Aging Influence on Fatigue Characteristics of RAC Mixtures Containing Warm Asphalt Additives

Aging is an important factor to affect the long-term performance of asphalt pavement. The fatigue life of a typical warm mix asphalt (WMA) is generally related to various factors of rheological and mechanical properties of the mixture. The study of the fatigue behavior of the specific rubberized WMA is helpful in recycling the scrap tires and saving energy in terms of the conventional laboratory aging process. This study explores the utilization of the conventional fatigue analysis approach in investigating the cumulative dissipated, stiffness, and fatigue life of rubberized asphalt concrete mixtures containing the WMA additive after a long-term aging process. The aged beams were made with one rubber type (−40 mesh ambient crumb rubber), two aggregate sources, two WMA additives (Asphamin and Sasobit), and tested at 5 and 20ºC. A total of 55 aged fatigue beams were tested in this study. The test results indicated that the addition of crumb rubber extends the fatigue resistance of asphalt binder while WMA additive exhibits a negative effect. The study indicated that the WMA additive generally has an important influence on fatigue life. In addition, test temperature and aggregate source play an important role in determining the cumulative dissipated energy, stiffness, and fatigue life of an aged mixture

The evaluation and specification development of alternate modified asphalt binders in South Carolina : final report.

SPR 703In this research project, asphalt binders containing various polymer modifiers were investigated throughexamining both binder and mixture properties.\ua0\ua0Two additional topics were also investigated, including: a) theeffects of liquid anti\u2010strip additives on asphalt mixtures; and b) the effects of natural sands in asphalt mixtures.\ua0\ua0The asphalt binder modifiers in this project included: two plastomers; an elastomer; PPA+SBS; terminallyblended ground tire rubber (GTR) binder; and a lab\u2010prepared GTR binder.\ua0\ua0The binder properties of 16 bindercombinations were obtained (e.g., viscosity, DSR, etc.) and compared.\ua0\ua0In addition, these modified binders wereused in mixtures with two aggregate sources, three anti\u2010strip additives, and varying RAP contents.\ua0\ua0There were32 different Superpave mix designs conducted for this project.\ua0\ua0Many engineering properties of the mixtureswere obtained, including: indirect tensile strength, tensile strength retained, rutting, and AMPT values.\ua0\ua0TheAMPT testing was conducted at different temperatures and frequencies.\ua0\ua0The results indicated that, in general,many of the alternate modified binders could be utilized in South Carolina hot mix asphalt (HMA) mixtures.\ua0\ua0Theresults also indicated that RAP and natural sand could be utilized, in limited quantities, in many mixtures usedon South Carolina secondary roads.\ua0\ua0In addition, the mixtures made with liquid anti\u2010strip additives in this projectin many cases produced moisture susceptibility values (e.g., ITS, TSR) that were compatible with those obtainedwith mixtures containing hydrated lime

Knowledge‐Based Expert System for Concrete Mix Design

In the United States, the American Concrete Institute method (ACI 211) is the most widely used concrete mix design. However, ACI 211 does not consider all factors regarding concrete mix design. The acceptance of a freshly mixed concrete depends on concrete quality control test results. If the results indicate that the concrete does not meet the specification, mix design adjustment must be made. Concrete mix design and adjustment are somewhat complicated and time‐consuming tasks that are performed best by experienced persons. In this project, a rule‐based expert system was developed to assist the user in concrete mix design, including the necessary adjustments to the design. The expert system can handle mix designs for normal‐weight concrete, normal‐weight‐mass concrete, normal‐weight no‐slump concrete, heavyweight concrete, and lightweight concrete. Besides workability, consistency, strength, durability, and density, the expert system considers other criteria such as admixtures, transportation, and air temperature that affect the concrete mix design. The system was tested on three projects. The system\u27s selection of concrete proportions compared favorably with the experts\u27 selections

Down-Cycling Sustainability of Flexible Polyurethane Foam in Improving Asphalt Performance through a Proper Pyrolysis Approach

The down-cycling process of waste polymers in asphalt binder achieves a win–win situation in terms of economic modification and efficient disposal of valuable waste. By combining the “controllable pyrolysis” and “down-cycling” concepts, this study specified the application potential of sustainable recycling flexible polyurethane foam (FPUF) in improving asphalt performance. A proper pyrolysis method was proposed to selectively decompose waste FPUF into fibers. Subsequently, eco-friendly and cost-effective properly pyrolyzed FPUF fiber-modified asphalt (PyFMA) was developed. The microscopic, chemical, and mechanical investigations were carried out to clarify modification mechanisms and application feasibility. The results showed that the proper pyrolysis method efficiently produced flexible reticulated PFUF fibers of different sizes grafted with polar groups. The PFUF fibers interlocked spatially and well-coordinated with the asphalt matrix, contributed an elastic component in the mixed hybrid, and positively influenced the asphalt performance. The performance enhancement was the result of a combination of chemical interaction, physical reinforcement, and the volumetric filling effect. In addition, the PyFMA had adequate workability at a high fiber dosage of 24% to achieve a massive recycling goal. It is promising and feasible to use waste FPUF as a sustainable and high-performance asphalt modifier, which countermeasures the rapidly increasing abandonment and meets economical asphalt modification requirements