PURPOSES : This study was performed to evaluate the short-term aging (SA) protocols of the normal hot-mix asphalt (HMA) mixture, to explore problems, and to suggest proper procedures based on fundamental principles of SA in terms of the SA temperature (T) and length of time (Lt) in existing specifications in several countries including Korea. METHODS : As the SA in our lab is a simulation of field SA, which is an inevitable procedure occurring naturally in the current field practice, major SA guidelines of foreign countries and Korea were reviewed to investigate problems that showed discrepancies with field practice. The aging quantity (Aq) model was introduced as a function of T and Lt, based on the correlation with absolute viscosity (AV) to estimate Aq by T and Lt. The normal SA (NSA) was suggested through an example procedure inducing binder aging level similar to the RTFOtreated binder AV or Aq. Based on the NSA Aq level, lower, proper, or higher SA conditions were discovered from the existing SA guidelines. RESULTS : As Aq has excellent correlation with AV, the proper T and Lt for NSA as an example was suggested based on the AV of RTFOtreated binder to induce an Aq range of 19,000-25,000 min.℃. It was found that there were several problems in the existing guidelines in USA and Korea. These included lower T, shorter or longer Lt, and air blowing or stirring the mix during SA, which were not matched with the practical condition of loaded HMA mixtures that were short-term aged under hot temperatures in trucks. CONCLUSIONS : It was concluded that there are several problems in the current SA guidelines, which do not provide proper HMA temperature to mixtures for proper (modal) length of time. Therefore, these guidelines should be reevaluated carefully and revised based on the fundamental field SA principle. The NSA condition should be suggested using proper HMA T and modal Lt for better simulation of field SA practice.

PURPOSES: The objective of this study was to investigate the effect of short-term aging level on the moisture resistance of a dense-graded asphalt mixture by measuring its deformation strength ratio (SDR). METHODS : Three short-term aging (STA) durations (1, 2, and 4 h) at two different temperatures (160℃ and 180℃) were used for the normal dense-graded hot-mix asphalt (HMA) mixtures prepared using PG 64-22 asphalt and 13mm aggregate with and without hydrated lime (HL). The specimens were prepared using a gyratory compactor, after each STA, to achieve a WC-1 gradation as defined by the Korean guide. The SDR was measured after freezing-and-thawing (F-T) conditioning, and submerging the specimen into water at 60℃ for 72 h. RESULTS: The results indicated that the moisture resistance decreased with the increase in STA duration. After STA at 160℃ and 180℃, the SDR values, measured after F-T treatment, or after submerging into 60℃ water for 72 h, decreased with the increase in STA duration. However, when HL was used in the same asphalt mixtures, the SDR improved, for identical STA conditions. Therefore, the moisture resistance of the asphalt mixture was affected by the short-term aging duration, and decreased with the increase in aging duration. However, HL effectively retarded aging, and the moisture resistance, as indicated by the SDR, improved in the HL-added mixes, which had aged lesser than the normal mixes. CONCLUSIONS : It was concluded that the moisture resistance of the asphalt mixture decreased with the increase in aging level, and hydrated lime was effective in preventing the degradation of the moisture resistance by reducing the age-hardening of the binder. However, since this study used a limited range of materials, further studies using more materials are required to reach a more generalized conclusion.

It is well known fact that the filed asphalt mixture is aged in the truck while hauling and queuing for one to four hours before dumping to the hopper of the paver. This aging, which is called short-term aging (STA), affect the physical and mechanical properties of asphalt mixture. For example, the maximum theoretical density of mixture is changed before and after STA. Therefore, when the asphalt mixture specimen is prepared for testing various physical and mechanical properties in laboratory, the mixture should be STA conditioned by a most-likely STA condition of the field. This is the reason why the STA should be performed properly. This study initiated to investigate STA conditioning protocols, set forth many agencies in the world, and to suggest a proper STA protocol which simulates field HMA condition as most likely as possible. According to this study, it was suggested that the blended loose mix for one specimen poured in a canister should be kept in a drying oven (no forced draft) without cap at 163±2℃ and for 70±15 min for normal HMA mix. This protocol was suggested based on that the absolute viscosity level of the recovered binder after STA should be a similar level of the same binder after a standard RTFO run.

PURPOSES: This study aims to show the difference of the binder aging level in the hot-mix asphalt (HMA) mixture after short-term aging (SA) under different aging conditions, such as mixture temperature and duration in hour. METHODS: Three SA times (i.e., 1 h, 2 h, and 4 h) at two temperatures (i.e., 160℃ and 180℃) were used for the normal mixtures prepared using a PG64-22 asphalt. The field long-term aging (LA) was simulated by applying the same LA procedure (65 h at 110℃) to all compacted specimens, prepared at the air void of 7% using each SA-treated mixture, in a convection oven. The binder aging level was measured in terms of large molecular size by gel-permeation chromatography (GPC) from the mixture and the absolute viscosity (AV) from the recovered binder. The aging levels were evaluated using those two properties after SA and LA, and then compared based on the normal SA (NSA) mixture (1 h at 160℃). The service life reduction caused by SA in various conditions was estimated based on the aging level of the field cores from different locations in various service lives. RESULTS: The results of the laboratory evaluation indicated that the binder of the mixture, which was treated at longer SA time and higher temperature, showed a significantly higher aging level than the NSA mixture. The binder aging level from a longer time, such as 2 h and 4 h SA, or at a higher temperature (180℃), were estimated to be similar to that of the mixtures, which had already been in field service for several years. CONCLUSIONS : The HMA mixture should be produced at a moderate temperature, such as 160℃, and placed within a limited hauling and queuing time to avoid a significant short-term aging of the binder before placement in the field pavement. The SA for a longer time at a higher temperature than the NSA condition was found to be detrimental to the service life of the asphalt pavement.

The effect of hydrated lime (HL) as an antioxidant (AO) for retarding aging of asphalt mixture using the large molecular size (LMS) of gel-permeation chromatogram (GPC) technique. A HL were used for preparing dense-graded asphalt (DGA) mixes to examine the effect of the HL on age retardation. The asphalt mixtures prepared with and without HL were aged artificially in two stages; the short-term aging (SA) for 1, 2, 4 hour at 160℃ and 180℃ on the loose mixes, and the long-term aging (LA) for 68 hours at 110℃ on the specimen. The specimen ( =100mm) of SA-treated mix was compacted to the air void of 7% using a gyratory compactor. The LMS values were used for estimating absolute viscosity (AV) for evaluating aging level and age- retardation effect in terms of viscosity. It was observed that the asphalt mixes which were short-term aged at 180℃ for over 2 hours were significantly aged, compared with the mix which was short-term aged for 1 hour at 160℃. It was also found that the use of 1.5% HL by wt. of mix resulted in a significant reduction of binder aging of SA and LA treated mixes. It was concluded that the HL did apparently have an effect of reducing aging of asphalt in the mixes after SA and LA. This result will be an applicable information for retarding aging of the field HMA mixture which is carried in the dump truck at hot temperature for 2-4 hours.