Concrete Technology: Study of Supplementary Cementing Materials Unit 2 Part 2

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. 

Que2.10. bandy fly ash in concrete. Give the advantages and  disadvantages of cover ash. 

Answer  Fly Ash Fly ash is one of the  remainders generated in combustion, and  comprises the fine  patches that rise with the stovepipe  feasts. In an artificial   environment, fly ash  generally refers to ash produced during combustion of  coal. 

Advantages of Fly Ash in Concrete Following are the advantages  of cover ash 

1. Lower permeability and better resistance to sulphate attack. 

2. Lower  loss and porosity as a result of the lower water content. 

3. bettered long term strength and  continuity performance. 

4. The rate of bleeding is reduced while plasticity is increased. 

5. Reduced water content for a given plasticity or  bettered plasticity  at the same water content. 

Disadvantages of Fly Ash in Concrete Following are the  disadvantages of cover ash 

1. It’s more  delicate to control the colour of concrete containing cover ash  than  fusions with Portland cement only. 

2. Fly ash reduces the  quantum of air entrainment, and concrete  fusions  high in cover ash  frequently bear more air- enplaning   amalgamation. 

3. Fly ash  cocktails can  outstretch the time it takes for concrete to set. 

4. Concrete changes from a liquid to a solid a many hours after pouring, but  the curing process may take much longer. 

Que2.11. What are the  groups of cover ash? Also give the use  of cover ash concrete. 

Answer  Types of Fly Ash Following are the two types of cover ash 

1. Class C Fly Ash  i. This class of cover ash has a high CaO content and used as a standalone  stabilizing agent.  ii. The strength characteristics of class C cover ash having a CaO  lower than 25  percent can be  bettered by adding lime. 

2. Class F Fly Ash 

i. This class of cover ash has a low CaO content. 

ii. Class F fly ash has an  inadequate CaO content for the pozzolanic  response  to  do. 

iii. It isn’t effective as a stabilizing agent by itself  still, when mixed  with either lime or lime and cement, the cover ash admixture becomes an  effective agent. 

Uses of Fly Ash Concrete Fly ash concrete are used in 

1. Pumped concrete. 

2. Road stabilization. 

3. Tunnelling concrete. 

4. Self compacting concrete. 

5. Water retaining structure. 

6. Marine  terrain concretes. 

7. Ready  blend and precast  operation. 

8. Mass concrete section. 

Que2.12. What are the  goods of cover ash on  colorful  parcels of  concrete? 

Answer  goods of Fly Ash on Concrete Following are the  goods of cover ash  on concrete 

1. On quantum of Mixing Water 

i. The use of cover ash in limited  quantities as a  relief for cement or as  an addition to cement requires a little  further water for the same depression  because of fineness of the cover ash. 

ii. It’s generally agreed that the use of cover ash, particularly as an  amalgamation  rather than as a  relief of cement, reduces,  isolation and  bleeding. 

iii. If the beach is coarse the addition of cover ash produces  salutary results;  for fine beach, its addition may increase the water  demand for a  given plasticity. 

2. On Compressive Strength An addition of cover ash up to 30 per cent  may affect in lower strength at 7 and 28 days, but may be about equal at  months and may further increase at  periods lesser than 3 months   handed curing is continued. 

3. On Modulus of Pliantness It’s lower at early  periods and advanced at  latterly   periods. 

4. On Curing Condition It’s  analogous to Portland cement concrete. 

5. On loss of Concrete Coarse cover ash and those having high  carbon content are more liable to increase drying  loss than the  finer cover ashes and those having low carbon content. 

6. On Permeability The permeability of concrete reduces on addition of  fly ash to cement. 

7. On Resistance to Chemical Attack Fly ash slightly improves the  resistance of concrete to sulphate attack. 

8. On Heat of Hydration Fly ash reduces the heat of hydration in  concrete. A negotiation of 30 cover ash may affect in a reduction of  50- 60 heat of hydration. 

9. On Air Entrainment The presence of cover ash reduces the  quantum of  air enplaning  agent.  

10. On Setting Time A 30 negotiation of cover ash may affect in an  increase of  original setting time over to 2 hours. 

Que2.13. What’s silica cloud? How is it produced? Give the  chemical composition of it. 

Answer  Silica Cloud  Silica cloud, also known as micro silica, is a derivate of the reduction of  high-  chastity quartz with coal in electric furnaces in the  product of  silicon and ferrosilicon  blends. 

ii. Silica cloud is also collected as a derivate of the  product of other  silicon  blends  similar as ferrochromium, ferromanganese, ferro magnesium,  and calcium silicon.  Chemical Composition 

1. It’s  substantially made of silica having silica percent  further than 80. 

2. The other chemical composition includes Fe2O3, Al2O3, CaO, MgO, Na2O,  K2O in small  probabilities. 

Que2.14. What’s the physical characteristics and functions of  silica cloud? 

Answer  Physical Characteristics Following are the physical  parcels of  silica cloud 

1. It should be in  decoration white and standard  slate colour. 

2. The specific  graveness of the silica cloud concrete is2.2. 

3. flyspeck size is  lower than 1 micron with average periphery of0.1 micron. 

4. Its specific  face area is to be,000 m2/ kg. 

5. The shape of the  flyspeck is  globular. 

6. It should be in  unformed in nature. 

Functions of Silica Cloud Following are the  colorful functions of  silica cloud 

1. The hydration of Portland cement produces  numerous  factors, including  calcium silicate hydrates( CSH) and calcium hydroxide( CH). 

2. The  fresh calcium silicate hydrates produced by the silica cloud is  more resistant to attack from aggressive chemicals  also the weaker  calcium hydroxide. 

3. The silica cloud is added to the calcium hydroxide for produce the   fresh calcium silicate hydrates to gain a  veritably good compressive  strength can exceed 15000 psi.

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