AASHO Road Test

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AASHO Road Test proving ground during the conversion to Interstate 80 , 1964

The AASHO Road Test was a large-scale test by the American Association of State Highway Officials for the empirical determination of road wear . The investigation, funded by the highway authorities of the individual US states through their joint association, took place north of Ottawa , Illinois in the USA from August 1956 to November 1960 . The service life of roads in relation to axle loads , tires , axle configuration and road structure was recorded on six circuits and then evaluated. The extensive investigations resulted in a guideline for road construction, the AASHO Interim Guide for the Design of Rigid and Flexible Pavements and thus laid the foundation for today's analytical consideration of road cross-sections and a large number of technical standards .

history

Inspection traffic on one of the bridges

In the middle of the last century there was a fundamental change in terms of goods transport and mobility. Trucks became increasingly heavier and more powerful, and national private transport continued to gain in importance. As a result, industrial nations began to build trunk road networks. In the USA, the government first regulated the construction of such a network with The Federal Aid Highway Act in 1921, after which the first routes were built. This was supplemented under President Dwight D. Eisenhower with the revised Highway Act of June 29, 1956, which provided for the expansion of the Interstate Highway network over the entire federal territory with connections to all major cities. On the other hand, there has been an inadequate - and, above all, poorly systematized - level of knowledge about the dependencies of the service life of roads, especially in relation to their construction and use, since planning. To remedy this discrepancy, the Association of Transportation Authorities of the Individual US States (AASHO) decided to conduct a series of investigations. The declared goal was to determine nationwide uniform guidelines and rules for the growing volume of traffic, whereby both the construction method of the road and the shape of its users should be regulated. The first of these investigations was the One-MD Road Test in Maryland in 1950 , in which different axle configurations were tested on an existing concrete road. A similar investigation on asphalt roads in Idaho followed in 1953 under the auspices of the Association of Western Transportation Authorities ( WASHO Road Test ). While these investigations were already taking place, the project of a large-scale experiment at the federal level was formed and by May 1955 a working group under the umbrella of the AASHO in cooperation with the National Research Council had developed project studies for implementation and financing. In July 1955, a branch office was opened in Ottawa, Illinois in preparation for the large-scale test. Illinois was chosen because it has a climate that is considered typical for North America, there was a level building site that saved time-consuming earthworks and, with the planned construction of Interstate 80, further use of the structures as a trunk road was foreseeable.

In July 1956, those responsible decided on the final test setup and the budget of US $ 27 million, and work on the circuits began in August of the same year. These were completed two months later, on October 15, 1958, and regular inspection began, which was to last two years. The permanent driving was only interrupted by a 5-hour break and several 20-minute breaks per day, during which the drivers changed and the vehicles were also serviced. By the time the inspection was completed on November 30, 1960, 1,114,000 axis transitions had been carried out on the bridges and the test areas. After the main tests were completed, a few more special studies followed in the spring and summer of 1961, in which a wide range of unusual loads were tested, while at the same time the conversion of the test facilities into a regular road began. For example, the use of oversized tires was tested, as well as the use of liquid containers that roll directly on the road, and against the background of the use of highways for military purposes, which was already laid down in the Highway Act , the testing of very high axle loads up to destruction was carried out the bridges. With the completion of these studies and the collection of data, the AASHO branch in Ottawa also ceased operations in January 1962.

Today the circuits are part of Interstate 80 or completely dismantled. Only route 1 has been preserved as a technical monument next to the trunk road ( location ).

Construction and measurements

Schematic representation of the circuits and location north of Ottawa

The test setup essentially consisted of six two-lane circuits, with routes 2 to 6 being used for driving. Section 1 was used to investigate environmental influences on the various materials used in road construction and was designed to be much shorter. In general, the circuits were made of asphalt or concrete in different thicknesses and with different base layers , right through to sections without any solidified substructure . The individual test sections of the designs were either 120  ft (37  m ) or 240 ft (73 m) long. The larger stretches 3 through 6 had a tangent length of 6,800 ft (2,073 m). By driving on the different road cross-sections with a vehicle type defined for each lane with constant weight, the interaction between vehicle load and structure could be examined. The routes were supplemented by two small bridges per lap, which, in addition to a variable construction, were also made of different materials. Among other things, compacted concrete, reinforced concrete or steel were used here.

Measuring the load-bearing capacity of the road with a Benkelman beam

In terms of data collection, the surfaces in particular were analyzed. The evenness was measured continuously, both longitudinally and transversely . There was also a continuous visual inspection of the damage. In addition, the control of stresses , settlement phenomena and load-bearing capacity was carried out using mobile and static measuring devices, such as the Benkelman beam and deflectographs installed on vehicles . In addition, vibrations were generated by means of heavy vibrators and their propagation in the underground and in the bridge structures was recorded. In addition, the position of the structure as a whole and its movement when crossing the bridge was measured. The development of crack formation was also monitored continuously. A system from IBM for electronic data processing was used to manage the extensive data - which was unusual for the time - which saved the extensive data on punched cards .

Results

The central finding from the tests was the confirmation of the assumption that the wear and tear on the road structure primarily depends on the axle load of the vehicles driving through it. The measured data even showed that the load on the road increases proportionally to the fourth power of the axle load. In other words: If the axle load doubles, the load on the road increases sixteen times (see also: Fourth power law ). The second key finding was the direct effect of layer thicknesses and the strength of the materials used on the life of roads. In order to have a uniform calculation and classification basis based on this knowledge, a load equivalence factor was introduced as a result of the data evaluation. This standardized load case is still an axis transition of 10 tons today , to which the real axis transitions are converted. A classification is then derived from the number of these standardized axis transitions , which in turn requires a minimum road cross-section. (For Germany: see also RStO .)

As a result, these findings were first published in 1961 in the AASHO Interim Guide for the Design of Rigid and Flexible Pavements . A set of rules that, in addition to specifications for the design of road cross-sections, also contained a concept for the maintenance-optimized, layered construction of asphalt pavements and emphasized the importance of the joint spacing and the connecting elements for concrete pavements. This set of rules has been continuously developed on the basis of more recent knowledge and is still widely used in the United States after extensive updates in 1972 and 1993.

meaning

In retrospect, the AASHO Road Test was probably the most extensive and important large-scale test of the 20th century in road construction research. The results formed an essential part of the basis of all modern roadway designs, especially in the area of ​​the North American highway system. In addition, the investigation led to clear requirements for the road structure and, based on this, to defined lifetimes of road surfaces. The results of the studies and the quality of the systemic evaluation were recognized worldwide and reflected accordingly in national standards. Even if the specific conditions of the tests in terms of location, environment and material properties were subject to the limits of their time and the actual driving with around 1 million axis transitions only represented a fraction of the current loads on roads, the results are supplemented by extrapolating , more contemporary mathematical Models and adaptations to regional environmental variables that take other local climatic conditions into account are still gaining ground in research.

Web links

Individual evidence

  1. ↑ Highway Histroy - AASHO Road Test. Federal Highway Administration, June 27, 2019, accessed August 11, 2020 .
  2. ↑ a b c d K.B. Woods, WA Bugge et al. a. (Ed.): The AASHO Road Test, Report 7, Summary Report . Highway Research Board, Washington, DC 1962, p. 6th f., 9 ff., 25 ff., 35 ff., 45 ( trb.org [PDF]).
  3. ↑ Key Events in AASHTO's History. AASHTO, accessed on August 24, 2020 .
  4. ↑ a b K.B. Woods, WA Bugge et al. a. (Ed.): The AASHO Road Test, Report 6, Special Studies . Highway Research Board, Washington, DC 1962, p. 5 f., 15 ff., 41 ff . ( trb.org [PDF]).
  5. ↑ a b AASHO Road Test. https://pavementinteractive.org , accessed August 11, 2020 .
  6. ^ AASHO Road Test - Ottawa, IL. Historical Concrete Pavement Explorer, 2016, accessed August 10, 2020 .
  7. ↑ a b Linda S. Watson, Neil J. Pedersen u. a .: Pavement Lessons Learned from the AASHO Road Test and Performance of the Interstate Highway System . In: Transportation Research Circular . Transportation Research Board, Washington, DC July 2007 ( trb.org [PDF]).
  8. ↑ S. Velske, H. Mentlein: Road construction technology . Werner Verlag, Düsseldorf 2002, ISBN 3-8041-3875-6 , p. 4 .
  9. ↑ Andreas Wolf and Regina Fielenbach: Model for road construction analysis of the stress on the BAB network induced by heavy traffic . In: Federal Highway Research Institute (Ed.): Reports of the Federal Highway Research Institute, Issue S61 . Verlag für neue Wissenschaft, Bergisch-Glattbach 2010, ISBN 978-3-86918-000-7 , p. 31 f . ( hbz-nrw.de [PDF]).
  10. ^ JP Hallin, TP Teng, LA Scofield: Pavement Design in the Post-AASHO road test Era . In: Transportation Research Circular . Transportation Research Board, Washington, DC 2007, p. 1-16 .
  11. ↑ WR Hudson, C. Monismith and JF Shook: AASHO road test Effect on Pavement Design and Evaluation After 50 Years . In: Transportation Research Circular . Transportation Research Board, Washington, DC 2007, p. 17-30 .
  12. ↑ Mesut Tiğdemir: Re-evaluation of the AASHTO Flexible Pavement Design Equation with Neural Network Modeling. November 14, 2014, accessed August 13, 2020 .

Coordinates: 41 ° 22 ′ 4 "  N , 88 ° 54 ′ 31"  W.