The objective of this task order is the continued advancement of the performance specification continuum for BMD+ and mechanistic pavement design. Advancement of efforts will be accomplished by the following tasks: 1. Development of Level 1 BMD+ methods and threshold values for Level 2 BMD index parameters (Sapp and RSI) 2. Performance testing for transfer functions to support BMD+ and advanced pavement design 3. Comparison of BMD and BMD+ testing for mixture performance comparisons and analysis 4. Advance in a collaborative approach for FlexPAVE pavement design methods 5. BMD+ training and parallel field construction projects 6. Interim stakeholders status meeting 7. Create a system of tools including guidelines and sample specifications for agencies to transition from their traditional standard specifications to BMD+ specifications using performance tests and advanced mechanistic pavement design

Current procedures for asphalt mixture design in North Carolina require contractors to conform to volumetric requirements on the air void content, voids in mineral aggregate, and other parameters at a fixed, traffic- and layer-specific compaction effort. The presumption in this case is that the mixtures produced under the same guidelines will have similar properties. However, recent findings by NCSU suggests that this presumption may be inaccurate and may have substantial implications in the design, performance, and management of roadways. This research study will address this issue by: i) identifying the most appropriate durability related testing protocol for incorporation into mix design and quality assurance/control operations; ii) establishing initial threshold limits for the test identified; iii) developing a draft balanced mix design (BMD) procedure for North Carolina, and iv) developing a draft protocol for integrating the identified performance tests into quality assurance and quality control operations. The primary outcome of the proposed research will be a test method and procedure that the NCDOT can deploy in asphalt mixture design and production to ensure that the mixtures delivered in the state have an acceptable level of performance.

This proposed research plan aims to complete the Asphalt Mixture Performance Tester (AMPT) tests and performance analysis that were started in the HWY-2017-29 project, evaluate the effects of construction variability on pavement performance using the AMPT tests, IDEAL-CT, and Hamburg wheel-tracking (HWT) test, and verify and potentially improve the acceptance limits and pay factor formulas in the NCDOT������������������s Quality Management System (QMS) manual.

The Federal Highway Administration (FHWA) has developed mechanistically based performance comparison models to evaluate the cracking and rutting performance of asphalt pavement mixtures. These models form the basis of an asphalt performance comparison development effort and are being implemented into a FlexPAVETM software program for analyzing pavements and predicting distress. In this research study, NCSU will assess current asphalt pavement cracking models that can be applied to reflective cracking and further research, develop, calibrate, train, and validate a mechanistically based asphalt pavement reflective cracking model that is consistent with existing FlexPAVETM methodology and performance tests; incorporate it into the FlexPAVETM software and the FlexMATTM and FlexMIXTM data analysis tools, and assess and incorporate run time improvements to the model, software, and analysis tools.

This proposed research plan supports the North Carolina Department of Transportation (NCDOT) Division 5 Maintenance field study of geosynthetic pavement interlayer performance. It includes designing and orchestrating field experiments with NCDOT engineers, performing laboratory tests using samples obtained from field test sections, analyzing the test results to assess the performance of different interlayer products, and verifying/calibrating/refining the recommendations that are based on laboratory tests of different interlayer systems conducted in previous and ongoing NCDOT projects. The research plan is designed to use the test procedures employed in the ongoing NCDOT project, RP 2019-19 Development of Geosynthetic Pavement Interlayer Improvements, which focuses on the laboratory evaluation of various geosynthetic interlayer products, including their resistance to reflective cracking and debonding failure. The candidate roadway for this proposed field study is NC 96 in Youngsville, Franklin County between Jack Jones Road in Wake Forest and Oak Grove Church Road in Youngsville. Geosynthetic interlayers that are included in the RP 2019-19 project will be installed prior to construction of the asphalt overlay. These geosynthetic product types are HaTelit G50 paving composite interlayer by Heusker, Mirafi MPG100 paving composite interlayer by Tencate, Tensar GlasPave 50 geotextile paving mat interlayer, GlasGrid 8511 (25 mm) paving grid interlayer by Tensar, and Petromat 4598 paving fabric interlayer by Propex/Tencate. In addition, chip seal and FiberMat������������� Type B interlayers will be included in the experimental design for the field study as well as a control section with no interlayer. The location of the project will be selected to avoid a significant grade and major intersections. Cracks in the existing pavement will be mapped before placement of the interlayers. The tack coat application rates will follow the geosynthetic manufacturers������������������ recommendations. The pavement conditions will be monitored by the North Carolina State University research team until the end of this proposed project and then by NCDOT personnel after this project is completed. Two 18-inch diameter cores will be taken from the center of the lane in each test section using the specially designed coring and sample extraction methods. Each core will produce two beam specimens and four 100-mm diameter cylindrical specimens. In addition, the asphalt mixtures, interlayer products, and tack coat materials used in the construction will be obtained from the field for the laboratory fabrication of performance test specimens. Shear strength tests and four-point bending notched beam fatigue tests will be conducted using both the field and laboratory-fabricated specimens to evaluate the debonding and reflective cracking mitigation potential of the different interlayer systems, respectively. The shear strength and reflective cracking performance of the specimens will be compared between the specimens obtained from the field cores and laboratory-fabricated specimens in the proposed study and the laboratory-fabricated specimens tested in the RP 2019-19 project. Pavement condition survey data and the performance test results will be used to verify/calibrate the results obtained from the NCDOT RP 2019-19 project. The experience gathered from the field construction of the geosynthetic interlayers will be used to develop construction guidelines for the different geosynthetic interlayer products. This research will also produce field-verified performance thresholds and project selection guidelines and long-term condition survey guidelines for interlayer-reinforced asphalt overlays. These products will be used to incorporate best practice techniques in the effort to make informed decisions when using interlayers as a maintenance application in the State of North Carolina.

The objective of this research is to develop guidance to integrate the performance predictive capabilities of the PASSFlexTM software and its suite of tools (FlexPAVETM version 2.0, FlexMATTM, and FlexMIXTM) within a statistically sound QA system in a PRS framework. The research shall address: (a) the use of the cyclic fatigue Sapp and SSR allowable traffic for rutting (ATR) index test parameters, index thresholds, and acceptance limits in support of performance engineered mixture design (PEMD) approaches and to facilitate further implementation of the tests and performance predictions, (b) material selection and mixture design changes that can impact the test results (cyclic fatigue, SSR, and their index parameters) and trends associated with owner agency specified performance thresholds, and (c) the major elements of a QA system (per TRB E-Circular 235, Glossary of Transportation Construction Quality Assurance Terms (http://onlinepubs.trb.org/onlinepubs/circulars/ec235.pdf) and associated buyer/seller and payment risks.

In this research study, NCSU will design, conduct, and provide recommendations relating to a two-phase ruggedness and interlaboratory study on a test method that has been identified as critical to asphalt pavement performance and design practice. AASHTO TP 132 (2019) Standard Method of Test for Determining the Dynamic Modulus for Asphalt Mixtures Using Small Specimens in the Asphalt Mixture Performance Tester (AMPT) has been developed, refined, and recently published as an AASHTO provisional standard; a statistically sound refinement procedure is needed to facilitate widespread adoption and implementation. Not only can this standard be used to obtain inputs to the AASHTO PavementME pavement structural analysis software, the standard is being used in ongoing FHWA efforts as part of a performance-related specification framework which seeks to increase pavement life through fundamental testing and predictive relationships. AASHTO TP 132 is of interest because of its fundamental nature, determination via the AMPT standardized equipment, and its ability to model and predict material performance over a wide range of loading and climate conditions a pavement may experience; resulting in better performing, safe, quiet, durable, long lasting asphalt roadways. Additionally, a draft practice for preparing small-scale specimens has been developed and published as AASHTO PP 99 (2019) Standard Method of Practice for Preparation of Small Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor (SGC) and Field Cores. This draft practice is of significant interest to the asphalt materials community due to anticipated materials, time, and cost savings associated with preparing and evaluating smaller performance test. NCSU will carry out the following tasks. Task 1 ������������������ Develop final research plans and project schedule ������������������ The proposed plan will be revised based on feedback from the FHWA. Task 2 ������������������ Kickoff meeting ������������������ NCSU will meet with the project panel to review the statement of work and work plans. Task 3 ������������������ Perform work plan and document efforts ������������������ NCSU will carry out the approved work plan by following the appropriate ASTM standard test methods to develop a rugged test method. Task 4 ������������������ Ruggedness study presentations and webinar ������������������ NCSU will present the findings to targeted stakeholders. Task 5 ������������������ Publication ready final deliverables ������������������ the AASHTO standards will be revised into a final form. Task 6 ������������������ Revise work ILS work plan ������������������ NCSU will revise the original work plan from Task 1 based on findings from Tasks 3-5 for conducting the ILS study. Task 7 ������������������ Perform work plan and document efforts ������������������ NCSU will coordinate the ILS according to the approved work plan. This will include identifying participants, sending materials, and analyzing their results statistically. Task 8 ������������������ ILS study presentation and webinar ������������������ NCSU will present their findings to targeted stakeholders. Task 9 ������������������ Publication ready final deliverables ������������������ the AASHTO standards revised in Task 5 will be modified to include repeatability and reproducibility statements.

The use of high Recycled Binder Replacement Percentages (RBRs%) in asphalt surface mixtures is increasing. The asphalt binders in recycled materials are generally hardened and embrittled from oxidization and may not fully mobilize and blend with virgin materials. Consequently, high recycled content mixtures may be prone to cracking if appropriate measures to consider this effect are not taken during the mixture design process. The objectives of the proposed research project are to: (1) modify the NCDOT������������������s procedures for the design of surface mixtures containing RAP and RAS to improve performance and (2) modify the NCDOT������������������s specifications to improve the consistency within and across RAP and RAS stockpiles within North Carolina. 1. To achieve these objectives, an operational review will be conducted to identify how contractors process, stockpile, characterize and use RAP and RAS under the current NCDOT guidelines. In addition, relationships between asphalt content and performance will be developed for recycled mixtures sourced from North Carolina. These relationships will be used to identify the maximum virgin binder content allowable and to maximize cracking performance without having the rutting performance fall below a critical performance threshold for each mixture. The collective results will be used to identify appropriate revisions to the NCDOT������������������s current recycled mixture design procedure to ensure reliable performance. The research results will lead improved specifications that will facilitate the design of better-performing surface mixtures containing recycled materials. These specifications will improve the durability of NCDOT pavements and consequently decrease life-cycle costs.

In this research study, NCSU will conduct experiments and analysis to improve the AASHTO TP 133 protocol by incorporating more scientifically based temperature selection guide and providing guidance on the maximum air void content for specimens that are subjected to this standard test method. In addition, NCSU will update the FlexPAVETM software to incorporate seasonal effects into the base layer and the user guides for improved usability. This research supports ongoing FHWA efforts as part of a performance-related specification framework which seeks to increase pavement life through fundamental testing and predictive relationships. Recent developments in these performance tests, adoption of standards, FlexMATTM, FlexMIXTM, and FlexPAVETM provide highway agencies and asphalt paving community with a unique opportunity to use performance tests and mechanistic models for asphalt PEMD, asphalt pavement design, and performance related specifications to integrate these different phases in pavement construction using the same test methods and mechanistic principles. These tools help link material characteristics from testing with mechanistic models to predict performance; and ultimately identify how to best design, construct, and accept a pavement. NCSU will carry out the following tasks. Task 1 ������������������ Develop final research plans and project schedule ������������������ The proposed plan will be revised based on feedback from the FHWA. Task 2 ������������������ Kickoff meeting ������������������ NCSU will meet with the project panel to review the statement of work and work plans. Task 3 ������������������ Perform work plan and document efforts ������������������ NCSU will carry out the approved work plan by following the appropriate ASTM standard test methods to develop a rugged test method. Task 4 ������������������ Draft Final Revised FlexPAVETM Software, Installation, and User Guides ������������������ NCSU will update the user interface, installation guide, and user guide for the FlexPAVETM software. Task 5 ������������������Presentation and webinar ������������������ NCSU will present their findings to targeted stakeholders. Task 6 ������������������ Publication ready final deliverables ������������������ the reports will be revised and finalized and AASHTO standards will be revised into a final form.

AASHTO TP 107 enables the practical, mechanistic performance characterization of asphalt concrete using cyclic fatigue testing in the Asphalt Mixture Performance Tester (AMPT). AASHTO TP 107 was initially developed for the use of 100-mm diameter specimens, which yield a single test specimen per gyratory sample. Recently, a modified version of AASHTO TP 107 was proposed for the testing of 38-mm diameter small specimens that improves the efficiency of specimen fabrication and enables the testing of field cores extracted from as-built pavement layers. The objective of the proposed research is to improve AASHTO TP 107 by conducting ruggedness and interlaboratory studies using both small and large specimens. The ruggedness evaluation will identify controllable experimental factors that significantly affect the test results and to establish limits for their control. The interlaboratory study will lead to precision statements that define the repeatability and reproducibility of small and large cyclic fatigue the test results.