Extract, Analyze According to ASTM D8159
BY Dr. Telma Keppler
Editor’s Note: The work item (WK58842) titled “New Test Method for Automated Extraction of Asphalt Binder from Asphalt Mixtures” from the American Society for Testing and Materials (ASTM) has resulted in the published document D8159-2018. It offers guidance on the use of the Asphalt Analyzer designed by InfraTest Testing Systems, Germany. The following article from InfraTest offers more information.
The “automated asphalt extraction” method is used for quality control/quality assurance (QC/QA), acceptance criteria and research activities. It has been shown, through research, to offer an efficient and safe solvent-based extraction of asphalt binder from asphalt mixtures, to characterize and control the quality of asphalt mixtures by measuring asphalt content and studying the aggregate gradations.
To perform the method, an operator uses the Asphalt Analyzer, which is designed to automatically extract asphalt binder from loose asphalt mixtures in a closed system while being exposed to almost zero solvent emissions coming from the extraction process. This system includes an extraction chamber, a high speed centrifuge, a solvent recycler and an aggregate dryer. This system also represents an alternative to traditional extraction methods used in the past. It offers some advantages:
- It extracts asphalt binder through heating, solvent and ultrasonic waves, thus measuring accurately while providing repeatability between different replicates.
- It recycles the solvent after each extraction.
- It collects all fines passing 75 microns (sieve #200) or 63 microns using built-in high speed centrifuge.
- It produces dry-washed aggregates that are ready for washed gradations, which minimizes the time spent washing and drying. Effective drying is completed through heating and ultrasonic wave pulses that agitate the solvent particles. The full process is typically performed in less than an hour.
- It allows the operator to collect recovered asphalt sample for binder recovery to study the properties of asphalt binder.
This technology allows QC/QA managers and researchers to evaluate the composition of their asphalt mixtures and eventually the performance in the field. The performance of this equipment was evaluated by comparing the asphalt content measured by the Asphalt Analyzer and the Reflux for four materials:
- 4.75 mm NMAS polymerized leveling binder;
- 9.5 mm NMAS N70 mixture;
- fine fractionated reclaimed asphalt pavement (FRAP); and
- coarse FRAP.
The study also looked at the repeatability of field-collected asphalt mixtures by measuring asphalt binder content and fines collected in the high speed centrifuge. Figure 2 demonstrates the results of the study.
In part A of the figure, comparison between the Asphalt Analyzer and the Reflux, the results show minimal variation (0 to 0.3 percent) in asphalt binder content measured by both with an average standard deviation of 0.07 and a coefficient of variation of less than 1.4 percent. The low variation is referred to the automation of the process, which standardizes the procedure to eliminate labor error.
Part B of the figure presents the variation of asphalt content by studying multiple replicates of the same material that were collected from the field. The measured asphalt content varied from 5.95 to 5.69 percent with an average of 5.82 percent, a standard deviation of 0.09 percent, and coefficient of variation of 1.5 percent. This proves the low variability within a large sample of replicates from the same material.
The impact of different operators was also studied using two different Asphalt Analyzer units and three different operators. This part of the study included three different materials:
- recycled asphalt shingles (RAS);
- 25 mm NMAS; and
- 9.5 mm NMAS.
Both asphalt binder content and amount of fines passing sieve #200 were studied. The results are shown in Figure 3. Minimal variation was noticed (0.1 percent) between different operators for the three materials due to the full automation of the process. The operator is not involved in the actual extraction of asphalt binder, which reduces variability due to human error.
Safe Solvent Handling and Limited Exposure
An environmental analysis was conducted to check the amount of emissions during extraction. A known volume of air was drawn through specially prepared sampling tube that contains two section of coconut shell charcoal (SKC 226-09 tube). Methylene chloride and Trichloroethylene (TCE) was tested using the Asphalt Analyzer. The investigation of the exposure of workers to solvent fumes involved the Asphalt Analyzer, regular centrifuge, and the results were compared to Occupational Safety and Health Administration’s (OSHA) 8-hour TWA-PEL limit of 25 ppm. During the study, the worker was exposed to methylene chloride at a concentration of 28.8 ppm using the centrifuge, which exceeds the aforementioned OSHA limit. Using the Asphalt Analyzer reduced the exposure to 0.6 ppm.
The aggregates gradations were also examined to ensure the automated extraction is offering comparable results to standard methods and not causing aggregate degradation during rotation in the washing chamber. Figure 4 presents sieve analyses conducted for aggregates of the same material after extraction using Reflux (one sample) and Asphalt Analyzer (three samples). The results show the Asphalt Analyzer does not alter the gradations in the washing chamber.
Based on the examination that was performed to evaluate the performance and operation of the Asphalt Analyzer, researchers determined this equipment is an effective tool to help QC/QA managers expedite the process of measuring asphalt content accurately, safely and efficiently. It is an automated operation that eliminates operator error and uses the labor time efficiently to perform the actual calculation of asphalt binder content.
Dr. Telma Keppler is a business development manager with InfraTest GmbH, Germany.