Carbon Storage through Concrete Block Carbonation

Abstract

Abstract-The effect of initial curing on carbonation curing of lightweight concrete masonry units (CMU) was examined. Initial curing was performed from 4 to 18 hours at a relative humidity of 50% and temperature of 25°C. Based on cement content, four-hour carbonation curing allowed concretes to uptake 22% to 24% CO 2 with initial curing and 8.5% without initial curing, while prolonged 4-day carbonation recorded an uptake of 35%. Carbonation curing can replace steam curing in CMU production to accelerate hydration and recycle cement kiln CO 2 in a beneficial manner.Index Terms-Concrete masonry unit, curing, carbonation, carbon uptake. I. INTRODUCTIONConcrete masonry units (CMU) have been widely used in building construction as load bearing and non-load-bearing walls. The North American market for concrete blocks and bricks is projected to increase to 4.3 billion units per year by 2014 [1].In comparison to cast-in-place concrete, masonry block structures not only exhibit superior performance due to precast quality, but also represent a low environmental impact construction system. With reference to 1 m 2 of solid concrete wall, a masonry wall using 200-mm CMU requires 48% less material due to internal cavities, leading to 65% less cement, and 65% less CO 2 emission.CMUs produced in North America are typically steam cured. While steam curing accelerates strength gain and shortens the production cycles, the process itself is energy intensive. It is estimated, for one cubic meter of concrete in block form, atmospheric pressure steam curing consumes 0.59 Gigajoules per m 3 of concrete and autoclave curing consumes 0.71 Gigajoules per m 3 of concrete [2].The alternative curing method for CMU production is carbonation curing which uses high purity carbon dioxide (99.5% of CO 2 ) or low purity flue gas (14% of CO 2 ) for accelerated hydration and durability improvement.However, carbonation curing has never been adopted in large-scale production. This was possibly because flue gas carbonation was not effective in hydration acceleration and Manuscript received June 10, 2013; revised July 23, 2013. This work was supported by the Natural Science and Engineering Research Council (NSERC) of Canada and Canadian Concrete Masonry Producers Association (CCMPA), and the supply of expanded slag aggregates by Lafarge Canada.Hilal El-Hassan is with the Dept. of Civil Engineering at the American University in Dubai, Dubai Media City, Dubai, UAE, and P.O. BOX 28282 (email: helhassan@aud.edu).Yixin Shao is with the Dept. of Civil Engineering and Applied Mechanics at McGill University, Montreal, Quebec, Canada, H3A 2K6 (email: yixin.shao@mcgill.ca). pure gas carbonation was expensive. The latter situation may change in the near future. Large quantities of high purity, low cost carbon dioxide could soon be available as regulations requiring reductions in CO 2 emissions are developed. In this case, pure gas carbonation can simultaneously accelerate the strength, stabilize the dimension, and enhance the durability. By reducing the hydroxyl i...

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Accelerated Carbonation Curing as a Means of Reducing Carbon Dioxide Emissions

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