Cold Central Plant Recycling Study: First-Level Analysis of Heavy Vehicle Simulator Testing

This first-level analysis research report summarizes the construction and instrumentation of a test track to study the behavior of cold recycled layers containing 100% recycled asphalt pavement (RAP) materials in a pavement structure (recycled in place or through a central plant), a first-level analysis of the results from six Heavy Vehicle Simulator (HVS) tests, and a forensic investigation. The six HVS tests covered three recycling agents, testing at two pavement temperatures (30°C [86°F] and 50°C [122°F] at 50 mm [2 in.] depth), and two moisture conditions (as-compacted and under constant water flow). The same loading program was followed on all sections, and testing was continued until either terminal rut (12.5 mm [0.5 in.]) or terminal cracking (2.5 m/m2 [0.76 ft./ft2]) was reached. A review of all HVS test data, together with observations from the forensic investigation, indicates that localized shear failures in the aggregate base after heavy rainfall and issues associated with the foaming water and mixing moisture contents in the cold central plant recycled material used in part of Lane 3 on the track had the biggest impacts on test section performance and contributed the most to when and how each section failed. The following conclusions were made based on the data presented in this report. Additional conclusions and, if justified, recommendations for changes in pavement management system decision trees, cold recycling design procedures, and cold recycling specifications will be made in a separate second-level analysis report. Appropriately designed and constructed cold recycled layers will perform effectively in maintenance, rehabilitation, reconstruction, and new construction applications on California highways. Reductions in life cycle cost and life cycle global warming potential will depend on appropriate recycling strategy selection and pavement designs (i.e., optimal recycling depth and overlay thickness) that, in turn, result in optimized intervals between initial construction and subsequent required maintenance and rehabilitation interventions. Optimum foaming water and mixing moisture contents determined during foamed asphalt mix designs must be used during construction to ensure good performance of the constructed pavement. Lower or higher than designed contents will have negative impacts on pavement performance. Pavement structures with marginal base course layers (e.g., containing uncrushed alluvial aggregates) that are susceptible to shear failures when wet and/or when subjected to heavy axle loads should be carefully evaluated when designing pavements where resilience is a primary consideration.