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Workshop on pavement design

Hotel Plaza, 15th November 2012, Ljubljana.
Number of participants: 70.

Objectives of the workshop:
The workshop was designed to review the existing methods of pavement design in the participating countries (Slovenia, Austria, Germany and the Czech Republic) and about the view of the future. The workshop involved the leading representatives of their countries from the universities and the industry. The organizer of the meeting was ZAS, the Slovenian Asphalt Pavement Association with the cooperation of the Austrian group OMV, which is in this part of Europe a leading producer and supplier of bituminous products.

ZAS had organized a similar workshop with only local participants in 2008, so that the conclusions of that workshop and the state of the art in this area were the initial contributions to the implementation of the workshop. The President of ZAS Slovenko Henigman gave a keynote speech and a presentation on his views to this area in Europe and the experiences and dilemmas in Slovenia.

Slovenko Henigman"Transport of people and goods is one of the most important priorities of the European Union, which is reflected in the constant increase in both individual and business travel. According to the information from the most powerful economy in European Union, that is Germany, the traffic loads will increase by 50 to 70% until 2025. By far the largest share of the burden will fall on the roads."


Mr. Henigman continued with an overview of the situation in Slovenia, where technical regulation in the last 15 years was continuously updated, though many challenges and dilemmas still remain opened. He praised the proposal for joint action in the organization of that meeting and thanked Dr Markus Spiegel from OMV Refining & Marketing GmbH for the participation in the organization and highlighted the next starting points of the workshop:

  •   •  The importance of the quality of the forecasts of the traffic loadings in the future, which are the basis for pavement design.
  •   •  How and to what extent should the climate changes be taken into account?
  •   •   What is the pavement design period for a new construction and for rehabilitation: 10, 20 or 40 years?
  •   •  What can be expected from possible increase in mass of commercial vehicles from 40 to 60 tons?
  •   •  Roads in the participation countries are mostly built, therefore the focus is on the rehabilitation and maintenance.
  •   •  Asphalt or cement concrete? When white and when black?
  •   •  What are the prospects for the semi rigid pavements?
  •   •  What should the integration between traffic load simulations and laboratory tests in pavement design be?
  •   •  When will the systematic life cycle cost analyses be introduced (LCC analysis)?
  •   •  The challenges for pavement designers and clients are in environmental protection (alternative use and re-use of materials, reduced energy consumption and noise reduction). Technologies and the knowledge are there, why these procedures are not widely used?
  •   •  Who can design pavements and what are the required qualifications?
  •   •  Is nowadays the knowledge of an individual enough for pavement design and technological processes?


The presentations in two sessions followed with the next highlights:

PART I: Practice and experience with the National Pavement Design Method
DI Jan JähnigDI Jan Jähnig:
In Germany guidelines for analytical pavement design were introduced in 2009. Apart from traffic loads and climatic conditions the material characteristics, especially for the asphalt layers, are one important influencing factor. Based on performance tests several material- characteristics, e.g. stiffness and fatigue, can be considered in the design process. One intention behind this was to ensure that asphalt pavements with longer lifetimes can be developed. Presentation >>

Doc. dr. Bernhard Hofko, dipl. inž., dr. tehn. zn.Univ. Ass. Dipl. Ing. Dr. techn Bernhard Hofko:
The current Austrian Pavement Design Guide has been established in 1986 with minor revision throughout the years. To design a pavement, standard structures are given for calculated design traffic loads (load classes). Standard structures are given for bituminous bound pavements, concrete pavements and block/slab pavements. The main input parameter of the Design Guide is the traffic load described by a cumulated number of equivalent single axle loads (ESALs) with 100 kN passing the road section over its prospected life time. Therefore the different types of commercial vehicles are taken into account by equivalent factors to convert the actual traffic to ESALs. The climatic loading is taken into account by two climatic zones (inner and outer alpine region) and four seasons which affect the subgrade bearing capacity. Finally, for flexible pavements the bituminous bound layers are described by a standardized “model asphalt”. The temperature dependent stiffness of these layers is taken into consideration by dividing the year into six seasons with characteristic temperature profiles for day and night time. Presentation >>

Mitja Jurgele, mag. grad.Mitja Jurgele, BSc CEng:
Pavement design in Slovenia is performed according to empirical procedure based on results of AASHO test. The procedure is described in Technical Specifications for Roads. Design life for pavements is 20 years for new constructions and 10 years for reconstructions. The main pavement type is semi-rigid with lane dependant structure on highway network and conventional flexible on all other roads. Each pavement construction has to be designed in a separate project; standardised pavement constructions are not used. The presentation shortly summarizes current practice in pavement design in Slovenia including the critical review.
Large problem on Slovenian highway network is the fact, that the majority of pavement constructions are under designed, because of the extreme traffic growth after the entry of Slovenia into the EU. The most problematic is the Highway A1 on which the traffic loads increased 4 times between 2002 and 2008. This results in quicker decay of pavements and also in increasing costs for reconstructions. Presentation >>


PART II: Needs and Trends for Improved Pavement Design Approaches

 Prof. Michael Wistuba, dipl. inž., dr. tehn. zn. 	  Prof. Michael Wistuba, dipl. inž., dr. tehn. zn.Univ.-Prof.DIpl.-Ing.Dr. techn. Michael Wistuba:
Innovations in asphalt pavement analysis, Mechanistic pavement design using hourly time-increments
Wistuba presented the mechanistic pavement design method which is used in Germany today, and which is documented in the FGSV Technical Standards (RDO Asphalt 09). In best accordance with RDO, the design method was recently extended by ISBS, Pavement Engineering Centre at TU Braunschweig. Through the new approach, the design method is significantly improved, as traffic loading and temperature loading are calculated in every single hour – even for long design periods. Hence, loading and stiffness are coupled with time through time-accurate superposition of traffic and temperature loading. Advantageously, the new approach improves design accuracy, on the one hand, and allows for new parameter studies, on the other hand. Based on two examples of use, Wistuba demonstrated the new design approach. In a first example, low-temperature top-down fatigue cracking of wearing course was analysed. Secondly, the effects of global warming on pavement design were analysed for various scenarios of climate change in Germany. The new approach is now transferred into a user-friendly design software, which shall be available by end of 2013. Presentation >>

Doc. dr. Bernhard Hofko, dipl. inž., dr. tehn. zn.Univ. Ass. Dipl. Ing. Dr. techn Bernhard Hofko:
Performance based requirements of HMA
As shown in the first presentation about the current Austrian Pavement Design Guide, the guide does not represent the latest state of the art. Thus, a number of improvements are planned for a revised version of the Guide expected in 2015. First of all, the climatic conditions in the present version are taken into account by two climatic zones. Today, weather data from hundreds of stations all over Austria are available. This data will be used for a revised Guide to get more specific information for pavement design on project level and thus, to take the climatic loading into more detailed consideration. Second, a number of traffic counting stations in combination with weight-in-motion (WIM) devises are available on the high level road network in Austria. These stations give detailed information about the distribution of different types of commercial vehicles and also about the distribution of the gross weight of each vehicle type. By mathematical means the distribution of the gross weight on the axles can be derived and used as far more detailed input parameters for traffic loading than the ESAL concept, again on project level. Finally, by modern, so called performance based test methods developed in the last 15 years, different bituminous bound materials can be described in their visco-elastic behaviour. Temperature-dependent input parameters for material models can be derived from these test methods. In addition the fatigue performance of bituminous bound mixes can be derived by performance based tests. By implementing and combining these new developments and data for climate, traffic loading and materials, pavement design will become more focused on specific information at project level, which will lead to more efficient pavements. Also, innovative products and construction techniques (recycling, etc.) can be taken into consideration by deriving material parameters for these products by performance based test methods. In addition with life cycle cost analysis (LCCA) tools, the decision for a pavement type can be made not only based on costs for construction but also on predicted costs for future rehabilitation depending on climatic and traffic loading. Presentation >>

Aleksander Ljubič, mag. grad.Aleksander Ljubič, BSc CEng:
The existing method for pavement design in Slovenia is based on results from AASHO test from the middle of former century and it is not suitable for actual number of axle loads passes caused by highly rised traffic volumes on main traffic routes, anymore. The influences of climatic conditions in terms of both the frost depth and surface temperatures of the pavements that vary considerably across the territory of Slovenia aren't taken enough into account by this method. The performance of the materials built into the pavement construction and their response to the loading is also too simplified by using the material equivalency factors for calculation of thickness index that doesn't determine their performance in various temperature and loading cases. All the before mentioned parameters are already taken into consideration by modern mechanistic pavement design methods like for example German RDO 09 method. The american 'perpetual pavement' concept of pavement design was also presented – it is a similar approach to those in Germany and Austria, based on the premise that pavement distresse with deep structural origins could be avoided if pavement responses such as stresses, strains and deflections could be kept below tresholds where the distresses begin to occur. Such pavement could last very long time (over 50 years) with only limited need for maintenance and rehabilitation of the top layer.
As an input value for the above mentioned mechanistic pavement design methods we need the performance-based material characteristics of pavement materials which we can now get from newly introduced modern equipment for performance-based testing on our institutes.
Because of all identified disadvantages of existing pavement design method there is a need for new and revised technical regulations, collection of data about climate influences and integration of performance-based testing with the pavement design method. Presentation >>



The closing words were presented by DI Dr. Markus Spiegl, who highlighted the following similarities of future pavement design in all four countries:

DI Dr. Markus Spiegl  •  Performing performance related laboratory tests like stiffness or fatigue testing (4 point bending beam or indirect tensile test) to get more realistic asphalt mixture properties which should be taken into account for a pavement design
  •  Climatic conditions of the various regions and the impact on the asphalt properties
  •  Traffic amount and the various heavy vehicles with their different axel loads
  •  Life cycle costs analysis.

Dr. Spiegl mentioned in his closing words that it would be very useful if the countries would collaborated much more in the future on this topic, because this would first speed up the whole development process of a more realistic pavement design approach and second save money either on research funds, which could be used for other research topics, or investments in infrastructure, which are currently very rar in all state budgets due to the economic crisis.
At the end he thanked the audience for their enthusiastic participation, which contributed to the success of this event and announced to organize in no later than 2 years a similar workshop with even more international participation in Austria.

Organizing Committee composed of Slovenko Henigman, Aleksander Ljubič, Mitja Jurgele, Jožica Cezar, Zvonko Cotič and Dr. Janez Žmavc agreed on the following conclusions:

  1. A new map of freezing zones must be created.
  2. For lower class roads (local, touristic, …) and for low traffic roads the standardized pavement structures must be prepared.
  3. The correction factors related to the replacement of bound with unbound layers (thermal conductivity) must be developed.
  4. The instructions for elaboration of project assignment for pavement design must be prepared.
  5. The criteria for pavement designers must be defined.
  6. The Technical Specifications for pavement design must be updated. The proposed time limit is 2014.
  7. A new SIST standard for fundamental tests for asphalts must be created.
  8. Methodology for life cycle cost analysis in pavement design (LCA) should be prepared

The aim is to carry out these decisions within 2 (two) years.

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