Que1.6. What’s hydration of cement? Explain the process of hydration of cement.
Answer Hydration of Cement 1. The response of cement when mixed with water is called hydration. Both C3S and C2S make up nearly 75 of cement. 2. The hydration of these composites is responsible for the setting and hardening of cement. 3. The hydration face response starts incontinently once cement comes in contact with water. It’s an exothermic response. 4. The hydration continues as long as heat and humidity are available. Concrete Technology 1 – 9 D( CE- Sem- 5) 5. All four Bogue’s composites along with gypsum are involved in the hydration response and only a veritably small quantum of water is demanded for it. B. Following stages passed in the process of hydration 1. Stage 1 A heat generation of rapid-fire order takes place for close to 15 twinkles. The calcium and hydrogen ions are released from the face and when certain situations of critical attention are reached, the elaboration of calcium hydroxide and calcium silicate hydroxide beings. The original responses are dependent on the temperature. 2. Stage 2 This stage tends to be the dormant period and the cement is forced to come plastic for a period of 2 to 4 hours. This process of response tends to decelerate down. 3. Stage 3 This is the acceleration period as the silicate hydrates fleetly on with critical attention of ions. The entire hardening takes place and the final set is released and the time period is generally for 4 to 8 hours. 4. Stage 4 This is known as the retardation stage. The overall rate of response tends to decelerate down performing in an independent prolixity response. 5. Stage 5 This is appertained to as the steady stage and the temperature has lower effect on the hydration stage. The response process is constant and is for a period of 12 to 24 hours. The individual response of minerals tends to be less effective than the concerted response of the hydration of cement. The hydration of cement can be resolve into several small factors it’s observed that the aluminate and the ferrite stage tend to reply first and also the responses tend to carry over to the silicate phase.
Que1.7. Describe the hydration response of important Bogue’s composites indicating the products of hydration.
Answer Hydration response of Bogue’s emulsion 1. Hydration of C3S i. The chemical response of C3S with water can be expressed as C3S water C – S – H C – H heat where, C- S- H is calcium silicate hydrate and C- H is calcium hydrate. ii. C- S- H, Calcium silicate hydrate constitutes 50- 60 of the solids in the paste. It forms a nonstop list matrix. It’s unformed and stringy and hence has a large face area. It’s an important factor for the strength development of cement paste. iii. C- H, Calcium hydrate makes up about 20 of the solids in the paste. It exists in the form of thick, liquid hexagonal plates and is bedded in the C- S- H matrix. Its growth fills the severance spaces. It does Cement product & summations 1 – 10 D( CE- Sem- 5) not significantly contribute to strength. Its filtering causes white patches and efflorescence. 2. Hydration of C2S i. The hydration of C2S is analogous to the hydration of C3S. The same products are generated. still, C2S reacts sluggishly and hence generates lower heat. ii. It contributes to strength development at after stages. 3. Hydration of C3A i. This hydration response produces a substance called ettringite as follows C3A gypsum water ettringite heat C3A ettringite water monosulphoaluminate , C3A will reply presto and can beget If the quantum of gypsum is toolittle.a ‘ flash set ’. iii. On the other hand, too important gypsum will delay setting and beget overdue expansion. It constitutes about 10 – 20 of the solid content. iv. It’s a long, slender, and polychromatic demitasse and is stable only in the presence of gypsum. v. It plays a minor part in strength development but contributes vastly to continuity. vi. Monosulphoaluminate is a stable hydration product. It’s fairly crystalline. 4. Hydration of C4AF i. The hydration of C4AF is analogous to that of C3A; the same products are formed. ii. still, C4AF reacts sluggishly and hence generates lower heat and combines well with gypsum.
Que1.8. What are the advantages of pozzolona portland cement.
Answer Advantages 1. In PPC, expensive clinker is replaced by cheaper pozzolanic material and hence provident. 2. Answerable calcium hydroxide is converted into undoable cementitious products performing in enhancement of permeability. Hence it offers, all round continuity characteristics, particularly in hydraulic structures and marine construction. 3. PPC consumes calcium hydroxide and doesn’t produce calcium hydroxide as much as that of OPC. 4. It generates reduced heat of hydration and that too at a low rate. 5. PPC being finer than OPC and also due to pozzolanic action, it improves the severance size distribution and also reduces the microcracks at the transition zone. 6. As the cover ash is finer and of lower viscosity, the bulk volume of 50 kg bag is slightly further than OPC. thus, PPC gives further volume of mortar than OPC. 7. The long term strength of PPC beyond a couple of months is advanced than OPC if enough humidity is available for continued pozzolanic action.
Que1.9. Explain compactly the physical parcels of ordinary portland cement and its uses.
Answer Physical parcels of Ordinary Portland Cement 1. Colour greenish grey. 2. One feels cool by thrusting one’s hand in the cement bag. 3. It’s smooth when rubbed in between fritters. 4. A sprinkle of cement thrown in a pail of water should float. Uses of Cement Following are uses of cement 1. It’s used in concrete for laying bottoms, roofs and constructing lintels, shafts, stairs, pillars etc . It’s used for making joints for rainspouts and pipes. 3. It’s used for water miserliness of structure. 4. It’s used in mortar for trouncing, masonry work, pointing,etc. 5. Cement is a veritably useful list material in construction. 6. It’s employed for the construction of wells, water tanks, tennis courts, beacon posts, telephone cabins, roads etc . It’s used in the medication of foundations, water tight bottoms, paths etc. 8. It’s used in the construction of important engineering structures similar as islands, acequias heads, coverts, light houses etc . It’s used for precast pipes manufacturing, piles, fencing postsetc.
Que1.10. Describe the pozzolanic accoutrements . What are the advantages of pozzolanic material?
Answer Pozzolanic Accoutrements 1. Pozzolanic accoutrements are siliceous or siliceous and aluminous accoutrements , which in themselves retain little or no cementitious value, but will, in finely divided form and in the presence of humidity, chemically reply with calcium hydroxide liberated on hydration, at ordinary temperature, to form composites, enjoying cementitious parcels. 2. Pozzolanic response is given by Pozzolana Calcium hydroxide Water C – S – H( gel) Advantages of Pozzolanic Accoutrements Following are the advantages of pozzolanic accoutrements 1. Lower the heat of hydration and thermal loss. 2. Increase the water- miserliness. 3. Reduce the alkali- aggregate response. 4. Ameliorate resistance to attack by sulphate soils and ocean water. 5. Ameliorate extensibility. 6. Lower vulnerability to dissolution and filtering. 7. Ameliorate plasticity. 8. Lower costs.
Que1.11. Describe the colorful types of pozzolanic accoutrements .
Answer Types of Pozzolanic Accoutrements Following are the colorful types of pozzolanic accoutrements 1. Fly Ash Fly ash is finely divided residue performing from the combustion of powdered coal and transported by the stovepipe feasts and collected by electrostatic precipitator. ii. Fly ash is the most extensively used pozzolanic material each over the world. iii. Fly ash is categorise into two classes Class F Fly ash typically produced by burning anthracite or bituminous coal, generally has lower than 5 CaO. Class F fly ash has pozzolanic parcels only. Class C Fly ash typically produced by burning lignite or subbituminous coal. Some class C cover ash may have CaO content in redundant of 10. In addition to pozzolanic parcels, class C cover ash possesses cementitious parcels. 2. Silica Cloud Silica cloud, also appertained to as microsilica or condensed silica cloud, is another material that’s used as an artificial pozzolanic amalgamation. ii. Silica cloud is veritably fine pozzolanic material composed of ultrafine, unformed glassy sphere( average periphery,0.10 to0.15 mm) of silicon dioxide( SiO2) produced during the manufacture of silicon or ferrosilicon by electric bow furnaces at temperature of over 2000 °C. Concrete Technology 1 – 13 D( CE- Sem- 5) iii. The micro silica is formed when SiO gas produced in the furnace mixes with oxygen, oxidizes to SiO2, condensing into the pure globular patches of micro silica that form the major part of the bank or cloud from the furnace. 3. Rice Husk Ash Rice cocoon ash is attained by burning rice cocoon in a controlled manner without causing environmental pollution. When duly burnt it has high SiO2 content and can be used as a concrete amalgamation. ii. Rice cocoon ash exhibits high pozzolanic characteristics and contributes to high strength and high impermeability of concrete. iii. Rice cocoon ash( RHA) basically consists of unformed silica( 90 SiO2), 5 carbon and 2 K2O. iv. The specific face of RHA is between 40 – 100 m2/g. 4. Surkhi Surkhi is an artificial pozzolana made by pulverizing bricks or burnt complexion balls. ii. In some major workshop, for large scale product of surkhi, complexion balls are especially burnt for this purpose and also pulverized. iii. Its characteristics are greatly told by the constituent mineral composition of soil, degree of burning and fineness of grinding. 5. Metakaolin Thermally actuated ordinary complexion and kaolinitic complexion is known as “ Metakaolin ”. ii. It showed certain quantum of pozzolanic parcels, they aren’t largely reactive. iii. largely reactive metakaolin is made by water processing to remove unreactive contaminations to make 100 reactive pozzolana. Such a product, white or cream in colour, purified, thermally actuated is called High Reactive Metakaolin( HRM). iv. High reactive metakaolin shows high pozzolanic reactivity and reduction in Ca( OH) 2 ever as beforehand as one day. 6. Ground Granulated Blast Furnace Sediment( GGBS) Ground granulated blast- furnace sediment is another important mineral amalgamation like cover ash a nonmetallic product conforming basically of silicates and aluminates of calcium and other bases. ii. The molten sediment is fleetly stupefied by quenching in water to form a glassy beach like grained material. iii. The grained material when farther ground to lower than 45 micron will have specific face of about 400 to 600 m2/ kg( Blaine).