1,387 research outputs found
Development of a mix design methodology for asphalt mixtures with analytically formulated aggregate structures
This research documents an extensive study on the design and characterization of asphalt mixtures for use as road pavement material. Several aspects of asphalt mixtures were addressed using the state of the art laboratory test equipment and technical literature from different information sources. The research was divided into two phases. Phase one included the design and detailed analysis of compaction and performance characteristics of asphalt concrete mixtures with aggregate structures that were designed using an analytical method of aggregate blending. Three aggregate types were considered in this study: limestone, sandstone, and granite. All the aggregates were crushed aggregates. Three different aggregate structures were designed for each aggregate type using the Bailey method of aggregate gradation evaluation. The Bailey method is a comprehensive gradation. Sandstone and Granite mixtures had a nominal maximum aggregate size (NMAS) of 12.5mm and were designed for high traffic level, while two types of Limestone mixtures were designed (25.4 mm and 12.5 mm NMAS) for two traffic levels (high and low traffic volumes). For the heavy traffic mixtures the binder type selected was PG 76-22M while PG70-22 was used for low volume mixtures. The outcome of this research suggests that suitable mixes can be developed with dense aggregate structures using the Bailey method of aggregate gradation that provides good resistance to permanent deformation while still maintaining adequate levels of durability. A systematic, simplified design approach was recommended in which asphalt mixtures are designed based on the locking point concept, analytical aggregate gradation method and fundamental mechanistic properties that describe the behavior of asphalt mixtures based on sound engineering principles
Laboratory and Field Evaluation of Modified Asphalt Binders and Mixes for Alaskan Pavements
In order to properly characterize modified asphalt binders and mixes for Alaskan pavements, this study evaluated properties of 13 asphalt binders typically used in Alaska from three different suppliers, and 10 hot mix asphalt (HMA) mixtures which were either produced in the lab or collected from existing paving projects in Alaska. Various binder and mixture engineering properties were determined, including true high binder grades, complex modulus (G*), and phase angle (δ) at high performance temperatures, multiple stress creep recovery rate and compliance, bending beam rheometer stiffness and m-value, Glover-Rowe parameter, ΔT, rheological index, and crossover frequency for binders, and rut depth, critical strain energy release rate (Jc), Indirect tensile (IDT) creep stiffness and strength for mixtures. Binder cracking temperatures were determined using asphalt binder cracking device. Mixture cracking temperatures were determined with IDT creep compliance and strength data. It was found that rutting and cracking resistances of the mixtures with highly modified binders were better than the mixture with unmodified asphalt binder (PG 52-28). Future recommendations for highly modified asphalt binders applications and research were provided based on laboratory testing results and field survey evaluation
Evaluation of the performance and cost-effectiveness of pavement sections containing open-graded base courses
Moisture induced distresses have been the prevalent distress type affecting the deterioration of both asphalt and concrete pavement sections. While various surface techniques have been employed over the years to minimize the ingress of moisture into the pavement structural sections, subsurface drainage components like open-graded base courses remain the best alternative in minimizing the time the pavement structural sections are exposed to saturated conditions. This research therefore focuses on assessing the performance and cost-effectiveness of pavement sections containing both treated and untreated open-graded aggregate base materials.
Three common roadway aggregates comprising of two virgin aggregates and one recycled aggregate were investigated using four open-ended gradations and two binder types. Laboratory tests were conducted to determine the hydraulic, mechanical and durability characteristics of treated and untreated open-graded mixes made from these three aggregate types. Results of the experimental program show that for the same gradation and mix design types, limestone samples have the greatest drainage capacity, stability to traffic loads and resistance to degradation from environmental conditions like freeze-thaw. However, depending on the gradation and mix design used, all three aggregate types namely limestone, natural gravel and recycled concrete can meet the minimum coefficient of hydraulic conductivity required for good drainage in most pavements. Tests results for both asphalt and cement treated open-graded samples indicate that a percent air void content within the range of 15-25 will produce a treated open-graded base course with sufficient drainage capacity and also long term stability under both traffic and environmental loads.
Using the new Mechanistic and Empirical Design Guide software, computer simulations of pavement performance were conducted on pavement sections containing these open-graded base aggregate base materials to determine how the MEPDG predicted pavement performance is sensitive to drainage. Using three truck traffic levels and four climatic regions, results of the computer simulations indicate that the predicted performance was not sensitive to the drainage characteristics of the open-graded base course.
Based on the result of the MEPDG predicted pavement performance, the cost-effectiveness of the pavement sections with open-graded base was computed on the assumption that the increase service life experienced by these sections was attributed to the positive effects of subsurface drainage. The two cost analyses used gave two contrasting results with the one indicating that the inclusion of open-graded base courses can lead to substantial savings
Evaluation of the Bailey Method as a tool for improving the rutting resistance of mix designs using New Hampshire aggregate
Currently the NHDOT uses the Superpave method to design and evaluate its asphalt pavements; however, this method lacks guidelines to adjust an aggregate blend that yields unacceptable mixtures. The objective of this project was to determine if the Bailey Method of aggregate blending would help improve the rutting resistance of mix designs that use NH aggregates. The rutting performances of six typical NH mix designs and two Bailey designs were measured using the Third Scale Mobile Model Load Simulator (MMLS3), an accelerated pavement testing (APT) device, in hot, dry conditions. Out of the two mixtures redesigned according to the Bailey Method, one showed improvement in rutting resistance while the other showed no change. Additionally, the Bailey Method failed to predict the voids in the mineral aggregate (VMA) in the redesigned mixes
A screening assessment of solidification/stabilization for storm water residuals
Metal species infused particulate matter associated with urban rainfall-runoff is a unique and profuse source of pollution. Generated from urban activities, such as traffic activity and vehicular/infrastructure abrasion, contaminated residual material is deposited to roadways during dry weather and transported to surrounding environments and/or best management practice (BMP) treatment facilities during wet-weather events. These particulates range in size from 1 ƒÝm to 10000 ƒÝm and are contaminated with metal species that originate from such sources as vehicular body wear (Cu), tire wear (Zn), and brake dust (Pb). Depending on the efficiencies of the BMP treatment facilities, these containment systems have the potential to be an abundant source of solid and potentially hazardous waste. Rainfall-runoff residual matter was collected from five urban BMP sites and characterized for granulometric indices. The sites were located in Baton Rouge, LA, Little Rock, AR, North Little Rock, AR, and Cincinnati, OH. The residual matter collected from the five BMP sites was characterized as a function of particle size for particle mass, particle size distribution (PSD), particle density (ƒâs), total surface area (SA), specific surface area (SSA), and metal species contamination. This characterization study showed that the majority of the metal species mass contamination is associated with the coarse to mid-sized range of particles with large amounts of SA, while the predominance of metal species concentration contamination is found in the fine particulates with high SSA. Cement-based solidification/stabilization (S/S) was applied to residual matter recovered from the BMP facility located in Baton Rouge, LA, using three cement types. Cement-based S/S has been used in the treatment of a wide range of metal contaminated wastes, but there is no record of the technology being applied to rainfall-runoff residuals. Three gradations (total (entire gradation), coarse (\u3e 75 ƒÝm), and fine (\u3c 75 ƒÝm)) of rainfall-runoff residuals were treated using a type I portland cement (PC), a slag cement (SC), and a 1:1 mass ratio of type I portland cement and slag cement (PS). An assessment of the solidification of the treated residuals was made using techniques to analyze the hydration behavior and physical strength and the leaching potential of the untreated and treated residuals was assessed in order to determine the stabilization effectiveness of the S/S application to the rainfall-runoff residuals
EFFECT OF AGGREGATE INHOMOGENEITY ON MECHANICAL PROPERTIES OF ASPHALT MIXTURES
Vertical and radial inhomogeneity of asphalt mixture components in laboratory-fabricated specimens have been of concern in asphalt mixture testing because of their potential effect on the mechanical response of the materials. Two important questions needed to be answered. First, can the existence of inhomogeneity in laboratory specimens definitively be distinguished? Second, if inhomogeneity exists, what effect would it have on the performance of asphalt materials?
Several new indices were developed to assess the extent of inhomogeneity. The level of accuracy of the suggested indices was evaluated by testing virtual and real specimens. Computer simulation was used to fabricate virtual specimens with various aggregate structures and to test the indices. The statistical power of the tests and the critical values for tests on the proposed indices were computed. The computed power of the tests indicated that the proposed tests are accurate for the measurement of both vertical and radial inhomogeneity.
Actual specimens, both homogeneous and inhomogeneous, were fabricated to validate the simulation results. The indices of homogeneity were computed from the x?ray computed tomography images of the specimens. Among the proposed indices, the z index on frequency proportion most clearly distinguished between the homogeneous and inhomogeneous specimens.
The specimens were then subjected to mechanical testing to examine the effect of inhomogeneity on the mechanical performance of the material. The effect of vertical and radial inhomogeneity was examined on compressive and shear properties of the mixtures, respectively. Statistical analyses on the results indicated that the compressive modulus (E*) of homogeneous specimens were slightly but not significantly higher than those of vertically inhomogeneous specimens, and the shear modulus (G*) of homogeneous specimens were significantly lower than those of radially inhomogeneous specimens.
A correlation analysis indicated insignificant correlation between the compressive properties and the index of vertical homogeneity but significant correlation between the shear properties and the index of radial homogeneity. The asphalt mixture was not sensitive to extreme level of vertical inhomogeneity when loaded axially but was responsive to radial inhomogeneity when loaded in shear
Developing Index Parameters for Cracking in Asphalt Pavements Through Black Space and Viscoelastic Continuum Damage Principles
Cracking is a major distress for asphalt concrete pavements and presents significant challenges to effective design and maintenance. Fatigue and thermal cracking decrease ride quality of the pavement and allow water to penetrate into underlying layers, which can result in major damage if left unchecked. The primary obstacle in predicting field performance for cracking in asphalt pavements is related to the interaction of material, structural, and environmental components. The major objective of this work is to develop index parameters to relate material and structural parameters, identifying whether a mixture is prone to fatigue or thermal cracking.
A Simplified Viscoelastic Continuum Damage (S-VECD) model, which relates material integrity and damage growth under repeated loading, is used in this project. The structural response is evaluated using layered elastic analysis principles in order to establish a material-structure space, where the pass/fail determination is based. This pass/fail index parameter is operationally efficient and easy to implement at a contractor or owner agency with capacity to test materials in the S-VECD configuration.
A thermal cracking parameter is developed for mixtures through a relation to laboratory and field performances in terms of Black Space. Since Black Space diagrams are able to capture changes in stiffness and relaxation, where separation would be indicative of poorly performing materials, these parameters provide insight into relationships among pavement structures and mixture designs. The results also lend themselves to the formation of performance-related specifications, where agencies can require a certain parameter value based on experimental and field observations. Opportunities exist to extend the parameter definitions among length scales, to further examine the effects of each on cracking performance. The capabilities of the parameter will influence design and funding decisions, resulting in cost savings at the owner agency and contractor levels through enhanced performance and a reduced testing framework
Green Low-Carbon Technology for Metalliferous Minerals
Metalliferous minerals play a central role in the global economy. They will continue to provide the raw materials we need for industrial processes. Significant challenges will likely emerge if the climate-driven green and low-carbon development transition of metalliferous mineral exploitation is not managed responsibly and sustainably. Green low-carbon technology is vital to promote the development of metalliferous mineral resources shifting from extensive and destructive mining to clean and energy-saving mining in future decades. Global mining scientists and engineers have conducted a lot of research in related fields, such as green mining, ecological mining, energy-saving mining, and mining solid waste recycling, and have achieved a great deal of innovative progress and achievements. This Special Issue intends to collect the latest developments in the green low-carbon mining field, written by well-known researchers who have contributed to the innovation of new technologies, process optimization methods, or energy-saving techniques in metalliferous minerals development
Advances in Hydraulics and Hydroinformatics Volume 2
This Special Issue reports on recent research trends in hydraulics, hydrodynamics, and hydroinformatics, and their novel applications in practical engineering. The Issue covers a wide range of topics, including open channel flows, sediment transport dynamics, two-phase flows, flow-induced vibration and water quality. The collected papers provide insight into new developments in physical, mathematical, and numerical modelling of important problems in hydraulics and hydroinformatics, and include demonstrations of the application of such models in water resources engineering
- …