Moisture Sensitivity of Hot Mix Asphalt (HMA) Mixtures in Nebraska - Phase II
As a consequential effort to the previous NDOR research project (P-564) on moisture damage, this report presents outcomes from this project incorporated with the previous project. Performance changes and fundamental material characteristics associated with moisture damage due to various anti-stripping additives in asphalt mixtures are studied through various experimental approaches and a numerical simulation. Three additives (i.e., one reference additive, hydrated lime, and two alternative additives: fly ash and cement) are investigated by adding them into two types of mixes (SP2 for low-traffic-volume roadways and SP5 for high-traffic- volume roadways) where two different asphalt binders (PG 64-22 for the SP2 mix and PG 70-28 for the SP5) are used. Two asphalt concrete mixture scale performance tests, the AASHTO T-283 and the APA under water, and two local-scale mixture constituent tests, the boiling water test (ASTM D 3625) and the pull-off test, are conducted to characterize the effects of binder-specific anti-stripping additives on the binder-aggregate bonding potential in mixtures. The pull-off tensile strength tests are then numerically modeled through the finite element technique incorporated with the cohesive zone modeling approach to seek more fundamental scientific insights into the effect of each anti-stripping additive on the overall moisture damage resistance. Results from laboratory tests and numerical simulations indicate that the SP5 mixtures, where high-quality aggregates and polymer-modified binder are used, are fairly self-resistant to moisture damage without treating any anti-stripping additive and do not show any visible sensitivity among additives, whereas the effects of additives and their sensitivity are significant in the SP2 mixes that use the unmodified binder PG 64-22 and low-quality aggregates. With the limited amount of test data, hydrated lime seems to perform slightly better than other additives, particularly with longer moisture-conditioning time. Fly ash contributes to reducing moisture damage by improving binder-aggregate interfacial properties, which are validated from the integrated experimental-computational evaluation.
Effect of Moisture Damage on Material Properties and Fatigue Resistance of Asphalt Mixtures
Dynamic mechanical analysis (DMA) has been used successfully to evaluate complex characteristics of fatigue damage and fracture of asphalt binders and mastics by measuring fundamental viscoelastic properties and damage characteristics. DMA was used to define the effect of moisture on fatigue damage and to concentrate on the fatigue damage susceptibility of the sand and asphalt mixture mastic fraction. Dynamic frequency sweep and time sweep tests were performed on cylindrical sand-asphalt samples in a dry state and after being subjected to moisture saturation. Test results clearly indicate that moisture reduces viscoelastic stiffness, fatigue resistance, and eventually fatigue life of sand-asphalt. The mechanistic role of moisture in fatigue was analyzed and quantified by using nonlinear viscoelastic theory based on pseudovariable concepts and a continuum damage fatigue model. The effect of material surface energies, which is strongly related to fracture and damage, is further discussed by using DMA fatigue test results and varying surface energy characteristics of individual mixture constituents. The DMA experimental procedure and analysis is an efficient way to identify the influence of moisture and to compare sand-asphalt mixtures in terms of moisture susceptibility.
A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England
Abstract A new genus and species of coelurosaurian theropod dinosaur from the Wessex Formation (Early Cretaceous, Barremian) of the Isle of Wight, England, is described and named. Distinctive characters of the premaxilla, its dentition, maxilla and nasals allow it to be diagnosed. The teeth in the premaxilla are D-shaped in cross-section and the nasals are fused. The hands are elongate and slender and the hindlimbs are gracile. Lack of element fusion elsewhere in the skeleton suggests that it is a subadult. Numerous character states are shared with tyrannosaurids but the new taxon appears to be excluded from the group that comprises aublysodontine and tyrannosaurine tyrannosaurids. We conclude that the taxon is a basal tyrannosauroid and as such it is one of the earliest and (with the exception of some teeth and an isolated ilium from Portugal) the first from Europe. Implications for tyrannosauroid biogeography and evolution are discussed. The animal was part of an unusual taphonomic assemblage in which some elements were partially articulated while others were scattered or broken.