Luis Loria

Long-Term Performance of Reflective Cracking Mitigation Techniques in Nevada

Hot-mix asphalt (HMA) overlay is one of the commonly used methods for rehabilitating deteriorated pavements. The Nevada Department of Transportation (DOT) uses HMA overlays as a rehabilitation technique for the majority of the states flexible pavements. One major type of distress influencing the life of an overlay is reflective cracking. In the past, Nevada DOT has experimented with a number of techniques— such as cold in-place recycling, reinforced fabrics, stress relief courses, and mill and overlay—to reduce the impact of reflective cracking on HMA overlays. Several projects were constructed under each category. The long-term field performance of various Nevada DOT reflective cracking mitigation techniques was evaluated; the techniques were used on flexible pavements at 33 field projects. Performances of the various projects were analyzed by fatigue, transverse, and block cracking measurements from Nevada DOTs pavement management system data. In addition, the statistical approach called principal component analysis was used to asses the effectiveness of each of the reflective cracking techniques. The study indicated that cold in-place recycling and mill and overlay were the most effective treatments for reflective cracking of HMA overlays over HMA pavements under Nevadas conditions, except when the existing pavement experiences severe alligator cracking. In such situations, it is recommended that HMA pavement be subjected to reconstruction or full-depth reclamation.

Optimum Time for Application of Slurry Seal to Asphalt Concrete Pavements

This study evaluated the field performance of asphalt pavements with and without slurry seal applications, developed performance models for asphalt pavements without slurry seals and asphalt pavements receiving slurry seals at various times following construction, and identified the optimum time for applying slurry seals on asphalt pavements in the Washoe County, Nevada, region. This determination was achieved by evaluating the long-term pavement performance data collected with the MicroPAVER system for the past 15 years and the cost-effectiveness of slurry seals applied to new and existing flexible pavements at Years 0, 1, 3, 5, 7, and 9 after construction. This study found that applying slurry seal immediately after or 1 year after construction of the asphalt layer is not effective in regard to the benefit to users and the benefit–cost ratio for the agency. The optimum time of applying slurry seal depended on the type of construction activity. For newly constructed pavements, the optimum time to apply slurry seal was 3 years after construction. For pavements subjected to overlays, the optimum time to apply slurry seal was between 3 and 5 years after construction. However, for uniformity purposes, it was recommended that the agency apply slurry seal 3 years after construction of the asphalt layer for both new and overlay constructions.

Performance Evaluation of Asphalt Pavement Preservation Activities

A 2-year research project was sponsored by the Nevada Department of Transportation (NDOT) and conducted by University of Nevada at Reno researchers to evaluate the long-term performance of asphalt pavement preservation activities that NDOT has implemented for the past 15 years. During this research project, 11 preservation activities were identified after several meetings with NDOT maintenance personnel. This study evaluated 847 field sections. The performance of the selected field sections was assessed on the basis of the pavement condition before and after treatment application. The analysis evaluated the likelihood of enhancing the pavement performance as well as the anticipated performance period for the various treatments. Benefit–cost ratios for the various treatments were also evaluated, given the pretreatment pavement condition, traffic level, and environmental conditions. A set of guidelines is provided to help select the most cost-effective preservation activities on the basis of the most favorable conditions with regard to environment, traffic, and conditions of the existing pavement (e.g., present serviceability index, international roughness index, rut depth, fatigue cracking, transverse cracking, and block cracking).

Effective Timing for Two Sequential Applications of Slurry Seal on Asphalt Pavement

This study evaluated the field performance of asphalt pavements with two sequential slurry seal applications, developed per- formance models for asphalt pavements without slurry seals and asphalt pavements receiving slurry seals at various times following con- struction, and identified the optimum time for the application of two slurry seals on asphalt pavements within the Washoe County, Nevada, region. This is a continuation of a previous study in which a single application of slurry seal was investigated. The MicroPAVER system was used to evaluate the long-term pavement performance data collected for the last 15 years and the cost-effectiveness of slurry seals applied to new and existing flexible pavements at 0, 1, 3, 5, 7, and 9 years after construction. The data generated in this study clearly reveal an optimum time window for slurry seal application. The optimum times and highest relative benefit of application of slurry seals for both overlaid and newly constructed pavements were when the first slurry seal was applied at 3 years after construction, followed by a second slurry seal at year 7 or 9. Accordingly, it was recommended to apply the first slurry seal for newly constructed and overlaid pavements, respectively, when the pavement condition index (PCI) is 90 and 87, followed by a second slurry seal when the PCI reaches a value of 86 and 77. DOI: 10.1061/ (ASCE)TE.1943-5436.0000521.

Bulk Specific Gravity of Reclaimed Asphalt Pavement Aggregate: Evaluating the Effect on Voids in Mineral Aggregate

Several methods are available for determining the bulk specific gravity (Gsb) of reclaimed asphalt pavement (RAP). However, a clear recommendation has not been had for determining this property. In this study, asphalt mixes with known aggregate properties were produced and aged in the laboratory to simulate RAP. The aggregates were recovered, and the aggregate properties, including Gsb, were reassessed. The aged mixtures were also tested to determine maximum theoretical specific gravity (Gmm), from which estimated Gsb values could be calculated. The Gsb values from both the extraction and Gmm methods were compared with the known or true Gsb values for these aggregates. The effects of the RAP Gsb errors on voids in mineral aggregate values from the various methods were also evaluated. On the basis of the results of this study, it is recommended that the Gmm method be used to determine the RAP Gsb when a regional absorption value is known.

Specific activity and derived intervention levels for Cesium-137 in Costa Rican export goods: Tuna fish, coffee and powdered milk

Abstract Cesium-137 is a fission product of 235 U and 239 Pu. After a major nuclear accident, it is released into the atmosphere and in the far field region it will produce radioactively contaminated food and drinking water. This paper will study the specific activity of 137 Cs in three Costa Rican export products: tuna fish, coffee and powdered milk. The average specific activities found are as follows: 0.89±0.41, 1.16±0.76 and 4.53±2.00 Bq kg −1 . They represent low values compared to their derived intervention levels: 1.25 × 10 7 , 1.25 × 10 7 and 2.44 × 10 5 Bq kg −1 , respectively.

Recommendations for the characterization of RAP aggregate properties using traditional testing and mixture volumetrics

A Federal Highway Administration (FHWA) funded study was conducted to investigate the influence of extraction methods on aggregate properties. The properties of the virgin aggregates were compared with those of aggregates extracted from laboratory-produced recycled asphalt pavement (RAP) from four different aggregate sources. The extracted and actual asphalt binder contents were also compared. The study investigated the influence of the extraction method on tendencies to under- or over-estimated certain mix design properties. The test results were also examined to determine the impact of the RAP aggregate properties on the voids in mineral aggregate (VMA) over different RAP percentages. Recommendations were made for the most appropriate method to estimate the RAP aggregate specific gravities based on acceptable levels of error in VMA for mixtures with varying levels of RAP.

Modelo de deformación permanente para la evaluación de la condición del pavimento

El desarrollo de deformaciones plasticas en pavimentos flexibles ha sido un topico de investigacion desde hace varias decadas. Actualmente se cuenta con modelos que permiten predecir este tipo de falla, siendo una practica comun considerarlos en el diseno estructural de pavimentos. Sin embargo, las variables requeridas para dicha prediccion son complejas o dificiles de obtener en campo, lo que hace que su aplicacion en el proceso de auscultacion no sea sencilla. La medicion de deflexiones es una tecnica de evaluacion estructural de pavimentos flexibles cuyo valor puede considerar la competencia del conjunto pavimento. Esta investigacion busca correlacionar los datos de deflexiones en la superficie del pavimento con las deformaciones plasticas probables en el tiempo y usar esta prediccion para estimar la vida remanente del pavimento usando como criterio el ahuellamiento maximo permisible. Se utilizaron datos adquiridos en 4 pistas distintas ensayadas a escala real por el Laboratorio Nacional de Materiales y Modelos Estructurales de la Universidad de Costa Rica. El modelo propuesto logra predecir el ahuellamiento futuro usando como insumo el espesor de la estructura de pavimento, la deflexion superficial medida a 40kN de carga, y la repeticion de ejes equivalentes, logrando una bondad de ajuste alta. Con la estimacion del nivel de ahuellamiento se espera que las politicas de mantenimiento y rehabilitacion propias de un sistema de administracion de pavimentos sean calibradas y aplicadas a su debido tiempo.

Assessment of Reflective Cracking Models for Asphalt Pavements

The research effort documented in this paper is directed toward identifying an analytical model that can be used to predict the resistance of hot mix asphalt (HMA) overlays to reflective cracking and predict their long-term performance. Various models were identified and three models were studied and compared in this research effort: 1) Virginia Tech Simplified Overlay Design Model, 2) Rubber Pavements Association (RPA) Overlay Design Model, 3) the New American Association of State Highway and Transportation Officials (AASHTO) model for Reflective Cracking. The identified models were assessed by the research team based on their ability to predict the performance of HMA overlays subjected to reflective cracking. An overlay design was conducted for three different HMA overlay mixes using the three identified overlay design methods. The overlay mixes were manufactured using different aggregate gradations from the Sloan pit in Southern Nevada and a PG76-22 polymer modified asphalt binder. The overlay was designed for 7,000,000 ESALs over the 20 years analysis period. Finally, a comparison was exerted among the various HMA overlay thicknesses required by each method and the material properties associated to such determination to accomplish the design traffic.

Derived intervention levels for the costa Rican diet

Abstract A theoretical analysis for the determination of particular derived intervention levels DILs for Costa Rica is presented. DILs for 15 radionuclides for the Costa Rican diet are calculated. Assuming all foodstuffs are contaminated only with 137 Cs and a total annual intake of 355 kg y −1 instead of the 550 kg y −1 proposed by the WHO, the corresponding DIL is approximately 2000 Bq kg −1 Four possible radionuclide combinations studied that might result from a nuclear accident are: 137 Cs and 134 Cs; 137 Cs, 134 Cs, 89 Sr and 90 Sr; 137 Cs, 134 Cs, 131 I, and 133 I; and 137 Cs 134 Cs 89 Sr, 90 Sr, 131 I, 133 I and 239 pu.