Paper by GRAF from ISCR 5th 1986 Aachen Germany
The Geneva - Lausanne moeorway, which was commissioned in 1964, comprises about ~5 km of concrete pavement consisting of 20 cm thick doweled slabs (10m x 4m) resting on a non-stabilized 55 cm thick gravel-sand sub-base (0 -100 mm particle size). The subgrade consists of non-stabilized natural insieu soils as encountered along the alignment. Defects have gradually appeared since 1964: polishing of the surface of the slabs, then rutting by studded tyres, finally longitudinal cracking of the concrete on tbe slow lanes. The polishing and rutting were eliminated by laying a bituminous wearing course with a rough surface texture and a thickness of 40 mm. Because the cracking was becoming increasingly serious, it was necessary to estimate the probable unexpired life of this motorway section. In 1983 and 1984 the dynamic deflection behaviour was measured on a number of slabs with the aid of the Vibraflect lightweight vibrator of the Highway Engineering Institute of the EPF, Zurich. However, for the motorway section as a whole these measurements were in the nature of spot checks. In 1984 continuous monitoring of the pavement over a length of 40 km with the Collographe apparatus of the LCPC, Nantes, revealed the bearing conditions for each slab and detected a very large number of spots where the slabs had become detached from the sub-base. Drilled core specimens and the removal of some of the slabs will make it possible better to ascertain the nature and extent of these defects and to decode the signals of the "collogram" (shapes and amplitudes of the dynamic deflection). The Collographe survey serves also as a "reference point" which, on comparison with a future recording, will enable the progressive changes in the condition of the carriageways to be monitored and their unexpired service life to be estimated. Continuous measurement of the PSI (present serviceability index) witb the Profilameter of the FMPA (Octo Graf Institute), Stuttgart, as well as deflections measured with the Vibraflect, compared with the resulcs of the AASHO test, should likewise yield information on the unexpired life of this stretch of road. Combination of these three monitoring methods, two of which are continuous and very efficient in terms of the amount of data obtained, should provide the information needed, in the years ahead, for carrying out major maintenace work in concrete on the Geneva- Lausanne motorway by giving precise indications as to which remedial operations are to be given priority.