Basic civil engineering questions pdf

Final setting time is the time lapsed from adding of the water to complete loss of plasticity. Vicat apparatus is used for finding the setting times [Ref. Vicat apparatus consists of a movable rod to which any one of the three needles shown in figure can be attached.

An indicator is attached to the movable rod. A vicat mould is associated with this apparatus which is in the form of split cylinder. The plunger is attached to the movable rod of vicat apparatus and gently lowered to touch the paste in the mould. Then the plunger is allowed to move freely. If the penetration is 5 mm to 7 mm from the bottom of the mould, then cement is having standard consistency. If not, experiment is repeated with different proportion of water fill water required for standard consistency is found.

Then the tests for initial and final setting times can be carried out as explained below: Initial Setting Time: gms of cement is thoroughly mixed with 0. Then it is freely allowed to penetrate. In the beginning the needle penetrates the paste completely. As time lapses the paste start losing its plasticity and offers resistance to penetration. When needle can penetrate up to 5 to 7 mm above bottom of the paste experiment is stopped and time lapsed between the addition of water and end if the experiment is noted as initial setting time.

Final Setting Time. The square needle is replaced with annular collar. Experiment is continued by allowing this needle to freely move after gently touching the surface of the paste. Time lapsed between the addition of water and the mark of needle but not of annular ring is found on the paste.

This time is noted as final setting time. Le Chatelier apparatus shown in Fig. It consists of a split brass mould of diameter 30 mm and height 30 mm. On either side of the split, there are two indicators, with pointed ends. The ends of indicators are mm from the centre of the mould. Glass plate 30 mm Glass plate Elevation Brass mould Thickness 0.

Then the whole assembly is kept under water for 24 hours. Note the distance between the indicator. Then place the mould again in the water and heat the assembly such that water reaches the boiling point in 30 minutes. Boil the water for one hour. The mould is removed from water and allowed to cool.

The distance between the two pointers is measured. The difference between the two readings indicate the expansion of the cement due to the presence of unburnt lime. This value should not exceed 10 mm. They are 4 mixed with trowel for 3 to 4 minutes to get uniform mixture. The mix is placed in a cube mould of A hopper is secured at the top and the remaining mortar is filled. The mould is vibrated for two minutes and hopper removed. The top is finished with a knife or with a trowel and levelled.

After specified period cubes are tested in compression testing machine, keeping the specimen on its level edges. Average of three cubes is reported as crushing strength. The compressive strength at the end of 3 days should not be less than Some of them are listed below: i Cement slurry is used for filling cracks in concrete structures.

This form of timber is known as rough timber. By sawing, rough timber is converted into various commercial sizes like planks, battens, posts, beams etc. Such form of timber is known as converted timber. Many ancient temples, palaces and bridges built with timber can be seen even today. The following are the important basis: i Mode of growth ii Modulus of elasticity iii Durability iv Grading v Availability.

These rings are known as annual rings. Hence it is possible to find the age of timber by counting these annual rings.

These trees may be further divided into 1 coniferrous and 2 deciduous. Coniferrous trees are having cone shaped leaves and fruits. The leaves do not fall till new ones are grown. They yield soft wood. Deciduous trees are having broad leaves. These leaves fall in autumn and new ones appear in springs.

They yield strong wood and hence they are commonly used in building construction. The classification as soft wood and hard wood have commercial importance. The difference between soft wood and hard wood is given below: 1. In soft wood annual rings are seen distinctly whereas in hard wood they are indistinct. The colour of soft wood is light whereas the colour of hard wood is dark.

Soft woods have lesser strength in compression and shear compared to hard woods. Soft woods are light and hard woods are heavy. Fire resistance of soft wood is poor compared to that of hard wood. The structure of soft wood is resinous while structure of hard wood is close grained. The cross-section of a exogeneous tree is as shown in the Fig.

Pith: It is the inner most part of the tree and hence the oldest part of exogeneous tree when the plant becomes old, the pith dies and becomes fibrous and dark. It varies in size and shape. Heart Wood: This is the portion surrounding pith. It is dark in colour and strong. This portion is useful for various engineering purpose. This is the dead part of wood. It consists of several annular rings. Sap Wood: It is the layer next to heart wood. It denotes recent growth and contains sap.

It takes active part in the growth of trees by allowing sap to move in upward direction. The annual rings of sap wood are less sharply divided and are light in colour. The sap wood is also known as alburnum.

Cambium Layer: It is a thin layer of fresh sap lying between sap wood and the inner bark. It contains sap which is not yet converted into sap wood. If the bark is removed and cambium layer is exposed to atmosphere, cells cease to be active and tree dies. Inner Bark: It is a inner skin of tree protecting the cambium layer.

It gives protection to cambium layer. Outer Bark: It is the outer skin of the tree and consists of wood fibres. Sometimes it contains fissures and cracks. Medullary Rags: These are thin radial fibres extending from pith to cambium layer.

They hold annular rings together. In some of trees they are broken and some other they may not be prominent. Fresh fibrous mass is in the inner most portion.

Examples of endogenous trees are bamboo and cane. They are not useful for structural works. Then timbers are classified as: High durability: If average life is more than 10 years. Moderate durability: Average life between 5 to 10 years. Low durability: Average life less than 5 years. The classification is based on permissible stresses, defects etc.

Less than m3 per year. Odour: It should be pleasant when cut freshly. Soundness: A clear ringing sound when struck indicates the timber is good. Texture: Texture of good timber is fine and even. Grains: In good timber grains are close. Density: Higher the density stronger is the timber. Hardness: Harder timbers are strong and durable. Warping: Good timber do not warp under changing environmental conditions. Toughness: Timber should be capable of resisting shock loads.

Abrasion: Good timber do not deteriorate due to wear. This property should be looked into, if timber is to be used for flooring. Strength: Timber should have high strength in bending, shear and direct compression. Modulus of Elasticity: Timber with higher modulus of elasticity are preferred in construction.

Fire resistance: A good timber should have high resistance to fire. Permeability: Good timber has low water permeability. Workability: Timber should be easily workable. It should not clog the saw. Durability: Good timber is one which is capable of resisting the action of fungi and insects attack Defects: Good timber is free from defects like dead knots, shakes and cracks. By doing so the durability of timber is increased. The various methods of seasoning used may be classified into: i Natural seasoning ii Artificial seasoning.

Air seasoning is carried out in a shed with a platform. On about mm high platform timber balks are stacked as shown in Fig. Care is taken to see that there is proper air circulation around each timber balk. Over a period, in a natural process moisture content reduces. This is a slow but a good process of seasoning. Water seasoning is carried out on the banks of rivers. The thicker end of the timber is kept pointing upstream side.

After a period of 2 to 4 weeks the timber is taken out. During this period sap contained in the timber is washed out to a great extent. Then timber is stalked in a shed with free air circulation. Air seasoning ii Artificial Seasoning: In this method timber is seasoned in a chamber with regulated heat, controlled humidity and proper air circulation.

Seasoning can be completed in 4 to 5 days only. The different methods of seasoning are: a Boiling b Kiln seasoning c Chemical seasoning d Electrical seasoning. Then it is dried slowly. Instead of boiling water hot steam may be circulated on timber. The process of seasoning is fast, but costly. Timber to be seasoned is placed inside it. The heat gradually reaches inside timber.

Then relative humidity is gradually reduced and temperature is increased, and maintained till desired degree of moisture content is achieved. The kiln used may be stationary or progressive. In progressive kiln the carriages carrying timber travel from one end of kiln to other end gradually. The hot air is supplied from the discharging end so that temperature increase is gradual from charging end to discharging end. This method is used for seasoning on a larger scale. Then the timber is dried in a kiln.

The preliminary treatment by chemical seasoning ensures uniform seasoning of outer and inner parts of timber. Resistance to electric current is low when moisture content in timber is high. As moisture content reduces the resistance reduces. Measure of resistance can be used to stop seasoning at appropriate level. This technique has been tried in some plywood industries but not in seasoning of timber on mass scale.

In the sawn pieces of timber the stump of fallen branches appear as knots. Knots are dark and hard pieces. Grains are distorted in this portion.

Figure 1. If the knot is intact with surrounding wood, it is called live knot. If it is not held firmly it is dead knot. Live knot Decayed knots Fig. Knots b Shakes: The shakes are cracks in the timber which appear due to excessive heat, frost or twisting due to wind during the growth of a tree. Depending upon the shape and the positions shakes can be classified as star shake, cup shake, ring shakes and heart shakes [Ref.

They appear as shown in Fig. Wind cracks Fig. Wind cracks d Upsets: Figure 1. This type of defect is due to excessive compression in the tree when it was young. Upset is an injury by crushing. This is also known as rupture. Upset ii Defects due to Defective Seasoning and Conversion: If seasoning is not uniform, the converted timber may warp and twist in various directions. Sometimes honey combining and even cracks appear.

This type of defects are more susceptible in case of kiln seasoning. In the process of converting timber to commercial sizes and shapes the following types of defects are likely to airse: chip marks, torn grain etc.

Due to fungi attack rotting of wood, takes place. Wood becomes weak and stains appear on it. Beetles, marine borers and termites white ants are the insects which eat wood and weaken the timber. Some woods like teak have chemicals in their compositions and resist such attacks. Other woods are to be protected by chemical treatment. Timber is to be seasoned well before application of preservatives. The following are the widely used preservatives: 1. Tar 2. Chemical salt 4.

Creosote 5. ASCO 1. Tar: Hot coal tar is applied to timber with brush. The coating of tar protects the timber from the attack of fungi and insects. It is a cheapest way of protecting timber.

Main disadvantage of this method of preservation is that appearance is not good after tar is applied it is not possible to apply other attractive paints. Hence tarring is made only for the unimportant structures like fence poles. Paints: Two to three coats of oil paints are applied on clean surface of wood. The paint protects the timber from moisture. The paint is to be applied from time to time. Paint improves the appearance of the timber. Solignum paint is a special paint which protects the timber from the attack of termites.

Chemical salt: These are the preservatives made by dissolving salts in water. The salts used are copper sulphate, masonry chloride, zinc chloride and sodium fluoride. After treating the timber with these chemical salt paints and varnishes can be applied to get good appearance. Creosote: Creosote oil is obtained by distillation of coal tar. The seasoned timber is kept in an air tight chamber and air is exhausted. Then creosote oil is pumped into the chamber at a pressure of 0.

After 1 to 2 hours timber is taken out of the chamber. This preservative is available in powder form. By mixing six parts of this powder with parts of water, the solution is prepared. The solution is then sprayed over the surface of timber. This treatment prevents attack from termites. The surface may be painted to get desired appearance. For heavy construction works like columns, trusses, piles. For light construction works like doors, windows, flooring and roofing.

For other permanent works like for railway sleepers, fencing poles, electric poles and gates. For temporary works in construction like scaffolding, centering, shoring and strutting, packing of materials.

For decorative works like showcases and furnitures. For body works of buses, lorries, trains and boats 7. For industrial uses like pulps used in making papers , card boards, wall papers 8.

For making sports goods and musical instruments. Discuss the geological classification of stones. Briefly explain physical and chemical classification of rocks.

Discuss the characteristics of good building stones. Explain any three tests performed on stones to find their properties. Write various uses of stones in civil engineering works. Name any four stones along with their characteristics and uses. What do you understand by the term brick? Explain different types of bricks. Describe the properties of good bricks. Explain briefly any four types of tests conducted on bricks in the laboratories to acertain their qualities.

What are the field tests carried out to determine the qualities of the brick? Explain classification of bricks based on their quality. What are the different uses of bricks? Differentiate between fat lime and hydraulic lime. What are the test carried on lime? Briefly explain. List the various uses of lime. What is cement? How quick setting and rapid hardening cement differs from portland cement? Write short notes on i Low heat cement ii Pozzulana cement iii Coloured cement and iv Expanding cement.

State chemical and physical properties of portland cement. What is standard consistency of cement? How it is determined in the laboratory? Explain the terms initial setting time and final setting time of cement. How they are determined?

Explain the following test procedure on cement: i Soundness test ii Crushing strength test List various uses of cement. Explain the terms: timber, standing timber, rough timber and converted timber. Draw and explain cross-section of an exogeneous tree. Differentiate between i exogeneous and endogeneous trees ii soft wood and hard wood. What are the requirements of good timber? What is meant by seasoning of timber?

Distinguish between natural and artificial seasoning. Write short notes on: i Air seasoning ii Water seasoning iii Kiln seasoning and iv Chemical seasoning.

Explain various defects in timber due to natural forces. Write short notes on defects in timber due to i defective seasoning and conversion ii attack by fungi and insects. What do you understand by the term preservation of timber? Briefly explain the different methods of preservation adopted. State different uses of timber. When water is added to the dry mixture of binding material and the inert material, binding material develops the property that binds not only the inert material but also the surrounding stones and bricks.

If the cement is the binding material, then the mortar is known as cement mortar. Other mortars commonly used are lime mortar and mud mortar. The inert material used is sand. In this chapter, first an introduction is given to the inert material sand and then the proportioning, mixing, curing, properties and uses of different mortars is explained.

At the end of the chapter various tests conducted on mortars is presented. However sea sand should not be used for the following reasons: 1. It contains salt and hence structure will remain damp. The mortar is affected by efflorenscence and blisters appear. It contains shells and other organic matter, which decompose after some time, reducing the life of the mortar.

Sand may be obtained artificially by crushing hard stones. Usually artificial sand is obtained as a by-product while crushing stones to get jelly coarse aggregate. Sand is used in mortar and concrete for the following purpose: 1. It sub-divides the paste of binding material into thin films and allows it to adhere and spread.

It fills up the gap between the building blocks and spreads the binding material. It adds to the density of the mortar. It prevents the shrinkage of the cementing material.

It allows carbon dioxide from the atmosphere to reach some depth and thereby improve setting power. The cost of cementing material per unit volume is reduced as this low cost material increases the volume of mortar. Silica of sand contributes to formation of silicates resulting into the hardened mass.

The properties of good sand are: 1. It should be chemically inert. It should be free from organic or vegetable matter. It should be free from salt. It should contain sharp, angular and coarse grains. It should be well graded. It should be hard. Water is gradually added and mixed with shovels. The cement to sand proportion recommended for various works is as shown is Table 2. Cement to sand proportions for various works S. Works Cement: Sand 1 Masonry works to 2 Plastering masonry to 3 Plastering concrete 4 Pointing to Curing: Cement gains the strength gradually with hydration.

Hence it is necessary to see that mortar is wet till hydration has taken place. Curing is ensured by spraying water. Curing normally starts 6—24 hours after mortar is used. It may be noted that in the initial period water requirement is more for hydration and gradually it reduces. Curing is recommended for 28 days. Properties of Cement Mortar: The following are the important properties of cement mortar: 1.

When water is added to the dry mixture of cement and sand, hydration of cement starts and it binds sand particles and also the surrounding surfaces of masonry and concrete. A mix richer than is prone to shrinkage. Well proportioned mortar provides impervious surface. Leaner mix is not capable of closing the voids in sand and hence the plastered surface is porous.

The strength of mortar depends upon the proportion of cement and sand. Strengths obtained with various proportion of cement and sand is shown in Table 2. If fat lime is used sand mixed is normally 2 to 3 times its volume. If hydraulic lime is used sand mixed is only 2 times the volume of lime. Lime is prepared by pounding, if quantity required is small or by grinding, if the required quantity is more.

Pounding: For pounding pits are formed in hard grands. The size of pit is usually 1. It is provided with lining of bricks or stones. Lime and sand dry mixed with required proportion is placed in the pit. Small quantity of water is added at intervals. In each interval the mix is pounded with wooden pounders and mortar is turned up and down.

The process is continued till uniform colour and desired consistancy is achieved. Grinding: This is the better way of getting good mix. The grinding may be carried out in bullock driven grinding mill or in power driven grinding mill. Figure 2. It consists of a circular trench of radius 3 to 4.

A wooden shaft pivoted at centre carries a stone wheel of width just 50 mm to mm less than that of trench. Bullock drive this wheel in the trench for grinding mortar. The dry mix is placed in the trench.

Water is added gradually and bullock driven stone wheels grind the mix. A worker turns the mix up and down regularly. This method of preparing mortar needs 6 hours and can produce about 1.

Bullock driven grinding mill Figure 2. Two rollers rotate in a pan of diameter 1. Either pan or roller is rotated with the help of oil engine or electric power. During mixing required quantity of water is added gradually. Power driven grinding mill Lime mortar is also having good grinding property. Fat lime mortar is used for plastering while hydraulic lime mortar is used for masonry construction.

This mortar was considered cheap in olden days and was commonly used in small towns. However the combersome process of preparation and ease in availibility of cement in market has almost replaced the use of lime mortar. It is kneeded well until it attains required consistancy. Sometimes fibrous materials like gobber is added in the mix.

It prevents cracks in the plaster. If plaster is to be used for outer walls, it is sprayed or painted with bitumen. It is cheap mortar. Its durability is less. It is normally used for the construction of temporary sheds and cheap houses in rural areas. Cement clay mortar 2. Gauged mortar 3. Decorative mortar. Cement Clay Mortar: Quality of clay mortar can be improved by adding cement to the mix. Normal proportion of clay to cement is It maintains the economy to some extent and there is sufficient improvements in the durability of mud-mortar.

Gauged Mortar: It is the mortar obtained by adding cement to lime mortar. The usual proportion of cement, lime and sand are , and This mortar is to be used within half an hour after mixing cement. Obviously, it is cheaper than cement mortar and its quality is between that of cement mortar and lime mortar. Decorative Mortar: These mortars are obtained by using coloured cement. They are used to give pleasant appearance to outer walls.

Crushing Test 2. Tensile Strength Test 3. Adhesive Test. Crushing Test: This test is carried out on a brick work with the mortar. This brick work is crushed in a compression testing machine and the load is noted down. Then the crushing strength is obtained as load divided by cross-sectional area. After curing the briquette [Fig. The ultimate load Elevation noted. Then the tensile strength of mortar is load divided by the central cross-sectional area. Adhesive Test: Two bricks are joined together with 38 mm 76 mm mortar to be tested as shown in Fig.

The upper brick is suspended from an overhead support. A board is hung from the lower brick. Then weights are added to the board till the bricks mm separate. The adhesive strength is the load divided by area of Plan contact. Why sea sand should not be used for making mortar? What are the different types of sand used in making mortar? Why sand is used in mortars? List the properties of good sand. What proportion of cement to sand do you recommend for the following works?

State the important properties of cement mortar. Where do you use cement mortar? Explain with sketches the methods of grinding lime mortar. Write short notes on mud mortar. Briefly explain tests conducted on mortar. This can be easily moulded to desired shape and size before it looses plasticity and hardens. Plain concrete is strong in compression but very weak in tension. In this chapter proportioning, mixing, curing, properties, tests and uses of plain concrete is dealt in detail. The other improved versions of concrete are explained and their special properties and uses are pointed out.

Binding material like cement, lime, polymer 2. Fine aggregate sand 3. Coarse aggregates crushed stone, jelly 4. A small quantity of admixtures like air entraining agents, water proofing agents, workability agents etc. Depending upon the proportion of ingredient, strength of concrete varies. It is possible to determine the proportion of the ingredients for a particular strength by mix design procedure.

In the 1 absence of mix design the ingredients are proportioned as , :3, , and , which 2 is the ratio of weights of cement to sand to coarse aggregate. In proportioning of concrete it is kept in mind that voids in coarse aggregates are filled with sand and the voids in sand are filled with cement paste.

Proportion of ingredients usually adopted for various works are shown in Table 3. Proportion of cement, sand and coarse aggregates in concrete S. Proportion Nature of Work 1 For machine foundation, footings for steel columns and concreting under water. Functions of Various Ingredients Cement is the binding material. After addition of water it hydrates and binds aggregates and the surrounding surfaces like stone and bricks.

Generally richer mix with more cement gives more strength. Setting time starts after 30 minutes and ends after 6 hours. Hence concrete should be laid in its mould before 30 minutes of mixing of water and should not be subjected to any external forces till final setting takes place. Coarse aggregate consists of crushed stones. It should be well graded and the stones should be of igneous origin. They should be clean, sharp, angular and hard. They give mass to the concrete and prevent shrinkage of cement.

Fine aggregate consists of river sand. It prevents shrinkage of cement. When surrounded by cement it gains mobility enters the voids in coarse aggregates and binding of ingradients takes place. It adds density to concrete, since it fills the voids. Denser the concrete higher is its strength.

Water used for making concrete should be clean. It activates the hydration of cement and forms plastic mass. As it sets completely concrete becomes hard mass. Water gives workability to concrete which means water makes it possible to mix the concrete with ease and place it in final position.

More the water better is the workability. However excess water reduces the strength of concrete. Figure 3. To achieve required workability and at the same time good strength a water cement ratio of 0.

Batching 2. Mixing 3. Transporting and placing and 4. Batching: The measurement of materials for making concrete is known as batching. The following two methods of batching is practiced: a Volume batching b Weight batching.

A gauge box is made with wooden plates, its volume being equal to that of one bag of cement. One bag of cement has volume of 35 litres. The required amount of sand and coarse aggregate is added by measuring on to the gauge box. The quantity of water required for making concrete is found after deciding water cement ratio. For example, if water cement ratio is 0. Suitable measure is used to select required quantity of water.

Volume batching is not ideal method of batching. Wet sand has higher volume for the same weight of dry sand. It is called bulking of sand. Hence it upsets the calculated volume required. A weighing platform is used in the field to pick up correct proportion of sand and coarse aggregates. Large weigh batching plants have automatic weighing equipments. Mixing: To produce uniform and good concrete, it is necessary to mix cement, sand and coarse aggregate, first in dry condition and then in wet condition after adding water.

The following methods are practiced: a Hand Mixing b Machine Mixing. Then the sand required for the batch is spread over coarse aggregate. They are mixed in dry condition by overturning the mix with shovels.

Then the cement required for the batch is spread over the dry mix and mixed by shovels. After uniform texture is observed water is added gradually and mixing is continued.

Full amount of water is added and mixing is completed when uniform colour and consistancy is observed. The process of mixing is completed in 6—8 minutes of adding water. This method of mixing is not very good but for small works it is commonly adopted. Required quantities if sand and coarse aggregates are placed in the drum of the mixer. Water is gradually added and drum is rotated for 2 to 3 minutes during which period it makes about 50 rotations.

At this stage uniform and homogeneous mix is obtained. Concrete mixer 3. Transporting and Placing of Concrete. After mixing concrete should be transported to the final position. In small works it is transported in iron pans from hand to hand of a set of workers. Wheel barrow and hand carts also may be employed. In large scale concreting chutes and belt conveyors or pipes with pumps are employed. In transporting care should be taken to see that seggregation of aggregate from matrix of cement do not take place.

Concrete is placed on form works. The form works should be cleaned and properly oiled. If concrete is to be placed for foundation, the soil bed should be compacted well and is made free from loose soil. Concrete should be dropped on its final position as closely as possible.

If it is dropped from a height, the coarse aggregates fall early and then mortar matrix. This segregation results into weaker concrete. Compaction of Concrete: In the process of placing concrete, air is entrapped. Hence it is necessary to remove this entrapped air. This is achieved by compacting the concrete after placing it in its final position.

Compaction can be carried out either by hand or with the help of vibrators. In intricate portions a pointed steel rod of 16 mm diameter and about a metre long is used for poking the concrete.

Vibration reduces the friction between the particles and set the motion of particles. As a result entrapped air is removed and the concrete is compacted. The use of vibrators reduces the compaction time. Vibration should be stopped as soon as cement paste is seen on the surface of concrete. Over vibration is not good for the concrete. The following types of vibrators are commonly used in concreting: a Needle or immersion vibrators b Surface vibrators c Form or shutter vibrators d Vibrating tables.

Needle vibrators are used in concreting beams and columns. Surface vibrators and form vibrators are useful in concreting slabs.

Vibrating tables are useful in preparing precast concrete elements. Curing of Concrete Curing may be defined as the process of maintaining satisfactory moisture and temperature conditions for freshly placed concrete for some specified time for proper hardening of concrete. Curing in the early ages of concrete is more important. Curing for 14 days is very important. Better to continue it for 7 to 14 days more. If curing is not done properly, the strength of concrete reduces.

Cracks develop due shrinkage. The durability of concrete structure reduces. The following curing methods are employed: a Spraying of water b Covering the surface with wet gunny bags, straw etc. It accelerates curing process, resulting into the reduction of curing period.

The compound shows affinity to the moisture and retains it on the surface. It keeps the concrete surface wet for a long time. Properties of Concrete Concrete has completely different properties when it is the plastic stage and when hardened. Concrete in the plastic stage is also known as green concrete.

Workability 2. Segregation 3. Bleeding 4. The properties of hardened concrete are: 1. Strength 2. Resistance to wear 3. Dimensional changes 4. Durability 5. Properties of Green Concrete 1. Workability: This is defined as the ease with which concrete can be compacted fully without seggregating and bleeding. It can also be defined as the amount of internal work required to fully compact the concrete to optimum density.

The workability depends upon the quantity of water, grading, shape and the percentage of the aggregates present in the concrete. Workability is measured by a The slump observed when the frustum of the standard cone filled with concrete is lifted and removed. The suggested values of workability for different works are as shown in Table 3.

Table 3. Concreting of shallow sections with vibrations — 0. Concreting of light reinforced sections with vibrators — 0. Concreting of lightly reinforced sections without 25 — 75 mm 0. Concreting of heavily reinforced sections without 75 — mm More than 0. Segregation: Separation of coarse particles from the green concrete is called segregation.

Because of the segregation, the cohesiveness of the concrete is lost and honey combing results. Ultimately it results in the loss of strength of hardened concrete. Hence utmost care is to be taken to avoid segregation. Bleeding: This refers to the appearance of the water along with cement particles on the surface of the freshly laid concrete.

This happens when there is excessive quantity of water in the mix or due to excessive compaction. Bleeding causes the formation of pores and renders the concrete weak.

Bleeding can be avoided by suitably controlling the quantity of water in the concrete and by using finer grading of aggregates. Harshness: Harshness is the resistance offered by concrete to its surface finish. Harshness is due to presence of lesser quantity of fine aggregates, lesser cement mortar and due to use of poorely graded aggregates.

It may result due to insufficient quantity of water also. With harsh concrete it is difficult to get a smooth surface finish and concrete becomes porous. Properties of Hardened Concrete 1. Strength: The characteristic strength of concrete is defined as the compressive strength of mm size cubes after 28 days of curing below which not more than 5 per cent of the test results are expected to fail.

IS grades the concrete based on its characteristic strength as shown in Table 3. But IS — specifies minimum grade of M20 to be used for reinforced concrete works. Strength of concrete depends upon the amount of cement content, quality and grading of aggregates, water cement ratio, compaction and curing. Strength of concrete is gained in the initial stages. In 7 days the strength gained is as much as 60 to 65 per cent of 28 days strength. It is customary to assume the 28 days strength as the full strength of concrete.

About this Book. All the basic elements and important aspects that involve Civil engineering have been properly covered by the author.

As such student of civil engineering should see this book as a necessity since they need interaction with civil engineers in their routine works. The book covers the entire syllabus on basic civil engineering. Neat sketches and illustrations with practical problems, has also been included where necessary, to make it more understandable to the students.

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