C T: Shrinkage and Durability of Concrete Unit 4 Part 6

Que4.29. What’s  loss of concrete? Explain about  bracket of  loss. 

Answer  loss 

1. loss of concrete is the time-dependent strain measured in an  disburdened and unrestrained  instance at constant temperature. 

2. loss is shortening of concrete due to drying and is independent of  applied loads. 

Types of Shrinkage Following are the  colorful types of  loss 

1. Plastic loss  Plastic  loss occurs  veritably soon after pouring the concrete in the  forms.  ii. The hydration of cement results in a reduction in the volume of concrete  due to evaporation from the  face of concrete, which leads to cracking. 

2. Drying loss  i. The  loss that appears after the setting and hardening of the  concrete admixture due to loss of capillary water is known as drying   loss.  ii. Drying  loss generally occurs in the first many months and decreases  with time. 

3. Carbonation loss  Carbonation  loss occurs due to the  response of carbon dioxide  CO2) with the doused  cement minerals, carbonating Ca( OH) 2 to  CaCO3.  ii. The carbonation  sluggishly penetrates the  external  face of the concrete.  iii. This type of  loss  substantially occurs at medium  moisture and results  increased strength and reduced permeability. 

4. Autogenous loss  Autogenous  loss occurs due to no  humidity movement from  concrete paste under constant temperature.  ii. It’s a minor problem of concrete and can be ignored.  

Que4.30. What are the different factors affecting of  loss.

 Answer  Affecting Factors of loss 

1. Drying Conditions  i. The most important factor is the drying condition or the  moisture in the  atmosphere.  ii. No  loss will  do if the concrete is placed in one hundred percent  relative  moisture. 

2. Time  i. The  loss rate will  drop  fleetly with time.  ii. It has been  proved that 14 to 34 of the 20 time  loss will   do within two weeks of it being poured.  iii. Within one time of the concrete being poured,  loss will be about  to 85 of the 20 time  loss. 

3. Water Cement rate  i. The water to cement  rate will  impact the  quantum of  loss that  occurs.  ii. The concrete’s  uproariousness also affects the  loss.  iii. The process of swelling and  also drying affects the concrete’s integrity  and the  loss.  

Que4.31. What are the effect of  loss on concrete and how is  it reduces? 

Answer  goods of Shrinkage Following are the  goods of  loss on concrete 

1. loss of concrete between movement joints causes joints to open  or makes it wider. thus joints must be designed to accommodate  the widening caused by  loss. 

2. Where other accoutrements ,  similar as ceramic penstocks, are fixed on top of concrete   face,  loss of the concrete causes relative movement between  the different accoutrements . The performing stresses can beget failure at the  interface. 

3. still, the concrete is put into pressure and when  If  loss isrestrained.tensile stress becomes equal to tensile strength, the concrete cracks. 

4. loss of the concrete causes the concrete to grip  buttressing bars  more tightly. This increases  disunion between concrete and  sword and so  improves bond strength, especially for plain bars . The  deviation of flexural members is increased by  loss. This is  because the  smoothly  corroborated  contraction zone is free to shrink  further  than heavily  corroborated pressure zone. 

6. loss causes a reduction in pre stressing force. 

Prevention of Shrinkage Following are the measures to be taken to  reduced  loss 

1. give sun  tones in case of arbor construction to control the  face  temperature. 

2. Dampen the subgrade of concrete before placement it’s liable to water   immersion but shouldn’t over damp. 

3. Try to start the curing soon after finishing. 

4. Use chemical  cocktails to accelerate the setting time of concrete.  

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. 

4. 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

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