Aggregate Gradation

CIVL 3137 2

Important Properties

Hardness (resistance to wear)Durability (resistance to weathering)

Shape and surface texture

Relative density and absorptionGradation

Deleterious substancesCrushing strength

Soft and lightweight particlesChemical stability

Gradation Analysis

A gradation analysis (or sieve analysis) is a procedureused to assess the particle size distribution (gradation)of a granular material by allowing the material topass through a series of sieves of progressivelysmaller mesh size and weighing the amount ofmaterial that is stopped by each sieve as a fraction ofthe whole mass. The size distribution is often ofcritical importance to the way the material performsin use.

CIVL 3137 3

CIVL 3137 4

Gradation Analysis

percent coarseror

percent retained

percent fineror

percent passing

Percentagesare calculatedby mass

CIVL 3137 5

Gradation Chart

0

20

40

60

80

100

Perc

ent

Pass

ing

Total mass percent passing each sieve

100 10 1 0.1 0.01

Opening Size (mm)

(typically used for soil)

4.75

CIVL 3137 6

Gradation Chart

0

20

40

60

80

100

Perc

ent

Pass

ing

Total mass percent passing each sieve

0.01 0.1 1 10 100

Opening Size (mm)

(typically used for aggregate)

4.75

Sieve Shakers

CIVL 3137 7

Mary Ann Shaker

Screen Shakers

CIVL 3137 8

Gilson Shaker

CIVL 3137 9

Sieve Sizes Used in Construction

CIVL 3137 10

Sieve Sizes Used in Construction

Openings vary bya factor of two

CIVL 3137 11

Gradation Chart

0

20

40

60

80

100

0.010.1110100

Perc

ent

Pass

ing

(%)

Opening Size (mm)

1½" ¾" 3/8" 4 8 16 30 50 100 200

CIVL 3137 12

Gradation Example

CIVL 3137 13

Gradation Example

CIVL 3137 14

Typical Aggregate Gradations

Open-graded aggregate

Gap-graded aggregate

Uniformly graded aggregate

Dense-graded aggregate

All of the particles are approximately the same size

Very little fine aggregate thus lots of void space between particles

Very little aggregate in the medium size range

Lots of different particle sizes thus very little void space

CIVL 3137 15

Uniformly Graded Aggregate

0

20

40

60

80

100

0.010.1110100

Perc

ent

Pass

ing

Opening Size (mm)

1½" ¾" 3/8" 4 8 16 30 50 100 200

“clear”gravel

uniformsand

CIVL 3137 16

Uniformly Graded Aggregate

Narrow range of sizesGrain-to-grain contactHigh void contentHigh permeabilityLow stabilityDifficult to compact

CIVL 3137 17

Open-Graded Aggregate

0

20

40

60

80

100

0.010.1110100

Perc

ent

Pass

ing

Opening Size (mm)

1½" ¾" 3/8" 4 8 16 30 50 100 200

Opengradedgravel

Opengradedsand

Few finesFew fines

CIVL 3137 18

Open-Graded Aggregate

Decent range of sizesVery few fine particlesGrain-to-grain contactHigh void contentHigh permeabilityHigh stability Difficult to compact

CIVL 3137 19

Gap-Graded Aggregate

0

20

40

60

80

100

0.010.1110100

Perc

ent

Pass

ing

Opening Size (mm)

1½" ¾" 3/8" 4 8 16 30 50 100 200

Opengradedgravel

Opengradedsand

Gapgradedblend

Missingsizes

CIVL 3137 20

Gap-Graded Aggregate

Wide range of sizesMissing middle sizesNo grain-to-grain contactModerate void contentModerate permeabilityLow stability Easy to compact

CIVL 3137 21

Dense-Graded Aggregate

0

20

40

60

80

100

0.010.1110100

Perc

ent

Pass

ing

Opening Size (mm)

1½" ¾" 3/8" 4 8 16 30 50 100 200

Densegradedgravel

CIVL 3137 22

Dense-Graded Aggregate

Wide range of sizesGrain-to-grain contactLow void contentLow permeabilityHigh stabilityDifficult to compact

CIVL 3137 23

Fuller’s Curve

Fuller, W.B. and Thompson, S.E. “The laws of proportioning concrete," Transactions of the ASCE, v. 159, 1907.

0.50i

idpD

pi = percent passing ith sievedi = opening size of ith sieveD = maximum particle size

Produces the highest density and lowest void content

CIVL 3137 24

Aggregate gradation curves: (a) maximum density gradations for 37.5 and4.75 mm sizes based on the Fuller relationship; (b) a uniform aggregate;(c) a gap-graded aggregate; (d) screenings.

CIVL 3137 25

FHWA Maximum Density Curve

In 1962 FHWA published a modified version of Fuller’s equation with a different exponent.

0.450.50

ii

dpD

pi = percent passing ith sievedi = opening size of ith sieveD = maximum particle size

Produces the highest density and lowest void content

CIVL 3137 26

Maximum density curves on Federal Highway Administration 0.45 power gradation chart.

CIVL 3137 29

Dense-Graded Aggregate

0

20

40

60

80

100

0.010.1110100

Perc

ent

Pass

ing

Opening Size (mm)

1½" ¾" 3/8" 4 8 16 30 50 100 200

TDOT 411-D

MaximumDensityCurve

CIVL 3137 30

Dense-Graded Aggregate

0

20

40

60

80

100

0 1 2 3 4 5

Perc

ent

Pass

ing

Opening Size (mm) Raised to the 0.45 Power

200

TDOT 411-D

1/2" 5/8"

MaximumDensity

Curve