Reza S. Ashtiani

Evaluation of the Impact of Fines on the Performance of Lightly Cement-Stabilized Aggregate Systems

The impact of increasing fines content on the performance of unbound (unstabilized) and lightly stabilized aggregate systems was evaluated. The aggregate systems analyzed varied in amount of mineral fines, the moisture state during curing and at the time of testing, and the amount of portland cement used to stabilize the blend. The evaluation was based on measurements of anisotropic resilient properties, permanent deformation, and unconfined compressive strengths of aggregate systems. In addition, the nonlinear anisotropic resilient properties of the aggregate blends were used in a finite element program to determine critical pavement responses. Aggregate systems with higher fines content were, as expected, more sensitive to moisture than control systems with standard fines content. The increase in the fines content in the unbound systems when molding moisture was wet of optimum dramatically diminished the quality of performance. However, the aggregate systems with higher fines benefited considerably from low percentages of cement stabilizer. It was found that with the proper design of fines content, cement content, and moisture, the performance of the stabilized systems with high fines content can perform equivalent to or even better than the systems with standard fines content. This was clearly evinced by enhancing the resilient properties (increase in stiffness and decrease in anisotropy), decreasing the rate and magnitude of permanent deformation, and increasing compressive strength. The beneficial use of mineral fines will result in benefit to the aggregate industry.

Performance prediction and moisture susceptibility of anisotropic pavement foundations

Significant work has been done by the International Center for Aggregate Research (ICAR) to identify the effects of the anisotropic nature of compacted base courses on the stress, strain, and permanent deformation characteristics of pavement foundations. As continuation to this effort, current paper presents a mechanistic approach for determination of the variation of pore water pressure under a moving wheel load. This paper also presents a methodology as to evaluate the effect of pore water pressure on the anisotropic response of aggregate layers. Sixty-two aggregate systems were tested with varying fine contents and water contents. The aggregate blends were molded according to AASHTO T-180 and tested using state of the art equipment called the Rapid Triaxial Tester (RaTT) at three saturation levels to capture the moisture susceptibility of the aggregate systems. Variable Dynamic Confining Pressure (VDCP) stress paths were in turn used to determine the anisotropic material properties for each aggregate system. This approach shows that the external pressure applied on the surface of the pavement results in a reduction of the initial negative pore water pressure. The change in pore water pressure induced by traffic load for high fines content specimens at elevated saturation levels results in positive pore water pressure which is synonymous with more critical conditions for plastic deformation. Further analysis on the results shows the agreement between the proposed approach and the principle of change in pore water pressure presented by Henkel. Mohr-Coulomb yield function was employed as a performance indicator in this study. The stress sensitive and anisotropic material model showed that the hardening component of the stiffness in vertical direction at the centerline of the load and at the top of the aggregate base layer is approximately 20% smaller when the influence of pore water pressure is considered in the formulations.

A Practical Approach for the Estimation of Strength and Resilient Properties of Cementitious Materials

Cementitious stabilization of granular soils has been proven to be a cost-saving option for the use of materials with marginal quality in the construction and rehabilitation of pavement structures. The orthogonal load distribution capacity of the Cement-Stabilized Materials (CSM) is typically characterized by Unconfined Compressive Strength (UCS), Indirect Tensile Strength (IDT), and Resilient Modulus (Mr) tests in the laboratory. The aforementioned parameters and properties are integral components of the analysis and design of pavements with stabilized layers. Time and budget constraints make it impractical for many state agencies to complete the full laboratory characterization protocols to determine all the design input parameters. Therefore, in many cases, the design engineers opt out of laboratory testing and primarily rely on past experience and engineering judgments to assign design input parameters. Such an approach compromises the reliability of the pavement life predictions, and can potentially incur unforeseen costs to the traveling public. This study was designed to bridge this gap by developing a series of statistically robust relationships between the laboratory achived data to provide an estimate of the design input parameters. To accomplish this objective, 570 stabilized cylindrical specimens were prepared and subjected to UCS, IDT, and submaximal modulus tests at three strength ratio levels. Subsequently, the relationships between the IDT, UCS, and resilient modulus at small-strain and intermediate strain levels were developed in this study. Such relationships can serve as a valuable means for the estimation of the tensile and compressive strength of the CSM for pavement design.

Comparative Study of Water-Blasting Equipment for Airfield Surface Decontamination

AbstractRunway rubber removal is a maintenance function employed to ensure safe landing areas for aviation operations. Rubber deposits accumulate on runway areas where aircraft tires touchdown and ...

Airport Rubber Removal: A Comparison of Ultra-High Pressure Water Runway Rubber Removal Systems

Runway rubber removal is a maintenance function employed to ensure safe landing areas for aviation operations. Rubber deposits accumulate on runway areas where aircraft tires touchdown and braking occurs. This tire rubber build up occludes pavement microtexture and macrotexture, causing a significant loss in available skid resistance during wet conditions. Reduction of available pavement microtexture in a wet environment prevents the development of adhesional friction, which can result in viscous hydroplaning. Reduction of pavement macrotexture prevents the removal of bulk water from the tire-pavement contact area and also prevents the development of the hysteresis frictional component. To restore friction to safe levels for aircraft operations, rubber must be periodically removed. Several techniques for rubber removal are available. Waterblasting is a proven surface decontamination technique which employs the use of high or ultra-high pressure water (UHPW) to blast rubber deposits from the runway surface. This effort provides a performance-based comparison between three commercially available UHPW waterblasting systems. The evaluation was conducted on an ungrooved Portland Cement Concrete (PCC) runway with heavy rubber contamination along the touchdown and breaking zones. Several testing equipment such as Circular Track Meter (CTM) and Dynamic Friction Tester (DFT) were used to characterize the surface properties of the runway before and after rubber removal. The measurements were used for statistical pairwise comparative analysis of International Friction Index (IFI), speed constant and Mean Profile Depth (MPD). Treatment effect analysis of pre-measured and postmeasured data revealed that UHPW systems improved the surface texture properties by at least 40% regardless of the decontamination equipment.

Performance Related Tests on Recycled Materials for Sustainable Design of Pavement Systems

This paper provides recommendations for performance-related tests to select recycled materials to be used in pavement foundations (base/sub-base layers). The test protocol presented in this paper will help transportation agencies, pavement design engineers and construction industry professionals to mechanistically evaluate and select sources of recycled hot-mix asphalt and portland cement concrete materials and identify factors that contribute most to the longevity of layers using recycled pavement materials. Extensive literature review was conducted on the aggregate specifications in the United States and other countries to identify the protocols used to evaluate the suitability of virgin and recycled aggregates in base and sub-base layers. The test procedures, typically designed for virgin aggregates, were modified to account for the recycled materials in the aggregate mix. The test procedures were further evaluated on the basis of mechanical performance, accuracy, practicality, complexity, precision, and test cost. The performance of the developed aggregate evaluation systems was determined through testing and analysis of 12 aggregates with different lithology and known field performance history. These samples were selected from seven states with different seasonal frost cycles. The performance tests were conducted and modifications were made to the tests procedures to better understand the mechanical behavior of aggregate systems with recycled materials. This study revealed that shear strength, toughness, abrasion, durability, and frost susceptibility influence the performance of the unbound aggregate layers. Statistical analysis of the data showed that shear strength of the aggregate systems has the most impact on the performance of the unbound systems consisted of recycled materials.