PURPOSES : The purpose of this study is to verify the influences on the compactibility evaluation of WMA (Warm Mix Asphalt) mixture by laboratory experiments. METHODS : Two types of WMA additives (chemical and wax types) and two types of compactors (marshall and gyratory) are used in laboratory experiments. In addition, two types of WMA processes (wet and dry) are tested to verify the impact of manufacturing process. RESULTS : The laboratory results show that the effects of compaction method on compactibility are different depending on the type of additive. The compaction method has a significant impact on WMA mixture with chemical type additive to extent that it determines whether required criterion is satisfied, but only little on WMA mixture with wax type additive. In the case of wet process for WMA mixture manufacturing, it is hard to assess the air void of HMA mixture made of same asphalt binder used in WMA mixture since the additive has already been added in asphalt binder. And the test results show that air voids of HMA mixture vary within properties of asphalt binder. CONCLUSIONS : Through this study, it is found that compactibility of WMA mixture is affected by the compaction methods depending on the additive types and by the WMA mixture manufacturing process. Therefore, those are recommended to be considered when evaluating compactibility of WMA mixtures.

If asphalt-aggregate mixture is produced at a high temperature, the mixture will suffer a significant higher shortterm aging (STA) due to the elevated temperature. The binder in that mixture will be oxidized (aged) more than expected during STA due to the highly elevated temperature. The STA at the high-temperature level is one of the reasons why the hot-mix asphalt (HMA) mixture shows many distresses in the early stage of service life. In this respect, adopting warm-mix asphalt (WMA) technology is another advantage in the asphalt pavement industry. In this study, various levels of STA were used to evaluate aging levels of the binder in the mixture before and after STA. A gel-permeation chromatography (GPC) test was performed on the mixture particles without binder recovery to estimate the significance of aging for each case of STA. Statistical analyses were carried out to determine the difference in aging levels among STA temperatures. Statistical test results found that the aging level of the binder after STA was significantly higher than that of binders before STA at an α = 0.05 level. It was also found that the aging level of binders in the WMA mixture was significantly lower than that of binders in HMA after STA at an α = 0.05 level. It was observed that if an HMA mixture was produced at high-temperature STA, its aging level was estimated to be approximately four years in service.

Since warm mix asphalt (WMA) was introduced in early 2000, many of these pavements were built more than 10 years ago. Therefore, the WMA recycling research is important and necessary. However, the recycling issue of WMA has lagged behind other researches such as moisture sensitivity and long-term performance of WMA. If the aged WMA is incorporated into the asphalt mixes, the mixing and compaction temperatures of the mixtures are expected to decrease by the warm additives. The effect of warm additive after in-service period needs to be evaluated to see if the aged WMA can be used in asphalt pavements. The main objective of this study was to evaluate the properties of recycled asphalt binders containing long-term aged (LTA) WMA binders through Superpave asphalt binder tests. The WMA binders were manufactured with two wax additives, LEADCAP and Sasobit, and artificially aged using rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. The aged WMA binders were recycled at 15% and 30%. The viscosity properties for the binders in the original state, the rutting properties in the original state and after RTFO aging, the fatigue cracking properties at intermediate temperature after RTFO+PAV aging methods, and the low temperature cracking properties after RTFO+PAV procedures were evaluated. The following conclusions were drawn for the materials used in this study: (1) Although the addition of LTA into virgin binder increased the binder’s viscosity, the binders containing wax additives had significantly lower viscosities compared with the unmodified binders at all recycling content (0, 15, and 30%). (2) Even though the binder with wax experienced the aging processes, the wax additive within recycled binder was effective to decrease the binder viscosity at almost the same degree, provided with the actual amount of wax in recycled binders. (3) The binders containing wax additive had higher G*/sin δvalues than control binders at each recycling content. It means that the wax additive still plays an important role in increasing rutting resistance, even though the additive was aged within asphalt binder. (4) From the DSR test at intermediate temperature, it appears that the higher recycling content seemed to have negative effects on resistance to fatigue cracking, regardless of the wax additive. (5) The recycled WMA binders at 30% recycling content were observed to have significantly lower resistance on low temperature cracking (measured by the BBR test). It is recommended that the WMA be recycled in a lower contents in cold regions.

PURPOSES: This research is to evaluate the mechanical performance of different types of Hot Mix Asphalt (HMA) pavement cells prepared for MN/Road field testing section through an extensive experimental analysis of air voids and simple statistical evaluation tools (i.e. hypothesis test). METHODS: An extensive experimental work was performed to measure air voids in 82 asphalt mixture cores (238 samples in total) obtained from nine different types of road cell located in MN/Road testing field. In order to numerically and quantitatively address the differences in air voids among the different test Cells built in MN/Road, a simple statistical test method (i.e. t-test) with 5% significance was used. RESULTS: Similar trends in air voids content were found among the mixtures including conventional HMA, Reclaimed Asphalt Pavement (RAP) and Warm Mix Asphalt (WMA) combined with taconite aggregate this provides support to the use of RAP and WMA technology in the constructions of asphalt pavement. However, in case of acid modified HMA mixtures, significant differences in air void content were observed between on the wheel path and between wheel path location, which implies negative performances in rutting and thermal cracking resistances. Conclusions : It can be concluded that use of RAP and WMA technology in the construction of conventional asphalt pavement and the use of PPA (Poly Phosphoric Acid) in combinations with SBS (Styrene Butadiene Styrene) in asphalt binder production provide satisfactory performance and, therefore, are highly recommended

PURPOSES : This study is to develop a method to evaluate lubrication of asphalt binder using WMA additives and compare their lubrication effects on two types of WMA additives and three types of asphalt film thicknesses. METHODS : This study is based on laboratory experiments and rheological analysis of the experimental results. Testing materials are aggregate diskes, asphalt, and WMA additives. The main testing method is stress sweep test by using dynamic shear rheometer (DSR). RESULTS : Sasobit gives more lubrication effects on film thicknesses 0.2mm and under but LEADCAP does on film thicknesses over 0.3mm. CONCLUSIONS : LVE-Limit is a better parameter to discern the lubrication effects on the thin film asphalt thickness. Both Sasobit and LEADCAP WMA additives provide effective lubrication at the compaction temperature.

PURPOSES : This study is to develop a method to evaluate the compaction effects of asphalt binders using WMA additives and compare their compaction effects on two types of WMA additives, two types of testing temperatures, and three types of asphalt film thicknesses. METHODS : This study is based on laboratory experiments and rheological analysis of the experimental results. Testing materials are aggregate disks, asphalt, and WMA additives. The main testing method is the stress sweep test by using dynamic shear rheometer (DSR). In addition, the testing parameters obtained from the stress sweep results to evaluate lubrication effects are complex modulus and LVE-Limit. RESULTS : At both the first compaction condition (110℃, 0.3mm) and second compaction condition (80℃, 0.2mm) assumed, LEADCAP showed better compaction effects than Sasobit. CONCLUSIONS : The temperature 30℃ lower than general compaction temperatures can provide a better sensitivity for the evaluation of compaction effects. If a testing temperature and film thickness are grouped for the proper compaction conditions in the testing results, the compaction performance of each WMA additive can be more clearly discriminated in the grouped testing results matched with the grouped conditions.

PURPOSES : Hot-mix asphalt(HMA) concretes show a trend of strength increase at low temperature due to binder stiffness increase, but strength decrease below a ceratin low temperature. This is due to the differential thermal contraction(DTC) which is induced by a significant difference in coefficients of thermal contraction between aggregate and asphalt which is coated around the aggregate. This DTC damage is well known to occur in HMA concrete, but is not yet investigated in warm-mix asphalt(WMA) concretes. METHODS : To evaluate DTC damage on WMA in this study, the flexural strength(Sf) of WMA concretes, which were produced at 30~40℃ lower temperature, was evaluated in comparison with that of HMA at -5, -15 and -25℃. RESULTS : Most of WMA and HMA mixtures showed flexural strength increase down to -15℃ and decrease below -15℃. this type of strength reduction below -15℃ can e explained as the effect of differential thermal contraction that is a consequence of the large difference in coefficients of thermal contraction between aggregate and asphalt. the property reduction of WMA is similar the result of previous works dealt with HMA mixtures. CONCLUSIONS : Even though there is some differences by materials used, the WMA concretes showed a significantly lower DTC damage than HMA concrete at low temperature at α=0.05 level.

본 연구에서는 국토해양부 기준으로 제시된 선회 다짐횟수를 가열아스팔트 혼합물과 중온아스팔트 혼합물을 이용하여 검증하는데 그 목적이 있다. 다짐횟수 검증을 위하여 굵은골재최대치수 13mm와 19mm 1등급 골재와 가열아스팔트 혼합물용 PG64-22와 PG76-22, 중온아스팔트 혼합물용 PG70-22 아스팔트를 사용하였다. 또한, 각각의 바인더 별로 권장 다짐온도를 기준으로 4가지 온도에서 선회다짐 100회와 마샬다짐 75회의 다짐량을 비교하였다. 두 다짐기를 공극률 상으로 평가할 때 전반적으로는 선회다짐기의 다짐이 다소 더 잘 되었다. 공극률에 대한 분산분석 결과 두 다짐기 사이에 19mm 혼합물에서는 통계적 유의차가 나타났고 13mm의 경우 유의차가 나타나지 않았다. 특히 일정 다짐온도 이하에서 다졌을 경우 두 다짐기 모두 다짐이 불량하여 다짐온도를 확보하여 다짐하는 것이 매우 중요한 것으로 나타났다. 따라서, "가열 아스팔트 혼합물의 생산 및 시공"에서 제시한 선회 다짐횟수 100회는 지침에서 제시한 아스팔트 혼합물의 다짐온도를 준수한다면 마샬다짐기 양면 75회 다짐과 유사하거나 다소 좋은 다짐 량을 나타내는 것을 알 수 있었다.