Aggregate Testing

Introduction

• Aggregates are the important constituents in concrete , they give body to the concrete ,reduce shrinkage and effect economy ..

• 70-80 per cent of the volume of concrete is occupied by aggregates .

• A sieve analysis (or gradation test) is a practice or procedure used (commonly used in civil engineering) to assess the particle size distribution (also called gradation) of a granular material.

• The size distribution is often of critical importance to the way the material performs in use. Being such a simple technique of particle sizing, it is probably the most common

• Sieve size used for fine aggregates 10mm, 4.75mm, 2.36mm, 1.18mm, 600u, 300u and 150u.

• Sieve size used for coarse aggregates 80mm, 63mm,, 40mm, 20mm, 16mm, 12.5mm, 10mm, 4.75mm, 2.36mm.

IS

Sieve

(mm)

Weight

Retained

(gm)

Cumulative

Wt.

Retained

(gm)

%

Cumulative

Wt. Retained

% Passing Allowed Range of

Values

10 0 0 0.0 100.0 100

4.75 40 40 8.0 92.0 90-100

2.36 58 98 19.6 80.4 75-100

1.18 88 186 37.2 62.8 55-90

600u 108 294 58.8 41.2 35-59

300u 120 414 82.8 17.2 8-30

150u 42 450 91.2 8.8 0-10

Pan 44 500 100.0 0.0 0

Dr. Ravi Kant Mittal, BITS, Pilani

Zone II

Aggregate crushing value test

• Aggregate crushing value gives a relative measure of the resistance of an aggregate sample to crushing under gradually appiled compressive load.

• The compressive strength varying from a minimum of about 45 MPa to a maximum of 545 MPa.

Procedure :

This test is made on single sized aggregate.

The aggregate used for testing should pass from 12.5mm sieve and retained on 10mm sieve.

The aggregate is placed in a cylindrical mould of 25mm height and 25mm diameter.

Then a load of 40 tons is applied through a plunger.

• The crushed aggregate is then sieved on a 2.36mm IS sieve.

• The material passed through the sieve is collected and weighted .

• The passed material is expressed as a percentage of the original weight.

• This give the aggregate crushing value of the aggregate.

The aggregate crushing value is restricted to 30% for concrete used for roads and pavements and 45% for other than wearing surfaces structures.

If the aggregate crushing value is 30 or more than results are not accurate. In that case aggregate is should be subjected to 10 % fines value test.

In 10 %fines value test we find the load required to produce 10 % fines by observing the plunger.

Aggregate impact test

• Toughness is the property of a material to resist impact.

• Due to traffic loads ,the road stones are subjected to pounding action or impact and their possibility of stones to break into smaller pieces evaluate the toughness of stones .

Procedure • Aggregate passing through 12.5mm and retaining on 10mm

sieve is taken for the test .

• It is than dired for 24 hrs at a temperature of 100 to 110 c.

• Then the ample is placed in a mould of 10.2 cm dia.

• Then a hammer of weight 14kgs is made to fall from a height of 38cms

• Then the crushed sample made to passed througth 2.36mm sieve .

• The ratio of the weight of the fines to the weight of the total sample is taken and expressed as percentage .

•

• As per IS 383-1970 the aggregate impact value should be 45% for concrete used in other than wearing surfaces.

• 30 % for concrete used in wearing surfaces such as runways ,roads , pavements etc.

Impact value Strength of the rock

Less than 10 % Exceptionally strong

10-20% strong

10-30% Satisfactory for road surfacing

More than 35 % Weak for road surface

Aggregate abrasion value

• This test gives the wear resistance of the aggregates against the appiled loads .

• There are three tests that are commonly used for testing the wear of the aggregate.

• 1.Deval attrition test

• 2.Dorry abration test

• 3.Loss angles test

Los angles abrasion test

• The principle of los angle test is to find the percentage wear due to relative rubbing of aggregate.

• Apparatus :it consist of a hollow steel cylinder , closed at both ends ,having an inside diameter 70cms and an inside length of 50cms.

• It rotates on a horizontal axis.

Procedure

• Dried aggregate is put into the machine.

• The weight of the aggregate that is used for the testing depends upon the table below

• The aggregate is than rotated at a speed of 30 to 33 revolutions per minute .

• After the desired number of revolutions the sample is removed out and sieved using 1.7mm sieve.

For grading A,B,C or D

5kg and 500 revolutions

For grading E,F and G 10kgs and 1000 revolutions

• loss in weight is then expressed as percentage of the original value.

• The abbrasion value should not be more than 30 % for wearing surfaces and 50 % for other than wearing surfaces.

Flakiness index

• The flakiness index of aggregates is the percentageby weight of particles whose least dimenssion is less than three-fifth of their mean dimenssion.

• This test is not applicable to sizes smaller than 6.3 mm

Procedure

• The sample is sieved with the sieves .a minimum of 200 pieces of each fraction to be tested are taken and weighted.

• In order to separate flaky materials ,each fraction is then gauged for thickness on a thickness gauge .

• the amount of flaky materials passing the gauge is weighted to an accuracy of at least 0.1 percentage of the sample .

Dimensions of thickness and length gauges

Thickness gauge

Elongation index

• The elongation index of an aggregate is the percentage by weight of particles whose greatest dimension is greater than one and four fifth times their mean dimension .

• This test is not applicable to sieves smaller than 6.3mm

Procedure

• The sample is sieved with the sieves .a minimum of 200 pieces of each fraction to be tested are taken and weighted.

• In order to separate elongated materials ,each fraction is then gauged for length on a length gauge .

• the amount of elongated materials retaining on the gauge is weighted to an accuracy of at least 0.1 percentage of the sample .

Length gauge

• The elongation index is the % by weight of those particles present in an aggregate sample whose greatest dimension(length) is greater than 9/5 th of their mean dimension.

• The flakiness index is the % by weight of those particles present in an aggregate sample whose least dimension(thickness) is lesser than 3/5 th of their mean dimension.

• Aggregates constitute 90 to 95 % volume of concrete

• It is well known that the shape of aggregate influences the specific surface of concrete. The specific surface governs the water demand of concrete and water demand in turn determines the cement content.

• There are no fixed limits on flakiness and elongation index used on the site.

Passing

through sieve

(mm)

Retained on sieve

(mm) Weight Retained

Weight of flaky

particles

Weight of

elongated

particles

25 20 262 86 84

20 16 1774 344 260

16 12.5 1786 308 242

12.5 10 602 116 130

10 6.3 574 114 106

Total 5000 968 822

Flakiness index = (968/5000) X 100 = 19.36

Elongation index = (822/5000) X 100 = 16.44

• This test is a simple test which is used to determine the amount of silt present as compared to a given amount of sand. It is measured in terms of volume and in terms of weight. The procedure for volume is quite simple, in which sand is filled into a cylindrical vessel with markings. Then water is introduced into the vessel and the vessel is shaken so that the sand completely mixes with the water. Then this mixture is allowed to settle for about 2 hours. This causes the silt to settle on top of the sand making two different layers. The markings on the cylinder help to determine the volume of silt as compared to the volume of sand which is expressed as a percentage.

• Range of silt is limited to 3% of total by wt. and 5% of total by volume