Concrete Technology: Concrete Production, Properties and Testing Unit 4 Part 3

Que4.5. Mention the different tests which are generally acclimated  to measure plasticity and explain any one test in detail.  Answer  Test for Measure Plasticity Following are the test used for  measure plasticity  Depression test.  ii. Compacting factor test.  iii. Vee- Bee test.  Concrete Depression Test Procedure  1. originally, the internal  face of the mould is  gutted precisely. oil painting can be  applied on the  face.  2. The mould is  also placed on a base plate.  3. The mould is filled with fresh concrete in three layers. Each subcaste is  tamped 25 times with a  sword rod.  4. After filling the mould,  redundant concrete should be removed and the   face should be leveled.  5. also the mould is lifted gently in the  perpendicular direction and  also   unsubstantiated concrete will slump. The  drop in height at the centre  point is measured to nearest 5 mm or0.25 inch and it’s known as  ‘ depression ’.   Que4.6. How do you conduct compacting factor test in  laboratory.  Answer  contraction Factor Test  1. The  contraction factor test gives the  geste

             of fresh concrete under  the action of external force.  2. In this test, the  contraction achieved through a free fall of concrete  determines its plasticity.  contraction Factor Test Procedure  1. The concrete sample is placed in the upper hopper.  2. also the door of hopper is opened. The sample drops into lower hopper  filling it to overflowing.  3. The trap door of the lower hopper is  also opened and the sample falls  into the cylinder which is also filled to overflowing.  4. The  fat concrete is removed from the top of the cylinder with the  help of a trowel.  5. The outside  face of cylinder is wiped and  gutted.  6. The cylinder is  also counted and it’s recorded as weight of  incompletely  compacted concrete.  7. The cylinder is again filled with concrete in layers not exceeding 50 mm  in consistence. Each subcaste is completely compacted with tamping rod.  8. The cylinder is again counted after wiping and  drawing the outside   face of cylinder. This weight is recorded as the weight of completely  compacted concrete.  9. The compacting factor is  also calculated from the formula  Compacting factor =  Weight of  incompletely compacted concrete/ Weight of  completely compacted concrete.   Que4.7. Explain the Vee- Bee test of determining plasticity with  neat sketch.  Answer  1. The test is suitable for stiff concrete mixes having low or  veritably low  plasticity.  2. Compared to the depression and compacting factor tests, the Vee- Bee test  has the advantage that the concrete in the test receives a treatment   analogous to what it would in  factual practice.  3. The test consists of moulding a fresh concrete cone in a spherical   vessel mounted on a  wobbling  table(Fig.4.7.1).  4. When the concrete cone is  subordinated to vibration using a standard  vibrator, it starts to  enthrall  the spherical  vessel by way of getting  remoulded.  5. The remoulding is considered complete when the concrete  face  becomes vertical.  6. The time( in seconds)  needed for the complete remoulding is considered  as a measure of plasticity and is expressed as the number of Vee- Bee  seconds.  7. The end point of the test, when the concrete  face becomes vertical,  has to be caught on  visually. 4.7.1. Vee- Bee  outfit.  Glass plate rider  Que4.8. What’s the effect of time and temperature on  plasticity?  Answer  Effect of Time on Workability  1. lately mixed concrete stiffens with the passage of time. This is different  from the hardening of the  blend.  2. As time passes, water is lost due to  immersion by  summations if they are  not  formerly  impregnated. Some water is lost due to evaporation, especially  if the concrete is exposed to hot rainfall and wind  also plasticity   drop.  Effect of Temperature on Plasticity  1. When temperature increases,  also in the same proportion plasticity  of fresh concrete  diminishments.  2. The reason that stands before is “ when temperature increases  also  evaporation rate also increases due to that hydration rate  diminishments and  hence, concrete will gain strength  before ”.  3. Due to fast hydration of concrete, a hardening comes in concrete and  that decreases the plasticity of fresh concrete.  Que4.9. Write about  isolation and its causes. How reduce   isolation of concrete?  Answer  isolation It’s defined as the separation of the  ingredients of a  homogeneous admixture of concrete. It’s caused by the differences in  sizes and weights of the constituent  patches.  Causes of isolation in Concrete  1. Transporting concrete  composites for long distances.  2. inadequately proportioned  blend, where sufficient matrix isn’t there to bind the   summations.  3. Dropping concrete from  further than 1m.  4. wobbling concrete for a long time.  Remedial Measures  To reduce  isolation, well  canted  summations are used and concrete is  placed with enough  contraction.  ii. The concrete shouldn’t be dropped from a height of  further than1.5m.  Que4.10. bandy the factors affecting bleeding of concrete.  Concrete Technology 4 – 11 D( CE- Sem- 5)  Answer  Factors Affecting Bleeding of Concrete Following are the factors  that affecting the bleeding of concrete  1. Water Content and Water Cement rate  Any increase in the  quantum of water or water- to- cementitious material   rate results in more available water for bleeding.  ii. A one- fifth increase in water content of a normal concrete admixture can  increase bleeding rate  further than two and a half times.  2. Cement  i. The type, content and fineness of cement can  prompt bleeding. As the  fineness of the cement increases, the  quantum of bleeding  diminishments.  ii. Increases in cement content, reduces the water- cement  rate, and also  reduces bleeding.  3. Supplementary Cementing Accoutrements  Fly ash, sediment, silica cloud, rice  cocoon ash and natural pozzolanas can  reduce bleeding by their  essential  parcels and by  adding  the  quantum  of cementitious accoutrements  in a admixture.  4. Aggregate  total that contain a high  quantum of ground,  complexion or other material  passing the75 μm sieve can have a significant effect in reducing bleeding.  5. Chemical amalgamation  Air- enplaning  agents have been used largely because the air bubbles  appear to keep the solid  patches in  suspense.  ii. Water reducers also reduce the  quantum of bleeding because they release  trapped water in admixture.  Que4.11. How would you reduce bleeding from concrete?  Answer  Controlling Measures of Bleeding Following are the controlling  measures of bleeding from concrete  1. Proper proportioning of concrete.  2. A complete and  invariant mixing of concrete.  3. still, the  If we can increase the traveling length of water to bebleeded.bleeding can be reduced  vastly. For this purpose we can use  finely divided pozzolanic accoutrements   4. An  preface of air- entrainment by using air enplaning  agent can  reduce bleeding.  5. The use of finer cement.  6. By using of a rich  blend rather than  spare  blend.  Concrete product, Properties & Testing 4 – 12 D( CE- Sem- 5) . Controlled vibration can reduce bleeding.   Que4.12. What are the  goods of bleeding on concrete  parcels?  Answer  Following are the  goods of bleeding on concrete  parcels  1. Due to bleeding concrete losses its unity.  2. Bleeding is responsible for causing permeability in concrete.  3. This accumulation of water creates a water voids and reduces bond  between the  total and cement  history. So the strength of concrete  reduces.  4. Water that accumulates below the  buttressing bars, particularly below  the cranked bars, reduces the bond between the  underpinning and  concrete.  5. The bleeding water flows at over the  unsubstantiated side of pavement  which causes collapsing of sides.  6. In pavement construction bleeding water detainments  face finishing and   operation of curing  emulsion.  7. Bleeding causes of ‘ Laitance in concrete ’. Due to the  conformation of  Laitance, structures may lose its wearing capacity and decreases its life.  8. Water while moving from bottom to the top, forms  nonstop channels.  Due to this channel, concrete becomes passable and allow water to  move, which forms water voids in the matrix and reduces the bond  between  total and the cement paste.  Que4.13. Describe the curing and  significance of curing. Explain  the different  styles of curing.  Answer  Curing It’s a procedure that’s  espoused to promote the hardening of  concrete under conditions of  moisture and temperature which are  conducive to the progressive and proper setting of the constituent  cement.  Importance of Curing Following are the  significance of curing of  concrete  1. To maintain  humidity content in the  blend for complete hydration of  concrete.  2. To maintain  invariant temperature of the concrete.  3. To  save the  parcels of concrete,  similar as impermeability,  continuity  and strength.  4. To reduce the  loss of the concrete.  styles of Curing of Concrete Following are the  styles of curing  Concrete Technology 4 – 13 D( CE- Sem- 5)  1. Ponding of Water over the Concrete face after it has Set  This is the most common  system of curing the concrete arbor or pavements  and consists of storing the water to a depth of 50 mm on the  face by  constructing small billabong

              complexion bunds  each around.  2. Covering the Concrete with Wet Straw or Damp Earth In this   system the damp earth or beach in layers of 50 mm height are spread  over the  face of concrete pavements. The material is kept  wettish by   journal  smattering of water.  3. Covering the Concrete with Wet Burlap The concrete is covered  with burlap( coarse jute or hemp) as soon as possible after placing, and  the material is kept continuously  wettish for the curing period.  4. smattering of Water  i. This is a useful  system for curing  perpendicular or inclined  shells of concrete.  ii. The spraying can be done in fine aqueducts through  snoots fixed to a pipe  spaced at set intervals.  iii. Flogging is done in the same way except that the flogging  snoots produce  a mist- suchlike effect, whereas  scattering  snoots exfoliate out fine spray.  5. Covering the face with Leakproof Paper  Leakproof paper prevents loss of water in concrete and protects the   face from damage.  ii. A good quality paper can be  frequently reused. The paper is  generally made of  two  wastes struck together by rubber latex composition.  6. Leaving the Shuttering or Formwork The thick watertight  formwork also prevents the loss of  humidity in concrete and helps in  curing the sides and the base of the concrete.  7. Membrane Curing of the Concrete  i. The process of applying a membrane forming  emulsion on concrete   face is  nominated membrane curing.  ii. frequently, the term membrane is used not only to  relate to liquid membranes  but also to a solid sheeting used to cover the concrete  face.  iii. The curing membrane serves as a physical  hedge to  help loss of   humidity from the concrete to be cured.  iv. A curing liquid membrane should dry within 3 to 4 hours to form a   nonstop coherent  tenacious film free from perforations and have no   injurious effect on concrete.  8. Chemical Curing  Chemical curing is  fulfilled by  scattering the sodium silicate( water  glass)  result on concrete  face.  ii. About 500 g of sodium silicate mixed with water can cover 1 m2 of   face and from a hard and  undoable calcium silicate film.  iii. It actually acts as a case hardener and curing agent.

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