The structural details of concrete and asphalt construction materials are crucial to their mechanical properties and performance. These details (such as porosity, cracks, pore connectivity, relative volume fractions of different constituents, density, etc.) can help to understand and improve the material properties for various structural applications in civil engineering. There are numerous well known methods used to measure these properties, but one particularly well-suited method for this application is still not widely known: 3D X-ray imaging – technically known as X-ray micro computed tomography (microCT). A recently published review paper in the journal Construction and Building Materials by researchers at Stellenbosch University provides a comprehensive overview of the various applications of this technique relevant to researchers in this field – and also discusses industrial applications for these materials.

MicroCT is increasingly becoming known for its ability to measure porosity, especially in this area for small concrete samples. However, it has many other very useful abilities which are still underutilized. Recent improvements in hardware and software tools allow improved quality and simplicity of obtaining results, which in some cases start to make it a “routine" method. For more advanced analysis types, there is also a great potential to better understand material properties based on more than a simple “porosity" value. 3D information which cannot be obtained by any other means include pore shapes, connectivity and relative pore sizes and their location in 3D relative to important other features. While there is lots of potential for academic and industrial application of the technique, the wider uptake is limited mainly by a lack of understanding of the technique. One way to overcome this is by standardization of workflows – fixed sample sizes, parameters and image analysis “recipes" for specific outputs. This is something proposed by the authors in a first attempt towards standardization (and has been used in the Stellenbosch CT facility for some time).

Other applications of the technique which are useful in this field are: analyzing failures by inspecting the cracks and internal details of a sample without cutting it open; performing permeability simulations or structural mechanics simulations (finite element analysis); non-destructively viewing the internal details of ongoing processes to view “time lapse" of processes such as corrosion of rebar, leaching of minerals or cracking due to mechanical testing. The authors used examples primarily from their work over the last seven years to demonstrate these capabilities and are thankful to the students and post-docs involved.

Fig. 1. Schematic of the microCT scan process, as applied to an asphalt sample. The 2D projection images are recorded as the sample is rotated, and shown below isan example of a CT slice image which can be viewed and analysed after reconstruction.

Media contact only:

Prof A. du Plessis

CT Scanner Facility, Central Analytical Facilities, Stellenbosch University

anton2@sun.ac.za

http://www.sun.ac.za/english/faculty/science/CAF/units/ct-scanner

www.sun.ac.za/ctscanner

Reference:

Du Plessis, A. & Boshoff, W.P. 2019. A review of X-ray computed tomography of concrete and asphalt construction materials. Construction and Building Materials. Vol 199 (2019): 637-651.  https://doi.org/10.1016/j.conbuildmat.2018.12.049