Usually, Munch says, the solution isn’t too complicated: just build infrastructure higher. But engineers can’t build roads and bridges to survive every disaster, which would lead to expensive, rebuilding projects that would “take generations to complete,” Munch says.
Rice Krispies Roads.
When engineers rebuild roads from scratch, they’ve also started using different materials to account for the possibility of a lot of water arriving really quickly. Over the past decade, road builders have increasingly installed more permeable, “spongy” roads.
Pervious concrete, unlike regular concrete, usually excludes sand from the typical “gravel, sand, cement, water” recipe. It also has a lower water-to-cement ratio that creates a thick paste before it dries. “It’s like caramel popcorn or a Rice Krispie bar,” says Nara Almeida, who studies the material as an assistant professor in the civil engineering program at the University of Washington Tacoma.
On normal concrete roads, water accumulates and collects, with stagnant water eventually damaging its various layers and especially critical subgrades that bear heavy vehicle loads. But the increased porosity of pervious concrete allows water to flow more easily through the material so it can reach and be absorbed into the ground—a good feature for roads exposed to very wet conditions.
Pervious concrete has its drawbacks. It’s weaker than normal concrete, which means it’s better suited for sidewalks, parking lots, and low-traffic streets than interstates that expect very heavy trucks. (Research into reinforcing the material with steel, natural, glass, and synthetic fibers continues.) Its porosity means it’s not well-suited to cold climates, where water can seep in, freeze, and destroy the material inside. Concrete also needs regular pressure washing or vacuuming to “unclog” the type of material often found on the roadway – dust, leaves. Because states sometimes have to switch suppliers and processes to use the newer material, projects can cost them more. But some places have loaded that material onto the shoulders of interstate highways, Almeida says, where they’re much less likely to get regular tire hits.
Ultimately, though, not much can be done when a huge volume of water is rapidly flowing across a roadway or bridge foundation, which engineers call a “wash.” “We’ve all played in the backyard with water and hoses — it’s very harmful,” says Muench, the engineering professor. Part of climate resilience is planning ahead – and putting quick-fix materials nearby – so communities can rebuild quickly.
