Concrete Technology: Cement Production and Aggregates Unit 1 Part 2

Que1.6. What’s hydration of cement? Explain the process of  hydration of cement. 

Answer  Hydration of Cement  1. The  response of cement when mixed with water is called hydration.  Both C3S and C2S make up nearly 75 of cement.  2. The hydration of these  composites is responsible for the setting and  hardening of cement.  3. The hydration  face  response starts  incontinently once cement comes  in contact with water. It’s an exothermic  response.  4. The hydration continues as long as heat and  humidity are available.  Concrete Technology 1 – 9 D( CE- Sem- 5)  5. All four Bogue’s  composites along with gypsum are involved in the  hydration  response and only a  veritably small  quantum of water is  demanded for  it.  B. Following stages  passed in the process of hydration  1. Stage 1 A heat generation of  rapid-fire order takes place for close to  15  twinkles. The calcium and hydrogen ions are released from the   face and when certain  situations of critical  attention are reached,  the  elaboration of calcium hydroxide and calcium silicate hydroxide beings.  The  original  responses are dependent on the temperature.  2. Stage 2 This stage tends to be the dormant period and the cement is  forced to come plastic for a period of 2 to 4 hours. This process of   response tends to  decelerate down.  3. Stage 3 This is the acceleration period as the silicate hydrates  fleetly   on with critical  attention of ions. The entire hardening takes  place and the final set is released and the time period is generally for 4  to 8 hours.  4. Stage 4 This is known as the  retardation stage. The overall rate of   response tends to  decelerate down performing in an independent  prolixity   response.  5. Stage 5 This is appertained to as the steady stage and the temperature  has  lower effect on the hydration stage. The  response process is constant  and is for a period of 12 to 24 hours.  The individual  response of minerals tends to be less effective than the   concerted  response of the hydration of cement. The hydration of cement  can be  resolve into several small  factors it’s observed that the  aluminate and the ferrite stage tend to reply first and  also the  responses  tend to carry over to the silicate phase.   

Que1.7. Describe the hydration  response of important Bogue’s   composites indicating the products of hydration. 

Answer  Hydration response of Bogue’s emulsion  1. Hydration of C3S  i. The chemical  response of C3S with water can be expressed as  C3S water C – S – H C – H heat  where, C- S- H is calcium silicate hydrate and C- H is calcium hydrate.  ii. C- S- H, Calcium silicate hydrate constitutes 50- 60 of the solids in the  paste. It forms a  nonstop list matrix. It’s  unformed and stringy  and hence has a large  face area. It’s an important factor for the  strength development of cement paste.  iii. C- H, Calcium hydrate makes up about 20 of the solids in the paste.  It exists in the form of thick,  liquid hexagonal plates and is  bedded in the C- S- H matrix. Its growth fills the severance spaces. It does  Cement product & summations 1 – 10 D( CE- Sem- 5)  not significantly contribute to strength. Its filtering causes white  patches and efflorescence.  2. Hydration of C2S  i. The hydration of C2S is  analogous to the hydration of C3S. The same  products are generated. still, C2S reacts  sluggishly and hence  generates  lower heat.  ii. It contributes to strength development at after stages.  3. Hydration of C3A  i. This hydration  response produces a substance called ettringite as follows   C3A gypsum water ettringite heat  C3A ettringite water monosulphoaluminate , C3A will reply  presto and can beget  If the  quantum of gypsum is toolittle.a ‘ flash set ’.  iii. On the other hand, too  important gypsum will delay setting and beget   overdue expansion. It constitutes about 10 – 20 of the solid content.  iv. It’s a long, slender, and  polychromatic demitasse and is stable only in the  presence of gypsum.  v. It plays a minor  part in strength development but contributes   vastly to  continuity.  vi. Monosulphoaluminate is a stable hydration product. It’s fairly  crystalline.  4. Hydration of C4AF  i. The hydration of C4AF is  analogous to that of C3A; the same products are  formed.  ii. still, C4AF reacts  sluggishly and hence generates  lower heat and  combines well with gypsum. 

Que1.8. What are the advantages of pozzolona portland cement. 

Answer  Advantages  1. In PPC,  expensive clinker is replaced by cheaper pozzolanic material  and hence  provident.  2. Answerable calcium hydroxide is converted into  undoable cementitious  products performing in  enhancement of permeability. Hence it offers, all  round  continuity characteristics, particularly in hydraulic structures  and marine construction.  3. PPC consumes calcium hydroxide and doesn’t produce calcium  hydroxide as much as that of OPC.  4. It generates reduced heat of hydration and that too at a low rate.  5. PPC being finer than OPC and also due to pozzolanic action, it improves  the severance size distribution and also reduces the microcracks at the  transition zone.  6. As the cover ash is finer and of lower  viscosity, the bulk volume of 50 kg  bag is slightly  further than OPC. thus, PPC gives  further volume of  mortar than OPC.  7. The long term strength of PPC beyond a couple of months is advanced  than OPC if enough  humidity is available for continued pozzolanic  action.

 Que1.9. Explain compactly the physical  parcels of ordinary portland cement and its uses. 

Answer  Physical parcels of Ordinary Portland Cement  1. Colour greenish grey.  2. One feels cool by thrusting one’s hand in the cement bag.  3. It’s smooth when rubbed in between fritters.  4. A  sprinkle of cement thrown in a pail of water should float.  Uses of Cement Following are uses of cement  1. It’s used in concrete for laying  bottoms, roofs and constructing lintels,   shafts, stairs, pillars etc . It’s used for making joints for rainspouts and pipes.  3. It’s used for water  miserliness of structure.  4. It’s used in mortar for  trouncing, masonry work, pointing,etc.  5. Cement is a  veritably useful list material in construction.  6. It’s employed for the construction of wells, water tanks, tennis courts,  beacon posts, telephone cabins, roads etc . It’s used in the medication of foundations, water tight  bottoms, paths etc.  8. It’s used in the construction of important engineering structures  similar  as islands, acequias heads, coverts, light houses etc . It’s used for precast pipes manufacturing, piles, fencing postsetc.  

Que1.10. Describe the pozzolanic accoutrements . What are the  advantages of pozzolanic material? 

Answer  Pozzolanic Accoutrements  1. Pozzolanic accoutrements  are siliceous or siliceous and aluminous accoutrements ,  which in themselves  retain little or no cementitious value, but will, in finely divided form and in the presence of  humidity, chemically reply  with calcium hydroxide liberated on hydration, at ordinary temperature,  to form  composites,  enjoying cementitious  parcels.  2. Pozzolanic  response is given by  Pozzolana Calcium hydroxide Water C – S – H( gel)  Advantages of Pozzolanic Accoutrements Following are the advantages  of pozzolanic accoutrements   1. Lower the heat of hydration and thermal  loss.  2. Increase the water-  miserliness.  3. Reduce the alkali- aggregate  response.  4. Ameliorate resistance to attack by sulphate soils and  ocean water.  5. Ameliorate extensibility.  6. Lower  vulnerability to dissolution and filtering.  7. Ameliorate plasticity.  8. Lower costs.  

Que1.11. Describe the  colorful types of pozzolanic accoutrements . 

Answer  Types of Pozzolanic Accoutrements Following are the  colorful types of  pozzolanic accoutrements   1. Fly Ash  Fly ash is finely divided residue performing from the combustion of  powdered coal and transported by the stovepipe  feasts and collected by  electrostatic precipitator.  ii. Fly ash is the most extensively used pozzolanic material  each over the world.  iii. Fly ash is categorise into two classes  Class F Fly ash  typically produced by burning anthracite or  bituminous coal,  generally has  lower than 5 CaO. Class F fly ash has  pozzolanic  parcels only.  Class C Fly ash  typically produced by burning lignite or subbituminous  coal. Some class C cover ash may have CaO content in  redundant  of 10. In addition to pozzolanic  parcels, class C cover ash possesses  cementitious  parcels.  2. Silica Cloud  Silica cloud, also appertained to as microsilica or condensed silica cloud, is  another material that’s used as an artificial pozzolanic  amalgamation.  ii. Silica cloud is  veritably fine pozzolanic material composed of ultrafine,   unformed glassy sphere( average periphery,0.10 to0.15 mm) of silicon  dioxide( SiO2) produced during the manufacture of silicon or ferrosilicon  by electric  bow furnaces at temperature of over 2000 °C.  Concrete Technology 1 – 13 D( CE- Sem- 5)  iii. The micro silica is formed when SiO gas produced in the furnace mixes  with oxygen, oxidizes to SiO2, condensing into the pure  globular   patches of micro silica that form the major part of the bank or cloud  from the furnace.  3. Rice Husk Ash  Rice  cocoon ash is  attained by burning rice  cocoon in a controlled manner  without causing environmental pollution. When  duly burnt it has  high SiO2 content and can be used as a concrete  amalgamation.  ii. Rice  cocoon ash exhibits high pozzolanic characteristics and contributes  to high strength and high impermeability of concrete.  iii. Rice  cocoon ash( RHA) basically consists of  unformed silica( 90  SiO2), 5 carbon and 2 K2O.  iv. The specific  face of RHA is between 40 – 100 m2/g.  4. Surkhi  Surkhi is an artificial pozzolana made by  pulverizing bricks or burnt   complexion balls.  ii. In some major  workshop, for large scale  product of surkhi,  complexion balls  are especially burnt for this purpose and  also  pulverized.  iii. Its characteristics are greatly  told  by the constituent mineral  composition of soil, degree of burning and fineness of grinding.  5. Metakaolin  Thermally actuated ordinary  complexion and kaolinitic  complexion is known as  “ Metakaolin ”.  ii. It showed certain  quantum of pozzolanic  parcels, they aren’t  largely  reactive.  iii. largely reactive metakaolin is made by water processing to remove  unreactive  contaminations to make 100 reactive pozzolana. Such a product,  white or cream in colour, purified, thermally actuated is called High  Reactive Metakaolin( HRM).  iv. High reactive metakaolin shows high pozzolanic reactivity and reduction  in Ca( OH) 2 ever as beforehand as one day.  6. Ground Granulated Blast Furnace Sediment( GGBS)  Ground granulated blast- furnace sediment is another important mineral   amalgamation like cover ash a nonmetallic product  conforming basically of  silicates and aluminates of calcium and other bases.  ii. The molten sediment is  fleetly stupefied by quenching in water to form a  glassy beach like  grained material.  iii. The  grained material when  farther ground to  lower than 45 micron  will have specific  face of about 400 to 600 m2/ kg( Blaine).

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