Development and evaluation of test procedures to identify moisture damage prone hot mix asphalt pavements

There are numerous factors that can cause a road to deteriorate, such as the traffic type, traffic volume, failure of materials used and climatic conditions. All four of the above listed factors can contribute to permanent deformation, commonly called pavement rutting. Most permanent deformation tests and simulation models have concentrated primarily on material properties and traffic loads. The effects of the environmental conditions are often neglected in these models with only a few accounting for climatic effects. The damaging effect of moisture on pavements, specifically hot mix asphalt (HMA), is a significant environmental distress that should be considered. As pavement is subjected to freeze/thaw cycling, the material expands and contracts. During expansion, water can seep into permeable air voids created with the increased volume and freeze. When the material contracts during thawing, the water can propagate cracks created during freezing for further damage in the next freeze cycle, which can weaken the structural strength of a pavement layer. Over time, the repetition of freeze/thaw cycling deteriorates a pavement and can lead to lengthwise indentations in roads appearing as ruts if a moisture susceptible mix is below the surface mix. Surface mixes that are susceptible to moisture damage would experience raveling. Identifying pavements susceptible to moisture damage and the effects of moisture damage on the life of a pavement can reduce maintenance costs accrued with the placement of a poorly performing HMA;In this dissertation, the affect of moisture on HMA materials is evaluated via an Asphalt Pavement Analyzer (APA) and a modified Dynamic Shear Rheometer (DSR). It was found that moisture damage of specimens tested in an APA after one freeze/thaw cycle yields similar results as Tensile Strength Ratio testing after three freeze/thaw cycles. The APA is seen as a viable alternative for evaluating moisture susceptible mixes. A new protocol for a modified DSR is outline and evaluated using 21 field collected HMA mixes. It was concluded that the new test protocol and modification have potential for being used as a method to determine the moisture susceptibility of a binder

Testing HMA Density with Electromagnetic Gauges

Electromagnetic gauges offer nondestructive testing of in-place HMA with real-time results for effective QC/QA decision making

Investigation of Electromagnetic Gauges for Determining In-Place HMA Density

Density is an important component of hot-mix asphalt (HMA) pavement quality and long-term performance. Insufficient density of an in-place HMA pavement is the most frequently cited construction-related performance problem. This study evaluated the use of electromagnetic gauges to nondestructively determine densities. Field and laboratory measurements were taken with two electromagnetic gauges—a PaveTracker and a Pavement Quality Indicator (PQI). Test data were collected in the field during and after paving operations and also in a laboratory on field mixes compacted in the lab. This study revealed that several mix- and project-specific factors affect electromagnetic gauge readings. Consequently, the implementation of these gauges will likely need to be done utilizing a test strip on a project- and mix-specific basis to appropriately identify an adjustment factor for the specific electromagnetic gauge being used for quality control and quality assurance (QC/QA) testing. The substantial reduction in testing time that results from employing electromagnetic gauges rather than coring makes it possible for more readings to be used in the QC/QA process with real-time information without increasing the testing costs

Large eddy simulation of inertial fiber deposition mechanisms in a vertical downward turbulent channel flow

The deposition pattern of elongated inertial fibers in a vertical downward turbulent channel flow is predicted using large eddy simulation and Lagrangian particle tracking. Three dominant fibers deposition mechanisms are observed, namely, diffusional deposition for small inertial fibers, free-flight deposition for large inertial fibers, and the interception mechanism for very elongated fibers. The fibers are found to exhibit orientation anisotropy at impact, which is strongly dependent on the fiber elongation. An increase in the fiber elongation increases the wall capture efficiency by the interception mechanism. The diffusional deposition mechanism is shown to dominate for fibers with large residence time, t⁺res, in the accumulation zone and small deposition velocities, v⁺z, while the free-flight mechanism governs deposition for fibers with small t⁺res and large v⁺z. This study describes how particles deposit on a surface and, ultimately for many practical applications, how such deposition may promote fouling

Funkcni charakteristiky neuronu sluchovych jader stredniho mozku a thalamu morcete

Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Development and evaluation of test procedures to identify moisture damage prone hot mix asphalt pavements

There are numerous factors that can cause a road to deteriorate, such as the traffic type, traffic volume, failure of materials used and climatic conditions. All four of the above listed factors can contribute to permanent deformation, commonly called pavement rutting. Most permanent deformation tests and simulation models have concentrated primarily on material properties and traffic loads. The effects of the environmental conditions are often neglected in these models with only a few accounting for climatic effects. The damaging effect of moisture on pavements, specifically hot mix asphalt (HMA), is a significant environmental distress that should be considered. As pavement is subjected to freeze/thaw cycling, the material expands and contracts. During expansion, water can seep into permeable air voids created with the increased volume and freeze. When the material contracts during thawing, the water can propagate cracks created during freezing for further damage in the next freeze cycle, which can weaken the structural strength of a pavement layer. Over time, the repetition of freeze/thaw cycling deteriorates a pavement and can lead to lengthwise indentations in roads appearing as ruts if a moisture susceptible mix is below the surface mix. Surface mixes that are susceptible to moisture damage would experience raveling. Identifying pavements susceptible to moisture damage and the effects of moisture damage on the life of a pavement can reduce maintenance costs accrued with the placement of a poorly performing HMA;In this dissertation, the affect of moisture on HMA materials is evaluated via an Asphalt Pavement Analyzer (APA) and a modified Dynamic Shear Rheometer (DSR). It was found that moisture damage of specimens tested in an APA after one freeze/thaw cycle yields similar results as Tensile Strength Ratio testing after three freeze/thaw cycles. The APA is seen as a viable alternative for evaluating moisture susceptible mixes. A new protocol for a modified DSR is outline and evaluated using 21 field collected HMA mixes. It was concluded that the new test protocol and modification have potential for being used as a method to determine the moisture susceptibility of a binder.</p

Couette flows of a granular monolayer: An experimental study

An experimental study concerning rapid flows of granular materials in a two dimensional planar granular Couette flow apparatus is performed. The device is capable of generating particulate flows in grain-inertia regime at different shearing rates and solid volume fractions. Multi-color spherical glass particles are sheared across an annular test-section for several wall angular velocities. A video recorder is used to record the motion of particles, and consecutive images are stored and analyzed by an image processing technique for evaluating individual grain velocities. Experimental data for the mean velocity, the root mean-square fluctuation velocity components and the solid volume fraction profile are obtained. The resulting mean velocity profiles have a roughly linear variation for the range of solid volume fractions and shear rates studied. The solid volume fraction profiles exhibit nonuniform variations with the highest concentration occuring near the center of the shearing cell. The RMS-fluctuation velocities are roughly constant, with the streamwise fluctuation being somewhat larger than the cross-stream direction. The experimentally measured flow properties are in reasonable agreement with the earlier theoretical and simulation results

A Model for Fuel Spray Formation with Atomizing Air

The formation of a liquid spray emanating from a nozzle in the presence of atomizing air was studied using a computational model approach that accounted for the deformation and break up of droplets. Particular attention was given to the formation of sprays under non-swirling flow conditions. The instantaneous fluctuating fluid velocity and velocity gradient components were evaluated with the use of a probability density function (PDF)-based Langevin equation. Motions of atomized fuel droplets were analyzed, and ensemble and time averaging were used for evaluating the statistical properties of the spray. Effects of shape change of droplets, and their breakup, as well as evaporation, were included in the model. The simulation results showed that the mean-square fluctuation velocities of the droplets vary significantly with their size and shape. Furthermore, the mean-square fluctuation velocities of the evaporating droplet differed somewhat from non-evaporating droplets. Droplet turbulence diffusivities, however, were found to be close to the diffusivity of fluid point particles. The droplet velocity, concentration, and size of the simulated spray were compared with the experimental data and reasonable agreement was found