BLEEDING can be defined as the water in the concrete mix eventually get up to the surface and cement paste is formed usually is called as “laitance”
Bleeding in the concrete occurs when aggregate tends to to settle down and water rise up to the surface. Movement of water which is upward in direction from bottom to top can make continuous channel. The water cement ratio should not be 0.6 or greater than that.The bleeding of the channel remains continuously this continue of bleeding can be responsible for the permeability of structure. Due to the water tends to rise that upward moment creates water voids between aggregate and reduces the bond between concrete and reinforcement. The bleeding is normal phenomenon if the rate of bleeding is less but if the rate will be increased it will weaken the bond. It is type of segregation in which water comes out of the concrete.
Causes of Bleeding in Concrete
The main cause of bleeding is segregation in the concrete mix. Can be defined as the heavy aggregate generally settles down, because of heavy aggregate settles down the water tends to move up world towards the surface and forms a layer and with water fine particle of cement is also carried out at the surface. This causes bad wearing quality at the top surface of slab and payment.
If the water cement ratio is higher the frequency of bleeding on the surface will be more. Some of the factors can affect the the bleeding searches quantity of fine aggregate type of cement we used.
Effects of Bleeding
Homeogeneity of concrete is lost due to building.
Permeability is caused due to bleeding.
The bond between reinforcement and concrete is reduced due to the water which is accumulated due to the bleeding
Reduction in bond between the cement paste and aggregate.
Ability of pumping is reduced.
It will increase the water cement ratio at the surface.
If the water is present at the surface to finishing process will be delayed
If the rate of your evaporation is equal to the bleeding of concrete bleeding is not that harmful. Sufficient amount of bleeding is good as it enhances the workability of concrete. Due to the bleeding surface of concrete does not dry up quickly before accumulating its full strength to resist cracking.
In the early age of concrete bleeding can be useful when concrete is fully plastic because concrete is in fully plastic condition it will get compacted. The problem arises when bleeding happens when the concrete lost plastic condition. Re vibration can be used to overcome effect of bleeding.
Methods of Reducing Bleeding
1) With minimum water content in the mix and adding suitable chemical admixture the vocabulary can be improved.
2) Design the concrete mix properly.
3) fly ash can be used as a supplementary material..
4)air entraining admixture is useful for reduction of bleeding.
5) Add more cement in the mix.
6) by increasing the the amount of of fine aggregate in the mix (fineness modulus of 2.5 to 2.8)
During the preparation of concrete mix proper care should be taken wild mixing so that bleeding can be reduced as it can cause structure to weak and construction will be delayed.
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