Tuesday, February 02, 2016

Concrete Specification

Non compliance of proper specification during construction results in failure of structures.

  •  Sand contains harmful sulphates/ chemicals, which affect durability of concrete.
  • Silt content present is more than permissible limit.
  • Fineness modulus not checked.
  • Inadequate mixing time.
  • Slump test not performed regularly.
  • Coarse aggregate oversize.
  • Test registers are not maintained. In some cases test are not done and in some other cases tests results are fictitious.
  • Less cement used. Accelerator should be avoided.
  • Beams made to span over larger openings in load bearing walls and in some cases where intermediate support is provided, the support is not tested to resist the compressive strength.
  • Providing reinforcement in conjested manner, making it difficult for concreting conditions. This result in weak pockets, which will permit accelerated corrosion.
  • Bearings of lintel and beams are less than 9 cm or 1/10 the span.
  • All load bearing walls should be provided with lintel band with minimum reinforcement of 2 no. 10 mm diameter tor steel bars, one at each face of the wall with 12 mm cover and 6 mm stirrups and 150 mm cement concrete.
  • Sometimes, the size of beams is out of plumb and buldge out. To avoid this, the bottom plate should be made wider than the finished width of the beam.
  • The top of the side shuttering should be prevented from tilting outwards by provision of inclined wooden struts nailed to the shuttering and bottom plate.
  • The concreting should be done in strips of width 1.5 meters to the length of the unit so that the thickness of the concrete is uniform throughout.
  • Concrete is not laid gently but poured or thrown from a height resulting in segregation.
  • "U" shape ties in pairs may be provided to form a close stirrup with the proper development length taken inside the beam. In such case, development length cannot be provided and "U" shaped ties may be be hooked around reinforcement and bent for 180 degrees and taken for 10 degrees beyond the end of the curve.
  • In case of highly corrosive environment with high sulphate/ chlorine contents in the sub- soil water, anti- corrosive reinforcement or galvanized reinforcement can be used or anti- corrosive coatings can be given.