Rheological Response of Asphalts

The rheological response of asphalt cements to shearing stresses is presented. The behavioral characteristics were measured using a rotating coaxial cylinder viscometer. Little or no development of theory is presented. The viscoelastic portion of deformation is discussed in terms of the creep function. Plastic deformation is described using the definitions of apparent and plastic viscosities. Curves showing the effects of temperature, stress level and penetration on these two major components of strain are presented and discussed. Analysis indicated that plastic deformation is the predominant component of strain and, thus, should be considered and incorporated in the design of flexible pavements

The Creep Response of Cohesive Soils: A Method of Design Using Rheological Strength Parameters

The creep response of four remolded soils and undisturbed soils from two landslide sites is presented. A method for obtaining the yield stress of soil from creep test data is presented and discussed. Viscosity diagrams , showing the location of the yield stress is approximately 50 percent of peak stress, were obtained from conventional triaxial tests. There is more scatter in data from undisturbed soils than in data from remolded soils. Mohr\u27s failure envelopes, constructed from yield stress data, give internal friction angles having values from approximately five to ten degrees. Strength data, calculated indirectly from peak relaxation modulus, are also presented. Stability analyses are presented on two selected landslides. Analyses are made and compared using peak, Residual , and yield stresses. Results indicate yield stress should be considered when designing earth structures

Stiffness of Solid-Liquid Mixtures: Theoretical Considerations

A rational approach to the solution of the stiffness of solid-liquid mixtures is presented. The stiffness of such mixtures is dependent on the stiffness of the viscous medium and the volume concentration and elastic modulus of the solid portion. Finally, the general solution is applied, in particular, to bitumen-aggregate mixtures; and the results are compared to experimental data

Review and Analysis of Pavement Management Practices in Kentucky

Pavement Management is becoming increasingly more important in an era of limited budgets and aging pavement structures, State Highway Agencies (SHA) are attempting to manage the pavements under their jurisdiction more carefully and economically. All pavement management systems include all or some of the following items as inputs: (1) pavement distress, (2) serviceability or rideability, (3) inventory of the system, (4) structural adequacy, (5) traffic volumes and loadings, and (6) some form of performance history. This report documents Kentucky\u27s present pavement management system. In addition, the duties and goals of the Pavement Management Branch are catalogged and described. Methods for rating pavements are described. The allocation of funds and how this allocation is calculated are described. Methods of determining estimates for rehabilitation needs are also described. A description of the organization and flow of information in the PMS is given in detail. Comparisons are made between Kentucky\u27s PMS and the elements of a pavement management system to be required by the Federal Highway Administration in 1993. Kentucky\u27s PMS is well advanced and most of the elements in the Federal Guidelines are already in place or are in some stage of development. Life-cycle costs analysis procedures need to be developed and adopted. Greater use of the present data bases is encouraged

Comparison of Three Methods of Pavement Design for Lexington-Fayette County

It is imperative in an era of limited budgets for construction and maintenance of streets and highways that a rational approach be followed for managing these funds. One of the first steps of this management process is the adequate and proper design of new streets and roads. In the interest of having a more rational system of design, representatives of the Lexington-Fayette Urban County Government requested the Kentucky Transportation Center to assist in the development of a new pavement design system that more clearly reflects differences in soils, traffic streams, environmental conditions, and materials. In fulfillment of that request, this. brief report compares three available methods of pavement design for flexible pavement and one method of design for rigid pavement. Comments and recommendations based upon pavement design experience and field performance of pavements are also included

A Computerized Analysis of Flexible Pavement Rutting Behavior (PAVRUT)

Flexible pavements are known to fail in several modes, one of which is rutting. In an effort to determine where in the pavement structure and to what extent rutting occurs and to determine the factors that control rutting, a comprehensive laboratory testing program was performed. Various traffic and environmental parameters were controlled in the study; and from the data, mathematical models that describe the rutting characteristics of an asphalt concrete, a dense graded aggregate, and a subgrade soil were formulated. Details of the materials, equipment, and laboratory procedures were reported by Allen in a previous report. Also, the mathematical models were described in that report and are listed again in this report for convenience. A traffic and a temperature model were also formulated to provide necessary input into the rutting models. These are described in this report. These models have been programmed and collected into a large computer program entitled PAVRUT. Using this program, an estimated rut depth can be calculated for any flexible pavement, assuming the volume and characteristics of the traffic stream are known

A Rheological Study of Cohesive Soils

An attempt has been made to describe the mechanistic behavior of remolded and undisturbed soils by application of the principles of rheology. This was accomplished by approximating and comparing the data obtained from transient creep tests and relaxation tests to the mathematical behavior of mechanical impedance models. The data were also analyzed by transforming static moduli and compliances into dynamic values by the application of Fourier transforms. Distribution functions of relaxation and retardation times, obtained by the application of LaPlace transforms, are presented. All soils tested exhibited similar dynamic moduli and complince curves indicating that soil type had little effect on the general shape of these curves. A generally direct, linear relationship existed between magnitudes of the dynamic moduli and confirming pressure for the remolded soils. Distribution functions proved to be useful indicators of mechanical behavior; however, they were not consistently affected by either confining pressure or static stress level

Visual Inspection of New Ramp Pavement at Bluegrass Airport Lexington, Kentucky

Personnel from the Kentucky Transportation Center performed a visual inspection of newly constructed ramp pavement at the Bluegrass Airport in Lexington, Kentucky. The inspection was conducted in May, 1996 at the request of airport engineers. The inspection revealed a number of concrete apron slabs that had cracked. Attempts had been made (apparently by the contractor) to seal the cracks by epoxy injection. The visual inspection indicated that the epoxy may not have been performing as hoped, and that some of the cracks did not appear to be sealed. As a result, it was decided to obtain cores of the cracked slabs in the area of the cracks in an attempt to determine if the epoxy was performing as it should have been. During the inspection, other concrete damage was noted along and associated with two drainage trenches constructed as a part of the new ramp. This damage will be described in detail later in this report

Evaluation of Drainage on Nicholasville Bypass

Construction of the Nicholasville Bypass (US 27) was completed in 1986. At the north end of the bypass is a raised, paved traffic median (Figures 1 and 2). The median was constructed with a lip curb and gutter. The roadway at that location is in a superelevated section. A raised, paved traffic median also is located at the southern end of the bypass, Figures 3 through 5 are photographs of that median. The median is located on a tangent section therefore, the roadway has a normal crown. The section of roadway at the southern end is located on a slight grade. The south median also is constructed with a lip and curb gutter. Soon after construction, water began to emerge from near the gutter line· of both medians. The Kentucky Transportation Research Program was requested to investigate the cause of the water problem and make recommendations for remedial solutions