Microstructure analysis and mechanical performance of crumb rubber modified asphalt concrete using the dry process

Abstract

Globally, the vast majority of waste tires are landfilled, with catastrophic ecological consequences and in particular, serious threats to human health (e.g. fire, pests and soil contamination). Because of the increasing environmental awareness, the use of crumb rubber modified asphalt has become an important recycling strategy for waste tires. The so-called crumb rubber (CR), which is the recycled rubber from tires, has become a common additive in hot mix asphalt mixture due to its improvement of the mechanical performances of asphalt mixtures. The purpose of this study is to investigate the effect of adding crumb rubber to asphalt mixtures using the dry process by relating mechanical performances with microstructural characterizations. It was possible to observe the influence of conditioning process (time during which the asphalt mixture is kept at a high temperature after mixing) on the mechanical performance of the mixtures that depend primarily on the properties of the crumb rubber used. Specifically, it is shown that the conditioning time has an influence on the Marshall test results as well as the viscosity measurements. By using the Environmental Scanning Electron Microscope (ESEM), the distribution of the crumb rubber within the mixture has been investigated. In particular, the distribution of the crumb rubber by changing the conditioning time is of interest. The results showed that crumb rubber is well dispersed in the asphalt mixture when the conditioning time is increased. The effect of crumb rubber on the microstructure using Atomic Force Microscopy-Infrared Spectroscopy (AFM-IR) indicated that the main chemical change takes place in the para domain and catana or the so-called bee structures diminish on the CR modified bitumen as a consequence of more conditioning time.