Mesostructural evolution of fine-aggregate bitumen emulsion–cement composites by X-ray tomography

ABSTRACT

This research quantified the temporal mesostructural evolution of bitumen emulsion–cement composites using the time-lapse high-energy X-ray tomography of a fine-aggregate matrix. The image post-processing and analysis showed that the mastic’s significant temporal decrease in volume complemented the expansion of the pore space. Nevertheless, the volume fractions determined by the image analysis essentially differed from the physical composition of specimens and were several times less sensitive to curing. Because of the extremely heterogenous microstructure and the abundance of calcium, the mastic phase had the highest attenuation of X-rays, but the attenuations of bitumen- and cement-dominated systems experienced contrary temporal trends. The sand and pore space had typically smooth and oppositely evolving axial distributions with the highest-density plateau in the middle, while the mastic was distributed uniformly. The radial distributions evolved less irregularly and notably interfered with the post-processing of beam hardening. The temporal increase in the pore space’s local thicknesses was extremely unevenly distributed across diameters. Except the sand particle size distributions, all results were almost excellently repeatable. Finally, the interaction with X-rays was identified as crucial for the interpretation and validity of the results. Moreover, although water could not be segmented using the conventional X-ray tomography, its discrete signature was present throughout the behaviour of other phases.

KEYWORDS:

• Multiphase systems
• fine-aggregate matrix (FAM)
• morphology
• pore space
• temporal evolution
• X-ray computed tomography (XCT)
• image analysis
• spatial distribution of phases
• local thickness distribution

Acknowledgements

The authors thank AkzoNobel Surface Chemistry AB (Sweden) for producing the bitumen emulsions, Normensand GmbH (Germany) for producing the modified standard sand, as well as HeidelbergCement AG (Germany) for providing the cement. Miomir Miljković: conceptualisation, methodology, formal analysis, investigation, writing — original draft, writing – review & editing, visualisation; Michele Griffa: methodology, software, formal analysis, investigation, writing – review & editing; Beat Münch: methodology, software; Mathieu Plamondon: methodology, software, investigation; Pietro Lura: writing – review & editing, supervision.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Swiss Confederation, Federal Commission for Scholarships for Foreign Students: [Grant Number 2017.0020 / Serbien / OP].