- Author
-
Nguyen, T.
|
Byrd, W. E.
|
Bentz, D.
- Title
- In Situ Measurement of Water at the Asphalt/Siliceous Aggregate Interface.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Book or Conf
- American Chemical Society (ACS). Fuel Division Proceedings. August 1992,
1992
- Keywords
-
water
|
asphalt
|
aggregates
|
spectroscopy
- Abstract
- Water at the asphalt/aggregate interface is the major contributor to the debonding of asphalt from mineral aggregates (stripping). This paper describes a spectroscopic technique to detect and measure in situ water at the interface between an asphalt and a siliceous aggregate, and the applicaton of the technique to studies of several asphalts. The technique employs Fourier transform infrared (FTIR) spectroscopy in the multiple internal reflection (MIR) mode. An asphalt layer of any thickness is coated on an Si0₂-covered Si internal reflection element (IRE) and a water chamber is attached to the asphalt-coated substrate. Spectra are taken automatically at specified time intervals without disturbance of the specimens. In the study, water at the asphalt-aggregate interface for five Strategic Highway Research Program (SHRP) core asphalts (ACC-1, AAD-1, AAG-1, AAK-1 and AAM-1) of about 60 mum thick on an Si0₂-Si substrate was measured using the technique. The amount and thickness of the water layer at the asphalt/siliceous aggregate interface were determined based on internal reflection spectroscopy theory, the water concentration-intensity calibration curve obtained using a series of H₂0/D₂0 mixtures, and the water uptake of the asphalts. The results indicated that the thickness of the water layer at the asphalt/siliceous aggregate interface increased as time of exposure increased. Water adsorption characteristics at the asphalt/Si0₂-Si substrate interface were different for the five asphalts. The technique should be useful for evaluating asphalt-siliceous aggregate mixtures in terms of water diffusion, water susceptibility, effectiveness of antistripping agents, and effects of aggregate surface contamination on water stripping.