Concrete Technology: Chemical and Mineral Admixtures Unit 2 Part 1

Que2.1. What’s  amalgamation? Why is it used with concrete? Also  give its types. 

Answer  amalgamation  cocktails are accoutrements  used to modify the  parcels of fresh hardened  concrete.  ii. They’re classified as chemical and mineral  cocktails.  iii. Chemical  cocktails are used in the construction assiduity for  erecting  strong, durable, and leakproof structures.  Reason for using cocktails with Concrete  Following are the purposes for which the  cocktails could be used with  concrete  1. To accelerate the  original set of concrete, i.e., to speed up the rate of  development of strength at early  periods.  2. To  slacken the  original set of concrete, i.e., to keep concrete workable for a  longer time for placement.  3. To enhance the plasticity.  4. To ameliorate the penetration( flowability) and pumpability of concrete.  5. To reduce the  isolation in grout and concrete  fusions.  6. To increase the strength of concrete by reducing the water content and  by densification of concrete.  7. To  drop the capillary inflow of water through concrete and to increase  in impermeability to liquids.  8. To inhibit the  erosion of  underpinning in concrete.  9. To increase the resistance to chemical attack.  10. To increase the bond between old and new concrete  shells.  Types of cocktails Following are the types of  cocktails  1. Accelerators.  2. Water reducing  cocktails.  3. Retarders.  4. Air- enplaning  agents. 

Que2.2. Explain the accelerators with suitable  illustration. Also  give the functions of accelerators. 

Answer  Accelerator An  amalgamation is use to speed up the  original set of concrete  is called accelerator.  exemplifications Calcium chloride, sodium nitrate, calcium nitrate,etc.  Functions Following are the functions of accelerators  1. These are added to concrete either  To increase the rate of hydration of hydraulic cement, and hence to  increase the rate of development to strength.  ii. To  dock the setting time.  2. An increase in the rate of early strength development may help in  i. before  junking of forms,  ii. Reduction of required period of curing, and  iii. before placement of structure in service.  3. Accelerating  cocktails are also used when the concrete is to be placed  at low temperatures.  4. The benefits of reduced time of setting may include  Early finishing of  face,  ii. Reduction of pressure on forms or of period of time during which the  forms are  subordinated to hydraulic pressure, and  iii. More effective plugging of leaks against hydraulic pressure.  5. With the vacuity of  important accelerators, the under- water  concreting, the basement waterproofing operations, the  form work of  the shorefront structures in the tidal zones have come easy. 

Que2.3. Describe the accelerator effect on the concrete  parcels. 

Answer  Following are the accelerator effect on the concrete  parcels  1. The general action of accelerators is to beget a more  rapid-fire dissolution of   composites of cement, particularly tricalcium silicate, in water and hence   grease more  rapid-fire hydration of these  composites.  2. The use of 2 calcium chloride by mass of cement can reduce the  setting time by one- third and raise the one to seven day compressive  strength by 3 to 8 MPa.  3. An increase in flexural strength of 40 to 80 of one day and up to 12  at 28 days in  attained.  4. Large boluses of CaCl2 result in flash set of concrete and the ambient  temperature.  5. Calcium formate( a fine greasepaint), which is  kindlyless answerable than  calcium chloride and is less effective doesn’t have the same adverse  effect on  erosion of bedded  sword as CaCl2. It’s added in the same  tablets. 

Que2.4. Explain the  part of  cocktails in concrete technology. 

Answer  Following are the  part of  cocktails in concrete technology  1. To Modify Fresh Property  Increase the plasticity without  adding  the water cement  rate or   drop the water content at the same plasticity.  ii. Retard or accelerate the time of  original setting.  iii. Reduce or  help the  agreement or  produce slight expansion.  iv. Modify the rate or capacity of bleeding.  2. To Modify Harden Property  Reduce the heat of  elaboration.  ii. Accelerate the rate of strength development at early stages.  iii. Increase the  continuity.  iv. drop the permeability of concrete. 

Que2.5. What’s air- detrained concrete? What are the  air- enplaning  agents? What are factors affecting the airentrainment  in the concrete? 

Answer  Air- Entrained Concrete  1. Air- entrainment is the internal creation of  bitsy air bubbles in concrete.  A concrete maker introduces the bubbles by adding to the  blend an air  enplaning  agent. The air bubbles are created during mixing of the  plastic concrete and  utmost of them survive to be part of the hardened  concrete.  2. It contains billions of  bitsy air cells per boxy  bottom. These air pockets  relieve internal pressure on the concrete by  furnishing  bitsy chambers for  water to expand into when it freezes.  3. It’s produced using air- enplaning  Portland cement, or by the  preface  of air- enplaning  agents, under careful engineering supervision, as the  concrete is mixed on the job.  4. The  quantum of detrained air is  generally between four to seven percent of  the volume of the concrete.  Air- enplaning  Agents Following are the air- entrainment agent used  in the concrete  1. Natural wood resins.  2. Beast and vegetable fats and canvases   similar as tallow, olive  oil painting and their adipose  acids  similar as stearic and oleic acids.  3. colorful  wetting down agents  similar as alkali  mariners or sulphonated organic   composites.  4. Water answerable  detergents of resins acid.  5. eclectic accoutrements   similar as sodium  mariners of petroleum sulphonic  acids, hydrogen peroxide and aluminium greasepaint,etc.  Factor Affecting Air Entrainment Following are the factor affect  the air entrainment  1. Type and  volume of air enplaning  agents used.  2. Water cement  rate of  blend.  3. Type and grading of  summations.  4. Mixing time.  5. Temperature.  6. Type of cement.  7. Influence of  contraction.  8. cocktails other than air enplaning  agents used.  

Que2.6. What are the  goods of air entrainment  amalgamation on  the  parcels of concrete? 

Answer  Effect of Air Entrainment on Concrete parcels Following are  the effect of air entrainment on concrete  parcels  1. Reduction in strength.  2. enhancement in plasticity.  3. Increased resistance to freezing and thawing.  4. Reduces the tendencies of  isolation.  5. Reduces the bleeding and laitance.  6. Decreases the permeability.  7. Increases the resistance to chemical attack.  8. Permits reduction in beach content, water content, cost and heat of  hydration.  9. Reduces unit weight, alkali aggregate  response and modulus of pliantness.  10. Enhance the  continuity of concrete against cycles of climatic freezing  and thawing and against the  goods ofde-icing  mariners.  

Que2.7. What are the different types of superplasticizers? 

Answer  Types of Superplasticizers Different types of superplasticizers are  as follows  1. Lignosulphonates These are  deduced from neutralization,   rush, and  turmoil processes of the waste liquor  attained  during  product of paper- making pulp from wood  2. Sulphonated Melamine Formaldehyde( SMF) It’s manufactured  by normal resinification of melamine- formaldehyde.  3. Sulphonated Napthalene Formaldehyde( SNF) Produced from  naphthalene by oleum or SO3 sulphonation;  posterior  response with  formaldehyde leads to polymerization and the sulphonic acid is  annulled with sodium hydroxide or lime.  4. Polycarboxylic Ether( PCE) Free radical medium using peroxide   inaugurators is used for polymerization process in these systems.  

Que2.8. bandy the  part of plasticizers when used as an  amalgamation for concrete. 

Answer  part of Plasticizers cocktails are used for following purposes  1. To achieve a advanced strength by  dwindling the water cement  rate at  the same plasticity.  2. To achieve the same plasticity by  dwindling the cement content so as  to reduce the heat of hydration in mass concrete.  3. Water reduction  further than 5 but  lower than 12.  4. To increase the plasticity so as to ease placing inapproachable  locales.  

Que2.9. Describe the effect of superplasticizer on the  parcels  of fresh and  toughened concrete. 

Answer  Effect on Fresh Concrete  1. Superplasticizers enhance plasticity. The effect depends on type,  lozenge, and time of addition( stylish with mixing water). Water  demand  is reduced by 15 to 30. Performing concrete has advanced strength and  lower permeability.  2. Superplasticizers produce advanced than normal plasticity for 30- 60 min  and there will be  rapid-fire loss of plasticity.  3. Generally bleeding is  dropped( less water). still,  If flowing concrete ismade.precautions are  demanded not to induce bleeding and  isolation.  Effect on Hardened Concrete  1. Water reduction allows producing high- strength concrete.  2. loss of superplasticized concrete is  similar to or  lower than  normal concrete.  3. Creep of superplasticized concrete is  analogous to that of a reference  concrete.  4. The use of superplasticizers allows advancements in the bond between  concrete and  buttressing  sword.  Effect on Durability  1. Lower water/ cement  rate leads to lower permeability and enhanced  strength and  continuity.  2. In normal concrete, the critical distance between air bubbles is 200m.  In superplasticized concrete, that value is exceeded. Better  snap- thaw   continuity can be anticipated for air detrained superplasticized concrete.  3. continuity to sulphate attack depends on the particular medium of  sulphate attack and exposure type. For expansion, lower permeability (  lower  face penetration) can lead to better  continuity.  4. Lower water/ cement  rate leads to lower permeability and  bettered  resistance to chloride penetration and  erosion of  sword.  5. Lower water/ cement  rate leads to lower  humidity penetration, which  could enhance resistance to alkali expansion.

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