Elongation index of the aggregate

Elongation Index of Aggregate

[BS 812 – Part 105.2: 1990]

·         Preparation of Specimens:

1.       Take quantity material of aggregate (bulk sample) randomly from source.

2.       Reduce the Sample to test portions by Sample Divider or Quartering with minimum mass as shown in Table 1:

Nominal size of material (mm)	40	28	20	14	10
Minimum mass of test portion (kg)	15	5	2	1	0.5

3.        

Dry the test portion in oven at (105±5) ^oC until constant mass, and then record M_o in (g).

·         Testing:

-          Place the test portion into container.

-          Discard all aggregates retained on 50.0 mm test sieve and Passing 6.30 mm.

-          Pour the residue on top of coarsest sieve and shake it manually or by mechanical shaker for sufficient time to separate into size fractions as in table 2:

Nominal size of test sieve (mm)	100% passing	50.0	37.5	28.0	20.0	14.0	10.0
	100% retained	37.5	28.0	20.0	14.0	10.0	6.30
Gaps between pins of gauge (mm)		78.7	59.0	43.2	30.6	21.6	14.7
Minimum mass of test portion (kg)		35	15	5	2	1	0.5

-           

-        

  Check the separation is complete by hand sieving.

-          Weigh the individual size-fractions retained on each sieve in (g).

-          Sum the masses of the fractions (M₁) in (g).

-          Calculate the individual percentage retained and discard fraction of less than 5%.

-          Record the remaining mass by (M₂) in (g).

-          Gauge each size-fraction by length gauge.

-          Combine all Elongated particles (not passing) and weigh (M₃) in (g).

·         Calculation:

-          Calculate the corrected mass of elongated particle (M₄) in (g) = (M₁/M₂) xM₃.

-          Calculate the % elongated particle (M₅) = (M₄/M₁) x100.

-          Calculate the value of Elongation Index = (M₅xM₁)/100.

-          Express Elongation Index to nearest whole number.