Concrete Technology 2

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By Dr.Kamaran Gardy Concrete Technology II References : 1 - Concrete technology (theory and practice) by M.S.SHETTY –New Delhi India-2010 . 2 - Concrete technology by A.M. Neville, Second edition . 3 - Properties of Concrete by A.M. Neville, Fourth edition . 4 - Advanced concrete technology by Jon Newman. Ban Seng Choo . 5 - Concrete Technology , by B.L. GUPTA, 3 rd edition, 2004 Content: 1- Quality of Water. 2- Fresh concrete. 3- Concrete mix design. 4- Admixtures and construction chemicals. 5- Strength of Concrete. 8-Elasticity, creep and shrinkage. 9-Durabilty of Concrete. 1

Transcript of Concrete Technology 2

Page 1: Concrete Technology 2

By Dr.Kamaran Gardy

Concrete Technology II

References:

1-Concrete technology (theory and practice) by M.S.SHETTY –New Delhi India-2010.

2-Concrete technology by A.M. Neville, Second edition.

3-Properties of Concrete by A.M. Neville, Fourth edition.

4-Advanced concrete technology by Jon Newman. Ban Seng Choo.

5-Concrete Technology , by B.L. GUPTA, 3rd edition, 2004

Content:

1- Quality of Water.

2- Fresh concrete.

3- Concrete mix design.

4- Admixtures and construction chemicals.

5- Strength of Concrete.

8-Elasticity, creep and shrinkage.

9-Durabilty of Concrete.

10-Testing of hardened Concrete.

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QUALITY OF WATER.

The quality of water is important since some available impurities within the used water may cause reduction in strength of concrete or affecting on the time of setting or may leads to corrosion of reinforcement. For these reasons, the suitability of water for mixing and curing purposes should be considered. A popular yard-stick to the suitability of water for mixing concrete is that, if water is fit for drinking it is fit for making concrete. This does not appear to be a true statement for all conditions. Some waters containing a small amount of sugar would be suitable for drinking but not for mixing concrete and conversely water suitable for making concrete may not necessary be fit for drinking. Some specifications required that if water is not obtained from source that has proved satisfactory, the strength of concrete or mortar made with questionable water should be compared with similar concrete or mortar made with pure water. Some specification also accept water for making concrete if PH value of water lies between 6 and 8 and water is free from organic material. Instead of depending upon PH value and other chemical composition, the best course to find out whether a particular source of water is suitable for concrete making or not, is to make concrete with this water and compare its 7 day's and 28 day's strength with companion cubes made with distilled water. If the compressive strength up to 90%, the source of water may be accept. the harmful impurities in water and their effects me be listed as:

1- Sodium carbonate, this type of salts may cause quick setting of cement. Test for setting time and 28 days strength of concrete should be carried out if the limit content of this type of salts exceed 1000ppm.

2-Bi-carbonates of sodium and potassium, these salts may either accelerate or retard the setting time of cement ,also the allawable limits for these types of salts in the water is 1000ppm.

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3- Brackish water, may contains chlorides and sulphates. If the limit of chloride and sulphate does not exceed 500ppm and 3000ppm respectively, the water considered as harmless water.

4- Salts of Manganese, Tin,Zinc,Copper and Lead cause reduction in strength of concrete.

5- Silits and suspended particles are undesirable as the interfere with setting, hardening and bond characteristics. The identified limits of these impurities are 100ppm. Below table shows the tolerable concentration of some impurities in mixing water.

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Use of Sea Water for Mixing Concrete.

The salinity of sea water of about 3.5 per cent (78 per cent of the dissolved solids being NaCl and 15 per cent MgCl2 and MgSO4).Such water leads to a slightly higher early strength but a lower long-term strength: the loss of strength is usually not more than 15 per cent and can therefore be tolerated. However, this loss of strength could be made up by redesigning the mix. Water containing large quantities of chlorides in sea water may cause efflorescence. When the appearance of concrete is important sea water may be avoided. In case of reinforced concrete, sea water increase the risk of corrosion of the reinforcement, especially if cover of reinforcement is not adequate or the concrete is not sufficiently dense. In case using sea water cannot be avoided for making reinforced concrete, particular precautions should be taken be making concrete dense and less permeable by using less possible w/c ratio and using adequate vibration.

Effect of sugar content on the propitiates of concrete.

Usually Sugar, (carbohydrate) exhibit retarding action. 0.05%

of sugar by weight of cement may retards the setting time up to 4 hours. 0.06% of sugar maybe considered as the optimum percentage of sugar content to produce maximum retarding for initial and final setting. Some researchers showed that any percentage beyond 0.06% may cause opposite effects. Akogu Elijah observed that the increases in initial and final setting times are apparent up to sugar content of 0.06%. Reduction in setting times begins from 0.08% sugar content and flash setting occurs from 0.2% to 1%. Some researchers showed that sugar content more than 1% by weight of cement may produce very destructive effect on setting and strength of concrete.

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Water for curing of concrete.

Generally water suitable for mixing concrete, is also suitable for curing of concrete. However curing water should be free from the following impurities:

1-Iron or organic impurities .the presence of these materials may cause staining of concrete particularly.

2- Water should be free from carbon dioxide (CO2) as attacks hardened concrete.

3-Water formed by melting ice or by condensation should not be used for curing as it contains little CO2. This CO2 in water dissolves forming Ca(OH)2 and cause surface erosion. Sea water should be also avoided for curing purposes.

Fresh Concrete.

Fresh concrete or plastic concrete is a freshly mixed material which can be molded into any shape.

Workability.

Workability can be defined as the amount of useful internal work necessary to produce full compaction. The useful internal work is a physical property of concrete alone and is the work or energy required to overcome the internal friction between the individual particles in the concrete. In practice, however additional energy is required to overcome the surface friction between concrete and the formwork or the reinforcement. Workability may be one of most important characteristics of concrete under the following situations.

1-if the concrete is to be placed in deep beams, thin sections and closely spaced reinforcement.

2-If the concrete harsh due to poor grading or poor characteristics of aggregate.

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3-For making high strength concrete with low w/c ratio.

4-under special cases where special means of placement are required as chute or pumping requirement etc.

Factor affecting on the workability.

1-water content.

Water content considered as the main factor that influences the workability of concrete. More water content or more w/c ratio results in better workability. In the other hand any increasing in water content resulting in reduction in strength of concrete.

2- Size of aggregate particles.

Increasing in the maximum aggregate sizes, without changing in the mix contents, improves the workability of the concrete.

3- Coarse and fine aggregate ratio.

For a constant aggregate/cement ratio, if the quantity of coarse aggregate is increased and fine aggregate decreased to maintain the total aggregate/cement ratio constant, the total surface area of the aggregate is reduced. Thus for a constant water/cement ratio the quantity of water available per unit, area of aggregate surface is increased resulting in improved of the workability.

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4- Shape of aggregate.

The shape of aggregate influences the workability of the concrete in high range. Angular, elongated, or flaky aggregate makes the concrete very harsh when compared to rounded aggregates, this due to that rounded shape produce less surface area and less frictional resistance than other shapes.

5- Surface texture.

Surface texture of aggregate observably influences the workability of the concrete. Aggregate have smooth texture provide more workability than aggregate have rough texture, this is due to increase the interlock bond and frictional resistance between grains of aggregate.

6-Grading of aggregates.

Grading of aggregate significantly influence on the workability of the concrete. A well graded aggregate is the one which has least amount of voids in a given volume. When a total voids are less, excess past is available to give better lubricating effect. With excess amount of past, mixture becomes cohesive and fatty which prevents segregation of particles. Aggregate particles will slide past each other with the least amount of compaction efforts.

7- Use of admixtures.

Some admixture has significant affect on the workability of concrete. Plasticizer and super-plasticizer are significantly increase workability of the concrete.

Measurement of workability.

Usually the following tests can be adopted to determine the workability of concrete.

1- Slump test.

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2- K slump test.

3- Compacting factor test.

4-Kelly ball test.

5- Flow test.

6- Vee. Bee consist-meter test.

Slump Test.

Slump test is the most commonly method of measuring consistency of concrete which can be employed either in laboratory or at site of work. It is not suitable method for very wet or very dry concrete. the prescriptions of ASTM C143-05a are summarized below.

The mould for the slump test is a frustum of a cone, 305mm (12in.) high. The base of 203 mm (8in.) diameter is placed on a smooth surface with the smaller opening of 102 mm (in.) diameter at the top, and the container is filled with concrete in three layers. Each layer is tamped 25 times with a standard 16mm diameter steel rod, rounded at the end, and the top surface is struck off by means of a screeding and rolling motion of the tamping rod. The mould must be firmly held against its base during the entire operation. Immediately after filling, the cone is slowly lifted, and the unsupported concrete will now slump-hence the name of the test. The decrease in the height of the center of the slumped concrete is called slump, and measured to the nearest 5mm. in order to reduce the influence on slump of the variation in the surface friction, the inside of the mould and its base should be moistened at the beginning of every test.

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Below figure show different types of slump (true, shear and collapse).

If shear slump type occurs a test should be repeated.

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The degree of workability and the suitable situations for concrete having maximum aggregate size 38mm are shown below.

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K-slump Test. this test can be used to measure the slump directly within one minute after the tester is inserted in the fresh concrete to the level of the floater disc. This tester can also be used to measure the relative workability. Blow figure show the K-slump apparatus.

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Compacting factor test.

The compacting factor test can be done either in the laboratory or in the field. It is more precise and sensitive than slump test and is particularly useful for concrete mixes of very low workability as are normally used when concrete is to be compacted by vibration. Compacting factor apparatus consists of two hoppers of a frustum of a cone and one cylinder. The hoppers are hinged on a vertical frame one above other as shown in the below figure.

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The sample of concrete to be tested is placed gently in the upper hoper A by the hand scoop in such way that no work is done on the concrete at this stage to produce compaction. After filling the concrete in hopper A, the cover from hopper B is removed and the hinged bottom door of hopper A is released and the concrete is allowed to fall into the lower hopper B. the hopper B being smaller than upper hopper A is filled to over flowing state. Thus always contains approximately the same amount of concrete in a standard state. Now the cover from the cylinder is removed and the bottom door of the lower hopper B is released and concrete is allowed to fall into cylinder. The excess concrete in the cylinder is cut off by the help of two trowels sliding across the top of the cylinder. The outside of the cylinder is wiped clean and cylinder weighed. The net weight of concrete in the cylinder is called as weight of partially compacted concrete and dividing it by the volume of cylinder, its density determined. Now the cylinder is filled with the concrete in four layer with compacting each layer by tamped rod or using vibrator compacted, and hence the density of fully compacted concrete will be obtained. The ratio of the two densities or weights of partially compacted concrete and fully compacted concrete will give its compacting factor

Compacting Factor=Weight of partially compacted concreteWeight of fully compacted concrete

The value of compacted factor varies from 0.78 to 1.0.

Kelly ball test. 2

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This is a simple field test devised by J.W.Kelly. The apparatus that used for this test it consist of 15.2 cm diameter spherical metal ball weighing 14kg with a measuring scale on the stem (vertical rod) of the handle. Below figure show Kelly ball, the ball should be placed and lowered carefully on the leveled concrete surface. The depth of penetration of the ball in the concrete from the scale of its stem to nearest 6mm.

Vee. Bee consist-meter test.

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In this method, the consistency of concrete is determined be Vee- Bee consisto-meter, which determines the time required to transform by vibration a concrete specimen in the shape of a conical frustum into a cylinder. This is a very good laboratory test, particularly for dry mixes; in the other hand this test is not suitable for concrete having slump 75mm or more. The Vee. Bee consisto-meter is shown in the below figure.

The relationship between slump and consistency by Vee. Bee consisto-meter is shown below.

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Effect of Time and Temperature on Workability.

It has been observed that freshly mixed concrete stiffens with time due to the fact that some water from the mix is absorbed by the aggregates and some is lost by evaporation. The relationships between slump and time, and between slump and temperature are shown below:

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Q- Draw the relationships between:

A- Kelly ball penetration and slump.

B- Compaction factor and Vee. Bee time.

Solution.

Segregation.

In considering the workability of concrete, it is pointed out that concrete should not be segregate. The absence of segregation is essential if full compaction is required. Segregation can be defined as separation of the constitutents of a heterogeneous mixture so that their distribution is no longer uniform.

Types of segregation.

Segregation can be classified 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 mixes.

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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 occurs with a too wet mixes.

3- Water separation, when water separates out from the rest of the mix, then water segregation (bleeding) occurs.

To remedy the segregation, one or more of the flowing points may be adopts:

1- Using aggregate with continues grading.

2- Increasing the amount of the cement in the mix cause increasing in cohesion and reducing in the segregation.

3-By correctly proportioning the mix.

4- Avoid dropping concrete from a considerable height, passing along chute, particularly with change direction, and discharging against an obstacle.

5- Proper handling, transporting and placing.

6- By proper compacting and finishing; excessive vibrations cause separate the coarse aggregate toward the bottom of the form and the cement past toward the top.

7- The danger segregation can be reduced by the use of air entrainment.

8-Avioed using coarse aggregate whose specific gravity is greater than that of the fine aggregate.

Bleeding.

Bleeding, known also as water gain. It is a form of segregation in which some of the water in the mix tends to rise to the surface of the freshly placed concrete, being of the lowest specific gravity of the all ingredients

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of the concrete. The phenomenon of bleeding is caused due to the inability of the solid materials of the mix to hold the mixing water when they settle down.

Causes of bleeding.

Bleeding is observed under the following conditions:

1-In highly wet mixes (w/c ratio high).

2- Badly grading of aggregate.

3- Insufficient mixed concrete.

4-In thin members like roof slabs or road slab.

5-Increasing percentage of fine materials in the mix.

Effect of bleeding. 3

Due to the bleeding the following effects are observed.

1- Due to bleeding, water comes up and accumulates at the surface. Sometimes along with this water, certain quantity of cement also comes to the surface. When the surface is worked up with trowel and floats, the aggregate go down while water and cement go up toward the surface. This formation of cement past at the surface is known as "Laitance". This formation of Laitance on the pavement will form dust in summer and mud mud in raining state. This can be avoided by delaying the finishing operation till the bleeding water has evaporated.

2- If the bleeding occurs, the top surface of the slabs become rich reign with high water content and less mount of aggregate. In this case, developing of shrinkage cracks occurs widely.

3- Due to the bleeding, the top of every layer of concrete placed may become too wet and if this water is trapped by placing another layer over

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it, a porous and weak layer of none durable concrete will result. The bond with the next layer will be poor due to formation of a plane of weakness. This can be avoided by removing the laitance before pouring the next layer.

4- If the rate of evaporation from the surface of bleeding water is faster than the bleeding rate, the plastic shrinkage cracks would develop.

5-Water rising from bottom to top makes continuous capillary channel. If w/c ratio used is more than 0.7, the bleeding channels remains as such and do not get filled by the development of cement gel. These capillary channels are responsible for the development of permeable concrete structure.

Prevention of bleeding.

Bleeding can be reduced by:

1- It can be reduced by increasing the finenesses of cement.

2- By adding high contents of C3A in the cement.

3- Decreasing w/c ratio.

4- Adding gelatin additives.

5- Using expansive cement; with this case bleeding equal to zero.

Bleeding Test method for Concrete.

The method of test as below:

A cylinder container having an inside diameter of 250mm and inside height of 280mm is fill with a sample of concrete in 5 layers each layer is 50mm, and should be tamp with the standard rod. The top surface should be made smooth by trowel. The test specimen is weighed and the weight of the concrete is noted. The cylindrical container is kept in a level

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surface free from vibration at a temperature of 27+2Co.It is covered with a lid. Water accumulated at the top is drawn by means of pipette at 10mintues interval for the first 40minutes and 30 minutes interval subsequently till bleeding ceases. To facilitate collection of bleeding water the container may be slightly tilted.

BleedingWater percentage=Total quantity of bleedingwaterTotal quantity of water∈sample

x100

Process of Manufacture of Concrete.

The various stages of manufacture of concrete are:

a- Batching.

b-Mixing.

c- Handling (Transporting).

d-Placing.

e-Compacting.

f-Curing.

g-Finishing.

a- Batching .

The measurement of materials for making concrete is known as batching. There are two methods of batching.

1-Volume batching.

Volume batching is not a good method for proportioning granular materials such as sand or gravel. Volume of moist sand in a loose condition weighs much less than the same volume of dry compacted sand. However, for small jobs, aggregate may be batch by volume.

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Cement is always measured by weight, and generally for each batch mix, one bag of cement is used. The volume of one bag of cement is taken as thirty five (35) liters. Gauge boxes are used for measuring aggregates (sand or gravel). The typical sketch of a gauge box is shown in the below figure. The volume of the box is made equal to volume of one bag of cement or multiple thereof.

The batch volume of materials for various mixes is shown in the below table.

Water is measured either in kg. or liters. The quantity of water required is a product of water/cement ratio; for example, if the water/cement ratio is equal to (0.5), the quantity of mixing water required per bag of cement is 0.5x50=25kg. or 25 liters. The quantity should include of any percentage of surface moisture of the aggregate. The following table gives the approximate surface moisture carried by aggregates.

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Water is measured either in kg. or liters. The quantity of water required is a product of water/cement ratio; for example, if the water/cement ratio is equal to (0.5), the quantity of mixing water required per bag of cement is 0.5x50=25kg. or 25 liters. The quantity should include of any percentage of surface moisture of the aggregate. The following table gives the approximate surface moisture carried by aggregates.

2-Weigh batching.

It is well known that weigh batching is the correct method of measuring the materials. Use of weight system in batching, facilitates accuracy, flexibility and simplicity. Different types of weigh batchers are available. The particular type to be used, depend upon the nature of the job.

Large weigh batching plants have automatic weighing equipment. Below figure shows a concrete mixer with built-in weigh batching mechanism.

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b-Mixing.

The mixing operation consists essentially of rotating or stirring, the objective being to coat the surface of all the aggregate particles with cement paste, and to blend all the ingredients of concrete into a uniform mass: this uniformity must not be disturbed by the process of discharging from the mixture. Mixing of concrete can be done either by hand or by machines.

i- Hand mixing.

Mixing of concrete by hand is less efficient than mixing by machines, but it is suitable for small or unimportant works. Hand mixing should be avoided on the ground of (soil, dry grass, etc.); and maybe applicable over platform of rigid and impermeable material.

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ii- Mixing by machines.

Concrete mixed by machine provide better quality, faster production, and less cost than hand mixed concrete. The usual type of mixer is a batch mixer, which means that one batch of concrete is mixed and discharged before any more materials are put into the mixer. There are several types of batch mixers.

1- A tilting drum mixer. This type of mixer have conical or bowl shaped drum with inside vanes, which revolve on an inclined axis. Concrete discharged by tilting the drum. Below sketch show the operation of working of typical tilting mixer.

2-Non tilting mixers.

In this type of mixers, the drum is cylindrical and always rotates about a horizontal axis i.e. its axis is always horizontal. In this case the material is charged by means of a cable operated loading skip or a charging hopper. Below figure shows a diagrammatic sketch of the non tilting type mixture.

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Due to the low rate of discharge concrete from non tilting type mixture, the segregation may be occur and large size of aggregate tends to stay in the mixer so that the discharge starts as a mortar and end as a collection of coaled stones.

Pan mixers.

This type of mixer is not mobile and maybe used at a central mixing plant, at large concrete projects, at a precast factory, or used in concrete laboratory. The mixer consists of a circular pan rotating about its vertical axis, with one or two star of paddles rotating about a vertical axis not coincident with the axis of pan (below figure). Pan mixers are efficient with stiff and cohesive mixes and thus are useful for precast factories.

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Continuous mixers.

These types of mixers are designed to feed materials into the drum at rates related to the mix proportions required. The drum, which mounted horizontally, consists of a long cylinder open at both ends and with internal blades of spiral shape so that they move the materials forward as the drum rotates. The materials are fed in by means of spiral conveyers and bucket elevators. For this type of mixer, the proportions of materials are obtained on the bases of volume batching. Thus the concrete obtained by these types of mixers, has less strength than obtained by batch mixers. These mixers usually used for big projects such as construction of dams.

Mixing time.

On site, there is often a tendency to mix concrete as rapidly as possible, and, hence, it is important to know the minimum mixing time necessary to produce a concrete of uniform composition and, of reliable strength. The optimum mixing time depends on the type and size of mixer, on the speed of rotation, and on the quality of blending of ingredients during charging of the mixer. Generally, a mixing time of less than (1 to 1.25) min produces non-uniformity concrete with lower strength. Mixing times reckoned from the time when all the solid materials have been charged into the mixer; water should be added not later than one-quarter of the

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mixing time. Below time, the recommended minimum mixing time according to ACI 304R and ASTM C94-05.

In case of using lightweight aggregate, mixing time should be not less 5 min, (sometimes divided in 2 min of mixing of aggregate and water, followed by 3min with cement added). In the case of air-entrained concrete, a mixing time of less than 2 min or 3 min may cause inadequate of entrainment of air. Blow figure shows the effect of mixing time upon the strength of concrete at several stages of live.

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c-Handling (Transporting).

After mixing, concrete should be transported and placed at site as quickly as possible without (segregation, drying, etc). Depending upon the type of work and available equipments, various methods of transporting of concrete can be employed. There are many possibilities, ranging from wheelbarrows, buckets, skips and belt conveyors, special trucks and pumping equipments to transport the concrete.

To avoid segregation, in the cases that concrete should be transformed from one conveyance to another by using of hoppers, baffles, and short vertical drops, concrete should be discharged through a pipe to the center of receiving container with a correct methods as shown in the below figures.

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As far as placing is concerned, the main objective is to deposit the concrete as close as possible to its final position so that segregation is avoided and the concrete can be fully compacted (below figures).

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To avoiding segregation, the following rules should be taken:

a- Hand shoveling and moving concrete by immersion or poker vibration should be avoided.

b- The concrete should be placed in uniform layers, not in large heaps or sloping layers.

c-The thickness of a layer should be compatible with the method of vibration so that entrapped air can be removed from the bottom of each layer.

d- The rates of placing and of compaction should be equal.

e-Where a good finish and uniform colour are required on columns and walls, the forms should be filled at a rate of at least 2m per hours( long delays can result in the formation of cold joints).

f-Each layer should be fully compacted before placing the next one, and each subsequent layer should be placed whilst the underlying layer is still plastic so the monolithic construction is achieved.

g-Collision between concrete and formwork or reinforcement should be avoided. For deep sections (below figure), a long down pipe should be used to ensures accuracy of location of the concrete and minimum segregation.

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h- Concrete should be placed in vertical plane. When placing in horizontal or sloping forms (below figure), the concrete should be placed vertically.

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Ready Mixed Concrete.

Concrete available for placing from a central plant is known as ready mixed concrete. There are several advantages for this type of mixing as listed below:

a- This type of concrete is particularly useful for congested sites.

b- For road construction where little space is available mixing plant and for stocking aggregate etc.

c- Ready mixed provide better quality control than site mixing type.

Ready mix has several disadvantages; the main of these, is the high cost which is about (10-15%) higher than site mixing.

There are two types of ready mix.

1-Centaral mixed concrete.

In this case, the mixing is done at a central plane and the mixed concrete is transported in a special type of truck known as an agitator truck. The truck revolves slowly while moving. The agitating container is conical in

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shape having small blades. The rate of revolution of container is about (2-6) rpm.

2- Transit mixed Concrete (Truck –mixed concrete).

With this category, materials are batched at a central plant but are mixed in the truck either in transit or immediately prior to discharging the concrete at the site. The rate of revolution of the container of this type is about (4-16) rpm. It may be noted that the speed of mixing affects the rate of stiffening of the concrete whilst the number of revolutions controls the uniformity of mixing.

Pumped concrete.

The first patent for concrete pump was taken in USA in 1913. Nowadays, large quantities of concrete can be transported by means of pumping through pipelines over quite large distance to locations which are not easily accessible by other means. The system consists essentially of a hopper into which concrete is discharged from the mixer, a concrete pump, and the pipes through which the concrete is pumped. Pumps may of direct- acting contain a horizontal piston with semi-rotary valves set so as to ensure the passing of the largest particles of aggregate (below figure).

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Outputs of up to (60m3per hour) can be achieved through 220mm diameter pipes. With piston pumps, concrete can be moved up to about 450m horizontally or 40m vertically.

In some cases small portable peristaltic type called squeeze pumps used for small jobs up to (20m3 per hour) (blow figure). Concrete placed in collecting hoper is fed by rotating blades into flexible pipe connected to the pumping chamber, which is under vacuum of about (600mm) of mercury.

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Squeeze pumps transport concrete for distances up to 90m horizontally or 30 m vertically. The pipe diameter must be at least three times the maximum aggregate size. Rigid or flexible pipe can be used but the latter causes additional frictional losses and cleaning problems. Aluminum pipes should not be used because this metal reacts with the alkalis in cement to form hydrogen, which then creates voids in the hardened concrete with consequence loss of strength. The mix required to be pumped must not be harsh or sticky, nor too dry or too wet. A slump of (40-100mm), or compacting factor (0.9-0.95), or Vebe time of (3-5 sec) is generally recommended for the mix in the hopper and using pumping.

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