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      • KCI등재

        Determination of Dynamic Modulus of Cold In-place Recycling Mixtures with Foamed Asphalt

        김용주,이호신 한국도로학회 2009 한국도로학회논문집 Vol.11 No.1

        A new mix design procedure for cold in-place recycling using foamed asphalt (CIR-foam) has been developed for Iowa Department of Transportation. Some strengths and weaknesses of the new mix design parameters were considered and modified to improve the laboratory test procedure. Based on the critical mixture parameters identified, a new mix design procedure was developed and validated to establish the properties of the CIR-foam mixtures. As part of the validation effort to evaluate a new CIR-foam mix design procedure, dynamic moduli of CIR-foam mixtures made of seven different reclaimed asphalt pavement (RAP) materials collected throughout the state of Iowa were measured and their master curves were constructed. The main objectives of this study are to provide: 1) standardized testing procedure for measuring the dynamic modulus of CIR-foam mixtures using new simple performance testing (SPT) equipment; 2) analysis procedure for constructing the master curves for a wide range of RAP materials; and 3) impacts of RAP material characteristics on the dynamic modulus. Dynamic moduli were measured at three different temperatures and six different loading frequencies and they were consistent among different RAP sources. Master curves were then constructed for the CIR-foam mixtures using seven different RAP materials. Based upon the observation of the constructed master curves, dynamic moduli of CIR-foam mixtures were less sensitive to the loading frequencies than HMA mixtures. It can be concluded that at the low temperature, the dynamic modulus is affected by the amount of fines in the RAP materials whereas, at the high temperature, the dynamic modulus is influenced by the residual binder characteristics. A new mix design procedure for cold in-place recycling using foamed asphalt (CIR-foam) has been developed for Iowa Department of Transportation. Some strengths and weaknesses of the new mix design parameters were considered and modified to improve the laboratory test procedure. Based on the critical mixture parameters identified, a new mix design procedure was developed and validated to establish the properties of the CIR-foam mixtures. As part of the validation effort to evaluate a new CIR-foam mix design procedure, dynamic moduli of CIR-foam mixtures made of seven different reclaimed asphalt pavement (RAP) materials collected throughout the state of Iowa were measured and their master curves were constructed. The main objectives of this study are to provide: 1) standardized testing procedure for measuring the dynamic modulus of CIR-foam mixtures using new simple performance testing (SPT) equipment; 2) analysis procedure for constructing the master curves for a wide range of RAP materials; and 3) impacts of RAP material characteristics on the dynamic modulus. Dynamic moduli were measured at three different temperatures and six different loading frequencies and they were consistent among different RAP sources. Master curves were then constructed for the CIR-foam mixtures using seven different RAP materials. Based upon the observation of the constructed master curves, dynamic moduli of CIR-foam mixtures were less sensitive to the loading frequencies than HMA mixtures. It can be concluded that at the low temperature, the dynamic modulus is affected by the amount of fines in the RAP materials whereas, at the high temperature, the dynamic modulus is influenced by the residual binder characteristics.

      • KCI등재

        교직 정체성의 탐구를 위한 분석적 연구

        김용주 한국교원교육학회 1999 한국교원교육연구 Vol.16 No.2

        '스콜라' 이용 시 소속기관이 구독 중이 아닌 경우, 오후 4시부터 익일 오전 7시까지 원문보기가 가능합니다.

        이 연구의 기본 목적은 교사의 직무특성 분석을 통하여 교직의 직업적 정 체성을 탐구하는데 있다. 이를 위해서 연구자는 첫째,교직의 성격규정 시 가장 빈번하게 거론되는 개념인 전문직업의 의미와 그것이 교직에 어떻게 적용 되는지의 여부 등을 고찰하고,둘째,문헌분석을 통하여 도출된 내용과 교육자의 교직성격에 대한 지각 사이의 차이를 분석함으로써,셋째,우리가 새롭게 인식해야 할 교직의 의미를 탐색하였다.이 연구를 통해 연구자는 첫째,교직의 직업적 정체성을 도덕성이 강조되는 전문직업(morel profession)임을 규명하였고, 이는 본 연구의 조사결과 - 교수행위에 관한 교육자들의 덕육, 인격적 성숙성 및 정의적 능력 강조경향 - 와 큰 괴리가 없음을 밝혔으며,둘째,교직이 도덕적 전문직으로서의 정체성을 확립하기 위해 요구되는 조치들을 제시하였다.

      • KCI등재

        Comparing Laboratory Responses of Engineered Emulsified Asphalt and Foamed Asphalt Mixtures for Cold In-place Recycling Pavement

        김용주,이호신 한국도로학회 2010 한국도로학회논문집 Vol.12 No.1

        Cold in-place recycling (CIR) using emulsified asphalt or foamed asphalt has become a more common practice in rehabilitating the existing asphalt pavement due to its cost effectiveness and the conservation of paving materials. As CIR continues to evolve, the engineered emulsified asphalt was developed to improve the field performances such as coating, raveling, retained stability value and curing time. The main objective of this research is to compare the laboratory responses of the engineered emulsified asphalt (CIR-EE) mixtures against the foamed asphalt (CIR-foam) mixtures using the reclaimed asphalt pavement (RAP) materials collected from the CIR project on U.S. 20 Highway in Iowa. Based on the visual observation of laboratory specimens, the engineered emulsified asphalt coated the RAP materials better than the foamed asphalt because the foamed asphalt is to create a mastic mixture structure rather than coating RAP materials. Given the same compaction effort, CIR-EE specimens exhibited lesser density than CIR-foam specimens. Both Marshall stability and indirect tensile strength of CIR-EE specimens were about same as those of CIR-foam specimens. However, Marshall stability and indirect tensile strength of the vacuum-saturated wet specimens of CIR-EE mixtures were higher than those of CIR-foam mixtures. After four hours of curing in the room temperature, the CIR-EE specimens showed less raveling than the CIR-foam specimens. On the basis of test results, it can be concluded that the CIR-EE mixtures is less susceptible to moisture and more raveling resistant than CIR-foam mixtures.

      • KCI등재

        Development of Moisture Loss Index Based on Field Moisture Measurement using Portable Time Domain Reflectometer (TDR) for Cold In-place Recycled Pavements

        김용주,이호신,임수혁 한국도로학회 2011 한국도로학회논문집 Vol.13 No.2

        The practice of asphalt pavement recycling has grown rapidly over the decade, one of which is the cold in-place recycling with the foamed asphalt (CIR-foam) or the emulsified asphalt (CIR-emulsion). Particularly, in Iowa, the CIR has been widely used in rehabilitating the rural highways because it significantly increases the service life of the existing pavement. The CIR layer is typically overlaid by the hot mix asphalt (HMA) to protect it from water ingress and traffic load and obtain the required pavement structure and texture. Most public agencies have different curing requirements based on the number of curing days or the maximum moisture contents for the CIR before placing the overlay. The main objective of this study is to develop a moisture loss index that the public agency can use to monitor the moisture content of CIR layers in preparation for a timely placement of the wearing surface. First, the moisture contents were measured in the field using a portable time domain reflectometry (TDR) device. Second, the weather information in terms of rain fall, air temperature, humidity and wind speed was collected from the same location. Finally, a moisture loss index was developed as a function of initial moisture content, air temperature, humidity and wind speed. The developed moisture loss index based on the field measurements would help the public agency to determine an optimum timing of an overlay placement without continually measuring moisture conditions in the field.

      • KCI등재SCOPUS

        Performance Evaluation of Cold In-place Recycling Mixtures Using Emulsified Asphalt Based on Dynamic Modulus, Flow Number, Flow Time, and Raveling Loss

        김용주,이호신 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.4

        The need for a Cold In-place Recycling using emulsified asphalt (CIR-emulsion) mixture with specific engineering properties calls for the use of a mix design and, recently, a new mix design procedure was developed for CIR-emulsion. As a part of CIR-emulsion mix design process, dynamic modulus, flow number, flow time and raveling tests were conducted to evaluate short- and long-term performance of CIR-emulsion mixtures at various testing temperatures and loading conditions. Based on the test results, the optimum emulsified asphalt content for CIR was determined. Dynamic modulus, flow number and flow time of CIR-emulsion mixtures using CSS-1h (cationic slow setting emulsion) were higher than those of HFMS-2P (high-float medium-setting emulsion modified with a polymer). Flow number and flow time of CIR-emulsion mixtures using RAP materials with softer residual asphalt was higher than those of CIR-emulsion mixtures using RAP materials with harder residual asphalt. The dynamic modulus, flow number and flow time were affected by both emulsion type and residual asphalt stiffness of RAP materials. Raveling loss of CIR-emulsion mixtures with 1.5% emulsified asphalt was significantly less than those with 0.5% and 1.0%

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