Ahmad Alhasan

Low-Temperature Characterization of Foamed Warm-Mix Asphalt Produced by Water Injection

This study evaluated the low-temperature performance of foamed warmmix asphalt (WMA) produced by water injection and compared it with that of hot-mix asphalt (HMA). Two asphalt binders (PG 70–22 and PG 64–28), two aggregate types (limestone and crushed gravel), and two aggregate gradations [nominal maximum aggregate size (NMAS)] (12.5-mm NMAS and 19.0-mm NMAS) were used in this study. The low-temperature properties of the asphalt binders were measured with the bending beam rheometer, and the low-temperature behavior of the asphalt mixtures was evaluated with the thermal stress restrained specimen test after being subjected to short-term and long-term aging. As expected, the fracture temperatures obtained for the short-term aged specimens were lower than those obtained for the long-term aged specimens. This was the case for both foamed WMA and HMA mixtures. The HMA mixtures exhibited colder fracture temperatures than did the foamed WMA mixtures for the short-term aged specimens, but fracture temperatures comparable to those for the long-term aged specimens. This comparison suggests that the traditional HMA mixtures may have better resistance to low-temperature cracking than foamed WMA does during the initial service life of the asphalt layer, but may have similar resistance to low-temperature cracking at later stages. This study also showed that the low-temperature binder grade had the most significant effect on fracture temperature, whereas the aggregate type had the most significant effect on fracture stress.

Quantifying Roughness of Unpaved Roads by Terrestrial Laser Scanning

Unpaved roads represent a major component of the roadway network in Iowa and require regular surface grading to control roughness (e.g., corrugation). This paper presents a study that shows how terrestrial laser scanning can characterize road roughness in relation to (a) a spatially analyzed international roughness index (IRI), (b) a fast Fourier transform (FFT) spectral analysis, and (c) surface texture characterization that uses statistical analysis. Algorithms are presented for each of the roughness calculations. The spatial nature of terrestrial laser scanning makes possible the determination of IRI values along any selected path within the scan area. In this study, median IRI values were used to characterize overall road roughness. To characterize the nature of road roughness, FFT was used to decompose the laser scan height spectrum. Examples are presented for unpaved road sections with a relatively smooth surface, a smooth surface with corrugations, an unsystematically rough surface, and an unsystematically rough surface with corrugations. On the basis of the observation that the surface aggregate materials were segregated, selected small regions were studied with a scan with spacing of 0.5-mm points. These scans were filtered and statistically analyzed for variations in height by using root mean square, skewness, and kurtosis parameters. These parameters were studied in relation to the values for particle size index for the surface materials of the three distinct gradations. The algorithms presented will be of value to terrestrial laser scanning users interested in characterizing unpaved roadway conditions.