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WHAT IS BMB? |
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The asphalt made with tires’ recycled rubber (BMB), which production procedures are defined by the ASTM D 6114 incorporates at least 20 to 22% crumb rubber, over the binder’s total weight. |
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When was the BMB invented? |
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Since 1920 chemical engineers have tried to incorporate rubber into asphalt. However, most of the times they didn’t succeed.
In 1960, Charles McDonald, an ex member of the federal Bureau of Highways (currently FHWA) in the USA, who later became a Supervisor Engineer of the Material Tests Section for the city of Phoenix, Arizona, also in the USA, developed the first successful time/temperature formula for the tire residue incorporation in road paving.
This process is frequently referred to as the McDonald process, Arizona process or wet track process. |
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How and where is the BMB made? |
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The bitumen modifying procedure is made in the plants that produce asphalt mixes with the appropriate equipment, which includes a mixer and reaction tanks, with temperature control, proportionally to the asphalt plant’s production. |
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What are the advantages of the introduction of big percentages of granulated rubber into the bitumen? |
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The introduction of the granulated rubber into the hot bitumen causes the rubber to react and at the same time, absorbs and sticks the malthenes, which constitute one of the volatile and aromatic bitumen fractions.
This bitumen component’s fixture allows to obtain a significant raise in the resistance towards the ageing of the asphalt rubber mix with BMB, comparatively to the conventional asphalt mixes where the malthenes are lost in time by the action of the UV rays.
On the other hand, introducing the crumb rubber into the bitumen allows us to obtain a binder with 15 to 20 times more viscosity than a conventional asphalt mix. This viscosity level allows the incorporation of big amounts of BMB in the asphalt mixes without putting in risk the resistance of the mixes to the permanent deformations.
Putting big amounts of BMB into the mixes, approximately from 9 to 10%, we can obtain remarkable performances such as high resistance to fatigue, high resistance to cracks formation, etc. |
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Is the BMB more expensive than regular bitumen? |
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The cost of the BMB is approximately twice the cost of regular bitumen.
However, we can say that, after analysing every technical question, in most of the projects, the construction costs are similar.
In fact, according to the physical characteristics of the BMB and the asphalt mixes with this binder, namely the greater resistance to fatigue (10 times more than a conventional asphalt mix) and the also high resistance to cracks formation, the thickness used in this kind of mixes can be half the thickness used in the conventional mixes. It is important to refer that the use of this kind of mixes allows the elimination of a few previous works that exist in the traditional projects, such as the milling of the ruined areas by fatigue, the sealing of cracks, etc.
In the case of using asphalt mixes with BMB on pavements that are treated with hydraulic binders (cement soil, in situ recycling with cement, concrete slabs, etc.) the economy concerning the traditional solutions is quite obvious, because the thickness reduction goes up to 60% without the necessity of setting any crack delaying device. |
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How many recycled tires are used to make a road? |
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When an asphalt rubber BMB mix is used, around 3 tires are reused for each ton of asphalt mix; which corresponds, in average, to approximately 4000 tires per km (to a road 12m wide and a 4 cm asphalt thickness). |
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What advantages does the reutilization of crumb rubber from used tires bring to BMB? |
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In the industrialized countries, like the USA, the utilization of tires in the specific case of road pavement has been, for forty years now, the reason for great researches and experiments. Since then, the introduction of the tires’ recycled rubber has proven to be a possible way to eliminate the tire residue, and, more important than that, modify the basic characteristics of the bitumen’s making them more elastic and consequently, avoid cracks on the surface of the pavements.
Furthermore, they concluded that the costs conserving the pavement are less, when compared to the traditional paving solutions. |
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There are some studies about the BMB utilization? |
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The utilization of the BMB in Portugal has been followed by the National Laboratory of Civil Engineering (LNEC) and by the universities of Minho and Coimbra, that elaborated reports on the product’s characteristics and on the following of already made works, whether to Recipav or to other clients, namely the Portuguese Road Institute (IEP), Brisa, the Atlantic Highways, etc.
Recipav has also the support of the University of Madrid to perform some specific tests. |
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What kind of asphalt mixes and which percentages of BMB are used? |
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Until now, in Portugal, 2 kinds of asphalt mixes have been used, the gap graded with air voids content between 4,5 and 6% and the other, a open graded with porosity between 12 and 16%. The first one incorporates at least 8% of BMB, while in the second one it can go up to 10.5%. |
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What are the main applications? |
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The utilization of asphalt rubber mixes is very directed to applications in new constructions, or pavement rehabilitations, in municipal paths, roads and highways, whether in wearing courses or in lower courses.
In pavement rehabilitations, its preferential utilization will be in pavement precocious ageing situations because of a high level of fatigue, or in a way that improves its superficial characteristics concerning circulation noise. It’s important to enhance the significant improvement of the pavement friction, already tested in Portugal, which presents values 25% higher when comparing regular wearing course to a BMB wearing course.
Concerning the circulation noise, one can say that according to tests made in the USA, noise reductions will be achieved in the tire/pavement contact, from 6 to 9 dBA in asphalt rubber mixes.
Still concerning the pavement rehabilitation, the utilization of asphalt rubber mixes is often connected to in situ recycling with cement from the existing pavements, and in high state of ruin. This solution, or solutions combination, allows, by one side, the valuation of the ruined road through recycling and on the other the application of thin layers of asphalt mixes with incorporation of tires recycled rubber, which guarantees the quality of the road in time. |
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What are the important advantages of the BMB? |
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The utilization of asphalt rubber mixes in pavements has several advantages, such as:
- High resistance to crack formation
- High pavement flexibility
- Reduction of the pavement maintenance costs
- Raise in the tire/pavement security
- Reduction of the circulation noise
- Recycling, reduction and reutilization of the tire residue. |
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Concerning the crack formation issue, how does it behave? |
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The fatigue tests made in Portugal had confirmed the results from USA and presents a resistance to fatigue that can be up ten times higher when compared to a conventional asphalt mixes. This facts allows in conventional terms a significant reduction of the pavement’s thickness with BMB, approximately 50% comparing to conventional asphalt mixes, what in a certain way, equalize the construction costs of this kind of mix with the conventional mix. In spit of this thickness reduction, the tests that were realized presents a 60% reduction of conservation costs in this kind of pavements. |
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What is the impact in noise levels when the BMB mix is used? |
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In the studies made in the USA and in Portugal, a reduction of the noise provoked by the contact tire/pavement is possible from 6 to 8 dBA when the open asphalt mix with BMB. In order to understand what represents such reduction, you can say that, to obtain a circulation noise reduction of 3 dBA, one would have to reduce in 50% the traffic of a certain road.
In a study made by the Atlantic Highways, a case was registered where there was a noise reduction of 9 dBA when compared to a concrete pavement.
These studies were made at the A8 between Torres Vedras Sul and Torres Vedras Norte.
According to specialists, the sound pollution constitutes one of the biggest environmental problems of today. Nowadays, it is estimated that over 40% of the European population is being subjected to a noise level caused by road traffic, over 55 dBA and 20% to over 65 dBA. During the night 30% of the population will be exposed to levels that pass the advised 55 dBA.
As a way of minimizing the environmental impacts caused by noise, it’s usual to appeal the utilization of acoustic barriers and eventually soundproof building windows. The American experiment reveals that, working at the pavement’s level with the setting of asphalt rubber mixes; you can eliminate, in a few situations, the setting of acoustic barriers. |
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What’s the experience of the utilization of BMB in Portugal? |
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Recipav has initiated its activity, in Portugal, in 1999, having supplied until this day around 20 000 tons of BMB, which corresponds to approximately 250 000 tons of asphalt mixes and approximately 300 km of paved roads with the reutilization of 900 000 tires. |
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How has been the acceptation of the BMB throughout Europe? |
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Recipav has initiated in 2000 its internationalisation trough Spain, Germany and Austria. The receptivity has been quite good in most of the cases, and there has been work, year after year, in those countries.
Nowadays Recipav has a partnership with a Spanish company for the Iberian market. |
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