Wednesday, 10 April 2019

Tests On Aggregates

Aggregates Crushing Value
·       Aggregates crushing value gives a relative measure of ' resistance of an aggregates to crushing under gradually applied compressive load'
·       The crushing value of aggregate is restricted to 30% for concrete used for roads and pavements and 45%b may be permitted for other structures.

Aggregates Impact Value
·       Measures toughness of aggregates.
·       Toughness is usually considered as the resistance of the material to failure by impact .
·       Aggregates impact value shall not exceed 45 % by weight for aggregate used for concrete other than wearing surface and 30% by weight of concrete for wearing surface such as runways roads and pavements.

Aggregates Abrasion Test
·       Measures hardness or 'resistance against wear' which is important for aggregates to be used for road and pavement construction.
Common test t measure abrasion resistance are
a) Deval attrition test
b) Dorry abrasion test
c) Los Angels test

Bulking of Aggregates
·       Free moisture content in fine aggregate results in bulking of volume.
·       Free moisture from a film around each particle, and this film exerts surface tension which causes the bulking of sand.

Flakiness Index
·       It is the % by weight of particles in it whose least dimensions' ( thickness) is less than three fifth of their mean dimension.
·       This test is not applicable to sizes smaller than 6.3 mm.

Elongation  Index
·       It is the % by weight of particles whose greater dimensions ( length ) is greater than 1.8 million  their mean dimension.
·       This test is also not applicable to sizes smaller than 6.3 mm.

Specific Gravity and water absorption
Test methods for determining these properties are based on' Archimedes principle'.
·       Specific Gravity = C/B - A
·       Apparent specific Gravity = C/ C - A
·       Water absorption = 100 (B - C ) /C
Where ,
A = Weight ( in g) of saturated aggregates in water.
B = Weight ( in g) of saturated surface dry aggregate in air
C = Weight ( in g ) of oven - dried aggregates in air
·       Specific gravity for aggregates commonly used in construction varies between 2.5 -3.
·       Water absorption is  generally regarded as measure of 'porosity' and varies from 0.1-2 percent.

Stripping Value Test :
·       Also known as bitumen affinity test and it is carried out to known the behavior of aggregates towards bitumen.
·       Aggregates can be classified into 2 categories
a) Hydrophilic
b) Hydrophobic
·       Hydrophilic are water liking and they lose their bituminous coating in presence of water. on the other hand , hydrophobic retains bituminous coating even in presence of water.

Angularity Number
·    It indicates the amount by which the percentage voids exceeds 33% after being compacted in prescribed manner.
·       Angularity number = 67% solid volume
·       The Angularity number is expressed to the nearest whole number , and it ranges for aggregates used in construction is from 0 to 11.


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