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Concrete Technology Unit-II

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Concrete Technology Unit-II

  1. 1. Concrete Technology Unit-II
  2. 2. Syllabus • General: • Historical background, composition of concrete, general note on strength mechanism, current practice and future trends.
  3. 3. General • Historical Background • The use of cementing material dates back to several hundred years. The ancient Egyptians used claimed impure gypsum to grout the space between huge rocks of stone in pyramid. • The Greeks and Romans used claimed limestone and later learned to add to lime and water, sand and crushed stone or brick and broken tiles. This was first concrete in History.
  4. 4. Historical Background
  5. 5. General • Lime mortar does not harden under water, and for construction under water the Romans ground together lime and a volcanic ash or finely ground burnt clay tiles. Roman builders used volcanic tuff found near Pozzuoli village near mount Vesuvius in Italy. This Volcanic tuff or ash mostly siliceous in nature thus acquired the name pozzolana, having nearly the same composition as that of volcanic tuff or ash found at Pozzuoli.
  6. 6. Historical Background
  7. 7. General • Some of the structures in which masonry was bonded by mortar, such as the Coliseum in Rome and the Pont du Gard near Nimes, have survived to this day, with the cementations material still hard and firm. In the ruins at Pompeii, the mortar is often less weathered than the rather soft stone. The superiority of Roman mortar has been attributed to thoroughness of mixing and long continued ramming. • It is learnt that the Romans added milk, blood and lard to their mortar and concrete to achieve better workability. Hemoglobin is a powerful air-entraining agent and plasticizer, which perhaps is yet another reason for the durability of roman structures Probably they didn’t knew about the durability aspect but used them as workability agents.
  8. 8. Historical Background
  9. 9. General • In India, powdered brick named surkhi has been used in mortar. The Indian practice of thoroughly mixing and long continued ramming of lime mortar with or without addition of surkhi yielded strong and impervious mortar which conformed the secret of superiority of roman Mortars. However, not much light has been thrown on cementing material used in the construction of the cities of Harappa and Mohenjo-Daro.
  10. 10. Historical Background
  11. 11. History of Modern Cement • John Smeaton was called upon to rebuild the Eddystone lighthouse in 1756. He made extensive inquiry in the state of art existing in those days and also conducted experiments to view to find out the material to withstand the severe action of sea water. He found that the best mortar was produced when pozzolana was mixed with limestone containing a high proportion of clayey matter. He was the first to understand the chemical properties of limestone.
  12. 12. History of Modern Cement
  13. 13. History of Modern Cement • In 1796, hydraulic cement was produced by calcining nodules of argillaceous lime-by calcining an intimate mixture of limestone and clay. • In 1811, James Frost patented a cement and established a factory in london district. • In 1824. Joseph Aspdin , a Leeds builder took the patent of Portland cement • The fancy name of Portland was given owing to the resemblance of this hardened cement to the natural stone occurring at Portland In England, Hard limestone and finely divided clay were used as raw materials.
  14. 14. History of Modern Cement Portland, UK
  15. 15. History of Modern Cement: • In India, the South India Industrial ltd, first manufactured Portlands cement near madras in 1904. • In 1912, the Indian Cement Co. Ltd. Was established at Porbandar (Gujarat) and by 1914 this company was able to deliver about 1000 tonnes of Portland Cement. • Prior to the manufacture of Portland Cement in India, it was imported from U.K. A three storeyed structure build at Byculla, Bombay is one of the oldest RCC structures built using Portland cement. • The Cement Corporation of India, a government owned company is set up with the aim of surveying prospecting and providing limestone deposits in the country and establishing cement manufacturing capacity.
  16. 16. Concrete • Concrete= Cement + Sand+ Aggregate+ Water+ Admixture+ Air • The mixture of Cement and water is paste. The function of paste is to bind sand and aggregate particles by chemical process of hydration. It also fills the voids between sand and aggregate particles. • The strength of concrete depends upon the property of cement, sand, aggregate, etc.
  17. 17. Composition of Concrete • Concrete is composed of, • Concrete= Cement + Sand + aggregate+ water+ admixtures + air • Cement: The funtion of cement is to bind the aggregates. It also fills the void between sand and aggregate. • Aggregate: • The aggregate occupy about 75 % of the volume and hence their influence on various properties of concrete is considerable. Aggregates are generally cheaper than cement and impart greater volume, stability, and durability to concrete. The aggregate generally provides bulk to the concrete.
  18. 18. Composition of Concrete • Water: Water is required for carrying out chemical reactions in cement. If the water content is less the heat of hydration is not possible, hence the strength of concrete will be reduced. If water content is in excess water will cause undesirable capillary cavities and concrete becomes porous. • Admixtures: Admixtures is defined as a material other than the basic ingredient of concrete mixed immediately before or during mixing to modify some properties of concrete in the fresh or hardened state. • The use of admixtures like accelerators, retarders, air- entraining agents, pozzolanic material, water proofing admixtures etc.
  19. 19. Cement
  20. 20. Aggregate
  21. 21. Admixtures
  22. 22. Admixtures
  23. 23. Composition of Concrete • The properties commonly modified using admixtures are setting time, workability, air entrainment, dispersion etc. The admixtures are generally added in small quantity from 0.005 to 2 % by cement weight. Overuse of admixtures have detrimental effect on the properties of concrete. • Air: The voids in the mass of concrete can be classified into two groups • Entrapped air • Entrained air
  24. 24. Composition of Concrete • Entrapped air: The entrapped air is the void present in the concrete due to insufficient compaction • Entrained air: The entrained air is the intentionally incorporated minute spherical bubbles
  25. 25. Entraped Air
  26. 26. Entrained Air
  27. 27. Ingredients of Concrete
  28. 28. Strength Mechanism • When water is added to cement, ingredients of cement react chemically with water and form various complicated chemical compounds. The chemical reaction that takes place between cement and water is reffered as hydration of cement. • Anhydrous cement does not bind fine and course aggregates. It acquire adhesive property only when water is mixed. • The silicates (C3S, C2S) and aluminates of cement react with water and form hydro silicates and hydro aluminates These products are thick and sticky. It is called gel. Gel posses adhesive property and binds aggregate and sand together. It also fill the voids between sand and aggregate.
  29. 29. Strength Mechanism • The hydration of cement may happen in two ways. The one is ‘through solution’ mechanism in which the cement compound dissolve in water to produce a supersaturated solution from which different hydrated products gets precipitated. The second theory is that water attack cement compound in the solid state converting them into hydrated products. • It is possible that both the ‘ through solution’ and solid state’ type of mechanism occur during the so called reaction between cement and water. Obviously the through solution mechanism take place in the early stages of hydration when large quantity of water is available. The ‘solid state’ mechanism may occur during the later stage of hydration
  30. 30. Current Practice and Future Trends • Concrete is a versatile material possessing good compressive strength. But it suffers from many drawbacks like low tensile strength, permeability to liquids, corrosion of reinforcements susceptibility to chemical attack and low durability. • Modifications has been made from time to time to overcome the deficiencies of cement concrete. The recent developments in the material and construction technology have led to significant changes resulting in improved performance, wider and more economical use.
  31. 31. Current Practice and Future Trends • Research work is going on in various concrete research laboratories to get improvement in the performance of concrete. Attempts are being made for improvements in the following areas. • Improvement in mechanical properties like compressive strength, tensile strength, impact resistance etc. • Improvement in durability in terms of increased chemical and freeze resistance • Improvements in impermeability, thermal insulation, abrasion, skid resistance etc.
  32. 32. Current Practice and Future Trends
  33. 33. Current Practice and Future Trends • Ready Mix Concrete • Self Compacting Concrete • High Performance Concrete • Fly ash Concrete. • Translucent Concrete • Biological Concrete (Self Healing Concrete)
  34. 34. Current Practice and Future Trends • Ready mix Concrete • Ready Mixed Concrete, or RMC as it is popularly called, refers to concrete that is specifically manufactured for delivery to the customer's construction site in a freshly mixed and plastic or unhardened state. Concrete itself is a mixture of Portland cement, water and aggregates comprising sand and gravel or crushed stone. In traditional work sites, each of these materials is procured separately and mixed in specified proportions at site to make concrete. Ready Mixed Concrete is bought and sold by volume - usually expressed in cubic meters. RMC can be custom-made to suit different applications. • Ready Mixed Concrete is manufactured under computer- controlled operations and transported and placed at site using sophisticated equipment and methods. RMC assures its customers numerous benefits..
  35. 35. Current Practice and Future Trends
  36. 36. Current Practice and Future Trends • Self Compacting Concrete: • Self-consolidating concrete or self-compacting concrete (SCC) is characterized by a low yield, high deformability, and moderate viscosity necessary to ensure uniform suspension of solid particles during transportation, placement (without external compaction), and thereafter until the concrete sets. • Such concrete can be used for casting heavily reinforced sections, places where there can be no access to vibrators for compaction and in complex shapes of formwork which may otherwise be impossible to cast, giving a far superior surface than conventional concrete.
  37. 37. Self Compacting Concrete
  38. 38. Self Compacting Concrete: • The first generation of SCC was characterized by the use of relatively high content of binder as well as high dosages of chemicals admixtures, usually super plasticizer to enhance flowability and stability. Such high-performance concrete had been used mostly in repair applications and for casting concrete in restricted areas. The first generation of SCC was therefore characterized and specified for specialized applications. • The relatively high cost of material used in such concrete continues to hinder its widespread use in various segments of the construction industry, including commercial construction, however the productivity economics take over in achieving favorable performance benefits and works out to be economical in pre-cast industry.
  39. 39. Current Practice and Future Trends • High Performance Concrete: (HPC) • The development of high performance concrete (HPC) is a giant step in making concrete a high-tech material with enhanced characteristics and durability. High performance concrete is an engineered concrete obtained through a careful selection and proportioning of its constituents. The concrete is with the same basic ingredients but has a totally different microstructure than ordinary concrete. • The low water cement ratio of HPC results in a very dense microstructure having a very fine and more or less well connected capillary system. • High performance concrete can hence be defined as an engineered concrete with low water/ binder ratio to control its dimensional stability and when receive an adequate curing.
  40. 40. High Performance Concrete (HPC)
  41. 41. Current Practice and Future Trends • Translucent concrete (concrete) is a concrete based building material with light-transmissive properties due to embedded light optical elements - usually Optical fibers. Light is conducted through the stone from one end to the other. Therefore the fibers have to go through the whole object. This results into a certain light pattern on the other surface, depending on the fiber structure.. • Translucent concrete is used in fine architecture as a façade material and for cladding of interior walls. But light-transmitting concrete has also been applied to various design products.
  42. 42. Translucent Concrete
  43. 43. Current Practice and Future Trends • Fly Ash Concrete • Owing to its pozzolanic properties, fly ash is used as a replacement for some of the Portland cement content of concrete. • Use of fly ash can replace up to 30% by mass of Portland cement, and can add to the concrete’s final strength and increase its chemical resistance and durability. Due to the spherical shape of fly ash particles, it can also increase workability of cement while reducing water demand. The replacement of Portland cement with fly ash is considered to reduce the greenhouse gas "footprint" of concrete, as the production of one ton of Portland cement produces approximately one ton of CO2 as compared to zero CO2 being produced using existing fly ash. Since the worldwide production of Portland cement is expected to increase replacement of any large portion of this cement by fly ash could significantly reduce carbon emissions associated with construction.
  44. 44. Fly Ash Concrete
  45. 45. Current Practice and Future Trends • Biological Concrete (Self Healing Concrete) • In manufacturing of biological concrete a specially selected bacteria of the genus Bacillus, alongside a combination of calcium lactate, nitrogen and phosphorus, is used to create a healing agent within the concrete. • If untouched, these agents can remain dormant in the concrete for centuries. But if water begins to seep into the cracks, the spores of the bacteria start to germinate and feed on the calcium lactate. This consumes oxygen, which in turn converts the calcium lactate into limestone that solidifies and seals the surface. The removal of oxygen also improves the durability of the steel reinforcement.
  46. 46. Biological Concrete (Self Healing Concrete)
  47. 47. Authorities in the Field of Concrete Research • Concrete Related Institutes and Associations • 1. Asian Concrete Federation • 2. Concrete Institute of Australia • 3. Portland Cement Association • 4. FIB International Federation for Structural Concrete • 5. The Institution Of Engineers(Malaysia) • 6. Concrete Reinforcing Steel Institute • 7. American Concrete Institute • 8. American Society of Concrete Contractors • 9. Institution of Civil Engineers , UK • 10. National Information Center for Earthquake Engineerings • 11. Korean Concrete Institute
  48. 48. Authorities in the Field of Concrete Research • 12. Indian Roads Congress • 13. Precast Prestressed Concrete Institute • 14. International Association for Bridge and Structural engineering • 15.Institution of Structural Engineers, UK. • 16. Japan Concrete Institute • 17. The Institution of Engineers (India) • 18. Thai Concrete Association • 19. American Society of Civil Engineers • 20. ASTM Standards • 21. For Civil Engineer • 22. RILEM • 23 Indian Concrete Institute
  49. 49. References • Concrete Technology by: R.P. Rethaliya • Concrete Technology by . M.S. Shetty • Internet websites • http://www.foundationsakc.org/
  50. 50. Thanks….

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