Concrete Technology: Mix Design and Rhealogy of Concrete Unit 3 Part 2

Que3.9. What do you mean by Rheology of fresh concrete?  Explain the parameters of Rheology.  Answer  1. Rheology It may be defined as the  wisdom of the  distortion and  inflow of accoutrements , and concerned with  connections between stress,  strain, rate of strain, and time.  2. The term rheology deals with the accoutrements  whose inflow  parcels are  more complicated than of simple fluids( liquids or  feasts).  Parameters of Rheology Following are the parameter of rheology  1. Stability  It’s defined as a condition in which the aggregate  patches are held in  homogeneous  dissipation by matrix, and  arbitrary  slice shows the  same  flyspeck size distribution during transportation, placing and   contraction.  ii. The stability of concrete is measured by its  isolation and bleeding  characteristics.  2. Mobility  i. The mobility of fresh concrete is its capability to flow under  instigation  transfer, i.e., under mechanical stresses. The inflow is  confined by  cohesive,  thick and frictional forces.  ii. The cohesive force develops due to adhesion between the matrix and  aggregate  patches. It provides tensile strength of fresh concrete that  resists  isolation.  iii. The  density of the matrix contributes to the ease with which the  aggregate  patches can move and rearrange themselves within the  matrix.  iv. The internal  disunion occurs when a admixture is displaced and the  aggregate  patches  restate and rotate.  v. The resistance to  distortion depends on the shape and texture of the   total, the  uproariousness of the admixture, the water- cement  rate, and  the type of cement used.  3. Compactability  i. It measures the ease with which fresh concrete is compacted.  ii. Compacting  correspond of expelling  entangled air and  displacing the  aggregate  patches in a  thick mass without causing  isolation.  iii. Compactability is measured by the compacting factor test.    Que3.10. Describe the Bingham model of Rheology of fresh  concrete.  Answer  1. The inflow  geste

of fresh concrete doesn’t conform to Newtonian  liquid.  2. The  rate of shear stress to shear rate isn’t constant but depends upon  the shear rate at which it’s measured, and may also depend on the  shear history of the concrete sample being delved .  3. still, at low shear rates that are important in practice, the   geste

             can be represented by a straight line which doesn’t pass  through- the origin, i.e., which has an intercept on the stress axis.  4. The intercept indicates the minimum stress below which no inflow occurs.  5. The fact that concrete can stand in a pile( as in the case of the depression  test) suggests that there’s some minimum stress necessary for inflow to   do at all.  6. The minimum stress is called yield stress and designated by the symbol  0. therefore the simplest inflow equation of concrete illustrated in 3.10.1 can be written as  Rate of shear,  trial point  Alternate  trial  point  needed  to fix the line 2  1  =  0  pitch =  1/  0 Shear stress, Fig.3.10.1. Bingham model.  =  0  where, 0 =  Yield value indicating the cohesion of the  material.  =  Constant having the  confines of  density  and  nominated plastic  density.  7. This  fine relationship is called the Bingham model.  8. Bingham model relates the shear stress of the material expressed in  terms of its cohesion to plastic  density, and the rate at which the  shear  cargo is applied.  9. To establish a straight line, at least two points are  needed. Consequently,  the plasticity of concrete can not be defined by the single- point tests  that determine only one parameter, i.e., produce only single point, and   thus have to be used in combination with other tests to achieve a  better understanding of concrete rheology.  10. For  illustration, the Vee- Bee test can be used with compacting factor test  to measure mobility and compactability.   Que3.11. Explain the affective factors of rheological  parcels  of concrete.  Answer  Following are the affecting factors of rheological  parcels of concrete  1. Mix Proportion A concrete  blend having an  redundant  quantum of coarse   total will warrant sufficient mortar to fill the void system, performing in  a loss of cohesion and mobility.  2. thickness The  thickness of concrete, as measured by the depression  test, is an  index of the relative water content in the concrete  blend.  3. Hardening and harshening  Elevated temperature, use of  rapid-fire- hardening cement, cement deficient  in gypsum, and use of accelerating  cocktails, increase the rate of  hardening which reduces the mobility of concrete.  ii. The dry and  pervious  total will  fleetly reduce plasticity by   gripping water from the admixture or  adding  the  face area to be  bathe.  4. Aggregate Shape and Texture  i. The rough and  largely angular  total  patches will affect in advanced  chance of voids being filled by mortar,  taking advanced fine  aggregate contents and  similarly advanced water content.  ii. also, an angular fine  total will increase internal  disunion in  the concrete admixture and bear advanced water content than  well- rounded natural beach.  5. Aggregate Grading A well- graded  total gives good plasticity.  These  goods are lesser in the fine  total than in coarse  total.  6. Maximum Aggregate Size An increase in the maximum size of   total will reduce the fine  total content  needed to maintain a  given plasticity, and will thereby reduce the  face area to be bathe.  7. cocktails The  cocktails which have significant effect on the  rheology of concrete are plasticizers andsuper-plasticizers, airentraining  agents, accelerators and retarders.  Que3.12. Describe the effect of rheological  parcels on different  types of concrete.  Answer  Effect of Rheological parcels on Different Types of Concrete.  1. Different types of concrete Fig.3.12.1 shows the three- dimensional relationship between different  types of concrete and the rheological parameters.  For illustration  Compared to reference concrete, a wet concrete can be produced by   dwindling both yield stress and plastic  density, whereas a stiffer  concrete can be produced by  adding  the yield stress.  ii. originally, addition of silica cloud decreases  density( fine  flyspeck content  increases the inflow), whereas advanced lozenge increases the yield stress  as well as  density.  2. Different Complements The effect of air, water, and other mineral   cocktails on rheological parameters of concrete is shown in  3. Rheological parcels of Different Concretes  Shear yield stress of  tone- compacting concrete is in the range of 0- 50  Pa, whereas for normal concrete it’s high in the range of 100- 300 Pa as  shown inFig.3.12.3.  ii. Plastic  density of normal concrete is in the range of 0- 40 Pa-s.  iii. still, plastic  density for  tone- compacting concrete is fairly high  having a range of 50- 90 Pa-s.  Answer  1. Target Mean Strength  Characteristic strength fck =  45  Target mean strength, f ck =  fck1.65 × =  451.65 × 5 = 53.25 N/ mm2  Where is the standard  divagation taken as 5 N/ mm2.  2. Water/ Cement rate  Water/ Cement  rate is taken from the experience of the  blend  developer  grounded on his experience of  analogous work away.  W/ C  rate = 0.42  ii. This water cement  rate is to be  named both from strength  consideration and maximum w c denoted in Table 5 of IS 456 and   lower of the two is to be  espoused  continuity  demand.  iii. W/ C proposed is0.42. This being  lower than0.45, we should borrow  W/ C  rate as0.42.  3. Selection of Water Content  Maximum water content as per table3.8.3 is 186 litre. This is for 50 mm  depression.  ii. Estimated water content for 125 mm depression  =  186 ×  9  100  186 203 litre  3 increase for every 25 mm depression over and above 50 mm depression)  iii. Really speaking separate trials are  needed to be done to find out the   effectiveness of plasticizers.  iv. In the absence of  similar trial, it’s assumed that the  effectiveness of super  plasticizer used 25 percent. thus  factual water to be used  =  203 ×0.75 152 litre.  4. computation of Cement Content  W/ C  rate = 0.42  Water used =  152 litre  ii. Cement content =   W  C  = 0.42  C =   152   =  362 kg/ m3  iii. This cement content is to be checked against  minimal cement content  given in table 5 of IS 456 for  continuity  demand.  Mix Design & Rhealogy of Concrete 3 – 20 D( CE- Sem- 5)  iv. As the calculated cement 362 kg/ m3 is  further than  minimal cement  mentioned in table 5 of IS 456 i.e., 320 kg/ m3, the cement content of  kg/ m3 should be accepted. Borrow cement content of 362 kg/ m3.  5. computation of Coarse and Fine Aggregate Content  i. From Table3.8.5 volume of coarse  total corresponding to 20 mm  size  total and fine  total zone II, for w/ c  rate of0.50 is  set up  out to be0.62.  ii. In the present case w/ c0.42 i.e., it’s  lower by0.08. As the w/ c is reduced  it is desirable to increase the coarse  total proportion to reduce the  fine  total content.  iii. The coarse  total is increased at the rate of0.01 for every  drop  in w/ c  rate of0.05.     ×0.08 = 0.016  Volume of CA = 0.62 =     iv. Corrected proportion of volume of CA = 0.636  Since it’s angular  total and the concrete is to be pumped, the  coarse  total can be reduced by 10.  Final volume of coarse  total  = 0.636 ×0.9 = 0.572 say0.57  vi. Volume of fine  total = 0.43  6. computation of Mix Proportions  Volume of concrete =  1 m3  ii. Absolute volume of cement =  362 1  1000  m3 = 0.115 m3  iii. Volume of water =  152 litre = 0.152 m3  iv. Volume of chemical  amalgamation  =   362 1 3621.2  1001.1 10001101000  Assuming lozenge of1.2 by weight of cementitious material and  assuming specific  graveness of  amalgamation as1.1.)  Absolute volume of all the accoutrements  except total  summations  = 0.1150.1520.004 = 0.271 m3  vi. Absolute volume of total aggregate  =  1 –0.271 = 0.729 m3  vii. Weight of coarse  total  = 0.729 ×0.57 ×2.80 × 1000 1163 kg/ m3  viii. Weight of fine  total  = 0.729 ×0.43 ×2.70 x 1000 846 kg/ m3  7. Mix Proportions for Trial Number 1  Cement 362 kg/ m3  Water 152 kg/ m3  Fine  total 846 kg/ m3  Coarse  total 1163 kg/ m3  Concrete Technology 3 – 21 D( CE- Sem- 5)  Chemical  amalgamation 4 kg/ m3  Wet  viscosity of concrete 2527 kg/ m3  w/ c  rate0.42  8. point Correction  immersion of fine  total = 1.0  iii. Total  immersion = 14.28 litres  iv. factual  quantum of water to be used =  15214.28 = 166.28 litres  factual weight of FA to be used =  846 –8.46 = 837.5 kg/ m3  vi. factual weight of CA to be used =  1163 –5.82 = 1157.20 kg/ m3  vii. Proportion of accoutrements  at the  point  Cement 362 kg/ m3  Water166.28 kg/ m2  CA1157.2 kg/ m3  FA837.5 kg/ m3  amalgamation4.0 kg/ m3  viii. With the below proportion of accoutrements  carry out trial  blend number- 1  and see the quality of concrete. , 3 and 4 as indicated  If it isn’t satisfactory carry out trial  blend number 2.  before under trial mixes. Arrive at the final proportions of concrete   blend to satisfy the  needed parameters.

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