In 1990, Switzerland crushed an old A13 road and reused 66% to 100% of it in new concrete; 20 years later, every recycled test mix was still rated good or very good

If you've driven on an American interstate lately, you're no stranger to the pitted blacktop, the ubiquitous orange cones, and the nagging sense that the entire enterprise only survives through federal funding disputes. To the youth, who grew up sneering at the phrase "infrastructure week," it's understandable. But that doesn't mean we're right. A pilot program on a Swiss highway has quietly been experimenting with this method of road construction and repair since before many of us had student loans.

In 1990 and 1991, engineers laid new highway surfaces on a rebuilt section of the A13 motorway in Switzerland's St. Gallen Rhine Valley using concrete mixes of between 66-100 percent recycled material, as compared to traditional concrete mixes made up of entirely new material, while reinforcing the base using the crushed-up old concrete. According to a 2011 paper titled “Durability of concrete pavements made from concrete granules,” published in the Transportation Research Record: Journal of the Transportation Research Board, the peer-reviewed journal of the US-based Transportation Research Board, researchers later observed the roads after twenty years and found that every mix of recycled material tested was in good to very good condition, including the roads made up of concrete built nearly entirely from the crushed-up old road surface.

The twenty-year follow-up


The 2011 assessment wasn't a casual observation. The researchers performed a full structural survey of the pavement to gauge the condition of the slabs after two decades of freeze-thaw cycles, de-icing salt, and traffic. It also notes that the traditional concrete mixes made of "virgin" materials were found to perform only marginally better in many cases, and that the roads made of recycled material, and their conventional counterparts, were both expected to last the full 40-to-50-year design lifespan. One particular mix of recycled material was found to perform worse than some of the others, but not by much, and it appears to have been due to differences in the gradation of the aggregate rather than an inherent flaw in the use of recycled material.

Why you should care

Concrete production is a major source of carbon emissions worldwide, primarily due to the amount of energy needed to make cement, one of the main ingredients in concrete. For a generation that finds itself waiting for climate and infrastructure policy to move at any level of government, an example of a road built primarily of recycled concrete standing the test of time is worth more than a social media rant. A road in Switzerland built this way has quietly been standing the test of time for 36 years, and will soon be seen by millions as a potential model for transportation infrastructure spending in the United States, where budget bills for the Federal Highway Administration are currently being debated.

The United States isn't starting from a position of ignorance when it comes to the value of using old materials in new construction, however. According to the Federal Highway Administration, concrete made up of recycled aggregate is already used extensively in American highway construction as a base material, though its use as a surface-layer material: the application the Swiss pilot focused on, remains far less common. Several states, including Minnesota, Texas, and Michigan, are already using it in that more limited surface application, though to a much lesser extent than in the Swiss example described above.

The fine print

No one is suggesting that recycled material concrete is some kind of miracle material. The 2011 report notes that the results can't be extrapolated beyond the specific material tested, and that concrete to be recycled must first be tested for things like alkali-aggregate reactions before it can be used for new construction. It's also worth noting that roads and runways are often excellent candidates to be recycled due to the generally high standards of quality control applied to their construction and maintenance.

Not every old parking lot is going to be a good candidate to become a new highway. It's not only highways that are being recycled in Switzerland, either. In a case study by Agora Energiewende, the city of Zurich has been supporting the region's concrete recycling industry for about two decades by constructing buildings using mostly recycled concrete, including some of the country's first uses of recycled building material dating back to 1994.

The key takeaway

Nothing in this article should be taken to mean that a complete replacement of concrete roads and highways in the United States using this method is imminent. Budgets, taxes, and material recycling operations have to be established before any large-scale replacement programs can begin, and those things don't typically happen quickly; Zurich isn't unique in that regard. However, the next time infrastructure spending comes up at the dinner table, it's worth remembering that the idea of using recycled materials for construction has been around and accepted in Switzerland for nearly 36 years.