Test & Measurement 2012C O N F E R E N C E & W O R K S H O P2 - 5 SEPTEMBER 2012

Dr Joseph Anochie-BoatengCouncil for Scientific & Industrial Research (CSIR)Pretoria, South Africa

Improved measurement of aggregate

properties for asphalt mix design

05 September 2012

HMA

Unbound base

Cemented subbase

Upper selected subgrade

Lower selected subgrade

In situ subgrade

Wheel loading

HMA

Unbound base

Cemented subbase

Upper selected subgrade

Lower selected subgrade

In situ subgrade

Wheel loading

� Aggregates constitute ~ 80 - 95% by mass of layer materials� Function as load transfer and drainage medium� Play an important role in the performance of pavement/track structures

� Road pavement structure � Railway track structure

Aggregates in pavements & railway track structures

Coarse aggregates in roads & railway structures

� Rock aggregates > 85% Portland cement concrete & 90% of asphalt pavements (by mass)

� Railway track ballast, seal roads are essentially coarse aggregates

� Coarse aggregates constitute the skeleton & occupy by far the highest mass or volume!...

Shape/surface properties

� Equi-dimensional preferred over flaky (flat) and elongated

� Crushed/angular preferred over rounded� Rougher surface textured preferred over smooth� Larger specific surface area preferred

� better bonding of aggregates with Portland cement� better binding of aggregates with bituminous binder

Challenges in aggregate measurements

� Current standard test methods for quantifying shape/surface properties have several limitations

Test methods for aggregate shape properties

Shape property Test method

Flakiness Gauge slots THM1- Method B3

Flat & elongation Proportional callipers ASTM D 4791

AngularityCoarse aggregates: Visual inspection of fractured faces ASTM D 5821

Texture Particle index test ASTM C 3398

Observations on the conventional methods

� Time consuming, laborious and subjective (low repeatability)

� No standard test for texture; combined with shape and angularity

� Current tests provide average values and not a distribution of shape properties

� Contradictory findings in the literature on the influence of shape on performance

Current state-of-the-practice

� All aggregates presented here are retained on 19 mm sieve by current standard grading methods (TMH 1-Method B4, ASTM C 136, AASHTO T27)

Current state-of-the-art

Image-based techniques

� Generally fast, efficient and automated

� Eliminates subjectivity associated with the conventional methods

� Mostly 2D & quasi-3D

3D Laser-based techniques

� Directly measures 3D properties of aggregates with higher accuracy

� Realistic quantification of shape/ surface properties

Conventional methods� Shape properties not

differentiated� Time, labour intensive� Subjective, low

repeatability� Lack of numerical

quantification

CSIR 3D Laser device

Need for improved methods

� CSIR strategic basic and applied research project� Three year project (2011 – 2014)� Funding is provided by CSIR R&D office through

Department of Science & Technology� Total estimated cost of R7,5 million over three years

Element built in Discrete Element Method (DEM) with desired shape properties

Aggregate processed through 3D Laser scanning

Particle interactionLab testing

F1

F1

F2

F2

F3

F3

F4

F4F5

F5

F6 F6

Aggregate sourcing

3D Polyhedrons

Project overview

Objective

� Employing a modern 3D laser scanning and numericaltechniques to effectively quantify aggregate/ballast shape and surface properties� quantitatively relate the properties of aggregate particles

(pavements) and track ballast (railway) to performance � influences of aggregate/ballast shape, size, orientation,

angularity and surface roughness on performance of pavements and rail track structural layers will be understood

� DEM models will be used to simulate stress/strain transfer within the unbound aggregate/ballast layers of pavements and railway track structural layers

� Originally designed for solid shape modelling in medical and manufacturing applications

� Uses advanced non-contact sensor to scan objects up to 100 microns (0.1 mm) resolution

� Operates in both rotational and plane scanning modes

� Captures flat areas, hollow objects, oblique angles and fine details of objects with a laser beam

3D Laser scanning device at CSIR

Rapidform software

3D Laser scanning at the CSIR

Page 10 from 17

Aggregate scanning & processing

Modelled aggregate particles

Actual Scanned

Actual Scanned

17

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30 35

Mea

sure

d su

rfac

e are

a (m

m2 )

Particle number

19-mm 13.2-mm9.5-mm 6.7-mm4.75-mm

Mix 1

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30 35

Mea

sure

d su

rfac

e ar

ea (m

m2 )

Particle number

19-mm 13.2-mm9.5-mm 6.7-mm4.75-mm

Mix 2

Mix 1

Mix 2

Surface areas of coarse aggregates in 5 asphalt mixes

18

0

500

1000

0 5 10 15 20 25 30 35

Mea

sure

d su

rfac

e are

a (m

m2 )

Particle number

9.5-mm 6.7-mm4.75-mm Mix 3

0

500

1000

0 5 10 15 20 25 30 35

Mea

sure

d su

rfac

e are

a (m

m2 )

Particle number

9.5-mm 6.7-mm4.75-mm Mix 4

Mix 3

Mix 4

Surface areas of coarse aggregates in 5 asphalt mixes

19

Mix 5

0

500

1000

1500

0 5 10 15 20 25 30 35

Mea

sure

d su

rfac

e are

a (m

m2 )

Particle number

13.2-mm 9.5-mm6.7-mm 4.75-mm

Mix 5

Surface areas of coarse aggregates in 5 asphalt mixes

∑= PC SA 100

1

SA = Surface area of the aggregate (m2)P = Percentage by mass passing sieve sizesC = Surface area factor (m2 /kg)

Sieve sizes (mm)

Surface area Factor (m2/kg)

26,5

0,4119,013,29,56,7

4,75 0,412,36 0,821,18 1,640,600 2,870,300 6,140,150 12,290.075 32,77

� Surface area is obtained from the following formula:

� Current method specifies surface area factors for coarse and fine aggregates

Surface area for asphalt mix design

)000,1(MSA

VT asp

F ×=

Typical surface area results

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30

Mea

sure

d S

urf

ace

Are

a (m

m2 )

Particle Number

19-mm 13.2-mm 9.5-mm 6.7-mm 4.75-mm

Comparison of surface area factors

Particle size (mm)

SA factors in TRH8,

MS-4 (m2/kg)

Laser based surface area factors (m2/kg)

Mix 1 Mix 2 Mix 3 Mix 4 Mix 5

19

0,41

0,141 0,124 - - -

13,2 0,173 0,164 - - 0,199

9,5 0,242 0,210 0,233 0,257 0,236

6,7 0,322 0,301 0,304 0,315 0,315

4,75 0,41 0,462 0,389 0,435 0,423 0,458

Comparison of surface areas

Mix SA based on

factors (m2/kg)

SA based on 3D Laser scanner

(m2/kg)% Difference

1 0,619 0,867 28,6

2 0,615 0,796 22,7

3 0,664 0,734 9,5

4 0,652 0,735 11,4

5 0,521 0,625 16,7

Conclusion remarks

� Laser based approach can overcome and improve limitations associated with conventional methods for aggregates

� There are variations in the surface area factors determined through the laser (automated) and conventional (manual) methods

� The laser scanning approach offers South Africa an opportunity to optimize aggregate resource utilization in roads and railways track structures

� Industry, universities, research institutions have shown interest (technology transfer)

Angularity? Form? Texture? Surface area?

Thank you!