Search

The focus of this study is the evaluation of the effects of deficiencies in design-level values of effective binder content ([DELTA][V.sub.be]) on the top-down (TD) and bottom-up (BU) fatigue cracking performance of hot-mix asphalt (HMA) mixtures using AASHTO-Ware Pavement ME Design structural simulation program. Using an analytical-mathematical- based methodology, this study also aims to predict the reduction in fatigue service life (i.e., TD, and BU fatigue cracking) of asphalt pavements that are most sensitive to the variation ([DELTA][V.sub.be]). Two types of mixes with varying levels of [V.sub.be] are used to simulate the fatigue cracking performance of a full-depth (FD) pavement structure. For each of the three studied cases, one asphalt course has a variable value of [V.sub.be], while the two other courses have a fixed value of [V.sub.be]. Results indicate that the [DELTA][V.sub.be] of 3% reduced 50%-70% of fatigue cracking service life. Additionally, Pavement ME shows a limitation to account for the effect of [V.sub.be] in the intermediate course on the BU fatigue cracking. Key words: effective binder content, fatigue service life, bottom-up fatigue cracking, top-down fatigue cracking, AASHTO-Ware pavement ME design L'objet de la presente etude est l'evaluation des effets des lacunes dans les valeurs au niveau de la conception de la teneur efficace en liant ([DELTA][V.sub.be]) sur la performance de la resistance a la fissuration par fatigue descendante et ascendante des melanges d'asphalte a chaud (<< HMA >>) au moyen du programme de simulation de structure AASHTOWare Pavement ME Design (<< Pavement ME >>). A l'aide d'une methodologie analytique et mathematique, cette etude vise egalement a predire la reduction de la duree de vie en fatigue (c.-a-d. la fissuration par fatigue descendante et ascendante) des chaussees en asphalte qui sont les plus sensibles a la variation ([DELTA][V.sub.be]). Deux types de melanges avec differents niveaux de teneur efficace en liant ([V.sub.be]) sont utilizes pour simuler les performances de fissuration par fatigue d'une structure de chaussee pleine profondeur. Pour chacun des trois cas etudies, une couche d'asphalte a une valeur variable de [V.sub.be], tandis que les deux autres couches ont une valeur fixe de [V.sub.be]. Les resultats indiquent que la variation [DELTA][V.sub.be] de 3% a reduit la duree de vie liee a la fissuration par fatigue de 50 a 70%. De plus, Pavement ME presente une limitation au niveau de la prise en compte de l'effet de Vbe dans la couche intermediaire sur la fissuration par fatigue ascendante. [Traduit par la Redaction] Mots-cles : teneur efficace en liant, duree de vie en fatigue, fissuration par fatigue ascendante, fissuration par fatigue descendante, AASHTOWare Pavement ME Design (<< Pavement ME >>), 1. Introduction Although the field performance of hot-mix asphalt (HMA) pavement depends on many factors, properly designed, constructed, and maintained structures will achieve adequate service life. The procedure of assuring [...]

In a book published in 1906, Richard Meade outlined the history of portland cement up to that point1. Since then there has been great progress in portland cement-based construction materials technologies brought about by advances in the materials science of composites and the development of chemical additives (admixtures) for applications. The resulting functionalities, together with its economy and the sheer abundance of its raw materials, have elevated ordinary portland cement (OPC) concrete to the status of most used synthetic material on Earth. While the 20th century was characterized by the emergence of computer technology, computational science and engineering, and instrumental analysis, the fundamental composition of portland cement has remained surprisingly constant. And, although our understanding of ordinary portland cement (OPC) chemistry has grown tremendously, the intermediate steps in hydration and the nature of calcium silicate hydrate (C-S-H), the major product of OPC hydration, remain clouded in uncertainty. Nonetheless, the century also witnessed great advances in the materials technology of cement despite the uncertain understanding of its most fundamental components. Unfortunately, OPC also has a tremendous consumption-based environmental impact, and concrete made from OPC has a poor strength-to-weight ratio. If these challenges are not addressed, the dominance of OPC could wane over the next 100 years. With this in mind, this paper envisions what the 21st century holds in store for OPC in terms of the driving forces that will shape our continued use of this material. Will a new material replace OPC, and concrete as we know it today, as the preeminent infrastructure construction material?

Reinforcing strategies for three-dimensional printing (3DP) of cementitious materials (mostly mortars) have been extensively studied in recent years. Among various reinforcement strategies available for 3DP of cementitious materials, the use of fibers is frequently mentioned as a promising approach to enhance their mechanical performance. This work aims to evaluate the influence of four types of fibers (polyvinyl alcohol [PVA], nylon, rayon, and basalt) on the flowability and flexural strength of mortars used in 3DP. The flexural behavior of 3DP beams was compared with that of cast specimens, and the digital image correlation (DIC) technique was used to evaluate the development of the cracks. The fiber orientation in the reference (cast) and 3DP samples was examined using optical microscopy. The results revealed that, among four types of fibers used, the PVA fibers were most effective in increasing the flexural strength of both the cast and 3DP specimens. In addition, the results show that all fibers preferentially aligned parallel to the printing direction. 3DP specimens with filaments aligned in the direction perpendicular to the direction of the applied load showed superior flexural strength when compared to the cast specimens. [ABSTRACT FROM AUTHOR]

Excessive drying shrinkage, and associated cracking, can lead to serious durability problem in concrete pavements and bridges. In the course of this study, the magnitude of drying shrinkage and cracking potential was evaluated for several concrete pavement mixtures as a function of packing density of the aggregate and paste contents. The results indicated that both, the shrinkage and the cracking potential depend on the volume of voids between aggregate particles (packing density), paste content of concrete mixture, and the paste-aggregate void saturation ratio.