Merits of concrete vs asphalt considered in quest for greener pavements

Could permeable and high-albedo materials for road surfaces that replace asphalt across towns and cities reduce the urban heat island effect at the height of summer as well as reduce the risk of flash floods and groundwater depletion?

An idea put forth in an article in the International Journal of Student Project Reporting hopes to answer that very question.

Julianna Syros, Alexander Villiers, Ginger Arnold, Bryan De La Paz, and Trevor Fai of the University of Florida in Gainesville, Florida, U.S., allude to how urbanization has become synonymous with progress, bringing with it modern amenities, economic growth, and improved living standards.

However, this expansion has brought with it serious environmental challenges, notably flash floods, groundwater depletion, and the Urban Heat Island (UHI) effect. These issues largely arise from the extensive use of impermeable materials like asphalt in road construction, revealing a critical need to rethink our choices when it comes to transport infrastructure.

Asphalt is relatively low cost when compared to concrete and so has become the primary material used in road surfacing in urban areas the world over. However, this preference comes at a significant environmental cost.

The impermeable nature of asphalt prevents rainwater from being absorbed into the ground, leading to rapid runoff and flash floods. This runoff can carry pollutants to water bodies and also hinders groundwater recharge, depleting vital water resources.

Moreover, asphalt's heat-absorbing properties contribute to the heat island effect. This effect sees urban areas experiencing higher temperatures than their rural counterparts, a problem that will become increasingly worrying as global temperature rises through climate change.

The phenomenon is largely driven by the high density of heat-absorbing surfaces, such as roads and buildings, which trap heat and only slowly release it from the "island" as a whole.

For towns and cities in hot countries and those facing increasingly common temperature spikes, the effect is to increase urban energy demands as those living and working there rely more and more on air conditioning to keep cool. Those without access to that luxury will suffer the heat, which could lead to health problems and increased fatalities among the vulnerable during a heat wave.

Concrete, despite its higher upfront cost, presents a viable alternative with long-term benefits. Unlike asphalt, concrete is more durable and requires less maintenance, leading to lower costs over its lifespan.

Furthermore, concrete can be designed to be permeable, allowing water to percolate through and recharge groundwater, thereby mitigating flash floods. High-albedo (reflective) concrete surfaces can also reflect more sunlight, reducing heat absorption and alleviating the UHI effect.

The team suggests that overcoming the societal and economic barriers is essential if sustainable transport infrastructure is to be developed to address the increasingly detrimental effects of urbanization.

Investment may well attract greater initial costs, but in the long term, fewer flash floods, conservation of groundwater resources, and a significant reduction in the heat island effect would offer immediate payback when compared to sticking to asphalt.