Neutron Scattering for Moisture Detection in Foamed Asphalt

Foamed warm-mix asphalt (WMA) has been widely accepted and used in the United States and many other countries around the world. However, several key concerns about WMA technology still need to be answered, including the major issue of moisture-induced damage. Because of the reduced production temperatures and the foaming process with water, moisture may be entrapped in pavements after compaction. The trapped moisture decreases the adhesion between asphalt binder and aggregates and the cohesion among asphalt binder, resulting in stripping and other forms of pavement distress. The neutron scattering technique provides a unique tool for the determination of the microscopic structure of asphalt and for the detection of the presence of moisture and its spatial distributions in asphalt. In particular, small-angle neutron scattering (SANS) in the wave vector transfer range from is suitable to probe the spatial density fluctuations in the real space from , which has a resolution several orders of magnitude higher than direct imaging techniques. In this study, the SANS technique was utilized to characterize the microstructure of asphalt and to detect the water spatial distributions in foamed asphalt. Two types of asphalt binder and ordinary and heavy water were used to make samples at 150 degrees C using a laboratory foaming device. The samples were then measured using the SANS instrument at the National Institute of Standard and Technology (NIST) Center for Neutron Research (NCNR). The results show that there is no water entity less than 0.1m present in the foamed asphalt. Even if moisture does exist in foamed asphalt, it does not cause any structural changes to the asphalt within 0.1m.