How 20,000 tires buried under a road in 1993 ended up influencing Brazilian asphalt

Twenty thousand old tires shredded and buried under 183 meters of road reduced the penetration of ice into the ground by half. The experiment was conducted in 1993 in Richmond, Maine (USA), by civil engineer Dana N. Humphrey, then a professor at the University of Maine, and gained repercussions after being reported by the Los Angeles Times that same year.

The proposal answered a practical problem: what to do with the mountain of tires that no one else wanted. Instead of discarding them, Humphrey advocated cutting them into pieces of 5 to 30 cm and using them as a base layer under the pavement, taking advantage of three properties of rubber—low weight, good drainage, and thermal conductivity much lower than that of earth and stone.

In the Richmond section, the tires were chopped into fragments of 5 to 7.5 cm and spread in a layer 15 to 30 cm thick, covered by up to 60 cm of gravel. Sensors installed on the road showed that, in addition to stopping the freeze, the road better resisted the spring thaw, a period in which saturated soil usually gives way and opens holes.

From experiment to engineering

material Humphrey named the material tire derived aggregate (TDA), or aggregate derived from tires, and spent the following decades taking the technique to construction sites in the United States and to consultancies in Canada, Australia, and Europe. In later work, he pointed out the low density of the aggregate as an attraction for light landfills on soft soils and for backfilling retaining walls. The obstacles continue to be the high initial investment and the complexity of execution.

In Brazil, rubber enters through the

asphalt mixture In a country without severe soil freezing cycles, the reuse followed another path: rubber powder incorporated into the asphalt binder. The first national stretch with rubber-asphalt was inaugurated in 2001 on the BR-116, between Guaíba and Camaquã (RS), based on technology developed by Greca Asfaltos with the UFRGS pavement research center. According to the company, the product takes about 15% rubber powder and has already consumed 30 million tires in 25 years.

The material is in the Anhanguera-Bandeirantes system and in sections of the Washington Luís, Régis Bittencourt and Imigrantes highways, in São Paulo. A 2021 Artesp survey counted more than 1,355 km with recycled rubber on 22 São Paulo state highways. According to Anip, an association that represents tire manufacturers, the pavement is 40% more resistant than conventional pavement and lasts an average of 14 years, compared to 10 for common asphalt. The addition of rubber powder to the mixture can also reduce rolling noise by up to 5 dB.

The scale of the liabilities explains the interest: data from Ibama point to 7.7 million tons of waste tires properly disposed of between 2009 and 2020, under Conama Resolution 416/2009, which obliges manufacturers and importers to collect the equivalent of what they sell. Even so, academic estimates indicate that the country recycles about a third of what it discards.