Concrete with Exposed Aggregates – Experiences in Germany

Concrete road surfaces with useful properties and a long useful life have been constructed for many decades, but further development is still required due to changing boundary conditions. Here, the important challenges are the increase in traffic load as well as specific requirements to traffic safety, environmental compatibility and economic efficiency. Designing the concrete road surface with a surface texture that results in a permanent high tire grip and low tire/carriageway noise has recently become one of the most urgent tasks. Since the 70s the usual production of texture in Germany, i.e. impressing a structure into the fresh surface mortar, had to be adapted to the changing requirements a few times already. A genuine alternative to the presently used standard procedure, drawing a burlap acrosss the fresh concrete surface, is the removal of the surface mortar based on the exposed aggregate concrete method. Indications of optimal concrete surfaces as well as their evaluation result from the influences of the surface texture and its components microtexture, macrotexture and megatexture on the skid resistance and the tire/carriageway noise. Hence advantages for exposed aggregate concrete compared to other presently used concrete surfaces can be gained in addition to the results of the observation and trial routes supervised by the Federal Highway Research Institute.