New York City: from 2025 only “green concrete” will be used in public works

New York always makes headlines. It is perhaps one of the most observed cities in the world, where everything becomes a trend, where there’s everything and its exact opposite. Where a social event becomes a must, and where an accident is more serious than elsewhere but is absorbed before anywhere else. At the end of September, streets were flooded, cars were carried away like drifting boats, shops and offices were underwater, a real environmental disaster resulting from torrential rains mixed with gusts of wind and outdated sewer systems.

For a couple of days, the city seemed, once again, vulnerable and unprepared. Then, as the water and mud flowed towards the sea, even the “disaster” slipped away, giving the city back its everyday spirit, the city that never sleeps. What remained was the analysis of experts on why cities like New York, and not only, can suffer from these types of floods. This analysis takes into account the higher impermeable surfaces of cities compared to rural areas, as there are more roads, roofs, parking lots, asphalt, and concrete. More effective drainage infrastructure and careful monitoring are called for.

According to statistics published in the days of the flooding, New York City and most American cities are under-designed because it would be very expensive to build structures to handle events that, statistically, can happen very rarely, perhaps once in a hundred years, with some estimating this probability at 1 percent.

The New York Times reported that the city’s drainage systems have a limit of 1.75 inches (4.5 cm) per hour, which was exceeded during the late September storm, overwhelming 7,400 miles (almost 12,000 kilometers) of pipes that transport rainwater and wastewater under the city’s surfaces to treatment plants or into the nearest rivers and bays. The overflow spilled into the streets, causing flooding in subway stations in Brooklyn and Queens.

According to Rohit Aggarwala, commissioner of the New York City Department of Environmental Protection, the city is in a “climate emergency.” “This shift in weather patterns is the result of climate change, and the sad reality is that the climate is changing faster than our infrastructure can respond.”

On the other hand, just two years ago, with Hurricane Ida, we saw the same scenes, with rivers of water flooding the streets, putting the drainage system to the test, combining stormwater with wastewater in the same pipes. This mix of rain and untreated sewage, with heavy rainfall like these, ends up directly in waterways like the East River, but if the pipes get clogged, it risks infiltrating the water systems of homes and offices.

To get to the root of the problem, the causes of climate change, the State of New York, a few days before the flood, had issued an innovative measure for the United States to limit the impact of harmful emissions in the atmosphere. The measure, called “Buy Clean Concrete,” – as explained by Governor Kathy Hochul – “represents a fundamental step in New York State’s commitment to environmental sustainability.”

The regulation, announced in mid-September as Executive Order 22, imposes limits on emissions from the concrete used in public construction and transportation projects funded by the state. According to Ian Wells, the director of industrial decarbonization at the Natural Resources Defense Council, “Concrete is the most commonly used building material in the world and one of the biggest contributors to carbon emissions. We want to turn concrete from a climate burden into a climate resource.”

The “clean concrete” requirement will come into effect from 2025 and will apply to state agency contracts over a million dollars that involve the use of more than 50 cubic meters of concrete or to Department of Transportation contracts over 3 million dollars with the planned use of at least 200 cubic meters of concrete. Thanks to these regulations, among other things, New York aims to achieve carbon neutrality at the economic level by 2050.

The use of eco-friendly concrete in private or public construction is not new to the building industry, especially not in the United States, although it has often been the result of best practices of some builders rather than targeted laws. An example of this is the Northeast Boundary Tunnel (NEBT), just completed in Washington D.C. by Webuild and its American subsidiary Lane Construction, designed to improve the quality of the capital’s rivers’ water and reduce flooding by managing the flow of rainwater and wastewater effectively. The project, a model in its category, was built using a low-carbon composite, with low emissions, thanks to the use of binders alternative to traditional cement.

This formula has been experimented with since 2015 by Webuild and used in construction sites in Italy and abroad to create Clean Concrete for major infrastructure projects such as the Airport Link light rail for connecting the city to Perth Airport in Western Australia, which aims to reduce 2 million tons of CO2 per year. Special attention has been paid to cement mixtures in the construction of the new Eni Headquarters, the Italian energy giant. In this case, a special type of cement was used that allowed – along with all the other sustainability features of the building – to obtain LEED certification.

Over the years, Webuild has studied and developed special optimized concrete mixtures coming from other industrial chains (for example steel industry), which allow to reduce the use of cement by up to 65%, as well as the use of highly recycled steel.