PURPOSES: The object of this study is to select appropriate inorganic materials, and find the best mixing formula to secure fast curing time and enough initial strength, and then to evaluate the durability of the asphalt mixtures according to the degree of addition of the compound manufactured by the determined blending ratio. METHODS : The breaking time and reactivity between seven kinds of inorganic minerals, and the selected recycled aggregate and emulsified asphalt were compared to determine the best initial curing strength for the mixtures. Then, three inorganic materials were chosen as the materials that provide good breaking time and reactivity, and the best mixing formula for the three materials was determined. The chemical composition of the compound manufactured using the mixing formula was analyzed by energy dispersive x-ray system method. Finally, indirect tensile strength (ITS) test was performed (for two days) at room temperature to determine the proper amount of additives that will provide the best initial strength. RESULTS: From the results of the reactivity test, the best mixing formula (A:C:G = 60:30:10) for the three selected inorganic materials with short braking time and high reactivity was determined. The four types of cold reclaimed asphalt mixtures for ITS testing were manufactured by adding the inorganic material compounds at 0%, 3%, 5%, and 7%, and the ITS values were measured after two curing days. The ITS values at 5% and 7% were 0.308 MPa and 0.415 MPa, respectively. The results of quality control tests (Marshall stability, porosity, flow value, etc.) at 5% and 7% satisfied the specification criterion for the cold recycled asphalt mixtures. CONCLUSIONS : The selected inorganic materials (A, C, and G) and the best mixing formula (A:C:G = 60:30:10) accelerated the reaction with emulsified asphalt and shortened the curing time. Depending on the inorganic material used, the breaking time and reactivity can be directly related or unrelated. This is because of the chemical compositions of recycled aggregates, infiltrated foreign matter, and chemical reactions between the inorganic materials and other materials. Therefore, it is important to select the proper materials and the best mixing formula when evaluating the characteristics of the practically used materials such as recycled aggregates, inorganic materials, and emulsified asphalt.

PURPOSES : The purpose of this study is to examine the manufacturing method for emulsified asphalt and its bond performance by analyzing the properties of the emulsifier used to produce cold recycled asphalt mixtures. METHODS: In this study, four types of slow-setting cationic emulsifiers, a microsurfacing emulsifier, and six types of nonionic emulsifiers were used to manufacture emulsified asphalt. Because each emulsifier requires its own unique effective dose to provide the best performance, the optimum asphalt content for each effective dose was determined. Then, the optimum asphalt content for the emulsified asphalt mixture was determined by the tests to check its basic physical properties. By using the determined optimum content, asphalt mixtures were manufactured and dynamic immersion and tensile strength tests were conducted on the mixtures to analyze the influence of the emulsifier on the physical properties of the mixtures. RESULTS : The dynamic immersion test results showed a coating ratio of 54-85%, which is considerably higher than that of using ordinary straight asphalt. The tensile strength test yielded noncompliant values less than 0.4 N/mm, which is the standard requirement for dry indirect tensile strength. The correlation analysis between the dynamic immersion and tensile strength ratio tests showed very high correlation of 0.78. The correlation between the emulsifier content and water resistance performance was low, between -0.55 and -0.24. CONCLUSIONS : While the storage stability improves with increasing emulsifier, the effectiveness proportional to the increase is weaker as the emulsifier increases. The performance testing of asphalt residues before and after manufacturing the emulsified asphalt showed no significant change. It is proved that the emulsified asphalt maintains high coating resistance according to the dynamic immersion test results. In addition, according to the results of tensile strength ratio, cold recycled asphalt mixtures manufactured by the materials normally and commercially used are not compliant with the national standard specification; thus, additional effective materials will be needed for quality compliance. In conclusion, it is evident that the dynamic immersion and tensile strength ratio tests have good correlation, but the quantity of emulsifiers used is not related to the level of moisture resistance.

PURPOSES: Using recyclable materials in asphalt pavement industry is one of the essential tasks not only for saving construction budgets but also for mitigating environmental pollutions. Over the past decades, several efforts have been made by road maintenance agencies to incorporate various recyclable materials into virgin asphalt paving mixtures. As a result, reclaimed asphalt pavement (RAP), which consists of old pavement material was selected as one of most widely used recyclable materials. In this paper, the effects of using different amounts of single-recycled RAP (SRRAP) and double-recycled RAP (DRRAP) on the low-temperature characteristics of asphalt mixtures were investigated. METHODS: To evaluate the low-temperature characteristics of SRRAP and DRRAP mixtures, two experiments, the bending beam mixture creep test and semicircular bending fracture test were performed. The experimental parameters: creep stiffness, m-value, thermal stress, critical cracking temperature, fracture energy, and fracture toughness were computed then compared. RESULTS : RAP mixtures (SRRAP or DRRAP) showed lower mechanical performance compared with conventional asphalt mixtures. The differences became distinct with increased RAP addition. However, the performance differences between SRRAP and DRRAP mixtures were not significant in all cases, which indicate the possible application of re-recycling technology (DRRAP) in the asphalt pavement industry. CONCLUSIONS : The addition of RAP to virgin asphalt can mitigate low-temperature performance despite the improvement in fracture performance observed in some cases. Therefore, using RAP (SRRAP or DRRAP) mixtures on inter or sublayer construction, but not on the surface layer, is recommended. Moreover, the possibility of applying double-recycling technology in asphalt pavement industry can be introduced in this study because not significant performance differences were found between SRRAP and DRRAP mixtures especially at low temperature.

PURPOSES: Using recycled asphalt materials (called Reclaimed Asphalt Pavement: RAP) from existing asphalt pavement layers in newly constructed asphalt pavement is an essential option not only for lowering the construction budget but also for mitigating environmental pollution for society. For this reason, many pavement agencies in South Korea, the USA, and Canada have observed the effect of RAP on conventional asphalt pavement to evaluate and set proper material specifications and addable amounts. In this paper, effect of recyclable material on low-temperature performance of asphalt materials was investigated with two different mechanical tests. Among the recyclable material sources, RAP and Taconite Aggregate (TA), which is mainly produced in northern Minnesota (USA), were considered. METHODS : To evaluate the low-temperature mechanical performance of a RAP mixture, two different experimental tests (In-Direct Tensile (IDT) low temperature creep test and Semi-Circular Bending (SCB) test) were considered. The mechanical parameters creep-stiffness, relaxation modulus, fracture energy, and fracture toughness were computed then compared. RESULTS: More brittle characteristics were observed with RAP-added asphalt mixtures compared to the conventional asphalt mixtures, as expected. However, the differences of computed mechanical performances were not significantly distinct for RAP mixtures compared to conventional mixtures when the RAP proportion was around 20%, and with the addition of TA up to 20%. CONCLUSIONS : It can be concluded that up to 20% of RAP addition (along with TA up to 20%) in a virgin asphalt mixture does not provide significant performance reduction. This addable proportion can be viewed as a successful minimum level when considering the addition of RAP to hot-mix asphalt (HMA). Moreover, applying TA with RAP could offer a successful alternative for asphalt recycling and the materials industry.

PURPOSES: The objective of this study is to evaluate the physical properties of recycled asphalt mixtures reinforced with glass fiber. METHODS: Firstly, mixing design was conducted on recycled asphalt mixture for use of 50% recycled aggregate. Various laboratory tests were performed on four types of recycled asphalt mixtures with different glass fiber content to evaluate the physical properties. The laboratory tests include indirect tensile strength test, dynamic modulus test, Hamburg wheel tracking test and tensile-strength ratio to evaluate cracks, rutting and moisture resistance of mixtures. RESULTS: The indirect tensile strength of fiber reinforced glass increased about 139.4%. As a result of comparing the master curves obtained by the dynamic modulus test, the elasticity was low in the low temperature region and high in the high temperature region when the glass fiber was reinforced. The glass fiber contents of PEGS 0.3%, Micro PPGF 0.1% and Macro PPGF 0.3% showed the highest moisture resistance and rutting resistance. CONCLUSIONS : The test results show that use of glass fiber reinforcement can increase the resistance to cracking, rutting, and moisture damage of asphalt mixtures. It is also necessary to validate the long-term performance of recycled asphalt mixtures with glass fiber using full scale pavement testing and field trial construction.

PURPOSES: In order to apply high-speed weigh-in-motion (HS WIM) systems to asphalt pavement, three high-durability asphalt concrete mixtures installed with a WIM epoxy are evaluated. METHODS: In this study, dynamic stability, number of loading repetitions to reach the rut depth of 1 mm, and rut depth measurements of three asphalt mixtures at 60℃ were compared using an Asphalt Pavement Analyzer (APA). Laboratory-fabricated material and field core samples were prepared and tested according to KS F2374. RESULTS : Through the laboratory tests, it was found that all three modified asphalt mixtures (stone-mastic, porous, and semi-rigid) with WIM epoxy showed favorable permanent deformation results and passed the dynamic stability criterion of 3000 loading repetitions per 1 mm. In addition, it was confirmed that the modified SMA mixtures cored from the field construction yields satisfactory rutting testing results using the APA. Finally, the epoxy used for the HS WIM installation shows good adhesion with the three asphalt mixtures and permanent deformation resistance.

PURPOSES : Asphalt concrete pavement is damaged by various causes such as traffic and environmental loads. The distressed pavement should be maintained by various methods to provide a comfortable and safe pavement for the driver. This study evaluates the effect of adding a mixing procedure to enhance the mixture quality in the hot in-placement recycled asphalt pavement method, which is an asphalt-pavement maintenance method. METHODS: Various test methods such as Marshall stability and dynamic stability, were employed to estimate the recycled asphalt mixture with and without an additional mixing, using the hot in-placement recycled asphalt pavement method. RESULTS : The mixture samples used in this study were taken before and after the addition of the mixer in the hot in-placement recycled asphalt pavement method (HIR) at field construction sites in GongJu and JinJu in South Korea. The test results of both mixtures satisfied the asphalt-mixture standard specifications. CONCLUSIONS: This study confirmed that adding a mixer in the HIR method results in a well-mixed new asphalt mixture, rejuvenator, and reclaimed asphalt mixture.

PURPOSES: The purpose of this study is to evaluate the mechanical properties of a cold-recycling asphalt mixture used as a base layer and to determine the optimum emulsified-asphalt content for ensuring the mixture’s performance. METHODS: The physical properties (storage stability, mixability, and workability) of three types of asphalt emulsion (CMS-1h, CSS-1h, and CSS-1hp) were evaluated using the rotational viscosity test. Asphalt emulsion residues, prepared according to the ASTM D 7497-09 standard, were evaluated for their rheological properties, including the G*/sinδand the dynamic shear modulus (|G*|). In addition, the Marshall stability, indirect tensile strength, and tensile-strength ratio (TSR) were evaluated for the cold-recycling asphalt mixtures fabricated according to the type and contents of the emulsified asphalt. RESULTS: The CSS-1hp was found to be superior to the other two types in terms of storage stability, mixability, and workability, and its G*/sinδ value at high temperatures was higher than that of the other two types. From the dynamic shear modulus test, the CSS-1hp was also found to be superior to the other two types, with respect to low-temperature cracking and rutting resistance. The mixture test indicated that the indirect tensile strength and TSR increased with the increasing emulsified-asphalt content. However, the mixtures with one-percent emulsified-asphalt content did not meet the national specification in terms of the aggregate coverage (over 50%) and the indirect tensile strength (more than 0.4 MPa). CONCLUSIONS : The emulsified-asphalt performance varied greatly, depending on the type of base material and modifying additives; therefore, it is considered that this will have a great effect on the performance of the cold-recycling asphalt pavement. As the emulsified-asphalt content increased, the strength change was significant. Therefore, it is desirable to apply the strength properties as a factor for determining the optimum emulsified-asphalt content in the mix design. The 1% emulsified-asphalt content did not satisfy the strength and aggregate coverage criteria suggested by national standards. Therefore, the minimum emulsified-asphalt content should be specified to secure the performance.

PURPOSES : The purpose of this study is to estimate the optimum content of an inorganic additive for cold-recycled asphalt mixtures and evaluate its performance. METHODS: An indirect tensile test, a tensile-strength ratio test, and an indirect tensile-fatigue test were conducted on cold-recycling asphalt mixtures with various additives. RESULTS: The laboratory performance tests indicated that granulated blast-furnace slag mixed with inorganic and cement activators provided optimum performance. The performance results of the cold-recycled asphalt pavement were similar to the inorganic and cement activators’ performance in terms of the indirect tensile strength, tensile strength ratio, and indirect tensile-fatigue test. CONCLUSIONS : Overall, the performance of a cold-recycled asphalt mixture using inorganic additives and emulsion asphalt was comparable to a warm-recycled asphalt mixture. However, more experiments aimed at improving its performance and studying the effect of the inorganic additives must be conducted.

PURPOSES: The main distress of asphalt pavements in monsoon climate regions are caused by water damage and plastic deformation due to repeated rain season and increased heavy vehicle traffic volume. In this study, the mechanical properties of polymer-modified warm mix asphalt (PWMA) materials are evaluated to use in monsoon climate regions such as Indonesia. METHODS: Comprehensive laboratory tests are conducted to evaluate moisture resistance and permanent deformation resistance for three different asphalt mixtures such as the Indonesian conventional hot-mix asphalt (HMA) mixture, the polymer-modified asphalt mixture, and the polymer-modified warm mix asphalt (PWMA) mixture. Dynamic immersion test and indirect tensile strength ratio test are performed to evaluate moisture resistance. The wheel tracking test is performed to evaluate rutting resistance. Additionally, the Hamburg wheel tracking test is performed to evaluate rutting and moisture resistances simultaneously. RESULTS: The dynamic immersion test results indicate that the PWMA mixture shows the highest resistance to moisture. The indirect tensile strength ratio test indicates that TSR values of PWMA mixture, Indonesian PMA mixture, and Indonesian HMA mixture show 87.2%, 84.1%, and 67.9%, respectively. The wheel tracking test results indicate that the PWMA mixture is found to be more resistant to plastic deformation than the Indonesian PMA. The dynamic stability values are 2,739 times/mm and 3,150 times/mm, respectively. Moreover, the Hamburg wheel tracking test results indicate that PWMA mixture is more resistant to plastic deformation than Indonesian PMA and HMA mixtures. CONCLUSIONS: Based on limited laboratory test results, it is concluded that rutting resistance and moisture susceptibility of the PWMA mixture is superior to Indonesian HMA and Indonesian PMA mixtures. It is postulated that PWMA mixture would be suitable for climate and traffic conditions in Indonesia.

This study evaluates the healing performance of asphaltmixture via microwaves heating method. Three different conductive additive types with various percentages were used, includingsteel wool fibers (SF), carbon fibers (CF), and graphite (G). The healing performance of asphalt mixture wasinvestigated through 10 damage-heal cycles of semi-circular samples using three-point bending test. The infraredcamera was also employed to recordthe heat transmitting in the test samples. The test results indicated that the healing effectiveness reduced after every healing cycles. It was found that microwave radiation provided great healing performance for almost all test samples. Among all types of conductive additives, SF mixtures achieved the highest healing performance with the healing level of higher than 50 percent after 10 cycles. However, microwaves heating may promote the faster aging of asphalt binder at late cycles which lead to the brittle behavior of samples. Finally, homogenous mixing is a critical factor to avoid the cluster formation of conductive additives which causes the overheating of asphalt binder.

이상기후의 원인으로 주목되는 온실가스 배출 억제를 위하여 세계 각 국가들은 1992년 유엔기후변화협약 발효, 2005년 교토의정서 발효, 2015년 파리기후협약을 체결하였다. 온실가스 배출 저감을 위한 각종 협약에 따라 우리나라는 2008년부터 2020년까지 온실가스 감축목표를 30%로 설정하였다. 국내의 경우 2016년을 기준으로 생산된 아스팔트 콘크리트는 약 2,300만톤이며, 이중 재활용 아스팔트 혼합물로 재사용된 양은 약 187만톤으로 전체 생산량 대비 약 8.1%에 불과하다. 국내 아스팔트 플랜트 504개 중 208개가 재활용 아스팔트 플랜트로 인증, 운영되고 있으며 추후 사회적, 기술적, 제도적인 변화를 통하여 재활용 아스팔트 혼합물의 사용량이 증가될 것으로 기대된다. 현재 상온 재활용 아스팔트 혼합물은 대부분 시멘트를 첨가하여 생산하고 있다. 시멘트를 첨가제로 사용할 경우 저렴하고 높은 강도를 발현할 수 있지만 시멘트 생산 및 운반과정에서 다량의 이산화탄소가 발생하고 높은 시멘트 사용률로 포장의 조기 균열 발생과 장시간 양생이 필요함에 따라 조기 교통개방이 불가능한 문제점이 발생하고 있다. 따라서 상온 재활용 아스팔트 혼합물 생산 및 시공과정에서 폐 아스팔트의 재사용 및 온실가스 배출 저감에 따른 경제적 효과와 함께 양생시간의 단축과 조기강도 발현을 위한 무기질 첨가제의 연구가 필요하다. 본 연구는 상온 재활용 아스팔트에 적용하는 첨가제를 개발하기 위해 무시멘트와 무기질 첨가제를 적용한 2가지 혼합물을 중온 재활용 아스팔트 혼합물의 실내 공용성 시험 결과와 비교평가 하였다. 실내 공용성 시험을 위하여 선회다짐기와 마샬다짐기를 이용하여 시편을 제작하였으며, 공극률, 간접인장강도, 수분저항성(TSR)시험, 동탄성계수, 피로시험 등의 실내 공용성 평가를 진행하였다. 동탄성계수 시험은 아스팔트 혼합물의 거동과 재료의 특성을 분석하기 위한 시험으로 5개의 온도조건(-10, 5, 20, 40, 54℃)과 6개의 하중 주기(0.1, 0.5, 1, 5, 10, 20Hz)를 통하여 혼합물의 E 와 Master Curve를 도출하였으며, 피로 시험은 10Hz의 사인파 응력을 20℃의 조건에서 시험을 수행하였다. 간접인장강도와 수분저항성(TSR) 시험은 KS F 2398를 준수하여 수행하였다. 상온 재활용 아스팔트는 혼합할 때 물을 사용하여 다짐을 하기 때문에 양생과정 중 수분증발로 추가 공극이 발생한다. 따라서 KS F 2398에 명시된 7±0.5%를 맞추어 수분저항성 시험을 진행하기에는 어려움이 있으므로 시편 공극률의 70∼80% 사이로 수분처리 후 실험을 실시하였다.

온실가스 배출 등으로 인한 지구 온난화, 이상기후 현상 등이 발생함에 따라 온실가스를 줄이기 위한 운동이 범세계적으로 확산되었다. 이 운동에 일조하기 위해 우리나라에서는 ‘저탄소 녹생성장 기본법’, ‘건설폐기물의 재활용촉진에 관한 법률’을 시행하였고, 우리나라 전체 온실가스 배출량의 16%를 차지하고 있는 도로분야에서는 지속 가능한 친환경 도로포장 기술의 개발이 진행되고 있다. 또한, 국토교통부는 “순환골재 및 순환골재 재활용제품의 의무사용에 관한 고시”를 개정 예정이며, 그 내용은 다음과 같다. 도로포장 공사구간이 1km 이상 또는 포장 면적이 9,000m2 이상인 신설 또는 확장공사의 도로, 단지, 주차장 등에 순환골재를 40%이상 의무사용 해야 하며, 향후 순환골재 의무사용 대상이 기존의 신설·확장공사뿐만 아니라 유지·관리공사를 포함하는 방향으로 확대될 예정이다. 아스팔트 콘크리트 분야에서 온실가스 배출 저감을 위한 방법으로는 순환골재 사용과 중온 아스팔트 혼합물 사용 등이 있다. 중온 아스팔트 혼합물은 가열 일반 아스팔트 혼합물 대비 생산 및 시공온도를 약 30℃ 이상 낮춰 탄소저감 효과를 볼 수 있는 혼합물을 말하며, 이 때 사용하는 첨가제를 중온 첨가제라 한다. 또한, 재생 첨가제란 재활용 아스팔트 혼합물 생산시 폐아스팔트 바인더의 물리·화학적 성질을 신규 아스팔트 바인더와 유사하게 회복시킬 수 있는 기능을 가진 첨가제를 말한다. 본 연구에서는 가열 일반 아스팔트 혼합물과 중온 일반 및 중온 재활용 아스팔트 혼합물의 실내 시험 결과를 비교하였다. 중온 일반 및 중온 재활용 아스팔트 혼합물의 실내 공용성 평가를 위해 다짐도, 동탄성계수, 피로 시험, 휠 트레킹, 수분저항성, 동적수침 시험을 수행하였다. 가열 아스팔트 혼합물 간 공용성 비교·평가시에는 동일한 공극률의 시편을 제작하여 시험을 실시하지만, 중온 혼합물의 경우에는 가열 아스팔트 혼합물과 비교해 다짐특성이 다르기 때문에 동일한 공극률에서 공용성을 비교하기에는 무리가 따른다. 다짐도, 동탄성계수, 피로 시험의 경우 현장에서 동일한 다짐 에너지를 적용한다는 가정하에 실내 시험시 선회다짐기를 사용하여 동일한 다짐 에너지로 시편을 제작하였다. 표층용 중온 재활용 혼합물의 공극률이 4%가 되게 하는 선회다짐 횟수를 기준으로 삼는 경우 중온 일반 혼합물의 공극률이 너무 작아 실내 시험 결과 비교에 문제가 있을 것이라고 판단되어 중온 일반 혼합물의 공극률이 4%가 되는 선회다짐 횟수(55회)를 기준으로 표층용 아스팔트 혼합물을 제작하였고, 기층용 혼합물의 경우 가열 일반 혼합물은 50회, 중온 재활용 혼합물은 44회를 적용하였다. 가열 일반 혼합물에 44회의 선회다짐을 한 시편의 경우 공극률이 너무 높아 시험을 진행할 수 없어 다짐횟수를 50회로 증가하였다.

국내 법적 기준에 따라 2016년부터 거의 모든 도로 포장에 아스팔트 혼합물 물량의 40% 이상을 재활용 아스팔트 혼합물로 사용하게 되었다. 이에 따라 폐아스팔트 콘크리트를 이용한 재활용 아스팔트 혼합물의 품질확보가 중요한 이슈로 부각되고 있다. 아스팔트 콘크리트 포장은 아스팔트 플랜트에서 아스팔트 혼합물이 생산되어 현장에 시공된 후 공용 중에 환경하중, 교통하중 등에 의하여 물성이 변화되고, 누적된 피로에 의해 결국은 파손에 이르게 된다. 이에 따라 도로에서 발생된 폐아스팔트 콘크리트는 아스팔트 혼합물 생산시의 품질, 공용기간, 환경하중이나 교통하중 등에 따라 노화정도가 다르며 물성이 다양하다. 그러므로 폐아스팔트 콘크리트를 이용한 아스팔트 콘크리트 순환골재(이후 순환골재라고 함)의 품질은 폐아스팔트 콘크리트 발생 당시의 물성과 밀링 방법, 순환골재 생산과정에서의 파쇄 및 선별 방법 등에 따라 영향을 받아 변동된다. 따라서 재활용 아스팔트 포장의 조기 균열 등의 문제가 발생하지 않기 위해서는 배합설계시 순환골재의 물성에 따라 노화된 아스팔트를 회복시켜 줄 수 있는 재생 첨가제 등의 적합한 함량을 결정하고, 생산된 아스팔트 혼합물에 포함된 아스팔트의 점도 회복이 중요하다. 본 연구의 목적은 재활용 아스팔트 혼합물 배합설계시 아스팔트 점도를 회복시키기 위한 설계 방안을 제시하는 것이다. 국내 기준에서 재활용 아스팔트 혼합물에서 추출한 아스팔트의 점도는 5,000 Poise 이하이어야 한다. 이에 따라 국내에서는 혼합물 생산 및 운반의 단기노화 과정에서의 점도변화를 감안하여 대부분 설계점도를 2,000 Poise로 설정하고 배합설계를 수행한다. 그런데, 해외 연구 결과 재생 첨가제의 특성에 따라 단기노화 과정에서의 점도 변화율이 다른 것으로 나타났다. 이에 따라 본 연구에서는 혼합 전의 설계점도, RFTO 단기 노화 후의 점도, 제작된 아스팔트 혼합물에서 추출된 아스팔트 점도 등을 비교하여 적합한 배합설계 방안을 검토하였다

국토교통부고시 제 2014-105호와 환경부고시 제 2014-33호에 따라 2016년부터 순환골재를 제품소요량 대비 40% 이상 의무적으로 사용해야함에 따라 건설 분야의 순환골재 활용은 권장사항이 아닌 의무사항이 되고 있다. 순환골재라 함은 “건설폐기물의 재활용촉진에 관한 법률” 제2조 제7호의 규정(건설폐기물을 물리적 또는 화학적 처리과정 등을 거쳐 제35조의 규정에 의한 품질기준에 적합하게 한 것)에 적합한 골재로 폐아스콘, 폐콘크리트, 슬래그 등이 이에 해당된다. 슬래그는 철을 제조할 때 생성되는 산업폐기물로 일반적으로 고로 슬래그 미분말이 순환골재로써 콘크리트 제조시 사용되나 본 연구에서는 제강슬래그를 활용하였다. 제강슬래그는 팽창성과 환경적인 이유로 활용이 어려웠으나 선행연구를 통해 기초물성 및 환경성을 검토하여 아스팔트 골재로써 활용성을 검증하였다. 이에 따라 본 연구에서는 순환골재인 폐아스콘와 제강슬래그를 활용하고 최적의 혼입비율을 확보하기 위하여 폐아스콘 혼입 비율을 구분하여 실용화를 목적으로 13mm 밀입도(WC-1), 20mm 밀입도(WC-3) 로 중온 재활용 아스팔트 혼합물을 설계하여 공용성능을 분석하였다. 본 연구에 사용된 재료는 P사 광양제철소에서 생산된 3개월 이상 에이징된 제강슬래그(전로슬래그 90%, 전기로슬래그 10%)를 사용하였으며 인천지역 폐아스콘을 활용하였다. 공용성능 평가를 위하여 소성변형과 밀접한 관련이 있는 변형강도 실험을 수행하였다. 실험결과, 골재의 크기가 큰 WC-3가 WC-1에 비해 변형강도가 우수하였으며 WC-1는 제강슬래그의 비율이 높을수록 변형강도가 우수하였으며 WC-3는 제강슬래그의 비율에 영향을 받지 않았다.

아스팔트 혼합물이 운반·대기 중에 단기노화(short-term aging: STA)되는 것은 잘 알려진 사실이며 노화정도는 혼합물의 온도가 높음에 따라 그리고 시간이 길어짐에 따라 지수 함수적으로 증가되는 것으로 알려져 있다. 또한 같은 온도와 시간에 같은 바인더, 골재 및 입도를 사용한 같은 혼합물이라도 사용되는 첨가제의 종류에 따라 노화도에 차이가 난다. 그리고 혼합물의 종류에 따라서도 노화도에 차이가 큰 것으로 알려져 있다. 따라서 본 연구에서는 박리방지제(anti-stripping agent: ASA)의 종류와 혼합물의 종류에 따른 노화도의 차이를 비교분석 하였다. ASA로는 박리방지효과가 우수한 분말의 소석회와 액상 ASA를 비교하였다. 혼합물은 밀입도 아스팔트 (dense-graded asphalt: DGA) 표층용 혼합물과 쇄석 매스틱 아스팔트 (stone mastic asphalt: SMA) 혼합물을 비교하였다. 노화도는 아스팔트 노화의 척도로는 가장 많이 쓰이는 절대점도(absolute viscosity: AV)를 이용하였다. STA 온도와 시간에 따른 AV의 차이를 STA 처리된 혼합물로부터 추출·회수하여 60℃에서 측정하였다. 시험결과 같은 온도와 시간으로 STA 처리된 혼합물에서 소석회가 사용된 혼합물의 노화도가 월등히 낮았으며, 혼합물의 종류로는 SMA 혼합물의 노화도가 DGA 혼합물보다 낮게 나타났다. 이는 소석회가 박리방지효과 뿐만 아니라 노화억제 효과가 크기 때문이며, SMA는 바인더 함량이 높아 골재를 피복한 아스팔트 필름의 두께가 두꺼워 노화도가 적게 나타난 것으로 판단되었다.

PURPOSES :Conductive and convective heat transfer simulations for an asphalt mixture were made by using discrete element method (DEM) and similarity principle.METHODS :In this research, virtual specimens composed of discrete element method particles were generated according to four different predetermined particle size distribution curves. Temperature variations of the four different particles for a given condition were estimated and were compared with measurements and analytical solutions.RESULTS :The virtual specimen with mixed particles and with the smallest particle show very good agreement with laboratory test results and analytical solutions. As particle size decreases, better heat transfer simulation can be performed due to smaller void ratio and more contact points and areas. In addition, by utilizing the similarity principle of thermal properties and corresponding time unit, analytical time can be drastically reduced.CONCLUSIONS :It is concluded that the DEM asphalt mixture specimens with similarity principle could be used to predict the temperature variation for a given condition. It is observed that the void ratio has critical effect on prediction of temperature variation. Comparing the prediction for a 4 mm particle specimen with a mixed particle specimen, it is also concluded that predicting the mixed particle specimen temperature is much more efficient considering the number of particles that are directly associated with computational time in DEM analysis.

PURPOSES:The objective of this study is to evaluate the performance of asphalt mixtures containing inorganic additive and a high content of reclaimed asphalt pavement (RAP).METHODS:The laboratory tests verified the superior laboratory performance of inorganic additive compared to cement, in cold recycled asphalt mixtures. To investigate the moisture susceptibility of the specimens, tensile strength ratio (TSR) tests were performed. In addition, dynamic modulus test was conducted to evaluate the performance of cold recycled asphalt mixture.RESULTS:It was determined that NaOH solution mixed with Na2SiO3 in the ratio 75:10 provides optimum performance. Compared to Type B and C counterparts, Type A mixtures consisting of an inorganic additive performed better in the Indirect tensile strength test, tensile strength ratio test, and dynamic modulus test.CONCLUSIONS:The use of inorganic additive enhances the indirect strength and dynamic modulus performance of the asphalt mixture. However, additional experiments are to be conducted to improve the reliability of the result with respect to the effect of inorganic additive.