C T: Mechanical Properties of Concrete Unit 4 Part 5

Que4.21. What are the conditions of non destructive testing of  concrete? Also give their advantages and disadvantages. 

Answer  demand of Non Destructive Test Following are the  demand  of NDT 

1. Assessment of being structures in the absence of  delineations. 

2. Quick assessment of the structure. 

3. Quality control of construction, in situ. 

4. Determining position of  underpinning. 

5. position of cracks joints honeycombing. 

6. In some cases, it  needed to assess of concrete damaged due to fire or  any other natural  disaster due judge the condition of structure. 

Advantages Following are the advantages of non destructive testing 

1. Access to  retired  particulars- “ see through walls ”. 

2. More  examinations with NDT. 

3. Rapid and on  point accumulation of data. 

4. Generally less  precious than destructive testing. 

5. Gives result without structural damage. 

Disadvantages Following are the disadvantages of non destructive  testing 

1. further than one test  system may be  needed. 

2. Environmental conditions may affect or distort results. 

3. Construction details and  structure  factors may affect results. 

4. Some conditions can not be determined with a reasonable degree of   delicacy without destructive testing. 

Que4.22. What’s modulus of pliantness of concrete? With the help  of stress- strain  wind, describe the  colorful types of modulus of  pliantness? 

Answer  Modulus of Pliantness of Concrete It’s defined as the  pitch of the  line drawn from a stress of zero to a compressive stress of0.45 fc. 

Types of Modulus of Pliantness 

1. original digression Modulus It’s given by the  pitch of a line drawn   digression to the stress- strain  wind at the origin. It’s used to characterize  concrete  deviation at  veritably low stresses.  

Que4.23. What are the affecting factors of modulus of pliantness of  concrete? 

Answer  Following are the factor affecting the modulus of pliantness of concrete 

1. Coarse Aggregate parcels Coarse  total  parcels like elastic  modulus of  total, type of  total( crushed or natural), petrology  and mineralogy, and  volume of  total. The advanced the volume of   total in the  blend, the advanced the elastic modulus. 

2. Mix Design Mix design includes total cementitious content and w/ c   rate. lower paste is good for advanced elastic modulus. 

3. Curing Conditions wettish cured  instance showed better results  than that of dry cured, due to  loss and associated cracks. 

4. Loading Rate High  lading rate will affect in advanced compressive  strength and advanced elastic modulus. 

5. Chemical amalgamation It doesn’t have  important influence on elastic  modulus. But some type of  amalgamation can produce advanced cement  dissipation and  therefore will affect in advanced compressive strength and elastic  modulus. 

6. Mineral Admixture Mineral  amalgamation as they affect the strength of  concrete, they affect the elastic modulus too. 

Que4.24. bandy the relationship between modulus of pliantness  and strength concrete. 

Answer  Relation between Modulus of Pliantness and Strength of  Concrete 

1. Modulus of pliantness of concrete is a  crucial factor for estimating the   distortion of structural  rudiments, as well as a abecedarian factor for  determining modular  rate, n, which is used for the design of structural  members  subordinated to flexure. 

2. The modulus of pliantness of concrete is directly commensurable to the square  root of characteristic compressive strength in the range of normal  concrete strength, . The IS 456 2000 gives the modulus of pliantness of concrete as  

Que4.26. What’s creep? What are the factors  impacting creep of  concrete? 

Answer  Creep 

1. When concrete is  subordinated to compressive  lading it deforms   presently. This immediate  distortion is called immediate  strain. Now, if the  cargo is maintained for a considerable period of time,  concrete undergoes  fresh  distortions indeed without any increase  in the  cargo. This time-dependent strain is  nominated as creep. 

Factor Affecting Creep Following are the factors affecting creep of  concrete 

1. Concrete Mix Proportion  Creep increases with increase in water/ cement  rate. 

ii. A poorer paste structure undergoes advanced creep.

  iii. The  quantum of paste content and its quality is one of the most important  factors  impacting creep.

 iv. Creep is equally commensurable to the strength of concrete. 

2. Aggregate Properties  Light weight  total shows  mainly advanced creep than normal  weight  total.

 ii. The advanced the modulus of pliantness the  lower is the creep.  iii. summations  impact creep of concrete through a restraining effect on  the magnitude of creep. 

3. Age at Loading  Age at which a concrete member is loaded will have a predominant  effect on the magnitude of creep.  ii. The  humidity content of the concrete being different at different age  also influences the magnitude of creep. 

4. Curing Condition Larger the curing  lower the creep. 

5. Cement Properties  i. The type of cement  goods creep in so far as it influences the strength of  the concrete at the time of  operation of  cargo. 

ii. Fineness of cement affects the strength development at early  periods and   therefore influences creep. 

iii. The finer the cement the advanced its gypsum  demand so that re  grinding of cement in laboratory without the addition of gypsum produces  an  inaptly retarded cement, which exhibits high creep. 

6 Temperature  i. The rate of creep increases with temperature over to about 70 °C when,  for a 17  blend and0.6 w/ c  rate. It’s  roughly3.5 times advanced than  at 21 °C.  ii. Between 70 °C and 96 °C it drops off to1.7 times than at 21 °C. 

iii. As far as low temperature is concerned,  indurating produces a advanced   original rate of creep but it  snappily drops to zero. 

iv. At temperature between 10 °C and 30 °C, creep is about one half of  creep at 21 °C. 

7. Stress position  Advanced the stress advanced will be the creep.  ii. There’s no lower limit of proportionality because concrete undergoes  creep indeed at  veritably low stress.  

Que4.27. What’s the effect of creep on concrete structures? 

Answer  goods of Creep on Concrete Structures 

1. In  corroborated concrete  shafts, creep increases the  deviation with time  and may be a critical consideration in design. 

2. In eccentrically loaded columns, creep increases the  deviation and can  lead to buckling. 

3. Loss of prestress due to creep of concrete in prestressed concrete structure. 

4. Creep property of concrete will be useful in all concrete structures to  reduce the internal stresses due tonon-uniform  cargo or  subdued   loss. 

5. In mass concrete structures  similar as  heads, on account of  discrimination  temperature conditions at the interior and  face, creep is  dangerous and  by itself may be a cause of cracking in the innards of  heads.

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