New building materials and new construction methods for greatest loads in the future due to climate and traffic: fibre concrete

Due to changes in economic processes and the expansion of the EU, the volume of long-distance road haulage is growing from just under 1.5 billion tons in 2004 to an expected 2.2 billion tons in 2025. In addition to these increasing stresses, road pavements are more exposed than ever to extreme weather conditions. In particular, prolonged heat caused a lot of damage in recent years due to rutting or blow-ups.

The two established road construction methods of concrete or asphalt are no longer able to cope with the increased demands. The aim of the research is to combine the advantages of the individual construction methods (durable, jointless, noise-reduced, etc.) in a new type of construction while eliminating the known disadvantages.

One approach is the use of high-ductility concretes with polymer short fibers with an elongation at break up to 300 times higher than conventional concretes. The high deformation capacity of the material is brought about by the formation of many finely distributed cracks that are bridged by fibers. The crack widths are only a few tens of μm, so that harmful media can penetrate the building material only very slowly.
In the project, among other things, a promising formulation is to be subjected to highly cyclic large-scale tests. The test field in the OML was 2.5 m × 2.5 m in size, and the road structure height was 1 m. The load was applied centrally via a hydro-pulse system, which simulated the rolling over of a truck wheel per cycle. Four different road superstructures were tested. The first two variants were executed with complete bedding of the 15 cm thick fiber-reinforced concrete slab on gravel or on a 4 cm thick asphalt intermediate layer, variants 3 and 4 only with edge bedding, whereby the slab thickness varied between 7.5 and 15 cm. All four superstructures were subjected to a total of 3 million cycles, the first 2 million cycles at maximum permissible axle load of 55 kN/wheel and then 1 million cycles at double load.

The results obtained show a significant increase in the load-bearing capacity of the construction method with a simultaneous reduction in slab thickness and form the basis for further development in concrete road construction.

(Author: Steffen Müller)