Producers reduce cost—and gain more—with mix optimization
By Craig Yeack
The canals in Venice and the skies in Delhi are … clear. The roads are almost empty between Los Angeles and Palm Springs. What’s going on and how does this relate to us? Let’s examine how we can take yet another step in turning the table on carbon dioxide in our industry.
The concept of a matrix binder and coarse material has been used for millennia. Egyptians with straw and mud, Romans with volcanic pozzolan and stone, and us with portland cement, crushed aggregate, and a host of additives. Modern society is built on modern concrete; usage per person is often cited second only to fresh water. What’s not to love?
Aggregate, cement, and ready-mix concrete are heavy energy users in the mining and manufacturing process, leaving a CO2 footprint at every step. In response, our industry has been in the forefront with many approaches to mitigating environmental impact: judicious use of materials; producing high-quality products to prevent unnecessary replacement; and, mix optimization with pozzolans such as fly ash and GBBS (commonly known as slag) to reduce CO2 impact and improve concrete’s durability and lifespan. Now we have a new option: Direct CO2 injection to reduce total carbon impact.
INJECTING CO2: HOW IT WORKS
Academics have long pondered the process of portland cement’s rehydration. There are many fancy chemical formulations and Latin words, but let’s jump to the punchline. If we inject certain chemicals or compounds into the process, it can be changed for the better. It turns out, one such compound is CO2.
Several companies have taken the academic research to industrial application, including one called CarbonCure Technologies. The concept is to inject a small amount of CO2 during batching that will result in higher strengths of the otherwise unchanged mix. This allows producers to achieve the same strength with less cement.
Having started out in the industry designing batching systems and associated mixes, I have been surrounded by quality control professionals for decades. Many of these folks from marquee concrete producers swear that, properly conducted, direct CO2 injection during batching does indeed produce strength bumps. The catch has been to make it economically viable for producers.
CHANGING OUTPUT TO INPUT
|The CarbonCure carbon dioxide dosing and injection technology is installed in 200 concrete plants across North America. To date, the strength-enhancing, cement-optimizing process has been utilized to reduce over 78,000 tons of embodied carbon from concrete production. PHOTO: CarbonCure Technologies Inc., Halifax, N.S.
Many producers use CO2 injection technology provided by CarbonCure. Through widespread use, indications are that injecting a pound of the gas saves approximately 26 lbs. of cementitious material. Each producer must do the math on the blended cost of cementitious material and injection technology, but in general, depending upon region, there should be room for savings (see sidebar for a sample calculation).
One C-suite leader of a well-known U.S. producer takes it even further and says it’s not just about cost savings. Most importantly, many infrastructure owners from companies large and small strongly support sustainability. This allows contractors to differentiate themselves for new business development, and even more, reinforce a positive culture of sustainability to help recruit and retain employees.
We all live on this earth and want to make the best world for our children and grandchildren. Our industry seeks to provide necessary infrastructure with minimal environmental impact. We have pushed hard on slag and fly ash with great results. While there are more incremental gains for pozzolanic substitutes, let’s take a cue from innovators in the producer community and the folks at CarbonCure and take the next step.
HOW DOES MIX OPTIMIZATION COMPUTE?
Consider a scenario of a 5-½ bag mix using 30 percent fly ash with the following:
- In-bin cement at $150/ton
- In-bin fly ash at $50/ton
- Post-industrial CO2 at $0.25/lb.
- An average load size of 7.25 CY
- A direct CO2 injection strength savings of 5 percent
Before technology costs, this calculation results in a savings of just south of $10 and between 130 and 150 lbs. of CO2 per load if we use the conservative 1:1 measure for CO2 generated in portland cement production. The savings are actually more considering the injected CO2 is post-industrial, and transporting fewer truckloads of cementitious materials saves roughly 22 lbs. of CO2 per gallon of diesel fuel (according to the U.S. Energy Information Administration; www.eia.gov).
Craig Yeack has held leadership positions with both construction materials producers and software providers. He is co-founder of BCMI Corp. (the Bulk Construction Materials Initiative), which is dedicated to reinventing the construction materials business with modern mobile and cloud-based tools. His Tech Talk column—named best column by the Construction Media Alliance in 2018—focuses on concise, actionable ideas to improve financial performance for ready-mix producers. He can be reached at [email protected].