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1. CEMENT, 1.1 OBJECTIVES, After studying this unit, you should be able to:, 1., , Describe the manufacturing process of cement,, , 2., , Explain the chemical composition of cement,, , 3., , Describe the physical properties of cement,, , 4., , Classify the various types of cement explaining their uses,, , 5., , Verify the quality of cement by the field test, and, , 6., , Get acquainted with the laboratory testing of Portland cement., , 1.2 DEFINITION OF CEMENT, Cement is defined as the product manufactured by burning and crushing to powder an, intimate and well-proportioned mixture of calcareous and argillaceous materials., , Calcareous Materials, The materials which contain calcium or lime as their major constituent are known as, calcareous materials. The various calcareous materials used in the manufacture of cement are, lime stone, marl, chalk, shells, etc. These materials provide the required proportion of lime to the, cement., , Argillaceous Materials, The argillaceous materials contain alumina as their major constituent. The various, argillaceous materials used in the manufacture of cement are shale, clay, laterite, etc. These, materials provide the required proportion of silica, alumina, oxide of iron, etc. to the cement., Cement is manufactured in a variety of forms these days. The cement, which is generally, used for preparing concrete, is the Ordinary Portland Cement. But for special purposes other, qualities of cement such as Low Heat Cement, Rapid Hardening Cement, High Alumina Cement,, White Cement, Blast Furnace Slag Cement, Sulphate Resisting Cement, etc. are also used., The selection of a particular type of cement to be used for manufacturing of concrete depends, upon the following factors:, Concrete Technology/ Cement, , 1

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(a) The required strength of the concrete structure., (b) The type of structure., (c) The conditions under which the construction of structure is to take place., , 1.3 MANUFACTURING PROCESS OF CEMENT, The process of manufacture of cement consists of grinding the raw materials (calcareous, and argillaceous materials) mixing them intimately in certain proportions and burning them in a, kiln at a temperature of about 1500°C at which the material sinters and fuses to form nodular, shaped clinker. The clinker is cooled and ground to a fine powder with addition of about 2 to 3 %, of gypsum. The product obtained by this procedure is called as Portland cement. There are two, processes known as Wet and Dry processes depending upon whether the mixing and grinding of, raw materials is done in wet or dry condition. The wet process requires more fuel as slurry, contains about 35-50 % water. The dry process requires less fuel as materials are already in dry, state., , A. Wet Process, In this process, the limestone is crushed to smaller fragments and then it is taken to a ball, or tube mill where clay or shale is mixed with it and ground to a fine consistency of slurry with, the addition of water. The slurry is pumped to slurry tanks where it is kept in an agitated, condition by means of rotating arms with chains to prevent setting of limestone and clay, particles. At this stage, the chemical composition of slurry is adjusted as necessary. The, corrected slurry is stored in storage tanks and kept in homogeneous condition by the agitation of, slurry., The corrected slurry is injected at the upper end of a rotary kiln. Rotary kiln is formed of, steel tubes. The diameter of rotary kiln varies from 3 m to 8 m and length varies from 30 m to, 200 m. The kiln is supported at intervals by columns of masonry or concrete. It is laid at a, gradient of about 1 in 25 to 1 in 30. The refractory lining is provided on the inside surface of, rotary kiln. It is so arranged that the kiln rotates at about one to three revolutions per minute, about its longitudinal axis. The burning is carried out in this rotary kiln., The hot gases or flames are forced through the lower end of the kiln. The portion of the, kiln near its upper end is known as dry zone and in this zone; the water of slurry is evaporated., As the slurry gradually descends, there is rise in temperature and in the next section of kiln; the, Concrete Technology/ Cement, , 2

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carbon dioxide from slurry is evaporated. The small lumps, called as nodules, are formed at this, stage. These nodules then gradually roll down passing through zones of rising temperature and, ultimately reach to the burning zone, where temperature is about 1500°C. In burning zone, the, calcined product is formed and nodules are converted into small hard dark greenish blue balls,, which are known as clinkers. The size of clinkers varies from 3 mm to 20 mm and they are very, hot when they come out of burning zone of kiln. The temperature of clinker at the outlet of kiln, is nearly 1000°C. The clinker drops into a rotary cooler where it is cooled under controlled, conditions., , Figure A: Flow Diagram of Wet Process, Concrete Technology/ Cement, , 3

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The clinkers as obtained from the rotary kiln are finely grounded in ball mills and tube, mills. During grinding a small quantity, about 2 to 3% of gypsum is added. If gypsum is not, added, the cement would set as soon as water is added. The gypsum controls the initial setting, time of cement. The gypsum acts as a retarder and delays the setting action of cement. Thus,, gypsum permits cement to be mixed with the aggregates and to be placed in position. A ball mill, consists of several compartments charged with progressively smaller hardened steel balls. The, particles crushed to the required fineness are separated by currents of air and taken to storage, silos from where the cement is bagged or filled into barrels for bulk supply to dams, bridges or, other large work sites., , B. Dry Process, In the dry process, the raw materials are crushed dry and fed in correct proportions into a, grinding mill. The raw materials are dried and crushed into a very fine powder. The dry powder, is called raw meal. The dry powder is further blended and corrected for its right composition and, mixed by using compressed air. The aerated powder tends to behave almost like liquid and in, about one hour of aeration a uniform mixture is obtained. The sieved blended meal fed into a, rotating disc called as granulator. The pellets of blended meal are formed by adding water, approximately 12% to permit air flow for exchange of heat for chemical reactions and, conversion of the same into clinker., The dry process is economical. In this method, equipment used is comparatively smaller., The consumption of coal in this method is very low as compared to wet process. In case of, mixing of raw materials by dry process, the raw mix is formed and in case of mixing of raw, materials by wet process, the slurry is formed. The remaining operations, e.g. burning and, grinding are same as that of the wet process. The flow diagram of dry process of cement, manufacturing is given in Figure B., , Concrete Technology/ Cement, , 4

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Figure B: Flow Diagram of Dry Process, Concrete Technology/ Cement, , 5

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1.4 CHEMICAL INGREDIENTS OF CEMENT, The chief chemical ingredients and their proportions in ordinary cement are given in Table 1.1., Sr. No., , Chemical Ingredients, , Formula, , 1, , Lime, , CaO, , 63, , 60 to 67, , 2, , Silica, , SiO2, , 22, , 17 to 25, , 3, , Alumina, , Al2O3, , 6, , 3 to 8, , 4, , Iron Oxide, , Fe2O3, , 3, , 0.5 to 6, , 5, , Magnesium Oxide, , MgO, , 2.5, , 0.1 to 4, , 6, , Sulphur Oxide, , SO3, , 1.25, , 1 to 3, , 0.25, , 0.2 to 1, , 7, , Alkali’s such as Soda & Lime Na2O3, K3O, , Commonly Used % Range (%), , Table 1.1: Chief Chemical Ingredients of Cement, The functions and effects of various chemical ingredients of cement are as follows:, Lime, Lime is the major ingredient of cement. It makes the cement sound and also provides strength to, the cement. Lime in excess makes the cement unsound and causes the cement to expand and, disintegrate. The deficiency of lime will decrease the strength and cause the cement to set, quickly., Silica, Silica provides strength to the cement. Silica in excess causes the cement to set slowly., Alumina, Alumina lowers the clinkering temperature. It provides quick setting property to the cement., Alumina in excess weakens the strength of the cement., Iron Oxide, Iron oxide provides colour, hardness and strength to the cement. It helps the fusion of material at, lower temperature during the manufacturing of cement., Magnesium Oxide, Magnesium oxide provides colour and hardness to the cement. Excess magnesium oxide remains, in Free State and makes the cement unsound., Sulphur Trioxide, Sulphur trioxide makes the cement sound if present in very small quantity. Excess sulphur, trioxide makes the cement unsound., Concrete Technology/ Cement, , 6

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Alkalis, Alkalis may be present in a very small quantity. Alkali’s in excess cause efflorescence., , 1.5 CHEMICAL COMPOUNDS OF CEMENT, Table 1.2 shows the major chemical or final compounds of cement. They are also known as, Bouge’s’ compounds., Sr., No., 1, 2, 3, 4, 5, , Chemical, Formula, , Compounds, , Tri-calcium Silicate, 3CaO.Sio2, Di-calcium Silicate, 2CaO.Sio2, Tri-calcium, 3CaO.Al2O3, Aluminate, Tetra, Calcium, 4Cao.Al2O3.Fe2O3, Alumino Ferrite, Other, -, , C3 S, C2 S, , Common, Proportion, (%), 40, 30, , 25 to 50, 21 to 45, , C3 A, , 11, , 5 to 11, , C3AF, , 11, , 9 to 14, , -, , 8, , 8, , Accepted, Abbreviation, , Range, (%), , Table 1.2: Chief Chemical Compounds of Cement, These final compounds of cement are formed during calcinations in the following order:, C4AF, C3A, C2S and C3S, The properties of all these final compounds of cement are discussed below:, Tri-calcium Silicate (C3S):, It possesses the following properties:, (a) It hydrates rapidly., (b) It generates more heat of hydration., (c) It develops early strength., (d) It has less resistance to sulphate attack., , Di-calcium Silicate (C2S), It possesses the following properties:, (a) It hydrates slowly., (b) It generates less heat of hydration., (c) It hardens more slowly., Concrete Technology/ Cement, , 7

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(d) It contributes a little in early strength development., (e) It gives good ultimate strength to the cement., (f) It has more resistance to sulphate attack., Tri-calcium Aluminate (C3A), It possesses the following properties:, (a) It generates large amount of heat of hydration., (b) It reacts fast with water., (c) It causes initial setting of cement and thus helps in early strength development in the, concrete., (d) It has less resistance to sulphate attack., (e) It does not contribute to develop ultimate strength., Tetra-calcium Alumino Ferrite (C4AF), It possesses the following properties:, (a) It is slow in reaction., (b) It generates less heat of hydration., (c) It is comparatively in-active and thus poor in early strength., (d) It does not contribute to develop ultimate strength as it has poor cementing value., (e) It has less resistance to sulphate attack., , It has been analyzed that C3S and C2S control most of the strength developing properties, of cement. The sum of their percentage range varies from 70 to 80 %.By changing the relative, proportions of these compounds, different types of cements can be manufactured., , 1.6 TYPES OF CEMENT, 1., 2., 3., 4., 5., 6., 7., 8., 9., , Ordinary Portland Cement (OPC), Rapid Hardening Portland Cement (RHPC), Low Heat Portland Cement, Sulphate Resisting Cement, Blast Furnace Slag Cement, White and Colour Cement, High Alumina Cement, Pozzolana Cement, Oil Well Cement, Concrete Technology/ Cement, , 8

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10. Expanding Cement, 11. Quick Setting Cement, , 1.6.1 Ordinary Portland Cement (OPC), This type of cement is also called normal setting cement since its setting is normal when, mixed with water. It is general-purpose cement suitable for general concrete construction work,, which requires no special consideration. It has medium rate of strength development and heat, generation. It has less resistance to chemical attack., Following are the uses of ordinary Portland cement:, (a) It is used in important structures, where great strength is required such as heavy, buildings and bridges, etc., (b) It is used in structures subject to the action of water such as foundations, under water, reservoirs, water tight floors, dock yards, etc., (c) It is used for making cement mortar, plain cement concrete, reinforced cement concrete, etc., (d) It is used for plastering and painting., (e) It is used for drainage and water supply works., , 1.6.2 Rapid Hardening Portland Cement (RHPC), This cement is similar to Ordinary Portland cement but with higher tri-calcium silicate, (C3S) content and finer grinding. It gains strength more quickly than OPC, though the final, strength is only slightly higher. This type of cement is also called as High-Early Strength, Portland Cement. The one-day strength of this cement is equal to the three-day strength of OPC, with the same water-cement ratio., Following are the advantages of the rapid hardening Portland cement:, (a) It is used where formwork has to be removed as early as possible in order to reuse it., (b) It is used where high early strength is required., (c) It is generally used for constructing road pavements, where it is important to open the, road to traffic quickly., (d) It is used in industries which manufacture concrete products like slabs, posts, electric, poles, block fence, etc. because moulds can be released quickly., (e), , It is used for cold weather concreting because rapid evolution of heat during, hydration protects the concrete against freezing., Concrete Technology/ Cement, , 9

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1.6.3 Low Heat Portland Cement, Percentages of tri-calcium silicate (C3S) and tri-calcium aluminate (C3A) are lower in, this cement than OPC and RHPC while that of di-calcium silicate (C2S) is higher. This results in, a slower rate of reaction, lower evolution of heat of hydration and lower early strength. But the, ultimate strength remains more or less unaffected., Following are the uses of low heat Portland cement:, (a) This cement is used only in large mass concrete works such as dams, bridges,, abutments, retaining walls, etc., (b) It is also used in works where the rate of heat of generation must be kept to, minimum., , 1.6.4 Sulphate Resisting Cement, This type of cement is also known as super sulphate cement. In this cement, the, percentage of tri-calcium aluminate (C3A) is kept below 5 percent and it results in the increase in, resisting power against sulphate attacks., Following are the uses of sulphate resisting cement:, (a) It is used for canal lining in severe alkali conditions especially in the arid western, regions., (b) It is used for marine works, mass concrete jobs to resist the attack of aggressive, water., (c) It is used for works underside of bridges, over railway tracks and for concrete sewers, carrying industrial effluents., (d) It is used in the construction of reinforced concrete pipes and also for construction, works to be done in sulphate bearing soils., , 1.6.5 Blast Furnace Slag Cement, The blast furnace slag, which is a waste product obtained during manufacture of iron,, contains all the basic elements of cement, i.e. silica, alumina, lime, iron, etc. It is crushed, preliminary to a granulated form, which is then intimately mixed with cement clinkers in the, proportion of 65 % of slag to 35 % of clinkers and both are then grounded together to form, cement. It is cheaper than OPC. It develops low heat of hydration and has less early strength., Concrete Technology/ Cement, , 10

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Following are the uses of blast furnace slag cement:, (a) It is used for mass concrete works such as retaining walls, bridge abutments,, dams, etc., (b) It is used for all purposes for which OPC is used., , 1.6.6 White and Colour Cement, White cement is manufactured from special raw materials like white chalk and china clay, having low contents of iron oxide (less than 1 %). Coloured cements are manufactured by adding, suitable mineral pigments (oxide of lead, etc.) to Portland cement during grinding. The, proportion of the pigment varies 5% to 10%. The cobalt gives blue colour. The iron oxide in, different proportions gives brown, red or yellow colour. The manganese dioxide gives black or, brown coloured cement. These cements are costlier than OPC because of specific requirements, imposed upon the raw materials and manufacturing process., Following are the uses of white and coloured cement:, (a) They are used in decorative works such as finishing coat of concrete floors, face, plaster to walls, etc., (b) They are also used in mortars to be used for floors and wall tiles and for, ornamental concrete works., , 1.6.7 High Alumina Cement, It is produced by grinding clinkers formed by calcining bauxite and lime. The proportion, of alumina varies from 35% to 45% and the ratio of alumina to lime is in between 0.85 to 1.3. It, is not only rapid hardening cement but also higher ultimate strength cement. It resists the action, of acids and can withstand high temperature. This cement is costlier than OPC., Following are the uses of high alumina cement:, (a) It is very useful for chemical plants and lining of furnaces., (b) It is used for structures subjected to the action of sea water, chemical and other, such agents., , Concrete Technology/ Cement, , 11

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1.6.8 Pozzolana Cement, The pozzolana cement is a volcanic powder. It resembles surkhi, which is prepared by, burning bricks made from ordinary soils. It can also be processed from shales and certain types, of clays. The pozzolana material should be 10% to 30%., Following are the use of pozzolana cement:, (a) It is used in sewage works and for laying concrete under water., (b) It is used for marine structures., , 1.6.9 Oil Well Cement, This is a special type of cement required for sealing oil wells. Sealing is necessary to, prevent the sides of the freshly drilled well from collapsing and to keep ground water out of the, well shaft. This type of cement is manufactured by adjusting the proportion of iron oxide so that, all the alumina is converted to tetra-calcium alumino ferrite (C4AF). Due to this the proportion, of the compound tri-calcium aluminate (C3A) formed is very small and thus the setting time of, cement is increased., Following are the uses of oil-well cement:, (a) It is used for cementing the oil wells., (b) It is also used to protect the oil well casing from corrosion., , 1.6.10 Expanding Cement, It is manufactured by adding an expanding medium like sulpho-aluminate and a stabilizing agent, to ordinary cement. Hence, this cement expands whereas other cements shrink., Following are the uses of expanding cement:, (a) It is used for repairing the damaged concrete surfaces., (b) It is used for the construction of water retaining structures., , 1.6.11 Quick Setting Cement, It is manufactured by adding a small percentage of aluminium sulphate and by finely, grinding the cement. The low percentage of gypsum or retarder is used for quick setting action of, cement. The setting action of cement starts within five minutes after addition of water and it, becomes hard like stone in less than 30 minutes or so. It is used to lay concrete under static, water or running water., Concrete Technology/ Cement, , 12

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1.7 TESTING OF PORTLAND CEMENT, To know the quality of a Portland cement, it should be tested before its use is, recommended for any important engineering work. Care should be taken to collect the sample of, cement. In order to make a representative sample, it is desirable to collect the sample from at, least 12 different bags or barrels or containers or from 12 different positions in a heap if the, cement is loose. The quantity of cement so collected is intimately mixed and the final sample of, cement weighing at least 5 kg is prepared. It is then stored in air-tight container till the tests are, started., The properties of concrete mainly depend upon the quantity of cement used. To know the quality, of Portland cement it should be tested before its use for any important engineering work. Testing, of cement can be done by two ways., (a) Field testing, and, (b) Laboratory testing., , 1.7.1 Field Tests, The following are the field tests on cement:, (a) The colour of the cement should be uniform. It should be grey colour with a light, greenish shade., (b) The cement should be free from any hard lumps. Such lumps are formed by the, absorption of moisture from the atmosphere. Any bag of cement containing such, lumps should be rejected., (c) The cement should feel smooth when touched or rubbed in between fingers. If it is, felt rough, it indicates adulteration with sand., (d) If hand is inserted in a bag of cement or heap of cement, it should feel cool and not, warm., (e) If a small quantity of cement is thrown in a bucket of water, the particles should float, for some time before it sinks., (f) A thick paste of cement with water is made on a piece of glass plate and it is kept, under water for 24 hours. It should set and not crack., , Concrete Technology/ Cement, , 13

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(g) A block of cement 25 mm × 25 mm and 200 mm long is prepared and it is immersed, for 7 days in water. It is then placed on supports 15cm apart and it is loaded with a, weight of about 34 kg. The block should not show signs of failure., (h) The briquettes of a lean mortar (1: 6) are made. The size of briquette may be about, (75 mm × 25 mm × 12 mm). They are immersed in water for a period of 3 days. If, cement is of sound quality such briquettes will not be broken easily., , 1.7.2 Laboratory Tests, For examining the suitability of cement the following laboratory tests are usually performed., (a) Chemical composition, (b) Fineness, (c) Consistency, (d) Setting time, (e) Soundness test, (f) Compressive strength, (g) Tensile strength, , 1.7.3 Chemical Composition, The various tests are carried out to determine the chemical constituents of cement. Following are, the chemical requirements of ordinary cement as per BIS 269-1975:, (a) Ratio of percentage of alumina to that of iron oxide should not be less than 0.66., (b) Ratio of percentage of lime to those of alumina, iron oxide and silica should not be, less than 0.66 and it should not be greater than 1.02, when calculated by the, following formula., , (c) The total loss on ignition should not be greater than 4 %., (d) The total sulphur content is calculated as SO3 and it should not be greater than 2.75 %., (e) The weight of insoluble residue should not be greater than 1.50 %., (f) The weight of magnesia should not exceed 5 %., , Concrete Technology/ Cement, , 14

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1.7.4 Fineness Test, It is carried out to check proper grinding of cement. The fineness of cement particles may, be determined either by sieve test or by permeability apparatus test. In sieve test, 100 gm. of the, cement is taken and it is continuously passed for 15 minutes through standard BIS sieve No. 9, (90 micron). The residue is then weighed and this weight should not be more than 10% of, original weight for OPC. In permeability apparatus test, specific surface area of cement particles, is calculated. This test is better than sieve test and it gives an idea of uniformity of fineness. The, specific surface acts as a measure of the frequency of particles of average size. The specific, surface of cement should not be less than 2250 cm2/gm., , 1.7.5 Consistency Test, The purpose of test is to determine the quantity of water required for standard, consistency. For finding out setting time and soundness of cement standard consistency has to be, used. Standard or normal consistency of a cement paste is defined as that consistency which will, permit the ‘Vicat plunger’ 10 mm diameter and 40 to 50 mm in length to penetrate to a point 5 to, 7 mm from the bottom (or 33 to 35 mm from the top) of the Vicat mould when the cement paste, is tested within 3 to 5 minutes after the cement is thoroughly mixed with water. Vicat apparatus, consists of a metal frame, movable rod with cap at the top and plunger at the bottom end and a, mould. The weight of movable rod along with cap and attachment is limited up to 300 gms. It is, provided with a releasing pin to make the rod free and is attached with an indicator to take, readings on a vertical scale, which is graduated from 0 to 40 mm in either direction., To perform this test take about 400 gm of cement and prepare a paste with a weighed, quantity of water, say 25%. The paste obtained should be filled in the mould of the Vicat, apparatus. The interval of time between the instant of adding water to the dry cement and the, instant of commencement of filling the mould is called the time of gauging. The time of gauging, must be between 3 to 5 minutes., The plunger of diameter 10 mm is lowered gently on to the paste in the mould. The, settlement of the plunger is noted. If the settlement is between 5 to 7 mm from the bottom of the, mould (or 33 to 35 mm from the top), the amount of water added is correct and is corresponding, to standard consistency of cement. If this condition is not satisfied, the test must be repeated, , Concrete Technology/ Cement, , 15

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again changing the percentage of water until the required extent of penetration of the plunger is, reached., Let, , W 1 = Weight of cement taken for the test, and, W 2 = Weight of water added for desired penetration, Percentage of water for normal consistency = P = (W 2/W 1) × 100., It varies from 25 % to 35 %., , 1.7.6 Setting Time Test, This test is used to check the initial and final setting times of the cement. The initial, setting time is determined so as to give sufficient time for various operations like mixing,, transportation, placing and compaction of cement concrete or cement mortar. The final setting, time is determined to find that after laying the cement concrete or mortar, the hardening should, , Concrete Technology/ Cement, , 16

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be rapid so that the structure may be made in use as early as possible. For determining the setting, time of cement Vicat apparatus is used., , Initial Setting Time, The initial setting time is the interval between the addition of water to cement and the, stage when needle (1 mm square; 40 to 50 mm length) fails to pierce the test block by about 5, mm from the bottom. The cement of weight 400 gm. is taken and it is mixed with 0.85 P, percentage of water where P is the % of water as determined in consistency test. The cement, paste is filled in the Vicat mould. The square needle of cross section 1 mm × 1 mm called as, initial setting time needle is attached to the moving rod of the Vicat apparatus. The needle is, quickly released and it is allowed to penetrate the cement paste. In the beginning, the needle, penetrates completely. It is then taken out and dropped at a fresh place. The procedure is, repeated until the needle fails to pierce the cement paste in block for about 5 mm, measured from, the bottom of the mould. The time thus recorded shall be the initial setting time. The care should, be taken that each time the needle should be cleaned and released at a new place, on the top, surface of the paste. The time from the stopwatch and readings from the scale should be recorded, continuously., , Final Setting Time, The final setting time is defined as period elapsing between the time when water is added, to cement and the time at which the final setting time needle of 1 mm square section with 5 mm, diameter attachment makes an impression on the test block while the attachment fails to do so., In this test, the initial setting time needle is replaced by final setting time needle, with an annular, attachment. It is released on the top surface of the mould at regular intervals and the time is, recorded. In the beginning, the needle and the collar will make impression on the surface of the, paste. When the cement is finally set, only needle will make the impression and the collar will, fail to do so. The time thus recorded shall be the final setting time. Care must be taken to clean, the needle each time and the needle should be released at a new place in each trial., , 1.7.7 Soundness, The phenomenon by virtue of which cement does not undergo large change in volume, when treated with water is called as soundness. If the quantity of free lime and magnesia is, present in excess during the manufacture of cement, it is liable to remain uncombined and be, Concrete Technology/ Cement, , 17

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over-burnt in the kiln. The cement concrete or mortar of such cement is liable to expand after the, setting action is completed. It is one of the causes of cracking of cement., Soundness test is performed to accelerate the slaking action of free lime and magnesia, if, they exist by the application of heat, thereby detecting the defect in a short time., The unsoundness may be reduced by, (a) Fine grinding,, (b) Thorough mixing,, (c) Limiting the MgO content to less than 0.5 %, and, (d) Allowing the cement to aerate for several days., Unsoundness is generally expressed by the expansion of cement paste by Le-Chatelier, method. Le-Chatelier apparatus consist of a small split cylinder of spring brass of thickness 0.5, mm, forming a mould 30 mm high. Two indicators with pointed ends are attached on both sides, of the split (which should not be more than 0.5 mm). The distance from these ends to the center, of the cylinder is 165 mm., , Fig1.4: Le-Chatelier Apparatus for finding soundness of Cement, In this test, 100 gm of cement is taken and 0.78 P water is added, where P is the, percentage of water required for normal consistency paste. It is mixed thoroughly for about three, minutes. Remove air bubble from the cement paste, if any. Cement paste is then filled into the, mould, resting on a glass plate (within five minutes from the instant water is added). The mould, is then smoothened and covered with another glass plate. A small weight is placed on the top and, whole assembly is immediately submerged in water at a temperature of 27oC to 32oC for 24, hours. Then the mould is removed from water and the distance separating the indicator points is, Concrete Technology/ Cement, , 18

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measured. The whole assembly is submerged again in water and the water is heated till it reaches, the boiling point in 25 to 30 minutes. The mould is kept in boiling water for three hours. Then, the mould is taken out of water and allowed to cool. After cooling, the distance between pointers, is again measured. The difference between these two measurements represents the expansion of, cement. For ordinary Portland cement, rapid hardening cement and low heat cement the, expansion shall not be more than 10 mm., , 1.7.8 Compressive Strength Test, This test is carried out to determine the compressive strength of cement. The mortar of, cement and standard sand is prepared. The proportion is 1: 3 which means that x gm. of cement, is mixed with 3x gm. of standard sand. Instead of standard sand, ordinary sand passing through, 850 micron IS sieve and not more than 10 % by weight passing through 600 micron IS sieve may, be used., To perform this test, 200 gm. of cement and 600 gm. of standard sand by weight are, taken and mixed dry in a non-porous mixing pan to uniform colour with the help of a trowel for, one minute. The water is added at the rate of P/4 + 3 percent of water when ordinary sand is used, by weight of cement and sand mix together where P is the percentage of water required for a, paste of standard consistency. It is mixed thoroughly to an even colour for about three minutes., The cube mould made of metal of size 70.6 mm is placed on a non-porous base plate and is oiled, from inside. The mould is fitted on the table of the vibrating machine. Immediately after mixing,, the mortar is put into the cube mould and is compacted for two minutes by the vibrations of the, machine, which runs at a speed of 1200 ± 400 vibrations per minute. The filling and compaction, of mould should be finished within 5 minutes from the instant water is added to mortar. The, mould is then removed and the top surface is smoothened off by the single stroke of a trowel., The prepared cubes are kept at a temperature of 27oC ± 2oC in an atmosphere of at least 90%, relative humidity for 24 hours. Then the cubes of mortar are removed from the mould and, immersed in water for curing until taken out for testing, i.e. after 3 or 7 or 28 days., , Concrete Technology/ Cement, , 19

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1.7.9 Tensile Strength Test, This test was formerly used to get an indirect indication of compressive strength of, cement. Generally, it is used for rapid hardening cement. The procedure is given below., (a) The mortar of cement and sand is prepared in the proportion of 1: 3., (b) The quantity of water 8% by weight of cement and sand is added to the mortar., (c) The briquette mould is filled with mortar and then a small heap of mortar is formed at, its top. It is beaten down by a standard spatula till water appears on the surface., Same procedure is repeated for the other face of briquette. Twelve such standard, briquettes are prepared., (d) The briquettes are kept in a damp cabin for 24 hours., , Figure 1.5: Briquette Mould, (e) The briquettes are carefully removed from the moulds and they are submerged in, clean water for curing., (f) The briquettes are tested in testing machine at the end of 3 days and 7 days. Six, briquettes are tested in each test and average is found out. During the test, the load is, to be applied uniformly at the rate of 35 kg/cm2, (g) The cross-sectional area of briquette at its least section is 6.45 cm2. Hence the, ultimate tensile stress of cement paste is obtained from the following relation., , (h) The tensile stress at the end of 3 days should not be less than 20 kg/cm2 and that at, the end of 7 days should not be less than 25 kg/cm2., Concrete Technology/ Cement, , 20