What is bleeding and Laitance?

BLEEDING in concrete is a phenomenon in which free water in the mix rises up to the surface and forms a paste of cement on the surface known as “laitance” . Bleeding occurs in concrete when course aggregates tends to settle down and free water rises up to the surface.

What is the meaning of Laitance?

Definition of laitance

: an accumulation of fine particles on the surface of fresh concrete due to an upward movement of water (as when excessive mixing water is used)

What is segregation and bleeding?

Segregation occurs when the principal ingredients in a concrete mix – in other words, gravel aggregate, cement, and water – separate prior to and during the curing process. Moreover, Segregation causes excessive amounts of water to rise to the surface. This process is know as bleeding.

What causes Laitance?

Laitance is a weak, easily-crumbled layer on the surface of concrete, consisting of cement and fine aggregates that rise to the surface when too much water is added. Laitance may also be caused by over-trowelling, rain damage, or poor curing.

What is meant by bleeding concrete?

Bleed in concrete is the result of excess water being forced to the surface of the concrete. Understanding the cause of bleed can assist in properly managing and eliminating its occurrence. The four primary ingredients of concrete are stone, sand, cement and water.

Segregation, Bleeding ,Harshness and Laitance - Properties of Concrete -Advanced Concrete Technology

What is Slump value?

In case of a shear slump, the slump value is measured as the difference in height between the height of the mould and the average value of the subsidence.

Why curing is done?

Curing ensures hydration of the cement, which in turn enhances it, s strength and durability. Curing takes place immediately after placing of the concrete and deals with maintenance of the desired temperature and moisture for extended periods of time.

What does Laitance look like?

Laitance is the weak, milky or powdery layer of cement dust, lime and sand fines that appear on the surface of concrete.

How do I stop Laitance?

Laitance can be avoided by controlling the amount of water in the concrete mix during construction. If too much water is introduced into the concrete various other issues can occur such as greater shrinkage with the possibility for more cracks and reduced compressive strength overall.

When can I remove Laitance?

Laitance should be removed by light abrasion using a suitable sanding machine. The best time to do this is 7 to 14 days after the installation of the screed. It will also help to dry the screed as it allows the moisture to escape.

What is meant by segregation in concrete?

Segregation in concrete is a case of particle segregation in concrete applications, in which particulate solids tend to segregate by virtue of differences in the size, density, shape and other properties of particles of which they are composed.

What is settlement and bleeding in concrete?

Bleeding in fresh concrete refers to the process where free water in the mix is pushed upward to the surface due to the settlement of heavier solid particles such as cement and water. Some bleeding is normal but excessive bleeding can be problematic.

What is the importance of segregation in concrete?

Segregation of concrete affects strength and durability in structures. In a good concrete, all concrete aggregates are evenly coated with sand and cement paste and forms a homogeneous mass.

What is meant by Laitance and how it can be reduced?

Laitance can be avoided by reducing or controlling water during the mixture of concrete. It too much water exists, then other issues also be happening like greater shrinkage and the possibility of more cracks in the structure. If you want to remove laitance, then It is very easy to remove by acid etchings solution.

What is concrete scaling?

Scaling is defined as a general loss of surface mortar or mortar surrounding the coarse aggregate particles on a concrete surface.

What is water cement ratio in concrete?

Water–cement ratios of 0.40 to 0.60 are more typically used. For higher-strength concrete, lower ratios are used, along with a plasticizer to increase flowability. Too much water will result in segregation of the sand and aggregate components from the cement paste.

How do you prevent Laitance in concrete?

How do you remove screed?

If you have a grinder with a brick blade do a few cuts in opposite direction to what your trying to hammer. It gives the screed somewhere to break as you hammer it. I found once I got down to slab level and could get the jackhammer on an angle it then started lifting without doing the cuts. Remove all tiles first.

What is shot blasting concrete?

Shot blasting concrete is a resurfacing process that uses metal beads “shot” out of a machine to “blast” away tough debris and contaminants. It's a comparable method to sand blasting, but it provides a much more powerful clean due to the size and speed of the metal pellets.

What is concrete efflorescence?

Efflorescence appears as a white deposit of mineral salts on face of concrete walls and/or floors. Efflorescence usually appears in underground car park areas and other subfloor areas. Efflorescence is driven by hydrostatic pressure – the pressure exerted by moisture as it moves through concrete to the lowest point.

What is the difference between PCC and RCC?

The main difference between PCC and RCC is that RCC contains steel rods or reinforcement within it but PCC does not contain reinforcement within it. So, RCC can bear the maximum tensile load on it.

What are the types of curing?

Why curing is done for 28 days?

Basic purpose to cure 28 days is there to obtain compressive strength 99%. If we cure 1 day cure it may retain 20% compressive strength which go against the building application. With 3 day curing another 20% increment in compressive strength, 7 days 65%, 14 days its up to 90%.

What are the 4 types of slump?

What are the three types of slump?

There are three types of slump that may occur in a slumps test, namely, true slump, shear slump and collapse slump.