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Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS) * at Purdue University in 1 957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dissemination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the thought that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this joint undertaking we had concluded that it was in the interest of all con cerned if the printing and distribution of the volumes were handled by an interna tional publishing house to assure improved service and broader dissemination. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Cor poration of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 36 (thesis year 1991) a total of 11,024 thesis titles from 23 Canadian and 161 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this important annual reference work. While Volume 36 reports theses submitted in 1991, on occasion, certain univer sities do report theses submitted in previous years but not reported at the time.
This project dealt with the molecular composition of asphalts and with the changes in asphalt composition that have been found to result from the inclusion of aggregate, additives, fillers and extenders in bituminous paving mixtures under normal production conditions in Montana. The method used in this project was high pressure liquid chromatography in the gel permeation mode. Changes in the molecular size distribution (MSD) of an asphalt, under carefully controlled laboratory processing, were shown to depend not only upon the specific asphalt, but also upon the aggregate, the additive, the mixing temperature and the time held at that temperature. Consequently, the MSD of the asphalt in a finished pavement cannot be predicted from the MSD of the original asphalt cement alone. A test method was developed, however, to simulate the net effect of plant mix processing, thus yielding an accurate prediction of the final MSD. In a continuing sub-study on asphalt 'aging', the molecular size characteristics of asphalts in highway pavements were shown to undergo only very minor changes after approximately two years. Earlier predictions of pavement performance, based on molecular profiles of asphalts from core samples removed soon after construction, were actually borne out in two cases that were major paving projects. Several recycling agents were shown to consist mainly of very small molecular size materials. When mixed with salvaged bituminous material, they appeared to be inadequate to compensate for, or to otherwise change, excessive amounts of large molecular size (LMS) material often found in the salvaged asphalt. In another common method of recycling, it was found that the MSD of a mixture of asphalts can be estimated from the MSDs of the individual asphalts and their proportions in the mixture. As an example, a salvaged asphalt containing an excessive amount of LMS material may be modified with a virgin soft asphalt (i.e., 200-300 penetration grade asphalt with few LMS components) so that the resulting mixture closely matches the model for high quality asphalt cement.
Gel permeation chromatography (GPC), Corbett analysis, Heithaus test and other physical and chemical tests have been used to characterize asphalts and to relate chemical properties, physical properties and performance. The asphalts used in the present study consisted of periodic samples of virgin asphalt from various suppliers to Texas in the last two years, the test pavement asphalts in Dickens, Dumas and Lufkin, Texas from study 287, and a group of asphalts which had been rated according to tenderness.
In this project the researchers studied a correlation between molecular structure and corresponding compositional analysis of asphalt binders of conventional hot mix asphalt mixtures (HMA) as well as mixtures containing reclaimed asphalt pavement (RAP) and/or recycled asphalt shingles (RAS) with their cracking potential at intermediate temperature. The molecular size and structure of asphalt components of RAP and RAS undergo large changes during their exposure to environmental factors, which affects the physical properties imparted to their mixtures with conventional asphalt liquids. The composition of the mixtures prepared using a PG 70-22M binder was ascertained using thin layer chromatograpy/FID detection (Iatroscan), gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The distribution of species by molecular mass as determined by deconvoluting gel permeation chromatographs, emphasizing in particular, the amount of asphaltenes as they are related to the age hardening of asphalt materials. The extent of sample aging is apparent from the carbonyl oxygen content from FTIR measurements of the mixtures. Fracture resistance of laboratory produced mixtures was assessed using the Semi Circular Bend Test (SCB) test procedure; a minimal value of 0.5 kJ/m2 was considered acceptable. Mixtures containing up to 5% RAS, 15% RAP and 15% RAP/5% RAS met the SCB standard. Molecular fractionation through GPC of mixtures containing RAS confirmed the presence of highly associated asphaltenes in greater concentrations than mixtures containing recycled asphalt pavement (RAP). High concentrations of high molecular weight associated asphaltenes (mol wt > 20K Daltons) which are present in RAS samples decrease the fracture resistance of the asphalt mixtures. The use of recycling agents, Cyclogen-L, Hydrogreen, Asphalt Flux and Re-refined engine oil bottoms (REOB), did not reduce the concentration of the highly associated asphaltenes, further they failed to improve the cracking resistance of the asphalt mixtures evaluated in this study. However, the recycling agents effected quantitative extraction of the RAS asphalt component.