Tabatabaee, Hassan

Cold-recycling processes such as Cold in Place Recycling (CIR) and Cold-Central Plant Recycling (CCPR) offer opportunities for innovation through the use of recycling additives (RAs). The objective of this project was to evaluate the efficacy of rejuvenating asphalt emulsions in the CIR and/or CCPR process in terms of potential performance benefits relative to existing stabilization options. An experimental matrix was designed to include several of the mix design factors known or thought to control mix performance. Rejuvenating asphalt emulsions containing both Bio-based and petroleum-based RAs were produced and compared to a control engineered emulsion with a proven field history of performance. Inclusion of RAs did not negatively impact mixture stability or the mechanism of strength, while generally improving the CT Index of the tested cold recycled mixes compared to the use of a similarly graded control emulsion. The concept of utilizing a “Balanced Mix Design” approach was explored to quantify the performance attributes of these materials. Mixture stability at 40 °C and mixture IDEAL CT Index at 25 °C were ultimately selected as the performance tests used in the balanced mix design framework. To aid rapid implementation of the results, the recommendations were also written in the form of a specification amendment document, included in the appendix of this report.

The work detailed in this report represents a continuation of the research performed in phase one of this national pooled fund study. A number of significant contributions were made in phase two of this comprehensive research effort. Two fracture testing methods are proposed and specifications are developed for selecting mixtures based on fracture energy criteria. A draft SCB specification, that received approval by the ETG and has been taken to AASHTO committee of materials, is included in the report. In addition, alternative methods are proposed to obtain mixture creep compliance needed to calculate thermal stresses. Dilatometric measurements performed on asphalt mixtures are used to more accurately predict thermal stresses, and physical hardening effects are evaluated and an improved model is proposed to take these effects into account. In addition, two methods for obtaining asphalt binder fracture properties are summarized and discussed. A new thermal cracking model, called "ILLI-TC," is developed and validated. This model represents a significant step forward in accurately quantifying the cracking mechanism in pavements, compared to the existing TCMODEL. A comprehensive evaluation of the cyclic behavior of asphalt mixtures is presented, that may hold the key to developing cracking resistant mixtures under multiple cycles of temperature.