Sustainable Pavements from Recycled Stone Could Help Urban Areas Beat the Heat

Researchers from the IUAV University of Venice, in collaboration with the Building Physics Laboratory and the LabSCo Laboratory of Strength of Materials, have conducted an ambitious study on how permeable pavements made of recycled natural stone can help cities fight the Urban Heat Island (UHI) effect. Their work, published in Energy & Buildings (2025), moves beyond laboratory speculation by combining material testing, field experiments, and advanced climate simulations. The team’s results highlight the potential of sustainable pavements not only to reduce surface overheating but also to enhance stormwater management, offering a double dividend for climate-stressed cities.

The Heat Island Challenge

Urban Heat Islands are a familiar yet worsening problem in modern cities. Asphalt and concrete trap solar energy during the day and release it at night, causing cities to remain hotter than surrounding rural areas. This phenomenon is further intensified by climate change, raising health risks, straining energy systems, and reducing urban livability. Numerous strategies have been attempted: reflective coatings to bounce back sunlight, cool pavements designed with lighter surfaces, and even embedded cooling devices. While some approaches show promise, results are inconsistent and often dependent on local environmental conditions. Against this backdrop, the Venetian researchers proposed a new alternative, recycled, porous paving blocks designed to combine the cooling benefits of higher reflectivity with the hydrological advantages of permeability.

Testing a New Kind of Block

At the center of the study is the Recycled Light Block (RLB), a porous, light-colored paving element developed to both reflect solar energy and encourage evaporative cooling. To evaluate its performance, the researchers compared it with two other block types: the Typical Dark Block (TDB) and the Recycled Dark Block (RDB). Laboratory tests revealed that the RLB outperformed the other blocks in crucial ways. It had lower thermal diffusivity and higher heat capacity, meaning it absorbed less heat and slowed the rate at which it warmed up. This reduced the surface’s temperature rise during sunny conditions. Measurements of the Solar Reflectance Index (SRI), taken with precision instruments such as pyranometers, showed the RLB reflected more solar radiation than traditional blocks. In other words, its lighter surface meant it stayed cooler under the sun.

From Parking Lot to Climate Model

The researchers then brought their laboratory findings into the real world. They installed the blocks in a parking lot adjacent to the university and outfitted the site with sensors to monitor temperatures. At the same time, they created digital simulations using ENVI-met, a microclimate modeling software widely used to study urban thermal environments. Two scenarios were tested: a reference case featuring standard asphalt and concrete, and an analysis case where these were replaced with RLBs. The simulations confirmed what the laboratory had suggested. Pavements made of recycled blocks reduced peak surface temperatures and delayed the time of maximum heating. This “thermal lag” shifted the hottest point of the day away from the solar noon peak, reducing the intensity of urban heat when people are most exposed. In some cases, surface temperature reductions of several degrees Celsius were observed, while near-ground air temperatures also dropped modestly but significantly.

How Porous Surfaces Change the Game

The performance of the recycled blocks lies in their ability to alter the flow of heat and water at the surface. Conventional asphalt is impermeable, channeling nearly all incoming solar energy into sensible heat that raises surface and air temperatures. Porous pavements, by contrast, allow water infiltration, which later evaporates. This process divides incoming solar energy between sensible and latent heat, cooling the surface through evaporation and reducing the storage of heat in the pavement itself. In quantitative terms, the albedo values recorded showed a stark contrast: asphalt at 0.06, cement at 0.13, and RLBs at 0.31, reflecting far more sunlight. By integrating these dynamics into ENVI-met models, the researchers demonstrated how permeable pavements can play an active role in rebalancing urban heat budgets.

Toward Cooler, Greener Cities

The implications of the study stretch beyond material science. Recycled permeable pavements address two urban challenges at once: they mitigate overheating while also reducing stormwater runoff and filtering pollutants. These co-benefits align with European Union policies such as the Water Framework Directive and climate adaptation strategies that promote Nature-Based Solutions. The researchers, however, remain cautious. They note that the effectiveness of such pavements depends heavily on context, pavement thickness, porosity, nearby vegetation, and the geometry of urban spaces, all shape outcomes. In some cases, porous pavements may perform exceptionally well, while in others, the benefits may be modest. They argue that sustainable pavements should not be viewed as stand-alone solutions but as part of a broader urban strategy that integrates greenery, shading, and reflective materials.

The study concludes with optimism tempered by realism. The Recycled Light Block shows that engineering innovation can transform something as ordinary as a paving stone into a tool for climate adaptation. By redesigning everyday urban infrastructure, cities can take measurable steps toward cooler, more resilient futures. The IUAV University of Venice research team demonstrates that pavements are not passive surfaces but potential allies in the fight against rising urban temperatures.