3/20/2015 Exp 2 Angularity Number ­ Civil Engineers PK

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Exp 2 Angularity NumberEXPERIMENT NO. 2Determination of Angularity Number for the givenaggregate sample.This test is also carried out for determining shape of the aggregates. Based upon shape the aggregatesmay be classified as Rounded, Angular or Flaky. Angular particles possess well defined edges formed atthe intersection of roughly planer faces and are commonly formed in aggregates prepared by crushingof rocks.

Angularity in general is the absence of rounding of particles of an aggregate. This test is performed todetermine the angularity number i.e. the absence of roundedness or the degree of angularity of theaggregate specimen.

RELATEDTHEORY

SHAPES OF PARTICLES

The usual shapes of the particles are;

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3/20/2015 Exp 2 Angularity Number ­ Civil Engineers PK

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1. Rounded (river gravel)2. Flaky (laminated rock)3. Elongated4. Angular (crushed rock)

ANGULARITY

It is the absence of roundness. An aggregate particle, which is more rounded, is less angular and viceversa.

ANGULARITY NUMBER

Angularity number of an aggregate is the amount (to the higher whole number) by which the percentageof voids in it after compacting in a prescribed manner exceeds 33.

Where, “33” is the percentage of volume of voids, in a perfectly rounded aggregate. “67” is thepercentage of volume of solids in a perfectly rounded aggregate.

The value of angularity number generally lies between 0 & 11. In road construction angularity number of7 – 10 is generally preferred.

SIGNIFICANCE

The degree of packing of particles of single sized aggregate depends upon the angularity ofaggregate.The angularity of the aggregate can be estimated from the properties of voids in a sample ofaggregate compacted in a specified manner.The angularity number ranges from 0 for a highly rounded grave to about 11 for freshly crushedangular aggregates.Higher the angularity number, more angular and less workable is the concrete mix.In cement concrete roads (rigid pavements) rounded aggregates are preferred because of betterworkability and higher strength.In bituminous or water bound macadam construction (like flexible pavements), angular aggregateswith high angularity number are preferred because of high stability due to better interlocking andfriction.Higher the angularity number, more angular and less workable is the concrete mix.In road construction, angularity number of 7 ­10 is generally preferred.

APPARATUS

1 – A metal cylinder of about 3­liter capacity.

3/20/2015 Exp 2 Angularity Number ­ Civil Engineers PK

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2 – Temping rod of circular cross­section, 16mm Φ, 60cmin length. Rounded at one end.

3 – A metal scoop.

4 – A weighing balance.

PROCEDURE

This procedure is for aggregate size ¾ to No.4. If aggregateis coarser than ¾, a cylinder of large capacity shall berequired but amount of compactive effort or energy shouldbe proportional to the volume of the cylinder.

10 Kg of thesample is takenfor the test.The materialshould be ovendried. Theaggregate iscompacted inthree layers,each layerbeing given100 blowsusing thestandardtamping rod ata rate of 2blows/second by lifting the rod 5 cm above the surface of the aggregate and then allowing it to fall freely.The blows are uniformly distributed over the surface of the aggregate. After compacting the third layer,the cylinder is filled to overflowing and excess material is removed off with temping rod as a straightedge.

The aggregate with cylinder is then weighed. Three separate determinations are made and mean weightof the aggregate in the cylinder is calculated.

Calculations & ResultsMethod – 1

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Add measured quantity of water in the compactedaggregate till all the voids are filled and water appears tothe surface. Volume of water added is approximately equalto the volume of voids in the compacted aggregate.

Angularity Number = (Volume of water added/Total volume )x 100­33

Method – 2

Angularity Number = 67­(100W/CGs)

where,W = mean weight of the aggregate filling cylinder.C = Weight/Volume of water that can completely fill thecylinder (= 3 liters = 3000 ml – in our lab)G = Specific Gravity of the aggregate.

Notes:

1­ Method – 1 determines the angularity number from the solids point of view.2­ Method – 2 determines the angularity number from the voids point of view.

Observations & Calculations

Specific gravity of the aggregate = 2.67Total volume of the cylinder = 3042.18 cm3

MeanValue tobe used

Weight (grams) Volume ofWateradded (ml)

Angularity Number

EmptyCylinder

Cylinder +Aggregates

Cylinder +Aggregates +Water

Aggregate Method 1 Method 2

5040 9948 11233 4931.67 1261.33 8 6

5040 10032

5040 9935

5040 9971.67

Specific gravity of the aggregate = 2.67

s

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Total volume of the cylinder = 2970 cm3

MeanValue tobe used

Weight (grams) Volume ofWateradded (ml)

Angularity Number

EmptyCylinder

Cylinder +Aggregates

Cylinder +Aggregates +Water

Aggregate Method 1 Method 2

5040 9948 11233 4931.67 1261.33 9 5

5040 10032

5040 9935

5040 9971.67

COMMENTS

In the first table we have used the volume written on the container but in the second container wepoured water and then measured the volume , the container was not fully filled, So we can say the firsttable is more reliable and the difference between both the methods may be due to the face that we didnot measure the specific gravity. We used 2.67 which can be different then the actual value but both themethods should give the same result.

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