Lab Test On Aggregates

Various Lab Test On Aggregates

There are many tests which are conducted to check the quality of aggregates. Aggregates are a very important component of concrete, so the quality really matters when it comes to aggregates.

Various test which is done on aggregates is listed below.

1. Sieve Analysis

2. Water Absorption

3. Aggregate Impact Value

4. Aggregate Abrasion Value

5. Aggregate Crushing Value

1. Sieve Analysis of Aggregates

Sieve analysis helps to determine the particle size distribution of the coarse and fine aggregates. This is done by sieving the aggregates as per IS: 2386 (Part I) – 1963. In this, we use different sieves as standardized by the IS code and then pass aggregates through them and thus collect different sized particles left over different sieves.

The apparatus used is –

i) A set of IS Sieves of sizes – 80mm, 63mm, 50mm, 40mm,31.5mm, 25mm, 20mm, 16mm, 12.5mm, 10mm, 6.3mm,4.75mm, 3.35mm, 2.36mm, 1.18mm, 600µm, 300µm, 150µm and 75µm.

ii) Balance or scale with an accuracy to measure 0.1 per cent of the weight of the test sample.

The weight of sample available should not be less than the weight given below:-

The sample for sieving should be prepared from the larger sample either by quartering or by means of a sample divider.

Procedure to determine the particle size distribution of Aggregates.

i) The test sample is dried to a constant weight at a temperature of 110 + 5^oC and weighed.

ii) The sample is sieved by using a set of IS Sieves.

iii) On completion of sieving, the material on each sieve is weighed.

iv) Cumulative weight passing through each sieve is calculated as a percentage of the total sample weight.

v) Fineness modulus is obtained by adding a cumulative percentage of aggregates retained on each sieve and dividing the sum by 100.

Reporting of Results

The results should be calculated and reported as:

i) the cumulative percentage by weight of the total sample

ii) the percentage by weight of the total sample passing through one sieve and retained on the next smaller sieve, to the nearest 0.1 per cent. The results of the sieve analysis may be recorded graphically on a semi-log graph with a particle size as abscissa (log scale) and the percentage smaller than the specified diameter as ordinate.

2. Water Absorption of Aggregates

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.

apparatus:-

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 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 32^oC.

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 until 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 110^oC for 24hrs. It should then be removed 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 proforma for the record of the test is

3. Aggregate Impact Value

Aggregate Impact Value - This test is done to determine the aggregate impact value of coarse aggregates as per IS 2386 (Part IV) – 1963.

The apparatus - Impact 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 Sample

i) 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 110^oC 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 the Aggregate Impact Value

i) 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 the 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 Results

i) 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 is 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.

4. Aggregate Abrasion Value

This test helps to determine the abrasion value of coarse aggregates as per IS 2386 (Part IV) – 1963.

The apparatus - 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 Preparation

The test sample should consist of clean aggregates which have 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 Value

The 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 Results

i) The material coarser than 1.70mm IS Sieve should be washed, dried in an oven at a temperature of 100 to 110^oC to a constant weight and weighed (Weight ‘B’).

ii) The proportion of loss between weight ‘A’ and weight ‘B’ of the test the 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%.

Aggregate Crushing Value

This test helps to determine the aggregate crushing value of coarse aggregates as per IS 2386 (Part IV) – 1963.

The apparatus - used is Cylindrical measure and plunger, Compression testing machine, IS Sieves of sizes – 12.5mm, 10mm and 2.36mm

Procedure to determine Aggregate Crushing Value

i) The aggregates passing through 12.5mm and retained on 10mm IS Sieve are oven-dried at a temperature of 100 to 110^oC for 3 to 4hrs.

ii) The cylinder of the apparatus is filled in 3 layers, each layer tamped with 25 strokes of a tamping rod.

iii) The weight of aggregates is measured (Weight ‘A’).

iv) The surface of the aggregates is then levelled and the plunger inserted. The apparatus is then placed in the compression testing machine and loaded at a uniform rate so as to achieve 40t load in 10 minutes. After this, the load is released.

v) The sample is then sieved through a 2.36mm IS Sieve and the fraction passing through the sieve is weighed (Weight ‘B’).

vi) Two tests should be conducted.

Aggregate crushing value = (B/A) x 100%.