Quantifying Workability, Compactability, and Cohesion Gain of Asphalt Emulsion Cold In-Place Recycling

To maximize the life and quality of a pavement, proper maintenance and rehabilitation are essential. Strategies for pavement rehabilitation with many sustainable benefits are pavement recycling. This dissertation focuses on two types of in-situ pavement recycling: Cold in-place recycling (CIR) stabilized with asphalt emulsion and full depth reclamation (FDR) stabilized with asphalt emulsion or foamed asphalt. One white paper (Chapter 2), two accepted peer reviewed journal articles (Chapters 3 and 4), and one submitted peer reviewed journal article (Chapter 5) are presented in this document to create better understanding of the unique material characterization of asphalt emulsion cold recycled materials, along with factors which influence characterization, pertaining to the measurement of workability, compactability, and cohesion gain. In Chapter 2, a detailed review of the progression of mix design procedures for unbound granular materials (UGM), fully bound hot mix asphalt (HMA), and semi-bound asphalt emulsion CIR is presented to establish the current state of mix design for each material type and identify ways the design of asphalt emulsion CIR could become more engineered rather than empirical. Recommendations included development of additional guidance on use of active and inert fillers, a methodology to account for workability and compactability during mix design, curing procedures which more closely mimic conditions in the field to improve cohesion gain, and a procedure for determination of optimum water content. In Chapter 3, a study was conducted to evaluate different laboratory compaction methods for compaction of asphalt emulsion and foamed asphalt FDR. Both the Proctor hammer, typically used for UGM, and the Superpave Gyratory Compactor (SGC), typically used for HMA, were compared by evaluating densities, tensile strengths, and compaction metrics of FDR samples produced using each method. The modified Proctor hammer produced samples with the highest dry unit weights; however, samples produced using the SGC had higher tensile strengths, indicating compaction method affects material properties. Chapter 4 evaluates different test methods and equipment commonly available in asphalt laboratories for ability to quantify workability, compactability, and cohesion gain of asphalt emulsion CIR by measuring differences in performance due to changes in laboratory curing conditions. Cure temperature was found to have a more significant influence on test results than cure time. SGC metrics were recommended for quantifying workability and compactability. The direct shear test showed promise for quantifying cohesion gain. Finally, Chapter 5 measured effects of various sample fabrication factors on measurement of workability, compactability, and cohesion gain in order to address open questions associated with asphalt emulsion CIR laboratory procedures. Curing temperature most significantly influenced workability and compactability; while cohesion gain was more significantly influenced by mixing temperature and specimen test temperature. The direct shear test again showed promise for measuring cohesion gain of asphalt emulsion CIR. Therefore, a draft specification for this test method was prepared and is included as an appendix of this dissertation. A singular test method for quantifying workability and compactability for asphalt emulsion CIR has not yet been identified due to multiple mechanisms at play during mixing and compaction stages for this material.