Concrete Technology: Concrete Production, Properties and Testing Unit 4 Part 6

Que4.32. What do you mean by Poisson’s  rate of concrete. 

Answer  Poisson’s  rate  1. It’s determined as the  rate of side to longitudinal strain in   contraction test and may vary from0.13 to0.21. 

2. The Poisson’s  rate can also be determined from the abecedarian   reverberative  frequence of longitudinal vibration of concrete  instance using  ultrasonic  palpitation  haste  system. 

3. The Poisson’s  rate can be determined from  Concrete Technology 4 – 29 D( CE- Sem- 5)  v2  2nL    =   1)  1 2)( 1)    where, v =  palpitation  haste, mm/ sec  n =  reverberative  frequence of longitudinal vibration in Hz  L =  Distance between transducers, mm . The value of Poisson’s  rate as determined by dynamic tests is slightly  advanced and ranges from0.20 to0.25. 

Que4.33. Define  continuity of concrete. bandy the factor affecting  concrete  continuity. 

Answer  continuity 

1. The  continuity of concrete is defined as its capability to  repel riding   action, chemical attack, bruise, or any other process of deterioration. 

2. Durable concrete will retain its original form, quality, and  utility  when exposed to  terrain.  Factors Affecting continuity Following are the factors affecting the   continuity of concrete 

1. Physical Factors  Temperature  Unfavourable temperature conditions can lead to  loss cracks  and volume changes.  Variation in temperature changes beget secondary stresses in  structures. 

ii. humidity  humidity induces  erosion in  sword. humidity also acts as a carrier  of chemicals inside the body of concrete.  humidity can also beget efflorescence on structural  shells.  Seepage/ Leakages beget  vexation to  inhabitants and  deteriorates structures due to passable concrete.  iii. indurating and Deliquescing Leads to expansion of concrete and cracking. 

2. Chemical Factors 

i. When we’re dealing with  continuity, chemical attack which results in  volume change, cracking and consequent deterioration of concrete  come a major cause of concern. 

ii. Ice- melting  mariners beget  corrosion of concrete. 

3. Cement Content and w/ c rate of Concrete Volume change affect  in cracks and cracks are responsible for decomposition of concrete. Workmanship Batching, mixing, transportation, placing,  contraction  and curing bear proper workmanship for a durable concrete. 

5. Cover to Bedded sword( As per IS 4562000)  i. For main  underpinning up to 12 mm dia bar for mild exposures, the  nominal cover may be reduced by 5 mm  ii. Unless specified  else,  factual concrete cover shouldn’t  diverge  from the  needed nominal cover by 10 mm. 

6. Mineral Oil  generally  goods only fresh concrete in their hardening  process( petrol, petroleum distillates etc) . Organic acid has  sharp effect. 

8. Vegetable and beast canvases  and fats beget deterioration of concrete   shells due to their  sharp action. 

9. Action of sugar has braking effect on fresh concrete and has gradational   sharp effect on hardened concrete. 

10. Action of Sewage Concrete seamsters running full remain  innocent;  but in  incompletely filled seamsters where hydrogen sulphide gas is evolved and  sulphuric acid is formed, concrete above sewage  position gets affected due  to  sharp action of  similar acids.   Que5.1. What do you understand by high strength concrete?  Write down its advantages and disadvantages.  Answer  High Strength Concrete For  fusions made with normal- weight   summations, high- strength concretes are considered to be those which  have compressive strengths in excess of 40 MPa.  Advantages of HSC  1. High compressive strength. 

2. Increases rental space. 

3. Reduces space  enthralled by columns. 

4. Reduces dead  cargo.  5. Reduces  quantum of  sword. 

6. High rise  structures can be  make by reduced columns. 

7. To use the concrete service at early age,e.g., pavement in 3 days C. Disadvantages of HSC 

1. Must be  moxie in selection of  constituents. 

2. Damaged at high temperature i.e.,  lower resistance to fire. 

Que5.2. bandy the guidelines to selection of accoutrements  for HSC. 

Answer  1. For the advanced target compressive strength of concrete, the  outside  size of concrete  named should be small, so that the concrete can come  more  thick and compact and less void  rate.  2. Up to 70 MPa compressive strength can be produced with a good coarse   total of a maximum size ranging from 20 to 28 mm. 

3. To produce 100 MPa compressive strength  total with a maximum  size of 10 to 20 mm should be used. 

4. Concretes with compressive strengths of over 125 MPa have been  produced with 10 to 14 mm  outside size coarse  total. 

5. Using supplementary cementitious accoutrements ,  similar as blast- furnace sediment,  fly ash and natural pozzolanas, not only reduces the  product cost of  concrete, but also addresses the depression loss problem. 

6. The optimum negotiation  position is  frequently determined by the loss in 12 or  24 hour strength that’s considered  respectable, given climatic conditions  or the  minimal strength  needed. 

7. While silica cloud is  generally not really necessary for compressive strengths  under 70 MPa,  utmost concrete  fusions contain it when advanced strengths  are specified. 

Que5.3. What are the  colorful  styles to achieve high strength  in concrete? Also  bandy their  operations. 

Answer  styles to Achieve High Strength in Concrete Following are the  special  styles to achieve high strength in concrete 

1. sowing This involves adding a small chance of finely ground, completely  doused  Portland cement to the fresh concrete  blend. This  system may  not hold  important  pledge. 

2. Revibration Controlled revibration removes all the  blights like  bleeding, water accumulates, plastic  loss,  nonstop capillary  channels and increases the strength of concrete. 

3. High Speed Slurry Mixing This process involves the advance  medication of cement- water admixture which is  also blended with   total to produce concrete. 

4. Use of cocktails Use of water reducing agents are known to  produce increased compressive strength. 

5. Sulphur Impregnation Satisfactory high strength concrete have  been produced by  macerating low strength  pervious concrete by sulphur.  The sulphur  sneaked  concrete has given strength up to 58 MPa. 

6. Inhibition of Cracks If the propagation of cracks is inhibited, the  strength will be advanced. Concrete  cells made this way have yielded  strength up to 105MPa. 

Applications of High Strength Concrete 

1. High strength concrete is  needed in engineering  systems that have  concrete  factors that must  repel high compressive loads. 

2. High strength concrete is  generally used in the construction of high- rise  structures.  3. It has been used in  factors  similar as columns( especially on lower   bottoms where the loads will be  topmost), shear walls, and foundations. 

4. High strengths are also  sometimes used in ground  operations as well. 

5. High strength concrete is  sometimes used in the construction of  trace  islands. 

6. Use of HSC in column section decreases the column size. 

7. Use of HSC in column decreases  quantum of  sword  needed for same  column. 

8. In high rise  structure, use of HSC increases the  bottom area for rental  purpose. 

9. In islands, use of HSC reduces the number of  shafts supporting the  arbor. 

Que5.4. What’s  tone compacting concrete? What are the   parcels, advantages and disadvantages of  tone compacting  concrete? 

Answer  tone Compacting Concrete It’s defined as “ a concrete that’s  suitable to  inflow under its own weight and  fully fill the formwork, while  maintaining unity indeed in the presence of congested   underpinning, and  also consolidate without the need for  wobbling    contraction ”.  Properties of SCC In fresh state, SCC have the following  parcels . Filling Capability Flows  fluently at certain speed into formwork. 

2. Passing Capability Passes through  underpinning without blocking. 

3. isolation Resistance The distribution of aggregate  patches  remains homogeneous in both  perpendicular and vertical direction. 

Advantages of SCC Following are the advantages of SCC 

1. A faster rate of placing, without vibration. 

2. bettered pumpability. 

3. bettered  connection around  underpinning. 

4. Reduced permeability. 

5. Reduced wear and tear and gash on forms from vibration. 

6. Improves the quality,  continuity, and  trustability of concrete structures  due to better  contraction and unity of concrete. 

7. Ease of placement results in cost savings through reduced  outfit  and labour  demand. 

8. lower noise from vibrators and reduced  peril from hand- arm vibration  pattern( HAVS). 

9. Improves working conditions and productivity in construction assiduity. 

10. Reduced construction period. 

11. Elimination of problems associated with vibration. 

Disadvantages of SCC Following are the disadvantages of SCC 

1. More  strict conditions on the selection of accoutrements . 

2. Lack of encyclopedically accepted test  norms and mix designs. 

3. premium than conventional concrete grounded on concrete material cost  exception to placement cost). 

4. Requires  further trial batches at laboratory as well as at ready-mixed  concrete  shops.  5. More precise  dimension and monitoring of the  element accoutrements . 

Que5.6. Compare the hardened  parcels of normal concrete  and  tone compacting concrete. 

Answer  Following are the comparison of  parcels between normal concrete  and  tone compacting concrete 

1. Compressive Strength The compressive strength of SCC when  compared with normal concrete made for a particular strength is  nearly  the same. The  tone- compacting property of SCC has  veritably little effect on  the strength of concrete. 

2. Tensile Strength A comparison between cylinders made of SCC  and normal concrete of the same grade shows that there’s no major  difference between them. 

3. Bond Strength The pull- out test carried out to determine the bond  strength of SCC indicates superior bond strength of SCC. 

4. Modulus of Pliantness The modulus of pliantness for SCC and for  normal concrete is the same. 

5. snap- thaw Resistance The low- strength of SCC has  lower resistance  to  snap and thaw conditions as compared with low- strength normal  concrete. 

6. Creep SCC  typically is more  doughy as compared with normal concrete.  So its creep is slightly advanced. 

7. continuity continuity is slightly advanced in SCC because of the  elimination of  crimes which may  do during placing and  contraction  of normal concrete. SCC is likely to have  lower voids. 

8. Exposure to Fire SCC has a more compact microstructure. This can  lead to high vapour pressure. So SCC has a advanced  threat of spalling  when exposed to fire.   

Que5.7. Explain the tests used for inflow  parcels of  tone  compacting concrete. 

Answer  Following are the  colorful test that carried out on  tone compacting concrete  is fresh state 

1. Depression Flow and T50 Test  Depression inflow test is used to find the  stuffing capability of the SCC. 

ii. The SCC sample is poured in to the depression cone  also the depression inflow  periphery is measured. 

iii. The inflow time is measured and is known as T50 depression time. 

iv. The advanced the depression inflow value, the lesser its capability to fill formwork  under its own weight. 

2. L- Box Test 

i. The L- box test is used to find the  end capability of SCC. 

ii. The SCC sample is poured in to the L- box  outfit, now the plate is  removed to allow inflow. 

iii. The L- box  rate is calculated as H2/ H1. 

iv. When the  rate of H2 to H1 is larger than0.8,  tone compacting concrete  has good passing capability. 

3. V- Funnel Test and V- Funnel Test at T- 5 twinkles 

i. The V-  channel test is used to find the  isolation resistance of SCC. 

ii. The SCC sample is poured in to the V-  channel  outfit, now it’s allowed  to inflow by its weight. 

iii. The  evacuating time of V-  channel is noted. 

iv. This test measured the ease of inflow of the concrete, shorter inflow times  indicate lesser inflow capability. After 5  twinkles of setting,  isolation of  concrete will show a  lower  nonstop inflow with an increase in inflow time

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