John F Rushing

Stabilization mechanisms of nontraditional additives

Because of the high cost of quality construction materials, transportation engineers are often forced to seek alternative designs using substandard materials, commercial construction aids, alternative pavement materials, and innovative design practices. Nontraditional soil stabilization additives are being marketed as viable solutions for stabilizing marginal materials as a low-cost alternative to traditional construction materials. Nontraditional additives are diverse in their composition and the way they interact with soil. Unfortunately, little is known about their interaction with geotechnical materials and their fundamental stabilization mechanisms. The objective of this research was to advance current understanding of the chemical and physical bonding mechanisms associated with selected non-traditional stabilizers. The research consisted of conducting qualitative analyses of hypothesized stabilization mechanisms, examining historical literature for supporting documentation, and performing laboratory experiments to improve the understanding of how these nontraditional additives stabilize soils. Laboratory experiments included image analyses, physical characterization, and chemical analyses to determine the primary constituents of the mineral, soil, stabilizer, and stabilized soil composite. The focus of this effort was to provide insight into the proposed mechanisms by using the laboratory data to examine proposed mechanisms from the historical literature and to provide additional hypotheses for the interaction between nontraditional additives and different soil types.

Assessment of Warm-Mix Asphalt for Heavy Traffic Airfields

This paper presents the results of tests of warm-mix asphalt (WMA) mixtures designed for airfield pavements. The study was conducted in two phases. The first phase included laboratory tests on 11 WMA technologies. The tests in Phase 2 were performed on three WMA mixtures and one hot-mix asphalt (HMA) mixture produced in an asphalt plant. The evaluation included performance tests to assess WMA susceptibility to permanent deformation and moisture damage compared with that of HMA produced with the same aggregate blend. Test results indicated that WMA potentially was a viable product for surface mixtures on airfield pavements. Although WMA exhibited poorer performance than HMA in moisture damage tests on laboratory-produced specimens, the plant-produced mix indicated little difference compared with HMA. Rutting potential for WMA was somewhat greater than for HMA for mixtures produced both in the laboratory and in an asphalt plant according to asphalt pavement analyzer and Hamburg wheel tracking tests. Differences in performance of WMA mixtures were not attributed to a specific WMA technology category. Variations in performance test results between laboratory-produced specimens and plant-produced specimens were noted and indicated a need to require performance testing as part of a comprehensive quality assurance plan.

Static Creep and Repeated Load as Rutting Performance Tests for Airport HMA Mix Design

A performance test, rather than an empirical test, to evaluate rutting susceptibility is needed to accompany current volumetric property requirements of airport hot mix asphalt (HMA) designed using a superpave gyratory compactor. The new performance test will provide a level of confidence that pavement constructed using a selected HMA mixture will function according to its design. This paper presents results from a laboratory study to identify a performance test for accepting hot asphalt mixtures for constructing airport pavements designed for high tire pressure traffic. Performance tests intended to indicate rutting susceptibility were performed on 34 HMA mixtures. Twenty-nine of these mixtures met all aggregate and volumetric property requirements for airport pavement construction; the remaining five mixtures were designed with excessive percentage of natural sand (30%) as rut-susceptible mixtures. Results from asphalt pavement analyzer (APA), triaxial static creep, and triaxial repeated load tests are presented. Statistical analyses performed on the results indicate that the rate of increase in permanent strain and the flow time value determined from triaxial static creep testing provide the strongest correlation to APA simulated traffic rutting.

Asphalt Pavement Analyzer Used to Assess Rutting Susceptibility of Hot-Mix Asphalt Designed for High Tire Pressure Aircraft

Hot-mix asphalt (HMA) laboratory mix design is intended to determine the proportion of aggregate and binder that, when mixed and compacted under a specified effort, will withstand anticipated loading conditions. Current mix design procedures that use the Superpave® gyratory compactor rely on the engineering properties and volumetrics of the compacted mixture to ensure reliable performance; however, a definitive performance test does not exist. The asphalt pavement analyzer (APA) was evaluated as a tool for assessing HMA mixtures designed to perform under high tire pressure aircraft following FAA specifications. The APA used in this study was specially designed to test simulated high tire pressures of 250 psi, which are becoming more common for aircraft. Thirty-three HMA mixtures were included in the study. Each was designed with the Superpave gyratory compactor, according to preliminary criteria being developed by FAA. The study included some mixtures that contain excessive percentages of natural sand and that do not meet FAA criteria. These mixtures were included to provide relative performance for mixtures expected to exhibit premature rutting. APA testing with the high tire pressure APA resulted in rapid failure of HMA specimens compared with traditional APA testing at lower pressures. Data were analyzed, with a focus on the provision of acceptance recommendations for mixtures to support high tire pressures. A preliminary 10-mm rut depth criterion after 4,000 load cycles is recommended.

Selecting a rutting performance test for airport asphalt mixture design

This paper presents results from a laboratory study to identify a performance-based acceptance test for hot asphalt mixtures when constructing airport pavements designed to accommodate high-tyre-pressure traffic. Four performance tests, intended to screen for rutting susceptibility, were performed on 26 hot mix asphalt (HMA) mixtures using one neat binder. Eight of these mixtures were also prepared with a polymer-modified binder. Results from four candidate tests are presented: asphalt pavement analyzer, triaxial creep, triaxial repeated load, and dynamic modulus test. Preliminary criteria associated with these tests that can be used to screen or select airport HMA paving mixtures are proposed. The efficacy of the screening tests and associated criteria were evaluated by constructing and trafficking full-scale pavements using an accelerated pavement tester.

Comparing rutting of airfield pavements to simulations using Pavement Analysis Using Nonlinear Damage Approach (PANDA)

This study presents the rutting performance results of full-scale pavement test sections subjected to F-15E and C-17 aircraft wheels at two different temperatures. Pavement structures for the tests were constructed under shelter in the U.S. Army Engineer Research and Development Centers (ERDC) pavement test facility. The full-scale test results are used to validate viscoelastic, viscoplastic and hardening-relaxation constitutive relationships implemented in the Pavement Analysis Using Nonlinear Damage Approach (PANDA) model. PANDA is a mechanistic-based model which incorporates nonlinear viscoelastic, viscoplastic, hardening-relaxation, viscodamage, moisture-induced damage and ageing constitutive relationships. Results of dynamic modulus and different repeated creep-recovery laboratory tests are analysed to extract the parameters associated with viscoelastic, viscoplastic and hardening-relaxation constitutive relationships implemented in PANDA. Once calibrated, PANDA is used to predict the rutting performance observed in full-scale pavement test sections. The simulation results illustrate that PANDA is capable of predicting the rutting of airfield pavements subjected to heavy aircraft wheel loads at intermediate and high temperatures. It is shown that PANDA successfully predicts the effect of shear flow and upheaval at the edges of the wheel. The data from simulation suggested that PANDA, once calibrated, can provide insight into the critical locations of tensile and compressive stresses within the pavement structure. PANDA simulations not only provide a tool for evaluating existing structures, but also can be used in designing more sustainable pavement structures and materials.

Evaluation of Products and Application Procedures for Mitigating Dust in Temperate Climates

An evaluation of commercial dust palliatives was conducted to determine their effectiveness in mitigating fugitive dust on roads in temperate climates. Several types of dust palliatives were tested, including polymer emulsions, a polysaccharide solution, a calcium chloride solution, and synthetic fluids. Each product was placed in an individual test section; application rates ranged from 1.8 to 3.6 L/m2 with a topical or an admix construction method (grade, spray, till, compact, spray). Water-soluble products were diluted by using one part product and three parts water. Test sections were constructed and observed for 220 days to monitor product performance. Test sections were located along training routes at Ft. Leonard Wood, Missouri, and were subjected to heavy military truck and tracked vehicle traffic. Data from stationary and mobile particle collectors were analyzed to determine the ability of each product to suppress dust for extended periods. Nuclear density tests were performed to monitor soil moisture content and density. Several products are recommended for use on roads in temperate climates as a result of this evaluation.

Accelerated Pavement Testing of Warm-Mix Asphalt for Heavy-Traffic Airfields

The results from accelerated pavement testing on warm-mix asphalt (WMA) mixtures designed for airfield pavements are presented. Three WMA mixtures and one hot-mix asphalt (HMA) mixture produced in an asphalt plant were evaluated under simulated heavy aircraft traffic. The evaluation was conducted at extreme traffic conditions, including heavy aircraft loading, high tire pressure, and high pavement temperature. Pavement structural response and rutting were evaluated to assess the susceptibility to permanent deformation of WMA mixtures compared with that of HMA produced with the same aggregate blend. Test results indicated that WMA was a viable product for surface mixtures on airfield pavements.

Using the Asphalt Pavement Analyzer as a Mixture Performance Test to Select Appropriate Binder Grades for Airport Pavements

AbstractIn this study, the Asphalt Pavement Analyzer (APA) was investigated for its ability to detect asphalt paving mixtures designed for airfields that may be prone to rutting. The objective of t...

Criteria for using the Superpave gyratory compactor to design airport HMA mixtures

Asphalt concrete pavements for commercial airport applications in the USA are constructed according to guidelines in Item P-401, ‘Plant Mix Bituminous Pavements’, Federal Aviation Administration (FAA) Advisory Circular 150/5370-10E. Item P-401 specifies the material characteristics and construction requirements for airport asphalt pavements, but does not currently provide guidance for using the Superpave gyratory compactor (SGC) in the preparation of specimens used in the design of hot mix asphalt (HMA) mixtures. Nearly all state departments of transportation in the USA use the SGC along with the Superpave mix design procedure. Since most HMA mixes are used in roadways, many asphalt contractors no longer maintain expertise and equipment for conducting the Marshall mix design procedure currently used by the FAA. The lack of contractors familiar with the Marshall method may become a significant problem for the FAA in the future. This paper describes a laboratory study of the HMA mix design for airport pavements, which uses the SGC. The purpose of the study was to determine the number of gyrations with the SGC needed to design asphalt pavement mixtures for airports. A value of 70 gyrations is recommended for further evaluations based on the comparisons of volumetric measurements of HMA mixture specimens compacted using Marshall compaction with specimens from the same mixture compacted using Superpave gyratory compaction.