Concrete Technology: Mix Design and Rhealogy of Concrete Unit 3 Part 1

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.  Expression  According to Abram’s law, compressive strength can be expressed as  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.  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.    Que3.5. Write short note on quality control of concrete.  Answer  1. The strength of concrete varies from batch to batch over a period of  time.  2. The sources of variability in the strength of concrete may be considered  due to variation in the quality of the  element accoutrements , variations  in  blend proportions due to batching process, variations in the quality of  batching and mixing  outfit available, the quality of supervision  and workmanship.  3. These variations are  ineluctable during  product to varying degrees.  4. Controlling these variations is important in lowering the difference  between the  minimal strength and characteristic mean strength of  the  blend and hence reducing the cement content.  5. The factor controlling this difference is quality control.  6. The degree of control is eventually  estimated by the variation in test  results  generally expressed in terms of the measure of variation   Que3.6. bandy the statistical quality control of concrete.  Explain common  language used in statistical quality control of  concrete.  Answer  Statistical Quality Control of Concrete  1. Statistical quality control  system provides a scientific approach to the  concrete  developer to understand the realistic variability of the accoutrements   so as to lay down design specifications with proper forbearance to  feed  for  necessary variations.  2. The acceptance criteria are grounded on statistical evaluation of the test  result of samples taken at  arbitrary during  prosecution. By  contriving a  proper  slice plan it’s possible to  insure a certain quality at a  specified rise.  3. therefore the  system provides a scientific base of acceptance when is not  only realistic but also restrictive as  needed by the design conditions  for the concrete construction.  Common language The common  languages that are used  in the statistical quality control of concrete.  1. Mean Strength This is the average strength  attained by dividing  the sum of strength of all the  cells by the number of  cells.   Que3.7. Step by step explain the American Concrete Institute   system of  blend design.  Answer  Following are the  way in American Concrete Institute  system  1. Data to be Collected  Fineness modulus of  named fine  total.  ii. Unit weight of dry rodded coarse  total.  iii. Specific  graveness of coarse and fine  summations in SSD condition  iv. immersion characteristics of both coarse and fine  summations.  Specific  graveness of cement.  2. From the  minimal strength specified, estimate the average design  strength by using standard  divagation.  3. Find the water/ cement  rate from the strength and  continuity points of  view. Borrow the lower value.  4. Decide the maximum size of  total to be used. Generally for RCC  work 20 mm andpre-stressed concrete 10 mm size are used.  5. Decide plasticity in terms of depression for the given job.  6. The total water in kg/ m3 of concrete is determined, corresponding to  the  named depression and  named maximum size of  total.  7. Cement content is  reckoned by dividing the total water content by the  water/ cement  rate.  8. elect the bulk volume of dry rodded coarse  total per unit volume  of concrete, for the particular maximum size of coarse  total and  fineness modulus of fine  total.  9. The weight of CA per boxy  cadence of concrete is calculated by multiplying  the bulk volume with bulk  viscosity.  10. The solid volume of coarse  total in one boxy  cadence of concrete is  calculated by knowing the specific  graveness of CA.  11. also the solid volume of cement, water and volume of air is  calculated in one boxy  cadence of concrete.  12. The solid volume of FA is  reckoned by abating from the total  volume of concrete the solid volume of cement, CA, water and  entangled  air.  13. Weight of fine  total is calculated by multiplying the solid volume  of fine  total by specific  graveness of FA.

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