Concrete Technology Unit -1.pdf

## Concrete, A Construction Material ### Introduction Cement concrete is a mixture of hard inorganic materials called aggregates such as gravel, sand, crushed stone, slag etc. cemented together with Portland cement and water paste. The cement-water paste has its role to bind the aggregates to form...

## Concrete, A Construction Material ### Introduction Cement concrete is a mixture of hard inorganic materials called aggregates such as gravel, sand, crushed stone, slag etc. cemented together with Portland cement and water paste. The cement-water paste has its role to bind the aggregates to form a strong rock like mass, after hardening as a consequence of the chemical reaction between cement and water. Aggregates are classified into fine aggregates and coarse aggregates. Fine aggregates consist of sand whose particle size does not exceed 4.75 mm. Coarse aggregates consist of gravel, crushed stone etc. of particle size more than 4.75 mm. The paste that binds the aggregate consists of cement, water and some entrapped air. The cement-water paste acts as a slurry which fills the voids in sand forming mortar. The mortar so formed fills the voids in the coarse aggregates. (In modern days some admixtures are also introduced to provide certain special qualities to the concrete formed). Other materials used as aggregates include blast furnace slag, cinders and some artificial light weight aggregates obtained by burning clay or shale. Cement paste and air voids occupy about 25 percent of the total volume of a concrete mass. After placing the concrete, though it is well compacted, there will still remain some entrapped air within the concrete body. In a freshly made well compacted concrete mass, the unavoidable entrapped air is likely to exist to the order of 1 to 2 percent. For certain special purposes, sometimes certain air-entraining agents are incorporated in the concrete mass so that the small air voids distributed throughout the paste may form several percent of the total volume. When the above materials are mixed together so as to form a workable mixture, it can be moulded or cast into beams, slabs etc. A few hours after mixing, the materials undergo a chemical reaction and as a consequence, the mixture solidifies and hardens, attaining greater strength with age. In a concrete mix the principal components - the binder and the aggregate must be in such proportions, the following requirements are achieved viz., - In the freshly mixed state the mass should be workable and placeable. - In the hardened state, it should possess strength and durability to suit the purpose for which it is intended. The solid part of the hardened concrete consists of the mineral aggregate plus the hardened cement paste which may include some amount of the originally present cement and the new product which has resulted by combination of some cement and some water. At any stage free water present depends on the extent of combination of cement and water and also on the possible escape of water from the mass as a consequence of evaporation under drying conditions. ### 1.1 Roles of Cement-Water Paste and Aggregates The cement-water paste, the binding material is the active component of the concrete. It has two functions, viz. - It fills the voids between the inert aggregate particles providing lubrication of the fresh plastic mass and to provide water tightness in the hardened concrete. - It provides the strength to the concrete in its hardened state. The properties of the hardened concrete are governed by: - the characteristics of the cement - the relative proportions of cement and water - the extent to which the chemical combination of cement and water has taken place. This chemical process is generally referred to as hydration (although other processes are also involved). For hydration of the cement the requirements are favourable temperature presence of moisture and sufficient time interval. The interval of time during which the concrete is definitely subjected to the favourable temperature and moisture condition is called the curing period. A period of 3 to 14 days is used as curing period on construction works. In the laboratory, the curing period is 28 days. To produce good quality concrete, adequate curing is essential. ### Role of Aggregate Aggregates, the major source of ingredients of concrete constitute about 70 to 75 percent of the total volume acting as the strong economic fillers of the concrete body. As they form the major bulk of the concrete mass they have great influence over important properties of concrete. The aggregate performs three main functions. They are: - to provide a cheap filler for the cementing material - to provide mass suitable to resist the action of loads, to resist abrasion, to resist percolation of water and to resist the action of weather - to minimize the volume changes that may occur during the setting and hardening processes and moisture changes in the cement water paste. The concrete acquires its properties resulting from the use of particular aggregates. These properties depend on: - the mineral character of the aggregate particles particularly related to strength, elasticity and durability - the surface characteristics of the particles, particularly related to workability of freshly made concrete and bond within the hardened mass - the grading of the aggregate particularly related to workability, density and economy of mix - the amount of aggregate per unit volume of concrete particularly related to the cost and also volume changes due to drying. ### 1.2 Relative Proportions of Ingredients in Ordinary Concrete The characteristics as well as the relative proportions of the component ingredients influence the properties of both freshly mixed and hardened concrete. In fresh concrete, the aggregate is present suspended in the cement paste. For this condition, it is necessary that the cement paste should be in sufficient quantity so as to produce not only a coating over the aggregates but also to fill the voids between them. The degree of wetness or the consistency of the concrete mass is governed by the fluidity of the paste, by the amount of aggregate present per unit volume of the paste and also by the gradation as well as the shape of the aggregate particles. A plastic consistency is most desirable so that the mix is neither too dry, too wet or too harsh, to prevent occurrence of segregation and formation of defective concrete. In hardened concrete, properties like strength depend on the density of the paste which in turn depends on the ratio of water to cement in the originally made mixture. Thus we may realize that there exist practical limits to the proportions of cement, water and aggregate in normal concrete. ### 1.3 Supervision in the Process of Concrete Making It should be noted that while construction materials such as timber, steel are brought to the project site and fabricated, cement concrete happens to be the only material manufactured or prepared at the project site itself. This therefore justifies constant supervision by trained persons in the process of concrete making. The importance of making good concrete may be realized that concrete in building construction covers about 30 percent of the total cost. In the case of pavements, concrete alone covers about 70 percent of the cost of the project. Concrete may account for even 30 percent of the cost of project in the case of dams. Making good concrete is as important as working out the structural design. Even though the structural design may be absolutely safe and satisfactory, if the concrete made in the construction of the structure is defective, the result will be a weak structure liable to failure. The shortcomings of a defective concrete can not be rectified or made up and will remain ever. Concrete possesses a high compressive strength and is usually more economical than steel and is not subjected to corrosive weathering and such effects. Hence, concrete is used in all present day constructions. But, concrete has a low tensile strength and is liable to crack when subjected to tension. It also develops shrinkage stresses. Hence, by providing steel reinforcement within the concrete mass at the time of pouring, the resulting member will have both the properties of concrete and steel. By reinforcing the concrete with steel, the defects of concrete are made good. Freshly laid concrete undergoes shrinkage in the process of drying. The wetting and drying conditions to which it is subjected to, leads to expansions and contractions. Cracks are likely to occur as a consequence of drying shrinkage and movement of moisture. To prevent these it becomes necessary to provide contraction joints. Concrete is not absolutely impervious to moisture. Presence of soluble salts in concrete may result in effervescence. Concrete is heavy and massive and under continuous loading it undergoes creep. This becomes a very important consideration in the design of dams and prestressed concrete structures. To produce good quality concrete it is necessary to have a careful control on the various components of concrete. Cement generally used for making concrete is Portland cement which consists of compounds of calcium, silicon, iron and oxygen. Aggregates are naturally occurring materials such as sand, gravel or crushed stone. Now-a-days, some synthetic products and recycled materials are also used as aggregates. Water plays the important role to form a satisfactory quality of concrete. Admixtures which are certain chemical ingredients are used in the mixture of cement, aggregate and water, in order to minimize the water requirement and either to retard or accelerate the setting time or in some cases to enhance the durability characteristics. Besides the above, additional cementing materials called mineral additives may be added by hydraulic or pozzolanic action to improve the properties of hardened concrete. The generally used such additives are the pozzolanas, fly ash, granulated blast furnace slag etc. ### 1.4 Concrete, Mortar and Grout When sand, broken rock or gravel, cement and water are all mixed together, then placed in the mould, the mixture becomes hard and is called concrete. When the aggregate consists of sand-size material only, all less than 6 mm in diameter, the mixture is called mortar, the cement-water portion is called paste. Grout is a mixture of cement and water either with or without fine aggregate. Grout has a wetter consistency than mortar. All these mixtures can be made with or without admixtures. Ordinary or plain concrete is brittle and not suitable to resist tension. It is used in structures that are subject primarily to compressive loads. Reinforced concrete is concrete in which steel bars are embedded when it is cast to give it strength in tension. The steel and concrete complement each other, acting as a unit. The concrete also protects the steel from rusting and from fire. ### Fresh Concrete When concrete constituents are first mixed together the concrete formed is said to be in fresh condition. Fresh concrete is plastic i.e. it has no fixed shape and it changes shape easily. It can be manipulated and formed by means of moulds. The one property which is characteristic of fresh concrete is workability. Workability is the ease with which concrete can be handled and placed with a minimum loss of homogeneity. The slump test is a good indicator of the potential workability or placeability of fresh concrete. ### Hardened Concrete When the forms are removed from concrete after the concrete is several hours or a few days old, it is defined as green concrete. It still has high moisture content and has relatively low strength. The concrete can be damaged easily and must be supported, as it can not carry any load, not even its own weight. After curing, the concrete matures and becomes hard. It is in this condition, the concrete can support a load. The concrete is now in the hardened mature condition. It is in this condition that the concrete has developed the required qualities of strength and durability. If it has been properly made, it will be free from cracks and other blemishes, with a surface that has a good appearance in accordance with the requirements. ### 1.5 Role of Admixtures It has long been known that certain compounds, when mixed into the concrete in small amounts, significantly alter the concrete in both fresh and hardened state. Examples are adding calcium chloride to hasten setting and strength development, and sugar compounds to delay hydration. Numerous compounds have been proposed to reduce water requirement, entrain air, improve workability, accelerate, retard and otherwise improve or change the concrete. An admixture frequently provides the best way to achieve concrete with certain properties. ### 1.6 Water-Cement Ratio The ratio of the amount of water to the amount of cement in concrete is called the water-cement ratio. Water-cement ratio = Weight of water / Weight of cement Tests and field observations have conclusively proved the importance of what is known as the water-cement ratio law, viz., The strength, durability and other desirable properties of concrete are inversely proportional to the water-cement ratio, within the range of practical or usable mixes, all other factors remaining the same. However, because of the great number of aggregate sizes, shapes, types and qualities, variations in cements, different mixes, use of admixtures and great diversity of environmental conditions of mixing and placing, this law should be looked upon as a guide rather than as an inflexible rule that applies without question to all concrete under all conditions. The drying shrinkage of concrete is governed by the unit water content of the concrete than by the water-cement ratio. ### 1.7 Properties of Concrete The important properties of concrete are given below : - Concrete possesses a high compressive strength. - It is not liable to corrosion; and atmospheric agents do not affect the quality of concrete appreciably. - Concrete goes on hardening attaining great strength over a period of time. - Concrete is more economical than steel. The raw materials needed to make concrete like crushed stone, sand constitute 80 to 90 percent of the bulk of concrete and are economically available. - Concrete has the characteristic property of binding well with steel reinforcement to constitute reinforced concrete. - Concrete undergoes shrinkage in the following conditions: - It undergoes initial shrinkage due to any leakage of water through form work and any possible absorption of water by the form surfaces. - It undergoes shrinkage in the process of hardening. By good and proper curing of concrete, this shrinkage can be reduced. - Sometimes concrete is liable to become porous, due to the presence of voids formed while placing the concrete. To prevent the formation of voids the following precautions may be taken. - The aggregates should be well graded and consolidated - Water-cement ratio should be minimum. - Concrete possesses great resistance to abrasion. Despite the many good properties of concrete it presents some disadvantages such as the following: - It is very weak in tension. - A lot of time is needed for concrete to develop the required compressive strength. - Long walls and slabs may need expansion joints. - Contraction joints may become necessary to prevent drying shrinkage. - Concrete is heavy and is liable to creep. ### 1.8 Good Durable Concrete The concrete we describe as good, durable concrete or quality concrete is concrete that satisfies the structural and aesthetic requirements for the required life of the structure at maximum economy. The properties this concrete must have are the following : - Workability in the fresh condition. Concrete should be conveniently workable so that it can be moulded or cast into the required shape and size. - Strength. Concrete must have adequate strength to resist any damage due to loads with a good margin of safety. The strength should be in accordance with the design avoiding over strength (uneconomical) as well as understrength (dangerous). - Durability. Concrete should be durable, i.e. it should not be affected by atmospheric agents such as extremes of temperature, wind, rain etc. - Volume stability. This means that minimum drying shrinkage and changes in volume caused by moisture and temperature variation should occur. - Freedom from cracks. This is achieved by reducing the tendency to crack and installation of joints and crack-control devices. - Freedom from blemishes. This means freedom from such defects like rock pockets, scaling, popouts, surface softness and bug holes. - Water tightness in situations where applicable. - Economy - Good appearance Even though structures are designed absolutely correctly, if the concrete prepared is defective or of inferior quality, all the efforts of working out the designs will become waste. If concrete is not prepared properly and it is placed defectively, it will result in honey-comb formation with low strength. The defects remain permanently. The site engineer should be acquainted with making controlled concrete as well as mix design. He must be acquainted with the process of concrete making, like mixing the ingredients, placing the concrete and compacting the concrete. In case the concrete coming from the mixer is not workable, the engineer must be able to make necessary modifications in proportioning of the ingredients. It is important that only proper materials are to be selected. As far as possible fresh cement from the same factory from the same batch should be used. Sand and coarse aggregates should be of good quality and should not contain silt more than the permissible limits. The materials used batch after batch must be uniform in their properties. ### 1.9 Making Sound and Durable Concrete In order to make sound and durable concrete, the prime requirements are the following : - The aggregates should be strong, hard and durable. - The aggregates shall be properly graded in size from fine to coarse. - Quantity of cement should be sufficient to reach the required water tightness and strength. - The water used for mixing should be free from deleterious minerals or organic materials. - Adequate quantity of water should be added so as to produce the needed consistency. - Thorough mixing should be done so as to produce homogeneity. - It is important to note that concrete should fill every part in the forms. This is done by ramming or puddling. - It is necessary to ensure that the temperature of concrete is maintained above the freezing point until the concrete is thoroughly hard. This is done to avoid retarded hardening. ### 1.10 Denseness of Concrete The denseness of concrete is mainly due to the aggregate used in making the concrete. Concrete whose aggregate components are sand and crushed stone is said to be normal concrete. When light weight aggregates like pumice or pyroprocessed aggregates are used the concrete made is called light weight concrete. This concrete has its applications in situations where there is need to minimize the dead load. In some situations concrete is made using high density aggregates (like haematite and such heavy material). Such concrete is called heavy weight concrete. This concrete has its utility where there may be need to increase the dead load in order to provide greater stability. Normal concrete weighs 24 to 25 kN/m³, light weight concrete weighs about 18 kN/m³, while heavy weight concrete weighs about 32 kN/m³. ### 1.11 Fundamentals of Concrete Construction Good concrete construction is based on five fundamentals, viz. site investigation, structural design, material selection and mix, workmanship in handling materials and concrete and maintenance of the structure throughout its life. - Site selection. Site investigation is generally made before construction of a structure. Such investigation has a significant influence on the selection of materials and mix. Neither a satisfactory design can be made nor can logical use can be made of the materials available without a thorough investigation of all the features of the site. For proper evaluation of the site, three investigations may be made, viz. investigation of the fitness of the location to suit the requirements of the structure, investigation of the ability of the foundation to support the expected loads safely and an investigation of forces or substances that may attac' the concrete. - In this investigation we are concerned with the chemical or mechanical attack by outside agencies. Chemical attack is aggravated in the presence of water mainly because water acts as a vehicle for bringing substances into intimate contact with the concrete and sometimes even to the extent of transporting them into the concrete through cracks honeycomb and surface pores. - Structural design. This is the second fundamental aspect. It is no doubt important that the structural design should be adequate and made by competent engineers in accordance with accepted safe practices. It needs the intelligence and experience to design a structure adequately to provide safety and economy of the design, based on the results of the investigations. Failure or distress may range from small tension cracks to total collapse of a structure. Practical design should also include a consideration of the capabilities of the works and machines to provide good formwork and follow other construction procedures. - Material selection and mix. There are many instances where considerable defects have been traced to the use of faulty materials or improper mix proportions. In most cases, the materials which are available have been used for making concrete for a number of years. If such is the case, histories of these materials and also of the structures built with them should be examined. Information obtained by such studies can reveal whether the materials under consideration are suitable. - In such investigations one should also realize the fact that poor concrete can result even when good materials are used if insufficient care is not taken in proportioning and handling the materials and concrete. Very often, especially concerning structures built many years ago, there may not be reliable information about the materials and methods adopted. Despite this, the reputation of the local materials should be given careful consideration. - In the case of large and important works it is advisable to determine the suitability of materials by tests. - Concrete mix proportioning has as its objective, the production of concrete of maximum economy having sufficient workability, strength, durability and impermeability to meet the conditions of placing, exposure, loading and other requirements of the structure. Trial mixes, made under laboratory conditions and using the proposed materials should be made in the case of large and important works. Trial mixes must also be made in such cases where adequate information is not available relative to existing materials. Depending on the requirements of field conditions the mixes may be subjected to suitable revisions. Strength, water-cement ratio, maximum size of aggregate and slump are generally specified and the proportions of cement, aggregate, entrained air and admixtures are determined by these trial mixes. - Workmanship in handling the materials and concrete. Most of the concrete distress is caused by improper methods of handling the ingredients and the concrete itself after the ingredients have been combined in the batcher. Included in such minor failures are the many small discrepancies that appear and which in themselves may be unsightly but may not be serious. It is very important to realize that many serious difficulties start from small beginnings and a small surface defect can develop into a major one. - Workmanship includes preparation of aggregates, batching, mixing, transporting, placing and curing. - Maintenance of the structure. Maintenance of the structure means inspection of the structure at reasonable intervals to determine whether any unusual deterioration is taking place and to provide adequate protection or repair to minimize the deterioration. ### 1.12 Classification of Concrete Concrete can be classified in various ways as follows : - Classification on the basis of cementing material. Concrete can be classified into cement concrete, lime concrete, gypsum concrete. - Classification on the basis of proportions of the main constituents. On this basis the mixes are classified as 1:3:6 mix, 1 : 2 : 4 mix, 1:12 : 3 mix, 1 : 1 : 2 mix and so on. - The 1:3:6 mix is used for mass concreting and rear sides of dams. - The 1:2:4 and 1 : 1/2 : 3 mixes are used for general reinforced concrete work. The latter is also used for front faces of dams, water tanks, columns etc. - The 1:1:2 mix is used for piles. - Classification on performance oriented specification. On this basis concrete is classified into nominal mix concrete and design mix concrete. - Classification based on the grade of concrete (28 days compressive strength). - The following grades of concrete are used | Group | Grade designation | Approximate Mix Proportion | 28 days compressive strength fck | |---|---|---|---| | Ordinary concrete | M10 | 1:3:6 | 10 N/mm² | | | M15 | 1:2:4 | 15 N/mm² | | | M20 | 1:12:3 | 20 N/mm² | | | M25 | 1:1:2 | 25 N/mm² | | Standard concrete | M30 | | 30 N/mm² | | | M35 | | 35 N/mm² | | | M40 | | 40 N/mm² | | | M45 | | 45 N/mm² | | | M50 | | 50 N/mm² | | | M55 | | 55 N/mm² | | High strength concrete | M60 | | 60 N/mm² | | | M65 | | 65 N/mm² | | | M70 | | 70 N/mm² | | | M80 | | 80 N/mm² | - Classifcation based on density of concrete: Heavy, dense, lightweight. - Based on place of casting: Cast-in-situ, precast. ### 1) Cement Cement is a binding material used in the field of construction. Cement is cohesive and adhesive properties in the presence of water. Cement comprises of 2 types of components - Calcareous compound (Lime) (Ca): lime, chalk, marine shells. - Argillaceous compound (silica/clay) (Si): clay, marxe, shale. ### 9) Composition of cement [OPC] | Ingredients | Range | % | |---|---|---| | Lime (Cao) | 62-65% | 62 % | | Silica (Sio₂) | 17%-25% | 22 % | | Allumina (Al2O3) | 3%-8% | 4 % | | Iron Oxide (Fe2O3) | 3%-5% | 3 % | | calcium Sulphate (CaSo4) | 1%-4% | 2 % | | Magnesia (MgO) | 1%-3% | 1-4 % | | Sulpher (S) | 1%-3% | 1 % | | Αικάλι (Na2O, K20] | 02%-1% | 1 % | **Functions:** * Lime: [C00] - Lime imparts strength and soundness to the cement. - Soundness means resistance towards change in volume - If Lime is in excess it makes the cement unsound and cause it into disintegrate. * If Lime is deficient the strength of cement decreases. * Silica: [Cao] - It also imparts strength to cement. - If it is in excess it increases the strength but also increases the setting time of cement.. * Alumina - Alumina acts as a flux in reducing the clinicering temperature. It means cement is manufactured at low temperature. - If Alumina is in excess it weakens the cement. - It also imparts quick setting properties. * Iron oxide: SiO2 - It imparts color, strength and hardness. * Calcium sulphate: (Zypsum):-[CaS04] - It helps in increasing the initial setting time of cement. * Magnesia (Mgo):- - It imparts color (yellow) to the cement. - It also imparts hardness.. - If it is in excess it makes the cement unsound. * Sulpher (5):- - It is also responsible for the soundness of cement. - Lime, Magnesia & sipher are three compounds which effects the soundness of cement. - We can calculate change in volume due to Lime & Magnesia but no test is available for sulpher. * Alkali: - It accelerates the setting of the cement paste. - It causes Efflorescence when use in excess. - Efflorescence is that property of alkali by which it absorbs moisture from atmosphere and leaving behind gray or white spots over the structure. ### 4) Composition of Cement Clinker When cement compounds (raw materials) are put in kin it fuses and Clinker is formed. These compounds also known as Bogue compounds. | Bogue compounds | formula | Symbol | Name | |---|---|---|---| | Tri Calcium Silicate | 3Cao. 502 | CS | Alite | | Di Calcium Silicate | 2ca0-$ | C₂S | Belite | | Tri Calcium Alluminate | 3COOTAL | GA | Celite | | Tetra calcium Alumino ferrite | 4ca0-Abg. Fe₂O | CAF | Fellite | ### ① Tricalcium Silicate (45-65%) [C3S] - It hydrates rapidly, generating high heat and develops an early strength and hardness. - Raising of as increases heat of hydration. - Heat of Hydration is 500 J/gm. - It increases resistance to freezing & thawing. ### ② Di Calcium Silicate (2S)-- (15%-35%) - It hydrates and hardens slowly and takes a long time to contribute in strength. - It gives ultimate strength. - With in a month C₂S has best little influence on strength and hardness, while after 1 year it contribute to the strength and hardness almost equal to GS. - Raising of ₂S reduces early strength, increases ultimate strength & decreases heat of hydration. - It imparts resistance to chemical attack. - Heat of hydration 260 J/gm (very less') ### ③ Tri calcium aluminate (4%-14%) [Undesirable compound] - It rapidly reacts with water OR Immediate. Reaction. - It is responsible for flash set of cement - It is responsible for initial set ii high heat of hydration - It is greater change in volume change (Sulphate attack) - Raising the GA content reduces the setting time and decreases resistance to sulphate attack and lowers the ultimate strength. - Heat of hydration 1865 J/gm ### ④ Tetya Calcium Alumino ferrite: (10%-18%) - It is responsible for flastiset but generate lower heat of hydration - It has poor cementing properties and - Heat of hydration 420 J/gm - No Engineering use in cement. Note: - C3S. 195 (90%) control most of the strongth giving properties. - CA C4 AF contribute less in Strength. ### Q) Hydration of Cement:- When water is added to cement a chemical reaction between water and cement takes place which is known as hydration of cement. Heat is liberated during this chemical reaction. It is known as "Heat of Hydration". Product of hydration is Cao. SiO₂- H₂O. which is known as Tobermorite gel and commonly referred as (C-S-H gel) which gives cementing property/ binding property to the cement. - 2 GS+ 6H -> C35₂H₃ + 3 Co(OH) + Heat↑ - 2GS+ 4H ->32.H₃ +..ca(OH)2 + Heat ↑ Note: * It has been found that hydration of as produce lesser Calcium Silicate Hydrate (C-S-H gel) and more CaOH as compared to the hydration of ₂S. * Hence greater ₂S increase resistance against chemical attack. - (aOH)2 is soluble in water and leaches out with water and makes the concrete porous. - Particularly in hydraulic Structure cement with a small % of C3S & more ₂S is recommended. ### 2) (Ca(OH), also helps in Sulphate attacks. * Sulphate attack Cement is susceptible to attack of sulphates especially Mg504, which reacts with Ca(OH)2 and calcium Aluminate (GA) and forms calcium sulphate & cakium Sulpho. Alluminate respectively, whose volume is 227% more than its original volume which decompose/ decay the cement or concrete. - The only advantage of CaOH); is that it is alkaline in nature, it maintain pH value around 13 in cement concrete which resists the corrosion of reinforcement. ### Imp Factors effecting Hydration of Cement: - Temperature: Higher the temperature, Rapid is the hydration. - Fineness of Cement: Finer the cement; Rapid is the hydration. - Proportion of Ingredient, clinker: - C3S reacts with water rapidly, produce more heat of hydration and responsible for early strength of Cement. - C₂S hydrates slowly, produce less heat of hydration and is responsible for ultimate strength. - C3A: Hydration of C3A is very fast, may lead to flashset. - C4 AF: C4AF.contribute less in Strength and rate of hydration is very fast. Note: - Heat of Hydration - Tri-calcium aluminati > D-Calcium Silicate > CAAF? Di-caluum Sierats - CA C3S C4AF > C₂S - Rate of Hydration - C4 AF > C3A > C35 > QS ### 9) Water Requirement of Hydration of Cement: - About an average: 24% C3S & 21% ₂S. by wt. of Cement. - This water combines chemically with the cement. - This water for complete chemical reaction of cement compounds known as bound water, - It is further observed that about 15% of water -by weight of cement is required to fill the get pores - Hence Effective water required for complete hydration of cement is 23% +15% = 38% by wt. of cement. - [True Sp. Gravity] - 1 bag of cement: mass sp. boravity af cemerit = 50kg = 34.7 ets ### 6) Manufacturing of Cement Manufacturing of cement involves 3 basic operations. - Mixing of ingradients - Burning of ingradients in form of Clinkers - Grinding. Manufacturing of cement can be done by - dry process - Wet process ### a) Dry Process (. Modern Process) | Calcareous compound | Argillaceous compounds | |---|---| | crushing (in 25mmdia) | crushing (in 25mm Dia) | | fine grinding in Tube/Ball mill | fine grinding in Tubel Ball mill | | Mixing of ingredients in prie-determined proportion | | | (economiss) process | | | Pre-heat at 800°c by Hat gases | | | Rotary Kith [4000°c to 16000°c] | | | Clinker is formed | | | Cooling | | | Add [2-3%] gypsum | fine grinding in i tube mill | | storage in silos | | | Packaging | | - Clinker is obtained as a result of fusion at a temperature of about 1450℃-1500℃. - Generally 1350°c te mperature is kept in kiln. - Clinker is than cooled & grind in the tube mill where 2% to 31. of gypsum is added. ### 6) Wet process (old process) :- | calcareous compound | Argillaceous compound :: | |---|---| | crushing (in 25mmdia) | +H20 | | Storage | Wash mill | | Storage | | | wet grincling to form slurry | | | mixing to corrected proportion | | | Rotary kiln.. | | | Clinker is formed | | | Cooling | | | Acid + gypsum | fine grinding in Tube mill | | Storage in silos | | | Packaging | | - Dry process is considered to beleconomicall as compared to wet process, be cause of less consumption of fuel. - Longer kiln S. are required in wet process which are more costly... ### 68) Testing of cement: Testing of cement: Check its Engineering Performance for used In CONSTRUCHON. **Lab Test** | Field Test | Physical | Chemical | |---|---|---| | - colour test | - consistency test | - Loss o3 Ignition | | - Physical properties test | - Initial & final Setting time test | - Chemical Composition test. | | - Lump test | - Soundness test | | | - Strength test | - Strength test | | | | - Sp-gravity test | | | | - Fineness test | | | | - Heat of Hydration test | | **Field Test** - Colour Test: Colour of cement should be uniform. It means gray colour with a light greenish shade. - Physical test: [Fineness] The cement should be smooth when Yubbed between the fingers. A small quantity is thrown in a bucket of water, it should Sink immediately, it should not Float over the surface. - Lump test: The sample of cement should be free from presence of hard lumps, which are formed due to absorption of moisture from atmosphere, hence cement should not Store more than 90 days.. - Strength test:- - 340 N - 200 mm - K150mm - 25 - 25 - ⇒ Prepare a mould of cement having size 25×25×200mm. - ⇒ Place the sample of water for 7 days, then test-the mould for the load of 340N: - ⇒ sample should show no sign of failure if tested-on supports 150 mm apart. **Physical laboratory tests:** - Consistency test:- - This test is to estimate the quantity of mixing water to form a cement paste of normal consistency. - Normal consistency is defined as that water requirement of cement paste at which the viscosity of cement paste is such that the vicat plunger penetrate apto a point 5mm to 7 mm from the bottom of the vicat mould. - **Initial Setting time:** - Initial setting time is the lime, from the instant water is added into the cement upto that instant cement paste starts loosing its plasticity. - **Final setting time:** - Final setting time is the time, from the instant water is added into the cement upto the instant cement paste. looses all its plasticity. **Vicat apparatus:-** - [movable rod 300gm] - scale - 40 - movabte rod (300gm) - Indicator - k10mm - plunger - 50mm - 7. - 1mm needle - Front view - attachment - K80 mm - mould - 40mm - 105mm - Needle with Amular collar. - Side view - 1mm needle - plunger