Yoshitaka Hachiya

Effect of Recycling Rate and Asphalt Binder on the Performance of Recycled Asphalt Concrete for Airport Pavement Rehabilitation

ABSTRACT Aimed to prompt the extensive use of reclaimed asphalt aggregate (RAA) in airport pavement rehabilitation, a series of laboratory tests are conducted to intensively evaluate the effect of recycling rate and asphalt binder on the performances of recycled asphalt concrete (RAC). The results indicate that rutting resistance of RAC using either straight or modified asphalt binder increases with the increase of recycling rate, while the opposite trend is found in low temperature properties (increase in stiffness) and fatigue performance. The modified asphalt used does not exhibit superiority for producing RAC compared with straight asphalt except in rutting resistance. Increasing the recycling rate to 70% is feasible in the case of RAC using straight asphalt judging from its comparable and even superior performance to the control SRAC (contain 40% RAA) in terms of resistance to rutting, ravelling, moisture stripping and thermal cracking. It seems possible to use it in surface courses devoted to airport sections where fatigue processes are not prevalent.

Validation of Performance-based Method for Determining Rejuvenator Content in HMA

This paper presents the results of a laboratory study in which the recommended values of rejuvenator contents from previous binder studies were validated through laboratory mixture performance tests. The experiments consisted of the comparison of recycled asphalt mixtures at three rejuvenator contents: 0, 2.0 (lower recommended limit) and 7.4% (upper recommended limit). In addition, a control mixture with virgin asphalt binder was also included in the experiment. The mixture performance tests included the wheel tracking at 60°C and low temperature thermal stress restrain specimen (TSRS) tests. The results from this study indicated that: (1) the properties of HMA using recycled asphalt binders with the recommended rejuvenator contents from the previous studies were comparable to the control virgin mixture; (2) it was more reliable to use the median recommended rejuvenator contents for mixtures with both satisfactory high temperature stability and low temperature fracture resistance and (3) the rejuvenator content affects significantly the properties of recycled mixtures in a similar way to that of the properties of recycled asphalt binders, by increasing low temperature grade and decreasing high temperature grade.

Evaluation of airport runway pavement based on pilots' subjective judgement

The fourth runway at Tokyo Haneda International Airport is to be constructed in part on a pier structure where it extends across a river mouth. Factors expected to affect aircraft operation safety and riding comfort are the deflection of the pier deck and the faulting between the pier structure and the adjoining reclaimed land. The objective of this study is to investigate these effects using a subjective evaluation method and, on the basis of the results, to select a suitable pier structure. Flight simulators representing the operation of a Boeing 747 and a DC 9-81 are used for this purpose. Runway profiles are created to represent different magnitudes of deflection and faulting, and these are input into the simulation program. Responses obtained from participants (experienced pilots) in the form of a questionnaire are recorded on a four-point scale. Analysis indicates that the operation safety and riding comfort decrease with the increase in deflection or faulting. Riding quality ratings are poorer than those for operation safety. Based on the criterion that at least 50% of the pilots rated the riding quality of a runway surface as uncomfortable or worse, an appropriate pier structure and the critical value of faulting are recommended.

LABORATORY VERIFICATION ON PERFORMANCE OF PIER DECK PAVEMENTS AT RUNWAY D IN TOKYO INTERNATIONAL AIRPORT

As the fourth runway at Tokyo International Airport (Runway D), the hybrid structures consisting of asphalt pavements on the pier are planned in part. As their behaviors against aircraft loading have been scarcely studied, several aspects on asphalt pavements on the pier (concrete decks) are studied through a variety of laboratory tests. The following results were obtained. 1) The surface course asphalt mixture with type H polymer-modified asphalt has the sufficient durability against both the repeated loading and the segregation between asphalt and aggregates. 2) The bonding between asphalt mixture layer and concrete deck is secured after 20, 000 times of repeated wheel track loading. This is also true in the case of loading test under the submerged conditions. 3) Three kinds of asphalt mixtures composing the surface course on concrete deck have the sufficient fatigue resistance as they have never been failed in 200, 000 times of loadings.

Influence of Seed Layer Moduli on Finite Element Method-Based Modulus Backcalculation Results

The determination of pavement layer moduli from falling weight deflec-tometer test data is known as backcalculation analysis. Generally, back-calculation analysis is unstable—greatly influenced by several causes of error. They may be categorized as modeling error in the forward analysis, deflection measurement error, or numerical computation error due to instability in the backcalculation procedure, for example. Because of these problems, the seed values selected for layer moduli greatly influence backcalculation results. To reduce the effects of measurement error, truncated singular-value decomposition is used for regularization. Variable scaling, often used in optimization algorithms, is implemented to improve numerical accuracy. A Ritz vector reduction method is used to solve a large system of dynamic equations in dynamic backcalculation efficiently, and various other means are introduced to decrease computational time. Recent updates of Dynamic Back Analysis for Layer Moduli software, first developed ...

DURABILITY OF GROOVING IN RUNWAYS FOR AIRCRAFT LOADS

空港滑走路におけるグルービングの航空機荷重に対する安定性について研究し，それを保持するために必要となる方策について明らかにした．まず，現地調査と数値解析の結果に基づき，すべり抵抗性を確保するという滑走路の要求性能を満足するためには，グルービングの溝の容積減少率を20％以内に抑えることが必要であることを見出した．そして，一連の室内試験を行った結果に基づいて，これを可能ならしめる具体策は，表層アスファルトコンクリートに改質アスファルトを使用することであることを明らかにした．これに加えて，オーバーレイの場合にはストレートアスファルトを用いたとしても，骨材面での工夫をした上である程度の養生期間を確保することで対応しうることがわかった．

Airport pavement roughness evaluation based on aircraft response

Runway roughness affects primarily ride quality and dynamic wheel loads. The forces applied onto the airport pavement by aircraft vary instantaneously above and blow the static weight, which in turn increase the runway roughness. One method to effectively assess the ride quality of the airport runway is to measure its longitudinal profile and numerical simulate aircraft response performing a takeoff, landing or taxiing on that profile data. In this study the aircraft responses excited as the aircraft accelerates or moves at a constant speed on the runway during takeoff and taxi are computed by using the improved computer program TAXI. This procedure is capable of taking into account both the effects of discrete runway bumps and runway roughness. Thus, sections of significant dynamic response can be determined, and the maintenance and rehabilitation works for airport runways will be conducted.

PERFORMANCE EVALUATION OF JOINT SEALING MATERIALS FOR AIRPORT CONCRETE PAVEMENT

空港コンクリート舗装の目地に使用される目地材や目地板などの目地材料に関しては, 空港土木工事共通仕様書において規格が定められている. これらの規格では, 目地材料の材質によって規格が大きく異なっていることや, 試験方法が明確でないことから, 目地材料に要求される性能を反映しているとは言い難い. 本研究では, 空港コンクリート舗装に用いられる目地材料に要求される性能を示し, それらを評価するための室内試験を実施した. その結果, 目地材料の性能は, 温度条件, 環境条件, 繰返し圧縮回数等により大きく変化することが明らかになった.

A STUDY ON INFLUENCE OF REJUVENATING AGENTS UPON PERFORMANCE OF RECYCLED ASPHALT

再生アスファルトコンクリートの配合設計において重要となる, 再生用添加剤が異なる場合のアスファルトの基本的特性について, 成分が大きく異なる3種類の再生用添加剤による再生アスファルトならびに再生アスファルトコンクリートを用いて検討した. その結果, 再生用添加剤を添加して再生することにより旧アスファルトの性状は大幅に改善されること, 製造ならびに供用後の劣化・老化を考えた場合には再生アスファルトと新規アスファルトとの差は明確ではなくなるものの再生用添加剤の影響が残っていること, さらに, 再生用添加剤の違いによる再生アスファルトコンクリートの特性の違いは老化の進行により明確ではなくなることがわかった.

Study on Joint Spacings of Airport Concrete Pavements

This paper describes the possibility of elongation of joint spacings in airport concrete pavements. First, experimental pavements of which joint spacings were 7.5 m and 8.5 m (conventional and longer) were constructed, and strain and temperature in concrete pavements were measured to study the influence of joint spacings on shrinkage stress and thermal stress. Then, the influence of joint spacings on stress due to both load and temperature change were analyzed by using finite element method. As a result, it was found that the differences of stresses due to both load and temperature change were negligible between two joint spacings, and the current design method of the slab thickness was also applicable in the case of longer joint spacings.