Assessment of spray material distribution in winter road service. Part 1: Assessment of moist-salt scattering patterns and their influential variables. Efficient de-icing requires an even as possible distribution of de-icing salts in sufficient quantity. A prerequisite is the correct suitability of the spreading machines for an automatic, high quality distribution of the de-icing salts. The existing requirements of spreading machines do not suffice for this. A constant spreading layer at various spreading densities and driving speeds is not required and therefore not achieved by most types of spreader machines. The scattering patterns often change considerably under different operating conditions in practice. Therefore, readjustments need to be carried out during operation by the spreading machine drivers. The spreading machine drivers must be experienced for this. Prerequisite for this is appropriate training. For the new procurement of spreading machines, automatic compliance of a spreading width or track positions for different spreading densities and driving speeds are recommended. The de-icing salt used also has a considerable effect on the scatter pattern quality. The spreading machine needs to be calibrated accordingly for the de-icing salt used. For the assessment of scatter patterns when spraying moist-salt, no procedures for the quantitative determination of the spray material distribution exist up to now. The results of the project work show that the correct calibration of the spreading machine and the influence of the air flow at output represent two significant influence factors on the spray material distribution. Therefore, the calibration of the spray material output should be assessed visually, and if necessary corrected by following the spreader at practice orientated driving speeds. Although this is a subjective procedure, it is considered as sufficiently exact for the assessment of spray width and track position. For more exact, objective assessments, two new procedures were examined in the frame work of this project work. These procedures allow an assessment of moist-salt scattering patterns at practice orientated driving speeds. In the first procedure, the spray material is distributed over rubber mats and subsequently sucked up in segments. In the second procedure, the spray material is distributed on the carriageway and subsequently swept. In conclusion, the spray material is gathered in segments, and weighed. The first procedure is very accurate at taking up of spray materials. The assembly of the test area with rubber mats however, is quite costly, and the influence of the different surfaces of the rubber mats on the scatter patterns could not be determined yet. The second procedure can be executed much faster. The sweeping up can however result in larger errors in the assessment of moist-salt scatter patterns, as for one, parts of the de-icing solution used collect in the carriageway, and secondly, part of the de-icing salts cannot be gathered due to insufficient sweeping. In order to determine the repeatability of the measurement results, further examinations are required. The results of investigation already carried out have been published repeatedly. It is recommended to incorporate these findings in a revised TLG B3 or into the planned European Standard for Spreading Machines and into the Leaflet for the Assessment of Spreading Machines. For a wider implementation of the findings by manufacturers and users, a high quality and more economical distribution of spray materials is expected. / Part 2: Determination of the repeatability of spray pattern assessments. An even distribution of spray materials on the carriageway in accordance with the operating instructions is an essential prerequisite for effective winter road maintenance service. Many spreading machines with moist-salt technology used for winter road maintenance do not achieve the desired evenness in spray material distribution. The available requirements and test procedures for the spray material distribution (TLG B3) no longer comply with current practical requirements. The starting point for the requirements and test procedures for the scattering pattern assessments of the two investigations carried out were two working papers: The current work status for an European Standard for Spray Material Distribution and the testing thereof, as well as recommendations by a federal-state working group on quality assurance for spreading machines. The latter suggests a new procedure, the so-called sweeping procedure, the repeatability of which was to be examined in this project. Both work papers indicated equal average minimum spray quantity per 1 m vertical stripe as a requirement. In this procedure spray materials distributed vertically to the carriageway over a given length are swept under realistic conditions and subsequently gathered in 1 m sections diagonally to the traffic direction. By weighing the gathered spray materials the compliance with the respective requirements can be assessed. A decisive quality feature of a test procedure for the spray material distribution is the so-called recovery rate of the distributed spray materials. In specific experiments a recovery rate of > 80% for fine granular de-icing salts and > 90% for the most common rock salts in Germany could be established. A further decisive question for the assessment of results of an examination is the length of the surface to be treated. Here both work papers mentioned differ. While the European Standard is based on a testing field length of 10m, German recommendations demand an average minimum spreading density in vertical stripes of 20 m length. Experiments with spreading machines already used for winter road maintenance service resulted in very large ranges in the results, despite equal conditions. The length of the testing fields was 10m. No machine met the current requirements. Type examination tests with new spreading machines showed clearly improved results. Up to a speed of 40 km/h, a large part of the spreading machines met the requirements at a test field length of 20 m. At higher speeds up to 60 km/h, the requirements were not met, with the exception of one result. The obtained result ranges relating to the average value amounted to 85% out of 300 examined spreading stripe segments, to less than 30%. The amount of deviation is thereby independent of the settings at the control panel and the driving speeds. Asymmetrical spreading with a width of 12 m and a speed of 60 km/h forms an exception. The sweeping procedure has proved itself in the tests for the examination of moist salt distribution. The procedure is easy to implement, but based on the demands on the test field surface and the required dry environment requirements, it is tied to two very limiting prerequisites. It is recommended including the procedure in existing policies of the FGSV. A relevant procedure description is the result of the project. (Author/publisher)
Samenvatting