National Road Research Alliance

This research investigated the effects of incorporating recycled concrete aggregate (RCA) at low replacement levels on the properties of concrete. Four different RCA sources were used, each with different aggregate properties. For each source, replacement levels of 5, 10, and 15% were tested and compared to a control group, which had no RCA. Of the four RCA sources investigated, three had similar levels of absorption capacity and percent fines, while one source had higher levels of both properties. RCA replaced virgin aggregate of a similar gradation and replacement was on the basis of volume. Fresh and hardened concrete properties were tested, including air content, super air meter (SAM) number, slump, workability via the box test, compressive strength, flexural strength, elastic modulus, Poisson’s ratio, coefficient of thermal expansion, surface resistivity, freeze-thaw durability, and unrestrained shrinkage. Digital image correlation was used to visualize strain fields during compression testing. A statistical analysis was conducted to determine if any observed differences in hardened properties between the test mixes and the control group were statistically significant. This research found that using up to 15% of an RCA with reasonable values of absorption capacity and percent fines would not negatively impact most concrete properties. It also provided an outline for future research to develop a specification to define what constitutes reasonable values of RCA properties for future use.

Intelligent compaction (IC) is a roller-based innovative technology that provides real-time compaction monitoring and control. IC can monitor roller passes, vibration frequencies/amplitudes, and stiffness-related values of compacted materials or intelligent compaction measurement Values (ICMV). Various ICMVs have been introduced since 1978. Based on the five levels of ICMV in the 2017 FHWA IC Road Map, the current implementation of ICMV in the United States has been limited to Levels 1 and 2. However, Level 1 and 2 ICMVs fail to meet the FHWA IC Road Map criteria. To achieve the full potential of IC technology, Level 3 and above ICMVs are needed to gain the confidence of agencies and industry and the adoption of IC to soil and base compaction. This project aims to (1) evaluate Level 3-4 ICMV systems against Level 1 ICMV systems for soils, subbase, and base compaction and (2) develop a blueprint for future certification procedures of IC as an acceptance tool. This study also aligns with the goals of the ongoing HWA IC for foundation study and the TPF-5(478) pooled fund study. This final report details the ICMV background, field test efforts, analysis results, and an IC specification framework for compaction acceptance.

This study evaluated the impact of polymer modification, without changing the base binder, on the intermediate-temperature cracking resistance of asphalt mixtures characterized using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and the Illinois Flexibility Index Test (I-FIT). Twelve asphalt mixtures prepared with two mix designs and six virgin binders (including two unmodified and four polymer-modified asphalt binders per mix design) were evaluated. Each mixture was tested at three binder contents and two temperatures: 25°C and an equal stiffness temperature (T=G*). In almost all cases, the polymer-modified asphalt (PMA) and unmodified mixtures with the same base binder had statistically equivalent IDEAL-CT and I-FIT results, indicating a lack of sensitivity to polymer modification. Increasing the binder content or adjusting the test temperature to T=G* did not discriminate the PMA and unmodified mixtures in the two tests. Interaction diagram analysis of the IDEAL-CT and I-FIT results showed that polymer modification generally affected the toughness and post-peak behavior of the mixture, but these effects tended to offset each other on the final cracking index parameters. Unlike the IDEAL-CT and I-FIT, the two cyclic loading tests evaluated in the study demonstrated the benefits of polymer modification. This discrepancy highlighted the potential limitation of the monotonic loading tests in assessing the fatigue cracking resistance of PMA binders and mixtures. Finally, asphalt binders extracted from the PMA versus unmodified mixtures with the same base binder showed distinctly different rheological properties, but these differences were not captured in the IDEAL-CT or I-FIT when the test variability was considered.

Concrete overlays of full depth reclamation (FDR) are a pavement rehabilitation option involving reclamation of existing pavement layers while providing a new concrete surface to the roadway. This report reviewed nine concrete overlays of FDR that have been constructed in three states since 2006. Design and construction details were collected for each project and performance was analyzed through automated pavement condition data. Additional distress surveys and testing, including falling weight deflectometer (FWD) testing, were performed at one project in Freeborn County, MN, to further characterize the pavement condition and structural properties. Overall, the projects reviewed in this study were performing well to date, and concrete overlays of FDR appear promising as cost-effective, sustainable tools for helping agencies maintain their pavement network.

Real-Time Smoothness (RTS) measures pavement surface profiles during paving using sensors mounted on the back of a paver. The Federal Highway Administration (FHWA) has supported implementing RTS technology for concrete pavements through the SHRP2 Solutions program since 2014. Its study indicated that RTS technology's real-time diagnosis allows changing the paving operation to improve smoothness. This "proof-of-concept" research study aims to extend concrete RTS technologies to asphalt paving applications. The field demonstration results from two field projects show the feasibility of using asphalt Real-Time Smoothness (ARTS) to capture the roughness from various paving events. These results indicate some limitations of the ARTS prototype's measurements since the sensors were uncertified and mounted on a paver screed. The lessons learned from the demonstration projects are valuable for future ARTS technology and for further studies to improve asphalt pavement smoothness.

These appendices pertain to report NRRA202103, Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase.

This is the second revision of this handbook which was originally written in 1996. This update to the handbook, although still titled Minnesota Seal Coat Handbook, has changed all references of Seal Coat to Chip Seal, better aligning it with other state Department of Transportation’s (DOT‘s), Federal Highway Administration (FHWA), and industry. Minnesota Department of Transportation (MnDOT) specifications will eventually be updated to reflect this change. As preventive maintenance and preservation of bituminous pavements continues to evolve, this version of the handbook has been expanded to include a brief discussion on spray applied bituminous surface seals and additional similar types of thin bituminous pavement surface treatments which are often referred to as BSTs. Although information on the BSTs discussed above have been brought into this handbook, the intent is still the same, to provide guidance in the design and construction of high-quality chip seal surface treatments for bituminous pavements. Applying this treatment to the right pavement at the right time while paying attention to the quality of materials used and workmanship will result in better performing, longer lasting bituminous pavements. This revision of the handbook was sponsored by the MnDOT Pavement Section with assistance from WSB Consulting Engineers and input from a Technical Advisory Panel made up of MnDOT, City and County Engineers.

The air void system in concrete provides a strong influence on the behavior of cementitious materials in both the fresh and hardened state, especially as it relates to freeze-thaw resistance and deicer scaling. The most common test procedure to characterize the air void system is ASTM C457 – Standard Test method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete, which involves microscopic determination of the air content, paste content, air-void size distribution, and spatial dispersion of a sawn concrete sample. This procedure is reliant on the user to make hundreds of critical decisions per sample, which requires significant time, and is potentially subject to human error. Additionally, ASTM C457 provides minimal guidance regarding the exact steps and equipment necessary to prepare a sample for evaluation. The outcome of this research not only provides specific information regarding sample preparation for hardened concrete air void analysis, it also develops an alternative characterization technique that drastically minimizes evaluation time, human error, and increases reliability of key hardened air void characterization parameters. Specific results show on average air void difference of 0.5% and 0.7% between the alternative method versus ASTM C457 Procedure A and B, respectively. The results also show a significant reduction of analysis time from approximately 2 – 4 hours per sample to 15 minutes per sample when using the alternative method.

We provide a final summary report of the project executed during last 2.5-year period (January 2020 - June 2022). The project tasks are summarized in the following scope of work (SOW): • Task #1: Project Management and Administration • Task #2: Hardware Development (Seismic Data Acquisition System) & Testing • Task #3: Software Development & Testing • Task #4: Delivery and Demonstration of Seismic Data Acquisition System and Software • Task #5: Final Report Initial project development and its progress in tasks #1 - #3 have been summarized in the quarterly reports and updated every month on the dedicated website until the end of December 2021. This final report focuses on the delivery of the completed system and subsequent demonstration surveys (tasks # 4 and #5). Associated details are presented in Appendix I (delivery) and Appendix II (demonstration surveys). Background theories and historical development that led to this particular system are described in an expanded abstract submitted to Geo-Congress 2022 at Charlotte, NC, March 20-23, 2022, which is attached in Appendix III. The developed system is named "TAPPER 64," and it consists of four (4) 16-channel receiver arrays that are transversely arranged to survey a certain width of the pavement (e.g., 0.5-m) simultaneously. Detailed technical and operational contents in hardware and software components of TAPPER 64 are presented in the "TAPPER 64-User's Manual" attached in Appendix IV.

The overall objective of this study was to explore three novel rejuvenator application methods using the emulsion and foaming technologies and determine their impacts on the workability and long-term cracking resistance of high-reclaimed asphalt pavement (RAP) asphalt mixtures. To that end, a comprehensive experimental plan was developed, which consisted of four supplementary experiments focusing on rejuvenator characterization, foaming measurements of rejuvenators and rejuvenated asphalt binders, RAP pretreatment and marination evaluations, and mixture performance testing, respectively. Test results indicated that adding rejuvenators for RAP pretreatment improved the overall quality characteristics of RAP. Among the three rejuvenator application methods evaluated for RAP pretreatment, the emulsion method was found more effective than the spray-on and foaming methods. Marinating the pretreated RAP had a notable impact on the rheological and chemical properties of the extracted RAP binders, but it did not significantly affect the workability, appearance, and color consistency of RAP. Adding rejuvenators, in general, improved the workability and cracking resistance of high-RAP mixtures, although the improvement in mixture performance test results, in some cases, was not statistically significant. Among the different rejuvenator application methods, pre-blending the rejuvenator into the virgin binder (with or without foaming) provided slightly better or equivalent rejuvenating effectiveness and thus, mixture performance properties, than adding the rejuvenator for RAP pretreatment. Based on the findings of the study, it was recommended that asphalt contractors continue to use the pre-blending method of adding rejuvenators for the design and production of high-RAP mixtures due to performance and ease of operation considerations.