Francesco Asdrubali

A Review of Sustainable Materials for Acoustic Applications

Acoustical sustainable materials, either natural or made from recycled materials, are quite often a valid alternative to traditional synthetic materials. The production of these materials generally has a lower environmental impact than conventional ones, though a proper analysis of their sustainability, through Life Cycle Assessment procedures, has to be carried out.Airborne sound insulation of natural materials such as flax or of recycled cellulose fibres is similar to the one of rock or glass wool. Many natural materials (bamboo, kenaf, coco fibres) show good sound absorbing performances; cork or recycled rubber layers can be very effective for impact sound insulation. These materials also show good thermal insulation properties, are often light and they are not harmful for human health. Furthermore, many of these materials are currently available on the market at competitive prices.There is however a need to complete their characterization, both from an experimental and a theoretical point of view, and...

Properties of transparent sound-absorbing panels for use in noise barriers

Sound absorption and optical transparency are among the most useful properties of noise barriers. While the latter is required to reduce visual impact and for aesthetical reasons, the former is required whenever conditions of multiple reflections and presence of close, high receivers occur. The technical feasibility of a transparent, sound-absorbing panel for outdoor antinoise devices is investigated in this paper. An analysis of acoustical performance of multiple perforated plates is performed employing an existing theory for microperforated absorbers under normal incidence and diffused sound field. An optimization of the geometrical parameters is carried out on the basis of the European classification criteria of noise barriers for roadways. An optimized three-layer configuration can achieve sound-absorption properties similar to nontransparent products with only a limited loss of visual transparency and appropriate mechanical strength. Experimental data obtained with an impedance tube on small test sam...

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.

Environmental impact of an Italian wine bottle: Carbon and water footprint assessment

The food sector represents one of the major impacting sectors from an environmental point of view and, among all the products, wine emerges as one of the most studied by the literature. Single-issue approaches are commonly used, but a more comprehensive analysis is desirable, since a single indicator does not properly track the pressure on the environment. This paper presents a combined carbon and water footprint assessment, with a cradle to grave approach, for a protected designation of origin Italian red wine, and suggests a correlation among the two indicators across the life cycle phases. A total CF equal to 1.07±0.09kgCO2eq/bottle and a total WF equal to 580±30l/bottle were calculated for the studied product and a direct proportionality was found between the total CF and the sum of WFgrey(indirect) and WFblue.

Transmission loss measurement of consolidated granular media (L)

The normal incidence transmission loss of a new class of sustainable acoustic materials, i.e. consolidated granular media, has been measured to determine their sound insulating performance. Tests performed on different samples in a standing wave tube suggest that the traditional method employing an anechoic termination assumption can yield serious errors because its accuracy depends significantly on the properties of both the termination and the tested sample. Since it is not possible to implement a perfect anechoic termination over a wide frequency range, a well-developed alternative approach has been adopted. A simple theoretical analysis has been carried out to compare these two methods. It has been shown that the two-load method, based on two sets of measurements with different boundary conditions at the tube termination, can give more reliable and predictable results. Greater discrepancies have been observed in the case of the anechoic termination method applied to samples with higher values of flow ...

The Acoustic Properties of Expanded Clay Granulates

The purpose of this work is to characterise experimentally and theoretically the acoustic performance of mixes of loose expanded clay granulates. The surface acoustic impedance is obtained from measurements in the impedance tube and predicted using the Pade approximation approach. The random incidence absorption coefficient is measured using the ISO 345/85 method. Experimental data for the surface acoustic impedance are used to deduce the porosity, tortuosity and the statistical pore size distribution; these parameters are difficult to obtain directly, because of the relatively low density of the loose granulates and the fact that the granular base contains 5–30% of the closed, unconnected pores. Good agreement between the theory and the results is found; 50–100 mm layers of expanded clay granulates can be used efficiently for noise control over a broad frequency range.

Sound absorbing properties of materials made of rubber crumbs

Recycled tyre granules can be used for manufacturing acoustic insulating and absorbing materials, with applications in buildings and road barriers. Therefore, the production of these materials is a valid alternative to the disposal into landfill or incineration of used tyres. This paper presents the results of sound absorbing coefficient measurements of several samples manufactured at the Acoustics Laboratory of the University of Perugia. The sound absorbing panels were produced by mixing rubber crumbs and an adequate binder in a proper proportion and then by compacting the obtained mix. The methodology used to evaluate coefficient of absorption coefficient is indicated in ISO 10534‐2 standard, thanks to an impedance tube. The influence on the absorption performance of granules size, binder concentration, thickness and compaction ratio of the samples was investigated and an optimization process was carried out, in order to produce a sample with satisfying acoustical performances.

How reproducible is the acoustical characterization of porous media

There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of ScienceTM (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory measurements were performed on the same material specimens so that the naturally occurring inhomogeneity in materials was controlled. It also presented the reproducibility data for the characteristic impedance, complex wavenumber, and for some related pore structure properties. This work can be helpful to better understand the tolerances of these material characterization procedures so improvements can be developed to reduce experimental errors and improve the reproducibility between laboratories.

Detection of thermal bridges from thermographic images by means of image processing approximation algorithms

In this paper, we develop a procedure for the detection of the contours of thermal bridges from thermographic images, in order to study the energy performance of buildings. Two main steps of the above method are: the enhancement of the thermographic images by an optimized version of the mathematical algorithm for digital image processing based on the theory of sampling Kantorovich operators, and the application of a suitable thresholding based on the analysis of the histogram of the enhanced thermographic images. Finally, an improvement of the parameter defining the thermal bridge is obtained.

Self-sensing and thermal energy experimental characterization of multifunctional cement-matrix composites with carbon nano-inclusions

The recent progress of Nanotechnology allowed the development of new smart materials in several fields of engineering. In particular, innovative construction materials with multifunctional enhanced properties can be produced. The paper presents an experimental characterization on cement-matrix pastes doped with Carbon Nanotubes, Carbon Nano-fibers, Carbon Black and Graphene Nano-platelets. Both electro-mechanical and thermo-physical investigations have been carried out. The conductive nano-inclusions provide the cementitious matrix with piezo-resistive properties allowing the detection of external strain and stress changes. Thereby, traditional building materials, such as concrete and cementitious materials in general, would be capable of self-monitoring the state of deformation they are subject to, giving rise to diffuse sensing systems of structural integrity. Besides supplying self-sensing abilities, carbon nano-fillers may change mechanical, physical and thermal properties of cementitious composites. The experimental tests of the research have been mainly concentrated on the thermal conductivity and the optical properties of the different nano-modified materials, in order to make a critical comparison between them. The aim of the work is the characterization of an innovative multifunctional composite capable of combining self-monitoring properties with proper mechanical and thermal-energy efficiency characteristics. The potential applications of these nano-modified materials cover a wide range of possibilities, such as structural elements, floors, geothermal piles, radiant systems and more.