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Background

The widespread use of petroleum-based asphalt binders in the construction industry is accompanied by high material costs due to the volatility of the petroleum market and negative environmental impacts. Petroleum exploration and drilling has been shown to disrupt natural animal habitats and pollute natural water, land, and air resources. Further, hot mix asphalt (HMA) construction requires high working temperatures (135-165ºC), which necessitates large amounts of energy. Production of materials and construction methods used in HMA pavement applications emit greenhouse gases and toxic volatile organic compounds that present health risks to exposed construction workers. The construction industry is in need of greener novel materials and technologies to replace petroleum-based asphalt binders. In order to fulfill this environmental and economic need, direct alternatives for petroleum-based binders need to be investigated.

Research Objective

This research aims to contribute to the advancement of direct alternative materials for petroleum-based asphalt binders. Highly concentrated mixtures of agar hydrogels (i.e., 10% agar) possess similar viscoelastic and temperature-dependence properties when compared to conventional petroleum-based binders (e.g., bitumen, tar) which may make agar well-suited as an alternative binder for pavement applications.

To achieve this goal, the following sub-objectives have been identified:

• Evaluate agar-based binder properties using conventional asphalt binder laboratory testing standards (namely Superpave).
• Evaluate and optimize the stability and durability of agar-based binder asphalt mixes (i.e., agar-based binder and aggregate).
• Quantify system-scale life cycle environmental and economic benefits of agar-based binder use in order to establish quantitative comparisons between novel and traditional binders.

Contributions​

This research advanced the understanding of agar-based materials as a potential bio-based alternative to conventional petroleum-based materials in civil engineering. The work characterized the engineering and durability properties of high-concentration agar binders, evaluated chemical and physical methods for improving their moisture resistance, and assessed the mechanical performance of agar-based composites in pavement-like mixtures. Together, the findings provided a comprehensive empirical foundation—including predictive models and composition guidelines—to support the future development of sustainable biopolymeric materials for civil engineering applications.

This work resulted in the following publications:

• Frey, M.; Williams, S.; Srubar, W.; and Torres-Machi, C. (2025) Characterization and Evaluation of Agar as a Bio-Based Asphalt Alternative. Infrastructures, 10(9), 223. DOI: 10.3390/infrastructures10090223
• Frey, M; Torres-Machi, C.;ÌýSrubar, W.Ìý(2023) Agar-Based Binders for Use in Pavement Applications. Colorado Department of Transportation.
• Frey, M.; Williams, S.; Torres-Machi, C.; Srubar, W. (2023) Biobased Alternative Binders from Agar for Civil Engineering Applications: Thermal, Biodeterioration, and Moisture Sorption Properties. 5th International Conference on Bio-Based Building Materials (ICBBM-2023), RILEM Bookseries, 45, 665-675. DOI: 10.1007/978-3-031-33465-8_51

Funding

US Department of Education Graduate Assistance in Areas of National Need (GAANN) Fellowship: 2018-2023.
Colorado Department of Transportation (CDOT): 2021-2023.