Dynamic 4D imaging of foamed bitumen by X-ray micro computed tomography Iwan JERJEN1,2, Biruk HAILESILASSIE3, Philipp SCHUETZ5, Mathieu PLAMONDON4, Alexander FLISCH4, Manfred PARTL3

1) Institute for Biomedical Engineering, ETHZ, Gloriastrasse 35, CH-8092 Zurich, Switzerland

2) Laboratory for Macromolecules and Bioimaging, Paul Scherrer Institut, CH-5232 Villigen-PSI, Switzerland

3) Road Engineering/Sealing Components, Empa, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland

4) Center for X-ray Analytics, Empa, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland

5) Lucerne University of Applied Sciences and Arts, Technikumstrasse 21, CH-6048 Horw, Switzerland

Abstract

Experimental setup

References

Foamed bitumen allows mixing and compacting warm asphalt at lower

temperatures, therefore reducing energy consumption and costs [1]. By

mixing a small quantity of water, typically 1- 6.0 w-%, with hot bitumen,

a foam is formed, which has, at a given temperature, better wetting and

coating capabilities than bitumen alone [1]. The amount of water, the

bitumen temperature and additives influence the structure and dynamics

of foamed bitumen, which determines its properties, like expansion ratio

and half-life time [2, 3].

Fast X-ray computed tomography (4 s per 3D CT) allows investigating

the time-resolved morphology of foamed bitumen if a stabilizer* is added

to slow down the collapse of the foam. * TEGO Addibit FS 725 A, EVONIK, Switzerland

1

2

3

4

5

6

1) X-ray flat panel detector (Perkin Elmer, XRD 1621 CN3 ES)

2) Rotation table (Micos, UPR-160 F air) 3) XYZ stages (Micos, LS-270)

4) X-ray microfocus tube (XT9160-TXD) 5) Bitumen supply hose

6) Plexiglas cylinder with bitumen foam (Ø 104 mm)

Image analysis

Conclusion

Reconstruction method

By means of a fibre reinforced plastic hose, 180° hot foamed bitumen was

injected into a Plexiglas cylinder mounted on the rotation table of the X-

ray system. The microfocus X-ray source was operated at 80 kV

acceleration voltage and 300 µA (i.e. 24 W). The X-ray detector was read

out with ~14.5 frames/s. The rotation speed was between 90 °/s.

No filter Mean filter

(radius 3), final choice

Median filter Non-local means

filter [5] Gauss filter

Mean filter

(radius 5)

The three-dimensional shape of the foamed bitumen was calculated from

59 projection images acquired over 360° by a Feldkamp algorithm [3].

Because of the low SNR of the projection images, different filters were

applied on the projection images prior to the reconstruction:

[1] J. W. Button, C. Estakhri, and A. Wimsatt, System 7, 94 (2007).

[2] M. F. Saleh, Int. J. Pavement Eng. 8, 99 (2007).

[3] B. W. Hailesilassie, P. Schuetz, I. Jerjen, M. Hugener, and M. N. Partl,

J. Mater. Sci. 50, 79 (2014).

[4] L. A. Feldkamp, L. C. Davis, and J. W. Kress, J. Opt. Soc. Am. A 1, 612 (1984).

[5] http://www.ipol.im/pub/art/2011/bcm_nlm/

[6] http://fiji.sc/Fiji

[7] https://en.wikipedia.org/wiki/STL_(file_format)

[8] http://www.volumegraphics.com/products/vgstudio-max/basic-functionality/

[9] http://www.gom.com/de/3d-software/gom-inspect.html

Even a low power (24 W) microfocus X-ray tube allows obtaining

reasonable fast (4s) 3D CT measurements for visualizing the time-

evolution of foamed bitumen:

• The use of a high power X-ray source would improve the SNR and

spatial resolution considerably.

• A faster X-ray detector would help to reduce motion artefacts.

• Optimized noise filters may improve the results.

• A gantry CT scanner would eliminate the centrifugal force artefacts.

The 3D CT data was inverted and filtered with a Gaussian blur filter

(radius 4) using the freeware Fiji [6], then the bubbles were segmented

and the surface data saved in STL file format [7] using a trial version of

VGStudio MAX [8]. The final visualization was done with the GOM

Inspect freeware [9].

Results

t = 0 s

Result not reliable due to

motion artefacts!

Nevertheless, bubbles

are fairly flat and have a

preferential direction,

probably due to the

initial spraying.

t = 14 s

Bubbles as small as

~0.5 mm3 can be seen.

The bitumen cooled

down a bit and is

therefore less viscous:

The shape of the

bubbles becomes

spherical.

t = 34 s

The bitumen collapsed

considerably and the

surface approaches the

ROI. The CT data

indicates that the

bitumen is less dense

close to the surface.