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.