A B S T R A C T R [ S U M EDynamic material functions are among the most sensitive tools for determining the molecular weight distribution ofrheologically complex systems. The phase angle of the complex modulus especially is sensitive to the molecular weight of the studied material; it can therefore be used as the input to the inverse problem of determining the molecular weight from this important dynamic material function. Molecular weight distributions of several regular asphalts are calculated using the phase angle and compared with molecular weight distribution obtained by gel permeation chromatography. The problems of calculating molecular weight distributions from rheological parameters are also discussed.

There has been interest in modifying asphalt with polyethylene materials, which are a major plastic waste substance, especially low-density polyethylene (LDPE). In this study, combinations of three low molecular weight polyethylene (PE) wax materials and three recycled LDPE materials were used as asphalt modifiers. The modified asphalts were studied using the Superpave TM MP1 and MP1a specifications, 1% direct tension test (DTT) failure strain criteria, phase separation, and microscopy. When the molecular weight distribution of the polyethylene modifiers was widened, the bending beam rheometer thermal stress curve of the modified asphalt shifted to the low-temperature end, giving a better critical cracking temperature. Not all recycled LDPE are the same. When using recycled LDPE in asphalt modification, we have to consider the LDPE properties, such as molecular weight and molecular weight distribution, which have been found to play important roles in asphalt's low-temperature properties, hot storage stability, and polymer phase distribution. This study showed that LDPE with lower molecular weight and wider molecular weight distribution are more suitable materials for asphalt modification, compared with high molecular weight LDPE with very narrow molecular weight distribution.Résumé : Il se développe un intérêt envers la modification de l'asphalte par des polyéthylènes, des déchets de plastiques importants, surtout le polyéthylène à faible densité (LDPE). Dans la présente étude, des combinaisons de trois composés de cire de polyéthylène (PE) de faible poids moléculaire et de trois matériaux en LDPE recyclés ont été utilisées comme agents modificateurs de l'asphalte. Les asphaltes modifiés ont été étudiés selon les spécifications MP1 et MP1a Superpave TM , des critères de contrainte de défaillance par essai en traction pure (DTT) de 1 %, la séparation des phases et la microscopie. Lorsque la répartition des poids moléculaires des agents modificateurs du polyéthylène a été élargie, la courbe de contrainte thermique du rhéomètre de flexion de poutre Bending Beam Rheometer de l'asphalte modifié s'est déplacée vers l'extrémité de basse température, donnant une meilleure température critique de fissuration. Les LDPE recyclés ne sont pas tous les mêmes. Lors de l'utilisation de LDPE recyclés dans l'asphalte modifié, nous avons dû tenir compte des propriétés des LDPE telles que le poids moléculaire et la répartition du poids moléculaire, ce qui s'est avéré jouer un rôle important dans les propriétés de l'asphalte à basse température, la stabilité d'entreposage à chaud et la répartition des phases du polymère. La présente étude montre que les LDPE ayant un poids moléculaire plus faible et une répartition plus large du poids moléculaire sont de meilleurs matériaux pour la modification de l'asphalte par rapport aux LDPE de poids moléculaire plus élevé ayant une répartition très étroite du poids moléculaire.Mots clés : superpave, LDPE, polyéthylène, asphalte, recyclé, rhéomètre à flexion de poutre (« bending beam rheometer (B...

The viability of used lubricating oil as an asphalt modifier was studied, with the enhancement of the low-temperature grade as the specific goal. Used oil modification was found to improve the Superpave low-temperature performance grade (PG), but at the expense of the high-temperature PG grade. When evaluated according to the Superpave MP1 specification, the low-temperature grade of the modified asphalt was not significantly improved due to failure of the bending beam rheometer (BBR) test’s m value. When evaluated according to the Superpave MP1a specification, the modified asphalt overall PG grade temperature spread remained essentially constant, varying only by approximately two degrees. The asphalt took as much as 12% of oil and still had less than the maximum limit of 1.0% rolling thin film oven test (RTFOT) mass loss (emissions). However, the oil may possibly have a detrimental effect on the asphalt quality, such as reduced adhesiveness to the aggregates, leading to stripping and raveling. The field performance test should be checked before considering lubricating oil as a modifier.

Waste tire crumb rubber materials (CRM) were used to modify paving asphalts. The mixing time, hot-storage stability, Superpave grades, pumping and handling properties, phase separation tests, and repeated creep properties of the modified asphalts were studied using base asphalts of different hardness. Applying the Long-Term Pavement Performance (LTPP) program and the Transportation Association of Canada (TAC) model, optimal levels of CRM and suitable base asphalts were selected for the climatic conditions of Lethbridge, Alberta, Canada. High-temperature grade bumping protocol, regarding traffic volume and speed, was also considered. With joint efforts from the Tire Recycling Management Association of Alberta (TRMA), Husky Energy, and the City of Lethbridge, three test sections in different Lethbridge locations with various traffic volumes were paved from the years 2003 to 2005. So far, the City of Lethbridge is pleased with the initial performance of the test sections.Key words: waste tire, crumb rubber materials (CRM), paving asphalt, recycled, modification, Superpave, repeated creep, field test.

The introduction of the Superpave®asphalt binder specification provided the asphalt industry with a useful guideline for choosing appropriate materials to meet the requirements of a specific climate. Acid, alkaline, and polymer modification are just some of the ways to modify asphalt to meet the Superpave specification. The direct tension test (DTT) technique was applied to study the low-temperature properties of modified asphalt in terms of DTT failure stress values and the critical cracking temperature ( Tcritical). The bending beam rheometer (BBR) usually failed to detect improvement in low-temperature performance in polymer-modified asphalt (PMA). DTT results show that elastomeric polymer modification improves the low-temperature performance of PMA. In some PMAs, the failure stress value was higher than 9.5 MPa. The DTT technique for PMA was also reviewed. The effect of acid and alkaline modifiers on asphalt materials was studied. Acid or alkaline modification of asphalt was found to be only temporary and to be reversible. Acid modification of asphalt can be reversed by reaction with alkaline materials such as lime or antistripping agents. Alkaline modification of asphalt can be reversed by reaction with acidic materials such as carbon dioxide. Alkaline also can be washed away by water. Even though the BBR suggested a slight improvement in the low-temperature performance in acid- or alkalinemodified asphalt, the DTT failure stress values and Tcritical did not confirm this improvement. A relatively simple procedure that allows detection of acid or alkaline modification of asphalt materials is described.

Asphalt binder is a mixture of many different types of molecules. At the molecular level, one can visualize the asphalt binder as a colloidal system with asphaltene molecules dispersed in oil with naphthene and polar aromatics. The functional groups of the asphaltene molecules are essential in keeping them dispersed as colloids. These polar functional groups include alcohol, amine, carboxylic, and phenolic groups. The polarity of asphalt molecules are very important in allowing them to adhere to the inorganic aggregates, which also bear charges at the surface. The application of this understanding to the aging of paving asphalt, asphalt modification, the Superpave direct tension test, aggregate specific gravity determination, ash as modifiers in asphalt, low-volume road chemical stabilization, and the oil sands industry are discussed.

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