==>>DEFECTS IN CONCRETE==>>

==>>DEFECTS IN CONCRETE==>>

EFFLORESCENCE ==>> Is the appearance of fluffy white patches on the surface of concrete members. It
is caused by poorly washed aggregate, salty water used in making concrete the salts being leaching out to the surface by rain water afterwards. As the water evaporates white patches appear on the surface. This defect can be controlled to some extent by coating the surface by a water repellent.


SEGREGATION==>>

usually implies separation of: =>1 coarse aggregate from fine aggregate, =>2  paste from coarse aggregate, or water from the mix and the ingredients of the fresh concrete no longer remain uniformly distributed. It can be reduced by increasing small size coarse aggregate, air entrainment, using dispersing agents and puzzolana.The causes of segregation are dropping concrete from heights, badly designed mixes, concrete carried over long distances—pumping, belt conveyor system etc. over vibrations, and during concrete finishing extra floating and tamping.Segregation mainly occurs in dry non-sticky concrete mixes.

CRAZING ==>>

of concrete products results from differences in shrinkage between the surface and the interior. The cracks rarely exceed 12 mm or so in depth, and are therefore not serious, apart from the unsightliness. The best method to overcome crazing is to be either to use an earthmoist mix, or if a plastic mix is necessary use as low a w/c ratio as is practicable and remove the cement skin to expose the aggregate. Trowelling should be avoided, as the surfaces are prone to crazing.

BLEEDING==>>

defined as an autogeneous flow of mixing water within or emergence to the surface from freshly placed concrete is usually due to excessive vibrations imparted to concrete to achieve full compaction. However well concrete may have been compacted, the force of gravity.This upward migration of water known as bleeding ceases either when the solid particles touch each other and cannot settle any more, or when the concrete stiffens due to cement hydration and prevents further movement. It can be reduced by grinding cement fine, or by using air entraining agents, dispersing agents, puzzolanas and by imparting vibration. It is a

particular form of segregation in which some of the water comes out on the surface of concrete. Mixes which bleed excessively are those which are harsh and not sufficiently cohesive. Basically this is caused by the lack of very fine materials in mix. Obviously this is because of the coarse sand or when the sand content has been kept low. The causes of bleeding are highly wet mix, insufficient mixing, and thin sections (slabs) cast in sunny weather—being more in flaky aggregate and more in the first hours of concreting. The ill effects are reduced bond between aggregate and cement, and between cement and reinforcement.


Bleeding can be checked by the use of uniformly graded aggregates, puzzolana—by breaking the continuous water channel, or by using—entraining agents, finer cement, alkali cement, and a rich mix.

SULFATE ATTACK==>>

Sulphate attack is mainly caused by the soil containing sulphates or by sulphate water.