Concrete Technology: Chemical and Mineral Admixtures Unit 2 Part 3

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.

Leave a Comment