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Defects and remedies of building



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It includes all the building defects and their remedies to treat the building defects.

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Defects and remedies of building

  2. 2. In construction defects are mainly categorized into three categories:-  PRE CONSTRUCTION  DURING CONSTRUCTION  POST CONSTRUCTION (After construction) The common defects in the buildings are:-  CRACKS  DAMPNESS
  3. 3.  Cracks in building are a common occurrence and it is important to understand the causes and the measures to be taken for their prevention.  Tensile stress are produced due to restraint to contraction movements.  If these stresses exceed the tensile or shear strength of the material cracks develop.  In a tropical country like India, there is a large variation of atmospheric temperature and humidity, hence it would necessary to avoid materials which expand or contract considerably due to thermal and moisture movements.  And design of the structure is so that to minimize restraint to contraction or expansion of the material.
  4. 4.  STRUCTURAL CRACKS- These occur due to incorrect design, faulty construction or overloading.  NON-STRUCTURAL CRACKS- These are mostly due to internally induced stresses in building materials. Structural cracks Non-structural cracks
  5. 5. Type Width Thin Medium Wide < 1 mm 1-2 mm > 2 mm
  6. 6. Vertical Horizontal Diagonal Straight Toothed Stepped Map pattern Random Uniform throughout Narrow at one end and gradually widening at the other
  8. 8.  Drying shrinkage is defined as the contracting of a hardened concrete mixture due to capillary water, this causes an increase in tensile stress which may lead to cracking and warping.  FACTOR CAUSING DRYING SHRINKAGE  Cement and water content,  Maximum size, grading and quality of aggregates,  Presence of excessive fine in aggregates,  Chemical composition of cement,  Temperature of fresh concrete and relative humidity of surroundings.
  9. 9.  All materials more or less expand on heating and contract on cooling .  The thermal movement depends on a number of factors such as temperature variations, dimensions, coefficient of thermal expansion and some other physical properties of materials..  It is mainly the external walls especially thin walls exposed to direct solar radiation.  It can be avoided by introducing expansion joint, control joints and slip joints.
  10. 10.  The temporary change in length, volume or shape produced in a elastic substance by a stress  Structural components of a building undergo elastic deformation due to dead load and the live loads.  When the walls are unevenly loaded with wide variations in stresses in different parts, excessive shear stress is developed which causes cracking in walls.
  11. 11.  Creep is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses.  It can occur as a result of long term exposure to high levels of stress that are still below the yield strength of the material.  Factor affecting creep:-  Influence of aggregate.  Relative humidity.  Size of member.  Applied stresses  Effects of creep:-  Increasing the deflection in larger span beams.  Buckling of slander columns  Buckling of cladding in tall buildings
  12. 12. Buckling of slander columns Due to creep
  13. 13.  Certain chemical reactions in building materials results in appreciable increase in volume of materials. The materials taking part in reaction also become weak and lose strength .  Common instances of chemical reaction are:-  Sulphate attack on cement products.  Carbonation of reinforcement and brickwork, and  Alkali-aggregate reaction.
  14. 14. FOUNDATION MOVEMENT AND SETTLEMENT OF SOIL  Shear cracks in buildings occur when there is large diffferential settlement of foundation due to one of the following causes:  Unequal bearing pressure under different parts of the structure,  Bearing pressure being in excess of bearing strength of the soil,  Low factor of safety in the design of foundations,  Local variations in the nature of supporting soil, which remained undetected and could not be taken care of in the foundation design at the construction.
  15. 15. GROWTH OF VEGETATION  Roots of a tree generally spread horizontally on all sides to the extent of height of the tree above the ground and when trees are located in the vicinity of a wall, these should be viewed with suspicion  They can cause cracks in walls due to expansive action of roots growing under the foundation.
  16. 16.  Do not let trees grow too close to buildings, compounds walls, etc. If any saplings of trees start growing in fissures of walls etc. remove them at the earliest opportunity.  If some large trees exist close to a building and these are not causing any problem, as far as possible, do not disturb these trees if soil under the foundation happens to be shrinkable clay.  If from any site intended for new construction, vegetation including trees have been removed and the soil is shrinkable clay, do not commence construction activity on that soil until it undergone expansion and stabilized after absorbing moisture in at least one rainy season.
  17. 17. GENERAL MEASURES FOR PROTECTION OF CRACKS.. The measures for prevention of cracks could be broadly grouped under the following main sub heads :- a) Selection of materials:- Good quality of building materials according to the specification if used that will minimize the cracks in the building. b)Specifications for mortar and concrete:- The ratio of the mortar and concrete should be according to the prescribed design. Care should be taken that the coarse aggregate, fine aggregate should be free from silt suspended impurities and the mix should be homogeneous, well mixed and contain no excessive of water. c) Drawing and Design of the building:- While doing the construction work care should be taken that foundation of the building should not be laid on loose /muddy soil. The mortar, M S steel reinforcement should be according to the design. d) Good Construction practices:- It is necessary that work proceed uniformly in all part of building. The workmanship should be according to the prescribed norms and best practice in the building construction.
  18. 18. e)Weather Effect:-  The construction work should be avoided in very hot and dry weather, and during very low temperature also.  In general quality of water, sand ,Bajri , mixing of mortar ,quantity of water in mix , socking of bricks and workmanship have great effect on construction work. If possible the subsequent items of construction should be done after the drying of work previously done
  19. 19.  Cracks in masonry walls- Cracks in walls generally get localized at weak sections, such as door and window openings or staircase walls.  In external walls of buildings, shrinkage cracks generally run downward from window sill to plinth level an from window sill on an upper story to the lintel of a lower story.  Preventive measures- Shrinkage cracks in masonry could be minimized by avoiding use of rich cement mortar in masonry and by delaying plaster work till masonry has dried after proper curing and has undergone most of its initial shrinkage.  Masonry work done with composite cement-lime-sand mortar (1:1:6, 1:2:9 or 1:3:12), which are weak, will have lesser tendency to develop cracks because shrinkage in individual masonry units gets accomodated to a great extent in the mortar itself.
  20. 20.  Penetrating damp is the most common form of dampness in buildings. Dampness occurs as a result of water ingressing horizontally through gaps in the building structure.  Rising damp describes the action of ground moisture rising up a masonry wall by capillary action.  It potentially occurs where there is no damp-proof course (DPC) or where the DPC has been damaged or bridged. Theoretically, moisture can rise up the wall to a height of a meter.  "Rising Damp" is most often caused by damp penetration which is then absorbed by the plaster which is highly absorbent and due to the chemical reactions taking place inside the wall
  21. 21.  Dampness tends to cause secondary damage to a building.  The unwanted moisture enables the growth of various fungi in wood, causing rot.  Plaster and paint deteriorate and wallpaper loosens.  Stains, from the water, salts and from mold, mar surfaces.  Externally, mortar may crumble and salt stains may appear on the walls.  Steel & iron fasteners rust.  It may also cause respiratory illness in occupants.  In extreme cases, mortar or plaster may fall away from the affected wall.  The cracks developed as even and uniformly spread throughout
  23. 23.  Roof defects such as faulty flashing, cracked or missing slates or tiles.  Faults in the brickwork or masonry such as missing or cracked pointing. Porous bricks or stones.  Missing or defective mastic around windows and doors.  Blocked weep holes.  Missing or defective trays in cavity walls.  Condensation.  Damp proof membrane or Damp Proof course been buried by later building activities
  24. 24.  The cause of the dampness must first be eliminated, by providing better drainage or fixing leaking pipes. We can also install a physical or chemical DPC.  Then, any affected plaster or mortar must be removed, and the wall treated, before replacing the plaster and repainting.  Proper DPC must be provided and all the joints must be properly sealed