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.