Abstract:This paper discusses the test conditions (dry or soaked) of foamed asphalt mixes used to optimize mix design variables. It attempts to answer the following two questions: First, under which conditions should foamed asphalt material properties be tested in the laboratory to determine field performance? Second, under which laboratory conditions can the effectiveness of foamed asphalt stabilization be most easily distinguished? Four foamed asphalt full-depth reclamation projects showing distress were reviewed. It was found that the behavior of foamed asphalt treated base layers when soaked is critical to pavement performance. Laboratory testing indicated that under dry conditions, weak chemical cementation and suction from residual water in the mineral filler phase can dominate the material behavior, and obscure the effects of the foamed asphalt. On the other hand, under soaked conditions the efficacy of foamed asphalt treatment can be readily distinguished. Laboratory strength testing results involving a broad range of factors including recycled asphalt pavement (RAP) sources, RAP gradations, asphalt types, asphalt contents, test methods, etc. were used to validate the above analysis. In terms of resilient modulus, foamed asphalt transforms the material behavior from that of typical unbound granular materials to that of asphalt-bound materials. The effects of foamed asphalt on material stiffnesses are evident for soaked specimens, but complex and practically difficult to measure and distinguish in project level mix design procedures. Using resilient modulus tests to optimize mix design is not recommended. Solely using soaked tensile strengths as the objective function to optimize mix design variables as proposed based on the aforementioned findings.

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