Why Specs Matter: Breaking Down Barriers to Sustainable Concrete

By Christie Gamble, Senior Director of Sustainability, CarbonCure Technologies

In the eight years I’ve spent championing CarbonCure’s sustainability mission, the question I hear most often from developers, designers, and policymakers is, “CarbonCure sounds like a no-brainer—why aren’t you everywhere?”

CarbonCure reduces the carbon footprint of concrete by introducing recycled CO₂ as an admixture. The technology improves concrete strength so concrete producers can use less cement while maintaining the performance criteria. Concrete created with CarbonCure is supplied to construction sites with minimal, if any, cost differential. Quite simply, it’s the same concrete with less carbon.

So my job should be easy, right? Wrong! The reality is, CarbonCure—and any other sustainable building material innovation—faces barriers created by outdated specification practices in almost every market we operate in. 

This is at odds with emerging policy on climate change, industry missions to reduce carbon, and a host of other modern initiatives driving change in construction.

The Difference Between Prescriptive and Performance Specifications

Many commercial projects—and nearly all public building and infrastructure projects—include a form of concrete specifications known as prescriptive specs. 

These prescriptive specs outline criteria for how concrete is made. Prescriptive specs prescribe the methods of construction and impose restrictions on the compositional parameters of concrete mix. 

Common prescriptive specs include a minimum cement content, maximum water to cement ratio, and maximum percentages of permitted supplementary cementitious materials (cement-replacing materials such as fly ash and slag, which have significantly lower carbon footprints than Ordinary Portland Cement). In some cases, prescriptive specifications may entirely disallow certain ingredients. 

Performance specs, conversely, outline specific criteria for how the concrete needs to perform. These specs empower the concrete producers—the experts in concrete mix design—to propose the best concrete mix to meet the performance needs of the required application. 

Studies have shown that performance-based concrete specs are more likely to result in better performing concrete, with better sustainability profiles—and often with lower costs—than prescriptive specs.

The Problem with Legacy

Prescriptive specs are so prevalent in the industry, they can be difficult to change. Concrete producers often say things like, “We genuinely care about our community and the environment and we want to adopt sustainable solutions, but our market won’t allow us to.”

Herein lies the problem. A problem which, I must admit, has left me banging my head against a proverbial, over-cemented concrete wall for the past eight years.

There is a misconception that more cement makes better concrete. However, research over the past 100 years has shown that it’s not cement content that controls the strength or permeability of concrete, its water to cementing materials ratio. In some cases, more cement can actually result in poorer concrete. In all cases, over-prescribed cement increases the embodied carbon of the concrete. 

Movements for Positive Change

The good news is that change is coming. SE2050, Architecture2030, the Carbon Leadership Forum and a host of other industry bodies are pushing for change in the industry and actively seeking ways to reduce embodied carbon. Governments are creating policies, resolutions, and building codes to encourage a reduction in embodied carbon in the built environment. All of this will contribute to the move to performance-based specs.

Another good news story is that CarbonCure recently won the global NRG COSIA Carbon XPRIZE. The contest—which took place in three rounds over four and a half years—challenged us and over 2,000 applicants to develop breakthrough technologies to convert carbon dioxide (CO₂) emissions into usable products, with the ultimate goal of tackling climate change.

Our win was an incredible honour not only for CarbonCure, but also for our concrete partners and the concrete industry as a whole. 

It demonstrated that concrete represents a real solution to the global carbon challenge. But we can only gain momentum when more specificers move to performance-based specs.

Read our new eBook, Solving Embodied Carbon Challenges with Concrete Specifications, to learn more about strategies to eliminate embodied carbon, including adopting performance-based concrete specs.


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