Carbon-Neutral Granite Concrete is Used in a NYC Skyscraper

A new carbon-neutral concrete has been commercially applied for the first time in a prominent skyscraper under construction in Manhattan. This concrete uses a granite binder instead of the conventional limestone cement that emits greenhouse gases.

Concrete is composed of three primary components: cement, aggregates (like sand and/or gravel), and water. When mixed with water, the cement undergoes a chemical reaction that creates a solid material, effectively binding the mixture.

Traditional Portland cement is produced by grinding limestone and other raw materials, then heating the resulting powder to temperatures as high as 1,450 ºC (2,642 ºF). Unfortunately, this heating process generates significant carbon dioxide emissions.

The Environmental Impact of Calcination

Additionally, during the calcination process, the heated limestone transforms into cement and releases trapped carbon dioxide as a byproduct. Together, the CO2 emitted from heating and the calcination process is estimated to contribute to 5% to 8% of all human-caused greenhouse gas emissions.

Various organizations are working to reduce the carbon footprint of cement by substituting limestone with materials such as discarded clay, fly ash, and magnesium silicate. Last year, we learned about C-Crete, a type of concrete developed by C-Crete Technologies in California that is free of Portland cement. A version of this material using slag as a binder was utilized to retrofit the foundation of a 120-year-old building in Seattle.

Innovative Application

In July, a new version using granite as a binder was used to create a 12-cubic-yard (9.2-cubic-meter) topping slab in the upper lobby of 270 Park Avenue, a 1,388 ft (423 m) tall skyscraper currently under construction in New York City. A topping slab is a layer of concrete added over another concrete surface to improve its appearance and functionality.

C-Crete president Rouzbeh Savary explains that this new cement alternative is produced by grinding raw granite and undergoing several proprietary processes that make the powdered granite reactive with water, enabling it to function as a binder. Importantly, no heat is needed at any stage of production.

The Benefits of Granite in C-Crete Production

Moreover, granite is a non-carbonate rock, meaning it does not contain or emit any CO2. Since granite is one of the most abundant rocks on Earth, availability is not a concern. Savary notes that the cost of granite-based C-Crete should be comparable to that of traditional concrete.

In terms of performance, the new version of C-Crete is reported to exhibit pumpability, workability, setting time, and surface finish similar to conventional concrete. It also complies with ASTM international standards for mechanical and durability properties, as confirmed by independent third-party assessments.

Read the original article on: New Atlas

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