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.
Que2.15. Explain the goods of silica cloud on concrete parcels.
Answer Effect of Silica Cloud on the parcels of Fresh Concrete 1. Plasticity Reduced plasticity. ii. Water demand increases in proportion to silica cloud added. Water demand is 1 for every 1 relief of cement. iii. Lower depression and further cohesive blend. 2. Bleeding and isolation Bleeding is reduced as silica cloud patches find their way in between two cement grains. ii. isolation is reduced has the concrete blend is more cohesive due to increase in number of solid to solid contact points. 3. Time of Setting The original setting time and final setting time is not greatly told . The increase may be 30 min or so. 4. Plastic loss Since silica cloud concrete show no bleeding, fresh concrete is subordinated to plastic loss. goods of Silica Cloud on the parcels of Hardened Concrete 1. Drying loss Long term loss of concrete isn’t affected significantly by the addition of silica cloud. 2. Creep The creep of concrete containing silica cloud will be lower than corresponding Portland cement concrete. 3. Chemical Resistance A major reason for the bettered resistance of concrete to acidic and sulphate waters is the reduction in the Ca( OH) 2 content of the cement paste, which decreases linearly with the quantum of silica cloud added. 4. Alkali Aggregate response lower than 10 of silica cloud is set up acceptable for reducing the alkali total expansion as compared to fly ash which requires 30-40 relief. 5. Strength Strength of 62- 80 MPa can be fluently achieved. 6. Permeability Silica cloud reduce the size of voids in doused cement paste, therefore making them nearly impermeable indeed at early periods with addition of silica cloud by weight of cement. 7. snap and thaw Effect The effect of silica cloud concrete on freezethaw affect isn’t veritably significant.
Que2.16. What are the advantages, disadvantages and uses of silica cloud?
Answer Advantages of Silica Cloud Following are the advantages of silica cloud 1. Lowers concrete permeability. 2. Significantly increases concrete continuity. 3. Increases ultimate strength gain. 4. salutary in all types of high strength concrete operations. 5. Improves bond strength to sword. 6. Significantly reduces alkali- silica reactivity. 7. Provides excellent resistance to sulphate or seawater attack. 8. Reduces sword erosion. 9. Improves snap/ thaw continuity of concrete. Disadvantages of Silica Cloud Following are the disadvantages of silica cloud 1. Silica cloud concrete loss rate is a large. 2. Silica cloud concrete plasticity is poor. 3. It’s easy to produce temperature cracks. Uses of Silica Cloud 1. For product of high strength concrete, erosion- resistant concrete, bruise- resistant concrete, and low permeability concrete. 2. Used to make seamster and manhole form products. Reduces answer in shotcrete operation.