Erosion of concrete pavement sub-bases

A special session of the 65th annual meeting of the Transportation Research Board in Washington, in January 1986, brought together some 50 practitioners and research workers on the theme "Erosion of sub-bases; stepping of slabs and pumping of concrete pavements"; ~he presentation of 3 U.S. papers and two French ones made it possible to compare the U.S. and European theoretical, experimental and operational approaches. On the basis of a very large consensus about the problem of the erodability of bases and hard shoulders for emergency stop badly drained or not drained at all and the qualitative and quantitative significance of such phenomenon vis-à-vis the performance of pavements in use, a very coherent core of results and conclusions of laboratory investigations on specimens has come to light. Similar testing principles are found both in the U.S. and Europe (brushing, erosion by means of vibration or impact; jet tests); the equipment is different and might gain in being standardized, even though they make it possible to detect similar trends in the results. The very high complementarity of U.S. and European investigations is to be noted, the former developed model or bed tests in which slices of pavement are subject to accelerated fatigue stresses, and specific equipment of the type rotary shear test under water. For their part, the latter, in addition to the above common core, developed preliminary theoretical aspects and findings on the relationship between the erodability of materials in situ and the performance of the pavement in use. Such collation of results brings about improved knowledge concerning the phenomena, and above all the means to prevent them. Guidance for the selection of foundation materials is given regarding the specific context of each project in terms of climate and traffic objectives. The latest results presented to the TRB confirm the validity of the options taken by several managers in various countries,i.e. the selection of little or non erodable materials and drainage of the slabfoundation- emergency stop shoulder interface in new heavily trafficked pavements. They also justify the trends cowards a larger number of drainage systems being built subsequently on old pavements under specific conditions and the development of equipment allowing to do it operationally witn a sui cable rate of progress on pavements (drainage screens, and flexibl, irains in particular). This series of experiences already appears significant enough to undertake the drafting of a recommendation to managers freshly faced with such problems. The PLARC Committee for Concrete Roads is endeavouring co deal with this task.