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Quality Control lab
As per the schedule we have to work for few days in quality control laboratory to understand the strength and other parameters of material used.
Here are the few tests that we performed in the quality control lab.
Lab tests on cement :
DETERMINATION OF COMPRESSIVE STRENGTH OF CEMENT. (IS: 4031 – Part – 6)
Object:Determination of the compressive strength of standard cement mortar cubes compacted by means of a standard vibration machine.Apparatus:Vibration machine, cube moulds of size 7.06 cms(confirming to IS : 4031 – 1968), and Standard Sand to be used in the test shall be confirm to IS : 650 – 1966.Procedure:Mix Proportions and Mixing: Clean appliances shall be used for mixing and the temperature of the water and that of the test room at the time when the above operations are being performed shall be 270 +/- 20C. Place in a container a mixture of cement and standard sand in the proportion of 1 : 3 by weight; mix it dry, with a trowel for one minute and then with water until the mixture is of uniform colour. The quantity of water to be used shall be as specified below. In any event, it should not take more than 4 minutes to obtain uniform colored mix. If it exceeds 4 minutes, the mixture shall be rejected and the operation repeated with a fresh quantity of cement, sand and water.
The material for each cube shall be mixed separately and the quantity of cement, standard sand and water shall be as follows: Percentage of water to be added to the cement and sand in ( 1:3 ) cm (P/4 + 3) X % combined weight of cement and sand = (P/4 + 3) X 800/100.
Cement 200 gms, standard sand 600 gms, water (P/4 + 3) per cent of combined weight of cement and sand, where P is the percentage of water required to produce a paste of standard consistency.
Molding Specimens:In assembling the moulds ready for use, cover the joints between the halves of the mould with a thin film of petroleum jelly and apply a similar coating of petroleum jelly between the contact surfaces of the bottom of the mould and its base plate in order to ensure that no water escapes during vibration. Treat the interior faces of the mould with a thin coating of mould oil. Place the assembled mould on the table of the vibration machine and firmly hold it in position by means of suitable clamps. Securely attach a Hooper of suitable size and shape at the top of the mould to facilitate filling and this Hooper shall not be removed until completion of the vibration. Immediately after mixing the mortar, place the mortar in the cube mould and rod with a rod. The mortar shall be rodded 20 times in about 8 seconds to ensure elimination of entrained air and honey combing. Place the remaining quantity of mortar in the Hooper of the cube mould and rod again as specified for the first layer and then compact the mortar by vibration. The period of vibration shall be two minutes at the specified speed of 12000 +/- 400 vibrations per minutes. At
the end of vibration remove the mould together with the base plate from the machine and finish the top surface of the cube in the mould by smoothing surface with the blade of a trowel.
Curing Specimens:Keep the filled moulds at a temperature of 270C +/- 20C in an atmosphere of at least 90% relative humidity for about 24 hours after completion of vibration. At the end of that period remove them from the moulds immediately submerge in clean fresh water and keep them under water until testing. The water in which the cubes are submerged shall be renewed every 7 days and shall be maintained at a temperature of 270C +/- 20C. After they have been taken out and until they are tested, the cubes shall not be allowed to become dry.
Testing: Test three cubes for compressive strength at the periods mentioned under the relevant specifications for different hydraulic cements, the periods being reckoned from the completion of vibration. The compressive strength shall be the average of the strengths of the three cubes for each period of curing. The cubes shall be tested on their sides without any packing between the cube and the steel platens of the testing machine. One of the platens shall be carried base and shall be self-adjusting and the load shall be steadily and uniformly applied, starting from zero at a rate of 350 kgs/cm2/min.
Calculation:Calculate the compressive strength from the crushing load and the average area over which the load is applied. Express the results in kgs/cm2 to the nearest 0.5 kg/cm2. Compressive strength, kg/cm2 = P/A, where ‘P’ is the crushing load in kg, and ‘A’ is the area in cm2.
CEMENT: FINENESS BY DRY SIEVING REFERENCE: IS 4031 – (PART – 1) 1996
IMPORTANCE: During manufacturing, cement must be ground to be uniformly fineOtherwise concrete needs large amount of water for mixing which results in bleeding as well as poor workmanship.
• Test sieve of non-corrodible metal having 150 mm to 200 mm dia, and 40 mm to 100 mm depth fitted with 90 µm mesh sieve cloth of woven stainless steel or other abrasion resistant non- corrodible wires.• Suitable tray with lid to fit sieve size.
• Stoppered jar with blunt ended stirrer rod
• Weighing balance to weigh up to 10 gms to nearest 10 mg.
• Nylon or pure bristle brush (25 mm / 40 mm bristles) for cleaning sieves.
PROCEDURE: Determination of cement residue:
• Agitate the cement sample by shaking for 2 minutes in a stoppered jar to disperse the agglomerates. Wait for few minutes.
• Stir the resulting powder gently with dry rod to distribute the fines throughout the sample.• Weigh approx. 10 gm of cement and put in sieve fitted with bottom tray and top lid.
• Agitate and shake the sieve thoroughly• Weigh the residue – retained on sieve.• Clean base of sieve gently by brush to remove fine material.
• Find out % (R1) of residue in comparison with total weight of sample.• Repeat the procedure at least twice till results do not differ by more than 1%.
CALCULATION Find out mean of observations and express this percentage as R
CEMENT: DETERMINATION OF SETTING TIME REFERENCE: IS 4031 – (PART – 5) 1996
IMPORTANCE OF TEST: The object is to distinguish between, quick setting and normal setting time and to detect the deterioration due to storage.
APPARATUS • Vicat Apparatus• Balance (capacity 1000 gms, accuracy 0.1 gm)• Annular attachment of Vicat Apparatus
TEMPERATURE • Dry Materials, Water and Moulding Room : 27 + 2O C& HUMIDITY • Relative Humidity in Laboratory : 65 + 5 %
PROCEDURE On a non-porous platform
• Mix neat cement with enough water to give a paste of StandardConsistency.
• Start stop watch immediately on adding water to cement. NoteStop watch reading (To)
• Rest Vicat mould on non-porous plate and fill it completely with cement paste. Level of top surface and expel air by shaking.
• Place test block with mould under the rod bearing needle of Vicat apparatus and b r ing rod l eve l with t op o f test specimen. Release needle slowly and let it penetrate in the test block.
• Repeat the procedure until needle stops of distance of (5 + 0.5) mm from base of test block. Read the stop watch and note the time (T1).
• Replace needle by annular attachment. Repeat procedure of releasing the needle till needle makes an impression on top of test block while attachment fails to do so. Read the stop watch and note time (T2).
CALCULATION Initial Setting Time (IST) = (T1 – T0)
Final Setting Time (FST) = (T2 – T 0)
REPORTING Report IST & FST to nearest 5 minutes
Lab Tests on Aggregates:
WATER ABSORPTION TEST:This test helps to determine the water absorption of coarse aggregates as per IS: 2386 (Part III) – 1963. For this test a sample not less than 2000g should be used. The apparatus used for this test are :-Wire basket – perforated, electroplated or plastic coated with wire hangers for suspending it from the balance, Water-tight container for suspending the basket, Dry soft absorbent cloth – 75cm x 45cm (2 nos.), Shallow tray of minimum 650 sq.cm area, Air-tight container of a capacity similar to the basket and Oven.Procedure to determine water absorption of Aggregates.i) The sample should be thoroughly washed to remove finer particles and dust, drained and then placed in the wire basket and immersed in distilled water at a temperature between 22 and 32oC.
ii) After immersion, the entrapped air should be removed by lifting the basket and allowing it to drop 25 times in 25 seconds. The basket and sample should remain immersed for a period of 24 + ½ hrs afterwards.
iii) The basket and aggregates should then be removed from the water, allowed to drain for a few minutes, after which the aggregates should be gently emptied from the basket on to one of the dry clothes and gently surface-dried with the cloth, transferring it to a second dry cloth when the first would remove no further moisture. The aggregates should be spread on the second cloth and exposed to the atmosphere away from direct sunlight till it appears to be completely surface-dry. The aggregates should be weighed (Weight ‘A’).
iv) The aggregates should then be placed in an oven at a temperature of 100 to 110oC for 24hrs. It should then be re moved from the oven, cooled and weighed (Weight ‘B’).
Formula used is Water absorption = [(A - B)/B] x 100%.Two such tests should be done and the individual and mean results should be reported. A sample Performa for the record of the test is
AGGREGATE IMPACT VALUEThis test is done to determine the aggregate impact value of coarse aggregates as per IS: 2386 (Part IV) – 1963. The apparatus used for determining aggregate impact value of coarse aggregates isImpact testing machine conforming to IS: 2386 (Part IV)- 1963,IS Sieves of sizes – 12.5mm, 10mm and 2.36mm, A cylindrical metal measure of 75mm dia. and 50mm depth, A tamping rod of 10mm circular cross section and 230mm length, rounded at one end and Oven.
Preparation of Samplei) The test sample should conform to the following grading:- Passing through 12.5mm IS Sieve – 100%- Retention on 10mm IS Sieve – 100%
ii) The sample should be oven-dried for 4hrs. at a temperature of 100 to 110oC and cooled.
iii) The measure should be about one-third full with the prepared aggregates and tamped with 25 strokes of the tamping rod.
A further similar quantity of aggregates should be added and a further tamping of 25 strokes given. The measure should finally be filled to overflow, tamped 25 times and the surplus aggregates struck off, using a tamping rod as a straight edge. The net weight of the aggregates in the measure should be determined to the nearest gram (Weight ‘A’).
Procedure to determine Aggregate Impact Valuei) The cup of the impact testing machine should be fixed firmly in position on the base of the machine and the whole of the test sample placed in it and compacted by 25 strokes of the tamping rod.ii) The hammer should be raised to 380mm above the upper surface of the aggregates in the cup and allowed to fall freely onto the aggregates. The test sample should be subjected to a total of 15 such blows, each being delivered at an interval of not less than one second.
Reporting of Resultsi) The sample should be removed and sieved through a 2.36mm IS Sieve. The fraction passing through should be weighed (Weight ‘B’). The fraction retained on the sieve should also be weighed (Weight ‘C’) and if the total weight (B+C) is less than the initial weight (A) by more than one gram, the result should be discarded and a fresh test done.ii) The ratio of the weight of the fines formed to the total sample weight should be expressed as a percentage.
Aggregate impact value = (B/A) x 100%iii) Two such tests should be carried out and the mean of the results should be reported.
AGGREGATE ABRASION VALUEThis test helps to determine the abrasion value of coarse aggregates as per IS: 2386 (Part IV) – 1963.The apparatus used in this test are Los Angles abrasion testing machine, IS Sieve of size – 1.7mm, Abrasive charge – 12 nos. cast iron or steel spheres approximately 48mm dia. and each weighing between 390 and 445g ensuring that the total weight of charge is 5000 +25g and Oven.Sample PreparationThe test sample should consist of clean aggregates which has been dried in an oven at 105 to 110oC to a substantially constant weight and should conform to one of the gradings shown in the table below:
Procedure to determine Aggregate Abrasion ValueThe test sample and the abrasive charge should be placed in the Los Angles abrasion testing machine and the machine rotated at a speed of 20 to 33 revolutions/minute for 1000 revolutions. At the completion of the test, the material should be discharged and sieved through 1.70mm IS Sieve.
Reporting of Resultsi) The material coarser than 1.70mm IS Sieve should be washed, dried in an oven at a temperature of 100 to 110oC to a constant weight and weighed (Weight ‘B’).ii) The proportion of loss between weight ‘A’ and weight ‘B’ of the test sample should be expressed as a percentage of the original weight of the test sample. This value should be reported as,
Aggregate abrasion value = (A-B)/B x 100%.
Flakiness index and Elongation Index of Coarse Aggregates
AIM:
i. To determine the elongation index of the given aggregates
ii. To determine the flakiness index of the given aggregates
APPARATUS:
The apparatus for the shape tests consists of the following:
(i) A standard thickness gauge
(ii) A standard length gauge
(iii) IS sieves of sizes 63, 50 40, 31.5, 25, 20, 16, 12.5,10 and 6.3mm
(iv) A balance of capacity 5kg, readable and accurate up to 1 gm.
THEORY:
The particle shape of aggregates is determined by the percentages of flaky and elongated particles contained in it. For base course and construction of bituminous and
cement concrete types, the presence of flaky and elongated particles are considered undesirable as these cause inherent weakness with possibilities of breaking down under heavy loads. Thus, evaluation of shape of the particles, particularly with reference to flakiness and elongation is necessary.
The Flakiness index of aggregates is the percentage by weight of particles whose least dimension (thickness) is less than three- fifths (0.6times) of their mean dimension. This test is not applicable to sizes smaller than 6.3mm.
The Elongation index of an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than nine-fifths (1.8times) their mean dimension. This test is not applicable for sizes smaller than 6.3mm.
PROCEDURE:
i) Sieve the sample through the IS sieves (as specified in the table).
ii)Take a minimum of 200 pieces of each fraction to be tested and weigh them.
(iii) In order to separate the flaky materials, gauge each fraction for thickness on a
thickness gauge. The width of the slot used should be of the dimensions specified in
column (4) of the table for the appropriate size of the material.
(iv) Weigh the flaky material passing the gauge to an accuracy of at least 0.1 per cent of
the test sample.
(v) In order to separate the elongated materials, gauge each fraction for length on a length
gauge. The width of the slot used should be of the dimensions specified in column (6)
of the table for the appropriate size of the material.
(vi) Weigh the elongated material retained on the gauge to an accuracy of at least 0.1 per
cent of the test sample.
Size of aggregates Weight of
fraction
consisting
of at least
200
pieces,g
Thickness
gauge
size, mm
Weight of
aggregates
in each
fraction
passing
thickness
gauge,mm
Length
gauge
size,
mm
Weight of
aggregates
in each
fraction
retained on
length
gauge,mm
Passing
through
IS Sieve,
mm
Retained
on IS
Sieve,
mm
1 2 3 4 5 6 7
63 50 W1 23.90 X1 - -
50 40 W2 27.00 X2 81.00 Y1
40 31.5 W3 19.50 X3 58.00 Y2
31.5 25 W4 16.95 X4 - -
25 20 W5 13.50 X5 40.5 Y3
20 16 W6 10.80 X6 32.4 Y4
16 12.5 W7 8.55 X7 25.5 Y5
12.5 10 W8 6.75 X8 20.2 Y6
10 6.3 W9 4.89 X9 14.7 Y7
Total W = X = Y =
OBSERVATIONS:
Flakiness Index = (X1+ X2+…..) / (W1 + W2 + ….) X 100
Elongation Index = (Y1 + Y2 + …) / (W1 + W2 + ….) X 100
RESULT:
i) Flakiness Index =
ii) Elongation Index =
Lab Tests on Concrete
DETERMINATION OF COMPRESSIVE STRENGTH OF CONCRETE.(IS: 516 – 1959)
Apparatus:
Testing Machine: The testing machine may be of any reliable type of sufficient capacity for the tests and capable of applying the load at the specified rate. The permissible error shall not be greater than 2 percent of the maximum load. The testing machine shall be equipped with two steel bearing platens with hardened faces. One of the platens shall be fitted with a ball seating in the form the portion of a sphere, the center of which coincides with the central point of the face of the platen. The other compression platen shall be plain rigid bearing block. The bearing faces of both platens shall be at least as larger as, and preferably larger than the nominal size of the specimen to which the load is applied. The bearing surface of the platens, when new, shall not depart from a plane by more than 0.01mm at any point, and they shall be maintained with a permissible variation limit of 0.02mm. the movable portion of the spherical seated compression platen shall be held on the spherical seat, but the design shall be such that the bearing face can be rotated freely and tilted through small angles in any direction.
Age at test: Tests shall be made at recognized ages of the test specimens, the most usual being 7 and 28 days. The ages shall be calculated from the time of the addition of water of the dry ingredients.
Number of Specimens: At least three specimens, preferably from different batches, shall be made for testing at each selected age.
Procedure:
Specimens stored in water shall be tested immediately on removal from the water and while they are still in the wet condition. Surface water and grit shall be wiped off the specimens and any projecting find removed specimens when received dry shall be kept in water for 24 hours before they are taken for testing. The dimensions of the specimens to the nearest 0.2mm and their weight shall be noted before testing.
Placing the specimen in the testing machine the bearing surface of the testing machine shall be wiped clean and any loose sand or other material removed from the surface of the specimen, which are to be in contact with the compression platens. In the case of cubes, the specimen shall be placed in the machine in such a manner that the load shall be applied to opposite sides of the cubes as cast, that is, not to the top and bottom. The axise of the specimen shall be carefully aligned with the center of thrust of the spherically seated platen. No packing shall be used between the faces of the test specimen and the steel platen of the testing machine. As the spherically seated block is brought to bear on
the specimen the movable portion shall be rotated gently by hand so that uniform seating may be obtained. The load shall be applied without shock and increased continuously at a rate of approximately 140 kg/cm2/min.until the resistance of the specimen to the increasing load breaks down and no grater load can be sustained. The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted.
Calculation: The measured compressive strength of the specimen shall be calculated by dividing the maximum load applied to the specimen during the test by the cross sectional area, calculated from the mean dimensions of the section and shall be expressed to the nearest kg per cm2. Average of three values shall be taken as the representative of the batch provided the individual variation is not more than +/-15 percent of the average. Otherwise repeat tests shall be made.
A correction factor according to the height / diameter ratio of specimen after capping shall be obtained from the curve shown in Fig.1 of IS:516-1959. The product of this correction factor and the measured compressive strength shall be known as the corrected compressive strength this being the equivalent strength of a cylinder having a height/diameter ratio of two. The equivalent cube strength of the concrete shall be determined by multiplying the corrected cylinder strength by 5/4.
DETERMINATION OF FLEXURAL STRENGTH OF CONCRETE.(IS: 516 – 1959)
Object: Determination of the flexural strength of concrete specimen.
Apparatus:a) Standard moulds of size 15 X 15 X 70 cms for preparing the specimen.b) Tamping bar.c) Testing Machine.
Procedure:Test specimens stored in water at a temperature of 250C to 300C for 48 hours before testing shall be tested immediately on removal from the water, whilst they are still in a wet condition. The dimensions of each specimen shall be noted before testing. No preparation of the surface is required.
Placing the specimen in the testing machine: The bearing surfaces of the supporting and loading rollers shall be wiped clean, and any loose sand or other material removed from the surfaces of the specimen where they are to make contact with the rollers. The specimen shall then be placed in the machine in such a manner that the load shall be applied to the upper most surface as cast in the mould, along two lines spaced 20 or 13.30 cms apart. The axis of the specimen shall be carefully aligned with the axis of the loading device. No packing shall be used between the bearing surface of the specimen and the rollers. The load shall be applied with shock and increasing continuously at a rate such that the extreme fiber stress increases at approximately 7
kgs/cm2/mm for the 10 cm specimens, the load shall be increased until the specimen falls, and the maximum load applied to the specimen during the test shall be recorded. The appearance of the fractured faces of the concrete and any unusual features in the type of failure shall be noted.Calculation:
The flexural strength of the specimen shall be expressed as the modules of rapture ‘ fb’ which if ‘a’ equals the distance between the line of fracture and the nearer support measured on the centerline of the tensile side of the specimen, in cm, shall be calculated to the nearest 0.5 kg/cm2
as follows.fb = ( p X l ) / ( b X d2 )
When ‘a’ is greater than 20.0 cm . for 15.0 cm specimen or greater than 13.30 cm for a 10.0 cm specimen, or
fb = ( 3p X a ) / ( b X d2 ) When ‘a’ is less than 20.0 cms. but greater than 17.0 cms for 15.00 cms specimen, or less than 13.30 cms but greater than 11.0 cms for a 10.0 cms specimen, where b = measured width in cms of the specimen, d = measured depth in cms of the specimen at the point of failure, l = length in cm. of the span on which the specimen was supported, and p = maximum load in kg. applied to the specimen.If ‘a’ is less than 17.0 cm. for a 15 cm specimen or less than 11.0 cm for a 10.0 cm specimen, the result of the test shall be discarded.
