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Coupled Impact of Moisture and Oxidation on the Properties and Performance of Asphalt Mixtures

Description:

Assessing the influence of climate-related factors on the mechanical response and performance of asphalt mixtures is a critical topic in the area of pavement engineering. Besides temperature, the presence of air and moisture strongly alter the properties of these mixtures, affecting their overall performance and durability. While moisture promotes the deterioration of the adhesive bonds between the aggregates and the asphalt binder and the degradation of cohesive properties within the asphalt binder – a phenomena commonly called moisture damage –, the oxygen molecules present in the air are added to the polar aromatic compounds of the asphalt binders, promoting hardening processes in this material with accompanying changes in viscosity and brittleness.

A main difficulty related to the characterization and assessment of these phenomena is that these are complex processes that occur at different intensities and rates during the service life of the mixtures. In the case of oxidation, the associated irreversible chemical reactions result in the generation of carbonyl groups and other chemical products. The higher polarity of these new compounds increases the stiffness of the asphalt binder and, consequently, impacts the mechanical response of asphalt mixtures. The rate and magnitude of asphalt oxidation depend on the chemical properties of the asphalt binder, the volumetric properties of the material, the amount and availability of oxygen sources and other external conditions, like temperature and pressure. Most studies reported in the literature on this topic have focused on: i) identifying and characterizing the chemical reactions associated with this phenomenon, ii) quantifying the effect of oxidation on certain physical and rheological properties of asphalt binders, iii) formulating models of asphalt oxidation kinetics, and iv) quantifying the impact of asphalt oxidation on the mechanical response and performance of asphalt mixtures. On the other hand, moisture damage involves different physical, chemical, thermodynamic and mechanical processes that induce diverse pavement distresses, ranging from stripping and potholes to raveling across the entire surface of a pavement structure. The initiation and progress of these distresses impact the structural capacity of the mixture, as well as the serviceability and safety conditions of the pavement. Most works related to moisture damage in the literature have focused on three main aspects: i) proposing experimental tests to characterize the moisture sensitivity of asphalt mixtures, ii) identifying and understanding the mechanisms related to moisture damage, and iii) developing strategies to prevent or remediate its associated distresses, including the use of antistrip additives and the development of quality control procedures both at the mix plant and in the field.

Although important advancements have been achieved in the characterization of moisture damage and asphalt oxidation processes, most of these works have been conducted independently. In other words, the combined effects of these two climatic-related phenomena on the mechanical properties and performance of asphalt mixtures are still unclear. However, moisture-oxidation processes occur simultaneously in the field, and the limited studies available on this topic demonstrate that these coupled phenomena should be deeper studied, and highlight the need for counting with mix characterization procedures that could account for the long-term effects of these joint degradation processes.

Objective:

Conduct a comprehensive experimental plan to understand and identify the combined mechanisms and effects caused by moisture and asphalt oxidation on asphalt mixtures. A second objective is to propose new experimental procedures to quantify the sensitivity of asphalt mixtures to these coupled effects and/or proposed new environmental conditioning processes that could be implemented as part of currently available mechanical characterization methods of asphalt mixtures. Initial recommendations on how to incorporate these coupled climatic effects as part of existing mechanistic-based pavement design methodologies are also an expected outcome of this research.

Benefits:

A clearer understanding about the short, medium and long-term combined role of moisture damage and oxidative hardening on asphalt mixtures would permit to design strategies for enhancing the durability of these materials. Besides, the results from this work could be incorporated as reliable input data in life cycle and life cycle cost analyses of flexible pavements.

Related Research:

Among the limited studies dealing with the effects of moisture-oxidation on asphalt binders it is worth highlighting the work by Thomas (2002) who monitored the chemical and rheological changes in several asphalts that were long-term aged, and long-term aged in the presence of water. It was concluded that the samples aged in the presence of moisture contained larger amounts of carbonyl compounds, and that the changes caused by oxidative aging and water were source-dependent. In a similar approach, Ma et al. (2011) modified the Pressure Aging Vessel (PAV) test to also include the long-term moisture-aging effects on unmodified and polymer modified asphalt binders. Chemical tests showed that heat, oxygen, pressure and water had a combined effect on the aging processes of asphalt binders, and that the ‘moisture plus heat and oxygen’ conditioning process caused the highest increased in the stiffness of the binders. Huang et al. (2012) compared the rheological properties on asphalts that were aged with and without the presence of moisture (i.e. 99% relative humidity), and concluded that moisture had no significant effect on the oxidation kinetics of the asphalt binder under atmospheric pressure and 60ºC. Figueroa (2015) and Hernández et al. (2014) quantified the physical, chemical and rheological changes in thin film samples of unmodified asphalts that were submerged in distilled water during two years. It was found that the presence of oxygen in water was a significant source of asphalt aging. More recently, Pan et al. (2016) used Molecular Dynamics (MD) simulations to evaluate the physical properties of unaged and aged asphalt binders that were subjected to conditioning processes at different moisture contents (0, 1 and 10% moisture). The authors observed that the modulus and zero shear viscosity decreased in both types of binders when the moisture content increased, and that the oxidized asphalt was more susceptible to moisture damage than the unaged asphalt. In summary, the findings of the works conducted on binders suggest that the changes in their properties depend on the specific selected moisture and oxidation conditioning processes, and that there is still no consensus about the influence of the combined processes on the properties of these materials.

Regarding the works conducted on full mixtures, Huang et al. (2005) evaluated the role of oxidation on the moisture resistance of asphalt mixtures, and found that oxidative aging improved their resistance to moisture damage, supporting the fact that carboxylic acids play a critical role in determining the moisture sensitivity of these materials. More recently, López-Montero and Miró (2016) evaluated the fracture energy and fatigue life of asphalt mixtures that were subjected to moisture and/or aging environments. The authors observed that water caused minor aging effects on the mixture, which seemed to improve the mechanical response of the material. Yang et al. (2016) evaluated the combined effects of moisture and aging on the viscoelastic, fracture and compaction properties of HMA (with and without RAP) and WMA mixtures. The main findings were that moisture reduced the fracture energy of the mixtures at all aging levels, and that, at longer aging periods, the dynamic modulus of the moisture-conditioned mixtures tended to decrease with respect to the samples that were not moisture-conditioned. Abuawad (2016) assessd the impact of five different additives (liquid antistrip, hydrated lime, SBS, SBS with liquid antistrip, and polyphosphoric acid with hydrated lime) on the moisture sensitivity of asphalt mixtures that were pre-aged at different levels. The author found that aging had a mixed impact in the moisture susceptibility of the mixtures; e.g. the improvements in moisture resistance promoted by the liquid antistrip decreased with aging, while the resistance of the mixture with hydrated lime to moisture damage increased with aging. More recently, Bazuhair et al. (2018) evaluated the capability of different aging-moisture coupled laboratory conditioning protocols to detect damage in asphalt mixtures subjected to the weather of the southeastern region of the United States (US) and Smith and Howard (2018) compared field aging of an asphalt mixture in a segment trial with no traffic in the same region of the US with against that obtained through several lab conditioning protocols that included aging and moisture processes. Other related works on this topic include the studies conducted by Souliman et al. (2014), Das et al. (2015) and Valentová et al. (2016).

Tasks:

This research is composed by four main tasks:

  1. Literature Review: the research team will conduct a comprehensive literature review on the combined effects of moisture and oxidation on asphalt materials. As part of this effort, it is critical that the team includes recently completed and currently on-going projects funded by Departments of Transportation (DOT) and other agencies on this topic.

  2. Research Plan: based on the results of the literature review, the research team will propose a research experimental plan to assess the combined oxidation-moisture effects on asphalt materials. This plan includes two phases: the first phase should assess the coupled mechanisms on asphalt binders, while the second should evaluate the impact of these combined environmental processes on asphalt mixtures. The team would need to propose a set of materials to be studied (types of mixtures, e.g. dense or open HMA or WMA; materials, e.g. modified or unmodified binders and mineralogical properties of aggregates; and use of additives; e.g. antistripping) and different climatic conditioning processes, as well as the tests to quantify the properties and expected performance of the materials.

  3. Execution of the plan, analysis of results and recommendations: after analyzing the experimental results, the team should provide information about the fundamental mechanisms responsible for changing the properties and performance of the materials, and propose experimental protocols that could be used to evaluate the effects of moisture-oxidation conditioning processes on asphalt mixtures. Also, it is expected that the authors provide initial recommendations about how to include these combined processes as part of currently used mechanistic-empirical design methodologies for asphalt pavements.

  4. Final Report: the final task consists in the preparation of a final report with a detailed description of the different stages of the work.

Implementation:

Highway agencies and contractors would be able to use the results of this research to design more durable mixtures. Some adaptations of the experimental protocols proposed to match the specific climatic conditions of each region are anticipated.

Relevance:

Potential users of the research results include highway agencies, agencies at all levels dealing with the use of asphalt pavements, pavement consultants, pavement contractors, suppliers, private asphalt mix laboratories

Sponsoring Committee:AFK40, Surface Requirements of Asphalt Mixtures
Research Period:Longer than 36 months
Research Priority:High
RNS Developer:Silvia Caro, Timothy Aschenbrener, Danny Gierhart, Edith Arámbula-Mercado, Louay Mohammad, Amir Golalipour, Shane Underwood, Amy Epps-Martin
Source Info:Abuawad, I.M.A. (2016). “ Mechanical and Surface Free Energy Characterization of Asphalt Concrete for Moisture Damage Detection”. Ph.D. dissertation. University of Illinois at Urbana-Champaign.
Bazuhair, B., Pittman, C.V., Howard, I.L., Jordan III, W.J., Hemsley, J.M. Jr., Baumgardner, B. (2018) “Conditioning & Testing Protocol Combinations to Detect Asphalt Mixture Damage”. Proceeding of the TRB Annual Meeting, Washington, D.C.
Das, P.K., Baaj, K., Kringos, N. and Tighe, S. (2015). “Coupling of Oxidative Ageing and Moisture Damage in Asphalt Mixtures”. Road Materials and Pavement Design. 16(1), 265-279.
Figueroa Infante, A. S. “Investigación sobre el Efecto del Agua en el Asfalto y su Impacto en la Mezcla Asfáltica” (2015). Ph.D. Dissertation. Pontifical Universidad Javeriana (Bogotá, Colombia).
Hernández, J.A., Rondón, H.A. and Fernández, W. (2014). “The Influence of Water on the Oxidation of Asphalt Cements”. Construction and Building Materials, 71, 451-455. https://doi.org/10.1016/j.conbuildmat.2014.08.064
Huang, S-C., Robertson, R.E., Branthaver, j.F., and Petersen, C. (2005). “Impact of Lime Modification of Asphalt and Freeze-Thaw Cycling on the Asphalt-Aggregate Interaction and Moisture Resistance to moisture Damage”. Journal of Materials in Civil Engineering (ASCE). 17 (6), 711-718.
Huang, S-C., Glaser, R. and Turner, F. (2012). “Impact of Water on Asphalt Aging”. Transportation Research Record: Journal of the Transportation Research Board. 2293: https://doi.org/10.3141/2293-08
López-Montero , T. and Miró, R. (2016). “Differences in cracking resistance of asphalt mixtures due to ageing and moisture damage”. Construction and Building Materials. 112, 299-306: https://doi.org/10.1016/j.conbuildmat.2016.02.199
Ma, T., Huang, X-M, Mahmoud, E. and Garibaldy, E. (2011). “Effect of Moisture on the Aging Behaviour of Asphalt Binder”. International Journal of Minerals, Metallurgy and Materials. 18 (4), 460: https://doi.org/10.1007/s12613-011-0463-4
Pan, J., Rafiqul A. Tarefder, A. and Hossain, M.I. (2016). “Study of Moisture Impact on Asphalt Before and After Oxidation Using Molecular Dynamic Simulations”. Transportation research Record: Journal of the Transportation Research Board. 2574: https://doi.org/10.3141/2574-04.
Smith, B.T., and Howard, I.L. (2018) “Matching Asphalt Mixture Longer Term Aging in the Southeast United States to Laboratory Conditioning Protocols”, Poster presented at the TRB Annual Meeting, Washington, D.C.
Souliman, M.I., Hajj, E.Y., Sebaaly, P.E. (2014). Impact of Antistrip Additives on the Long-Term Aging Rheological Properties of Asphalt Binders. Journal of Materials in Civil Engineering (ASCE). 27 (8).
Thomas, K.P. (2002). “Impact of Water during the Laboratory Aging of Asphalt”. Road Materials and Pavement Design. 3 (3), 299-315.
Valentová, T., Altman, J., Valentín, J. (2016). “Impact of Asphalt Ageing on the Activity of Adhesion Promoters and the Moisture Susceptibility”. Transportation Research Procedia. 14
768-777.
Yang, S., Braham, A., Wang, L., Wang, Q. (2016). “Influence of Aging and Moisture on Laboratory Performance of Asphalt Concrete”. Construction and Building Materials. 115, 527-535: https://doi.org/10.1016/j.conbuildmat.2016.04.063
Date Posted:01/16/2018
Date Modified:07/31/2018
Index Terms:Moisture damage, Oxidation, Asphalt mixtures, Mechanical properties, Pavement performance, Asphalt pavements,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Materials
Pavements

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