Q. Disadvantages of excessive concrete covers?
In reinforced concrete structures cover is generally provided to protect steel reinforcement from corrosion and to provide fire resistance. Though the use of cover more than essential is undesirable in the subsequent ways:
(i) Size of crack is controlled by the distance of longitudinal bars to the point of section under consideration. The closer a bar is to this point, smaller is the crack width. Thus closely spaced bars with smaller cover will give narrower cracks than widely spaced bars with larger cover. Thus with an increase in concrete cover the crack width will increase.
(ii) Weight of the concrete structure is increased by an increase in concrete cover. This effect is a critical factor in design of floating ships and platforms where self-weight is a significant design criterion.
(iii)For the same depth of concrete section increase of concrete cover results in reduction of the lever arm of internal resisting force.