Effect of segregation and bleeding on quality of concrete

Segregation in concrete: Segregation means the detachment of ingredients in concrete. In concrete, the following types of segregations mainly occur:-

1. Detachment of coarse aggregate from the concrete mixture,
2. Detachment of cement pastes from the concrete throughout its plastic phase.
3. Detachment of water from the concrete mix (Bleeding in concrete)

Concrete is formed by mixing cement, fine and coarse aggregates. In a standard quality concrete, is all the ingredients are grouped properly to develop a uniform mixture. Segregation in concrete is primarily occurred due to variations in specific gravities of the ingredients.

Specific gravity of Cement remains among 3.1-3.6g/cc, and for aggregate it remains among 2.6-2.7g/cc. Because of this variation, the aggregate is detached from the matrix and segregation in concrete occurred.

There are various other factors to create segregation in concrete :-

1. Moving concrete mixes for long distances.
2. Weak mix ratio, where adequate matrix does not exist to unite the aggregates.
3. When concrete falls from over 1m.
4. Vibrating concrete for a prolonged period.

Guidelines to reduce segregation in concrete:-

Segregation is managed properly with exact mix ratio.

Handling, placing, transporting, compacting and finishing of concrete in perfect manner.

With the addition of air entraining agents, admixtures and pozzolanic materials in the mix, the segregation is controlled to some extent.

Bleeding in concrete: Bleeding is a type of segregation in which existing water in the concrete mix is forced upwards owning to the settlement of cement and aggregate. Since specific gravity of water is low, the water may proceed upwards. Bleeding normally occurs in the wet mix of concrete.

Due to greater amount of water cement ratio, the bleeding is found in concrete. If the water-cement ratio is higher, the concrete becomes weak and as a result excessive bleeding happens.

The bleeding in concrete is not a cause of great concern when the rate of evaporation of water is identical to the rate of bleeding. Normal bleeding improves the workability of concrete.

When the concrete becomes completely plastic, bleeding is not injurious. However, concrete still remains in the plastic stage and it is subsidized and compacted in due course.

How bleeding impacts the stability of concrete :-

1. Since water is pushed upwards in bleeding, sometimes with this water, specific amount of cement proceeds together with water to the concrete surface. If the top surface is worked up with the trowel, the aggregate comes downward and cement paste is developed at the top surface and it is known as ‘Laitance in concrete.’ As Laitance is developed, the wearing strength of structure is reduced and the longevity of structure is hampered.
2. While directing to the top from bottom, water produces continuous channels. Because of these channels, concrete turns out to be porous and facilitates water to move, that develops water voids in the matrix and decreases the bond among aggregate and the cement paste.
3. If water is accumulated at the top surface of concrete, the surface finishing is deferred.
4. Concrete becomes porous and its consistency is affected.
5. Excessive bleeding results in rupturing the bond among the reinforcement and concrete.

Remedies to control the bleeding :-

1. Bleeding in concrete is managed with the inclusion of minimum water content in the concrete mix.
2. Allowing the application of air en-training admixtures in the mix.
3. By providing more cement in the mix.

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Published By
Rajib Dey
www.constructioncost.co
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Importance of Self-leveling Overlays in concrete construction

Self-leveling overlays are set up rapidly. It is possible to place and finish more product each day, each worker as compared to any other cast-in-place decorative product.

Self-leveling overlays become effective when substrate conditions are less than standard: obsolete or worn concrete surfaces, unflat or unlevel floors, and concrete surfaces getting damaged with other floor treatments.

Self-leveling overlays are normally used in commercial building lobbies and corridors, retail spaces, residential floors, restaurants, and warehouse floors.

Self-leveling overlay products are susceptible to atmosphere conditions. Due to this, most applications are kept in controlled indoor environments. Specific jobsite conditions should be administrated with the purpose of attaining the following results :-

• Keeping uniform temperature
• Managing air movement to remove drafts
• Protecting from the direct sunlight to the work area
• Maintaining even relative humidity all through the jobsite

There should be a good bond among the subfloor and an overlay, so exact mechanical preparation of the accessible slab is vital. Bead-blasting equipment and diamond grinders are commonly applied tools but scarifiers are also utilized, particularly for thicker placements. The size of the required equipment is based on the size of a project concerning productivity.

Self-leveling overlay products are formed by mixing cement, fine aggregates, pozzolans, and admixtures comprising of superplasticizers, polymers, shrinkage compensators, and other components. Manufacturers' mixing instructions need applicators to mix a proper amount of water with each bag of material to attain the desired properties.

Initially, the material is placed on a sub slab, the average working time is only about 12 minutes, accompanied quick strength formation. Regular application thicknesses commence at about ¼ inch but can go beyond 2 inches devoid of shrinkage or cracking problems.

The toughened product is very solid and long-lasting and it contains compression strengths of roughly 6000 psi, and attains good flexural strengths.

When inherent colors are added to self-leveling overlays, the final product demonstrates strong color devoid of any efflorescence.

To get more details, go through the following link www.concreteconstruction.net



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Published By
Rajib Dey
www.constructioncost.co
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Various types of concrete mixers

The concrete is built up through a concrete mixer by mixing cement with aggregates like sand or gravel, and water. The concrete mixers attain the consistency of the mix as well as set the mix keeping the consistency unchanged.

The process for mixing the material of concrete may vary but it should be accomplished carefully to make sure that the consistency is maintained for allotment of materials in concrete mass. It can be evaluated with uniform color and reliability of concrete.

The machine that is employed for mixing concrete is called as the mechanical concrete mixer, or just concrete mixer.

Given below, two main types of Concrete Mixers:

01. Continuous Mixer: Continuous mixers are mostly found in large constructions like dams, bridges, etc., where large masses of concrete are utilized and the constant flow of concrete is needed.

02. Batch or Drum Mixer: Batch or Drum mixer is mostly recognized in construction sites. It contains a rotating drum with blades or baffles inside it. Under this type of mixer, all the materials of the desirable proportioned mix should be entered into the hopper of the rotating drum and then drum on being revolved at a specific speed combines the materials through a series of blades arranged inside. The produced mix is finally released from the drum and transported for use.

There are following two Types of Batch Mixers.

• Tilting Mixers: Tilting mixers contain a conical or bowl-shaped drum having vanes inside. They are suitable for mixes of low adaptability and for those comprising of large size aggregate. The mixing chamber that is called as drum, is designated for discharging.

• Non-Tilting Mixers: In non-tilting mixers, the axis of the mixer always remains in horizontal direction. The discharge is accomplished either by implanting a chute into the drum or by changing the direction of rotation of the drum to the reverse or hardly by partition of the drum.

To get more information, go through the this link Gharpedia.Com




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Published By
Rajib Dey
www.constructioncost.co
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