Segregation in Concrete

Segregation in Concrete
Student Name: Nzar Braim Omar
Class: 4th
Stage
Course Title: Elective Subject
Department: Geomatics (Surveying)
College of Engineering
Salahaddin University-Erbil
Academic Year 2019-2020

2
Abstract
The main explanation of this report of Segregation in concrete in terms of
concrete and self-compacting. The aim was to find an analytical relation to
estimate the risk of sedimentation, using the characteristics of the particles
and those of the mortars. The prediction of surface effect segregation (i.e.
transportation of different particle size fractions during heap formation) has
been the subject of a significant level of study.
Explanation the type of segregation in term size, dry, wet, and water separate
and effect segregation in concrete in term strength and cracks, and
Prevention of Segregation in Concrete.
I brought up an example that supports segregation in concrete which is used
in Kurdistan Region, and explaining the example in term caused segregation
effect in concrete.

3
Table of Content
Abstract .................................................................................................... 2
Table of Content....................................................................................... 3
Introduction.............................................................................................. 4
Method...................................................................................................... 5
Evaluation................................................................................................. 6
Types of segregation................................................................................. 8
Effect of Segregation in Concrete............................................................ 9
Prevention of Segregation in Concrete.................................................. 10
Example of segregation.......................................................................... 11
Conclusion .............................................................................................. 12
Reference ................................................................................................ 13

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Introduction
The segregation phenomena can be significant in several fields, such as in
production processes of the pharmaceutical, chemical, food, steel, and
cement industries, and its quantitative prediction is vital to improving
product quality and design of the material handling equipment [1]. Thus, it
has been well established in material science that granular systems are
capable of undergoing segregation by virtue of a variety of physical property
differences, such as particle size, density, inelasticity, or surface roughness,
and grain friction.
Segregation which corresponds to the loss of homogeneity between both the
granular and the suspending phases, remains one of the major problems of
both traditional and self-compacting concretes. Consequences of this
pathology are numerous and may affect the long-term properties of the
structures (resistance, durability). To ensure the concrete’s quality and
characteristics, it is essential to be able to control its homogeneity both
during manufacture and also once the concrete has been poured into
formworks. Some techniques and tests, concrete index of segregation,
column of static segregation, sieve segregation resistance test, stability test,
allow the control of fresh concrete at the concrete mixing plant and prevent
some problems of delivery and implementation of the concrete. There are
however presently very few methods allowing the measurement of on-site
segregation in order to check or to diagnose the structure pathology.

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Method
Several approaches describing the sedimentation of aggregates in SCC are
commonly known. In some cases only single particles in a homogeneous
fluid are regarded whereas in other cases the complex polydisperse system
of concrete is considered. Applying Stoke's law to a single particle it
becomes obvious that the viscosity of the surrounding medium controls the
sinking speed whereas a stagnation Of the movement is only caused by a
distinct yield stress 𝜏 𝑜 Several authors describe a critical particle diameter
dlim as defined in Eqn. (l).
𝑑𝑙𝑖𝑚 = 𝐶.
𝜏 𝑜
∆𝜌.𝑔
(1)
For d > dlim sedimentation occurs. C is a model-depending constant, with
values between 1 .5 and 20.97. In Roussel [1]
, however, proves 1.5 to be
wrong. He concludes that the minimum possible theoretical value lies at
4.71. The key question of the above approach is the correct assumption of
the effective yield stress 𝜏0 and the shape and location of the activated
shear area.

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Evaluation
Regarding the concrete specimens, a strong influence of the mortar content
on the segregation behavior could be observed, High mortar contents allow
achieving the aimed concrete properties by using a mortar with high yield
stress. Thus the coarse aggregates are rather stable in the mix. Decreasing
the mortar Content. The mortar's theological properties have to be changed
to achieve the same concrete properties, thus increasing the sedimentation
risk. By increasing the amount of coarse aggregates the supporting effect of
the granular lattice and thus the segregation resistance is improved. Figure
(2) shows a concrete with good sedimentation stability whereas Figure (3)
Figure 2: Concrete sample without sedimentation.
Figure 3: Concrete sample with significant sedimentation
Figure 4: Concrete sample with evenly distributed coarse aggregate despite
heavy segregation behavior

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shows significant sedimentation. On the first view the coarse aggregates in
Figure (4) are well distributed. However, this concrete showed heavy
segregation features. Due to the high aggregate content this segregation is
only visible in the first top centimeter. Taking a closer look a 1-2 mm pure
paste layer without sand was detected on the top.
Figure 5: Segregation of concrete. Upper and lower slice in concrete
specimen.

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Types of segregation
Segregation can be classified [2] into the following forms:
1- When the coarse particles tend to separate out since they travel
further along a slope or settle more than finer particles. This type of
segregation occurs with a too dry lean mix.
2- When segregation occurring particularly in wet mixes, is manifested
by the separation of grout (cement plus water) from the mix. This type
of segregations is occurring with a too wet mix.
3- Water separation, when water separates out from the rest of the mix,
then water segregation (bleeding) occurs.

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Effect of Segregation in Concrete
Nowadays houses are made of concrete to get the long service life of house.
But, generally segregation in concrete reduces the strength of structural
members of houses [3]. This may result into the failure of building during
the earthquake or other natural disasters or will reduce its overall life.
Following are the awful effects of segregation:
1. Segregation results into the lower strength of concrete.
2. Segregation causes the porous or honeycombed concrete which
develops the problem of leakages in your house. It ultimately results
into the defects like corrosion in concrete, carbonation, etc.
3. Segregation develops the cracks in concrete which ultimately leads to
the early repair of house. A segregated concrete is a concrete of a
variable strength and is relatively prone to cracking and leakages.
Therefore, it is very important.

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Prevention of Segregation in Concrete
Following are useful tips to avoid segregation in concrete
1. The concrete mix should be properly designed with optimum quantity
of water i.e. not too wet nor too dry.
2. Make sure the concrete is properly mixed at the correct speed in a
transit mixture for at least two minutes. Regularly check the
performance of mixer with respect to adequate uniformity of
distribution of constituents in each batch.
3. Transport the concrete mix correctly. Choose the shortest route for
transportation of concrete mix.
4. Place the concrete in its final position as soon as possible. Never place
a concrete from large heights.
5. Formwork should be water tight so that paste should leakage from the
forms. Do not vibrate formwork.
6. Do not allow concrete to flow.
7. Use the vibrator correctly and never use the vibrator to spread a heap
of concrete over a large area.
8. Vibrate the concrete for just the right time-not too long, not too less.
9. Use chemical admixtures such as air entraining agent in the mix.
Entrained air reduces the danger of segregation.
10. If any segregation is observed in concrete, remixing should be done
so to make it homogeneous again.

11
Example of segregation
Example of segregation available in Kurdistan Region if we see in the
column determine the sedimentation in below of column in figure (6), this
cause as follow:
1-In casting concrete in the column using a lot of hit vibrator in the
column.
2-The sequence between sand and gravel does not the same perfect ratio.
3-If the concrete used is very heavy.
4-If the number of bars a lot did not pass concrete in column.
5-If the side of a concrete casting does slope.
6-The segregation of column steel determines so bad of building, and
some cause we have, etc.
Figure 6: example of segregation in Felid

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Conclusion
It could be shown that the overall mixture proportioning has a significant
influence on sedimentation (segregation). The sedimentation resistance is
mainly controlled by the yield stress of the mortar. The viscosity is only of
minor importance. At rest the yield stress of the mortar must be able to
prevent all aggregates from moving. A high viscosity cannot stop the
segregation of particles; it can only control the speed of the movement.
However, the viscosity should not be too low to limit the distance the
aggregates may move at times when the yield stress is disrupted by
unexpected external influences. Having the choice between a high viscous
mixture with low yield stress and a low viscous mixture with high yield stress
in terms of segregation risk the latter should always be favored.

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Reference
[1]. Petrou, M.F. et al. (2000), A unique experimental method for
monitoring aggregate settlement in concrete, Cement and Concrete
Research, vol. 30, n. 5, pp. 809-816.
[2]. Concrete Technology by A.M. Neville, second edition.
[3]. Website name: Engineering Discoveries,
https://engineeringdiscoveries.com/2019/03/05/what-is-segregation-in-concrete-mix-
tips-to-reduce-segregation-in-concrete/

Segregation in Concrete

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