Design and structure of pavements
Experience in using RSO Asphalt (3416002)
The current draft of the guidelines for the assessment of the structural substance of pavements of traffic areas executed in asphalt (RSO Asphalt) are to become FGSV standards and specifications. Within the scope of this project and working in collaboration with the regional road construction authorities, an empirical background for the use of the procedure described in the RSO Asphalt is to be created. For this purpose, different road sections in the federal trunk road network of different age are to be considered in accordance with the RSO Asphalt and the respective remaining useful lives determined by the regional road construction authorities, under the lead of the Federal Ministry of Transport, together with the Federal Highway Research Institute. The findings made on the theoretical and practical application of RSO Asphalt will be put up for discussion in the responsible committee in finalisation of the current draft.
Possibilities and limits of ground penetrating radar (GPR) (04.284)
Ground penetrating radar is used in structural evaluation throughout the world. The method is being used increasingly in the German road network particularly due to the latest technical advances which permit it to be deployed at speed. It specifically permits a non-destructive inventory to be compiled of the bound and unbound road surface structure by determining layer thicknesses and layer sequences and by identifying damaged and inhomogeneous areas. Ground penetrating radar is currently limited primarily due to the laborious evaluation which has to be done almost completely by hand. This also entails the risk of incorrect interpretation. Using detailed analysis of the process chain and sample applications, the objective of the project is to demonstrate the limits and possibilities of ground penetrating radar, and thus to deliver a continuous, adapted recording and evaluation procedure in the course of recording road structure at an object and network level.
Europe faces rising maintenance costs for the road infrastructure, which is why new methods are being sought and developed to facilitate better cost control and increased cost efficiency. The aim is also to distinctly extend the time before extensive road infrastructure measures are required in the form of repairs and renewal. The associated challenges were a topic in the ERA-NET Plus INFRAVATION Call 2014 for the “Horizon 2020” programme. They include increasing the availability of relevant goods transport routes in the road network by fewer blocks caused by maintenance and repair work, and extending durability. The HEALROAD research project (induction heating asphalt mixes to increase road durability and reduce maintenance costs and disruptions) pursues this objective by developing a self-healing asphalt mix that extends the durability of the asphalt wearing course using induction heat so that damage such as cracks or holes does not arise or is repaired inductively as soon as it starts to develop. The research syndicate consists of universities, research institutions and industrial partners. With its fast-motion full-scale load tests, the Federal Highway Research Institute (BASt) will act as the link between laboratory research and field experiments. BASt’s own Pave®MLS30 will be used to create damage in the wearing course in a very short space of time. BASt will be conducting its own experiments in advance to develop an optimum testing structure for the tests which will take place in the Netherlands. A further focus of BASt activities in the EU project will be the life cycle analyses of the project results (www.healroad.eu).
The Continued Development and Assessment of New and Established Procedures for Assessing Load-Bearing Capacity on the Basis of Field Trials on Road Surfaces with Clearly-Defined Material Damage (89.314)
In several ongoing research projects, it has been possible to show that the data on material parameters collected in non-destructive testing procedures can be quantified with the help of FEM simulations and back-calculation procedures on the basis of artificial neuronal networks. These results can then serve as the basis for drawing a general inference about the degree of fatigue distress on roads. One of the most important indicators of fatigue distress on asphalt roads is the formation of cracks on the underside of the bound layers. With this in mind, any non-destructive testing procedure for assessing the structural integrity of road surfaces must be able to identify this type of crack formation. This challenge will be examined within the parameters of this research project by using a large-scale test field.
Compressive Stress Sensor CANopen (3415000)
A variety of instrumentation is used to provide information on ways in which a road reacts to the stresses of heavy goods traffic. Compressive stress and strain are the two most important physical variables in this context. The type of sensor used to measure these variables previously could not be calibrated following its installation, something that proved to be a significant shortcoming which also led to high default rates in the strain sensors. The intention is now to develop a production-ready compressive stress sensor. Besides updating the interface, the project seeks to develop the multi-sensor by integrating environmental sensors (for temperature and humidity); this process is to be supported by the inclusion of considerations in the “Feasibility Study on the Development of Sensors for the Recording of Structural Condition” published by the Fraunhofer Institute for Physical Measurement Techniques IPM in 2012.
Innovation programme: Performance and evaluation of load tests using the MLS10 (3414002)
In the next few years, it will become increasing important to keep the existing infrastructure functional and upgrade it to meet the increasing loads caused by heavy goods vehicles. The early recognition and detection of damaged sections and weak points are therefore of elemental importance. For this reason, methods are required for the purpose of evaluating the structural substance of road stabilisations in a non-destructive manner. In order to achieve this, it is intended as part of the project to undertake staggered load tests on the BASt model road (constructed with the asphalt construction method) with the MLS10 that the BASt has as its disposal. On the one hand, corresponding investigations will take place in the national Road Innovation Programme with the title "Innovations in road construction – Non-destructive methods for evaluating the structural substance" to be carried out by external partners. On the other hand, the BASt will gather its own data by means of appropriate investigations. These will include not only the continual recording of data from strain and temperature sensors but also the collecting of data obtained from the Falling Weight Deflectometer (FWD). In addition, measurements of the transversal planes (lateral profiles) will also be made using both a profilometer and ZEB vehicles. These measurements add to the insights gained from previous tests and provide further experience in evaluating test beds with regard to the structural substance. Key insights will be derived from the results for the evaluation of surfaces under load in future test programmes.
Improvement of safety and cost-effectiveness of calculative dimensioning of asphalt fortifications by means of a finite element model (04.259)
The RDO asphalt 09 allow for the first time dimensioning of asphalt fortifications on a calculative basis with realistic consideration of traffic load, climatic conditions and material parameters. The stress conditions on which the records are based have up to now been calculated by means of the multi-layer theory. Using the finite elements method, it is now possible to reproduce the behaviour of construction materials using acceptable computing time. The objective of this project is to define a finite elements model which improves the exactness of the predicted stress conditions in the dimensioning period by realistic modelling. This way, one of the most important principles for increasing the safety of calculative dimensioning and in particular the cost-effectiveness of superstructures dimensioned by calculation is ensured. Applying these procedures for functional and conventional construction contracts, in particular in the area that is exposed to heavy loads, it is possible to achieve important business-related and economic effects for construction and maintenance of road fortifications as well as for users.
Regular investigation of a test track with cold-recycling layer (3410002)
The cold-recycling method can be used to produce base courses at a building site by adding binder to bound and/or unbound layers of the superstructure. This allows complete use of road-building materials according to the Recycling Economy and Waste Act. The information sheet for cold recycling in situ for road superstructures , Version 2005, states that pavements with cold-recycling layers are only planned up to Building Class III as specified in the RStO 01 (Code of Practice for Road and Pavement Construction). During the general renovation of the B 52, sub-sections were implemented as test sections for the use of cold-recycling layers, although the traffic load exceeded Building Class III. Initial experiences with other road sections of this kind look promising. The main purpose of the test section is to extend the experience with cold recycling layers in pavements to traffic loads above Building Class III. The test section will also provide information concerning the effect of different bituminous binders, the share of the cold-recycling layer in the total carrying capacity of the pavement and a possible comparison of the capacities of the asphalt base courses and the cold-recycling layer. The current project also includes non-destructive measurements with a falling weight deflectometer and geo-radar as well as an evaluation of the data. Experience concerning the computational dimensioning of cold-recycling layers is to be gained as well.