Rate of Carbonation in Concrete Made With Blended Cement

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Title: Rate of Carbonation in Concrete Made With Blended Cement

Author(s): K. Horiguchi, T. Chosokabe, T. Ikabata, and Y. Suzuki

Publication: Special Publication

Volume: 145

Issue:

Appears on pages(s): 917-932

Keywords: accelerated tests; blast furnace slag; blended cements; calcium hydroxides; carbonation; concrete; density (mass/volume); fly ash; microstructure; portland cement; Materials Research

Date: 5/1/1994

Abstract:
In the design of concrete structures, carbonation is one of the most important factors determining service life. Environmental conditions, mix proportions, and cement type are also significant. It has been generally indicated that carbonation rate of concrete made with blast furnace slag or fly ash cements is greater than that provided by portland cement alone. In this study, an accelerated carbonation test was conducted on concrete made with binary and ternary blended cements containing large quantities of admixture. The binary and ternary cements used in this study consisted of three types of portland cement (normal, moderate heat, and belite low-heat), blast furnace slag, and fly ash. The influence of portland cement type and blending ratio of cementitious materials on carbonation rate is discussed. The study focused particularly on calcium hydroxide content in concrete, microstructural density, and the relation between these factors and carbonation rate. The following conclusions were drawn. In binary and ternary blended cement, when the blending ratio of blast furnace slag and fly ash increased, the carbonation constant increased. When the blending ratio of blast furnace slag was more than 60 to 70 percent, the carbonation rate increased rapidly. When fly ash was blended within the range of up to 30 percent, the carbonation constant increased in proportion to the blending ratio, and this tendency did not change, regardless of the portland cement type. Also, to evaluate the carbonation rate of blended cement, both the effective water-cement ratio and calcium hydroxide content, determined by the balance between the amount of calcium hydroxide produced by the hydration of portland cement and the amount required for the complete reaction of blast furnace slag, must be taken into account.