RESUMO
There is a growing interest in multifunctional composites and in the identification of novel applications for recycled materials. In this work, the design and fabrication of multiple particle-loaded polymer composites, including micronized rubber from end-of-life tires, is studied. The integration of these composites as part of ultrasonic transducers can further expand the functionality of the piezoelectric material in the transducer in terms of sensitivity, bandwidth, ringing and axial resolution and help to facilitate the fabrication and use of phantoms for echography. The adopted approach is a multiphase and multiscale one, based on a polymeric matrix with a load of recycled rubber and tungsten powders. A fabrication procedure, compatible with transducer manufacturing, is proposed and successfully used. We also proposed a modelling approach to calculate the complex elastic modulus, the ultrasonic damping and to evaluate the relative influence of particle scattering. It is concluded that it is possible to obtain materials with acoustic impedance in the range 2.35-15.6 MRayl, ultrasound velocity in the range 790-2570 m/s, attenuation at 3 MHz, from 0.96 up to 27 dB/mm with a variation of the attenuation with the frequency following a power law with exponent in the range 1.2-3.2. These ranges of values permit us to obtain most of the material properties demanded in ultrasonic engineering.
RESUMO
Sustainable composite brake pads were processed by employing recycled end-of-life tire (ELT) rubber particles obtained by means of cryogenic grinding and ambient grinding. The effect of the grinding mechanism and concentration of ELT rubber particles was then reported. From the friction result test, better behavior in terms of coefficient of friction (COF) was obtained when 3% of ELT rubber particles were introduced into the composite. It was demonstrated that the size of the particles is not as determinant as the friction mechanism in the wear properties of the sustainable brake pads. Whereas, while increasing the ELT rubber particle size acts as detrimental to the COF either in the ambient or cryogenic grinding, at high friction distances, the better adhesion of the particles because of the rough surface of the particles subjected to ambient grinding enhances the long-life behavior of the composite brake pads.
RESUMO
Stone mastic asphalt (SMA) mixtures exhibit excellent behaviour; they are highly resistant to reflective cracking and permanent deformation, as well as providing the wearing surface with an optimal texture. However, the production and compaction temperatures are similar to conventional mixtures, which means that there is a significant consumption of energy, as well as greenhouse gas emissions. Warm mix asphalt (WMA) technology, which has been developed over the last few years, might allow lower temperatures without compromising the mechanical behaviour of the mixtures. Also, over the last few decades, rubberized asphalt has proved to be effective in improving the performance and being environmentally suitable, but it requires higher production temperatures than conventional mixtures. In this study, several tests were performed to evaluate the effect of a chemical WMA additive on the compactability and water sensitivity of rubberized SMA mixtures with both the Marshall and the gyratory compactor. The investigation has shown that the gyratory compactor is more suitable for studying compactability and the water sensitivity of rubberized SMA with WMA additives.
