Let's Get Technical- Research Articles

Development of a Performance-Based Approach to Asphalt Emulsion Selection for Cold In-Place Recycling Applications

The article describes the current methodology for selecting asphalt emulsion for Cold-In-Place recycling and similar treatments.  Currently the methodology involves simply passing the specification for a CSS-1H for example, which may not encompass all of the performance characteristics necessary to make a successful CIR project.  A CSS-1H could also be a tack coat or slurry seal for two examples.  Slurry seal, however, possesses the advantage of having performance specifications written around the mix.  Cold-In-Place, however, does not currently have performance specifications directly tied to the emulsion specification and its performance in the field.

The article defines performance in terms of workability, compaction, and cohesion gain.  Current testing methodologies do a good job at testing final mix properties, but these properties are related more to asphalt content and aggregate structure than the asphalt emulsion itself, generally speaking.  The work tested the Superpave Gyratory Compactor, the loose triaxial, raveling, direct shear, and compacted triaxial tests.  Overall, in terms of final density and workability index the Superpave Gyratory Compactor showed the most promise and the Dongre workability test also showed some potential.  Further work will need to be done to bring these into full specifications, but this work shows a lot of promise on specifying emulsions for Cold-In-Place with an eye towards performance.

Casillas, S., & Braham, A. F. (2022a). Development of a performance-based approach to asphalt emulsion selection for cold in-place recycling applications. Transportation Research Record: Journal of the Transportation Research Board, 2676(5), 104–115. https://doi.org/10.1177/03611981221082569

Measure of Asphalt Emulsion Stability by Oscillatory Rheology

Emulsified asphalts play a crucial role in various road construction applications. Understanding their stability and behavior during storage and application is essential for optimizing performance. To date, asphalt emulsion stability is commonly evaluated via two different traditional standard test methods including ASTM D6930 (settlement/storage stability tests) and ASTM D6933 (measuring oversized particles). In this study, researchers investigated the use of rheological properties to assess the stability of emulsified asphalts by oscillatory rheology, a technique used to measure the viscoelastic properties of an asphalt emulsion. Therefore, the stability of an asphalt emulsion could only be evaluated by oscillatory rheology if the emulsion initially exhibits viscoelasticity.

The researchers evaluated the stability of two different cationic asphalt emulsions by standard ASTM methods and rheological measurements to compare the efficiency of standard methods verses rheological techniques. Both methods yielded similar conclusions, however a better understanding of the emulsion behavior is observed when evaluating the rheological properties over time. It was found that the elastic and viscous modulus of the emulsions decreased over time as coalescence proceeds, that is, the elasticity of the emulsion decreases while asphalt droplet size increases. The emulsions evaluated initially exhibit non-Newtonian behavior, but as the emulsions become unstable the emulsion begins to exhibit behavior closer to Newtonian. In conclusion, certain rheological parameters may be able to predict the behavior of emulsified asphalts during storage and application and understanding these rheological behaviors may aid in optimizing emulsion performance.

Mercado, J., & Fuentes, L. (2017). Measure of asphalt emulsions stability by oscillatory rheology. Construction and Building Materials. 155, 838-845. https://doi.org/10.1016/j.conbuildmat.2017.08.095

An Acceptance Test for Chip Seal Projects Based on Image Analysis

The researchers were looking at image analysis of both lab and field chip seals to compare to the sand patch test and Ames Laser Texture Scanner.  For the field core specimens, the cores were cut vertically for image analysis and a document camera was used.  Three types of imaging were conducted: peak and valley height, area and embedment depth of each aggregate.  For peak and valley height measurements, aggregate and binder height were determined to calculate embedment depth.  For this method, some additional prep might be needed depending on the type of aggregate used.  In this study, blast furnace slag was one of the aggregates used and due to it having some holes and a darker color, the researchers had to color the aggregates white and fill in the holes for proper analysis.  In the area method, the intensity threshold of the imaging was important to make sure all aggregates were captured and to prevent noise.  The final image analysis that was used was embedment depth of each aggregate.  In this method, part of the previous two methods were incorporated and total embedment depth was an average of each individual aggregate embedment.  For the sand patch test, glass beads of known volume were spread to determine area covered.  That coupled with aggregate height was used to calculate embedment.  Lastly, the Ames Laser determined the estimated texture depth which is an indicator of mean texture depth and assumed to be the same in this paper. 

Results from the study concluded that sand patch test and Ames Laser Scanner give very different results, but follow the same trend.  When looking at the image analysis, the each aggregate embedment depth test gave much higher results than the peak/valley and area testing.  Comparing sand patch and Ames laser scan to the imaging methods only looked good on one of three test sections.  The two test sections that did not correlate well to sand patch and Ames were fog sealed making it difficult for the glass beads to fill voids. 

Kutay, M. E., & Ozdemir, U. (n.d.). (publication). An Acceptance Test for Chip Seal Projects Based on Image Analysis.