In order to prevent early distress in asphalt pavement and save on subsequent operational and maintenance costs, modifying asphalt is an effective approach. Styrene–butadiene–styrene (SBS) block copolymers, due to their excellent physicochemical properties, have become a mature and widely used asphalt modifier. Carbon nanotubes (CNTs) possess advantages such as a large specific surface area and high modulus, which, when incorporated into asphalt, can enhance its deformation resistance. To analyze the effect of incorporating CNTs on SBS-modified asphalt (SBS-A), this study analyzed the influence of different CNT concentrations on the high and low-temperature performance and aging properties of SBS-A through penetration, softening point, ductility, dynamic shear rheometry, and short-term aging tests. The optimal CNT concentration was determined to be 1.0%. Furthermore, the changes in the modified asphalt during the aging process were analyzed using infrared spectroscopy.

PURPOSES : A mechanistic-empirical (ME) predictive design logic that can compute the reflective cracking life of hot-mix asphalt (HMA) overlaid on top of a composite pavement is proposed herein. METHODS : The overlay thickness design and analysis logic of the HMA were formulated based on the ME concept of reflection crack propagation. Climate data, traffic load data, the pavement material properties, and the thickness of each layer of the pavement are the main inputs for the ME-Reflective Cracking Rate (RCR) prediction algorithm. An Microsoft Excel Virtual Basic for Application (VBA) program was created to aid designers in assessing the expected performance of an HMA overlay design. Calibration was done using data from the Long-Term Pavement Performance (LTPP) sections. Sensitivity analysis was conducted to compare the results yielded by the program and data from a report by the Texas Transportation Institute. RESULTS : The predictive model performance effectively generates the dynamic and relaxation modulus curves. The correlation value of the calibration factors, R2, is 0.79. The calibration factors used for the Asphalt Overlay Thickness Design (AOTD) program and the sensitivity analysis, i.e., k1, k2,, and k3,, are set to 5, 5, and 150, respectively. The sensitivity of the AOTD program affords reasonable results. Additionally, the program yields results similar to the trends presented in a report by the Federal Highway Administration. CONCLUSIONS : The proposed ME design logic is successfully translated into an Excel VBA program, AOTD, which can perform routine assessments of laboratory tests for HMA overlays. The program can effectively perform numerous iterations and computations to predict an HMA overlay. The predictive model can generate reasonable dynamic modulus and relaxation modulus curves for the characterization of HMA overlays. Under the same asphalt binder grade and HMA type, doubling the HMA overlay thickness yields three times the expected reflective cracking service life.

PURPOSES : In this study, the results of an intensive field survey of a composite pavement applied to an expressway in Korea are analyzed. The results are intended to be used as basic data for evaluating the composite pavement and for preparing quality control measures through a review and analysis of the change in the state of the tensile bonding strength of the composite pavement. METHODS : To evaluate, repeated field coring and indoor tensile bonding strength evaluations are conducted for five years, and the commonality evaluation of pavement using pavement condition investigation equipment is conducted annually. RESULTS : The results of this study show that the degree of reflective crack generation varies depending on the type of concrete pavement and type of asphalt mixture applied to the intermediate layer, and that the CRCP composite pavement exhibits better initial commonality than the JCP composite pavement. In addition, it is confirmed that the composite cross-section pavement section with MASTIC applied as an intermediate layer shows excellent adhesion performance between the lower concrete layers from the beginning of construction in all sections, as well as satisfied the quality control standards for good pavement and tensile adhesion even after approximately five years of public use. CONCLUSIONS : Based on a follow-up survey of the composite pavement testing sections, it is confirmed that the section constructed with the MASTIC intermediate layer and CRCP satisfies the quality control standards for good pavement conditions and tensile adhesion even after approximately five years of public use.

To be better fit for highways, pavement systems are required to provide comfortable and safe driving and be structurally durable. Composite pavements can be an effective option as they are more durable by placing a high functional asphalt overlay on a rigid concrete base layer. In order to apply a composite pavement system to the field, it is necessary not only to develop technologies that prevent reflecting crack and deterioration of the base layer, but also to improve bonding performance of materials and ensure structural performance as a pavement system against traffic loading. In advanced countries like Japan, USA and Europe, high-functional composite pavement systems are being put into practice across new highway networks. In this study, we evaluated structural performance (rutting, reflecting crack, and deflection) by applying traffic loads of actual highways through an accelerated pavement tester (APT) of a composite pavement section made up of a quiet porous surface laid over a water-proofing layer, a continuously reinforced concrete base, and a lean concrete sub-base layer, which was developed with new pavement methods used for each layer prior to field application. The APT specimen was constructed with paving materials and equipment actually used on site in the same dimensions (W3.5m*L14m*H2m) as actual highway sections in Korea, and 3-axle double-wheel heavy load (45ton) cart type KALES(Korean Accelerated Loading and Environmental Simulator) traveling on the specimen in both directions was used to simulate traffic loading. After applying around 8,574,000 ESALs of traffic loads, no reflecting crack occurred on the asphalt surface of the composite pavement, without surface distress except for rutting. In order to examine what causes rutting of pavements, we surveyed thickness of pavements by layer and measured asphalt density.

Asphalt pavement overlay method is one of widely chosen construction methods for remodelling existing aged concrete pavement layer. However, in this case reflective cracking is a challenging issue due to movement of transverse joints: built in existing concrete pavement layer with constant interval length. In this paper, collecting field data: collection of displacement and temperature data on existing concrete pavement layer for further complicated pavement performance analysis, was performed. To fulfil this objective, various types of thermometer were embedded into concrete layer with different depth level. Then, movement of existing concrete layer was measured numerically. Each Displacement Measuring Gauge (DMG) along with thermometer was embedded with depth of 3cm and 15cm, respectively. Additional thermometers were embedded at the middle depth of overlaid asphalt pavement layer for further extensive analysis and data collection. Total four testing sites were considered based on different asphalt mixture type and construction method. The 1st site was constructed with conventional construction approach, the 2nd site was constructed with a new pavement equipment contains simultaneous tack-coating function, the 3rd site was similar to 1st site but Guss-asphalt was constructed as a binder course, and in 4th site Noise-Reduction Porous Asphalt (NRPA) was constructed as a surface course and regular Dense Grade Asphalt (DGA) was constructed as a binder course. A field asphalt pavement layer sample coring works: along with basic material property tests, were also performed to acquire not only overlaid asphalt but also existing concrete pavement materials. This gauge measuring work in this study is an initial step therefore, long-term movement data of each pavement layer was not able to be collected, unfortunately. However through collecting and analysing initial data on each test site, two crucial findings were acquired. First, in all four tested site highest temperature variations were observed at the upper asphalt pavement layer and the variation trends decreased with increase of pavement depth (in case of concrete pavement layer, temperature and movement variations also decreased with increase of pavement depth). Secondly, when Guss-asphalt was applied as a binder course temperature variations of existing concrete pavement layer was crucially smaller than those of other comparison cases. These current findings and collected data set can provide successful input information for further pavement structure analysis such as 2D (and/or 3D) Finite Element Method (FEM) analysis as a future study.

Roller Compacted Concrete Pavement (RCCP) is placed by roller compaction of a mixture of less cement and unit water content and more aggregates and provides excellent early strength development with the help of interlocking of aggregates and hydration. The unit cement content of RCC pavements accounts for 85% of conventional pavements, with low drying shrinkage. As low drying shrinkage leads to smaller crack widths than ordinary concrete, RCC pavements can help elevate reflecting crack resistance if applied to a base layer of a composite pavement system. In a composite pavement with an asphalt surface laid over a concrete base, pavement temperature change is important in predicting pavement performance. As movement of the lower concrete layer is determined by temperature depending on pavement depth, temperature data of the pavement structure serves as an important parameter to prevent and control reflecting crack. Among the causes of reflecting crack, horizontal behavior of the lower concrete layer and curling-caused vertical behavior of joints/cracks are considered closely related to temperature change characteristics of the lower concrete course (Baek, 2010). Previous studies at home and abroad about reflecting crack have focused on pavement behavior depending on daily and yearly in-service temperature changes of a composite pavement (Manuel, 2005). Until now, however, studies have not been conducted on initial temperature characteristics of concrete in composite pavements where asphalt surface is placed over an RCC base. Annual temperature changes of in-service concrete pavements go up to 60 ℃, and those of asphalt overlays become around the twice at 110 ℃. This study evaluated initial crack behavior of composite pavement by investigating pavement temperature by depth of an RCC base and analyzing joint movement depending on change to temperatures of continuously jointed pavements. Findings from the study suggest that in composite pavements and asphalt overlays, time of laying asphalt has an important impact on crack behavior and reflecting crack.

Composite pavements are constructed by placing a high functional asphalt surface layer on a high performance concrete rigid base layer and provide a more durable, high functional surface to road users. Service life of composite pavements is dependent on the bonding performance of the lower rigid base and the flexible surface layer. Accordingly, it is necessary to place an impermeability layer between the functional surface layer and the rigid base to enhance bonding performance and to prevent moisture penetration into the rigid base and deterioration of pavement. In order to use optimal composite pavement sections, two types were applied to impermeability layer: highly impermeable water-tight SMA and mastic asphalt currently in use. APT (Accelerated Pavement Testing) and experimental construction were carried out to evaluate bond strengths between the rigid base and the impermeability layer depending on the type of impermeability layers. Composite pavement sections for the APT had a 22 cm concrete rigid base layer and a 5cm functional surface, as well as either 5cm of SMA impermeability layer and 5cm of mastic layer. After applying around 8,574,000 ESALs, pull-off test was conducted, which showed that the mastic section outperformed the SMA section. In the experimental construction, three types of rigid base layers, JCP (Jointed Concrete Pavement), CRCP (Continuously Reinforced Concrete Pavement), and RCCP (Roller Compacted Concrete Pavement), were used for composite pavement sections, and as in the APT, two types of impermeability layers, SMA and mastic, were used per rigid base layer of new and deteriorated concrete pavement. Therefore, seven composite pavement sections in total were constructed. We measured the bond strength over one year or so following the construction of these composite pavement sections and found that regardless of the type of rigid base layer and whether it was new or not, those sections with a mastic impermeability layer had high bond strengths.

PURPOSES: This study develops eco-friendly asphalt reinforcement materials applicable to bridge deck pavement. The main purpose is to ensure highly reliable quality applicable to structures and the possibility of practical application. The main target of the study is to develop materials that are environmentally friendly and capable of improving performanceMETHODS: The application of double-reinforcement fiber improves the performance of the road pavement. 1. We use recycled film for application of sheet-typed reinforcement. 2. We use preprocessing fibers to reinforce the properties of composite pavement materials.RESULTS : The developed products may produce materials that fit the purpose of achieving stability and environmental friendliness. Sheettyped reinforcements use more than 50% recycled resin. The most important type of damage to the asphalt layer is deflection (plastic deformation). These products have a very high deflection resistance of not less than 6,000 cycles/mm. In addition, all performance is excellent. Thus, it will be easier to access the field in the future.CONCLUSIONS: Fiber-reinforced asphalt pavement showed excellent performance. Sheet-typed reinforcements containing 50% recycling resin produced good performance in terms of functionality as well as environmental friendliness. Thus, enhancing the field applicability will enhance the usability of the reinforcements.

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.

PURPOSES: Analysis and design of asphalt concrete (AC) and continuously reinforced concrete (CRC) composite pavements. METHODS: In this study, the service life of the AC/CRC composite pavements was determined based on the probabilistic method in the mechanistic-empirical pavement design guide(MEPDG). Typical pavement design was provided with respect to heavy truck traffic volume of highways. RESULTS: The service life of the composite pavements based on IRI was shorter than that based on rutting at lower traffic volume, but this trend was switched at higher traffic volume. CONCLUSIONS : It is concluded that the main distress affecting the service life of the composite pavements was longitudinal roughness and rutting. Roughness became lower, but rut depth became greater as the stiffness of the CRC increased.

PURPOSES: This study is to investigate the mechanical performance of the fiber reinforced lean concrete with respect to different types of fibers. METHODS: Increased vehicle weight and other causes from the exposed conditions have accelerated the deteriorations of road pavement. A new multi-functional composite pavement system is being developed recently in order to extend service life and upgrade the pavement. A variety of tests were conducted before and after hardening of the concrete. RESULTS: From the test results, it was found that the use of different types of fibers did not affect the compressive strength development. This might be due to the inherent property of the lean concrete. When steel fibers were used relatively greater flexural strength and flexural fracture toughness were developed. Also addition of fly ash by replacing a part of Portland cement the fracture toughness was slightly increased. CONCLUSIONS: It has been known that the addition of fibers and use of mineral admixture can be positively considered in the development of multi-functional composite pavement system as its required mechanical performance is obtained.

고속도로에서 재령이 20년이 넘는 노후 콘크리트가 늘어남에 따라 콘크리트 포장의 보수/보강이 중요한 이슈로 대두되고 있다. 노후 콘크리트 포장의 보강 대안으로서 아스팔트 덧씌우기가 많이 사용되고 있으나 반사균열 및 포트홀 등 체류수로 인한 문제가 심각하게 대두되고 있다. 본 연구는 반사균열 및 체류수의 문제를 최소화하기 위해 고안된 접착식 방수층을 소개하였으며 포장가속시험을 통해 일반 택코팅을 적용한 합성단면포장과 비교평가를 실시하였다. 실험은 강우를 모사하기 위해 물을 뿌리면서 진행하였고 덧씌우기 포장체의 거동 및 수분 저항 특성을 분석하였다. 연구결과 접착식 방수층은 아스팔트 포장과 콘크리트 포장이 일체로 거동하는 것을 도와주기 때문에 아스팔트 포장체에 발생하는 거동이 일반 택코팅 구간과 완전히 다른 것으로 나타났다. 또 수분의 유입을 최소화하므로 결과적으로 반사균열의 발생을 약 70% 지연시키는 것으로 나타났으며, 체류수로 인한 손상도 줄여주는 것으로 나타났다.