The construction industry accounts for a staggering 37% of global emissions, according to the United Nations. Identifying ways to lower the industry’s embodied carbon – the complete footprint, design, production and deployment – is essential. Using reclaimed or recycled materials in asphalt mixes, which reduce the cost and the amount of energy to produce new asphalt, has been widely adopted as an industry practice. However, the quantity of reclaimed asphalt pavement in the mix has long been held at about 20%. Environmental and economic benefits are driving an increase to 25-30% or higher. However, higher contents of RAP can be problematic if the undesirable properties within RAP become more prominent. This can cause many construction and performance problems including compactibility and cracking, particularly at low temperatures.
For a new study in the Journal of Materials in Civil Engineering, researchers Jaime Preciado, Saqib Gulzar, Andrew Fried, Cassie Castorena, Shane Underwood, Jhony Habbouche, and Ilker Boz focus on developing a framework to assess the acceptance of recycled agents using low-temperature performance-related parameters. “Low-Temperature Performance Evaluation of Recycled Binder Blends for Assessing Recycling Agents’ Acceptance” explores an expedited characterization of low-temperature properties of recycled binder blends. A total of 26 binder blends were evaluated, using three approved Virginia Department of Transportation AC mixes and one from the North Carolina Department of Transportation. Learn more about how recycled materials impact the stiffness and relaxation properties of asphalt mixtures at https://doi.org/10.1061/JMCEE7.MTENG-17661. The abstract is below.
Abstract
The use of high contents of recycled materials in asphalt mixtures has an adverse effect on the low-temperature cracking performance of these mixtures if not accounted for properly due to the high stiffness and poor relaxation properties of the reclaimed asphalt pavement (RAP) binder. This concern has driven some to suggest using recycling agents (RAs) in the asphalt mixture to restore the rheological properties of the RAP binder without compromising the short- and long-term performance of the mixture. However, the relationships between RA type and dosage, virgin and RAP binder characteristics, and low-temperature properties, i.e., creep stiffness and 𝑚-value, need to be investigated further to assess the acceptance of RAs. In this study, 26 recycled binder blends from a combination of three virgin binders, four RAP sources, and eight RAs were used to study these relationships. First, the use of a method based on the dynamic shear rheometer to predict low-temperature properties of recycled binder blends successfully is demonstrated. Second, a linear relationship is found to exist between the low-temperature properties and RA dosage of these blends. Third, a parameter based on low-temperature properties is proposed to select an RA that yields a balance in the stiffness and relaxation properties of the recycled binder blends. Fourth, a conceptual framework is proposed to assess the acceptance of RAs based on low-temperature performance-related parameters.
Explore more on the low-temperature performance of recycled binders in the ASCE Library: https://doi.org/10.1061/JMCEE7.MTENG-17661.
