Lorena Garcia Cucalon

Evaluation of the Moisture Susceptibility of WMA Technologies

Over the past decade, the use of warm mix asphalt (WMA) for asphalt pavement construction has increased in the United States. However, questions remain about the long-term performance and durability of WMA pavements. One key issue is the moisture susceptibility of WMA pavements. Concerns about WMA moisture susceptibility include the possibility that aggregates will be inadequately dried at lower production temperatures and the fact that several WMA technologies introduce additional moisture in the production process. The objectives of National Cooperative Highway Research Program (NCHRP) Project 9-49 were to (1) assess whether WMA technologies adversely affect the moisture susceptibility of asphalt pavements and (2) develop guidelines for identifying and limiting moisture susceptibility in WMA pavements. The research was conducted through coordinated laboratory and field experiments that investigated the potential for moisture susceptibility in WMA compared to hot mix asphalt (HMA). Design of the experiments was guided by a survey of the state departments of transportation and industry on WMA pavement construction and performance. The survey identified no instances of moisture damage to WMA pavements in service through 2010. This negative finding is supported by the results of recently completed NCHRP Project 9-47A, which conducted intensive evaluations of WMA pavements constructed across the United States between 2006 and 2011. Project 9-49 then focused on development of guidelines for WMA mix design and quality control to identify and minimize any possibility of moisture susceptibility. The laboratory experiments evaluated (1) laboratory-conditioning protocols for WMA before moisture susceptibility testing, (2) the ability of standard test methods to detect moisture susceptibility of WMA, and (3) potential differences in WMA moisture susceptibility measured on laboratory-mixed and -compacted specimens; plant-mixed, laboratory-compacted specimens; and plant-mixed, field-compacted cores. The guidelines are presented in the form of a workflow of conditioning protocols and standard test methods that first assess the potential moisture susceptibility of a WMA mix design or field mixture and then recommend remedies to minimize such susceptibility. Specific test thresholds in the guidelines are based on the results of testing of WMA from field projects in Iowa, Montana, New Mexico, and Texas. This report fully documents the research and includes the following Appendixes: Appendix A, Laboratory Conditioning Experiment; Appendix B, Moisture Conditioning Experiment; Appendix C, Performance Evolution Experiment; Appendix D, Construction Reports and Performance of Field Projects; Appendix E, Mixture Volumetrics; Appendix F, Proposed Draft Revisions to the Appendix to AASHTO R 35; Appendix G, Future Work Plan to Evaluate Moisture Susceptibility of HMA and WMA; and Appendix H, Statistical Results. Appendix F is included herein. Appendixes A—E, G, and H are available on the TRB website.

Novel Method for Moisture Susceptibility and Rutting Evaluation Using Hamburg Wheel Tracking Test

The Hamburg wheel tracking test (HWTT) has been widely used as a standard laboratory test to evaluate the moisture susceptibility and rutting resistance of asphalt mixtures. The stripping infection point and the rut depth at a certain number of load cycles are two common parameters obtained from the test. Although these parameters have been widely adopted by several transportation agencies, the accuracy and variability in characterizing mixture properties of these parameters have been questioned. In this study, a novel method to analyze the HWTT results is introduced and three new parameters are proposed to measure the moisture susceptibility and rutting resistance of asphalt mixtures. The new parameters are compared against the current ones to assess their capability to discriminate between three types of asphalt mixtures with different performance results in the HWTT. Significant advantages in characterizing mixture resistance to stripping and rutting are demonstrated by the new parameters. In addition, the effect of antistripping additives and recycled materials on mixture performance in the HWTT is evaluated with mixtures from a field project in Texas. Test results for the new parameters show that the addition of antistripping additives improves the susceptibility of asphalt mixtures to moisture. Specifically, the use of lime is more beneficial for improving mixture performance than a liquid antistripping agent. Conversely, the addition of recycled materials provides mixtures with increased moisture susceptibility but improved rutting resistance.

Evaluation of Moisture Susceptibility Minimization Strategies for Warm-Mix Asphalt: Case Study

AbstractWarm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphalt concrete mixtures, allowing for savings in fuel consumption and extending haul distances and construction season. The reduced temperatures also provide a greener technology as emissions are lowered at the plant and the construction site. Engineering and environmental benefits promoted the rapid implementation of WMA technologies, but concerns remain regarding the difference in mixture performance of WMA versus hot-mix asphalt (HMA) because of the changes in the production process, specifically in terms of moisture susceptibility. This case study evaluates moisture susceptibility through the use of laboratory tests including the wet indirect tensile (IDT) strength test, the tensile strength ratio (TSR), and the Hamburg wheel tracking test (HWTT) analyzed with a novel methodology. The performance of two WMA technologies (Evotherm DAT and foaming) versus a control HMA is analyzed with and without antist...

Effect of warm mix additives on the interfacial bonding characteristics of asphalt binders

Abstract The quality of the interfacial bonding between asphalt binder and aggregates plays a significant role in determining the durability of asphalt mixtures. Warm mix asphalt (WMA) modifiers have been used extensively in the last decade primarily to reduce production and compaction temperatures as well as to improve workability of asphalt mixtures. This study aimed to provide better understanding of the effects of these WMA modifiers on the interfacial bonding between asphalt binders and aggregates. The evaluation focused on measuring surface energy of binders in unaged and aged states and aggregates and then calculating energy parameters that describe the potential of a given asphalt-aggregate combination to resist fatigue cracking and moisture damage. Results show that the combination of asphalt-WMA additive, as well as the content applied of WMA additive has a significant impact on the fatigue cracking and moisture damage resistance. The results suggest that it is poor practice to use a given type and percentage of WMA modifier without regard for binder type. Instead, test methods are recommended to evaluate the compatibility of asphalt binder, WMA additive type/content, and aggregates for improved performance at different conditions.

Fundamental evaluation of moisture damage in warm-mix asphalts

Warm-mix asphalt (WMA) technologies have been used extensively in the last decade. The benefits of WMA have motivated stakeholders to expedite the implementation of this technology. However, some research studies have raised concerns regarding WMA laboratory performance in terms of resistance to moisture damage, while WMA has demonstrated good performance in the field. These experiences led to further research to understand the fundamental characteristics of WMA. This study conducted a comprehensive evaluation of WMA prepared using different aggregate sources, asphalt binders, and WMA additives. A dynamic mechanical analyser was used to test the mastic phase of conventional hot-mix asphalt and WMA. The test specimens were evaluated at different conditions – dry and wet – and at different ageing stages – unaged and three-month aged – in a controlled environmental room (i.e. 60°C). A fracture mechanics approach was used to analyse the test results. This approach incorporated fundamental material properties, including adhesive bond energy between aggregates and asphalt binder. The results show that WMA performance improved with ageing and the overall performance of the WMA can be improved if the selection of materials (i.e. aggregate source, asphalt binder, WMA technology) is optimised based on the compatibility of their surface energy. In addition, surface energy results were able to explain some findings from the mechanical testing related to moisture susceptibility of WMA.

The crossover temperature: significance and application towards engineering balanced recycled binder blends

Increased quantities of asphalt-based recycled materials can be incorporated in asphalt paving mixtures by using recycling agents. Previous studies demonstrated that restoring the required performance grade (PG) by the inclusion of recycling agents may not be sufficient to guarantee long-term durability. In this study the crossover temperature was used to characterise the viscoelastic properties of asphalt binders at the intermediate service temperature range for asphalt pavements. Durability thresholds for crossover temperature with aging were proposed on a trial basis from a correlation to the Glover–Rowe parameter. In combination with high PG, crossover temperature was used to evaluate rheological balance: resistance to early rutting and long-term embrittlement. Practical recommendations are provided in terms of appropriate materials selection (base binder, recycled, binders, and recycling agents) towards engineering long-lasting rejuvenated binder blends with increased quantities of recycled materials. Limitations and additional considerations for extending the rheological balance approach to evaluate polymer-modified materials are also summarised.

Performance of asphalt mixtures with high recycled materials content and recycling agents

ABSTRACT Recycled asphalt mixtures with high amounts of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) can be excessively stiff, brittle, and prone to cracking. The use of recycling agents, or rejuvenators, can significantly reduce mixture stiffness and improve performance, specifically cracking resistance. In this study, the performance of recycled and rejuvenated asphalt mixtures from several field projects, located in different environmental zones across the United States, was evaluated considering various recycling agent dosages determined by the contractors. Field core test results and the visual distress surveys of the field projects demonstrated that using the field recycling agent dosages yielded poor mixture performance. Laboratory test results demonstrated that adding the recycling agent at the dosage to match the continuous high-temperature performance grade (PGH) of the rejuvenated binder blend (virgin/base binder, recycled binder, and recycling agent) to that of the target binder PGH specified based on climate and traffic requirements yielded improved mixture performance. The rejuvenated mixtures at this recycling agent dosage showed significant reduction in stiffness and improved cracking resistance, and facilitated the use of higher quantities of recycled materials, regardless of aging level, while maintaining rutting resistance after short-term aging.