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Asphalt overlays are commonly used to rehabilitate deteriorated Portland cement concrete (PCC) pavements. However, mechanically or thermally driven movements at joints and cracks in the underlying pavement usually lead to development of reflective cracks in the overlay. The formation and propagation of reflection cracking is controlled by the mechanical properties of the asphalt and the condition of the overlaid pavement. Current state of practice for asphalt overlay design is policy oriented and lacking an engineered design approach. There is need for establishing state of practice in design of overlays as well as for assessment of PCC pavement condition and recommending improvements to existing pavement prior to overlay construction. The objective of this study is to develop a simple decision tree-based tool for selecting suitable asphalt mixtures and overlay designs to prolong overlay lives by lowering reflective cracking and improving in-situ density. This research will leverage the current National Road Research Alliance (NRRA) effort of constructing, instrumenting, and monitoring 12 MnROAD test sections, laboratory performance tests on asphalt mixtures from the test sections, and past field performance data. The proposed tool incorporates field performance data, performance modelling, and life-cycle cost analysis to develop best practices for rehabilitation of PCC with asphalt overlays.

Most cold In-place recycled (CIR) construction uses asphalt emulsion or foamed asphalt with or without active fillers as a stabilizing agent. To ensure the CIR layer gains appreciable stiffness and strength to support traffic, the stabilizing agents have to undergo curing (to dry additional moisture). If traffic is allowed on the CIR layer before sufficient strength and structural capacity is gained, premature damage will occur. Lack of a fast and reliable procedure to determine the extent of in-situ curing significantly increases the risk of such damage. Current construction specifications rely on empirically based time recommendations to ensure sufficient curing. Current empirical time estimates do not account for material variations, climatic inputs and construction process differences. This research uses a combination of in-situ testing of actual CIR construction projects and supplementary laboratory tests to develop a model for pavement engineers and practitioners to reliably predict the recommended time (as a function of mechanical property) for placing of overlay on CIR layers. The prediction model incorporates the critical factors that influence curing in CIR including stabilizer type and amount, presence of active filler, initial moisture content, in-situ density and curing temperature. Due to the large number of possible model variables and their interactive effects, rigorous regression analysis is conducted to determine the most significant variables. The model provides an option of defining sufficient curing based on criticality of the project. The major outcome of this research is a user-friendly spreadsheet-based tool with pre-programmed curing model predictive equations.

This spreadsheet tool pertains to report 2022-11, Evaluation of Curing Effects on Cold In-Place Recycled (CIR) Materials.

Modern asphalt mixtures are usually a combination of various materials from different sources, including reclaimed asphalt pavement (RAP) and recycling agents (RAs), and are used to attain sustainable growth. However, the lack of a well-established method for determining compatibility between various sources and types of virgin binder, aged binder within RAP, and RAs has been a major impediment in current asphalt material selection and specification. Therefore, the objective of this study was to evaluate various binder and mixture testing methods to characterize the compatibility between complex components of asphalt mixtures, specifically from the perspective of assessing their cracking performance. The primary evaluation consisted of laboratory-prepared materials that used three RAP sources, three asphalt binders (one PG 58–28, two PG 64–22), and two RAs (petroleum-based and bio-oil-based) for both binder and mixture characterization. The binder tests consisted of rheological characterization using the dynamic shear rheometer (DSR) and thermal analysis using the differential scanning calorimeter (DSC), whereas the mixture tests included complex modulus (E*), semi-circular bend (SCB), and disk-shaped compact tension (DCT) tests. The results indicated that the rheological characterization of asphalt binder and mixture may not adequately capture the incompatibility between virgin binder, RAP, and Ras. However, binder DSC analysis and mixture fracture tests have shown promising results for evaluating the compatibility of various mixture components. Therefore, the findings of this study provide agencies with a framework to select the most compatible component materials from various sources for their projects.

Asphalt rejuvenators, or recycling agents (RA), are used to incorporate higher amounts of Reclaimed Asphalt Pavement (RAP) in Hot Mix Asphalt (HMA) without detrimentally impacting the long-term performance of the pavement. The National Road Research Alliance (NRRA) Flexible Team constructed field test sections as part of a mill and overlay project in northern Minnesota in August of 2019. These field sections included wearing courses with 40% RAP that incorporate seven different RA products, with the dosage determined by the supplier to meet a target extracted and recovered performance grade (PG) of XX-34. In addition to the RA test sections, there were control sections with 40% RAP and 30% RAP (the maximum level allowed on the remainder of this project). The objective of this research project was to evaluate the effectiveness of the seven RA products over time and evaluate their performance as compared to the control mixtures. This was accomplished through a combination of binder (chemical and rheological) and mixture characterization and performance testing using different laboratory aging levels, field core testing, and performance monitoring of the field sections over time. This report documents the results after four years in service with cores taken annually. The study showed that all RAs exhibit improved rheological properties in 1-year field cores. However, the benefits of RA diminish with field aging, and after four years, some RAs show comparable properties with controls. In terms of mixture properties, the inclusion of RA enhances both rheological properties and fracture and fatigue crack resistance initially.