Suggested Citation:
Harvey, John T., Jeffrey Buscheck, Justin Yu, Julian Brotschi, Mohammad Rahman, Hanyu Deng, Angel Mateos, Michael Bowman, Irwin M. Guada (2026)

RAP and RAS in HMA Pilot Project on SJ 26: Material Testing, Observations, and Findings

. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-23-92

Abstract:

A pilot project for the inclusion of high percentages of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in hot mix asphalt (HMA) was built on State Route 26 in San Joaquin County in September 2022. Six mixes were included in short test sections: (1) a control mix with no RAS or RAP, (2) a mix with 25% RAP and recycling agent (RA) (3) a mix with 30% RAP and RA, (4) a mix with 35% RAP and RA, (5) a mix with 40% RAP and RA, and (6) a mix with 25% RAP, 3% RAS, and RA. A seventh mix, which was a typically used mix with 12% RAP and no RA, was used for construction of the rest of the overall project. This technical memorandum presents the laboratory test results from plant mix produced for job mix formula verification and from one or two quality assurance (QA) samples, depending on the test, taken during test section construction, as well as observations of plant production and construction. None of the mixes passed the Delta Tc specification, which is not uncommon for polymer-modified binder mixes. There is FHWA guidance and past UCPRC experience with other polymer-modified Caltrans mixes that indicate Delta Tc may not be a good parameter to use with modified binders. The mixes with 40% RAP and 25% RAP/3% RAS and one of the two QA samples for the mixes with 30% and 35% RAP and RA did not meet the performance grade (PG) specification low temperature limit. All mixes passed high and intermediate temperature PG specifications, and the other QA samples passed the low temperature PG specification. The 25% RAP with RA mix and one of the two QA sublots of the 30% RAP with RA mix missed the IDEAL cracking tolerance (IDEAL-CT) index number by a small amount, and one of the sublots for the 35% and 40% mixes missed by a wider margin. Results are presented for volumetric tests, flexural and axial dynamic modulus tests, repeated load triaxial tests, flexural fatigue tests, and Hamburg Wheel-Track tests. IDEAL-CT tests were done with both reheated and medium-term oven-aged samples, and results are reported for the IDEAL-CT index and indirect tensile strength for both aging conditions.