Que2.17. What’s ground granulated blast furnace sediment( GGBS)? What are its benefits and also write down the chemical composition of the sediment GGBS.
Answer Ground Granulated Blast Furnace Sediment( GGBS) 1. The blast furnace sediment is a derivate of the iron manufacturing assiduity. Iron ore, coke and limestone are fed into the furnace and the performing molten sediment floats above the molten iron at a temperature of about 1500 °C to 1600 °C. 2. The molten sediment has a composition of about 30 to 40 SiO2 and about 40 CaO, which is close to the chemical composition of Portland cement. Benefits of GGBS in Concrete 1. Heat of Hydration Gradational hydration of GGBS with cement generates lower heat than Portland cement. This reduces thermal slants in the concrete. 2. Water Demand GGBS is a glassy material and its smoother face requires lower water to adequately cover the patches. 3. Setting Time Increased setting time may be profitable in extending the time for which the concrete remains workable and, may reduce the threat of cold joints. 4. Appearance GGBS cement also produces a smoother, more disfigurement free face, due to the fineness of the GGBS patches. ii. GGBS is effective in precluding efflorescence when used at relief situations of 50 to 60. 5. Bleeding GGBS reduce bleeding than that of Portland cement and thus reduces threat of delaminations. 6. Workability GGBS patches are less water absorptive than Portland cement patches and therefore GGBS concrete is more workable than Portland cement concrete. For original plasticity, a reduction in water content of over to 10 is possible. 7. Sulphate Resistance GGBS is a sulphate- defying, specifying GGBS at 50-70 content gives optimum protection against sulphate attack. 8. Alkali Aggregate response( AAR) GGBS reduce the injurious effect of AAR due to its low reactive alkali content and its capability to inhibit AAR.
Que2.18. What are the goods of using GGBS in concrete?
Answer goods of GGBS on the parcels of Fresh Concrete 1. The cementitious material containing GGBS displayed lesser plasticity due to the increased paste content and increased cohesiveness of the paste. 2. generally, an increase in time of setting can be anticipated when GGBS is used as relief for part of the Portland cement in concrete fusions. 3. GGBS is finer than the Portland cement and is substituted on an equalmass base, bleeding is reduced; . When the GGBS is coarser, the rate and quantum of bleeding may increase. goods of GGBS on the parcels of Hardened Concrete 1. drop strength and rate of strength gain. 2. Increase the resistance to freezing and thawing. 3. Increase the resistance to deicing chemicals. 4. Increase the resistance to the erosion of underpinning. 5. Reduction of expansion due to alkali- silica response( ASR). 6. Increase the resistance to sulfate attack. 7. Reduce the permeability.
Que2.19. What’s the use of GGBS in concrete?
Answer Following are the uses of GGBS in concrete 1. GGBS is used to make durable concrete structures in combination with ordinary Portland cement and/ or other pozzolanic accoutrements . 2. Two major uses of GGBS are in the product of quality- bettered sediment cement, videlicet Portland Blast Furnace Cement( PBFC) and High- Sediment Blast- Furnace Cement( HSBFC), with GGBS content ranging generally from 30 to 70; and in the product of ready-mixed or point- batched durable concrete.
Que2.20. Describe the metakaolin. bandy the advantages and disadvantages of metakaolin.
Answer Metakaolin 1. Metakaolin is an amalgamation used as an partial relief of cement in HSC( high strength concrete). 2. A concrete is said to be high strength concrete if its compressive strength is further than 40MPa. 3. Metakaolin is prepared by calcination of humus( complexion mineral) at an temperature of 650- 800ºC. It has pozzolanic parcels. 4. Chemical formula of Metakaolin is Al2O3.2 SiO2.2 H2O 5. It reacts with Ca( OH) 2 one of the by- products of hydration response of cement and results in fresh C- S- H gel which results in increased strength. Advantages of Metakaolin Following are the advantages of metakaolin 1. Strength and continuity of concrete increases. 2. Accelerates original setting time of concrete. 3. Compressive strength of concrete increases by 20. 4. Cross section of structure can be reduced safely i.e., quantum of concrete used can be reduced. 5. Reduces loss in concrete. 6. Eco-friendly by reducing quantum of CO2 emigration. 7. Reduces heat of hydration leading to loss and crack control. Disadvantages of Metakaolin Following are the disadvantages of metakaolin 1. Increased cost price. 2. Advanced water rate. 3. Plasticity. 4. fresh raw material. 5. At low addition rate increase loss.
Que3.1. What do you mean by ‘ blend design ’ in concrete? Explain its types and objects.
Answer Concrete Mix Design Mix Design is the wisdom of determining the relative proportions of the constituents of concrete to achieve the asked parcels in the most provident way. Types of composites Following are the types of mixes 1. Nominal composites In the specifications for concrete specified the proportions of cement, fine and coarse summations. These composites of fixed cement total rate which ensures acceptable strength are nominated nominal mixes 2. Standard Mixes IS456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40. In this designation the letter M refers to the blend and the number to the specified 28 day cell strength of blend in N/ mm2. 3. Design Mixes In these mixes the performance of the concrete is specified by the developer but the blend proportions are determined by the patron of concrete, except that the minimal cement content can be laid down ideal of Mix Design Following are the ideal of blend design 1. To achieve the designed/ wanted plasticity in the plastic stage. 2. To achieve the asked minimum strength in the toughened stage. 3. To achieve the asked continuity in the given terrain conditions. 4. To produce concrete as economically as possible.
Que3.2. What are the colorful principles of proportioning of blend design?
Answer Principles of Mix Design Following are the colorful principles of blend design 1. The terrain exposure condition for the structure. 2. The grade of concrete, their characteristic strength’s and standard diversions. 3. The type of cement. 4. The types and sizes of summations and their sources of force. 5. The nominal maximum sizes of summations. 6. Maximum and minimal cement content in kg/ m3. 7. Water cement rate. 8. The degree of plasticity of concrete grounded on placing conditions. 9. Air content inclusive of detrained air. 10. The outside/ minimum viscosity of concrete. 11. The outside/ minimum temperature of fresh concrete. 12. Type of water available for mixing and curing. 13. The source of water and the contaminations present in it.
Que3.3. bandy the Abram’s water/ cement rate law and its validity. How strength of concrete is estimated by Abram’s law.
Answer Abram’s Water/ Cement rate Law 1. According to Abram’s law the strength of completely compacted concrete is equally commensurable to the water- cement rate. 2. Then the water- to- cement rate is the relative weight of the water to the cement in the admixture. For utmost operations, water- to- cement should be between0.4 and0.5, lower for lower permeability and advanced strength. Validity If not duly compacted, the concrete blend will contain large valids, which contribute to porosity. therefore, at low water/ cement rate where full contraction is hard to achieve, Abram’s law isn’t valid.
Que3.4. What are the different factors in the choice of blend proportions?
Answer Factors impacting Choice of Mix Design According to IS 4562000 and IS 13431980 following are the factor affecting the design of concrete blend 1. Grade of Concrete i. The grade of concrete gives characteristic compressive strength of concrete. ii. The grade M20 denotes characteristic compressive strength fck of 20 N/ mm2. Concrete Technology 3 – 5 D( CE- Sem- 5) iii. Depending upon the degree of control available at point, the concrete blend is to be designed for a target mean compressive strength( fck) applying suitable standard divagation. 2. Type of Cement i. The advanced the strength of cement used in concrete, lower will be the cement content. ii. The use of 43 grade and 53 grade of cement, gives saving in cement consumption as much as 15 and 25 independently, as compared to 33 grade of cement. 3. Maximum Nominal Size of summations It’s designated by the sieve size advanced than larger size on which 15 or further of the total is retained. ii. The maximum nominal size of total shouldn’t be further than one- fourth of minimal consistence of the member. iii. For heavily corroborated concrete members as in the case of caricatures of main shafts, the nominal outside size of the total should generally be confined to sum lower than the minimum clear distance between the main bars or 5 mm less the minimal cover to the underpinning, whoever is lower. 4. Grading of Combined summations i. The relative proportions of the fine and coarse total in a concrete blend is one of the important factors affecting the strength of concrete. ii. For thick concrete, it’s essential that the fine and coarse total be well canted. 5. Maximum Water/ Cement rate The lower the water/ cement rate, the lesser is the compressive strength. 6. Plasticity Plasticity of fresh concrete determines the case with which a concrete admixture can be mixed, transported, placed, compacted and finished without dangerous isolation and bleeding. 7. continuity continuity bear low water/ cement rate. ii. It’s generally achieved not by adding the cement content, but by lowering the water demands at given cement content. iii. Water demand can be lowered by through control of the total grading and by using water reducing cocktails.