1,721,691 research outputs found
Discussion on SPT N-value and S-wave velocity for gravelly soil with different grain size distribution.
No full textFatigue and healing properties of rubberised asphalt binders produced with pre-treated recycled rubber
No full textIn this paper, the fatigue and healing properties of Recycled Tyre Rubber Modified Bitumens (RTR-MBs) produced with pre-treated recycled rubber were investigated. Using the pre-treated rubber has resulted in a considerable decrease in the High Temperature Viscosity (HTV) compared to none-pre-treated rubber which is important for better handling and workability. Fatigue cracking is considered the main distress mode of asphalt pavement at intermediate temperatures, as pavement is subjected to a considerable number of repetitive traffic loads. Thus, selecting an appropriate test method and parameters is crucial to realistically rate the binder contribution to fatigue damage resistance. Utilising the dynamic shear rheometer (DSR), time sweep tests were conducted by applying repeated cycling of stress or strain loading at selected temperatures and loading frequency. The healing potential of binders was evaluated by introducing short rest periods (RPs) after a certain number of load pulses. The unique energy parameter known as the Plateau Value (PV), which is obtained using the Ratio of Dissipated Energy Change (RDEC) approach, was applied to evaluate the fatigue binder damage and healing phenomenon. The results showed that both rubberised bitumens produced by activated recycled rubber are better fatigue and healing performers than the straight-run bitumen
Use of 1D and 2D seismic response analyses of soil deposits for seismic Microzonation of urban areas in Tuscany (Italy)
No full textThe paper firstly summarizes the main factors affecting seismic response of natural soil deposits with special attention to soil nonlinearity. Then, the available simplified approaches to assess stratigraphic and topographic amplification effects in various codes are discussed.In the second part, the paper shows the results of 1D and 2D Seismic Response Analyses (SRAs), that were performed for the urban centre of Castelnuovo di Garfagnana which is in one of the most seismic areas of Tuscany (Italy). More specifically, the construction of the geotechnical models for seismic response analyses carried out for three cross-sections is illustrated, based on geological and geotechnical information and data available in the Tuscany Region database developed in the framework of the VEL Project. The paper also describes this interactive, georeferenced database. The last part of the paper presents the results of the numerical analyses on selected representative points located along the surface of soil deposit in terms of bar plots of amplification factors. Various available criteria to express 2D amplification effects were considered and summarised. Anyway, the possible aggravation effect was computed by means of an ad - hoc defined parameter. Moreover, possible criteria to extend the SRA results that were obtained for a given geological section over the whole study area were discussed. Use of the average shear wave velocity parameter, V-s,V-30, revealed the most appropriate and cost-effective criterion
Improved Testing Setup for Real-Time Monitoring of PMBs During Manufacturing and Rotational Viscosity Measurements
No full textPolymer modified binders (PMBs) are a practical solution to design
asphaltmixtures with superior performance. Although these polymers often improve
bitumen properties to some extent, their final performance are linked to the accurate
control of the properties during manufacturing and storage. However, some
of the common procedures used to characterise neat bitumen are not suitable with
these binders making their characterisation challenging. This study presents a novel
laboratory procedure to produce SBS-MB through a real-time monitoring of the
rotational viscosity, as well as an attempt to understand the suitability of current
testing geometries to measure viscosity of such a complex bituminous binder. The
proposed innovation lies in the adoption of a Dual Helical Ribbon (DHR), as a
novel mixing/measuring device for rotational viscometers. The laboratory tests were
undertaken by using the DHR and a standard coaxial cylinder configuration with
a spindle geometry (SC27) as a control to record eventual differences in viscosity
measurements of PMBs. As a result, the real-time monitoring procedure improved
the governing of the modifications process, furthermore, it was proven that when
blends with high polymer content and no cross linker are tested, the conventional
coaxial cylinder setup for rotational viscosity measurements might not be adequate
and spindle geometries should be replaced with the DHR
Evaluating degree of compaction of levees using cone penetration testing
Full text linkPermeability and strength parameters of compacted soils (i.e., levees as well as other earthworks) may be correlated to the degree of compaction. Since the use of conventional and recent testing methods for the assessment of density and water content of earthworks, under construction, cannot be applied to existing levees, an expeditious and accurate method for the assessment of the degree of compaction of existing and new levees, after their completion, appears extremely useful. The purpose of this research is to develop a simple tool for the assessment of the degree of compaction of "compacted", partially saturated, fine grained soils. This paper illustrates the proposed method which combines in situ testing such as electric CPT or CPTu with laboratory penetration testing performed with a mini-cone in a calibration chamber (CC). © 2018, Taiwan Geotechnical Society
Are we correctly measuring the rotational viscosity of heterogeneous bituminous binders?
Full text linkModified bituminous binders allow asphalt technologists to design asphalt mixtures with superior performance. However, several recent studies highlighted that due to the complexity of these material, their characterisation can be challenging since common procedures used to characterise neat bitumen might not be adequate. For instance, during high temperature rotational viscosity testing of recycled tyre rubber modified binders (RTR-MB), a number of changes may occur to the sample leading to the here-defined sample stability which in turn provides misleading results. In this study the authors want to first provide a deeper understanding of this phenomenon by a numerical analysis using a bespoke Computational Fluid Dynamics (CFD) model to simulate the laboratory tests and use innovative visual aids to monitor the sample stability of heterogeneous bituminous binders during the rotational test. The numerical analysis was complemented by a laboratory campaign aiming at proving the occurring of sample stability during viscosity measurement of heterogeneous bituminous binders with a standard testing setup (SC-27). Furthermore, a dual helical ribbon (DHR) is here introduced as a solution to overcome the issue. Hence, laboratory tests were undertaken also with DHR and differences in viscosity measurements of neat bitumen, SBS-MB and RTR-MB were recorded. Results of this combined numerical and empirical approach proved that the standard setup for rotational viscosity measurements seems not be adequate for RTR-MB and depending on the level of modification and test temperatures, might not be best suited for SBS-MB either. The DHR seems to solve the issue and authors strongly recommend the adoption of this testing geometry to obtain more realistic high-temperature viscosity measurement of heterogeneous bituminous binders
Evaluating liquefaction potential of soils using CPT: a case study in the central Po River Plain, Italy
No full textNumerical simulation of seismic response of earth dams
No full textThe paper aims at evaluating the capabilities and limitations of some numerical tools for estimating the seismic response of earth dams. In particular, the recorded acceleration time histories and permanent displacements are compared against those predicted by using a 2D FEM code (Quake/W). Acceleration time histories and displacements were recorded during centrifuge tests of reduced scale model of an earth-core rockfill dam (ECRD). Such tests were carried out by researchers at KAIST (Korea Advanced Institute of Science & Technology) and results were recently published. This paper summarizes the essential aspects of these experiments for the sake of clarity
3D FEM and DEM Analyses of Underground Openings in Competent Rock Masses
Full text linkThe paper is aimed at comparing the results of numerical analyses of underground openings in
competent rock masses like the Carrara Marble (Italy) by considering a real and well documented case
study. More specifically, 3D FEM and DEM analyses were carried out on a rock-mass model interested by
two faults and three sets of discontinuities. The geometrical model is representative of deep underground
openings where spalling-cracks and rock bursts can occur. PLAXIS 3D and 3DEC were used for the
analyses. Intact rock and rock mass characterization of Carrara Marble was inferred from available
technical literature. The analysis results were compared in terms of principal stresses and displacements
in a number of monitoring points around the opening. The main practical interest is to find out a reliable
approach for evaluating the stability of very large openings in a competent rock mass like Carrara marble.
For such a purpose, a number of available in-situ stress measurements were used
EFFECT OF PROCESSING TEMPERATURE VARIATION ON STORAGE STABILITY OF TIRE RUBBER MODIFIED BINDERS
No full textTire Rubber Modified Binders (TR-MBs), produced through wet process and used worldwide (e.g. asphalt rubber), have been demonstrated to provide various benefits to pavements and, moreover, represent a good opportunity for recycling tire rubber. However, this technology is still struggling to be fully adopted in Europe, mainly because of the poor stability of TR-MBs during high temperature storage, which leads to high initial costs in modifying existing asphalt plants. No-agitation TR-MBs (also known as terminal blends) are proving to be a great option and their development could also be the key to spreading the use of tire rubber in paving applications in Europe. This paper aims to enrich this field of research by presenting the results of a study focused on the compatibility of tire rubber-bitumen blends as well as on the effect of processing temperature variation on storage stability of TR-MBs. The experimental program was carried out by a preliminary selection of materials, followed by the production of the TR-MBs, via practical laboratory protocols. A continual comparison between two commercially used SBS-MBs, with high and medium levels of modification, and the TR-MBs produced, helped to understand the effect of varying the selected processing conditions on binder properties. The results showed that an accurate binder design is fundamental in order to obtain high performance binders and to improve compatibility of TR-MBs. Moreover, the study highlights that dynamic mechanical analysis (DMA) is a suitable technique to assess the storage stability of modified binders
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