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Materials

79: Carbon negative concrete

Problem:

The traditional baking of bricks and mixing concrete creates CO₂. For those who manufacture bricks, there is a PROBLEM with emission of fluorine compounds in quantities hazardous to the health of people downwind.

Solution:

Carbon dioxide-free concrete.


Ryan J. Gilliam, Randy Seeker and a team at Calera Inc. (now Fortera)  in Los Gatos, California, have achieved an eco-friendly concrete by forming novel, metastable calcium and magnesium carbonate and bicarbonate minerals, similar to those found in the skeletons of marine animals and plants.

They refer to this as Mineralization via Aqueous Precipitation, or MAP for short. In its simplest form, MAP involves contacting gas from the power plant with natural waters found in abundance on Earth. Many of the crystallographic forms Calera synthesizes are poorly known. These novel ‘polymorphs’ make it possible to produce high reactive cements and aggregate precursors, with bulk chemistries that would usually be relatively inert.

Calera estimates that for every ton of cement produced using their method instead of the traditional one, half a ton of CO₂ is sequestered.

Led by Ivrin Chen, Calera, operates a pilot and demonstration plant next to BluePlanet a 1000 MW power plant in nearby Moss Landing.

The Calera process bubbles the plant’s waste gases through seawater. This removes about 90% of the carbon dioxide and combines it with minerals in the water, resulting in the creation of limestone that is composed of about 50% waste carbon dioxide.

Given that the Moss Landing plant produces more than 2 million tons (1.8 million tonnes) of carbon dioxide per year, the production of coarse or fine carbon neutral – or even carbon negative – concrete is very promising.

Mehrdad Mahoutian, Chris Stern and a team in Montreal, Quebec, Canada have developed Carbicrete, a cement-free construction material.

The concrete employs steel slag and CO₂ as raw materials. Steel slag is a byproduct of the steelmaking process that is often placed into landfills.

A traditional cinder block, known in the construction industry as a concrete masonry unit (CMU), weighs about 14 lb (6 kg). Within that, there is normally 4 lb (1.8 kg) of cement and in that there are 4 lb (1.8 kg) of CO₂ that is emitted.

Carbicrete sequester one kilogram of CO₂, so the total emitted or avoided is 6 lb per 14 lb (3 kg per 18kg) CMU. Mahoutian came across the material as he was researching alternatives to cement while doing his PhD at McGill University.

In 2018, Carbicrete won a CU$2.1m (US$1.57m) grant from Sustainable Development Technology Canada to build a production facility at an existing concrete plant and reach commercial production by mid-2021.

In April 2019, Carbicrete was awarded the Best CO₂ Utilisation prize by Germany’s Nova-Institute. Carbicrete has assembled a consortium of project partners that includes a concrete maker, an industrial gas company and steel slag handler. (carbicrete.com)

What you can do: Tell local builders about these materials and if you are having a building constructed, insist that eco-friendly building materials are used.

Discover Solution 80: Bricks without firing.

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