1,721,053 research outputs found
A comprehensive model to predict acoustic absorption factor of porous asphalt mixes
No full textThe aim of this study is to define an experimental model to predict acoustic absorption properties of porous asphalt concretes (PAC) as a function of composition and volumetric characteristics of mixes. The model can be used for the mix design of PAC and it enables to individuate which composition parameters to operate on in order to obtain optimum acoustic performances of low noise porous pavements.
In order to define the experimental model, a large number of asphalt concrete samples, with high void content and composed of both different aggregate grading and different bitumen percentages were compacted in laboratory. Noise absorption spectra were determined on these samples by means of the stationary wave impedance tube. The measured amplitudes of the acoustic absorption spectrum were fitted by the Neithalath microstructural model in order to determine, for each sample, the pore geometry which allows to reproduce the measured acoustic absorption spectrum. After that, the pore geometry was related to composition and volumetric characteristics of mixes by means of multivariate regression techniques. By this way, the acoustic absorption spectrum of PAC can be predicted as function of specific composition parameters
Peak Friction Prediction Model Based on Surface Texture Characteristics
No full textThe paper proposes a new model for predicting the speed gradient of peak friction values on asphalt pavements based on surface characteristics. The innovative feature of the proposed model is the reliable estimation of peak friction values experienced by vehicles equipped with anti-locking brake system (ABS) at a certain vehicle speed.
In order to define the experimental model, several types of Dense Asphalt Concrete (DAC) surface layers, with different surface characteristics, are analyzed by in situ tests. Friction is measured by the Skiddometer BV11 and the British Pendulum Tester whilst texture properties are measured by a laser profilometer.
The Rado model is used to predict peak friction values at 3 different vehicle speeds and, by using these data, the gradient of peak friction values is determined for each pavement section.
The spectral analysis of pavement profile data allows to define a texture parameter that is negatively correlated with peak friction values; this parameter is introduced in a new formulation of the speed number SP* that is a measure of the pavement macrotexture influencing peak friction values. The speed number SP* is used in the new exponential model proposed to defining the gradient of peak friction values. The obtained results show the model is highly reliable and, as it enables to identify texture characteristics to be modified in order to optimize peak friction values, it is particularly useful for the optimization of the mix design and maintenance of pavement surfaces
Studio e controllo di pavimentazioni stradali a bassa emissione sonora in ambito urbano - Usura con argilla espansa
No full textRapporto di Ricerc
Mixture design optimization of low-noise pavements
No full textThis paper proposes a tool to optimize the mix design of low-noise pavements. An experimental model was developed to predict the rolling noise of a reference car tire as a function of the composition and volumetric characteristics of mixes obtained from in-service pavements. The model enables an analyst to identify which composition parameters need to be altered to improve the acoustic performance of a low-noise pavement.
To define the experimental model, several types of asphalt surface layers composed of hot-mix asphalt mixtures with different void contents, different aggregate grading, and different bitumen percentages were analyzed in situ and by laboratory tests. The acoustical properties of pavement surfaces were evaluated by the close-proximity method. The model was defined by using a multivariate nonlinear regression technique to relate composition and volumetric characteristics of asphalt mixtures with rolling noise levels recorded at different speeds. This model, which is a function of several significant parameters of asphalt mixture composition and tire speed, has proved to be highly reliable in predicting car tire rolling noise. Because the model enables the identification of mixture characteristics that require modification in relation to the specific value of the mean traffic speed, it is particularly useful for the optimization of low-noise pavement mix design
Mechanical and Performance-related Properties of Asphalt Mixes Containing Expanded Clay Aggregate
No full textThe use of artificial aggregates such as expanded clay in the production of asphalt concrete makes it possible to reduce both natural aggregate extraction and the use of non-renewable raw resources, giving considerable environmental benefits. Moreover, the expanded clay production process allows non-dangerous waste materials to be reclaimed, thereby avoiding disposal as landfill or dumping, with consequent environmental and economic advantages. This paper reports on the results of laboratory and in situ tests carried out to evaluate the feasibility and advantages of using expanded clay in producing asphalt mixes for use in urban areas with the aim of reducing traffic noise. Some experimental low noise asphalt surfaces were laid, using 15 % of expanded clay by weight, and mechanical as well as performance properties were evaluated. The mechanical characteristics, friction and acoustic performance obtained, in comparison to results with traditional asphalt surfaces, showed that considerable benefits derive from use of expanded clay in asphalt mixes for surface layers. In particular, interesting results in terms of friction increase and noise spectrum reduction were observed
Empirical rolling noise prediction models based on pavement surface characteristics
No full textTyre/road noise is a complex phenomenon which is function of tyre, surface properties and speed. This study aims to define a rolling noise prediction model for a reference tyre, as a function of speed, on dense asphalt surfaces with medium-low macrotexture levels. The model was defined by relating texture levels of pavement profiles and rolling noise levels recorded at different speeds. The study also defines an extension of the model valuable for semi-porous surfaces, as a function of only surface characteristics. Both of the models serve as a support tool for mix design of low noise asphalt pavement surface
A New Step Towards Performance Based Specifications for Asphalt Pavements
No full textTechnical specifications of many Agencies are quickly moving from prescriptive to performance based, that requires field compliance tests of the constructed pavement, such as in situ pavement stiffness measurements by the Falling-Weight Deflectometer (FWD). This creates a number of issues for material suppliers, constructors, consultants, designers and end users who are now required to rely on data produced from such devices for design and compliance checks in the field. Whilst there is wide experience on the use of such devices, issues remain such as optimisation of test methodology, data interpretation and use, comparison between laboratory and in situ measured moduli.
The aim of this work is to define a data interpretation procedure and a framework for the analysis of results obtained by using such device to ensure high quality data and decision making, particularly for their role in performance based specifications. In a previous work, a particular testing and data interpretation procedure have been proposed in order to evaluate strains in pavement layers directly from FWD deflections and pavement layer thickness; here the values of elastic modulus back-calculated in the previous work are compared with those of resilient modulus MR evaluated by laboratory tests carried out on cores taken from pavement.
Stiffness Master Curves (SMC) have been developed by using the resilient modulus data determined at various test temperatures and loading frequencies, and they have been used for shifting data to the in-situ asphalt pavement conditions. The frequency spectrum of FWD load has been calculated in order to assume a representative loading frequency for this device. For this loading frequency, the back-calculated asphalt modulus has shown excellent correlation with the corresponding values of the SMC. This illustrates that reasonable estimates of the in situ asphalt modulus can be provided by using the Indirect Tensile Test for Cylindrical Specimens (IT-CY) protocol to determine resilient modulus on cores or specimens compacted in laboratory; values obtained by this test must be shifted to in situ test conditions in order to be related to in situ asphalt modulus values, and to be used with elastic theory in pavement design
Measurements of Pavement Macrotexture with Stationary and Mobile Profilometers
No full textThe ISO 13473-1 provides an equation to estimate Mean Texture Depth (MTD) from Mean Profile Depth (MPD) measurements. Many studies on determination of relations between MTD and MPD have been conducted, but they have not always given the same results.
The aim of this work is to describe a data analysis procedure that can estimate MTD values by analysing pavement profiles recorded with stationary and mobile profilometers. For this purpose, a statistical analysis of MPD values obtained with a mobile profilometer was carried out in order to determine the right data analysis procedure; the directional properties of the surface texture were evaluated by analysing profiles recorded in directions: parallel, perpendicular and at 45° to the direction of traffic
Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces
No full textThe principal advantage of introducing some percentages of crumb rubber in production of asphalt mixtures is related to pavement environmental sustainability, since this process allows to recycle a significant amount of an industrial waste and, in some specific cases, to reduce tire/road noise emissions; there are some other not unanimously recognized advantages related to this process that are the improvement of asphalt mixture mechanical properties and durability as well as friction on pavement surface. This paper reports on a research project carried out to evaluate the advantages of using crumb rubber in construction of low noise gap graded asphalt concrete surfaces, specifically designed to reduce rolling noise by optimizing surface texture. The study also aimed to define the mechanical and functional performances of the mix obtained by using the wet process in order to assess its potential for use as viable alternative to other low noise asphalt surfaces aimed to improve pavement sustainability by reducing environmental, social and economic impacts. Results of laboratory and on site tests, carried out on one specifically built field trial, clearly show this mix can have optimal mechanical and functional performance as well as it can reduce tire/road noise and warrant greater durability of wearing layers; this considering, crumb rubber modified asphalt concrete can be classified as a construction material that can enhance the three dimensions of sustainability
A Statistical Model for Prediction of Critical Strains in Pavements from Deflection Measurements
No full textExisting pavements of collector rural roads are often characterized by a strong dishomogeneity in pavement layer thicknesses and mechanical properties of materials. In order to evaluate structural conditions of these pavements, they must be delineated in homogeneous sub-sections with regard to variations both in the thickness and the mechanical properties of pavement layers, but this task is often very difficult. For this purpose, this paper proposes a statistical model for the straight evaluation of critical strains in pavements by using the deflections measured by the Falling Weight Deflectometer and the layer thicknesses without backcalculating layer moduli. The model is calibrated on the basis of experimental data and it is useful to evaluate statistical parameters of the homogeneous sub-sections with the aim to evaluate the residual pavement life taking into account the reliability concepts
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