Study of a hot asphalt mixture response based on energy concepts

The main objective of the research reported in this paper is to determine the response of a hot mix asphalt (HMA) in terms of both the tensile strength and energy parameters (based on the assessment of the force-displacement curve) as potential tools for improving the HMA mixture design. The HMAs analyzed were fabricated using a 60-70 penetration asphalt binder, dense-graded aggregate, mineral filler, and different types and contents of mineral filler replacements (i.e., lime, cement, and fly ash). The indirect tensile test was conducted to determine both the HMA tensile strength and force-displacement curve, which allowed for the computation of the HMA toughness as well as the energies involved in the process before and after reaching the tensile strength. Corresponding results suggest that the replacement of mineral filler by cement, lime, and fly ash modified the HMA response in terms of both the tensile strength and energy parameters. In addition, analysis of the energy parameters discussed proved to be useful for determining the optimum mineral filler content of HMA. Consequently, analysis of these energy parameters can benefit the HMA mixture design process. // El objetivo principal de la investigación fue determinar el comportamiento de una mezcla asfáltica en función de la resistencia a la tracción indirecta y parámetros de energía (calculados en función de la curva fuerza-desplazamiento) como herramientas potenciales para mejorar el diseño de mezclas asfálticas. Las mezclas asfálticas analizadas fueron fabricadas con asfalto de penetración 60/70, granulometría cerrada md10 y relleno mineral en diferentes porcentajes y materiales (cal, cemento y ceniza volante). El ensayo de tracción indirecta se utilizó para determinar la resistencia máxima a la tracción y la curva fuerza-desplazamiento, a partir de la cual se calcularon la tenacidad de la mezcla y las energías involucradas en el proceso antes y después de alcanzar la resistencia máxima. Los resultados obtenidos sugieren que reemplazar el relleno mineral por cemento, cal o ceniza volante modifica el comportamiento de la mezcla asfáltica en términos de la resistencia a la tracción y los parámetros de energía. Adicionalmente, el análisis de los parámetros de energía discutidos es útil para establecer el contenido óptimo del relleno mineral. En consecuencia, el análisis de estos parámetros de energía puede beneficiar el proceso de diseño de mezclas asfálticas.Peer ReviewedPostprint (published version

IMPROVING MIX DESIGN AND CONSTRUCTION OF PERMEABLE FRICTION COURSE MIXTURES

Permeable friction course (PFC), or new generation open-graded friction course (OGFC) mixtures, are hot mix asphalt (HMA) characterized by high total air voids (AV) content (minimum 18 %) as compared to the most commonly used dense-graded HMA. The high AV content confers to PFC mixtures both high permeability and noise reduction effectiveness. These characteristics and the high values of surface friction exhibited by PFC mixtures, as compared to dense-graded HMA, lead to improvements in safety and the environment, which make PFC one of the safest, cleanest, and quietest alternatives currently available for surface paving. The main objective of this study was improving the current PFC mix design method and construction practices in terms of compaction control. Corresponding results were integrated in an improved mix design method that is based on the guidelines of the current mix design method used by the Texas Department of Transportation. The improved mix design included modified computation of the inputs required to determine mixture density (or corresponding total AV content). These changes led to a proposed modification of the density specification for mix design from 78-82 % to 76-80 %. In addition, the water-accessible AV content was proposed as a surrogate of the total AV content for mix design and evaluation. The improved mix design method also includes verification of drainability, durability, and stone-on-stone contact. Computation of the expected value of permeability (E[k]) and measurement of the water flow value were recommended, respectively, for verification of drainability in the laboratory (using specimens compacted in the Superpave Gyratory Compactor (SGC)) and in the field. The Cantabro loss test conducted in both dry- and wet-conditions was suggested for assessing mixture durability. Improved criteria were proposed for verification of stone-on-stone contact based on the evaluation of the AV content in the coarse aggregate fraction of the mixture. In addition, comparison of the internal structure of field-and laboratory-compacted mixtures supported recommendation of a field-compaction control. Recommendations to reduce the horizontal heterogeneity of AV encountered in PFC specimens included using road cores with a minimum 152.4 mm diameter and coring SGC specimens from 152.4 to 101.6 mm in diamete

Efecto del contenido de solventes en larespuesta mecánica y la compactabilidadde mezclas asfálticas elaboradas con crudopesado de pavimentación de Castilla

The paving-heavy crude oils (PHCO) are natural cut-back asphalts composed by a high content of asphalt cement and a portion of solvents. These materials have been used in Colombia since the 90’s to improve low volume traffic roads. The existence of solvents in the PHCO allows mixing it with the aggregates in cold conditions. Then, before compaction, these asphalt mixtures require a curing process (i.e., process of partial loss of solvents from the PHCO) to ensure its proper performance. However, at present there is no consensus on the loss of solvents to specify for the curing process of mixtures fabricated with PHCO. Given this situation, this study assesses the effect of the partial content of solvents on both the mechanical response and compactability of asphalt mixtures produced using PHCO from the Castilla’s oil field (CA); a material extensively used in the East region of Colombia. The study included conducting and analyzing conventional characterization tests of the mixture constituent materials, surface free energy testing on both mastics and the aggregate, mix design, and characterization of both mechanical response and compactability of the mixtures fabricated using the CA and a control asphalt. Corresponding results led to identify and quantify a progressive improvement in both the adhesion quality of the mastic-aggregate interfaces and the mechanical response of the asphalt mixture as a function of the reduction of the solvents. These results suggest the convenience of compacting the asphalt mixtures fabricated using the CA after allowing a loss of 50% of the solvents obtained from the CA via atmospheric distillation at 360°C.Los crudos pesados de pavimentación (CPPs) son asfaltos líquidosnaturales compuestos por un alto contenido de cemento asfáltico y unaporción de solventes. Estos materiales han sido empleados en Colombiadesde los años90s para mejorar vías de bajo volumen de tránsito. Laexistencia de solventes en los CPPs permite que éstos sean mezcladoscon los agregados en frío. Posteriormente, para garantizar su adecuadodesempeño, estas mezclas asfálticas requieren de curado (i.e., proceso depérdida parcial de solventes de los CPPs), previo a su compactación. Noobstante, a la fecha no existe consenso sobre la pérdida de solventes aespecificar en el proceso de curado de mezclas fabricadas con CPPs. Dadaesta situación, el presente estudio evalúa el efecto del contenido parcial de solventes sobre la respuesta mecánica y la compactabilidad de mezclasasfálticas elaboradas con el CPP del campo de Castilla (CA); materialde amplio uso en el oriente colombiano. El estudio incluyó la ejecucióny análisis de ensayos de caracterización convencional de los materialesconstitutivos de la mezcla, ensayos de energía superficial libre de másticosy agregado, diseño de mezclas, y caracterización de la respuesta mecánicay compactabilidad de mezclas asfálticas fabricadas con el CA y un asfaltode control. Los resultados permitieron identificar y cuantificar mejorasprogresivas en la calidad de la adhesión de las interfases mástico-agregadoy en la respuesta mecánica de la mezcla asfáltica en función de la reduccióndel contenido de solventes. Estos resultados sugieren la convenienciade compactar las mezclas asfálticas fabricadas con el CA después depermitir la pérdida del 50%de solventes extraíbles del CA vía destilaciónatmosférica a 360◦C

Effect of the failure criterion on the laboratory fatigue response prediction of hot mix asphalt mixtures

El objetivo principal de esta investigación fue establecer la influencia del criterio de fallo, empleado para calcular el comportamiento a fatiga en laboratorio de mezclas asfálticas en caliente especificadas por el Instituto de Desarrollo Urbano de Bogotá D.C. (i.e., mezclas md10 y md20), en la predicción de la respuesta a fatiga. Las leyes de fatiga (i.e., curvas de fatiga) se determinaron a flexo-tracción con muestras trapezoidales ensayadas a desplazamiento controlado. Los criterios utilizados para establecer la vida de fatiga correspondieron al clásico (50% de la fuerza inicial), de daño y de rotura. Los resultados correspondientes sugirieron que la selección del criterio de falla puede conllevar a diferencias significativas en la predicción de la vida de fatiga en laboratorio (i.e., curvas de fatiga). Sin embargo, se estableció que para las mezclas con granulometría densa md10, la ley de fatiga fue similar al emplear cualquiera de los tres criterios analizados. Por el contrario, para las mezclas asfálticas con granulometría densa md20, la aplicación de los tres criterios de falla conllevó a diferencias significativas en la predicción de vida de fatiga; el menor número de ciclos de carga a la falla (más crítico) fue determinado con el criterio clásico. Investigaciones futuras deberán profundizar en establecer que criterio de fallo se debe utilizar para el subsecuente diseño estructural de pavimentos, especialmente para mezclas asfálticas con curvas granulométricas que contengan agregados de tamaño igual o superior a 20 mm

Analysis of connected air voids in warm mix asphalt

Warm mix asphalt (WMA) are asphalt mixtures produced at reduced temperatures as compared to conventional hot mix asphalt (HMA). Temperature reductions in the order of 10 to 50 C are possible through the incorporation of diverse WMA type additives. However, different aspects, including the mixture internal structure of WMA, are still object of research. Consequently, this paper focused on the assessment of the internal structure of WMA (computed in terms of the Connected Air Voids (CAV) characteristics), fabricated using three WMA additives: Asphamin®, Sasobit®, and Evotherm®. The CAV content corresponds to the fraction of Air Voids (AV) forming connected paths in a compacted specimen and is better related to the asphalt mixture response (e.g., permeability) than the total AV content. The CAV analysis was based on X-ray Computed Tomography scanning and subsequent image analysis. Corresponding results suggested the need of additional research to further characterize field compacted mixtures, produced at densification levels comparable to those achieved in the laboratory. In addition, the inclusion of WMA additives and corresponding temperature reductions did not substantially affect the internal structure of gyratory-compacted specimens (115 mm in height) produced for laboratory mixture evaluation

Internal structure of laboratory compacted warm mix asphalt

Warm mix asphalt (WMA) are asphalt mixtures fabricated at lower temperatures (i.e., 20 C to 50 C) than conventional hot mix asphalt (HMA). Therefore, as compared to HMA, WMA offer several engineering, economical, and environmental advantages. However, research is still required to identify the response, properties, and performance of WMA, since they still constitute a relatively new technology. This paper focuses on the analysis of the internal structure of WMA specimens compacted using both the Superpave Gyratory Compactor (SGC) and the Texas Gyratory Compactor (TxGC). This analysis was conducted in terms of the air voids (AV) characteristics assessed by applying X-ray Computed Tomography and image analysis techniques. The results obtained suggest that the addition of WMA additives and corresponding reduction of the compaction temperature for SGC specimens did not lead to significant changes in the vertical distribution of total AV content as compared to that of the control-HMA. However, some differences were reported in terms of the AV size, which suggests the existence of discrepancies in the aggregate packing condition. Therefore, additional research is suggested to fully validate the equivalence of the internal structure of both WMA and HMA