Let's Get Technical – April 2025

1. Feasibility of Polyphosphoric Acid in Emulsified Asphalt Modification: Emulsification Characteristics, Rheological Properties, and Modification Mechanism

The research paper investigates the feasibility of using polyphosphoric acid (PPA) to modify emulsified asphalt, focusing on its emulsification characteristics, rheological properties, compatibility, and modification mechanisms. The study prepared PPA-modified emulsified asphalt with different dosages (0%, 0.5%, 1.0%, 1.5%, and 2.0%) and evaluated its properties, including evaporation residue, storage stability, and rheological performance using dynamic shear rheometer tests. Additionally, Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy (FM) were employed to analyze the chemical composition and microscopic characteristics of the modified asphalt.

The results showed that increasing PPA dosage initially decreased the softening point of the modified emulsified asphalt, then increased it, while penetration and ductility first increased and then decreased. The study found that PPA modification improved high-temperature stability, fatigue properties, and low-temperature performance, with optimal compatibility achieved at a PPA dosage of 1.0%. However, excessive PPA dosage led to particle aggregation, weakening the modification effect. The study also noted that PPA underwent hydrolysis within the emulsified asphalt system, resulting in distinct modification mechanisms compared to base asphalt.

In conclusion, the research demonstrated that PPA could effectively enhance the performance of emulsified asphalt, particularly at a dosage of 1.0%. The study highlighted the importance of selecting an appropriate PPA content to optimize the properties of modified emulsified asphalt. Future research should focus on validating the long-term aging behavior and field performance of PPA-modified emulsified asphalt and further investigating the interaction mechanisms between PPA and emulsifiers to improve storage stability.

Pan, S., Liu, X., Li, X., Jia, J., & Yang, J. (2025). Feasibility of Polyphosphoric Acid in Emulsified Asphalt Modification: Emulsification Characteristics, Rheological Properties, and Modification Mechanism. Coatings, 15(4), 471. https://doi.org/10.3390/coatings15040471

2. Evaluation of the electrochemical interaction in the asphalt emulsion-aggregate system of cold mix asphalt through zeta potential and surface free energy analysis

In this article, researchers investigate the electrochemical interactions between asphalt emulsions and aggregates in cold mix asphalt. The study utilizes zeta potential and surface free energy analysis to understand these interactions, which play a key role in the performance and durability of CMA. By examining the electrical potential and interaction in the emulsion-aggregate system, this research aims to optimize the formulation and application of asphalt emulsions.

One of the key findings is the correlation between zeta potential, which measures the electrical potential at the boundary layer of particles in a suspension, and adhesion between asphalt emulsions and aggregates. Higher zeta potential values indicate better electrochemical compatibility, leading to improved bonding and stability of the asphalt mix. The study also highlights the role of surface free energy in determining the wettability and adhesion properties of the emulsion-aggregate system. Aggregates with higher surface free energy tend to perform better with asphalt emulsions, improving the performance of CMA.

The researchers then go on to explore the impact of different types of aggregates and emulsions on the electrochemical interaction. It was found that slow-setting cationic asphalt emulsions and certain Colombian aggregates, such as alluvial and quarried types, exhibit varying degrees of interaction based on their zeta potential and surface free energy characteristics. This variability highlights the importance of selecting appropriate materials to achieve optimal performance in cold mix asphalt applications.

In conclusion, the article provides valuable insights into the electrochemical mechanisms central to the interaction between asphalt emulsions and aggregates. By utilizing zeta potential and surface free energy analysis, the researchers suggest this could be used as a scientific basis for improving the formulation and application techniques of CMA.

Cuaran-Cuaran, Z. I., Castilla-Barbosa, M., Rincón, O., & Ocampo-Terreros, M. (2024). Evaluation of the electrochemical interaction in the asphalt emulsion-aggregate system of cold mix asphalt through zeta potential and surface free energy analysis. International Journal of Pavement Engineering, 25(1). https://doi.org/10.1080/10298436.2024.2361837

3. Maintenance mechanisms of rejuvenator-optimized asphalt emulsion in damaged porous asphalt mixture: Morphological, physicochemical, and rheological characterizations

In this article, authors were looking for a way to maintain porous asphalt mixtures that were aging and raveling faster than dense and gap graded pavements.  Previous studies had shown them that their typical surface treatments were only penetrating the pavement by 20mm.  In addition to improving penetration, they were looking for an emulsion composition that would also improve coating efficiency and faster diffusion into the mixture to improve bonding strength more quickly. 

Knowing that rejuvenators in emulsions have been successful in restoring aged binder characteristics, the authors decided to use one petroleum-based rejuvenator and one bio-based rejuvenator in their standard emulsion.  Both rejuvenators were emulsified separately at 60% by weight and then added back into the standard emulsion at 10% bwe for the petroleum based and 5% by weight for the bio-based rejuvenator.  The standard emulsion, containing 60% residue, served as the control.  For the mixtures, a polymer modified PG76-16 PAV aged binder was used.  The loose mixtures were aged at 135C for 8 hours and compacted.  Three freeze/thaw cycles were also applied to the compacted specimens to introduce cracking.  Cross sectional images of the mixtures were obtained using X-ray CT.  Binder was extracted at various cuts using dichlormethane for rheolgical and physiochemical properties.

Both the petroleum-based rejuvenators and the bio-based rejuvenator modified emulsions were found to penetrate the surface almost double the control emulsion as found by X-ray.  GPC testing confirmed these results.  FTIR analysis confirmed the penetration depth of the bio-based rejuvenator modified emulsion, but not the petroleum-based rejuvenator as the functional groups for both binder and oil were very similar.  G-R parameter and G* master curve analysis of the different binder layers showed that the modified emulsions were penetrating further and were rejuvenating the aged asphalt binder.  MSCR testing showed increased Jnr 3.2kPa for all three emulsions in layers 1-3, when compared to the aged asphalt binder.  %R, 3.2kPa was most affected by the petroleum based rejuvenator, but a reduction was seen across the board for all three emulsions. 

The authors recommended further work with additional slices of mix and varying asphalt aging levels in addition to monitoring cracking, rutting, water permeability, noise reduction and skid resistance outside of the lab. 

Yang, Bin, et al. “Maintenance mechanisms of rejuvenator-optimized asphalt emulsion in damaged porous asphalt mixture: Morphological, physicochemical, and rheological characterizations.” Construction and Building Materials, vol. 464, Feb. 2025, p. 140185, https://doi.org/10.1016/j.conbuildmat.2025.140185.