR STAGES ARE :
1). primary objective of the preliminary inspection is to assess and collect following necessary information for a thoughtful planning before a condition survey is physically undertaken.
2).to Define the scope of work of field investigation in consultation with the client.
It is always necessary to carry a camera with flash, during such preliminary inspection to take necessary photographs of the distressed structures and it members
Planning stage involves preparation of field documents, grouping of structural members and classification of damages.
1).PREPARATION OF FIELD DOCUMENTS.
2).GROUPING OF STRUCTURAL MEMBERS: Soon after the preliminary site visit and perusal of building plans, the structural member shall be grouped as per the type and based on similarity of exposure and condition for proper appreciation of cause of the distress. For example in a building subjected to normal environment attack, the grouping could be done as under (4)
3).CLASSIFICATION OF DAMAGES: Based on preliminary data collected on site visit the engineer should freeze the interpretation rules and divided 1thr repair classification into five classes as class 0 to class 4, cosmetic repair superficial repair, principle repair and major repair.
Visual inspection is very effective method for evaluation of structure condition. It also helps us in evaluating requirement of maintenance required for the structure as well as tell us the health of the building.
1).OBSTRUCTION TO VISUAL INSPECTION: False ceilings, carpets, recently done paints, replaster etc. Are likely to create obstructions to visual inspection such areas should be analyzed and recorded with due care.
2).STRUCTURAL SYSTEM: It is necessary that the engineer should be familiar with the structural system, structural behaviour and service ability requirements. In case of non-availability of structural drawings, the existing framing bracing have to be recorded during the inspection.
3).LEKAGE,SEEPAGE DUE TO IN-EFFECTIVE DRAINAGE SYSTEM: Water stagnating area in a structure attracts dampness, leakage etc. are subjected to alternate wetting/drying cycle, such areas are more prone to early corrosion of embedded steel reinforcement. Particularly at terrace floor of the building ,dampness due to improper terrace treatment, its slope or in-efficiency of rain water disposal system may not be noticeable to the eyes, but damage continues till spalling of cover concrete takes place, hence efficiency of rain water disposal system should be carefully examined during such inspection.(1)
4).TYPES OF CRACKS AND THEIR PATTERNS: It is generally easy to differentiate various types of cracks and relate them with the cause of distress. The location of cracks and their pattern gives the first indication of the problem. cracking and spalling and rust staining are the visual indication of corrosion of the steel in the concrete structures. Rest staining in freshly laid concrete is indicative of honeycombed concrete, which could result in serve rusting and deterioration of concrete at the later stage mesh pattern of cracks suggests, drying shrinkage, surface crazing, frost attack or AAR.
5).COLOURS AND TEXTURE OF CONCRETE SURFACE: The texture of a concrete surface may indicate the possibility of a chemical attack and associated with disintegration by leaching .in fire damaged structure the colour of the concrete gives an indication of maximum temperature level to which the surface has been subjected.
It may neither be feasible nor is the practice to conduct field/lab testing on every structural member in an existing distress building.
The field lab testing of a structural concrete and reinforcement is to be undertaken, basically for validating the findings of the visual inspection. The program of such testing has to be chalked out based on the record of the visual inspection.
Certification can be done by certified factory inspector or competent civil structural consultant for civil concrete structures after every 5 years.
Preventive maintenance is a technique to prevent untimely break down. Preventive maintenance is to prevent the failure of structures before it actually occurs. It is designed to preserve and enhance structures reliability by repairing/replacing worn structural components before they actually fail.
The objective of pm for civil structure is:
There shall not be any fixed frequency for preventive maintenance of civil structure preventive maintenance will be done as per requirement of plant operation against no production loss due to civil structures failure
Preventive maintenance criteria shall b decided on following input
Preventive maintenance of civil structures shall mostly as per requirements of plants and recommendation of civil inspection. Civil inspection along with plant operation shall decide whether it would cost more for regularly scheduled downtime and maintenance then it would normally cost to operate structure until repair is absolutely necessary. This may be true for some structures: however there should not be any comparison only on costs but the long term benefits and saving associated with preventive maintenance shall also be considered .without preventive maintenance for example; costs for lost production time from unscheduled structure breakdown will be incurred. Also preventive maintenance will results in saving due to an increase of effective system service life. Preventive maintenance also depends upon the uses of the structures.
Following points shall must be considered while deciding preventive maintenance:
Based on above preventive maintenance can be taken up keeping reliability as well as type of repair and estimated cost up to the life cycle of structure .as a result ,more insight into and control over the maintenance of structure ids desired.
Below three points are important for inspection and maintenance related to structure distress:
Based on inspection and diagnosis from the viewpoint of preventive maintenance is done by civil inspection on case to case basis during availability of plant and equipment and also during shutdown. Accordingly, preventive maintenance shall be carried out as a preventive maintenance programme for civil structures.
Generally, concrete structures are getting neglected in industries we must have inspection and maintenance at required interval for all industrial concrete structure reliability and durability of structures can be ensured if all care as mentioned in clause can be ensured.