24 Analytical Instrumentation - Focus on Lubricant & Condition Monitoring STANDARD TESTING METHODS FOR BITUMEN AND WAX
Bitumen is a heterogeneous crude oil by- product that is composed of complex hydrocarbon chains. It is commonly used for asphalt roads and roofi ng due to its hydrophobic qualities, adhesion, hardness, and general versatility [1]. Bitumen needs to be put through various quality assurance tests to confi rm its suitability for diff erent functions, most of which are established through the ASTM, that search for specifi c properties that arise from excess waste products like oil, water, and waxes; Waxes, specifi cally, have an ambivalent impact on bitumen depending on its intended function. In this paper, the various ASTM testing methods curated for bitumen and waxes will be outlined, as well as their signifi cance in industry use.
Distillation tests can be used to separate water or oil residue from bituminous material to determine its purity and inherent market value. Bitumen with a high-water content is inherently less desirable, especially when used for asphalt, as water causes the bitumen to foam when heated above 100 °C [2]. This can result in a cracked and undesirable appearance and reduced resilience of the asphalt. The acceptable amount of water in bitumen is 0.2% by weight to reduce this likelihood [3, 4].
To successfully test and ensure that this threshold is maintained, distillation through a Dean and Stark apparatus, as outlined in the ASTM D95, is utilized. This test method determines the volume of water in petroleum products in the range of 0% to 25% through distillation [4]. The Dean and Stark apparatus connects to a metal still and a condenser to separate water from bitumen. The apparatus is an addition to a refl ux condenser that condenses the solvent and water into a separate trap as opposed to the still. The higher density of the water in the water-immiscible solvent will result in two distinct layers forming that can be separated into a beaker. As the volume of the solvent increases towards the top of the trap, the solvent will begin to overfl ow back into the still, thus maintaining solvent volumes while extracting the water [4].
The ASTM procedure for carrying out this test consists of performing standard refl ux by mixing the bitumen sample and aromatic solvent and heating until refl ux begins. Then, as the two distinct water and solvent layers begin to appear in the Dean- Stark apparatus, wait until all the water is condensed from the
still. This can be determined by continuing refl ux for 5 minutes after the water level in the Dean-Stark apparatus, has stabilized. Once water levels become stabilized, the volume of the water collected in the trap must be observed and plugged into the following formula:
(volume in water trap,mL) - (water in solvent blank,mL) Volume in test sample,mL
*100 [5].
The precision of this test, as is consistent with most ASTM tests, is dependent on repeatability and reproducibility. Repeatability is defi ned as the difference between successive tests obtained by the same operator under the same lab conditions, and reproducibility is the difference between independent tests of identical test material conducted in different labs [4] [5]. For entirely precise results to be achieved, multiple iterations of this experiment must be undergone with a level of error within acceptable ASTM D95 standards.
Koehler sells the Dean-Stark apparatus (K31800) equipped with everything necessary for refl ux, including a metal still, gasket, O-ring seal, a ring burner, a 400 mL condenser, 10 mL and 25 mL traps, and mounting equipment. Additionally, Koehler sells an Aluminum alloy still (K31900), which can be used for oil and residue determination in emulsifi ed asphalt. This is a further method of quality control that can be used to determine the oil and residue content of emulsifi ed asphalt after distillation. The procedure includes standard distillation as per ASTM D244, in which the water content is separated from the asphalt leaving only the residue. A higher residue content indicates a higher concentration of asphalt binder which can enhance the adhesion and binding properties of the emulsion, whereas a lower residue content may result in a thinner asphalt fi lm which could impact the asphalt’s effectiveness [6].
Another important characteristic in bitumen testing is the softening point through the ring and ball test. This test determines when asphalt goes from semi-solid to liquid which is needed to test the proper climate for asphalt; asphalt with a lower softening point is not suitable for hotter climates, whereas asphalt with a higher softening point is more suitable for cooler climates [7]. The test is conducted by setting two balls on top of brass rings fi lled with hardened asphalt into a water bath that rises at 5 °C intervals [8]. Watch as the balls elongate the asphalt and note at what temperature the balls touch the bottom of the ball-centering apparatus. Koehler provides both an automatic and manual ring and ball apparatus, with the automatic having laser sensor detection for when the ball drops, a touch screen interface, and an integrated stirrer that makes the test easier and more exact. Koehler’s K95100 Automatic Softening Point Apparatus is shown in Figure 1.
Figure 1 K95100 Automatic Softening Point Apparatus
The Ductility test involves pulling the bitumen apart while immersed in water to gauge its ductility. The Bitumen sample is attached to a rectangular machine with a water basin and is pulled apart at 5 cm/min; the time at which the bitumen snaps is noted. After the ductility test is complete, the sample sits for an hour and is moved back so that the two ends are just touching. Elastic recovery can be calculated through the following formula:
Original elongation - elongation after completion of original elongation
[9].
Figure 2 K80050 Ductility Tester
These tests measure the adhesive property of the bitumen as well as its ability to stretch. Concrete expands during the day and contracts at night, so the bitumen will easily crack without proper ductility and elastic recovery [10]. The elastic recovery test determines the recovery of the AR binder after being stretched. A
PIN OCTOBER / NOVEMBER 2023
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