Sustainable Options in Concrete, Aggregates & Paving
In recent years, sustainability has become a central consideration in every industry. Government departments and industry organizations alike have been working tirelessly to promote sustainable practices through standards, regulatory mandates, and incentives. This has resulted in a shift in the way businesses are being operated all around the world.
In the field of rigid and flexible paving, the constant influx of innovative materials and processes has been keeping companies on their toes.
Whether it is through recycling old concrete or asphalt pavement, employing pavement preservation techniques and technologies to reduce the frequency of road work, or developing new materials to extend the lifespan of the pavement, the paving industry is committed to a sustainable future.
There are typically two types of pavement. Rigid pavement is made with coarse stone aggregate and cement as a binding agent, which together form concrete. Flexible pavement uses a less coarse aggregate and a crude oil product called bitumen as a binding agent, forming asphalt. The difference is that bitumen does not harden nearly as much as cement does, leaving the finished product a lot more pliable.
Concrete paving is still used for some applications, but roadways and parking lots typically made from asphalt today. As time passes, and particularly as the temperature changes with the seasons, the ground can shift underneath a roadway. The flexibility of asphalt enables it to adapt as these changes occur. Where concrete is rigid enough to crack under its own weight, asphalt will simply change its shape to fit the ground. Of course, anyone who has driven on an asphalt road knows that these roads are not completely immune to cracking, and ruts and potholes still form over time.
One cutting-edge innovation in the field of road paving is the use of nanomaterials in asphalt aggregate. Researchers from the University of Alberta published a paper in 2019 demonstrating the effectiveness of adding nano-clay, nano-carbon, and nano-silica particles to asphalt aggregate to improve its performance. Adding nanomaterial to the aggregate in a variety of combinations resulted in cases of improved tensile strength, improved resistance to thermal cracking, and more. By adding the right aggregate modifiers for a given climate, this technology could significantly improve the life of the pavement.
Another example of a new innovative asphalt material comes from the United Kingdom. Tarmac, a materials engineering company, has recently developed a new rubberized asphalt material that makes use of recycled tire waste. According to Tarmac, using rubberized asphalt will reuse 750 tires for every kilometre of highway that is surfaced with the material, eliminating roughly 120,000 tons of rubber waste a year.
These innovative materials are helping to make roads more sustainable, but they still depend on two key limited resources: crude oil product called bitumen and mineral aggregate.
Bitumen is the sticky black binding agent used to hold asphalt aggregate together, and crude oil and, therefore, bitumen is a finite resource. Also, the minerals used in asphalt aggregate have to be mined from quarries, processed, and transported great distances. This means that the entire process has a high carbon cost, and it is a significant obstacle to the sustainability of paving in general. Many companies have turned to recycling as a solution.
Traditionally, asphalt and concrete waste from roadway removal projects ended up in landfills for disposal. Eventually, recycling processes were introduced, but in the beginning, these processes could only generate low-quality, irregular material. This recycled waste could be used as filler for ruts and holes, but never in actual asphalt or concrete. Today, the process has been improved and refined to such a degree that recycled materials can be used in a wide range of applications, paving included.
High tech crushing equipment can be used to crush demolished concrete sidewalks, foundations, and building columns into uniform fragments that can then be reused as an aggregate to form new concrete. A similar process is used to crush asphalt into reusable aggregate.
According to an article from Recycling Today, asphalt is the most consistently recycled material in the United States. Asphalt is being pulled up, processed, and recycled into new highway and road development projects every single day. In 2018, more than 100 million tons of recycled asphalt pavement, commonly called RAP, was used in new projects, saving more than 60 million cubic yards of landfill space.
Clearly, the use of recycled material has been another factor in improving sustainability in the paving industry. Another key innovation has been the development of ‘warm-mix’ asphalt products. This is a relatively new technology that has drastically reduced the energy needed for paving. These products use a specially designed binding agent with a decreased viscosity, which enables it to work at a much lower temperature than traditional binders. By reducing the working temperature, warm-mix asphalt can be applied with a much lower energy cost, and fewer emissions are generated while it is being processed.
However, after warm-mix asphalt has been laid down, maintaining it comes with its own substantial carbon footprint. To reduce the carbon cost of upkeep, a number of pavement preservation products can be applied to a roadway to improve its life expectancy.
Pavement preservation is a preventative approach to road maintenance based on the idea that repairing damage is always significantly more expensive than periodic upkeep. Crackseal is used to seal large cracks in the asphalt to prevent water from getting into the pavement and causing further damage. Chipseal is a product with a similar purpose to crackseal, but for much smaller chips in the pavement’s surface. Microsurfacing and thin overlay use a specialized asphalt mixture to create a very thin surface that is used for levelling, rut filling, and improving the ride-ability of a roadway.
Taking a proactive approach to road maintenance consistently results in longer-lasting roadways and a more sustainable maintenance program overall. Pavement preservation products and techniques are being adopted throughout the world, and as that sector of the paving industry grows, those products will continue to improve.
The materials used in manufacturing asphalt and concrete pavement have changed significantly in recent years. As governments mandate and incentivize sustainability, the industry will continue to develop new technologies to meet those standards. According to the National Asphalt Paving Association, recycling has become so effective that nearly all reclaimed asphalt is reused or stockpiled for future use.
Asphaltsmart.com states that pavement preservation uses eighty percent less of the planet’s non-renewable resources than the traditional reparative maintenance approach. Finally, the many advancements in aggregate materials and binding agents continue to improve the industry’s overall carbon footprint. The world is ready to move toward a more sustainable future, and the paving industry is leading the charge.