EVALUATION OF EXISTING PAVEMENT BASED ON DEFLECTION AND RADIUS OF CURVATURE AND OVERLAY DESIGN

To perform maintenance and repair of an asphalt pavement having reached its service limit, it is necessary to make a mechanical evaluation of the existing pavement and subgrade. On a road being in service, however, it is difficult to perform destructive examination. It is therefore needed to establish an evaluation procedure by non-destructive method. In view of this, the author et al. have dealt with a procedure for evaluating existing pavements by determining the stiffness moduli of the subgrade and pavement from data obtainable from the surface of pavement. There are two methods of dividing the existing pavement into two layers: one into the subgrade and pavement and the other into the asphalt treated layer and bearing layer. The former is suitable for evaluation by compressive strain of the subgrade and deflection and the latter, by tensil strain at the bottom of asphalt treated layer and radius of curvature. Field verification was made on local roads being in service about 10 years and by comparing the stiffness moduli of the subgrade and pavement, which were estimated from material testing of the existing pavement with due consideration for environmental and traffic conditions, to those estimated by non-destructive method. Since it was ascertained that not only deflection but also the stiffness moduli of the pavement and subgrade follow a logarithmic normal distribution, field measurements of deflection and radius of curvature were statistically treated to present an adequate procedure for determining a typical structure of existing pavements. As the existing pavement was evaluated by the two-layer system, overlay design was made by the three-layer system. That is, examinations were made assuming the pavement structure as being divided into the subgrade, pavement and overlay when a limit is placed upon strain on the subgrade or deflection and as being divided into the bearing layer, asphalt treated layer and overlay when a limit is placed upon tensile strain at the bottom of asphalt treated layer or radius of curvature. The values of deflection and radius of curvature estimated by computation for two types of overlay used on the site were compared to the values measured after the overlaying. As the result, the computed values were found close to the average of the measurements, proving adequacy of the design. /Author/