distress of concrete

distress of concrete

1. Contents Definition of Distress Causes of Distress Constructional errors Design Deficiencies Deterioration of concrete Need for repairs in structure Concrete repair system Durable concrete repair

2. DISTRESS Distress means damage. Because of the varying conditions under which it is produced at various locations, the quality of concrete suffers occasionally either during production or during service conditions resulting in distress. 2

3. Causes of distress of concrete Structural causes - Externally applied loads - Environmental loads - Accidents - Subsidence etc. Errors in design and detailing Poor construction practice Construction overloads Drying shrinkage Thermal stress Weathering Corrosion 3

4. In addition to distress in hardened concrete, the plastic concrete may suffer damage due to, - Plastic shrinkage - settlement cracking - early removal of formwork - improper design of formwork 4

5. Construction Errors Use of inferior quality of construction materials. Use of waste water or saline water in construction. Adding of more water to improve workability which increase the w/c ratio. Poor grading of concrete ingredients. Poor mixing of concrete. Batching of concrete by volume using mortar pans. Insufficient compaction of concrete. Dropping concrete from the height results into segregation. Insufficient reinforcement into slab, beam, column etc. Improper location of reinforcing steel. 5

6. 11. Hooks , bends , overlaps are not properly provided. 12. Formwork props are not resting on a hard surface. 13. Early removal of formwork props. 14. Using props of insufficient strength. 15. Joints are not properly provided. 16. Improper curing of concrete. 17. Segregation of concrete during transportation. 18. Settlement of foundation 6

7. Design deficiencies Inadequate structural design : Error in load calculations. SBC is assumed without carrying out any field test. Design not confirming to IS - 456 : 2000 and IS – 1893 : 1987 guidelines. Design with many cantilevers. Shear wall is not designed in multi storey building. Stiffness in both direction is unequal resulting into torsion. Effect of the short column in single storey. Lack of knowledge of using structural design software like STAAD PRO, ETABS etc. 7

8. Poor design detailing : Abrupt change in section. Insufficient reinforcement at re – entrant corners and openings. Inadequate provision for deflection. Inadequate expansion joints. Inadequate provision of drainage. Material incompatibility. Bent up bars are not properly shown. Spacing of vertical stirrups is wrongly shown. Column spacing of lateral ties is wrongly shown. Ductile detailing is not as per IS – 13920. 8

9. DETERIORATION in concrete Causes of deterioration in concrete : Accidental loading Chemical reactions - Acid attack - Alkali carbonate rock reaction - Alkali silica reaction - Aggressive water attack - Sulphate attack 3. Construction errors 4. Corrosion of metals 5. Design errors - Inadequate structural design - Poor design details 9

10. 6. Erosion - Abrasion - Cavitations 7. Freezing and thawing 8. Settlement and movements 9. Shrinkage - plastic shrinkage - Drying shrinkage 10. Temperature changes - Internally generated - Externally generated 11. Weathering 10

11. Need for Repairs of structures Workmanship: Repair personnel are responsible for making repairs that are durable and well bonded to existing structure. Workmen should be fully instructed regarding repair procedures and critical aspects. Constant vigilance should be exercised by contractor’s and government forces to ensure maintenance of necessary standards of workmanship. 11

12. Procedures: Use procedures that have been successful or that have a proven high reliability factor. Repairs on new work will develop best bond and likely to be durable and permanent as original work. The method and materials proposed for use should be approved by an authorized inspector. 12

13. Materials: They must be of high quality, relatively fresh and capable of meeting specifications requirements for particular application or intended use. Mill reports or testing laboratory reports is required. New, unproven materials should be used only when, - Standard repair materials are unsuitable - The owners and parties should be informed about risks associated with it. 13

14. Evaluate structures Project needs Determine causes of damage & effect Repair analysis User needs Determine repair strategies Methods and materials Repair and protect Urgency Aesthetics Lifespan Environment Contractibility & Effectiveness 14

15. Durable concrete repair Determine the causes of damage Evaluate the extent of damage Evaluate the need of repair Select the repair method Prepare the old concrete for repair Apply the repair method Cure the repair properly 15

16. Determine the causes of damage : If the cause of the original damage to concrete is not determined and eliminated , or if an incorrect determination is made, whatever damaged the original concrete will likely also damage the repaired concrete. Evaluate the extent of damage : The intent of this step is to determine how much concrete has been damaged and how this damage will affect serviceability of this structure. Evaluate the need to repair : With early detection it may be possible to arrest the rate of deterioration using maintenance procedure . Even if repairs is required, early detection of damage will allow orderly budgeting of funds to pat the cost of repair. 16

17. 4. Select the repair methods : With insufficient information, it is very difficult to make proper , economical , and successful selections. This steps define the types of conditions the repair must resist the available repair construction time period and when repair must be accomplished. 5. Prepare the old concrete for repair : Preparation of the old concrete for application of repair material is of primary importance in the accomplishment of durable repairs. 6. Apply the repair material : The selected repair material should be applied on the prepared surface using equipment with proper care. 7. Cure the repair properly : The repaired concrete should be cured for about 14 days. 17

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