국내 태양광 산업은 2000년대 초 크게 성장하였으나 태양광 패널의 수명이 도래함에 따라 폐패널 발생량이 급격히 증 가할 것으로 예상된다. 그러나 태양광 패널의 주요 구성요소인 강화유리는 상용화된 재활용 기술이 부족하여 대부분 파 쇄 후 매립되고 있는 실정이다. 향후 대량 발생하게 될 폐패널의 재활용 기술 개발 필요성이 대두됨에 따라 태양광 폐패 널의 강화유리를 아스팔트 콘크리트 재료로서 재활용할 수 있는 기술을 개발하고자 하였다. 따라서 폐패널 유리 골재를 제조 및 이를 적용한 아스팔트 혼합물의 배합설계를 수행하였으며 일반 아스팔트 혼합물과 폐패널 유리 골재 아스팔트 혼합물의 성능평가 및 경제성을 비교·분석하였다. 그 결과 폐패널 유리 아스팔트 혼합물이 저온균열 저항성을 제외한 모 든 성능 시험에서 우수한 성과를 보였으며, 경제성 또한 일반 아스팔트 혼합물과 비교 시 뛰어난 것으로 나타났다.

지표면의 불투수층 증가는 빗물의 토양침투를 감소시키고 우수 침투를 제한하여 표면 유출에 의한 피해를 야기하였으며, 홍수 도달시간이 단축됨에 따라 첨두 유출량이 증가하므로 배수 시스템의 용량 부족 및 침수 피해를 초래하였다. 이에, 환 경부에서는 생태면적률 제도를 도입하여 저영향 개발(Low Impact Development, LID) 기술 도입의 활성화를 도모하고 있 으며, 이 중 투수블록포장이 약 40%를 차지하고 있다. 그러나, 주로 표층 콘크리트 블록의 품질기준 마련 및 성능 개선 연 구가 수행되었으며, 하부구조의 우수 침투 능력을 평가한 연구는 미흡한 실정이다. 특히, 투수성능이 증가할수록 구조적 지 지력이 감소하므로 내구성을 만족하는 범위에서 투수계수를 충족하는 입도분포를 실험적 연구를 통해 제시할 필요가 있다. 따라서, 시험체 내 수두를 일정하게 유지시켜 일정 시간동안 유입되는 하부 유출량을 측정하였으며, 같은 입도분포일 때 잔 골재 함량이 증가할수록 투수계수가 감소하는 것으로 나타났다. 이처럼 골재 입도분포 특성에 의해 물이 하부로 침투되는 유출량이 상이하므로 정량적인 평가를 통해 투수계수를 만족하는 적정 입도 기준의 제시가 가능할 것으로 판단된다.

도심부 도로에서 불투수면적 증가로 인해 발생한 홍수 및 물순환 장애 문제를 해결하기 위해, 투수블록포장이 도입되고 있으며, 물순환 시스템 강화의 필요성에 따라, 투수블록포장은 효과적인 대안으로 주목받고 있다. 투수성 포장의 성능 향상 을 위해서는 교통 하중 지지력을 만족하고, 투수 성능을 동시에 확보해야 하므로 표층뿐만 아니라 하부 투수기층의 설계 기준과 입도 특성에 대한 고려가 필요하다. 그러나, 국내의 경우 설계법이 잘 정립되어 있지 않고, 국외에서는 AASHTO 93 설계법을 구조설계법으로 적용하고 있으며, 투수성 포장재료의 상대강도계수에 대한 연구가 부족하여 다양한 재료에 대 한 설계 적용이 어려운 한계가 존재한다. 이에 본 연구는 투수블록포장 하부 투수기층 골재의 물리적 특성과 입도 기준에 관한 고찰을 통해, 내구성 향상을 위한 설계 요인과 투수 성능 간의 관계 분석 결과를 정리함으로써, 두 방향을 모두 고려하여 효율적인 골재 입도 구성을 도모할 수 있는 적합한 방향성을 정립하는 것을 목표로 한다. 다양한 투수성 포장 설계 조건과 성능에 관한 연구를 다루는 문헌을 수집해 투수 블록포장의 하부구조 단면 설계에 적용할 수 있는 기준 및 연구 방법론을 정리함으로써 실무 연구자들의 국내 연구 활성에 기여하고자 한다

PURPOSES : In this study, the applicability of the water content, suction, and suction stress in a resilient modulus prediction model for a subbase was reviewed. METHODS : To compare the applicability of water content, suction, and suction stress models for resilient modulus prediction, the suction stress was determined based on the soil water characteristic curve. The model parameters for each approach were derived from the measured resilient moduli. Finally, the relationships between the degree of saturation and resilient modulus were analyzed using the calculated model parameters. RESULTS : Prediction models of the resilient modulus based on water content and suction demonstrated high correlation with measured values, but overestimated the resilient modulus at saturation levels beyond the laboratory testing range. In contrast, the model accounting for suction stress effectively reduced this overestimation, likely owing to a decrease in suction stress as the suction increased. CONCLUSIONS : Based on the above results, the resilient modulus of subbase materials could be estimated through the change in the degree of saturation and the stress-dependent resilient modulus model using the suction stress proposed in this study.

Asphalt concrete, which is used as a road base material, accounts for >90% of a road pavement. A huge amount of waste concrete and waste asphalt concrete aggregates are generated. Recently, carbon neutrality is promoted across all industries for sustainability. Therefore, to achieve carbon neutrality in the asphalt concrete industry, waste asphalt concrete aggregates should be recycled. Additionally, road base materials are prepared using additives to ensure structural stability, durability, and economic efficiency. In this study, recycled asphalt concrete aggregates were used to evaluate the physical properties of road base materials according to the type of polymer additive and mixing method, and the applicability of road base each material was evaluated. Results showed that when the acrylate-based polymer additive was mixed, the uniaxial compressive strength was 30% higher. Furthermore, the compressive strength of the split mix was improved by ~29% compared to the total mix.

The asphalt concrete industry, accounting for >90% of road pavement, is a crucial contributor to construction waste. This study focuses on the recycling of asphalt concrete recycled aggregates, which currently exhibits a low rate. We investigated the application of these aggregates, combined with hardener and mixing water, in the development of ecofriendly road base materials using circular aggregates. Results revealed that the 13-mm asphalt concrete recycled aggregates met all quality standards. However, the 25-mm aggregates did not conform to the reclaimed asphalt content standard; however, they met other quality standards. Moreover, the experimental results for the hardener and mixing water indicated compliance with all quality standards.

PURPOSES : This study investigated the field applicability of pervious concrete to pavement base courses. Pervious concrete was developed at laboratory level, and the compaction methods, field moisture content, and fundamental properties when the material was constructed in the field were studied. METHODS : Field-applied pervious concrete was compacted at different levels using a tandem roller, and cores were taken to investigate the compressive strength, infiltration rate, continued porosity, and freeze-thaw resistance. In addition, the optimum field construction and quality control of the moisture content of a batch plant were measured. RESULTS : The moisture content of pervious concrete has an essential effect on workability and quality control during field test construction. From the test herein, the optimum value at a batch plant was found to be approximately 2.5±0.1%. The compaction level is also a crucial parameter at construction sites because it affects the mechanical and penetration properties. Considering both compressive strength and drainage, the recommended compaction was three times the round trip when a tandem roller was used. The penetration coefficient was 0.88 cm/sec when applying three times the round trip of the tandem roller. The freezing and thawing weight loss rates of the applied pervious concrete satisfied the required condition of 14% or less, regardless the compaction level. CONCLUSIONS : With the suggested mixed proportions of pervious concrete, the recommended compaction was three times the round trip of a tandem roller and a moisture content of approximately 2.5±0.1% from a batch plant. When these conditions were satisfied, the mechanical and drainage properties satisfied the required criteria.

PURPOSES : The purpose of this study is to present a cross section suitable for low-traffic road pavement considering the environmental characteristics of Vietnam. METHODS : The behavior of the pavement with respect to the axial load was numerically analyzed using the nonlinear finite element method. The elastic-plastic material model was applied to material properties such as subgrade, sub-base layer, and base layer, and whether the material yielded was determined. In order to evaluate the adequacy of the cross section of the Vietnamese low-traffic pavement, it was compared with the KPRP Lv 3 road pavement section. And it was compared with the newly proposed MAST composite Pavement. The design life of each pavement section was calculated using the results obtained from the pavement structural analysis. RESULTS : The cross section of the Vietnamese low-traffic road pavement, KPRP lv3, MAST composite Type1 road pavement did not satisfy the design criteria for fatigue cracking and rutting. MAST composite Type2 was analyzed considering CTAB having 100mm and 150mm thickness and compressive strength of 5MPa, 10MPa, 15MPa and 20MPa, and all of them satisfied the design criteria. CONCLUSIONS : The low-traffic road pavement section in Vietnam currently used is judged to be inappropriate, and the MAST Composite type 2 proposed in this study is evaluated as an appropriate alternative. Further studies such as field application are needed in the future.

PURPOSES : The purpose of this study is to evaluate the structural effects of subbase materials and surface layer thickness obtained from different sites. METHODS : Using a falling weight deflectometer, structural indexes such as SM(r), surface curvature index, base damage index, base curvature index, and AREA, were determined and compared with those of the control section. The back-elastic moduli for each layer were evaluated using the BALM program, and the tensile and compressive strains were analyzed using the KENLAYER program. The damage analysis was conducted to determine both the permanent deformation and fatigue cracking under repeated loading. RESULTS : Increasing the surface layer can improve the elastic moduli of the construction section and compensate for the inclusion of different percent finer within 5% in the subbase layer. CONCLUSIONS : The structural effect of adding 5% of 50 m/m aggregate can be compensated for by increasing the thickness of the surface layer.

PURPOSES: A composite pavement utilizes both an asphalt surface and a concrete base. Typically, a concrete base layer provides structural capacity, while an asphalt surface layer provides smoothness and riding quality. This pavement type can be used in conjunction with rollercompacted concrete (RCC) pavement as a base layer due to its fast construction, economic efficiency, and structural performance. However, the service life and functionality of composite pavement may be reduced due to interfacial bond failure. Therefore, adequate interfacial bonding between the asphalt surface and the concrete base is essential to achieving monolithic behavior. The purpose of this study is to investigate the bond characteristics at the interface between asphalt (HMA; hot-mixed asphalt) and the RCC baseMETHODS: This study was performed to determine the optimal type and application rate of tack coat material for RCC-base composite pavement. In addition, the core size effect, temperature condition, and bonding failure shape were analyzed to investigate the bonding characteristics at the interface between the RCC base and HMA surface. To evaluate the bond strength, a pull-off test was performed using different diameters of specimens such as 50 mm and 100 mm. Tack coat materials such as RSC-4 and BD-Coat were applied in amounts of 0.3, 0.5, 0.7, 0.9, and 1.1ℓ/m2 to determine the optimal application rate. In order to evaluate the bond strength characteristics with temperature changes, a pull-off test was carried out at -15, 0, 20, and 40 °C. In addition, the bond failure shapes were analyzed using an image analysis program after the pull-off tests were completed.RESULTS: The test results indicated that the optimal application rate of RSC-4 and BD-Coat were 0.8ℓ/m2, 0.9 ℓ/m2, respectively. The core size effect was determined to be negligible because the bond strengths were similar in specimens with diameters of 50 mm and 100 mm. The bond strengths of RSC-4 and BD-Coat were found to decrease significantly when the temperature increased. As a result of the bonding failure shape in low-temperature conditions such as -15, 0, and 20 °C, it was found that most of the debonding occurred at the interface between the tack coat and RCC surface. On the other hand, the interface between the HMA and tack coat was weaker than that between the tack coat and RCC at a high temperature of 40 °C.CONCLUSIONS: This study suggested an optimal application rate of tack coat materials to apply to RCC-base composite pavement. The bond strengths at high temperatures were significantly lower than the required bond (tensile) strength of 0.4 MPa. It was known that the temperature was a critical factor affecting the bond strength at the interface of the RCC-base composite pavement.

콘크리트 기층에 아스팔트 표층의 복합포장 구조에서 온도변화에 따른 반사균열의 거동은 반사균열 억제 및 제어에 중요한 정보로 작용한다. 반사균열의 주요 발생원인 중 포장의 온・습도 변화에 따른 하부 콘크리트의 수평 거동 및 컬링에 의한 줄눈/균열부 수직 거동은 포장의 특성(콘크리트 열팽창계수, 하부마찰계수, 포장두께 등)과 지역환경(대기의 온도, 상대습도, 태양 복사량 등)에 따라 다른 특성을 보인다. 본 연구에서는 롤러전압 콘크리트 기층에 배수성 아스팔트 표층의 복합포장 구조에서 현장의 온도변화에 따른 반사균열의 거동 특성을 분석하였다. 늦가을(11월 초)에 5cm 두께 배수성 아스팔트 덧씌우기 포장을 롤러전압 콘크리트 기층 상부에 시공하였다. 온도 조사는 표층 아스팔트 상/하부와 기층 콘크리트 상/하부, 대기온도를 계측하였다. 롤러전압 콘크리트 기층의 균열은 1년의 공용기간 동안 약 30m의 일정 간격으로 발생하였으며, 계측한 연속된 3개 균열의 움직임은 안정화되어 온도에 따라 유사한 거동을 보였다. 계측결과, 겨울철 온도에 따른 줄눈거동은 그림 1과 같다. 영하권의 겨울철 포장의 온도는 태양의 복사열과 기층하부의 지열로 인하여 대기온도보다 높았다. 표층 시공 후 큰 폭의 온도 저감이 발생한 이후 반사균열이 발생하였고 그림 2는 반사균열 발생 전・후의 1일 온도차에 따른 1일 균열 폭 변화량을 보인다. 추세곡선의 기울기는 온도변화에 따른 균열 거동에 저항하는 크기를 나타낸다. 두 곡선의 기울기 차인 0.008은 5cm 두께의 배수성 표층의 반사균열에 대한 저항 특성치임을 알 수 있다. 아스팔트 표층 반사균열 발생 전・후의 추세 곡선간 y축 절편의 차는 반사균열 발생에 따른 동일 온도변화에서 균열 거동량의 증가분을 나타낸다. 향후 배수성 표층 복합포장의 계절별 거동특성을 분석하여 복합포장 설계검토에 활용할 계획이다.

아스팔트 표층과 콘크리트 기층으로 구성된 복합포장은 강성기층의 높은 지지력과 아스팔트 표층의 소음저감, 평탄성, 미끄럼저항성 등을 확보할 수 있는 장점을 가진 포장이다. 롤러다짐콘크리트(RCC)는 빠른 시공속도와 경제성을 가져 복합포장의 기층으로 활용된다. 그러나 이러한 복합포장의 공용수명 및 성능은 포장 계면의 부착파괴로 인해 저하된다. 그러므로 아스팔트 표층과 콘크리트 기층사이의 적절한 부착은 복합포장의 단일거동(monolithic behavior)을 통한 포장성능 및 공용수명 확보를 위해 필수적이다. 복합포장에 적용되는 아스팔트와 택코트 재료는 역청혼합물을 포함하고 있는 재료로 시간-온도에 의존적인 점탄성 특성을 나타내며 콘크리트는 환경적 조건(온도 등)에 따라 컬링 및 수축·팽창 등이 발생하는 재료적 특성을 가진 재료이다. 복합포장의 역학적 거동은 이러한 각 재료 및 포장계면의 특성에 기반 한다. 그러므로 부착 성능을 평가함에 있어 국내의 계절별 기후에 따른 복합포장 내 온도특성을 반영하여 부착성능이 평가되어야 하며 겨울철 반복적 동결-융해가 발생하는 국내의 기후특성상 이를 고려한 부착내구성 평가 등이 수행되어야 한다. 그러나 국내의 경우 20 ℃의 표준온도만을 적용한 부착성능 평가를 통해 품질관리가 수행되고 있으며 이와 관련된 연구가 미흡한 실정이다. 또한, 복합포장의 경제적 강성기층으로 본 연구에 적용된 롤러다짐콘크리트(RCC)는 적은 단위수량 및 단위시멘트량을 사용하여 시멘트 페이트의 양이 일반콘크리트 포장에 비해 적으며 포설 후 롤러전압다짐이 적용되기 때문에 불규칙한 거친 표면을 형성한다. 그러므로 이러한 특성을 고려한 적정 택코트 재료 및 살포량 선정이 요구된다. 따라서, 본 연구에서는 롤러다짐콘크리트-기층 복합포장에 대한 부착특성을 분석하고자 하였다. RSC-4와 BD-Coat 두 종류의 택코트 재료가 실험되었으며 각 재료의 최적살포량을 선정하고자 0.3, 0.5, 0.7, 0.9, 1.1 ℓ/m2의 살포량이 적용되었다. 추가적으로 100 mm, 50 mm에 대한 core size effect가 고려되었다. 온도 조건에 따른 인장부착특성은 -15, 0, 20 40 ℃의 각 온도 조건에서 실험되었으며 반복적 동결-융해가 발생하는 국내의 기후 특성을 고려하고자 0, 50, 100 Cycle에 대한 부착내구성 실험이 수행되었다. 실험의 각 부착파괴단면은 이미지분석프로그램을 통해 검토 되었으며 검토 내용을 바탕으로 부착특성과 부착파괴단면과의 상관관계가 분석되었다.

PURPOSES:The objective of this study is to ascertain the curing period of cementless cold central plant recycled asphalt base-layer, using mechanical analyses and specimen quality tests on the field.METHODS :Cold central plant recycled asphalt base-layer mixture was produced in the plant from reclaimed asphalt, natural aggregate, filler for the cold mix, and the modified emulsion AP using asphalt mix design and plant mix design. In order to examine the applicability of the curing period during the field test, the international standards for the possibility of core extraction and the degree of compaction and LFWD deflection were analyzed. Moreover, Marshall stability test, porosity test, and indirect tensile strength test were performed on the specimens of asphalt mix and plant mix design.RESULTS :The plant production process and compaction method of cementless cold central plant recycled asphalt base-layer were established, and the applicability of the optical moisture content for producing the mixture was verified through the field test. In addition, it was determined that the core extraction method of the conventional international curing standard was insufficient to ensure performance, and the LFWD test demonstrated that the deflection converges after a two-day curing. However, the back-calculation analysis reveals that a three-day curing is satisfactory, resulting in a general level of performance of dense asphalt base-layer. Moreover, from the result of the specimen quality test of the asphalt mix design and plant mix design according to the curing period, it was determined that the qualities satisfied both domestic and international standards, after a two-day curing. However, it was determined that the strength and stiffness after three-day curing are higher than those after a two-day curing by approximately 3.5 % and 20 %, respectively.CONCLUSIONS:A three-day curing period is proposed for the cementless cold central plant recycled asphalt base-layer; this curing period can be demonstrated to retain the modulus of asphalt-base layer in the field and ensure stable quality characteristics.

PURPOSES: The main purpose of this study is to develop a high elastic modulus and low-shrinkage roller-compacted concrete base (RCCB) in order to prevent fatigue cracking and reflective cracking in the asphalt surface layer of composite pavement. Using a rigid base material with low shrinkage can be a solution to this problem. Moreover, a strong rigid base with high elastic modulus is able to shift the location of critical tensile strain from the bottom of the asphalt layer to the bottom of the rigid base layer, which can prevent fatigue cracking in the asphalt layer. METHODS: Sensitivity analysis of composite pavement via numerical methods is implemented to determine an appropriate range of elastic modulus of the rigid base that would eliminate fatigue cracking. Various asphalt thicknesses and elastic moduli of the rigid base are used in the analysis to study their respective influences on fatigue cracking. Low-shrinkage RCC mixture, as determined via laboratory testing with various amounts of a CSA expansion agent (0%, 7%, and 10%), is found to achieve an appropriate low-shrinkage level. Shrinkage of RCC is measured according to KS F 2424. RESULTS : This study shows that composite pavements comprising asphalt thicknesses of (h1) 2 in. with E2 > 19 GPa, 4 in. with E2 > 15 GPa, and 6 in. with E2 > 11 GPa are able to eliminate tensile strain in the asphalt layer, which is the cause of fatigue cracking in this layer. Shrinkage test results demonstrate that a 10% CSA RCC mixture can reduce shrinkage by 84% and 93% as compared to conventional RCC and PCC, respectively. CONCLUSIONS: According to the results of numerical analyses using various design inputs, composite pavements are shown to be able to eliminate fatigue cracking in composite pavement. Additionally, an RCC mixture with 10% CSA admixture is able to reduce or eliminate reflective cracking in asphalt surfaces as a result of the significant shrinkage reduction in the RCC base. Thus, this low-shrinkage base material can be used as an alternative solution to distresses in composite pavement.