Field Performance and Design Recommendations for Full Depth Recycling in Texas

In the early 1990s several Texas Department of Transportation (TxDOT) districts started using full depth recycling (FDR) techniques to rehabilitate their roadways. A variety of stabilizers were used including cement, lime, fly ash, and asphalt emulsions. Project 0-4182 was initiated to survey the performance of the initial FDR projects, to document what successes and problems have been identified, and to develop recommendations for those districts wishing to embark on FDR programs. In this project nondestructive testing (NDT) was conducted in six districts with both the falling weight deflectometer (FWD) and ground penetrating radar (GPR); visual condition surveys were completed and discussions were held with district and area office personnel. Although the majority of the pavements surveyed in this study were found to be performing well, several problems were documented. These problems include longitudinal cracking in sections built in East Texas on clay subgrades, bonding problems with primarily fly ash treated bases, and excessive cracking with some cement treated bases. To address each of these problems the TxDOT districts have developed new construction specifications and improved design criteria, which are documented in this report. Environmental factors also appear to play a big role in constructability and performance of emulsions and fly ash treated bases. Their performance has been good in west Texas and the panhandle, but they have not performed well in the high humidity/high rainfall areas of east Texas. The NDT in the project design phase to assist in the pavement design process and the heavy involvement of the district laboratory in selecting and controlling the stabilization process on a project-specific basis appear to be key factors in establishing a successful FDR program. Based on the results presented, consideration should be given to modifying current construction specifications.