Determination of slab rocking at the joints of a cement concrete pavement

The amplitude of the deflection at the ends of the slabs at the transverse joints under the passage of a heavy load is an impo.tant c.iterion for assessing the effecciveness of the load transfe. at the joints and for the degree of deterioration of the carriageway. The technique applied at the Road Research Centre (Belgimn) consists in measuring the vertical displacement of the end of a slab in relation to the end of che adjacent slab due to the passage, at low speed, of a lJ-tonne axle. The sensing devices are installed on the pavement itself; the signals they transmit are recorded on magnetic tape and are ultimately translated inca amplitudes of slab end movement. The threshold of detection is of the order of 0.01 mm in accual practice. Various examples of the application of this technique are described, ranging from the monitoring of a highway engineering experiment comparing different types of cransverse joint to the evaluation of the unexpired life of a 45-year-old concrete road before the construction of a thin overlay. The deflections recorded in this way comprise a range of amplitudes from O.Olmm to 3.5 mm. The relative vertical displacements measured by this technique 'ire compared with vertical displacements of the slab ends in relation to a fixed point outside the carriageway. There is good agreement between the two types of determination: the "absolute" method does indeed yield more information than the relative deflection met:hod, but is not:always practicable.