Effect of Temperature Fluctuations on the Bearing Capacity of Cold In-Depth Recycled Pavements

This study investigates the influence of the temperature fluctuations on the bearing capacity of cold in-depth recycled (CIR) pavements stabilized with foamed asphalt (FA). Aiming to achieve this goal, non-destructive testing was conducted during mild and high temperatures on a highway CIR pavement, utilizing mainly the FWD device. The back-calculated moduli values were utilized to estimate the strain values within the body of the pavement, while the strains induced using the FWD device were measured with a fiber optic sensors (FOS) system. Moreover, data from the fatigue behavior of the layer materials was also considered. The results of the related analysis indicate that for every 1 °C temperature increase within the body of the AC overlay, an approximately 5.7% increase of the critical tensile strain is expected. Moreover, for every 1 °C temperature increase within the body of the FA layer, an approximately 1.8% increase of the tensile strain at the bottom of the FA layer is expected. The new constructed layers, i.e., asphalt concrete (AC) and FA, sustain much more damage at high temperatures. This was more evident in the upper layer, i.e., the AC overlay.

Flexible Pavement Recycling Techniques: A Summary of Activities

Cold in-place recycling (CIR) involves the recycling of the asphalt portions (including hot-mix asphalt and chip, slurry, and cape seals, as well as others) of a flexible or composite pavement with asphalt emulsion or foamed asphalt as the binding agent. Full-depth reclamation (FDR) includes the recycling of the entire depth of the pavement and, in some cases, a portion of the subgrade with asphalt, cement, or lime products as binding agents. Both processes are extensively utilized in Illinois. This project reviewed CIR and FDR projects identified by the Illinois Department of Transportation (IDOT) from the Transportation Bulletin and provided comments on pavement designs and special provisions. The researchers evaluated the performance of existing CIR/FDR projects through pavement condition surveys and analysis of falling weight deflectometer data collected by IDOT. They also reviewed CIR/FDR literature and updated/modified (as appropriate) previously provided inputs concerning mix design, testing procedures, thickness design, construction, and performance as well as cold central plant recycling (CCPR) literature related to design and construction. The team monitored the performance of test sections at the National Center for Asphalt Technology and Virginia Department of Transportation. The researchers assisted IDOT in the development of a CCPR special provision as well as responded to IDOT inquiries and questions concerning issues related to CIR, FDR, and CCPR. They attended meetings of IDOT’s FDR with the Cement Working Group and provided input in the development of a special provision for FDR with cement. The project’s activities confirmed that CIR, FDR, and CCPR techniques are successfully utilized in Illinois. Recommendations for improving the above-discussed techniques are provided.

Effects of Asphalt Foaming on Damage Characteristics of Foamed Warm Mix Asphalt

In the asphalt foaming process, the foaming water content (FWC) controls the formation and characteristics of water bubbles. These water bubbles are expected to be expelled from the foamed warm mix asphalt (WMA) during mixing and compaction. However, foaming water may not be completely expelled, rather some of the microbubbles may be trapped in the foamed WMA even after compaction. These microbubbles, or undissipated water, can diffuse over time and cause damage to the foamed WMA. To this end, this study has determined the effects of foaming on the fatigue, moisture damage, and permanent deformation characteristics of foamed WMA. Foamed asphalt and mixtures were designed with varying FWCs and they were tested using linear amplitude sweep, multiple stress creep recovery, four-point flexural beam, and Hamburg wheel tracking tests. Primarily, asphalt foaming dynamics were assessed with a laser-based non-contact method. A simplified viscoelastic continuum damage concept and a three-phase permanent deformation model were used for damage evaluation. The study reveals that foaming softens the binder, which results in slightly higher rutting and moisture susceptibility, though an equivalent or slightly improved fatigue characteristic compared with the regular hot mix asphalt.

Advantages and limitations of using foamed bitumen

Foamed asphalt refers to a bituminous mixture of road-building aggregates and foamed bitumen, produced by a cold mix process. There are a lot of related issue that has not been sufficiently investigated so far. It is worthwhile to overview the main theoretical and practical results in the field in several countries including those of the authors of the paper. It is clear that the foamed asphalt is usually characterized by high quality and reasonable cost, can be used in cold road pavement rehabilitation, in addition to it the technique is environ-mentally friendly preserving natural resources. Using foamed bitumen reduces the emissions of carbon dioxide and gases resulting from combustion, especially when it is used as a cold rehabilitation binder and mixed with re-claimed asphalt pavement materials.