Rolling Weight Deflectometer with Thermal and Vibrational Bending Compensation

Abstract

A pavement deflectometer has been developed for continuous measurement of airfield pavements under a rolling load wheel. The rolling weight deflectometer (RWD) measures pavement deflection using a new method of laser triangulation. It also compensates for bending of the beam on which the sensors are mounted. This compensation allows accurate measurement of deflection in the presence of motion and thermal effects. The deflection measurement incorporates data from four equally spaced pavement sensors mounted on a beam. The method requires the sensors to remain in a straight line at all times. This method was previously plagued with measurement errors caused by thermal and vibrational effects. The RWD uses a laser beam to monitor the state of bending of the physical beam in real time. The bending data are used with pavement sensor data to produce accurate deflection measurements in the presence of any amount of beam bending. The bending-compensated RWD produces deflection measurements on 0.3-m (1-ft) intervals with an accuracy of 40 microns (0.0015 in.) while moving at 10 km/hr (6 mph). The RWD is composed of a towed trailer, a networked data-acquisition system, and a load platform. Its essential elements consist of a horizontally transported beam, strategically placed pavement sensors, sensors to measure beam bending, an odometer, and a data-acquisition computer. A brief history of pavement deflection methods is presented along with a description of the RWD. Preliminary field results include a comparison between data obtained by a falling weight deflectometer and the RWD.