Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!
Production of cement — the world’s most used commodity after water — currently produces 8 percent of global carbon dioxide emissions. Demand for cement, which is used to make concrete and mortar, is projected to increase by 50% in the near future as the world continues to urbanize. Ordinary Portland cement — often referred to a OPC — is the most common form of cement. It is made by heating crushed limestone and clay together in a large rotary kiln. Heating the kilns using fossil fuels contributes 40 percent of the carbon dioxide created in the cement making process. The other 60 percent is the result of the heat needed to break down the limestone — a sedimentary rock that is mostly calcium carbonate (CaCO3) — into calcium oxide (CaO) and carbon dioxide.
Researchers at the University of Michigan say they have devised a new electro-chemical approach that greatly reduces the amount of carbon dioxide released by the cement making process. They claim their process is low in cost and scalable. Furthermore, it can neutralize the most carbon-heavy step in cement production without changing the manufacturing process, according to a study recently published in Energy & Environmental Science.
While traditional cement production gets its necessary calcium carbonate from limestone that releases carbon dioxide when heated in a kiln, the University of Michigan researchers make calcium carbonate through an electro-chemical process that captures carbon dioxide from the air and binds it with abundant minerals or recycled concrete. “Our newly developed electro-chemical material manufacturing approach opens a new area in cement production and waste upcycling at scale,” says Jiaqi Li, an assistant professor of civil and environmental engineering, staff scientist at the Lawrence Livermore National Laboratory, and corresponding author of the study.
The proposed approach, which replaces naturally occurring limestone with electro-chemically produced calcium carbonate, neutralizes the CO2 released during kiln processing with the CO2 taken up from the air during the electrochemical production. If implemented at full capacity, the new strategy could reduce global carbon dioxide emissions by at least three billion metric tons — three gigatons — a year. For comparison purposes, 37.4 gigatons of energy-related global carbon dioxide emissions were reported in 2023. The 8 percent of global carbon emissions that cement production contributes today could be reduced to 3 percent using the new process or reduced even further to net-zero if carbon capture technologies are employed. That last part is a bit optimistic, as currently there are no carbon capture facilities in operation that are cost effective.
“The strategy can change the cement industry from a gigaton CO2 emitter to a gigaton-scale enabler for clean energy and carbon management technologies,” said Wenxin Zhang, a doctoral student at the California Institute of Technology, graduate research intern at Lawrence Livermore National Laboratory, and contributing author of the study. The non-carbonaceous precursors used in this new process are widely available worldwide. One of then is basalt, which comprises half the volume of the Earth’s crust, and industry wastes such as recycled concrete from construction and demolition waste.
Cement Without The Carbon Emissions
The process works by applying an electric potential across water containing a neutral electrolyte salt in an electrolyzer — a device with a positive electrode placed at one end and a negative electrode at the other and a cation exchange membrane in the middle. As electricity flows, water at the anode splits into oxygen gas (O2) and positively charged protons (H+), while water at the cathode produces hydrogen gas (H2), releasing negatively charged hydroxide ions (OH-). This process creates an increasingly acidic anodic electrolyte and alkaline cathodic electrolyte that is harnessed to process calcium silicates. Those protons break apart the calcium silicate to form solid silica (SiO2) and calcium ions (Ca2+). The calcium ions react with CO2 from the air and hydroxide ions in the water to form into solid, carbon-negative calcium carbonate.
While the calcium carbonate is the main product that will feed cement kilns, the solid silica can be blended into cement as a supplementary material to improve concrete or mortar strength and durability. Going a step further, the researchers assessed whether the technology is economically viable, taking carbon credit savings into account. The electro-chemical approach proved to cost less and be more efficient compared to existing techniques. “As the present strategy requires minimal or no modification to the business-as-usual cement plants, it has low entry barriers to be adopted by the large cement businesses,” said Xiao Kun Lu, a doctoral student of chemical engineering at Northwestern University and lead author of the study.
The researchers say their approach produces Portland cement feedstock and supplementary cementitious materials that are compatible with existing OPC manufacturing infrastructure and decarbonization technologies, thereby avoiding regulatory and safety concerns. Portland cement derived from using this technology complies with existing international and national standards. In addition, using it does not require new training for millions of materials and civil engineers or builders globally. They point out that the decreasing cost of renewable electricity (which now costs less than electricity from conventional thermal generation), together with potential carbon credit savings, provides further economic competitiveness in addition to it environmental benefits.
Two of the byproducts of the process are hydrogen gas and oxygen, both of which have additive economic value in many commercial applications. Hydrogen can be used for industrial heating, power generation, and chemical manufacturing. Oxygen can aid in sequestering concentrated carbon dioxide flue gas at cement plants. Another byproduct of the process is calcium bi-carbonate water, which can be used to mitigate ocean acidification. The researchers say they have studied this process in three electro-chemical reactor configurations, evaluated the products and performances, and performed life cycle assessment and techno-economic analysis to probe the embodied carbon, energy use, and economic viability.
Low Carbon Cement Advances
There are others working on reducing the enormous carbon emissions created by cement making operations. Sublime System, an MIT spinoff, is one of them that uses electricity in its process to slash emissions by 90 percent. It also has received the necessary certifications to allow its cement to be used in making concrete without using OPC. And while the researchers at the University of Michigan say that the process heat needed to make OPC can only be obtained by burning fossil fuels, there are changes happening there as well, with companies like Rondo Energy making advances in low carbon process heat. Another consideration is that part of the economic model for the U of M model is carbon offset credits, which could disappear as quickly as the smoke from yesterday’s campfire.
This is a story about something that works in the lab that could help lower carbon emissions in a meaningful way instead of the piddling reductions promised by carbon capture schemes. It has promise; it has potential. Now the test will be whether it can become a commercial success. If it performs as promised, the world is likely to beat a path to the University of Michigan.
Chip in a few dollars a month to help support independent cleantech coverage that helps to accelerate the cleantech revolution!
Have a tip for CleanTechnica? Want to advertise? Want to suggest a guest for our CleanTech Talk podcast? Contact us here.
Sign up for our daily newsletter for 15 new cleantech stories a day. Or sign up for our weekly one if daily is too frequent.
CleanTechnica uses affiliate links. See our policy here.
CleanTechnica’s Comment Policy
