Discussion of Deep In-Situ Recycling (DISR)

The mature road networks in most developed countries require rehabilitation more often than new construction. However, material sources are becoming scarce and traffic volumes on the major routes in these countries are high. There is an increasing international need for rehabilitation techniques that reuse existing paving materials with minimal traffic disturbance. The use of Deep In-Situ Recycling (DISR), particularly when used in combination with material stabilization processes, is gaining ground internationally as a viable option to meet these needs. The material stabilization options that have been successfully used with DISR include lime, cement, foamed bitumen, and emulsified bitumen treatment. The 2003-04 Strategic Plan for the Partnered Pavement Research Program (PPRP) listed DISR as a current experimental strategy under evaluation by the California Department of Transportation (Caltrans) to become a standard strategy. This evaluation process started as a special forensic investigation, but has been identified as a full research goal (HVS Goal 10) in the 2003-04 Strategic Plan. The evaluation process will encompass the following issues: • Selection criteria for identifying viable projects for DISR; • Pre-design site investigation procedures including field and laboratory testing; • Mix design procedures; • Structural design procedures; • Sound construction management procedures including specifications, planning, work methods and QC/QA; and • Future maintenance strategies tied to life cycle cost analysis. The DISR recycling process used in combination with foamed bitumen treatment, for example, is a fairly complex process with little room for error. The time available for mixing the material is limited and once the binder has been mixed in, no additional foamed binder can be applied. Hands-on training of the users of the technology is therefore of the utmost importance to ensure the successful deployment of this technology in Caltrans. The common thread that will therefore link all the above aspects is the transfer of the technology from experienced users to less experienced users. Although some expertise has already been developed in the use of DISR and foamed bitumen treatment in Caltrans District 3, it is not the primary function of the district personnel to provide training and they will probably lack the resources to do so. The Pavement Research Center (PRC) can provide the necessary resources to capture the existing expertise in Caltrans, expand it sufficiently, and develop and present practical, hands-on training courses on a statewide basis in addition to the further refinement of the technology through research. This documents sets out a framework for addressing the above issues in terms of an overall approach as well as the short-term planning of specific activities.