Breathing Highways and Sponge Cities

"We could do worse than to go back to the way nature manages rainfall."

During the 20th Century, the rate of global warming was twice as fast in Taiwan (1.7°C) as for the world as a whole (0.74°C). Partly as a result, the number of days with rainfall decreased dramatically and typhoons gained strength. In 2009, Typhoon Morakot dropped over 1,000 mm (39.4 inches) in a single day and caused the loss of 699 lives. A massive mudslide wiped out Xiaolin Village and 474 people were buried alive. In 2015, Typhoon Soudelor left similar damage. It took months to repair the roads.

Then Taiwan and East China were struck by Dujuan, known in the Philippines as Typhoon Jenny, a killer storm and the thirteenth typhoon of the 2015 Pacific typhoon season. Eight months later, Nepartak became the third most intense tropical cyclone on record with 114 deaths and more than $1.5 billion damage in Taiwan and East China. September brought Meranti, a super typhoon and the strongest ever to make landfall in China in more than 1000 years of records. Meranti’s peak sustained winds tied the record set by Haiyan in 2013, 195 mph (315 km/h), comparable to a tornado, or a Category 5 hurricane on the Saffir-Simpson scale. In Taiwan, nearly 1 million households lost power and 720,000 lost water supplies. Flooding in Zhejiang took 902 homes and affected 1.5 million people.

Between those punctuations, the erratic weather brought long droughts. New Taipei City had to enforce water restrictions when the Shihmen reservoir went dry in April. All cities along coasts or rivers have engineered means to remove excess water and to prevent flooding. Few have the means to sustain themselves in severe droughts.

As a city develops, the soil is slowly covered by hardscape. There is less and less water infiltrating through to reach soil. Typically cities build a drainage system that directs water out. During times of typhoons or heavy rainfall the level of external water in rivers may rise, so floodgates are closed to prevent external water from gushing in. Pumping stations swing into action to take the excess water out. If the level of rainfall exceeds the pumping stations’ capacity, the city floods, like New Orleans during Hurricane Katrina or New York during Superstorm Sandy.

We could do worse than to go back to the way nature manages rainfall. That was the inspiration of a Taiwanese road construction engineer, Jui-Wen Chen. His idea is to build a “permeable city” that allows internal water to infiltrate into the soil and return the natural water cycle.

In conventional road-building there are two kinds of suitable materials to allow a hard surface to drain: porous asphalt and porous concrete. Between the two, porous asphalt is more commonly used and has the longest history. It uses larger-graded aggregates in the asphalt mixture to increase the porosity, which allows water to infiltrate into the soil through the gaps. The other type is interlocking blocks that join together, forming small gaps between and allowing water to infiltrate. A wide variety of materials can be used as interlocking blocks, such as rocks, concrete bricks, permeable bricks, grass bricks, and others.

Jui-Wen Chen said that he was not a scholar, did not study a lot and could not understand the research on this topic written in other languages. As a boy he gave up on schooling and only graduated from junior high school. Although he had extensive experience of road construction in Taiwan, he had no knowledge of the current popular trends elsewhere in the world.

He considered that a good thing. When we met at the UN climate conference in Paris, and later at COP-22 in Morocco, he told us through a translator he was not limited by others’ ideas and was able to invent his own. He explored what interested him, thought creatively and acquired whatever skills and materials he needed to experiment.

When Jui-Wen Chen was a child he had allergies, but he could control them if he stayed away from places where pollen and dust were high. Then his own child developed a more severe condition than his and needed to go to the hospital regularly to receive treatments.

Over the years, Mr. Chen noticed there were more and more children suffering from similar allergies. The doctor told him it was mainly due to the increased levels of pollution. The doctor pointed to the road construction outside and explained that, with all the digging and paving, road construction could be one of the causes. Jui-Wen Chen was shocked to hear that his successful career may actually have contributed to his son’s suffering.

Realizing this, Chen became more sensitive to the impact of air pollution on human health. He also learned how his roads were having negative effects on marine life from the street runoff that ran into rivers and the ocean.

Then came the spate of super-typhoons and Chen noticed that, even with a higher embankment protecting the city, it would still flood because water was not able to discharge. The city kept building more pumping stations, but it cannot cope with a storm that can dump more than one meter per day.

Jui-Wen Chen started to think that maybe he could invent a new type of roadway to solve all these problems. He slowly formed the idea of making roads a part of the city’s drainage system.

He asked himself many questions. Can permeable pavement actually allow water to get to the soil? Would building a hard roadbed lead to more runoff? If the roadbed were soft, would it cause soil liquefaction when an earthquake hits? Would a soft pavement be able to withstand the weight of the road, or would it break during high traffic volumes?

From his construction experience, Chen knew that using reinforced concrete with embedded steel bars would be the most structurally stable and durable. A reinforced concrete structure does not need to compact soil below, like asphalt does, but only requires a layer of leveled gravel for support. To make pavement with high permeability, Chen came up with the idea of changing the steel reinforcing bars into steel pipes so that whenever it rains, the water could drain into the pipes and infiltrate through the loose gravel and then into the soil. His concept of an air-circulating aqueduct assembly was born.

The system Jui-Wen Chen invented is called an “aqueduct grate.” It is neither permeable porous pavement nor permeable interlocking pavement.

Steel pipe posed more problems, however. Pavement needs to withstand the test of time. Steel bars are susceptible to rust. Once the rust starts, the bars rupture and expand, resulting in cracks in the pavement and weakening its integrity. In his search for the perfect material, Jui-Wen Chen tried and failed with many. One after another — iron, aluminum, copper and more. And then he tried carbon.

Specifically he tried polypropylene — (C3H6)n.

Carbon was first made into a crystalline isotactic polymer in 1954. After polyethylene, polypropylene is the most important plastic, with revenues expected to exceed $145 billion by 2019. The sales of this material are forecast to grow at a rate of 5.8 percent per year until 2021. In isotactic polypropylene, the methyl (H) groups are oriented on one side of the carbon backbone. This arrangement creates a greater degree of crystallinity and results in a stiffer material, tough, flexible, and with good resistance to fatigue. It can resist both acidic and alkaline chemicals; it is structurally strong; and it can withstand heat as high as 140°C and cold as low as -40°C.
 

Chen resolved to make his aqueduct grate system from recycled plastics.The structural mechanics of the pavement would allow the weight to be evenly distributed, even for a load as heavy as a tractor-trailer truck hauling stone.

Jui-Wen Chen later added, “I didn’t expect to see such a perfect match of these two distinct materials, concrete and plastic, in road construction.” The carbon did not corrode the way steel does, nor did it expand and contract with temperature change. The concrete was more stable with carbon than steel, and would remain that way for a longer time.

 Jui-Wen Chen shopped around the city for women’s shoes to test his design. He designed pipe openings small enough to be safe for most high heels. To prevent silt buildup that might block the pipes, he designed the pipe ends as a cone — wide down below and narrow at the top. When cleaning the street, a pressurized water jet can easily and quickly wash the dirt down to the gravel layer.

To maximize the level of air-circulation in his Aqueduct Grate, Chen alternated narrow pipes and wide pipes. The narrow pipes allow water drainage into the gravel and soil where it will help create a suitable environment for microorganisms that clean the city air. Then, using the Bernoulli principle, the clean air and moisture move back to the atmosphere through the wide pipes. Chen thinks his design will play a significant role in reducing urban air pollution.

To the gravel layer under the pavement Mr. Chen added “water retention balls,” each about the size of a ping-pong ball. These are hollow, recycled plastic balls with perforations around their circumference. Chen asked us not to underestimate the look and design of these water retention balls — they have an astonishing impact.

At 0.5m height, the averaged level of CO2
over the JW pavement is about 84% lower than
that over the non-JW pavement.

The water retention balls are added into the gravel layer, about 30 percent by volume to the gravel. Rainwater can make its way into the balls through the perforations and that increases the amount of water that can be stored underneath the surface of the pavement. Microorganisms thrive in the hollow spaces, cleaning both air and water.

Depending on the needs of each area, there are five different types of water retention balls:

• Red balls: completely hollow balls for increased water storage.
• Green balls: filled with absorptive carbon — ashed rice hulls — to provide nutrients and a suitable environment for microorganisms.
• Blue balls: filled with sponges to retain water for long dry periods.
• Black balls: filled with biochar to detoxify water and air from heavy metals and other pollutants, and to encourage microbial diversity.
• White balls: filled with the topsoil taken up from that pavement site, to return the ecosystem and microbial life to its original health.

Jui-Wen Chen formed a company called JW Eco-Technology and started to market his “Structural Pervious Pavement” with several features that predecessor eco-pavement products had not been able to accomplish — heavy load bearing, low-maintenance, long term durability and ecological habitat. His pavement is a sandwiched system of multiple layers serving complementary functions. The top layer is concrete reinforced with the Aqueduct Grate to withstand high traffic volumes while drawing down water. Surface texture and color can be selected or changed as desired.

The gravel layer with water retention balls provides space for microorganisms and for both air and water to circulate. The pavement can become an air-conditioner using the moisture beneath the pavement to chill summer heat or melt snow in the winter. Finally, using the water it stores and the fertilizers the organisms create, the system builds healthy soils directly beneath the road.

Jui-Wen Chen’s urban planning passion has now advanced to what he calls his “Sponge City,” with terraced retaining walls, waterways, porous pavements, lakes and urban aquaculture irrigating urban farmland. By using his porous roads and tracks around the city, the land will become a reservoir all by itself. Farmers will have a constant supply of water and no need to deplete limited supplies in times of drought.

Mr. Chen’s work reminds us that it is only by finding a way to live peacefully with the natural world can we resolve the crisis caused by global warming and other negative effects of cities.

Jui-Wen Chen is a talented inventor pushing out the frontier of the carbon revolution. His work reflects his concern for people and planet, and he constantly tries to find the best way for humans and the natural world to return to living peacefully together.

The next step to cascade Mr. Chen’s pavement might be for each city to produce its own biochar. The city of Stockholm, Sweden is likely the first large city piloting an urban pyrolysis-based biorefinery. The Stockholm Biochar Project, one of 5 winners of the 2014 Bloomberg Mayor’s Challenge and recipient of $ 1 million in prize money, is carbonizing the city’s green waste and making the biochar available to city residents and for municipal landscaping.

Bjorn Embrén, Stockholm’s Tree Officer, has been using biochar successfully for nearly 10 years to improve urban forest survival rates and enhance growth. Looking to source more locally produced biochar, Embrén and a colleague, Jonas Dahlof, who heads up planning and development for the city’s waste disposal, developed a plan for converting park waste into biochar and using the excess heat to feed into the city’s district heating system.

Stockholm also significantly improved its stormwater management, demonstrating what Mr. Chen has been saying. Stockholm’s stormwater, like Taipai’s, is contaminated with total suspended solids, nutrients, heavy metals, PAHs, E.coli and other substances. Stockholm found it could mitigate many of these problems by installing biochar beds along roads and drainages. It found that different types of char are more effective at filtering different types of contaminants and that it can also increase hydropic conductivity — infiltration of water into soil.

Particle size and pore size distribution matter, and both are boosted with higher temperature kilns. Finer sizes may be better for sandy soils, while courser particles may be better for soils with high clay content. Higher temperatures can also produce biochars which are less hydrophobic.

In 2014 the U.S. Environmental Protection Agency (EPA) invited the Stockholm team to Washington D.C. to explain how carbon-structured soils has saved their city money and cut pollution.

Stormwater can be captured and treated in catch basins, French drains, porous sidewalks, rain and roof gardens, swales, storm drain channels and wetlands. Researchers at the University of Delaware are designing ways to incorporate carbon catchment into the greenways along highways. That will reduce the need for state and local governments to buy additional land for stormwater treatment right-of-ways, potentially saving millions of tax dollars and rescuing coastal cities from the nightmare storms climate change still has in store for the 21st century.

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