Defects in Concrete.pptx

Defects in Concrete Structures

1. Defects in Concrete Structures

2. What is the Concrete? CONCRETE Constituents of Typical Concrete Sample 60-75% of aggregates 25 to 40% of cement paste About 1 to 2% of voids

3. Concrete Defects Concrete is known to be a very versatile and reliable material, but some construction errors and construction negligence can lead to the development of defects in a concrete structure. These defects in concrete structures appear because of, due to poor construction practices poor quality control due to poor structural design and detailing

4. Honey-comb Honeycombs are hollow spaces and cavities left in concrete mass on the surface or inside the mass Improper vibration and workability of concrete are main causes of honeycombs in concrete Reduces the load-bearing capacity affecting the strength of the structure. Water and air penetrate inside the structure and Rusting and corrosion of reinforcement occur

5. Treatment for Honey-Comb Honey-combs were rectified by using special “ Non shrink, cementitious grout” Called Master Flow 810

6. Features of Construction Grout High strength Non shrink Versatile

7. Defects due to Poor Formwork Installation Formwork installation errors include misalignment, movement, loss of support, failure of forms Those mistakes can be repaired with surface grinding to maintain the verticality of the structure if the error is minor. In case of major error, the concrete member shall be repaired by removing the concrete in the defective area and then reconstructing that portion of the structural member using suitable methods

8. Efflorescence Leaching of lime compounds can lead to the formation of calcium carbonate or calcium sulphate on the surface of the concrete

9. Bug Holes Bug holes or surface voids are small regular or irregular cavities formed due to the entrapment of air bubbles in the surface during placement and consolidation By using Clean and well maintained formworks, can avoid from this defect

10. Cracks All Concrete is open to both in the plastic state and in the hardened state . properties of concrete and its constituent materials Design practices , Construction practices and. where in-service conditions, internal or external nature Conditions

11. Structural Cracks are Caused by applied loads Flexural Cracks / Tensile Shear Cracks These cracks can be controlled by providing proper tension reinforcement. Generally flexural stress occurs at the middle span of the beam where flexural stress is maximum. Internal Micro-Cracks (Compressive cracks) Micro cracking can occur in severe stress zones, due to large differential cooling rates due to compressive loading. These are discontinuous microscopic cracks which can become continuous and become a visible sign of impending structural problems.

12. Shear Cracks Cracks in concrete beams due to increase in shear stress appears near the supports These cracks are inclined at 45 degrees with the horizontal. These cracks in beams can be avoided by providing additional shear reinforcements near the support where the shear stress is maximum

13. Non Structural Cracks include Pre-hardening cracks Cracks in hardened concrete Cracking due to chemical effects Non-structural cracks are influenced by properties of concrete and its constituent materials, construction practices. Also ambient temperature , humidity Pre-hardening (Plastic) Cracks These cracks occur within a few hours after the placement and compaction of concrete Plastic Shrinkage Cracks (Rapid Drying of concrete surface with in 1st Six Hours) Plastic Settlement Cracks (Caused by concrete settling under its own weight)

14. Cracks in hardened concrete Craze Cracking (Characterized by a series of very fine closely spaced map pattern cracks Caused by the shrinkage of the Cementous material of the surface layer of concrete) Drying Shrinkage Cracks (Occur when concrete reduces in volume as a result of moisture losses into the atmosphere in its hardened state) Early Thermal Contraction (Movement) Cracks ( Occur when concrete reduces in volume as a result of moisture losses into the atmosphere in its hardened state)

15. Crack Repairing Bonding with Epoxies The Routing operation Resin injection Stitching Grouting Blanketing

16. Other Defects Concrete Spalling Blistering Dusting Delamination

17. Thank-you for your Attention!