What Is Bleeding In Concrete?
Bleeding in concrete is sometimes referred to as water gain. This is a special form of separation, in which some water from the concrete flows to the surface of the concrete, with the lowest specific gravity among all concrete components.
Excessive bleeding is seen in thin members such as roof slabs or road slabs, and when the concrete is placed in sunny weather.
Effect of Bleeding concrete?
Water comes up due to bleeding and freezes on the surface. Sometimes, with this water, a certain amount of cement also comes to the surface. When the surface is worked with a trowel, the aggregate moves down and cement and waterfall to the top surface.
This formation of cement paste on the surface is known as “latency.” In this case, the wear on the top surface of the slab and pavement will not be good. This wave created on the roads produces dust in summer and mud in the rainy season.
The water forms a continuous channel as it travels from the bottom to the top. If the use of the water-cement ratio is more than 0.7, the bleeding channel will remain constant and unpublished.
These continuous bleeding channels are often responsible for generating permeability of concrete structures. While the water of the mixture is in the upward process, it may be hindered by the aggregates. This accumulation of water creates a water solute and reduces the bond between the aggregate and the paste.
The above aspect is more obvious in the case of layered aggregates. Similarly, water that accumulates under reinforcing bars reduces the bond between reinforcement and concrete.
The poor bond between aggregates and paste or paste due to reinforcement and bleeding can be ameliorated by the re-vibration of the concrete. Delayed refinement can result in reduced ill-effects of delay and formation.
The rate of bleeding increases over time to about one hour, and thereafter the rate decreases but continues to decrease more or less until the final time of cementing.
Prevention of bleeding in concrete
- Bleeding can be reduced with appropriate proportions and uniform and complete mixing.
- Bleeding is reduced by the use of finely divided pozzolanic materials, making a long way to cross the water.
- The air-penetrating agent is very effective for reducing blood.
- Bleeding can be reduced by the use of fine cement or cement with low alkali content.
After draining the water, it had played its role in providing workability, healing the concrete from the body of the concrete through bleeding.
When the concrete mass is completely plastic, the initial bleeding may not cause much damage, because the concrete is in that state completely plastic, will freeze and shrink.
It is delayed bleeding when the concrete has lost its plasticity, causing undue damage to the concrete. Controlled re-vibration can be adopted to remove the ill effects of bleeding.
What Is Segregation In Concrete?
Segregation is usually caused by excessive vibration of cement. The different materials that make up the concrete mix have different weights, so while the concrete is in a liquid state there is a tendency for heavier materials to settle to the bottom, and the lighter slurry to rise to the top.
Isolation means the separation of newly designed solid ingredients from each other in a non-uniform mixture. More specifically, it implies the separation of coarse aggregates from the mortar in which they are composed due to differences in the size, density, shape, and other properties of the material.
Due to the separation, the hive is made into concrete, and it basically affects the strength of the concrete and its porosity. During concrete work, isolation in concrete can occur on-site, and this affects the durability of your structures. In fine concrete, all the ingredients are properly distributed and form a homogeneous mixture.
If a concrete sample exhibits a tendency to separate coarse aggregates from the rest of the material, it indicates the separation in the concrete.
Segregation Can Be of Three Types
- Separating or excluding coarse aggregates from the rest of the matrix.
- Separate paste from the coarse aggregate.
- Separate water from the rest, being the material of lowest specific gravity.
They are keeping in mind various parameters like well-made concrete, grading, Site badly mixed mixtures where there is not enough matrix to bind and contain aggregates Harmonious blend.
The harmonic and fatty features of the matrix do not allow the aggregate to collapse at the same time; The matrix itself is sufficiently contained by the set. Similarly, water is also not easy to get out of the rest of the material independently.
Conditions Favorable for Isolation :
- Inadequately mixed concrete with excess water content
- Concrete falling from height in case of placing concrete in column concreting
- When concrete is discharged from a badly prepared mixer, or from a mixer with worn-out blades
Conveyance of concrete by conveyor belt, wheelbarrow, long-distance slope by dumper, long lift by skip and hoist are other conditions that promote isolation of concrete
The vibration of concrete is one of the important methods of condensation. It should be remembered that only a comparatively dry mixture should be vibrated.
It is too wet a mixture is highly shaken; It is likely that the concrete falls apart. It should also be remembered that the vibration has been sustained for the time required for optimal results.
If the vibration continues for a long period of time, in particular, in a very wet mixture, it is likely to result in the separation of concrete due to the disposal of coarse aggregates in the matrix.
Harmful Effects Due to the Segregation of Concrete
- To comb the concrete honey.
- The high permeability of concrete.
- Low compressive strength.
- Poor finishing of surfaces.
Control of Segregation
We can control the separation of concrete in the following ways
- By proper selection of aggregates.
- By proper handling of concrete.
- Applying controlled vibration.
- Adopting leak proof formwork.
FAQ on Bleeding and Segregation in Concrete
What is bleeding in concrete?
Bleeding in concrete refers to the phenomenon where water rises to the surface of freshly placed concrete due to the settlement of heavier materials. This can result in a layer of water and cement on the surface, known as ‘laitance’.
What are the effects of bleeding on concrete?
Excessive bleeding can lead to poor surface quality, reduced durability, and increased permeability of concrete structures. It may also cause segregation issues if not managed properly.
How can bleeding in concrete be prevented?
Bleeding can be minimized by using appropriate mix proportions, ensuring uniform and thorough mixing, and utilizing additives like air-entraining agents or finely divided pozzolanic materials.
What is segregation in concrete?
Segregation in concrete occurs when the components of the mix separate, with heavier materials settling to the bottom and lighter materials rising to the top. This can lead to non-uniform distribution of aggregates and mortar.
What are the types of segregation in concrete?
Segregation can manifest as separation of coarse aggregates from the matrix, separation of paste from coarse aggregates, or even separation of water due to its lowest specific gravity.
What are the causes of segregation in concrete?
Segregation can be caused by inadequate mixing, excessive water content, improper handling during transportation or placement, and improper vibration techniques.
What are the harmful effects of segregation in concrete?
Segregation can result in decreased strength, increased permeability, poor surface finish, and reduced durability of concrete structures.
How can segregation in concrete be controlled?
Segregation can be controlled by using well-graded aggregates, ensuring proper handling and placement procedures, and employing appropriate vibration techniques during concrete placement.
What are some practical tips to prevent both bleeding and segregation in concrete?
Ensure proper mix design, use appropriate water-cement ratio, handle and transport concrete carefully, employ suitable vibration methods, and maintain proper curing conditions to minimize bleeding and segregation issues.
How do bleeding and segregation affect the overall quality and longevity of concrete structures?
Both bleeding and segregation can compromise the quality, durability, and aesthetic appearance of concrete structures if not properly managed. They can lead to structural defects, reduced performance, and higher maintenance costs over time.
