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Constituents of Concrete
• Cement [14-21%]
• Aggregate (fine and Coarse) [60-70%]
• Water [7-15%]
• Entrained air [0-3%]
•Admixtures [As per Design]
Concrete consist of:
1. Consists of Portland cement, water, and aggregate (Fine& Coarse )
2. Cement, water and fine aggregate – mortar
3. Admixtures added for specific purposes like
• Entrain numerous microscopic air bubbles
• Retard the initial set of the concrete
• Waterproof the concrete , etc.](https://image.slidesharecdn.com/chapter1introduction-240929063427-772ce97c/85/Chapter-1-Introduction-of-Concrete-Technology-9-320.jpg)
Chapter 1 Introduction of Concrete Technology
- 1. CONCRETE TECHNOLOGY AND MASONRY STRUCTURE Chapter1 Introduction
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- 3. 3 CONCRETE • Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement that hardens over time. • A composite material that consists essentially of a binding medium, such as a mixture of Portland cement and water, within which are embedded particles or fragments of aggregate, usually a combination of fine and coarse aggregate. • One of the very important and widely used material in construction • The Grade of the concrete is specified by its 28 day’s cube strength (E.g. M20 means the cube strength is 20 N/mm2) • Concrete used on works is specified according to IS 456 (2000).
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- 5. 5 Advantages of Concrete • High compressive strength. • Locally available materials can be used. • Can be easily moulded and handled. • Pumping makes concrete to be placed in different difficult places also. • Durable and fire resistant. • Requires comparatively little maintenance. • Can be sprayed to fill the voids. • Chemical resistant. • Can change the properties by using admixture.
- 6. 6 Disadvantages of Concrete • Low tensile strength. • Fresh concrete shrinks on drying and hardened concrete expand on wetting. •Expands and contracts according to change in temperature. • May cause efflorescence. • May undergo creep and fatigue. • Lack of ductility.
- 7. 7 Uses of Concrete in structure Concrete is used in wide range in different types of structures in various forms: • Building: Various structural and non structural components. • Bridge: Including pier and super structures. • Steel Structure: Foundation base for various steel structures. • Tunnel/ Underground structures. • Slope stabilization: shotcreting / ground retaining structures. • Offshore structures: various marine structures for oil/gas extraction. • Nuclear shield:As concrete is excellent in protection of radiation. • Fire proofing: widely used in fire proofing of steel structure. • Used in reinforced/ Precast/ prestressed concrete components.
- 9. 9 Constituents of Concrete • Cement [14-21%] • Aggregate (fine and Coarse) [60-70%] • Water [7-15%] • Entrained air [0-3%] •Admixtures [As per Design] Concrete consist of: 1. Consists of Portland cement, water, and aggregate (Fine& Coarse ) 2. Cement, water and fine aggregate – mortar 3. Admixtures added for specific purposes like • Entrain numerous microscopic air bubbles • Retard the initial set of the concrete • Waterproof the concrete , etc.
- 11. Properties of Cement exceed 10 mm. 11 Physical Properties of Cement: (i) It gives strength to the masonry. (ii) It is an excellent binding material. (iii) It is easily workable. (iv) It offers good resistance to the moisture. (v) It possesses a good plasticity. (vi) It stiffens or hardens early. (vii) Athin paste of cement with water should feel sticky between the fingers. (viii) Acement thrown in water should sink and should not float on the surface. (ix) The particles should have uniformity of fineness. To get an idea of fineness, specific surface area of cement particles is calculated. The specific surface area is a measure of the frequency of particles of average size, which should not be less than 2250 cm2/gm. (x) The consistency of cement should be checked with Vicat apparatus. If the settlement of plunger is between 5 mm to 7 mm from the bottom of mould, the water added is correct, otherwise repeat the process with different percentages of water till the desired penetration is achieved. (xi) The initial setting time for ordinary cement is about 30 minutes. The initial setting time is the interval between the addition of water to cement and the stage when the square needle of Vicat apparatus ceases to penetrate completely. (xii) The final setting time for ordinary cement is about 10 hours. The final setting time is the difference between the time at which water was added to cement and time required for needle with annular collar of Vicat apparatus ceases to make an impression on test block. (xiii)The cement should be tested for soundness using Le Chatelier apparatus. This test is to detect the presence of uncombined lime in cement. The expansion of cement after heating and cooling the mould, should not
- 12. 12 Cont… Mechanical Properties of Cement: (i) The compressive strength at the end of 3 days should not be less than 11.5 N/mm2 and that at the end of 7 days should not be less than 17.5 N/mm2. (ii) The tensile strength at the end of 3 days should not be less than 2 N/mm2 and that at the end of 7 days should not be less than 2.50 N/mm2. Chemical Properties of Cement: (i) The ratio of percentage of alumina to iron oxide should not be less than 0.66. (ii) The ratio of percentage of lime to alumina, iron oxide and silica, known as Lime Saturation Factor (LSF) should not be less than 0.66 and should not be more than 1.02. (iii) Total loss on ignition should not be more than 4 per cent. (iv) Total sulphur content should not be more than 2.75 per cent. (v) Weight of insoluble residue should not be more than 1.50 per cent. (vi) Weight of magnesia should not exceed 5 per cent.
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- 16. Manufacturing Process of Cement 16
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- 21. 21 Aggregate • Aggregate is a inert material used for the manufacture of mortar and concrete. • It may be natural and artificial. • Artificial aggregate : Furnace clinker, coke breeze, saw dust and furnace slag. FineAggregate • The aggregate passing through 4.75 mm IS sieve and entirely retain on 75 micron IS sieve . • It may be natural sand or crushed stone. CoarseAggregate • Aggregate of size whose particles are bigger than 4.75 mm but smaller than 75mm . •It may be crushed gravel or uncrushed gravel or partially crushed gravel. All in one aggregate • The all in one aggregate consist of different fractions of fine and coarse aggregate. • It is generally not used for high quality concrete. • The aggregate of rounded shape have minimum voids ranging from 32 to 33%. • It gives minimum ratio of surface area to the volume thus requiring minimum cement paste to make good concrete.
- 22. 22 Cont… According to shape , Aggregate are classified as: • Rounded • Angular • Irregular • Flaky ( least dimension < 0.6 times of mean dimension) • Elongated ( greatest dimension > 1.8 times of mean dimension) Aggregate are also can be classified on their density/unit weight.
- 23. 23 Desirable properties of Aggregate for Concrete • Size: The size of coarse aggregate depends on the use to which the concrete is to be put. For ordinary construction of residential or other building, 20mm is the maximum size that will be used. • Shape: The shape of aggregate is an important characteristic as it affects the workability of concrete. Angular aggregate shows better interlocking effect, which gives a superior concrete. • Surface texture: The surface of the aggregates may be smooth, polished, rough or dull. A rough surface provides more area for bonding with cement paste and gives more strength. Rounded aggregate with smooth surface will require less cement paste and hence increase the yield per bag. • Water absorption: The water absorption of coarse aggregate is measured by the percent increase in weight of an oven dry sample after immersion in water for 24 hours. This gives more realistic result. Water absorption will decrease the water content in concrete and the concrete will require a higher/ cement ratio. The water absorption will depend upon the porosity of aggregate, and more water absorption will affect both workability and durability of the concrete.
- 24. 24 Cont…. • Soundness: Soundness to the resistance offered by the aggregates, to any type of volume change. The change may be in temperature, alternate wetting and drying in potable water. The soundness measured by immersing the aggregate in either sodium or magnesium sulphate and oven drying it under specified conditions. • Specific gravity: It is ratio of dry weight of aggregate to the weight of equal volume of water. The specific gravity of aggregate is determined along with the water absorption as specified in IS 2386 part lll 1963. • Bulk density: The ratio of net weight of aggregate to the volume of aggregate given bulk density. The bulk density is generally expressed as kg/ liter .
- 25. 25 Water • Generally, quality of water for construction works are same as drinking water. • This is to ensure that the water is reasonably free from such impurities as suspended solids, organic matter and dissolved salts, which may adversely affect the properties of the concrete, especially the setting, hardening, strength, durability, pit value, etc. • The water shall be clean and shall not contain sugar, molasses or their derivatives, or sewage, oils, organic substances. • If the quality of water to be used for mixing is in doubt, cubes of 75 mm in cement mortar 1:3 mix with distilled water and with the water in question shall be made separately. The latter type of cubes should attain 90% of the 7 days’ strength obtained in cubes with same quantity of distilled water.
- 26. Cont… Limits ofAlkalinity: • To neutralize 200 ml of sample should not require more than 10 ml of 0.1 normal HCI using methyl orange as an indicator. Limits ofAcidity: • To neutralize 200 ml sample of water should not require more than 2 m of 0.1 normal NaOH (Caustic soda). The pH value of water shall generally be not less than 6. Type of Solid in water Permissible Limits for Construction • 26 • Organic matter200 mg/l • Inorganic matter3000 mg/l • Sulphates (SO4)500 mg/l • Chlorides (Cl) :1000 mg/l for RCC work and PCC work Suspended matter 20000 mg/l
- 27. Admixtures 27 • An admixture is a substance which can be added to concrete to achieve or modify its properties. Admixtures are added to the concrete, in addition to cement, water and aggregate, typically immediately before or during the mixing process. • Admixtures can be used to reduce the cost of building with concrete, or to ensure certain required properties or quality of the cured concrete. If problems arise with the concrete during the construction process, admixtures can be used as an emergency measure to try and prevent failure. In addition, some of the main functions of using admixtures include: • Water-reducing: Can reduce the water content needed to reach a required slump by 5-10%. • Retarding: Slow the setting rate of concrete, keeping it workable and are often used to counteract the accelerating effect of hot weather. • Accelerating: Increase the rate of early-strength development and reduce the time required for curing. • Super plasticizers: Can reS da un d ce e ee p wP a ar a tj eu l ri( B cE oC i nv i l t, eM nS c tC bM y12-30% to make a highly fluid but workable form of) , cS a on nd i p c. rp a er ta ej u l i k2 0 n5 o2 @ wg m na i al . c so m flowingconcrete.
- 28. 28 Cont…. • Corrosion-inhibiting: Used to slow the corrosion of reinforcing steel in the concrete. Often used in marine structures, bridges and others that will be exposed to chloride in high quantities. • Air-entraining: Small bubbles of air formed uniformly through the concrete mix to increase cohesion and resistance to freeze-thaw degradation. • Improving the curing of the concrete. • Providing waterproofing properties. • To improve hardness. • Providing colour. • Offsetting or reducing a chemical reaction. • Aeration to reduce the weight. • Offsetting or reducing shrinkage. • Dispersing cement particles when mixed with water. • Alkali-silica reactivity reduction. • Admixtures are usually provided in a liquid form. Some admixtures, such as pigments, pumping aids and expansive agents, are typically added manually from pre-measured containers as the amount used is very small.
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- 32. 32 Thank You