Category Archives: CONCRETE

Reinforced cement concrete is a topic you will need to familiarize at some point, if you are into civil engineering field. The category explicitly presents it. Reinforced cement concrete (RCC), a composite material has been accepted worldwide as a construction material, bridges, retaining walls, docks and harbour, airfield pavements, flyovers,multi-storey building,complexes and simple houses etc., Concrete is good in resisting compression but is very weak in resisting tension. Hence reinforcement is provided in the concrete wherever tensile stress is expected. The best reinforcement is steel since the tensile strength of steel is quite high and the bond between steel and concrete is good. As the elastic modulus of steel is high, for the same extension the force resisted by steel is high compared to concrete. However in tensile zone, hair cracks in concrete are unavoidable. Reinforcements are usually in the form of mild steel or ribbed steel bars of 6 mm to 32 mm diameter. A cage of reinforcements is prepared as per the design requirements, kept in a formwork and then green concrete is poured. After the concrete hardens, the formwork is removed. The composite material of steel and concrete now called R.C.C. acts as a structural member and can resist tensile as well as compressive stresses very well. Aggregates are the inert or chemically inactive materials which form the bulk of cement concrete. These aggregates are bound together by means of a cement. They can be classified into two. The selection of aggregate is based on the purpose and its maximum size.

CONCRETE, quality tests on concrete

Ultrasonic pulse velocity test || UPV Test – Types and Methodology

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The ultrasonic pulse velocity test, or UPV test, is an example of a non-destructive concrete test. Generally, hardened concrete is subjected to non-destructive testing (NDT) and destructive tests (DT). Concrete is the world’s oldest and most significant construction material. Therefore, concrete testing is crucial for assessing the stability, strength, durability, and condition of structures.

Non-destructive testing of concrete is a way of analysing concrete structures without causing damage. This aids in ensuring the structural quality and condition. The strength of the concrete is also influenced by various characteristics, including hardness, density, curing circumstances, ingredient quality, workability and water-to-cement ratio, etc.

This article discusses the UPV test, which is one of the most well-liked and reliable non-destructive tests carried out on concrete structures.

  1. Ultra sonic Pulse Velocity test (UPV Test)
  2. Relevant IS code for Ultrasonic Pulse Velocity Test (UPV Test)
  3. Ultrasonic Pulse Velocity tester
  4. Principles of Ultrasonic Pulse Velocity test
  5. Objective of UPV tests
  6. Factors affecting Ultrasonic pulse velocity test
  7. Methodology of Ultrasonic Pulse velocity tests
    1. Direct method
    2. Indirect method
  8. Result interpretation of UPV testing
  9. Conclusion

Also read : Bitumen tests – 9 tests for flexible pavements

Ultra sonic Pulse Velocity test (UPV Test)

The most efficient and fast method of testing concrete is through ultrasonic pulse velocity tests, or UPV tests. The quality of concrete is assessed using the results of UPV tests, which evaluate the period of travel of ultrasonic pulse waves. A 50–55 kHz range must be maintained for the ultrasonic pulse wave’s frequency. The pulses are generated by the UPV tester’s pulse generator and are allowed to travel through the concrete. By monitoring the traversing distance and the duration, the pulse velocity can be determined. Higher velocity indicates that the density and elastic modulus of the concrete are higher.

Cracks and defects in the structure are detected using UPV tests. Significant variations in pulse velocity values are indicative of broken and degraded concrete. The concrete’s density and wave velocity are related. Therefore, this test has a tremendous potential for evaluating the quality of concrete.

Relevant IS code for Ultrasonic Pulse Velocity Test (UPV Test)

IS-13311 (Part 1):1992 (Reaffirmed- May 2013) “Non-Destructive Testing of Concrete- Methods of Test (Ultrasonic Pulse Velocity)”

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Ultrasonic Pulse Velocity tester

The UPV tester is the name of the type of equipment used to measure ultrasonic pulse velocity. The following accessories are included in ultrasonic pulse velocity tester.

  • Electrical Pulse generator
  • Pair of Transducers (probes)
  • Amplifier
  • Electronic timing device
Ultrasonic Pulse Velocity Tester
Ultrasonic Pulse Velocity Tester

Principles of Ultrasonic Pulse Velocity test

The electrical pulse generator generates pulses that are sent through the UPV tester’s transducer. Through the concrete surfaces, the pulse generates many reflections. Using the formula shown below, the pulse velocity is calculated.

Pulse velocity, V = L/T

where L is the traverse distance, T is the time for the receiver to receive the pulse

The geometry of the material is unrelated to the UPV test. Better concrete strength is associated with higher velocity and vice versa. One of the dynamic tests for concrete is the ultrasonic pulse velocity test.

Objective of UPV tests

The main objectives of the ultrasonic pulse velocity test or UPV tests are

  • To learn the homogeneity of the concrete.
  • Determines the presence of cracks, voids and imperfections. 
  • To calculate the elastic modulus of concrete. 
  • Finds the quality of concrete relative to the standard requirements. 
  • To determine the age of concrete. 

Factors affecting Ultrasonic pulse velocity test

The UPV test detects cracks and assists in structure development. However, a number of factors influence how pulse velocity is measured. As a result, compressive strength cannot generally be approximated from the pulse velocity. The following are the elements that impact the UPV test.

  • Presence of reinforcement
  • Water content
  • Mix proportion
  • Temperature of concrete
  • Concrete age
  • Stress level of concrete

Methodology of Ultrasonic Pulse velocity tests

Piezoelectric and magneto strictive types of transducers are suitable for use with the UPV test. Additionally, its frequency range should be between 20 and 150 kHz. The electronic timing device monitors time with an accuracy of 0.1 microseconds.

The transducer transmits the waves that travel through the concrete surface. The receiver transducer detects the electric signals that are generated once the pulse waves are transformed to them. The traversal length will be displayed as ( L). The electronic timing device calculates how long it takes for signals to arrive. Time is shown as (T).


The Electronic timing device measures the receiving time of the signals. The time is denoted as (T).

Pulse velocity (v) = L/T

There are three common methods for doing UPV tests. They are direct method and indirect method.

  • Direct Method of UPV Testing
  • Indirect Method of UPV Testing
Methodology of UPV test
Methodology of UPV test

Direct method

The maximum energy is transmitted at right angles to the face of the transmitter. As a result, to achieve the greatest results, the receiving transducer must be placed on the side of the transmitting transducer. This is referred to as the direct approach or cross probing.

Ultrasonic pulse velocity test
Ultrasonic Pulse velocity test -Types

Indirect method

In some circumstances, the opposite side of the structure may be inaccessible. The receiving and transmitting transducers are installed on the same face of the concrete members in this scenario. This is known as the indirect method or surface probing. This approach is less effective than the direct approach. The test findings are mostly influenced by the surface concrete, which has different properties from the structural components’ core concrete.

Result interpretation of UPV testing

The density and elastic modulus of concrete are correlated with the ultrasonic pulse velocity. This in turn depends on the components, mixing processes, placement techniques, concrete compaction and curing, casting temperature, etc.

The main causes of internal cracks and pockets in concrete are lack of compaction and concrete segregation. Lower pulse velocity values are a result of these concrete defects. However, the laboratory tests might have confirmed a well-designed concrete.

The range of pulse velocity in the direct method is as shown below.

  1. Above 4.5 Excellent
  2. 3.5 to 4.5 Good
  3. 3.0 to 3.5 Medium
  4. Below 3.0 Doubtful

Conclusion

The final assessment of compressive strength from UPV is not the sole criterion used to determine concrete strength. The strength is confirmed by comparing it to a compressive strength estimate derived from the same ingredient mix and conditions. The results of the UPV test and site tests conducted using similar ingredients may be correlated. When compared to actual UPV intensities, the numbers may change by about 20%.

CONCRETE

Concrete Mixing || Mixing concrete – Objectives and types

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Concrete Mixing or Mixing of concrete is the complete blending of the ingredients necessary for the production of a homogeneous concrete. In the previous blogs, we saw different types of concrete and their quality tests. Today, let me walk you through the details of it.

To begin with, let’s try to understand the objectives of mixing concrete and concrete mixing types

  1. Objectives of Concrete Mixing
  2. Concrete Mixing Types
    1. Hand Mixing of concrete
      1. Process – Hand Mixing of concrete
    2. Machine Mixing of Concrete
      1. Concrete Mixing Machine
      2. Machine Mixing Process
    3. Ready Mix Concrete
    4. Mixing Ratios
  3. Conclusion

Objectives of Concrete Mixing

How many of you have wondered why we mix concrete? Read on to find the answers.

  • To manufacture high-quality fresh concrete, proper mixing of materials is critical. 
  • The surface of all aggregate particles is coated with cement paste during the mixing phase.
  • For the desired workability and performance of concrete in both the fresh and hardened states.
  • To avoid segregation and bleeding.

In the next section, we will learn the types of concrete mixing

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Concrete Mixing Types

There are three methods to produce efficient and high-quality concrete.

  • Hand Mixing – Mixing concrete manually without a mixer machine.
  • Machine Mixing – Mixing using a mixer machine.
  • Ready Mix Concrete – Mixing is done in an automatic or semi-automatic batch plant.

Let’s dig deeper into each of them.

Hand Mixing of concrete

  • Method of manually mixing the concrete materials without the use of a mixer machine. 
  • Hand mixing is done only for small jobs where the concrete demand is low and quality control is not critical. 
  • Uniformity of mixing is difficult to achieve by hand mixing. It necessitates extra caution and effort. 
  • In the case of hand mixing, 10% more cement should be applied to the nominal mix concrete proportion.
Hand mixing of concrete
Hand mixing of concrete

Process – Hand Mixing of concrete

  • Hand mixing is done on a flat iron sheet plate base that is hard, clean, and non-porous.
  • On the platform, a measured amount of sand is placed.
  • Then the cement is poured over the sand.
  • In a dry state, the sand and cement are thoroughly combined with shovels several times until the mixture achieves an even colour.
  • The coarse aggregates are then spread out on top of the above mixture and thoroughly mixed. 
  • The whole mixture is properly mixed by twisting it from centre to side, back to centre, and then to the sides several times.
  • After that, depression is rendered in the mixed materials’ nucleus.
  • 75 per cent of the necessary amount of water is then poured into the depression and mixed with shovels.
  • Finally, the remaining water is applied, and the mixing process is repeated until the concrete has a uniform colour and consistency. 

The total time for concrete mixing does not exceed 3 minutes.

Let’s move on to the next method ie mechanised concrete mixing.

Machine Mixing of Concrete

  • The method of combining concrete materials with a concrete mixer system is known as machine mixing. 
  • It meets the demands of fast mixing times, optimal consistency, and homogeneous concrete efficiency. 
  • Since it ensures uniform homogeneity, machine mixing of concrete is best suited for large projects requiring large quantities. 

Concrete Mixing Machine

It is also known as a concrete mixer is a machine that mixes cement, aggregate (such as sand or gravel), and water in a uniform manner to shape concrete. A rotating drum is used to combine the components in a traditional concrete mixer. Concrete mixers powered by gasoline, diesel, or electricity are now widely available. The mixer machine is mostly used for mixing ingredients by volume. They are also used for mixing ingredients by weight by providing weigh batcher.

Mixer machine in action
Mixer machine in action

Machine Mixing Process

  • Wet the inner surfaces of the concrete mixer drum first.
  • The coarse aggregates are added first, followed by sand, and finally cement, in the mixer.
  • In a mixing machine, combine the products in a dry state. In most cases, 1.5 to 3 minutes should suffice.
  • While the machine is running, slowly add the appropriate amount of water after the dry materials have been thoroughly mixed. 
  • Don’t use any extra water.
  • Concrete must be mixed in the drum for at least two minutes after adding water.

We have seen the details of machine mixing. How about getting an idea about ready-mix concrete?

Ready Mix Concrete

  • Ready Mix Concrete (RMC) is a specialised material in which the cement, aggregates, and other materials are weighed and batched at a central location, then mixed either in a central mixer or in truck mixers. Then it is shipped to construction sites.
  • The consistency of the resulting concrete is much superior to that of site-mixed concrete.
  • Useful on congested sites or in road construction where space for a mixing plant or aggregate storage is limited or nonexistent. 
  • Quality control of concrete is simple in this process.

So far, I have showed you the types of concrete mixing and its procedures. Now its time to throw some light on concrete mixing ratios.

Ready Mix concrete plant
Ready Mix concrete plant

Mixing Ratios

The proportions of concrete components such as cement, sand, aggregates, and water are known as concrete mix ratios. The method of building and mix designs are used to determine these ratios. In comparison to other mixing processes, the water/cement ratio in RMC can be easily managed.

Conclusion

To summarise,

  • Hand blending of concrete is the cheapest method.
  • It is only recommended for very limited projects requiring a small amount of concrete since consistent concrete consistency is difficult to achieve with this method. 
  • It ensures proper material mixing.
  • When compared to site mixing (both hand and machine mixing), RMC takes less time and produces a higher quality product.
  • It’s also very handy when you need a large amount of concrete per day.
CONCRETE, waffle slab

Waffle Slab or Ribbed slab details and Construction, Advantages

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Waffle slabs are ribbed reinforced concrete slabs. A waffle slab often referred to as a ribbed slab, is a structural component that is plain on top and has a grid pattern on the bottom. A waffle slab also called a two-way joist slab got ribs running perpendicular to each other in two directions on the underside. This slab resembles pockets of waffles because of its grid pattern. Hence they are named Waffle slab systems.

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For spans longer than 40 feet (12 metres), waffle slabs are chosen because they are stronger than flat slabs, flat slabs with drop panels, two-way slabs, one-way slabs, and one-way joist slabs. These are more expensive than other slabs but in turn, are more rigid and stable. Waffle slabs are apt for both ceiling and floor slabs. Slabs are one of the important structural components of a building. They provide a flat surface and help in transferring load. This article is about what is waffle slabs, the Construction process, Advantages and Disadvantages. 

  1. What is a waffle slab – Details and construction
  2. Waffle slab construction details
    1. In situ construction
    2. Precast
    3. Prefabricated
  3. Advantages of Waffle slab 
  4. Disadvantages of Waffle slab

What is a waffle slab – Details and construction

A waffle slab is a type of slab that is appropriate for industrial and commercial buildings. Waffle slabs are also referred to as two-way joist slabs or ribbed slabs. They have a flat top and grids on the underside. It has greater strength than flat slabs and hence is suited for longer spans. It enables both distributed and point vertical actions. The bottom layer of concrete reinforcement in waffle slabs is replaced by concrete ribs running in two orthogonal directions. Additionally, the rib depth should range from 135mm to 235mm. Because the overall depth of the floor increases as the depth of the ribs does. The structure’s lateral loading is impacted by this.

Waffle slab - supports and pods

Waffle slab construction details

The waffle slabs need only 70% of concrete and 80% of steel from the concrete and steel used for the construction of the raft slab. The construction stages of the waffle slab include the following

  • The first step is to create the forms
  • Place the formwork components in place.
  • Position your waffle pods or moulds on the shuttering. Generally, the pods are typically constructed of plastic, and they come in a variety of sizes and shapes. The size of the pod is determined by the requirements and span length. A significant number of pods are necessary for greater spans. Accordingly, the same size pods should be used for the entire slab.
waffle pods and beam supports
  • Place the support components horizontally and vertically according to the connectors.
  • Lay out the waffle pods and spacer within the formwork in a grid pattern beginning at one corner, following the instructions in the design.
waffle slab grid supports
Waffle slab supports
  • Fix the pod corners to the framework using cube joints.
  • Position reinforcement bars on the spacers between the waffle Pods.
  • Reinforcement is added in the two directions after the formwork has been fixed.
  • Lay the top mesh out according to the design specifications, then secure it where necessary.
  • Making sure connecting ribs are filled, pour the concrete and give it a good vibrating.
  • After the setting of the concrete, remove the frames into which the waffles are embedded. Then slowly remove the waffle forms. 

The construction of a waffle slab can be done in three ways

In situ construction

This process entails placing formwork and pouring concrete over it. A slab is cast on-site in the desired size and according to the design.

Waffle slab
waffle slab (https://styrofoamindustries.com.au/

Precast

Using this technique, the casting of the slab panel is done elsewhere, and it is then placed, connected, and reinforced with concrete.

Prefabricated

In this procedure, reinforcement is built into the slab panels using prefabricated steel bars. Slabs are manufactured elsewhere and brought to the location to be erected.

Advantages of Waffle slab 

  • It is suitable for large-span structures and can be achieved with less concrete and rebar than similar conventional slabs
  • They require only a fewer number of columns.
  • It possesses a higher load-carrying capacity
  • It has higher structural stability
  • They have a good aesthetic appearance. 
  • Waffle slabs are suitable for roof slabs and floor slabs.
  • Waffle slabs have high vibration control capacity
  • The construction of this slab can be done faster and easier.
  • They are light weighted 
  • They require low construction costs, Hence they are economical when compared to other conventional slabs of the same span
  • It requires only less amount concrete and can be reinforced with mesh or rebars.

Disadvantages of Waffle slab

  • Requires Expensive formwork
  • Requires skilled workmen and supervision for the construction of waffle slabs. 
  • Higher maintenance cost
  • The increase in the depth of ribs leads to an increase in the floor height.
  • This type of slab is not suitable for windy and slope areas.
CONCRETE, curing

Curing of Concrete – Concrete Curing Methods explained

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Curing concrete is the process of preserving the requisite moisture and temperature in hardened concrete for continued hydration. Concrete’s curing is crucial for sustaining the material’s longevity and design strength. This article discusses the importance of curing and the various concrete curing methods prevailing on construction sites.

  1. Curing of concrete methods
  2. Why Curing of concrete is important?
  3. Concrete Curing time as per IS 456-2000
  4. Concrete curing methods
    1. Water Curing method
    2. Membrane Curing method
    3. Steam curing method
  5. Conclusion

Curing of concrete methods

Curing is the process of retaining moisture to allow fresh concrete to reach its intended strength in a predetermined manner through a hydration reaction. Concrete is a mixture of cement, aggregates, and water in fixed designed proportions calculated based on specific strength requirements. The water to cement ratio is the most important factor in these proportions (Water cement ratio). In order to facilitate the hydration reaction, the water-cement ratio must be maintained. If the water evaporates quickly, there will not be enough water available for the hydration process. Because of this curing of concrete is required.

Curing assists in the retention of moisture until the hydration process is complete and it reaches the required strength. The American Concrete Institute (ACI) Committee 301 recommends a minimum cure duration equal to 70% of the required compressive strength. According to IS 456-2000 standards and construction norms, the curing period of 7 days/10 days is the time required to achieve at least 70% of the intended compressive strength. That is why concrete is cured for 7-10 days.

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Why Curing of concrete is important?

Perfect curing is necessary for the following reasons in order to achieve good strength and serviceability:

  • Curing prevents concrete from drying and maintains the acceptable temperature range by preventing moisture loss.
  • Curing increases the strength and decreases the permeability of hardened concrete.
  • Curing prevents the formation of cracks caused by thermal and plastic shrinkage.
  • Concrete curing maintains a strong link between the components and the reinforcement.
  • Curing can provide the desired strength and a durable concrete free of cracks.
  • Concrete curing assists in achieving high serviceability performance by improving abrasion resistance.

Also Read : Concrete Pumps Types – Application and advantages

Concrete Curing time as per IS 456-2000

According to the Indian Standard IS 456 – 2000, concrete should be allowed to cure for a minimum of seven days while using ordinary Portland cement and for a minimum of ten days while using blended cement or concrete with mineral admixtures. Additionally, it suggests that the curing time should not be less than 10 days for structures exposed to hot, dry weather and 14 days in case for or blended cement or cement with mineral admixtures.

OPC cement = 7 Days (Normal conditions) and 14 Days ( Hot and dry weather)

Concrete with mineral admixture or blended cement (PPC cement) = 7 Days (Normal conditions) and 14 Days ( Hot and dry weather)

Concrete curing methods

The curing method and time primarily depend on structure type, site conditions, and ingredient parameters. Some of the curing methods adopted in constructions sites are as follows.

  • Water curing
  • Membrane Curing
  • Steam curing

Water Curing method

Water curing is the most popular and common method adopted in construction sites. Basically, this method maintains or retains water on the concrete surface by various methods. This includes ponding, sprinkling and fogging, and saturated wet coverings or left-in-place forms.
Similarly, these methods prevent water loss from the concrete surface by continuous wetting of the exposed surface of the concrete.

Water curing
Water curing

Membrane Curing method

The basic concept of membrane curing is reducing the loss of water from the surface of the concrete. Generally, membrane curing methods uses curing compounds or impervious plastic sheets. Curing compounds are available in water-based and acrylic-based types. They form an impermeable membrane and reduces the loss of moisture.

Membrane curing /Curing compound
Membrane curing /Curing compound

Steam curing method

The steam curing process accelerates the process of strength gaining by using heat and providing additional moisture. Generally, this speeds up the early hardening process. Basically, these methods are familiar in prefabricated structures and factory-made precast components for the speedy recovery of form works.
Accordingly, Steam curing keeps the surface moist and raises the concrete temperature to speed up the strength achievement rate.

Steam curing - Precast factory
Precast factory

Conclusion

Now a days curing activity is not taken seriously and this hampers the strength and quality. Likewise, this is an activity to be done with utmost care to ensure design strength and serviceability of structures.

CONCRETE

Construction Joints in concrete – Construction joint types in slabs

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Construction joints in concrete are a crucial and fundamental component of civil engineering and construction. Changes in temperature and moisture can cause concrete to expand and contract. Because concrete is weak in tension, shrinkage and volume change in concrete cause cracks. The construction joints installed at strategic locations prevent the formation of cracks in concrete and the development of tensile stresses. A construction joint is a type of concrete joint used when a new section of concrete is poured next to an already set section of concrete. The purpose of a construction joint is to allow for some horizontal movement while remaining rigid against rotational and vertical movement. This article discusses the significance of construction joint types in concrete structures like slabs and pavements etc and their applications and features

  1. Construction joints in concrete – Significance
  2. Construction joints types
  3. Construction joints
  4. Expansion joints
  5. Contraction joints

Construction joints in concrete – Significance

In general, joints in concrete are strategically placed between slab and beam, wall and column, concrete floors, pavements and so on. Improper use of joints can result in defects, cracks, and the development of stresses. Construction joints can be filled or left empty. The space between joints is occasionally filled with materials like elastomers, bitumen asphalt mix, polysulphide sealents etc. Construction Joints also divide a larger span into smaller units, making construction easier. As a result, it also aids in preventing the total collapse of the structure. Depending on the type of joint, joints are installed either before or after the laying of concrete.

Construction joints types

On the basis of the functions, Joints in construction are classified into three types

  1. Construction joints
  2. Expansion joints
  3. Contraction joints

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Construction joints

Generally, construction is a time-consuming process. Construction joints separate the large concrete work into small units. This type of joint is apt for locations where the construction is stopped at the end of the day’s work. A construction joint is a type of concrete joint used when a new section of concrete is poured next to an already set section of concrete. The purpose of a construction joint is to allow for some horizontal movement while remaining rigid against rotational and vertical movement.Construction joints can be further classified into four types on the basis of the joint end. They are

  • Butt-type construction joint
  • Tong and groove type construction joint
  • Butt-type construction joint with dowels
  • Butt-type construction joints with tie bars
Concrete construction joints in concrete

On the basis of the structure, the construction joint can be vertical, horizontal and inclined. It is suitable for the construction of large slabs, irrigation channels, etc. These joints consist of keys at definite intervals. These keys help in resuming the work the next day. It also helps in uniform load distribution.

Expansion joints

Concrete tends to expand due to changes in temperature and moisture. This causes the development of cracks and leads to failure. To avoid this problem expansion joints are used. Another name for the expansion joint is the control joint. This joint allows the expansion of concrete without the development of stresses. Thus we can prevent cracks. Buildings longer than 45m typically have one or more expansion joints. The recommended c/c spacing in India is 30m. The joints are formed by leaving a space between the building components. Generally, the depth of the expansion joint is one-fourth of the slab thickness. Installation of expansion joints can be done before or after the laying of concrete. Before installing make sure to cut the joints deeply. It is apt between the bridge section, pavements, railway tracks etc. 

Concrete construction joints in concret

Contraction joints

Concrete is weak in tension, therefore contraction of the concrete induces stress leading to cracks. This occurs during the hardening of concrete. Contraction joints prevent the unnecessary development of cracks. This type of joint in construction is installed before the laying of concrete. It is apt during the construction of roads, retaining walls, floors, tunnels, canals, etc. Generally, the interval of contraction joints is between 5m to 10m. Jointing tools are used for the installation of contraction joints. If the concrete is reinforced, then contraction joints can be avoided. But in un-reinforced or lightly reinforced slabs this joint is necessary to minimise the formation of cracks. 

Construction joints in concrete
CONCRETE

Segregation and bleeding in concrete – Types, Causes and remedies

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Segregation is the separation of concrete ingredients from one another. Concrete is one of the most used construction materials. It consists of coarse aggregate, fine aggregate, cement and water. There are many reasons for the cause of segregation. This article is about segregation and bleeding and their types, causes and remedies.

  1. What is Segregation in Concrete?
    1. Causes of Segregation in Concrete
    2. Types of Segregation
  2. Bleeding
    1. Causes of bleeding in concrete
    2. How to reduce bleeding in concrete?

What is Segregation in Concrete?

Workability is an important property of concrete that reflects how easily we can place a particular concrete mix . Good concrete should be uniformly mixed and easily placeable without segregation or bleeding.

What is segregation in concrete ?

Segregation of concrete is the separation of ingredients in concrete. Since concrete is a non-homogeneous material, improper mixing is the main reason for the segregation. It occurs during transporting, handling and placing of concrete. Also, it affects the concrete properties. The strength of concrete decreases and leads to cracking. Therefore it should be properly mixed before use in construction. 

segregation
segregation

Causes of Segregation in Concrete

A good quality concrete mix is prepared by considering factors like the size of aggregate, water-cement ratio, compaction, etc. They are many reasons for the causes of segregation. They are

Prevention of segregation is very important as it adversely affects the properties of concrete. 

Types of Segregation

Segregation occurs in three types such as

  1. Separation of water and cement from other ingredients
  2. Segregation of coarse aggregate
  3. Separation of water content

Segregation is hard to measure since there is no particular test for determining it. However, the Flow table test measures the segregation. Also, the slump test of concrete can give an idea about segregation. Coarse aggregate in concrete tends to settle down from other ingredients. Usually, It occurs when the concrete mix is dry. While segregation by separation of water content occurs due to an insufficient amount of fine aggregates or due to the use of an excess amount of water content.

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Bleeding

What is bleeding in concrete?

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. Bleeding is also similar to segregation in which the water in the concrete rises to the surface of the concrete. As a result, the concrete becomes porous and weak.

Bleeding affects its strength and its durability of concrete . Likewise, It breaks the bond between the concrete and steel reinforcement. However, a proper proportion of concrete ingredients and controlled vibration can reduce bleeding. Moreover, air entraining admixtures can also be used for reduce bleeding. 

Bleeding of concrete
Bleeding of concrete

Causes of bleeding in concrete

The main causes of bleeding in concrete mix is as follows

  • Segregation is the main cause of bleeding in concrete
  • High water cement ratio causes bleeding.
  • Type of cement used and quantity of fine aggregate
  • Over vibration

How to reduce bleeding in concrete?

By adapting the following methods bleeding can be reduced

  • Minimum water cement ratio should be maintained.
  • A proper design mix
  • Use mineral admixtures like fly ash
  • Use air entrapping admixtures
  • Maintain fine aggregate ratio