01/02/2018
Image of an ASR-damaged and partially refur-bished concrete motorway, showing the typi-cal ASR damage spectrum in the joint areas ranging from dark coloring to cracks.

Image of an ASR-damaged and partially refur-bished concrete motorway, showing the typi-cal ASR damage spectrum in the joint areas ranging from dark coloring to cracks.

Source: BAM, Division Building Materials

In recent years the amount of damage in the German motorway network attributable to the alkali-silica-reaction (ASR) has increased. The associated, often drastic reduction in the service life of the concrete pavement has led to a great increase in research in this field. The spectrum of numerous research projects at the BAM ranges from the analysis of ASR-damage mechanisms, and the fundamental investigation of numerous sections of motorways, to the development of novel ASR avoidance strategies. The results of these research activities, carried out on behalf of or in close cooperation with the Bundesanstalt für Straßenwesen (BASt), are incorporated into the regulations for the future prevention of ASR damage in concrete pavements.

In addition, the BAM works together with the Ruhr Universität Bochum (RUB), the Bauhaus Universität Weimar (BUW) and the Karlsruher Institut für Technologie in the DFG research group 1498, which started in 2012. It pursues the overall goal of clarifying the influence of mechanically induced damage by traffic and climate change (fatigue stress) on the ASR damage process. To achieve the necessary description of the diverse interacting damage and transport processes, the experiments must be closely linked with multi-scale modeling. One important research aspect among others is the analysis of how cyclic damage and ASR influence the mechanical behavior of the concrete pavement. For this purpose, large-scale beams made of a pavement concrete with an increased ASR potential were cyclically pre-damaged. The fatigue-induced damage evolution was observed using an innovative non-destructive testing methodology developed at the BAM. The extraction of small size specimens from the cyclically damaged large-scale beams is the basis for further examinations. For example, the fatigue-induced cracks in the concrete were visualized and quantified using 3D X-ray tomography. Additional ASR-provoking storage of small-sized concrete test specimens with and without mechanical pre-damage prove that fatigue stress reinforces the ASR damage process in pavement concrete. Comparative fracture mechanical studies on small-sized specimens without and with various types of pre-damage confirm the significant influence of fatigue loading and ASR on the mechanical properties. The results obtained form the basis for the multi-scale modeling of the different damage processes in pavement concrete.

Effects of fatigue loading and alkali-silica reaction on the mechanical behaviour of pavement concrete
A. Wiedmann, Frank Weise, E. Kotan, H. S. Müller, Birgit Meng
Structural Concrete, Volume 18, Issue 4, August 2017, Pages 539–549
BAM Department Safety of Structures, Division Building Materials