Concrete Technology: Cement Production and Aggregates Unit 1 Part 4

Que1.17. What’s alkali aggregate  response? What are the factors  which affect this  response? How can this  response be controlled? 

Answer  Alkali Aggregate response  1. The  miracle is accompanied by  expansive expansion and may  lead in bad cases to complete  dislocation and decomposition of the  concrete and is known as alkali- aggregate  response or  occasionally  concrete cancer. 

2. The trouble is due to  response between silica in  total and alkalis in  the cement. 

3. In some cases alkalis,  substantially from the cement supplemented by alkalis  in the  total, reply with carbonates in the  total to produce   analogous result. 

4. The types of  jewels which contain reactive  ingredients include traps,  andesites, rhyolites, siliceous limestone and certain types of sandstones. 

5. The reactive  factors may be in the form of opals, cherts,  chalcedony,  stormy glass( excepting basaltic  spectacles), zeolites, and  tridymite.  Factors Affecting Alkali- Aggregate response 

1. Reactive Type of summations Reactive material have been  set up  to have serious  goods if present in small amounts but not if it  constitutes the  total of the  total. 

2. High Alkali Content Cement If the cement contains  lower than  alkalis(  reckoned as Na2O) no expansion or disruptive effect is  likely indeed with a  relatively  largely reactive  total, but due to difficulties  of manufacture it isn’t usual to specify an alkali content of  lower than . 

3. Vacuity of humidity Progress of the alkali- aggregate  response  takes place only in the presence of water. 

4. Temperature Condition The favourable temperature for the   response is 10- 38 °C.  Control of Alkali- Aggregate response 

1. By optingNon-Reactive Aggregate total can be  linked  by petrographic examination. The mortar bar test and the chemical  test are used. 

2. By Using Low Alkali Cement Cements with alkali  lower than  per cent should be used. 

3. By Controlling Moisture Old concrete shouldn’t be allowed to  come in contact with water. The stylish way is to apply mortar with water  proofing agents on concrete  face. 

4. By Pozzolanas When fly- ash or surkhi or crushed gravestone dust is  added this optimum condition of silica being in particular proportion  and fineness is disturbed and the  summations turn to be  innocuous. 

5. By Air Entraining Agents The alkali- silica- gel imparts bibulous  pressure over the set cement gel and this is  substantially responsible for   conformation of cracks. When air enplaning  agents are added they absorb  the bibulous pressure and control the expansion. 

Que1.18. Describe the test conducted to determine the crushing  value, impact value and bruise value of  summations. 

Answer  Determination of Crushing Value( IS 2386 Part 4- 1963) 

1. Crushing value of  total is a relative measure of resistance of an   total to crushing under gradationally applied compressive  cargo. 

2. Aggregate  end through12.5 mm sieve and retained on 10 mm  sieve is taken. About6.5 kg of  face dry  total filled in the  standard cylinder in three layers, tamping each subcaste 25 times by a  standard tamping rod. It’s leveled off. Its weight  set up out( A). 

3. The plunger is placed on the  total taking care that it doesn’t jam  the cylinder by  getting  listed.  4. The assembly is  also kept under  contraction testing machine and  total  cargo of 40 tonnes is applied slightly during 10  twinkles. 

5. The  cargo is released, the  total is taken out and sieve on2.36 mm  sieve. The bit passing through weight is( B). 

6. The  total crushing value is given by,  Aggregate crushing value =  B/ A × 100. 

7. Aggregate crushing value shouldn’t be  further than 45 for aggregate  used for concrete other than for wearing  face and 30 for concrete  used for wearing  face such a runway roads,etc.  Determination of Impact Value( IS 2386 part 4- 1963) 

1. This test gives relative measure of resistance of  total to suddenly  applied  cargo or impact  cargo. 

2. The test sample consists of aggregate passing through12.5 mm IS  sieve and retained on 10 mm IS sieve. The  total is oven dried at  110 °C for 4 hours. 

3. The  total is filled in the mug,( weight A). By lifting the handle,  hammer is allowed to fall freely as it’s released by the tripping  medium, on to the  total in the mug.  4. 15  similar blows are given and  also the  total is taken out and settled on2.36 mm sieve.  5. The bit passing through is counted( weight B). 

6. The bit retained is also counted( weight C). If( B C) is  lower than  A by  further than 1 gram, the result is discarded and a fresh test is made. 

7. The aggregate impact value is given by,  Aggregate impact value =  BA × 100  8. Standard value for this test is same as crushing value test.  Determination of Abrasion Value( IS 2386 Part 4- 1963) 

1. This test gives the relative resistance of  total to wearing. 

2. There are two  styles  specified in the IS  law  Deval waste Test, and  ii. Los Angeles Abrasion Value.

  3. But since LA test gives more realistic results, it’s  further generally  used. 

4. In this  system, the specified weight, 5 kg or 10 kg, depending on the  size of  total is taken and is placed in the cylinder of the LA machine  along with the abrasive charge. 

5. The bruise charge consists of specific number of  sword balls.  6. The cylinder is rotated at 20 to 33 rpm for 500 or 1000 revolution,  depending on the grading of the  total. 

7. The  total is removed from the cylinder and settled on1.75 mm  sieve. 

8. The bit passing through1.7 mm sieve is expressed as chance  of original weight give the aggregate bruise value.  

9. The chance of wear and tear shouldn’t be  further than 16 for cement  concrete  total.  

Que1.19. What tests are used to find out the shape of the   total? 

Answer  There are  substantially two types of test for chancing  the shape of  total,  which are as follows  Test for Determination of Flakiness Index 

1. The flakiness  indicator of  total is the chance by weight of  patches  in it whose least dimension( consistence) is  lower than three- fifths of their  mean dimension. The test isn’t applicable to sizes  lower than  mm. 

2. This test is conducted by using a essence consistence hand.  3. A sufficient  volume of  total is taken  similar that a  minimal number  of 200 pieces of any bit can be tested. 

4. Each bit is gauged in turn for consistence on the essence hand. 

5. The total  quantum passing in the hand is counted to an  delicacy of  of the weight of the samples taken. 

6. The flakiness  indicator is taken as the total weight of the material passing  the  colorful consistence needles expressed as a chance of the total  weight of the sample taken.  Test for Determination of Elongation Index 

1. The  extension  indicator on an  total is the chance by weight of   patches whose  topmost dimension( length) is lesser than1.8 times  their mean dimension. 

2. The  extension  indicator isn’t applicable to sizes  lower than6.3 mm.  3. This test is conducted by using essence length hand. 

4. A sufficient  volume of  total is taken to  give a  minimal  number of 200 pieces of any bit to be tested. 

5. Each bit shall be gauged collectively for length on the essence  hand.  6. The total  quantum retained by the hand length shall be counted to an   delicacy of at least0.1 of the weight of the test samples taken.  

7. The  extension  indicator is the total weight of the material retained on the   colorful length needles expressed as a chance of the total weight of  the sample gauged. 

8. The presence of  stretched  patches in excess of 10- 15 is generally  considered undesirable.  

Que1.20. Explain the procedure for determination of ‘ ten percent   forfeitures value ’. 

Answer  Procedure for Determination of Ten Percent forfeitures Value 

1. The sample of  total for this test is the same as that of the sample  used for  total crushing value test. 

2. The  outfit, with the test sample and plunger in position is placed in  the  contraction testing machine. 

3. The  cargo is applied at a  invariant rate so as to beget a total penetration  of the plunger in 10  twinkles of about  15 mm for rounded or  incompletely rounded  summations( for  illustration  uncrushed gravels)  ii.20.0 mm for normal crushed  summations, and 

iii.24.0 mm for honeycombed  summations(e.g., expanded shales and  stags). 

4. After reaching the  needed  outside penetration, the  cargo is released  and the  total of the material removed from the cylinder and settled on  a2.36 mm IS sieve. 

5. The  forfeitures passing the sieve is counted and the weight is expressed as  a chance of the weight of the test sample. 

6. This chance would fall within the range7.5 to12.6, but if it does  not,  reprise test is made and the  cargo is  set up out which gives a  chance of  forfeitures within the range of7.5 to12.5.

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