Eiffage Infraestructuras was in charge of the design at laboratory level of the noise-reducing asphalt mixes, with incorporation of waste that acts as raw material in the process (plastics of agricultural origin, plastics from electrical cabling, nylon fibres and powdered rubber from disused tyres). Specifically, the design is a high-durability SMA-type mix that incorporates waste materials with the aim of achieving a reduction in rolling noise at source owing to the interaction between tyre and road surface.
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| Plastic of agricultural origin | Plastic from electrical cabling | Nylon fibres | Powdered rubber |
The design of the working formulas was carried out in two phases:
1. Characterization of the raw materials
- Ophitic and limestone aggregates
- Recovered limestone filler
- 35/50 bitumen and bitumen modified with BM3c-type polymers for the reference mixes, AC16 surf and SMA respectively and 50/70 bitumen for mixes designed for noise-reducing purposes through the use of different types of waste as raw material.
- Waste additives: plastics of agricultural origin, plastics from electrical wiring, nylon fibres and powdered rubber from disused tyres.
2. Design of the mixes. On the basis of the characterised materials we proceeded to the design and development of the LIFESOUNDLESS mixes being studied at laboratory level. In doing this we performed the following work:
- Defining the particle size curve by taking as a reference the granulometric range of the Regulation Proposal of the Technical Specifications for SMA-type mixes. This proposal was drafted based on the experiences gathered in the SMA Project, “Environmentally friendly sustainable SMA mixes" funded by the Technology Centre for Industrial Development (CDTI).
- Formulating the LIFESOUNDLESS mixes based on their composition and granulometric range.
- Checking the characteristics of asphalt mixes, using the test methods corresponding to the UNE-EN 12697 standard
- Granulometry (UNE EN 12697-2
- Bitumen content (UNE EN 12697-39)
- Runoff (UNE EN 12697-18)
- Maximum density (UNE EN 12697-5)
- Bulk density (UNE EN 12697-6)
- Voids content (UNE EN 12697-8)
- Particle loss (UNE EN 12697-17)
- Marshall test (UNE EN 12697-34)
- Water sensitivity (UNE EN 12697-12)
- Wheel-tracking test (UNE EN 12697-22)
This characterisation is performed on laboratory-made samples. Below we graphically show the sequence of producing LIFESOUNDLESS mixes with the addition of waste:
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| Mixer | Drying of aggregate |
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| Weighing of aggregate | Weighing of waste |
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| Incorporation of aggregate | Incorporation of waste |
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| Mixing (aggregate waste) | Incorporation of bitumen |
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| Incorporation of filler | Mixing (aggregate waste) bitumen filler |
Once the new asphalt mix formulas have been designed, they will be materialised and their properties and characteristics will then be analysed. This characterisation has been carried out by the Acoustics and Vibrations laboratory of the CIDAUT Foundation.
The tests were conducted in 400 x 300-mm test tubes 25mm thick. Specifically, the following parameters were applied:
- Mechanical impedance:
This method measures the stiffness of the road surface and gives us an idea of how aggressive it can be in exciting vibrations that make sound radiate to the tyre.
- Texture:
Volumetric method: It measures the MTD (Mean Texture Depth) parameter. The measurement procedure is regulated by the EN 13036-1:2000 standard. It is used for measuring textures that fall into a range of between 0.25 mm and 5 mm.
- Sound absorption:
The purpose of this test is to assess the sound absorption of each one of the mixes we designed. The test consists of subjecting the round test tube 100 mm in diameter to white noise in the 50 to 1600 Hz range and assessing the acoustic energy absorbed by the test tube. For this test we used a Kundt’s tube such as the one shown in the second photograph.