CONCRETE

CONCRETE a composite material which consists of materials like cement, sand, aggregate, water and admixtures.

ADVANTAGES: -        i) Concrete is economical

                                    ii) Ability to cast into any shapes

                                    iii) Durable

                                    iv) Low maintenance

                                    v) High strength.

CONCRETE

TRANSPORTION:- Transportation of concrete from mixing plant to the construction site .care should be while transporting so that no any loss of ingredients occurs.

For manual mix or site mix wheel borrow is used for and for RMC (Ready Mix concrete)  Transit mixture is used.

CONCRETE MIX:-Concrete mix ratios are the proportions of concrete components such as cement, sand, aggregates and water. These mix ratios are decided based on type of construction, cost efficiency and availability of materials.

VOLUMETRIC MIX is concrete mix which is mixed by volume of material, rather than weight. Volumetric Concrete is typically mixed on-site in volumetric concrete mixers, which are self-contained portable batch plants.  These specialist trucks contain all the requisite concrete ingredient materials (sand, aggregate, cement, and water).

DESIGN MIX is the process of designing a concrete based on requirement of strength, workability by determining relative proportions of different ingredients (cement, coarse aggregate, sand, water and admixture) as economically as possible.

Typically design mix is done is certified 3^rd party testing labs by taking different mix propositions in hit and trail basis and checking their results for workability and strength keeping in eye the economical parameter.

PLACING OF CONCRETE:- Placing-Concrete should be placed as early as possible to formwork.as per IS code it should be placed in 3 hrs from the time of batching of concrete in plant. Care should be taken while placing as to ensure there is no loss of workability of concrete.

Placing of concrete is done by transit mixture, concrete pump ,Boom pleasure, chute etc.

CONCRETE PUMP                                     BOOM PLACER                               CHUTE

VIBRATION- after concrete is placed in there position compaction is to be done. Compaction educed air from the concrete and make it dense so to achieve proper strength. If compaction is not done properly then honeycomb occurs which reduces strength of the concrete.

Compaction is done by Needle vibrator, Surface vibrator, External vibrator and Table vibrator.

CURING is the way to maintain adequate moisture content & temperature in concrete at early to achieve designed strength.

Curing is done by Ponding, Moist curing (Gunny bags), Chemical curing.

CEMENT CONCRETE FLOORING

   Cement concrete flooring is one of the most common types of flooring used in both in residential as well as public buildings.

•       Advantages

1.       It is non-absorbent in nature.

2.       It is very useful for water stores.

3.       High Durability.

4.       Smooth in nature and pleasing in appearance.

5.       Good wearing Properties.

6.       Easy to maintain

7.       Economical

•But it requires proper attention while laying as defects in carelessly made floor cannot be rectified easily.

• They are used for very low maintenance cost and long life.

• For achieving more abrasion value metallic or chemical hardener is mixed, which is called ironite or chemical hardener flooring.

CONSTRUCTION OF ROOF SLAB

Construction of any roof slab comprises of these following steps..

1.Staging:-After completion of Columns upto Roof Beam Bottom Construction of Roof Slab is stats. The First stage is Staging. Staging is noting but erection of staging forms on which shuttering of Roof Slab or Beam will rest. Staging can be made of different type of materials starting wooden to metal parts, which hold is shuttering. Staging should be stable and firm to hold the load of the slab.It should be firm enough so that during concreting it should properly hold the concrete & shuttering so that shuttering do not bulge of settle.

2.Shuttering:- Shuttering is started after completion of staging. Plywood or metal any type of shuttering are used base on the load of slab. During shuttering proper alignment and level of shuttering is checked. Shuttering is properly sealed to avoid slurry lickage which will lead to honeycomb structure or segregation of concrete. Demolding agent are used in shuttering for smooth finishing of concrete surfaces and easy stripping of shuttering boards.

3. Reinforcement:- Reinforcement the third step is construction of roof slab. It can be started after completion of shuttering or it can be done together with shuttering for beams also. Reinforcement placement to be properly checked according to the BBS or Approved Bad Bending Schedule. Diameter of rods, length, spacing, lap length, no of chairs and location of rods to be properly checked before concreting.

4.Concreting:- After completion of Shuttering, Reinforcement Concreting of Slab is started. Concreting is to be properly done as per design with proper vibration (Surface & Needle Vibrator) for avoiding segregation. Extra care to be given for maintaining proper slump during concreting. No bleeding and creep should be there. After concreting Surface of Slab is finished by manual or mechanical means.

5. Curing:- Curing to be done by making ponds/ carry over the slab. Slab to be cured for 21 days.

6. De-shuttering:- De-shuttering is to be done after slab reaches its design strength ie. after 21 days. If quick setting cement or admixture is used during concreting shuttering can be removed earlier as per the specification of the chemical.

CONSTRUCTION OF RETAINING WALL

A retaining wall is a structure designed and constructed to resist the lateral pressure of soil, when there is a desired change in ground elevation that exceeds the angle of repose of the soil.

Construction  of Concrete Retaining wall:-Following are steps in Construction of RCC retaining wall..

• Excavation:-First Excavation of Wall base is done & it is well compacted via mechanical means and with sprinkling of adequate water.
• PCC:- Plain Cement Concrete of Grade M-10 to M-15 is laid over compacted earth. This PCC acts as a base for the retaining wall
• Reinforcement: & Shuttering- Reinforcement is tied as per drawings and specifications and shuttering is paced for concreting as per required shape of the wall.Before erection of shuttering they are properly oiled for smooth surface.
• 
• Concrete:- After Completion of Shuttering Concreting is done.Before concreting the joint of PCC and RCC are properly hacked, cleaned and treated with joining chemical.Concrete is then poured into shuttering with proper vibration. Normally M-25 or higher grade of concrete is used for Construction of retaining walls.During Concreting construction and expansion joints are provided for avoiding cracks in Construction Joints. Then the concrete is properly cured.
• Backfilling:- The final activity in construction of a retaining wall is backfilling of the wall. During backfilling it is to be ensured that there is no void in any layer of filling. Compaction checks in every layer of filling is to be checked.

PAVEMENT QUALITY CONCRETE FOR ROADS

Pavement Quality Concrete is a concrete which is used now a days for most type of Road Contraction works. Generally it is designed in High Grade (M-35 to M-50) and designed for 32mm size aggregates and low slump.

Materials Required:- The Following materials are required for Construction of PQC Road..

1. Ordinary Portland Cement (IS 269), Portland Pozzolana Cement (IS 459) & Portland Slag Cement (IS 1489) Can be used for PQC.
2. Crushed Aggregates with Max size 32mm can be used as per IS:383.
3. Clean Coarse river sand to be used for PQC conforming to IS:383.
4. Water conforming to IS:456-2000 to be used for PQC. In case of hot water concrete plant should have a arrangement for water cooling.
5. Different types of admixtures conforming to IS:6925 & IS:9103 to be used for PQC.

Procedure:-

• For concrete road or rigid pavements, the concrete shall be laid in alternate panels to avoid development of shrinkage & thermal cracks.
• The base shall be sprayed with water to ensure no moisture is drawn from the concrete.
• If specified in the drawing, polythene sheet shall be spread on the entire area to limit the loss of moisture from the concrete. polythene sheet of 125 micron (with Lap of 300mm) shall be overlapped at the junctions.
• In case continuous casting is desired, the same can be carried with saw cutting arrangement of the concrete pavement.
• Such pavement shall be cut to 1/3rd the depth at every 6m within 24 Hours after laying the concrete. Any deviation in this can result in irregular formation of cracks.

Construction & Expansion Joints:-

A typical constriction joint consist of placing a stopper across the length & width without affecting the spacing or placing of rebar’s. Necessary holes shall be made in the stopper for ensuring the same. All stoppers shall be applied with form release agents and removed as soon as concrete attains final set.

• The concrete surface shall be made rough by chipping the same with chisel immediately after de-shuttering.
• For expansion joints, additional MS bar ( Dowel Bar ) shall be provided at half the depth of the pavement with 50 % of the length of the rod in the previous concrete & remaining in the next pour.
• Expansion joints of 25mm (or More)  width and half of depth of pavement  to be provided after required concrete length (as instructed in drawing or technical specifications) .
• Construction joints of 12mm to be provided after required length.
• One end of the MS bar shall be coated with grease & covered in plastic sleeve for easy movement.
• If required as per drawing, an expansion board made of bitumen impregnated fibre or polystyrene shall be placed at the expansion joint area.
• Tie bars as shown in drawing shall be inserted at the longitudinal joints where load transfer is minimal.

Concreting:-

• Concrete of minimum M-35 grade shall be used for laying the pavement.
• Concrete shall start only after all arrangements for laying were in place including crack preventive measures & curing mechanism.
• Concrete shall be differed in windy or rainy weather.
• Necessary protective covers and its spreading mechanism without disturbing the texture shall be made available for every pour.
• Concrete slump shall be controlled to 50mm & placement shall start from one end.
• Concrete shall be spread evenly & rough levelled using wooden screeds.
• The levelled concrete shall be vibrated by surface mounted vibrators and finished to rough texture.
• Slump should be 15 to 45mm for placing of this concrete.

Curing:-

• Curing of completed pavement shall start immediately after concrete final setting.
• Initial curing shall be carried by covering the surface with wet hessian & latter by ponding

Joint Sealing:-

Joints to be sealed with bitumen sealant of Grade-A of IS-1834 in every expansion and construction joints.

Testing:-

• Cubes (For Compressive Strength) & Beams (For Flexural Strength)  to be taken for each 150 cum of concrete .If the volume of concrete done in one day is less than 150 cum, still 6 cubes & 6 Beams to be taken.
• These cubes & beams to be tested in 7 & 28 days of concreting and checked as per specifications.(Average strength of 3 cubes (28 days result) not to be less than Required Strength).
• Core test shall be carried out in case of failure of Cube or Beams as per engineer in charge.

CREEP OF CONCRETE

Creep of concrete is the  continued deformation with time under applied load. Sometimes it is defined as increase in strain in concrete with time under sustained stress. This is also known as plastic flow or time yield. The rate of creep decrease with time and the creep strains at five years are taken as terminal values. Creep increases rapidly with the stress, loading at an early age of concrete, broken ballast, soft and porous aggregate, poorly graded and improperly compacted concrete. The deformation of hardened concrete is shown in Fig. below.

The Causes of Creep are.

1. Closer of internal voids of Concrete

2. Viscous flow of the cement paste inside concrete

3. Flow of water out of the cement gel inside concrete.

In reinforced concrete structures it is of advantage since it causes better distribution of stresses. For example in a R.C.C. column there is a reduction of stress in concrete and a corresponding increase of stress in steel due to creep. As another example creep relieves the high stressed portions of concrete in a continuous beam and increases the stress in the adjacent less stressed portion. Creep causes large deformations and deflections and is undesirable.

RHEOLOGY

Originated from a Greek word “rheo” which means “flow” and “logia” which means “study” Rheology is the study of flow of matter in liquid, soft solid or solid state under conditions in which they respond to plastic flow other deforming elastically when a external force is applied.

Rheological properties of a cement mix means deformation of hardened concrete and placing and mixing of freshly mixed concrete.The mechanical behaviour of hardened cement paste,which exhibits both elastic and inelastic deformations, can be expressed in rheological terms.

Factors Affecting Rheological Properties:-

1. If the amount of coarse aggregate in a concrete mix is more the desirable amount the voids cannot be filled with the available mortar, which will lead to loss of cohesion and mobility. Such a mix is termed harsh and requires a great amount of effort to place and compact. On the other hand, an excessive amount of fine aggregate or entrained air in a concrete mixture will greatly increase the cohesion and render the concrete difficult to move.

2. Slump test is the measure of consistency of concrete mix or it is an indicator of relative water content of the mix. An increase in the water content or slump above that required to achieve a workable mix produces greater fluidity and decreased internal friction. Thus, a water content more than that needed will not improve the rheological properties of concrete. But very low slump with decrease the workability of a concrete mix making it impossible to place is some areas.

3. Elevated temperature, use of rapid hardening cement, cement deficient in gypsum and use of accelerating admixtures, increase the rate of hardening which reduce the mobility of concrete.

4. The rough and highly angular aggregate particles will result in higher percentage of voids being filled by mortar, requiring higher fine aggregate contents and correspondingly higher water content. Similarly an angular fine aggregate will increase internal friction in the concrete mixture and require higher water contents than well rounded natural sands.

5. A well graded aggregate gives good workability. Gap graded aggregate affects void system and workability. These effects are greater in fine aggregate.

6. An increase in the maximum size of aggregate will reduce the fine aggregate requirement to maintain a given workability and will thereby reduce the surface area to be wetted and hence the cement content necessary for a constant water/cement ratio .

7. The admixtures which have significant effect on the rheology of concrete are plasticizers and super-plasticizers, air-entraining agents, accelerators and retarders.Lignosulphate salt based plasticizers (0.15%) reduce the water content by 10% without any detrimental effect. Super-plasticizers and plasticizers prevent the formation of flocculated structure by changing the inter-particle attraction/repulsion.

With proper attention to the rheological properties can increase work efficiency and reduce the material cost as well as the cost of construction.

ORDINARY PORTLAND CEMENT

Cement is one of the most important base products of construction industry and Ordinary Portland cement or OPC is by far the most important type of cement. Prior to 1987, there was only one grade of OPC [which was governed by IS 269-1976]. After 1987 higher grade cements were introduced. The OPC was classified into three grades, namely..

1. OPC-33 Grade
2. OPC-43 Grade
3. OPC-53 Grade

These classifications are based on the strength of the cement at 28 days when tested as per IS 4031- 1988. If the 28 days strength is not less than 33N/mm2, it is called 33 grade cement, if the strength is not less than 43N/mm2, it is called 43 grade cement, and if the strength is not less then 53 N/mm2, it is called 53 grade cement. But the actual strength obtained by these cements at the factory are much higher than the BIS specifications.

The physical and chemical properties of different types of  OPC are shown in Table below.

It has been possible to upgrade the qualities of cement by using high quality limestone, modern equipments, closer on line control of constituents, maintaining better particle size distribution, finer grinding and better packing. Generally use of high grade cements offer many advantages for making stronger concrete. Although they are little costlier than low grade cement, they offer 10-20% savings in cement consumption and also they offer many other hidden benefits. One of the most important benefits is the faster rate of development of strength. In the modern construction activities, higher grade cements have become so popular that 33 grade cement is almost out of the market. Table shows the grades of cement manufactured in various countries of the world.
The manufacture of OPC is decreasing all over the world in view of the popularity of blended cement on account of lower energy consumption, environmental pollution, economic and other technical reasons. In advanced western countries the use of OPC has come down to about 40 per cent of the total cement production. In India for the year 1998-99 out of the total cement production i.e., 79 million tons, the production of OPC in 57.00 million tons i.e., 70%. The production of PPC is 16 million tone i.e., 19% and slag cement is 8 million tons i.e., 10%. In the years to come the use of OPC may still come down, but all the same the OPC will remain as an important type for general construction.

CEMENT MORTAR

Mortar is a material used in masonry construction to fill the gaps between the bricks and blocks used in construction. Mortar is a mixture of sand, a binder such as cement or lime, and water and is applied as a paste which then sets hard.

Puzzolana Portland cement and sulphate-resisting cement form mortar which are used for constructions exposed to aggressive and waste waters. Cement mortars are used for plastering, rendering smooth finishes and damp proof courses.
The mix proportions of cement mortar are given in Table below 

Preparation:-Manual mixing is applied for Small quantities of mortar; mechanical mixers are used for large quantities. 

For manual mixing,sand is sieved, cleaned with water to remove dirt and dust and dried. This dry sand is laid uniformly, on a pucca platform, over which cement is uniformly spread. The whole mass is then thoroughly mixed with spades till it becomes uniform in colour. A depression is then made in the middle of the mix and required quantity of water is added. The dry mix from the sides is moved and placed on the edges of the depression formed till the water is completely absorbed by the mix. The wet mix is then worked with spades to give a uniform consistency to the mortar.

For mechanical mixing the calculated quantity of cement, sand and water are fed into the cylindrical container of the mixer. A rotar with blades, inside the container, rotates and thoroughly mixes the ingredients. 

  

Precautions:-Basic property of Cement mortar should be uniformity and workability. It should be consumed within 30 minutes from the instant of adding water to the mix. The bricks, stones and blocks should be fully saturated in water before laying. The masonry and plastered or pointed surface should be kept completely wet by sprinkling water for at least 7 days. 

High-Performance concrete

Recently a new term has come in the field of concrete technology “High Performance Concrete” or HPC. The properties of HPC are

• High Workability
• High Strength
• High Modulus of Elasticity
• High Density
• High Dimensional Stability
• Low Permeability and
• Resistance to Chemical Attack

There is a little controversy between the terms high-strength and high performance concrete. High-performance concrete is also, a high-strength concrete but it has a few more attributes specifically designed as mentioned above. It is, therefore, logical to describe by the more widely embracing term “High Performance Concrete” (HPC).

In normal concrete, relatively low strength and elastic modulus are the result of high heterogeneous nature of structure of the material, particularly the porous and weak transition zone, which exists at the cement paste-aggregate interface. By densification and strengthening of the transition zone, many desirable properties can be improved many fold. A substantial reduction of quantity of mixing water is the fundamental step for making HPC. With reduction of w/c ratio strength concrete will increase. But reduction in w/c ratio to less than 0.3 will greatly improve the qualities of transition zone to give inherent qualities expected in HPC.
Use of silica fume is also found to be necessary to improve the qualities of transition zone.Silica fumes becomes a necessary ingredient for strength above to 80 MPa. The best quality fly ash and GGBS may be used for other nominal benefits. Inspite of the fact that these pozzolanic materials increase the water demand, their benefits will out weigh the disadvantages. The crux of whole problem lies in using very low w/c ratio, consistant with high workability at the time of placing and compacting. Neville opines that the lowest w/c ratio that could be used is 0.22^7.9
Only with the use of superplasticizer, w/c ratio in the range of 0.25 to 0.3 can be adopted and a high slump is possible to achieve. Therefore, use of appropriate superplasticizer is a key material in making HPC. The associated problem is the selection of superplasticizer and that of cement so that they are compatible and retain the slump and rheological properties for a sufficiently long time till concrete is placed and compacted.

PUMPABLE CONCRETE

Pumpable concrete is that type of  concrete which can be pushed through a pipeline for construction. It is made in such a manner that its friction at the inner wall of the pipeline does not become very high and that it does not wedge while flowing through the pipeline. It is very important to have a clear understanding of what happens to concrete when it is pumped through pipeline to any study of concrete pumping. Pumpable concrete emerging from a pipeline flows in the form of a plug which is separated from the pipe wall by a thin lubricating layer consisting of cement paste. The water in the paste is hydraulically linked with the interparticle water layer in the plug. Fig- 1 below shows the concrete flow under pressure.

The pressure generated by the flow resistance must not be greater than the pump pressure rating for maintaining continuous plug movement.  However, if the concrete is too saturated at higher w/c ratio, the concrete at certain pump pressures may be such that water is forced out of the mix, creating an increase in flow resistance and a possible blockage. Fig.2 illustrates such a condition. In other words, a very stiff concrete is not pumpable and also a concrete with high w/c ratio is also not pumpable. It is interesting to note that if a concrete is pumpable, it is implied that it is a good concrete.

 

Effect of Maximum size of Aggregate on Strength of CONCRETE

Earlier it was thought that the use of larger size aggregate leads to higher strength.This was due to the fact that the larger the aggregate the lower is the total surface area and, therefore, the lower is the requirement of water for the given workability. So, a lower water/cement ratio can be used which will result in higher strength of Concrete.
However, later it was found that the use of larger size aggregate did not contribute to higher strength as expected from the theoretical considerations due to the following reasons..

1. The larger maximum size aggregate gives lower surface area for developments of gel bonds which is responsible for the lower strength of the concrete.
2. Secondly bigger aggregate size causes a more heterogeneity in the concrete which will prevent the uniform distribution of load when stressed.

When large size aggregate is used, due to internal bleeding, the transition zone will become much weaker due to the development of micro-cracks which result in lower compressive strength.
Generally, high strength concrete or rich concrete is adversely affected by the use of large size aggregate. But in lean mixes or weaker concrete the influence of size of the aggregate gets reduced. It is interesting to note that in lean mixes larger aggregate gives highest strength while in rich mixes it is the smaller aggregate which yields higher strength. The Fig.  below shows the influence of maximum size of aggregate on compressive strength of concrete..

 
Following Figure depicts the influence of size of aggregate on compressive strength of concrete for different w/c ratio.

GEL/SPACE RATIO

       As propounded by Duff Abrams many research workers commented on the validity of water/cement ratio law. They have focused on a few of the limitations of the water/ cement ratio law and argued that Abrams water/cement ratio law can only be called a rule and not a law because Abrams’ statement does not include many qualifications necessary for its validity to call it a law. Some of the limitations are that the strength at any water/cement ratio depends on the following things…

   1.Degree of hydration 
   2.Chemical and Physical properties
   3.The temperature at which the hydration takes place
   4.Air content (in case of air entrained concrete)
   5.the change in the effective water/cement ratio and the formation of fissures and cracks due to bleeding or shrinkage

Instead of relating the strength to water/cement ratio, the strength can be more correctly related to the solid products of hydration of cement to the space available for formation of this product. Powers and Brownyard have established the relationship between the  strength and gel/space ratio. This ratio is  defined as the ratio of the volume of the hydrated cement paste to the sum of  volumes of the hydrated cement and of the capillary pores.
Power’s experiment showed that the strength of concrete bears a specific  relationship with the gel/space ratio. He  found the relationship to be 240 x3, where  x is the gel/space ratio and 240 represents the intrinsic strength of the gel in MPa for the type of cement and specimen used.
The strength calculated by Power’s expression holds good for an ideal case.
The fig. below shows the relationship between strength and gel/space ratio. It is pointed out that the relationship between the strength and water/cement ratio will hold.

SEGREGATION

Segregation is the separation of the different materials of concrete. A good concrete is one which is homogeneous in nature.If a sample of concrete exhibits a tendency for separation of say, coarse aggregate from the rest of the ingredients, then, that sample is said to be showing the tendency for segregation. Such concrete is not only going to be weak; lack of homogeneity is also going to induce all undesirable properties in the hardened concrete.

 

There are considerable differences in the sizes and specific gravities of the constituent ingredients of concrete. Therefore, it is natural that the materials show a tendency to fall apart.
Segregation may be of three types — firstly, the coarse aggregate separating out or settling down from the rest of the matrix, secondly, the paste or matrix separating away from coarse aggregate and thirdly, water separating out from the rest of the material being a material of lowest specific gravity. A well made concrete, taking into consideration various parameters such as grading, size, shape and surface texture of aggregate with optimum quantity of waters makes a cohesive mix. Such concrete will not exhibit any tendency for segregation. The cohesive and fatty characteristics of matrix do not allow the aggregate to fall apart, at the same time, the matrix itself is sufficiently contained by the aggregate. Similarly, water also does not find it easy to move out freely from the rest of the ingredients.
The conditions favourable for segregation are, as can be seen from the above para, the badly proportioned mix where sufficient matrix is not there to bind and contain the aggregates. Insufficiently mixed concrete with excess water content shows a higher tendency for segregation. Dropping of concrete from heights as in the case of placing concrete in column concreting will result in segregation. When concrete is discharged from a badly designed mixer, or from a mixer with worn out blades, concrete shows a tendency for segregation. Conveyance of concrete by conveyor belts, wheel barrow, long distance haul by dumper, long lift by skip and hoist are the other situations promoting segregation of concrete.
The most important method of concrete compaction is Vibration. Only comparatively dry mix should be vibrated. When a too wet a mix is excessively vibrated, it is likely to get segregated. Vibration also to be continued just for required time for optimum results. If the vibration is continued for a long time, particularly, in too wet a mix, it is likely to result in segregation of concrete due to settlement of coarse aggregate in matrix.
Concrete is used with very high slump now a days particularly in RMC. The slump value required at the batching point may be in the order of 150 mm and at the pumping point the slump may be around 100 mm. At both these points cubes are cast. One has to take care to compact the cube mould with these high slump concrete. If sufficient care and understanding of concrete is not exercised, the concrete in the cube mould may get segregated and show low strength. Similarly care must be taken in the compaction of such concrete in actual structures to avoid segregation.

In case of floors or pavement finishing, with a view to achieve a smooth surface, masons work too much with the trowel, float or tamping rule immediately on placing concrete. This immediate working on the concrete on placing, without any time interval, is likely to press the coarse aggregate down, which results in the movement of excess of matrix or paste to the surface. Segragation caused on this account, impairs the homogeneity and serviceability of concrete. The excess mortar at the top causes plastic shrinkage cracks. 
So it can be concluded that the tendency for segregation can be remedied by correctly proportioning the mix, by proper handling, transporting, placing, compacting and finishing. If segregation is observed, it is advisable to remixing for a short time which would make the concrete again homogeneous. As mentioned earlier, a cohesive mix would reduce the tendency for segregation. For this reason, use of certain workability agents and pozzolanic materials greatly help in reducing segregation. The use of air-entraining agent appreciably reduces segregation.
Segregation is difficult to measure quantitatively, but it can be easily observed at the time of concreting operation. The pattern of subsidence of concrete in slump test or the pattern of spread in the flow test gives a fair idea of the quality of concrete with respect to segregation.