A review of recently published literature indicates that changes in asphalts are of considerable concern to those responsible for designing, constructing, and managing pavements. Data indicate that the ranges of properties of asphalts have not changed significantly, but recent world petroleum supply and economic climate may have caused more rapid changes in asphalt from certain sources. New refining or manufacturing techniques may also affect asphalt properties, but these causes probably account for a smaller portion of reported changes than variations in feedstocks that are primarily petroleum crude oils. There appears to have been a statistically significant but small change to a population of more temperaturesusceptible asphalts, which may have been a result of specification changes and greater use of high smoke point asphalts (that may generally have higher temperature susceptibilities) with the use of increased mixing temperatures in drum mixers. Preferred methods of measuring low temperature performance are through the use of low temperature consistency measurements. Chemical analyses reported to date have not correlated well with performance because of the complex nature of asphalts. The changes in asphalt properties with use of antistripping additives is discussed and some factors affecting paving construction and pavement performance, which may be perceived as changes in asphalts, are listed.

Do asphalts really change? This probably depends on what is perceived as the material called asphalt. To the extent that most asphalts are sold to meet an accepted specification, it might be said that asphalts do not change, only specifications change. However, to the contractor, engineer, supervisor, or laborer responsible for constructing an asphalt concrete pavement, the mixture does change. This mixture of about 95 percent aggregate and 5 percent asphalt does have different behaviors at times, and, because the mixture is generally black in appearance, it might appear logical to say that the asphalt has changed. Not only are the persons responsible for constructing the pavement concerned about possible changes in asphalts, but the persons responsible for the management of the pavements are concerned that these reported changes in asphalts may have some harmful effect on the pavement's performance. The literature abounds with articles on this subject of changes in asphalts and also confirms the significance of the subject to the industry.