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Chemical Engineering

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A novel, structural, carbon-negative cement

| By Gerald Ondrey

Magnesia cements have been around for thousands of years, and have been explored extensively over recent decades primarily because of their capacity to absorb CO2 from the atmosphere at ambient temperatures. Until now, however, their use has been limited to rudimentary applications like cement block and non-load-bearing wall systems, because their formulations have been too corrosive to accommodate structural steel reinforcing agents, such as rebar. With support from Beton Consulting Engineers (Mendota Heights, MN;, MSB Global, Inc. (New York) has raised the pH of its reactive magnesia cement (RMC) to a level that meets the ASTM code compliance for a reinforcing steel agent, thereby making it suitable for structural, poured-in-place applications and enabling carbon negativity in as little as seven years.

It is well known that cement production accounts for about 8% of global CO2 emissions. Approximately 90% of these emissions come from the production of clinker used as the binder in ordinary Portland cement (PC). PC relies on the use of calcium carbonate (limestone), which is calcinated at high temperatures in a cement kiln to produce lime (CaO), along with a release of CO2 from the decarbonation of limestone. Finding an alternative to this limestone-based clinker has been the main hurdle to reducing the overall CO2 emissions from cement production.

In contrast to Portland cement, the patented MSB formulation derives its main binder components from waste products of two other industries: granulated blast furnace slag (GBFS) and/or flyash, along with rejected brine from desalination processes or deep-water brackish wells. The waste brine is used to create magnesium oxide, along with other useful materials and combined with GBFS, pozzolans and other proprietary ingredients to provide the binder. The binder components in MSC are processed at temperatures of 400–700°C, compared to 1,450°C required for Portland cement. Upon the MSB concrete curing, the product will absorb CO2 at the rate of 21.6 lb/yr per ton over its lifetime.

Beton’s Mark Lukkarila and Kevin McDonald have demonstrated technical performance data, according to ASTM compliance standards for structural cement. MSB is currently looking for strategic partners to assist in bringing this technology to commercial scale.