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

Que4.14. Explain maturity conception of concrete.  Answer  Maturity of Concrete  1. The strength of concrete depends on both the period of curing( i.e. age)  and temperature during curing, the strength can be  imaged as a  function of period and temperature of curing.  2. The maturity of concrete is defined as the  totality of product of time  and temperature.  Maturity = ( Time × Temperature)  3. Its units are °C hr or °C days.  4. A sample of concrete cured at 18 °C for 28 days is taken to be completely   progressed which is equal to  M28 days =  28 × 24( 18 –( – 11)) =  19488 °C hr.  5. The temperature is reckoned from – 11 °C as origin in the  calculation  of maturity, since hydration continues to take place up to about this  temperature.  Que4.15. The strength of a sample of completely  progressed concrete is   set up to be 40MPa. Find the strength of identical concrete at the age  of 7 days when cured at an average temperature during day time at  20 °C and night time at 10 °C. Take A =  32, B =  54. Use of strength of  concrete at maturity =  A B log10  Maturity.  Answer  Given Strength of  progressed concrete =  40 MPa, A =  32 and B =  45  To Find Strength of concrete the age of 7 days.  1. Maturity of concrete at the age of 7 days  = ( Time × Temperature)  =  7 × 12 ×( 20 –( – 11)) 7 × 12 ×( 10 –( – 11))  =  7 × 12 × 31 7 × 12 × 21  =  4368 °C-h.  2. The chance strength of concrete at maturity of 4368 °C-h.  =  A B log10  Maturity)  1000  =  32 54 × log10  4368  1000    = 66.5  3. The strength at 7 days = 40.0 ×   100  = 26.5 MPa   Que4.17. Explain the  colorful types of tests for compressive  strength and tensile strength of concrete.  Answer  Following are the  colorful test used for determining compressive and  tensile strength  1. In accelerated curing  compressive strength of a  concrete  blend is determined  by curing concrete  cells for  about 28 hrs.  2. In accelerated curing  temperature of curing water  is raised.  3. Carbonation depth under  accelerated curing is advanced.  In normal curing compressive  strength of a concrete  blend is  determined by curing concrete   cells for 28 days.  In normal curing temperature of  curing water is normal.  Carbonation depth under normal  curing is lower.  1. Concrete cell Test  Concrete  specific is determined by characteristics compressive   cell strength test of concrete.  ii. For  cell test two types of  samples either  cells of 15 cm × 15 cm × 15 cm  or 10 cm × 10 cm × 10 cm depending upon the size of  total are used.  iii. For  utmost of the  workshop boxy moulds of size 15 cm × 15 cm × 15 cm are  generally used.  iv. These  samples are tested by  contraction testing machine after  7 days curing or 28 days curing.  cargo should be applied gradationally at the rate of 140 kg/ cm2 per  nanosecond till  the  samples fails.  2. Tensile Strength Test  i. The concrete structures are  largely vulnerable to tensile cracking and  hence the determination of tensile strength of concrete is  veritably  important.  ii. The tensile strength of concrete structures is determined by  Split cylinder test.  Flexure test.  3. Core Strength Test  Cylindrical cores are cut from the finished structure with a rotary  slice  tool.  ii. The core is soaked,  limited and tested in  contraction to give a measure  of the concrete strength in the  factual structure.  iii. The  rate of core height to periphery and the  position where the core is  taken affect the strength.  iv. The strength is  smallest at the top  face and increases with depth  through the element.  v. A  rate of core height- to- periphery of 2 gives a standard cylinder test.  Que4.18. Describe the flexure test and split tensile test of concrete.  Answer  Flexure Test  1. The guidelines for performing the flexure test is as per BIS 1881 Part  118 1983.  2. Then a concrete ray  instance of dimension 15 × 15 × 75 cm is loaded.  3. The span of the ray  instance must be three times the depth.  4. As shown in theFig.4.18.1 equal  cargo  operation is done at one third  distance from the end supports. The  responses are equal at the support.  5. The  nethermost ray fibre  gests  increase in stress with the increase  in  cargo  operation.  6. The increase of stress is at a rate of0.02 MPa and0.10 MPa.  7. For low strength concrete we make use of low rate and for high strength  we use high rate.  8. The theoretical  outside tensile stress at the  nethermost face at failure is  calculated. This is  nominated the modulus of rupture. It’s about1.5 times  the tensile stress determined by the splitting test.  9. Modulus of rupture is given by, . The test  instance employed is 30 cm × 15 cm which is placed over a   contraction testing machine.  3. The  cargo is applied over the  instance diametrically and slightly through  the cylinder length till the cylinder undergoes failure.  4. The failure of the cylinder will be along the periphery in  perpendicular direction.  5. Between the  instance and the  lading plates, plywood strips are placed  to avoid direct stress due to direct point of  operation.  6. The tensile stress formed with the progress of  cargo will  resolve the cylinder  into two halves. The splitting takes place along the  perpendicular aeroplane

            . This is  caused due to the  circular tensile stress.  7. Split tensile strength is given by,  ft =  2P  DL  where, ft =  Tensile strength.  P =  Compressive  cargo.  D =  Periphery of cylinder.  L =  Length of cylinder.   Que4.19. Explain the  colorful  way involved in evaluation of  compressive strength of concrete from medication to testing of  sample.  Answer  Following are the step for  cell testing  1. cell Casting  Measure the dry proportion of  constituents( cement, beach and coarse   total) as per the design conditions. The  constituents should be  sufficient enough to cast test  cells.  ii. Completely mix the dry  constituents to  gain the  invariant admixture.  iii. Add design  volume of water to the dry proportion( water- cement  rate)  and mix well to  gain  invariant texture.  iv. Fill the concrete to the mould with the help of vibrator for thorough   contraction.  Finish the top of the concrete by trowel and tapped well till the cement  slurry comes to the top of the  cells.  2. Curing  i. After some time the mould should be covered with red gunny bag and  put  unperturbed for 24 hours at a temperature of( 21 ± 2) °C.  ii. After 24 hours remove the  instance from the mould.  iii. Keep the  instance submerged under fresh water at 27 °C. The  instance  should be kept for 7 or 28 days. Every 7 days the water should be  renewed.  iv. The  instance should be removed from the water 30  twinkles  previous to  the testing.  v. The  instance should be in dry condition before conducting the testing.  vi. The  cell weight shouldn’t be  lower than8.1 kg.  3. Testing  i. Now place the concrete  cells into the testing machine( centrally).  ii. The  cells should be placed  rightly on the machine plate( check the  circle marks on the machine). Precisely align the  instance with the  spherically seated plate.  iii. The  cargo will be applied to the  instance axially.  iv. Now  sluggishly apply the  cargo at the rate of 140 kg/ cm2 per  nanosecond till the   cell collapse.  v. The maximum  cargo at which the  instance breaks is taken as a  compressive  cargo.  4. computation Compressive Strength of concrete =  Maximum  compressive  cargo Cross sectional area.  Que4.20. Describe the non destructive testing of hardened  concrete.  Answer Non-Destructive Tests on Concrete The mainnon-destructive  tests for strength on hardened concrete are as follows  1. Rebound Hammer( Hardness) Test  i. The Schmidt hammer is used in the answer hardness test in which a  essence hammer held against the concrete is struck by another springdriven  essence mass and rebounds.  ii. The  quantum of answer is recorded on a scale and this gives an  suggestion  of the concrete strength.  iii. The larger the answer number is, the advanced is the concrete strength.  2. Ultrasonic Pulse Velocity Test  i. In the ultrasonic  palpitation  haste test the  haste of ultrasonic  beats that  pass through a concrete section from a transmitter to a receiver is  measured.  ii. The  palpitation  haste is  identified against strength.  iii. The advanced the  haste is, the stronger is the concrete.  3. Pull Out Test  i. The pull out test will determine the force that’s  needed to pull out a   sword rod especially shaped from hardened concrete to which the  sword  was cast.  ii. Pulling out of  sword is done with a cone of concrete that have a  pitch of  45 °.  iii. The force  needed to pull the concrete out is related with the compressive  strength of the concrete.  4. Penetration Resistance Test  Penetration resistance tests on concrete offers a means of determining  relative strengths of concrete in the same structure or relative strength  of different structures.  ii. Because of nature of accoutrements , it can not be anticipated to yield absolute  values of strength.  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.  2. Tangent Modulus It’s given by the  pitch of a line drawn  digression to  the stress- strain  wind at any point on the  wind. It’s used to  pretend  the structure to  lading or unloading at different unloading stages.  3. Secant Modulus It’s given by the  pitch of a line drawn from the  origin to a point on the  wind corresponding to a 40 stress of the  failure stress. It’s used to  pretend the structure during its  original  lading  stage when  endless  cargo prevail.

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