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Bleeding is a form of segregation where some of the water in the concrete tends to rise to the surface of the freshly placed material. This arises due to the inability of the solid components of the concrete to hold all of the mixing water when they settle downwards (water being the lightest of all the mix constituents). Bleeding of the water continues until the cement paste has stiffened enough to end the sedimentation process.
Cement types can influence bleeding capacity, increased proportions of, for example, cement combinations containing ground granulated blastfurnace slag (ggbs), leading to an increase in the time for bleeding continue due to a longer setting time. The presence of an adequate proportion of very fine aggregate (smaller than 150µm) reduces bleeding. Similarly polypropylene micro-fibres are known to reduce bleeding.
If the bleed water is remixed during the finishing of the top surface, a weak top surface will result. To avoid this, the finishing operations can be delayed until the bleed water has evaporated. Conversely, if evaporation of the surface water is faster than the rate of bleed, plastic shrinkage cracking may occur. BS 8500-1: 2015 Table A.9 c) states that "Cements or combinations containing more than a mass fraction of 55% ggbs might not be suitable for the wearing surfaces of pavement concrete due to the possibility of surface scaling in the top few millimetres."
In more severe cases, segregation of aggregates can also occur, with the heavier coarse particles moving towards the bottom of the concrete, leaving a cement sand paste layer on the top surface.
Excessive working of a concrete prone to bleeding can prolong bleeding and encourage further aggregate settlement.
Finishing an unformed surface can be adversly effected by bleeding
Bleeding is the tendency of the water to rise to the surface of freshly laid concrete. This results from inability of the solid material of concrete to hold the all the water mixed fro preparation of concrete and during the process of material downward settling. If we resort to surface finish in presence of bleeding it would weaken the top surface. Type of cement used also has influence on bleeding process.
In case of segregation, the heavy aggregate particles settle down leaving a sand cement mix on top affecting the quality adversely. Fine aggregate could be used to overcome the problems. However; design mix must be such that required strength could be achieved. Similarly water ratio may be catered for in design mix to avoid bleeding keeping in view the local material specifications.
Due to bleeding concrete loses its homogeneity.Bleeding is responsible for causing permeability in concrete.In the process of bleeding (i.e. while water is in the process of coming towards top) sometimes gets accumulated below the aggregate. This accumulation of water creates a water voids and reduces bond between the aggregate and cement past. So the strength of concrete reduces (Note: This aspect is more pronounced in case of flaky aggregates)Similarly, water that accumulates below the reinforcing bars, particularly below the cranked bars, reduces the bond between the reinforcement and concrete.If a slip form paver is used for construction of concrete pavement, the bleeding water causes very serious problems. If too much of bleeding water accumulates on the surface of pavement slab, the bleeding water flows at over the unsupported side which causes collapsing of sides.In pavement construction bleeding water delays surface finishing and application of curing compound.
Segregation of the concrete mean separation of particle from the mix due to the excess amount of w/c ratio. This phenomenon can be easily identified by visual inspection of the mix during the concrete pour/fresh concrete testing activity like slump, flow table etc. and this will make in honeycomb in structural member because particles of the mix are not in bond or non-cohesive mix.
Bleeding is rest of excess amount of water over the compacted concrete surface once completion of vibration process. This may result in shrinkage crack, nominal changes in structural member size.This can happen due to the exist amount of moisture in concrete ingredients ex. fine & coarse aggregate. before introduce the water to the mix need to confirm the moisture content of the raw materials and to be controlled with in the design W/C ration.
Bleeding is a form of segregation where some of the water in the concrete tends to rise to the surface of the freshly placed material. This arises due to the inability of the solid components of the concrete to hold all of the mixing water when they settle downwards. Bleeding of the water continues until the cement paste has stiffened enough to end the sedimentation process.
Cement types can influence bleeding capacity.
Segregation can be defined as the separation of the constituent materials of concrete. A good concrete is one in which all the ingredients are properly distributed to make a homogeneous mixture. There are considerable differences in the sizes and specific gravities of the constituent ingredients of concrete. Therefore, it is natural that the materials show a tendency to fall apart.
Segregation concrete--- is as per proper mix ratio as per requirement, and bleeding concrete is very loose and slips.
Segregation
Segregation in concrete is separation of some size groups of aggregates from cement mortar in isolated locations with corresponding deficiencies of these materials in other locations.
Segregation results in proportions of the laid concrete being in variation to those as designed. Segregation could result from internal factors such as concrete that is not proportioned properly and not mixed adequately, or too workable a mix.
It also could result from external factors such as too much vibration, improper transportation, placement, or adverse weather conditions.
The corresponding increase in proportion of cement paste in upper areas would tend to make them susceptible to increased shrinkage and formation of cracks. These cracks could be 10 µm to 500 µm wide, formed perpendicular to the surface, and be in the form of map patterns.
The effect of aggregate segregation on the mechanical and transport behavior of concrete has been the focus of both modeling as well as experimental investigation
Bleeding
Bleeding is a form of segregation where some of the water in the concrete tends to rise to the surface of the freshly placed material.
This arises due to the inability of the solid components of the concrete to hold all of the mixing water when they settle downwards (water being the lightest of all the mix constituents). Bleeding of the water continues until the cement paste has stiffened enough to end the sedimentation process.
Cement types can influence bleeding capacity, increased proportions of, for example, cement combinations containing ground granulated blastfurnace slag, leading to an increase in the time for bleeding continue due to a longer setting time. The presence of an adequate proportion of very fine aggregate (smaller than 150µm) reduces bleeding. Similarly polypropylene micro-fibres are known to reduce bleeding.
If the bleed water is remixed during the finishing of the top surface, a weak top surface will result. To avoid this, the finishing operations can be delayed until the bleed water has evaporated. Conversely, if evaporation of the surface water is faster than the rate of bleed, plastic shrinkage cracking may occur.
In more severe cases, segregation of aggregates can also occur, with the heavier coarse particles moving towards the bottom of the concrete, leaving a cement sand paste layer on the top surface.
