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Civil Engineering

Rubber in the safety barrier

Barriers produced with pieces of tires reduce impact in traffic accidents

Recognized as the cause of an environmental problem, old tires, which are often thrown into rivers or dumps irregularly in open air landfills, now have a nobler destination: the construction of highway barriers. These small walls, normally erected in the center or at the sides of lanes, will continue to be made of concrete, but part of the small stones, known as rock chips, used in its composition, will be substituted by pulverized rubber coming from car tires that are no longer of any use. Two stretched of these barriers are currently in a test stage, one at kilometer 27.3 of the Raposo Tavares highway, going towards the interior, that links the city of São Paulo to the west of the state, and the other along the ring road of the Tietê river, close to the Júlio de Mesquita Neto bridge, in the city of Sao Paulo.

“The main advantage of the new highway barrier is its capacity to absorb the impact of uncontrolled vehicles”, says engineer Paulo Bina, vice-president of the Via Viva Institute and a director of Monobeton Soluções Tecnológicas, the organizations responsible for this development. The company is a specialist in new technologies in the area of civil construction and the Via Viva Institute is a non-profit  entity located in São Paulo, established from a partnership between the company Monobeton and the Association for the Valuation and Promotion of the Handicapped (Avape in the Portuguese acronym), and has its headquarters in the town of Santo André, in the Metropolitan Region of Sao Paulo.

Static tests
“With the addition of rubber to its structure, the barrier stops being a rigid block and becomes a semi-deformable structure. The degree of deformability is going to vary according to the quantity and the size of the rubber pieces used in preparing the concrete”, explains Bina. In the opinion of the engineer, the exact percentage of absorption of energy of the new barriers is as yet unknown because dynamic testing has not been carried out (also called crash tests, in which a car, via remote control, is made to crash into the rigid structure), which is forecast for the next few months. Up until now, test statistics were carried out that verified the mechanical properties such as resistance to compression, traction and deformation.In order to make these tests, the company was able to count upon the collaboration of the Civil Engineering, Architecture and Urban Development School of the State University of Campinas (Unicamp).

Under the direction of professor Ana Elisabete Paganelli, the researchers used hydraulic presses in which a piston exerts a variable force upon the concrete. The tests showed that the barriers absorb and dissipate the energy of the impact, reducing the vehicle speed  after the crash. “By further reducing the car’s deceleration, we also diminish the probability of traumas among the passengers”, says Paulo Bina. The results of the tests carried out at Unicamp were also analyzed by the engineer Fernando Rebouças Stucchi, from the Polytechnic School of the University of Sao Paulo (USP).

The technical report made by him is being examined by the Highway Department (DER) of São Paulo, the organ that provided the standard parameters for the construction of highway barriers within the State. “The DER, one of our partners in the project, forecasts that over the next three years there will be a demand for 900 kilometers of DER barriers, as well as the 2,300 kilometers of barriers for the São Paulo highways operated by concessionaries”, says professor Bina. If the case where that they were to be built from concrete with rubber, some 32 million old tires would be used, also called unserviceable because they cannot be used for retreads.

Legal destiny
Over a five-year period the National Association of the Tire Industry (Anip in the Portuguese acronym) has collected 70 million tires, complying with  Resolution 258 from the National Environmental Council (Conama), of the 26th of August 1999, which indicated, for 2005, the collection of five tires for every four manufactured or imported. Consequently, cut up tires going in the construction of barriers fit perfectly well with the final destiny of these waste products that are the legal responsibility of the tire manufacturers. For this reason the Anip is involved in the development of the concrete barrier system with added rubber, being responsible for the contracting of companies that cut up these tires. Currently the used tires, to a large degree, are destined to be burned in furnaces.

“Besides the technical and ecological benefit, the project has a relevant social edge to it”, explains Jorge Gonçalves dos Santos, the coordinator of the Via Viva Institute. “The collection of unserviceable tires will be done at collecting stations called Via Viva Ecopoints, managed by the institute and operated by the mentally handicapped, people whose employability is highly limited, and their families”, he adds. With cooperation from Avape technicians, handicapped people will carry out the reception, washing, storing and dispatching of the tires to the locations for pulverizing.

The project forecasts the installation of sixty Ecopoints throughout the state, situated in locations of easy access and good visibility. The first of them should be built in the region of the industrial surburbs of São Paulo. Each Ecopoint will employ twelve handicapped people and will have a monthly cost of R$ 30,000.00. Since, at the start of the project, the cut up rubber will be delivered to the companies making the concrete barriers at no cost, the resources for financing the Ecopoints will be obtained via sponsors, such as tire manufacturers, car manufacturers, suppliers of tire parts highway concessionaries, transport companies, concrete manufacturers and car insurance companies.

Strong linkage
The process of the production of concrete with rubber chips, baptized as DI Concrete (Deformable and Insulating), is similar to conventional production. The percentage of cut up used tires is variable and depends on the characteristics of the desired performance of the concrete and the dimensions of the added rubber that, in this case, should be up to 2.5 centimeters in length. In the two barriers already constructed one quarter of the volume of concrete, the equivalent of half of the large stone chips added in, is of rubber. Another innovation in the process of the manufacture of DI Concrete is the addition of glass fibers, which avoids segregation, and is mixed in homogeneously.

The glass fiber acts like a web or bird’s nest, making a link between the rubber and the concrete In the opinion of those responsible for the Via Viva Institute,  DI Concrete has taken four years to be developed and its cost is comparable to conventional concrete. The product, as well as the barrier made from it, have already been patented at the National Institute of Intellectual Property (INPI). Shortly a patent will be filed in the United States. Besides the manufacturing of highway barriers, DI Concrete could be used for the construction of the flooring of apartments and of pavements of highways or town roads. The advantage in this case is a reduction in noise level of the flooring because the rubber acts as an acoustic insulator. Its use in pavements also brings benefits, since the DI Concrete has a high resistance to traction – or that is to say, when submitted to a force – such as the weight of a car, for example, thus supporting greater deformation without breaking up.