Team introduction – Dr. Esdras Ngezahayo
Esdras has over 10 years of academic and industry experience in Civil Engineering. He specialised in Geotechnical Engineering at the University of Birmingham (UoB). His research interest lies in sustainable and climate-resilient materials for roads and railways, and his PhD thesis investigated erodibility of soils in rural roads. His research paper recently won an award for the PIARC UK competition in the category of “Roads Adapting to a Changing World” and received his award in a Ministerial presentation. Before joining the CRISPS project as a Research Fellow, Esdras was a researcher on a railway’s stabilisation project, investigating how hydrotex geotextiles reduce sub-ballast water flow, prevent pumping of clay, and improve railway drainage conditions. His role with CRISPS involves developing quality control anti-fraud systems, undertaking HDM-4 calibration and life-cycle analysis of epoxy asphalt surfaces, and project management and outcomes dissemination
Development of an Anti-fraud and Quality Control Method for MEAS and MECS Mix Designs
CRISPS investigates the use of three different road surfacing technologies for low-income countries. These include Modified Epoxy Chip Seal (MECS), Modified Epoxy Asphalt Surfacing (MEAS) and Fibre Matic Asphalt (FMA) in order to improve the life-cycle cost and performance of the road. However, in order to achieve the long-term performance benefits, it is vital to control the quality of the mix design as well as the mix on site. Thus, CRISPS developed a robust system to ensure quality control and prevent fraud. Fraud could take place by reducing the amount of epoxy used in the mix as this is the more expensive material. The two technologies utilizing modified epoxy bitumen binders (i.e., MEAS and MECS) require precise mix designs of a variety of materials, deviation from which can significantly reduce the performance of the resulting pavement surfacings.
As part of CRISPS, trial sections for MECS and MEAS will be constructed in Ethiopia. Different laboratory and field tests were reviewed to assess their suitability to monitor the quality of the material and hence prevent fraud. This review identified that both Fourier Transform Infrared (FTIR) spectroscopy equipped with Attenuated Total Reflectance (ATR) and Fast Neutron Activation Analysis (FNAA) can be used to test samples in the laboratory. This would provide a fingerprint of both the raw material and the mix which can then be used to assess the mix-design on site. It should be noted that the FNAA analysis requires specialist equipment which is not commonly available. Thus, correlations between the two techniques will be investigated as FTIR instrumentation is more common and available at Addis Ababa University.
The FTIR-ATR uses an infrared signal which is sent through the sample to generate spectra. The heights and areas of the peaks of the spectra are used to calculate the mass percentages of epoxy components. Similarly, FNAA uses radioactive neutrons which are fired at the sample to determine the oxygen content in the mixes, from which the mass content of the epoxy in the mix could be determined. A comparison between FTIR-ATR and FNAA is a strong measure to ensure that quality is controlled, and the in-situ mixes of materials for MEAS and MECS meet the required standard at the mix plants. FTIR-ATR tests were conducted at the Aston University’s Energy and Bioproducts Research Institute (EBRI) in the UK and FNAA tests are being undertaken using the MC40 Cyclotron in the Department of Physics and Astronomy, UoB, in the UK.
Sample preparation, testing and findings
The total of 28 modified epoxy bitumen samples (100 g – 200 g) for both FTIR-ATR and FNAA tests were prepared by mixing each of the bitumen 60/70 and 80/100 with epoxy percentages ranging from 0% to 35% by weight. The epoxy fraction was composed of epoxy resins (Part A) at 14.6% and epoxy hardener or curing agent (Part B) at 85.4% by weight, according to the supplier’s recommendation. The samples were oven-heated at 125oC for 10 minutes, stirred for 1 minute and left to cool to the room temperature before being tested.
A triplicate spectrum was recorded over the range of 500 to 2000 cm-1 wavelength for each sample and an average considered for analysis. Analysis was done using baseline and tangential approaches. The heights and areas of spectra for the two functional groups – carbonyl and sulfoxide – which are known to affect rheological changes of modified epoxy bitumen mixes during the short- and long-term ageing processes, were analysed and calculations done to obtain the mass of epoxy components. Since curing affects the spectra, the coefficients of curing correction were applied to the spectral areas of the functional groups.
Results show that FTIR could be an appropriate approach to prevent fraud and improve quality of MECS and MEAS mix designs and surfacings. Furthermore, it was found that epoxy content determined with FTIR agreed with standard mixes, with a linear regression coefficient of determination R2 = 0.99 for both the mixes containing 80/100 and 60/70 bitumen grades. In the same order of the mixes, the mean difference (FTIR-standard mixes) was 0.22% and 1.8%, leading to the overall mean difference of 1.01%. For the samples containing 25% epoxy by weight, the difference was 1.08% and 0.8%, respectively for the mixes with 60/70 and 80/100 bitumen. Figures 1 to 3 summarises FTIR tests, analysis, and results. A detailed testing procedure was presented in the 4th CRISPS Webinar and important references were provided with the CRISPS Reading Pack 04.
The key finding is that FTIR can be used to develop a ‘fingerprint’ of the material and the mix which enables the prevention of fraud, i.e. incorrect mixtures being used on site. This is particularly important as the costs of the two main materials, namely bitumen and epoxy, is significantly different with the epoxy being more expensive. Moreover, it can be used as a quality control to ensure the right mix is used with the desired long-life characteristics. The tests conducted in the UK provide the fingerprint signatures which will be used to assess the materials and the mix in Ethiopia.
Comparison between FTIR and FNAA
Although FNAA tests for the 28 samples are still under way, a comparison done using the results obtained by the Texas A&M University’s FNAA facility on 10 samples proved that both approaches (FTIR and FNAA) agreed with each other. The samples were for the New Zealand Transport Agency and from two mix plants (bitumen 60/70 and 80/100 grades were used), with 25% epoxy content by mass. The mean epoxy content found was 24.45% by FTIR and 23.25% by FNAA. The overall mean difference (FTIR – FNAA) was 1.2%.