Supported by Natural Science and Engineering Research Council of Canada, the Canadian Concrete Masonry Producers Association (CCMPA) is working with the McGill University Department of Civil Engineering, Montreal, to investigate the possibility of using carbon dioxide curing to replace steam curing in concrete masonry unit production. Carbon dioxide curing of CMU is a carbon sequestration process. The reaction takes place between cement binder and carbon dioxide to form a hybrid microstructure of CSH with calcium carbonate. Carbonated CMUs can have strength comparable to steam cured and exhibit better resistance to shrinkage, absorption, sulfate attack and freeze-thaw cycling.
CO2-based curing is not new to masonry industry. In 1960's, NCMA and PCA had jointly supported research on flue gas carbonation technology to reduce carbonation shrinkage of CMU. Although a number of patents were issued, there was no large scale commercial application. The technology has gained renewed interest recently due to the fact that large quantity of high purity and low cost CO2 will be available in near future as product of emission regulation.
CMUs have the potential to utilize the recovered CO2 and claim carbon credits in reglatory-established trading schemes. The preliminary CCMPA study has shown, if cement binder can uptake 14 percent of CO2, fine aggregate 6 percent and coarse aggregate 12 percent, by their respective mass, one typical 8-in block can sequester 3 lbs. of CO2. Since most natural aggregates are not reactive with CO2, calcium-rich industry byproducts such as slag can therefore be utilized to sequester CO2 and make natural aggregate substitutes. If all CMUs in the United States and Canada are processed using carbon dioxide curing, the 4.3 billion units can uptake 6 Mt of CO2. For 100 Mt of cement annually produced in these two countries, the carbon emission is about 80 Mt. The use of 6 Mt of CO2 per year by CMU will help cement industry reduce carbon emission by 7.5 percent and gain a carbon credit of $120 million if traded at $20/tCO2.
Carbon dioxide curing also stands to significantly reduce energy consumption and its related cost in comparison to steam curing, the Canadian research team contends. The focus of the three-year project is on developing innovative technologies to achieve the uptake targets using existing kiln with modification. Launched in early 2010, the project will also develop a system including a gas transport mode to benefit both CO2 sources and sinks. Additional information on the research can be obtained from CCMA President Paul Hargest, 519/624-8396; [email protected].