Checking rubber asphalts
One of the important methods to improve the performance of asphalt mixtures in different temperature conditions is bitumen modification. Due to the important effect of bitumen on the operating conditions of asphalt mixtures, many studies have been performed to increase the quality of bitumen.
Polymer bitumen modification is one of the most common ways to increase the quality of bitumen. In recent years, the use of recycled polymers instead of pure polymers has grown significantly with the aim of adapting to the environment and as a suitable method for waste disposal. Increasing the number of vehicles on the roads leads to the annual production of millions of tires in developing countries.
Each year, about 1.4 billion tires are sold worldwide, many of which eventually expire in a few years. Due to the high production volume and long durability of tires, this is one of the biggest and most problematic issues in the field of resource recovery According to the U.S. Environmental Protection Agency, there were about 290 million worn-out tires in 2003, up from about 355 million in Europe each year.
The use of rubber powder in asphalt, in addition to a positive effect on environmental and economic issues, as an elastomer significantly improves the mechanical and rheological properties of bitumen. Rubber powder increases the hardness of bitumen and increases the elasticity (recoverable deformation) in the operating temperature range, also reduces the temperature sensitivity of the pavement, and improves the corrosion resistance and fatigue of asphalt concrete.
In addition, lower maintenance costs, lower noise production, higher braking resistance, and better night vision are the advantages of rubber asphalt over conventional asphalt concrete. On the other hand, rheological results confirm the improvement of the properties of bitumen modified with rubber powder in both cold and hot temperature ranges Adding rubber powder to bitumen can increase 1 to 3 functional categories at a high level and improve 1 to 2 functional categories at low operating temperature. Therefore, in general, the operating temperature range of bitumen increases on both sides. The following figure shows the process of using rubber in road paving.
Advantages of using rubber in asphalt pavements
1- Do not increase tire depots
Reuse used tires in industry instead of increasing daily warehouses and depots and creating environmental problems, is the first benefit of recycling worn tires. According to available statistics, more than 12 million tires (250,000 tons) are consumed annually in Iran, and it is predicted that 1,400,000 tons of worn tires will be produced annually in 1404.
2 – The most useful way to use worn tires
Burning worn tires for energy is an effective way to reuse worn tires, but this not only destroys the tires but also replaces the ashes that are disposed of ash. This is another problem. Research shows that the use of rubber asphalt in a one-kilometer-long, 25-mm-thick strip requires about 620 tires or 2 tires per ton of recycled rubber asphalt.
3- Noise reduction
and noise pollution in highways and intersections is one of the traffic and transportation problems that has been paid more attention to in recent years.
Reducing the noise of passing traffic (wheel noise) is another environmental benefit of using tires on asphalt, which has been studied and proven in different countries. . Studies show that the use of rubber asphalt reduces noise by up to 5 dB over the life of the pavement. The table below compares the sound effects of ordinary asphalt and rubber mixtures on the roads of Sacramento, California, USA.
4- Economic study The
the initial cost of rubber asphalt mixtures is higher than the initial cost of conventional asphalt mixtures. The higher initial cost of these mixtures is one of the barriers to their widespread use. In 1990, the Arizona Department of Transportation designed and built a large rubber asphalt project on one of the busiest interstate highways. According to the obtained results, after 9 years of service, the coating layer was still in use without cracks with good quality and high slip resistance. The benefits of using rubber asphalt mix in this project are reported to be about $ 18 million and four years longer.
More than 280 million scrap tires are produced in the United States each year, of which more than 60 million are unused and stored in warehouses. The use of rubber asphalt is a useful solution to this problem. Depending on the selected program and the percentage of rubber powder used, between 500 and 2000 scrap tires can be used per mile of pavement. In other words, for one mile of a four-lane highway, between 2,000 and 8,000 tires can be used, which increases safety and pavement resistance and reduces noise pollution and road maintenance costs.
5-Reducing pavement damage
According to a report by Clemson University, the use of rubber asphalt reduces pavement damage, which is evident in a variety of pavement damage.
6- Reduction of reflective cracks in asphalt pavements The images below are two adjacent sections of the I-40 route in the United States, one of which is made with a mixture of ordinary asphalt and the other with rubber asphalt. Although the thickness of the part made with rubber asphalt mixture is half the thickness of the part made with ordinary asphalt mixture, but after 8 years, it has a much better quality. The image on the left is related to the formation of reflective cracks in ordinary asphalt, and the image on the right shows the absence of reflective cracks in rubber asphalt.
7- Reducing maintenance costs
In general, paving roads with ordinary asphalt needs maintenance and repair every year. Rubber improves asphalt and increases the resistance to cracking and aging of pavement. In general, rubber powder increases the life of the pavement and reduces road maintenance costs. The following figure shows the occurrence of block cracks and fatigue (lizard skin) on ordinary asphalt.
8- Improving the grooving and slip resistance of asphalt
rubber powder increases the hardness and strength of asphalt bitumen, which increases the grooving resistance of the asphalt mixture. Also, the use of rubber asphalt improves slip resistance, which increases safety and reduces traffic accidents.
9- Increasing the life of pavement
Asphalt pavement after exposure to various elements and due to oxidation loses some of its elasticity and flexibility. During this process, the pavement material is exposed to repeated stresses due to expansion and contraction and temperature changes and begins to crack. Rubber asphalt mix generally responds better to the formation of this crack than conventional HMA. Not only does rubber asphalt have more flexibility than regular asphalt, but it also has a higher resistance to the aging phenomenon, which is due to the anti-aging effect of antioxidants in recycled rubber. The image below shows the cross-section of a road in both normal and rubber asphalt. The image on the right is before the use of rubber asphalt, and the image on the left shows 16 years of road paving performance.
