In 2021, Spain tested steelmaking slag in a porous road; after 3 years, the surface had no visible damage and its grip reading stayed above 70

A road surface that was built with waste from steelmaking was still in good condition after three years of use in Spain, with the project using porous asphalt that contained up to 10% ladle furnace slag, a by-product of steel production. Trial measurements found that the surface retained a skid-resistance score above 70, while visual inspections found no significant damage.The findings are a result of a field study published in Case Studies in Construction Materials in July 2025, which reported that the mixture could be manufactured and compacted on a full-scale test section after earlier laboratory work. The trial covered a parking area and a two-lane road, and a thin layer of porous asphalt was placed over existing pavement.The surface kept its grip during the trialA good measure of how resistant a road surface is to slipping is skid resistance, and the researchers used the British Pendulum Number, or BPN, to assess the pavement's friction. The readings were consistently above 70 during the monitoring period, including the final measurements that were taken in 2024.Testing took place more frequently during the first year and continued at six-month intervals as the pavement aged, with the final readings showing that the surface was able to maintain good skid resistance over the three-year period. The researchers also assessed the pavement's durability under conditions that included moisture, frost, abrasion and ageing, and the results met the requirements considered suitable for urban roads carrying medium levels of heavy traffic, according to the full research paper published in Case Studies in Construction Materials.The road still had a drainage issue to manageThe purpose of porous asphalt is to let water pass through its connected gaps, and that drainage performance can change if dust and loose material collect on the surface, even if the pavement remains structurally sound. In the Spanish trial, it was found that the central part of the road and the parking area retained their drainage capacity relatively well, but sections near the road's beginning and end experienced more clogging, which the researchers attributed to loose material that was carried in from nearby areas.The permeability remained above the minimum levels that were discussed by the researchers for the pavement's intended use, despite those changes. The findings show why road performance cannot be judged by surface appearance or grip alone, since drainage also needs to be measured over time.The material could reduce demand for conventional inputsLadle furnace slag is usually generated during the production of steel, and using it in asphalt could be a potential way to reuse an industrial by-product instead of having to completely rely on conventional materials. The research team tested a mixture that contained up to 10% slag without needing preliminary physical or chemical treatment of the material. Could substances leach out of the mixture? The reported results remained below the applicable regulatory limits, and that finding is important to the assessment of whether industrial by-products can be used in road construction, although it applies to the material and conditions examined in this trial.The researchers stated that the pilot was successful, right from laboratory design to road construction and field monitoring, but three years of observations do not establish how the surface will perform over the full life of a road. The paper pushes for longer monitoring periods, which could potentially span 10 to 20 years, as a useful next step.Currently, the trial provides field evidence that porous asphalt that has ladle furnace slag can maintain skid resistance and an acceptable surface condition over several years. Its long-term durability and drainage performance will need further observation before the results can be applied more widely.You use AI every day. Now get your AI Quotient. Take the AIQ test.