Experiences of Developing and Validating a New Mix Design Procedure for Cold In-Place Recycling Using Foamed Asphalt

Asphalt pavement recycling has grown dramatically over the last few years as the preferred way to rehabilitate existing asphalt pavements. Rehabilitation of existing asphalt pavements has employed different techniques; one of them, cold in-place recycling with foamed asphalt (CIR-foam), has been effectively applied in Iowa. However, Iowa’s current cold in-place recycling (CIR) practice utilizes a generic recipe specification to define the characteristics of the CIR mixture. The contractor is given latitude to adjust the proportions of stabilizing agent to achieve a specified level of density. As CIR continues to evolve, the desire to place CIR mixture with specific engineering properties requires the use of a mix design process. First, some strengths and weaknesses of the mix design parameters were identified, and the laboratory test procedure was modified to improve the consistency of the mix design process of CIR-foam. Both Marshall and indirect tensile strength test procedures were evaluated as foamed asphalt mix design procedures using reclaimed asphalt pavement (RAP) materials. Based upon the critical mixture parameters identified, a new mix design procedure using indirect tensile testing and vacuum-saturated wet specimens was developed. The second phase was then launched to validate the developed laboratory mix design process against various RAP materials in consideration of its predicted field performance. The optimum foamed asphalt contents, for all RAP materials, were consistently found at values between 1.5% and 2.5%. The dynamic modulus values were affected by both foamed asphalt contents and RAP aggregate structure. The flow number is affected dominantly by the RAP aggregate structure.