The united states currently has a large and growing mileage of portland cement concrete (pcc) highway pavement overlaid with asphaltconcrete (ac). Evaluation of existing ac/pcc pavements and selection of second rehabilitation strategies are thus becoming increasinglypressing concerns of state highway agencies. Use of deflection testdata to interpret the condition of the underlying pcc is crucial toa structural evaluation and second overlay design for this type of pavement. However, interpretation of deflection measurements is perhaps more difficult for ac/pcc pavement than for any other pavement type. Many of the available tools for backcalculation of pavement layer moduli are limited in their ability to successfully analyze ac/pcc pavement. A simple and straightforward procedure for backcalculation of ac/pcc pavement layer moduli is described. The approach is built on available closed-form solutions to backcalculation for bare pcc pavement, with adjustments made to measured deflections to accountfor the influence of the ac layer. An example using deflection datacollected on an ac-overlaid pcc interstate highway section indicates that the backcalculation procedure produces reasonable results that are consistent with those obtained from other backcalculation methods and with the known condition of the pavement. This paper appearsin transportation research record no. 1293, Backcalculation of pavement moduli 1991 .
Samenvatting