Calyx Global has published a rating for the first reduced-CO2 concrete project on the voluntary carbon market (VCM). In this blog post, we’ll provide an overview of CO2 injection technology, discuss the global importance of reducing emissions from concrete production and highlight several opportunities and challenges facing this nascent project type. 

We introduce several methodologies for reducing emissions from concrete via CO2 injection. We focus primarily on VM0043 Methodology for CO2 Utilization in Concrete Production, v1.0 under Verified Carbon Standard (VCS) which is responsible for most of the concrete credits currently on the market.

Is concrete really a major source of emissions? 

The world uses more than 30 billion tons of concrete annually for buildings, bridges, infrastructure and other applications, and demand is forecasted to grow. Concrete, the finished product we see everywhere in our daily lives, is not to be confused with portland cement, a key ingredient in concrete used to bind the aggregate material. Portland cement (referred to simply as ‘cement’ below) is the focus of VM0043 as it requires a very carbon-intensive production process.

Global cement manufacturing released 1.5 billion tons of carbon dioxide (tCO2) in 2024, about 4% of the world’s total CO2 emissions. Reducing emissions from cement production is critical to achieving global climate targets.

Two emission sources drive cement manufacturing’s significant carbon footprint. Fossil fuels, whose emissions account for ~40% of cement production emissions, are often used to achieve the very high temperatures necessary to convert limestone to clinker, a precursor to cement. The remaining ~60% of emissions originate from the calcination reaction that occurs when limestone is heated, releasing CO2 from the calcium carbonate in limestone. 

How does ‘CO2 utilization in concrete production’ work?

CO2 utilization in concrete starts with CO2 captured from point-source industrial processes or directly from the atmosphere (i.e., direct air capture). The captured CO2 must then be transported to a concrete facility where a small quantity is injected into fresh concrete during the production process. Calcium ions react with the injected CO2 to form calcium carbonate, which becomes embedded in the concrete. These calcium carbonate nanoparticles act as nucleation sites for the subsequent hydration (reaction with water) of calcium silicates, accelerating the concrete’s setting and strengthening process.

Critically, CO2 injection allows producers to decrease the concrete’s cement content without compromising performance. These curtailments in cement content are the primary source of concrete project emission reductions. Projects also mineralize a much smaller quantity of CO2 through injection. 

The way emission reductions are achieved under VM0043

Efforts to reduce the GHG intensity of cement production and concrete use

The concrete industry has traditionally tried to reduce its carbon footprint by substituting supplementary cementitious materials (SCMs) such as fly ash sourced from coal-fired electric and steam-generating plants for clinker, the main component of portland cement. However, as the power sector also moves towards decarbonization, fly ash may grow scarce. Although barriers to CO2 injection remain, adoption throughout the industry is accelerating.

A growing number of concrete facilities are participating in registered carbon projects. In the future, demand for low-carbon concrete is likely to increase with the increased prevalence of state and country-wide emission reduction targets. In addition to high-level targets, government policy supports decarbonizing concrete use. The US, where our first rated VCS project is registered, has implemented the following initiatives:

• Clean Energy Tax Credits and Incentives. The Section 45Q Tax Credit incentivizes the capture and storage of carbon dioxide, including for cement plants. The Infrastructure Investment and Jobs Act includes funding for projects that promote the use of low-carbon materials, ostensibly supporting the cement sector in its transition.
• Research and Development. The U.S. Department of Energy’s Carbon Management Program funds research into carbon-neutral or low-carbon cement formulations. The Industrial Decarbonization Program supports pilot projects and private sector collaborations in hard-to-abate sectors.
• Green Procurement. Federal and state governments are increasingly setting requirements for low-carbon or carbon-neutral materials in public construction projects, creating a market for low-carbon cement products.

How will the VCM play a role?

Calyx Global has developed a framework to evaluate the GHG integrity of credits generated from projects that utilize CO2 in ready-mix concrete. We have begun to rate CO2 utilization in concrete projects that are designed under the VM0043 protocol. As of January 2025, There are only three actively issuing projects registered with VCS and five that are at some stage of development. 

However, several other methodologies have been developed, with only a few currently in use by projects issuing credits. They are outlined in the table below. 

Summary of concrete methodologies in the VCM [1]:

Calyx Global will continue to assess these methodologies and rate credits that use them as they emerge, so stay tuned. Meanwhile, for more information on CO2-injected concrete, Calyx Global Platform subscribers can check out our first project rating. If you’re not yet a subscriber and want a demo, reach out. For our (surprising) findings on CO2-injected concrete removals, read our first blog post on the topic available to subscribers and non-subscribers.

Citations

[1] Quantum Commodity Intelligence. (2025, January 30). Feature: Roll call of registries offering methods that utilise low-carbon concrete. Accessible at: https://www.qcintel.com/carbon/article/feature-roll-call-of-registries-offering-methods-that-utilise-low-carbon-concrete-35338.html