Strain analysis of UTW composite section using accelerated pavement testing

Ultra-thin whitetopping (UTW) is a relatively new pavement rehabilitation technique that involves the placement of a thin layer of portland cement concrete (PCC) over a distressed hot mixture asphalt (HMA) pavement. The new pavement is essentially a thin bonded concrete overlay. Thus, its composite performance depends on the stiffness of the underlying pavement layers. One goal of this project is to develop models that can be used for the mechanistic design of UTW pavements. Additionally, UTW performance models will be developed. To accomplish this task, a UTW pavement section was constructed in the Indiana Department of Transportation - Purdue University Accelerated Pavement Testing facility. The pavement section consisted of a UTW overlay over an existing composite pavement section (thin HMA layer over a PCC layer). The performance of the UTW overlay was monitored using destructive and non-destructive methods, including measurements of cumulative strain, strength, stiffness, debonding, and extent of cracking. PCA design guidelines were investigated to assess their applicability to cases of UTW placed over composite pavements. Preliminary results indicate that the equations may be able to be used if the concept of an equivalent thickness is employed. Further, the effective radius of relative stiffness calculated from falling weight deflectometer testing of in-situ pavements may be able to be modified to account for the proposed UTW overlay and input into the design equations. The UTW section was subjected to more than 500,000 standard APT load applications (single axle, dual tire, and 9,000 lbs (40 kN)). Results indicate that the UTW section performed well. The bond between the UTW and the underlying HMA remained intact. However, the strength of this bond may vary at different locations under the UTW slab. Multilayered elastic analysis program (ELSYM5) was used to compute the stresses/strains in the composite UTW section. A good agreement was found between the measured strains (stresses) in the composite UTW section and the computed strains and stresses from the ESLYM5 program.