James M Signore

Water Quality Evaluation of Leachate Produced from Pavement Specimens under Controlled Laboratory Conditions

ABSTRACT An experimental apparatus and procedures were used to evaluate the organic and inorganic quality of leachate produced from ten different asphalt and concrete pavement specimens under controlled laboratory conditions. Triplicates of both fresh and aged specimens were tested at three controlled laboratory temperatures of 4, 20, and 45 °C. Leachate samples were taken at various times during each experiment for eight hours to examine the metal pollutants concentration variability. Results showed that, in general, the leachate concentrations for most water quality parameters were below or near the method detection limit. However, dissolved chromium and vanadium concentrations were consistently detected from concrete specimens, particularly during the first three hours of the experiment and gradually reduced to below the reporting limit at the conclusion of the experiments. From this study we can conclude that the concentration of chemical constituents solely generated from pavement surfacing materials is negligible and the pollutants in roadway runoff is mostly related to other road use and land use sources.

Short-Term Laboratory Conditioning of Asphalt Mixtures

This report develops procedures and associated criteria for laboratory conditioning of asphalt mixtures to simulate short-term aging. The report presents proposed changes to the American Association of State Highway and Transportation Officials (AASHTO) R 30, Mixture Conditioning of Hot-Mix Asphalt (HMA), and a proposed AASHTO practice for conducting plant aging studies. The report will be of immediate interest to materials engineers in state highway agencies and the construction industry with responsibility for design and production of hot and warm mix asphalt.

RUTTING OF RUBBERIZED GAP GRADED AND POLYMER MODIFIED DENSE GRADED ASPHALT OVERLAYS IN COMPOSITE PAVEMENTS

The rutting performance of polymer-modified dense-graded and rubberized gap-graded asphalt mixes used in composite pavement was evaluated with full-scale accelerated pavement testing with the heavy vehicle simulator (HVS) and laboratory test results. The effect of asphalt layer thickness on measured surface deformation for both mix types was also investigated for recommendations for future design. In addition, the progression of the rutting failure mechanism for both mix types was evaluated with transverse cross sections measured with a laser profilometer at various HVS load repetitions. The polymer-modified dense-graded mix performed better than the rubberized gap-graded mix under both laboratory and HVS testing. The greater shear movement of the rubberized gap-graded mix under HVS loading caused larger humps, which consequently increased the maximum deformation and resulted in earlier failure. Larger aggregate size and denser gradation for the polymer-modified dense-graded mix resulted in more efficient dissipation of shear stresses and created greater permanent deformation resistance.

Fiber-Optic Sensing Technology for Rail-Buckling Detection

Buckling and cracking of steel rails is a contributing factor in accidents on railroads today. Detection and notification of buckled track sections before a train reaches these locations will significantly increase rail safety. A fiber-optic-based sensing system, with the fiber affixed to a beam, was developed and evaluated to detect buckled regions. The purpose of this research is to evaluate the sensitivity of the fiber-optic sensing system to buckling of a long structural member. Numerous facets of fiber-optic sensing have been explored. Fiber-to-steel bonding techniques were examined and tested. Full-scale laboratory testing was conducted by elastically buckling a 24.4-m-long (80-ft) wide-flange section with hydraulic rams. Typical measurement accuracy within 10 percent of theoretical predictions was achieved by optical time domain reflectometry techniques. For field testing, however, a more robust solution is sought and is currently under development. It is suggested that a lower-cost fiber break or bend detector is a suitable option. The optical fiber will break or bend at the location of rail elongation in the buckled area, allowing the detection equipment to locate the buckled area.

Cracking and Rutting Performance of Composite Pavements under Testing with Heavy Vehicle Simulator: Rubberized Hot-Mix Asphalt with Gap-Graded Aggregates over Portland Cement Concrete:

As part of SHRP 2, the University of California Pavement Research Center conducted two accelerated pavement tests to evaluate the effects of overlay thickness on the cracking performance of composite pavement composed of rubberized hot-mix asphalt with gap-graded aggregates and portland cement concrete (RHMA-G–PCC) by using the heavy vehicle simulator. Cracking failure mechanisms in these tests included both reflective cracking near the PCC joints and fatigue cracking in the PCC slabs. Increasing overlay thickness led to a significant increase in cracking life but at the same time increased rutting susceptibility. The data collected provide insights for design of RHMA-G–PCC composite pavements as well as calibration of related mechanistic–empirical models. The observations and findings from the two accelerated pavement test sections are summarized.