1,721,004 research outputs found
Shear failure characterization of time-temperature sensitive interfaces
No full textPoor interlayer bonding can lead to early failures and thus to a reduction in service life of bituminous pavements. For this reason, it is important to identify the parameters influencing the interlayer shear failure and to characterize their effect by means of laboratory test. In particular, this study is focussed on the effects of test temperature and deformation rate on the interlayer shear strength (ISS) of double-layered asphalt concrete specimens. First, the ISS was measured at temperatures ranging from 0 °C to 30 °C and deformation rates ranging from 0.5 mm/min to 9 mm/min using the Ancona Shear Testing Research and Analysis (ASTRA) device. Then the experimental data were analyzed using a two-stage statistical modelling approach. In the first stage, the variation of ISS versus deformation rate, at each testing temperature, was modelled using both a power-law and a logarithmic function. In the investigated range of deformation rate, the models allowed to estimate the mean ISS with residual standard error varying from 0.062 MPa to 0.128 MPa. Moreover, the linear regression coefficients, which measure the influence of the deformation rate on ISS, changed with temperature. In the second stage, both temperature and deformation rate were used as joint predictors of ISS by using an approach based on the superposition of their effects. Results showed that the time–temperature superposition approach is applicable and a sigmoid-shaped master curve for ISS was obtained. The proposed approach was validated by using ISS measurements obtained on the same materials with different test devices
Verifica prestazionale di materiali impiegati per la realizzazione di segnaletiche orizzontali
Full text linkRoad marking functional retraining is a maintenance operation that more and more often involves road pavement management. These maintenance operations, extended to the whole road network, become very expensive both for direct costs and for indirect costs due to traffic slowing down.
Road marking noticeably influences road safety. On the subject, some studies show that the decrease of accident risk is strongly connected with typical road marking characteristics as right visibility (day-time and night-time), suitable adhesion level and durability compatible with road network management. The Standard UNI EN 1436/98, according to the provisions of the Italian Road Code, fixes the principles to control road marking performances through the service life concept. It mainly depends on the frequency of vehicular passing, on the traffic variety, on the pavement characteristics and on the particular climatic conditions. However, it ignores engineering aspects tightly connected with the material life. In this sense, the above-mentioned Italian Road Code and the relative Regulations underline the need to characterize road marking as a material and not only as a “furniture”.
The present work shows the results of an experimental study carried out on a trial section. The characteristics of 6 different materials (3 solvent paints and 3 waterborne paints) were studied to evaluate both photometrical and adhesion properties employing the Standard provisions. Through direct comparisons and periodic monitoring, it has been possible to estimate, on two different pavement surfaces, the material life and the effects of environmental conditions on required performances
Validation of a hydraulic model to prevent emulsion flowing in chip sealing
No full textChip sealing is a pavement surface treatment that consists in the application of an asphalt binder (bitumen or bituminous emulsion) on an existing pavement followed by the spreading of aggregate chips and by the rolling of the surface, in order to embed the aggregate into the binder. This treatment is typically used as preventive maintenance technique of asphalt pavements, in order to seal fine cracks and improve skid-resistance of road surfaces. Moreover, chip sealing is often employed on rural roads, that carry low traffic volumes and are often characterized by critical conditions such as small radius of curvature and/or high longitudinal slopes. In the latter case, the application of the bituminous emulsion becomes a crucial concern as an excessive flowing of the bitumen could take place due to the high pavement slope and its spreading could become not uniform. In order to investigate these aspects, in this study ahydraulic model of the theoretical flow of bituminous emulsions on high longitudinal slope road surfaces was proposed and validated through a laboratory experimental investigation. To this aim, an original laboratory equipment (Chip Seal Laboratory Simulator), that allows the simulation of the most critical conditions during field activities, was properly designed and realized. The theoretical analysis and the experimental validation suggested practical recommendations in terms of longitudinal working speeds in critical contexts, very usual in practice. © 2015, Chinese Society of Pavement Engineering
Laboratory characterisation and field validation of geogrid-reinforced asphalt pavements
No full textIn order to improve the mechanical properties of pavements, reinforcement systems can be employed in asphalt layers. However, the presence of a grid at the interface causes an interlayer de-bonding effect. Moreover, a real challenge is related to the proper in situ installation of grids. The present research aims to evaluate the effectiveness of pavement rehabilitation with fibreglass geogrids. To this purpose, a real-scale field trial was constructed and monitored through Falling Weight Deflectometer measurements. Interface shear tests and flexural tests were also carried out on double-layered samples prepared in the laboratory reproducing realscale field trial characteristics. Moreover, shear tests were also performed on in situ cored specimens. Results mainly showed that a proper installation of the reinforcement is fundamental in order to obtain suitable test results and good pavement performance
Full-depth reclamation for the rehabilitation of local roads: a case study
No full textFull-depth reclamation (FDR) techniques for pavement construction and rehabilitation have gained general recognition
because of their technical, economical and environmental advantages. The use of cement–bitumen-treated material
(CBTM) has rapidly increased over the last 10 years mainly in motorways. Public administrations have recognised the
advantages of FDR, and this technique has also begun to be applied for the rehabilitation of local and/or rural roads. This
paper shows the results from a trial section built to verify the suitability of FDR for the rehabilitation of local roads.
The design planned the in situ stabilisation with styrene-butadiene-styrene (SBS)-modified bituminous emulsion and cement of hot mix asphalt and foundation course. The mechanical characteristics of CBTM were evaluated by means of stiffness modulus tests at different temperatures and fatigue tests. The obtained results offer good prospects for the application of FDR in the maintenance project of local roads
Influence of polymer modification on asphalt binder dynamic and steady flow viscosities
No full textAsphalt pavement performance such as rutting, crack initiation and propagation as well as fatigue behaviour are substantially affected by the rheological properties of the bitumen. In this sense, the use of polymer modification in road paving applications has been growing rapidly over the last decade as it allows significant enhancements in bitumen properties with consequent improvement in road service life. In fact, the use of polymer modified bitumens (PMBs) leads to pavements characterized by higher resistance to rutting and thermal cracking and lower fatigue damage, stripping and thermal susceptibility. This paper presents a laboratory investigation concerning the effect of polymer modification on the flow behaviour of bitumens. Two different polymers, an elastomer and a plastomer, were used as bitumen modifying agents at three different percentages (2%, 4% and 6% by bitumen weight). Oscillatory mechanical analysis as well as viscosity measurements under steady state conditions were performed taking into account different testing parameters such as temperature, loading frequency and shear rate. The results confirm that the rheological properties of PMBs are strongly influenced by polymer nature and polymer content. The bitumen viscosity on the dynamic domain was combined with that in the steady-state domain, confirming the applicability of the Cox–Merz relationship for the plain bitumen and the PMBs with low polymer content. Finally, the Cross and the Carreau models were found to be suitable to fit the steady state and the dynamic results in order to determine the viscosity function of the investigated bitumens
Shear and flexural characterization of grid-reinforced asphalt pavements and relation with field distress evolution
No full textThe use of geogrids at the interface of asphalt layers is currently adopted to improve pavement performance in terms of rutting, fatigue and reflective cracking. Several test methods have been proposed in order to simulate the complex mechanical behavior of reinforced pavements and assist practitioners in the selection of the appropriate reinforcement product. A particular subject of debate is the evaluation of geogrid effects in terms of both flexural strength and interlayer bonding. In this context, an interlaboratory experiment has been organized as part of the RILEM TC 237-SIB/TG4 with a twofold objective: to compare the predictive effectiveness of different experimental approaches and to analyze the behavior of different geogrid types. For this purpose two experimental reinforced test sections have been realized, the first one to prepare samples for the interlaboratory experiment, the second one to analyze the geogrid field performance under heavy traffic conditions. This paper describes the test results obtained by one participating laboratory on double-layered asphalt samples extracted from the first experimental section and compares them with the periodic visual observation of the reflective cracking evolution occurred in the second test section. The laboratory tests were performed following a specific testing protocol that combines interlayer shear tests, repeated loading tests in a four-point bending configuration and quasi-static three-point bending tests, in order to investigate the overall performance of double-layered asphalt systems. Results have shown that geogrid reinforcement does not noticeably influence the flexural stiffness and strength in the pre-cracking phase, whereas the crack propagation speed can be significantly reduced and the failure behavior may change from quasibrittle to ductile, depending on the interlayer shear resistance. Laboratory results were confirmed by periodic visual observation of field performance in terms of reflective cracking evolution
Experimental characterization of transparent synthetic binder mixes reinforced with cellulose fibres
No full textThe use of synthetic binders in wearing course mixes allows to integrate road pavements into urban surroundings. In fact, the mixes prepared with this binder mitigate the visual impact that common asphalt materials produce, allowing a pavement coloration depending on the aggregate dyes to be obtained. In this paper, the characterization of open graded mixes prepared with a synthetic binder, reinforced or not with cellulose fibres, was performed. In particular, nine mixes, with different binder and cellulose fibre contents, were investigated through several laboratory tests to find the ‘optimum’ mix in terms of both mechanical performance and durability. The study of all mixes was performed in two steps. In the first step, traditional tests were carried out: Marshall, Indirect Tensile and Cantabro tests. Moreover, to investigate the water effect on these open graded mixes, the traditional tests were also performed on specimens immersed in water for 15 days, and the results were compared. In the second step, the same nine mixes were investigated in terms of rutting behaviour by using Wheel Tracker Machine, and stiffness modulus and fatigue strength through Nottingham Asphalt Tester (NAT). Finally, the comparison with a traditional open graded mix (with SBS hard bitumen) was performed showing higher laboratory performance for the synthetic binder mix. This paper shows that specific synthetic binder and cellulose fibre contents provide an ‘optimum’ open graded mix
Repeatability of Interlayer Shear Resistance determined With Two Test Procedure
Full text linkInterlayer bonding significantly influences the performance of multi-layered pavement systems. To correctly know how this bonding modifies the interlayer mechanical performance, theoretical and experimental projects are currently in progress in many countries. However, different equipments generally provide different results because these results are obtained under different test conditions in terms of applied stress and strain, rate of displacement, specimen size and specimen confinement. Since in European Standards there is a normative gap regarding interlayer resistance tests, in Italy a draft of a standard is currently under development based on a laboratory direct shear device called ASTRA (Ancona Shear Testing Research and Analysis). In the present paper, the repeatability of ASTRA test method is studied by analyzing the results obtained in two experimental investigations. In the first investigation, specimens prepared with the same material and the same compactor were tested with ASTRA test method and with another shear test method, the LPDS (Layer-Parallel Direct Shear), which is compatible with Swiss Standards (Schweizer Norm SN 671961, 2000). In the second investigation, the first series of ASTRA results were compared with repeatability results obtained by using different materials and different compaction methods for the double-layered specimens. The study shows that the two shear test equipments provide the same precision level in terms of scatter of the results. Moreover, the ASTRA investigation shows that the repeatability depends not only on the test method but also on the pavement material and compaction method. This study allows supporting Italian standardization of interlayer shear resistance testing and, at the same time, it shows that it is necessary to further investigate different materials and different compaction methods to improve the knowledge on repeatability
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