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?
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.