Tests on aggregates civil engineering.pptx

Tests on Aggregate

1. Aggregate Impact Value Ten Percent Fines Value Aggregate Crushing Value Aggregate Abrasion Value Edwin . A M.Tech –Structural Engg.

2. Aggregate Impact Value The apparatus consists of a steel test mould with a falling hammer as shown in figure. The hammer slides freely between vertical guides so arranged that the lower part of the hammer is above and concentric with the mould. The material used is aggregate passing a 12.7 mm sieve and retained on a 9.52mm sieve. It shall be clean and dry (washed if necessary) but it must not be dried for longer than 4 hours nor at a temperature higher than 110℃ otherwise certain aggregates may be damaged. The whole of the test sample (mass A) is placed in the steel mould and compacted by a single tamping of 25 strokes of the tamping rod.

3. The test sample is subjected to 15 blows of the hammer dropping 381mm, each being delivered at an interval not less than 1 second. The crushed aggregate is sieved over a 2.36mm sieve. The fraction passing 2.36mm is weighed to the nearest 0.1g (mass B). The reaction retained on the sieve is also weighed (mass C). If [A-(B+C)]>1g, the result shall be discarded and a fresh test is made. The aggregate Impact value (AIV) is (B/A) x (100%).

4. Result: An avg. is taken of the two tests and the results is recorded to the nearest whole no. As the Aggregate Impact value. The AIV is normally about 105 % of the aggregate crushing value and it can be used for the same purpose. For week aggregate, the required load for the first 10% fines test can be estimated by means of the formula: Required load ( kN ) = 4000/AIV.

5. TEN PERCENT FINES VALUE: The apparatus (as in fig) consist of a case hardened steel cylinder 154mm dia and 125mm high together with a plunger which just fits inside the cylinder and a base plate. Other items are a steel tamping bar 16mm diameter by 450-600mm long and a metal measuring cylinder 115mm diameter by180mm deep. Also required is a compression testing machine capable of applying a force of up to 500 kN and which can be operated to give a uniform rate of loading so that this force is reached in 10 minutes. The material used is aggregate passing a 12.7mm sieve and retained on 9.52mm sieve. It shall be clean and dry(washed if necessary) but it must not be dried for longer than 4 hrs nor at a temp. Higher than 110℃ otherwise certain aggregates may be damaged.

6. The required volume is obtained by filling the measuring cylinder in 3 layers, each tamped 25 times with the rod and top struck level. This volume is then weighed to the nearest 0.1g (mass A) The material from the measuring cylinder is placed in the test cylinder in 3 layers, each tamped 25 times with rod. The depth of the sample will then be about 100mm. The Plunger is lowered onto the sample and rotated gently to seat it and level it. The cylinder, plunger and sample are placed in the compressing testing machine. Force is applied at a uniform rate so that the total penetration in 10 minutes is about: 15mm for uncrushed gravel 20mm for normal, crushed aggregate, 24mm for honeycombed aggregate. ( eg : some slag and volcanic rocks).

7. The sample is then sieved over a 2.36mm sieve. As this is a fairly fine sieve, it is preferable to pass the whole sample over a larger sieve.(say 4.75mm) first. The material passing 2.36mm is then weighed (mass B) and expressed as a %age of original mass [y= 100% x B/A]. If the %age fines lies between 7.5% and 12.5%, the following calculation for ten percent values is made: TFV = Force to produce 10% fines = (14x/ y+4) Where, x= max. Forced used ( kN ). y= %age fines from the test(%).

8. Aggregate Crushing Value: The apparatus and samples are same that of ten percent fines value. The cylinder, plunger and sample are placed in the compression test machine. It is loaded at a uniform rate so that a force of 400 kN is reached in 10 minutes. The load is then released. The %age fines is then determined as the material passing 2.36mm is weighed (mass B) and expressed as a %age of the original mass (mass A) to give the aggregate crushing value. ACV = (B/A) X100% As a result, the average is taken of two tests and ACV value is recorded.

9. Aggregate Abrasion Value: 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 g. Oven .

10. Procedure: The test sample and the abrasive charge should be placed in the Los Angles abrasion testing machine. The machine is 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.

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