Edith Arámbula-Mercado

Implementation of balanced mix design (BMD) tests during mixture production is crucial for assuring the quality and consistency of BMD mixtures. However, the BMD system lacks engineered testing frequency protocols and can require extensive sampling, labor, time, and equipment during quality control (QC) and quality assurance (QA). The main goal of this study is to determine appropriate production testing frequencies for IDEAL-CT and IDEAL-RT during BMD mixture production. In this study, eight asphalt mixtures with Superpave aggregate gradations, produced across 21 days and forty-nine sublots were evaluated to capture the variabilities occurring at sublot, day, and mixture-level production. IDEAL-CT and IDEAL-RT tests were performed on these reheated plant-produced and laboratory-compacted (RPMLC) mixtures. From the production variability analysis, the coefficient of variation (CoV) for the corresponding sublot, day, and mixture-level production was determined to be 21.1%, 27.7%, and 30.6% for CT _index , and 5.7%, 7.4%, and 9.6% for RT _index . The study also identified reduced sampling scenarios to capture daily production averages in CT _index and RT _index within 5%, 10%, 15%, and 20% deviation from the actual day average. To confidently determine CT _index and RT _index for a production day, 3S-2R (two replicates each from any three sublots) and 2S-2R (two replicates each from any two sublots) sampling scenarios can be adopted, respectively. Further, the study recommends multiple sublot sampling to determine approximate production day average over single sublot sampling. Overall, the study concludes that it is practically possible for consistent daily BMD mixture productions and incorporation of IDEAL-CT and IDEAL-RT tests during QC&QA.

Validation of balanced mix design (BMD) test thresholds is essential for building confidence in performance-based asphalt mix designs. To support Texas’ BMD implementation, multiple field test sections statewide have been monitored, accumulating data from preconstruction through several years of service. These sections, exposed to traffic levels ranging from 600 to 23,000 average annual daily traffic (AADT) and up to 1.0 million equivalent single-axle loads (MESALs), provide valuable insights into test thresholds across diverse traffic and regional conditions. Complementary data from three national center for asphalt technology test track sections subjected to accelerated loading compare traditional volumetric designs and BMD specifications. Additionally, materials from the original WesTrack test track were evaluated with current cracking and rutting tests to relate historical field performance with present protocols. Despite challenges in collecting long-term field data and variability from traffic and environmental factors, key conclusions emerged. The indirect tensile asphalt cracking test and Texas overlay tester effectively gauge cracking resistance differences among mixtures, correlating well with field outcomes. The Hamburg wheel tracking (HWT) test reliably identifies mixtures prone to rutting, supported by minimal rutting observed in TxDOT sections. The IDEAL-rutting test (IDEAL-RT) consistently differentiates rutting resistance and predicts field rutting performance, underscoring its value in mix design. Early reflection cracking observed within two years exhibited strong correlation with the cracking tolerance index (CT Index), indicating higher CT Index values improve cracking resistance. Gradation also significantly influences CT Index and crack progression rate (CPR) results, emphasizing the need to incorporate gradation-specific thresholds. These findings enhance understanding of BMD test strengths and limitations, informing refinements aimed at improving pavement durability statewide.

The increased use of recycled asphalt pavements (RAP) is motivated by the need to enhance resource efficiency and reduce environmental effects. Asphalt recycling agents may also be added to high RAP mixtures to mitigate the impact of stiff, brittle RAP binder, leading to enhanced performance. This study evaluated the properties of binders and mixtures that contain high RAP (i.e., 40%) and a recycling agent. The results were compared against a mixture with 25% RAP and no recycling agent. Concerning the binder properties, the recycling agent enhanced the low-temperature properties and decreased stiffness more than it affected the high-temperature properties. However, the recycling agent increased the aging susceptibility of the asphalt binder. Mixture performance tests showed that the high RAP mixture with recycling agent had comparable or even better performance at intermediate and high temperatures than the mixture with 25% RAP. These findings demonstrate the benefits of adding the recycling agent utilized in this study to increase the RAP content in the mixture while restoring binder properties and improving cracking resistance. However, one must consider the potential impact of recycling agents on accelerating mixture aging.

Motivations for using recycled asphalt materials (RAM) in new asphalt mixtures include economic savings in material costs, conservation of natural resources, and preservation of landfill space. However, the use of RAM requires careful engineering of a unique combination of materials (specific component materials at selected proportions) to achieve adequate durability and avoid premature failure. Currently, state departments of transportation (DOTs) limit or prohibit the use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in new asphalt mixtures, commonly expressed in terms of the recycled binder ratio (RBR). This limitation arises from the lack of guidance for designing durable mixtures with RAM, particularly those with high RAM contents. This study aims to propose a comprehensive draft American Association of State Highway and Transportation Official (AASHTO) standard practice with practical tools and guidelines for evaluating and designing durable asphalt mixtures with 0.3–0.5 RBR. Through extensive laboratory testing involving different component materials used in asphalt mixtures with varying RBRs, this study successfully designed mixtures with different RAM contents that are resistant to the most prevalent distresses (cracking, rutting) and durability concerns (raveling, moisture susceptibility). The results helped identify important parameters of component materials that influence performance, such as the quantity and quality of virgin and RAM binders and aggregate type. Overall, this paper describes proposed revisions to an existing draft AASHTO standard practice, providing examples that support each proposed modification. These modifications include guidelines for selecting and proportioning component materials and a framework that includes a stepwise approach with tests, protocols, and thresholds tied to climatic zones.

The economic and environmental benefits of incorporating recycled asphalt materials (RAMs) into new asphalt mixtures are achieved only if the durability of the asphalt mixtures is maintained. This study, conducted under National Cooperative Highway Research Program project 09-65, aims to evaluate the durability of asphalt mixtures with high RAM contents, considering component materials, mitigation strategies, and balanced performance. The evaluation included existing mix designs with variable RAM contents typically produced in each U.S. climatic zone (north/freeze and south/no freeze). In addition, this study considered alternative binders, partial RAM binder availability, a bio-based recycling agent, a liquid anti-stripping agent, and lime as potential strategies to improve the durability of high RAM asphalt mixtures. Four sets of experiments were selected to address the primary durability issues (surface cracking, moisture susceptibility, and raveling), while verifying rutting resistance for balanced performance. The results indicate that the high RAM strategies required to improve cracking performance can still result in durable asphalt mixtures within the context of a balanced mix design. In addition, the results show that liquid anti-stripping agents and lime are effective in improving the moisture resistance of the recycled mixtures. Finally, two screening tools based on component materials and mix design parameters are proposed to preliminarily evaluate the moisture resistance of high recycled binder ratio asphalt mixtures. Overall, this study provides valuable tools and guidelines for the evaluation and design of durable asphalt mixtures, focusing on those with high RAM contents and balanced performance.

This study aims to investigate promising mitigation strategies for improving the cracking performance of high recycled binder ratio (RBR) asphalt mixtures. Moisture-resistant aggregates that do not require anti-stripping agents, reclaimed asphalt pavement (RAP), and recycled asphalt shingles (RAS) were sampled for this study from sources in two climatic zones, south and north. The south-moisture-resistant (SR) mixtures were designed with 0.16 and 0.29 RBRs with RAP, while the north-moisture-resistant (NR) mixtures included 0.21 and 0.37 RBRs with RAP and 0.44 RBR with RAP/RAS. The mitigation strategies evaluated included a softer binder, a different binder source with higher ΔT _c , a recycling agent (RA), reduced recycled binder availability (RBA), polymer-modified asphalt (PMA), and hybrid approaches including softer binder + RBA and PMA+RBA. The Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and Disc-Shaped Compact Tension (DCT) test were conducted to capture intermediate-temperature and low-temperature cracking performance, respectively. In addition to the cracking tolerance index (CT _index ), an IDEAL-CT interaction diagram analysis was added to further understanding the effect of mixture variables on cracking performance. The findings suggest that while no single strategy works for all RBR mixtures tested, RA, RBA, softer binder, or their combinations yield adequate cracking performance depending on factors including RAP binder stiffness and quantity, RA dose, climatic zone, and RBA.

This paper develops a simple asphalt pavement field aging model using IDEAL-CT data from 24 field sections from seven field projects that were monitored for 1–4 years each. Field distress surveys were conducted, and field cores were procured and tested in the laboratory approximately every 12 months for each field section. The model predicts IDEAL-CT parameter l₇₅/ m₇₅ (mm²/kN) from the post-peak load–displacement curve. An R² of 0.91 was achieved when comparing predicted values to measured values indicating that this ratio behaves predictably with field aging. A good correlation is also seen between this ratio and measured field cracking data, making it an excellent candidate for evaluating pavement cracking performance with field aging. This simple model has promising potential use cases including as a tool for mix design, pavement monitoring, and pavement forensics.