HOW TO PAVE THE WAY FOR EASIER BITUMEN ANALYSIS
Schwechat is a community located in Lower Austria, to the south-east of Vienna. Mainly known for its airport connecting the eastern part of Austria to the rest of the world and for the Schwechat refi nery, Schwechat has another signifi cant institution to offer: the I.M.U. (“Institut für Mineralölprodukte und Umweltanalytik”), an independent testing laboratory and consulting offi ce specialized in petrochemical and environmental analysis.
It is no mere coincidence that I.M.U. settled down in Schwechat: the refi nery is its main customer. Founded in 1996, I.M.U. employs around 50 people who cover all relevant analysis parameters for the requested sample analyses. In the well-equipped laboratories of I.M.U.’s seven specialized departments, fossil fuels, renewable raw materials, lubricants, petrochemical products as well as sediments, eluents, and microbiological samples are analyzed. Most analyses are performed according to standards and norms such as ASTM, EN, IP, ISO and AASHTO, but I.M.U. is also always ready to test new equipment and evaluate new procedures. One of the most requested samples to be analyzed is bitumen – or asphalt, as it is also called in some areas.
What “bitumen” means to the world
Many different standards for analyzing relevant bitumen parameters are valid worldwide such as ASTM and ISO standards. Other standards, such as BS and DIN, are linked to certain countries. The nomenclature may vary in different standards on the same topic: In Europe a differentiation is usually made between the expressions “bitumen” and “asphalt”. Americans tend to use the term “asphalt” for both materials.
Whatever the denotation, this substance is a highly sought- after building material worldwide because of its stability against environmental infl uences, mechanical and chemical stability, thermoplastic behavior and workability.
Bitumen, according to DIN 55946 and DIN EN 12597, is a dark high-molecular hydrocarbon mixture, its consistency ranging from semi-solid to glassy hard. Bitumen acts as a binder, while asphalt is a mixture of bitumen and crushed stone, mainly to be used for paving roads.
Bitumen is not only used for road construction, but also for roof tiles, in the protection of buildings against humidity, as a dampening coating for vehicles and dividing walls, as fl oor cover for frequently walked-on areas and for many other applications.
The classical way: Density measurement of bitumen with a pycnometer
Density measurements on bitumen have to be carried out with a pycnometer according to EN 15326 titled “Bitumen and bituminous binders - Measurement of density and specifi c gravity - Capillary-stoppered pycnometer method”, the equivalent to ASTM D70. This determination method requires a lot of experience, skill, and time, not only for the measurement itself, but also for the cleaning procedure after each measurement. Samples are usually submitted to the laboratory in tin cans, and have to be brought to elevated temperatures to liquefy the bitumen so it can be transferred into the pycnometer according to a standard which clearly defi nes the duration and temperature for heating the sample.
The hot container is grabbed with a rubber glove. Sample is poured into the pycnometer to around three quarters of its capacity through its neck which is only about 2 centimeters wide – without splashing and without the bitumen touching the inner walls above the fi nal fi lling level. Considering the possibility that in the hot, black liquid an air bubble could get trapped that
Figure 1. A hot bitumen sample is injected into the heated DMA 4200 M measuring cell
cannot be seen, the norm requires double determinations. If the two results are not in agreement, a third determination has to be performed. After a determination is fi nished – this takes up to three hours –, the pycnometer has to be cleaned of any residues, which requires a considerable volume of solvent, e.g. toluene, and protective equipment.
“It takes more time and effort to clean the pycnometer than to perform the measurement,” states Natascha Schultze, leading employee at the I.M.U. laboratory. “After the measurement I need to place the pycnometer in the oven for some time to soften the sample, and while pouring it out afterwards it hardens again. Then the pycnometer is soaked in toluene. The rest is removed manually by mechanical cleaning.”
Fortunately, there is more than one way to determine the density. Several ASTM standards (ASTM D4052, D5002, D7777) specify
Due to its many uses, the demand for bitumen is high, and the specifi cations vary with respect to its intended use. No wonder that the daily number of bitumen determinations in the I.M.U. laboratories is so high.
Several tests are performed to characterize the bitumen samples such as the Ring-and-Ball test and the Fraass breaking point or tests with a dynamic shear rheometer because viscosity, rheological properties and the softening point are among the interesting characteristics. Orders of bitumen are usually delivered by volume, but the bitumen price is based on weight. Thus, the volume needs to be converted into weight by means of the bitumen’s density. For that reason, another regular test on the daily to-do list is the determination of the density of bitumen.
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