Effects of Fly Ash on Carbonation of Concrete With Portland Blast-Furnace Slag Cement


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Title: Effects of Fly Ash on Carbonation of Concrete With Portland Blast-Furnace Slag Cement

Author(s): J. Bijen and R. Van SelstI

Publication: Special Publication

Volume: 126


Appears on pages(s): 1001-1030

Keywords: blast furnace slag; carbonation; concretes; durability; fly ash; Materials Research

Date: 8/1/1991

An investigation has been carried out on the effects of cement replacement by fly ash on the carbonation rate of concrete. The research was mainly devoted to portland blast furnace slag cement because this cement has a major market share in the Netherlands. It has been concluded that in the case of portland blast furnace slag cement concrete, replacement up to 25 percent by mass results in a substantially higher carbonation rate, while for a similar portland-cement concrete, the difference between concrete with and without replacement is relatively small. This observation corresponds with the finding that the pH development of the pore water in concrete with portland blast furnace slag cement is too low to initiate a substantial fly ash dissolution. As a consequence, pozzolanic activity will be slight. However, in portland-cement concrete, pozzolanic action can develop more effectively and contribute to strength and densification of the matrix. A useful relation exists between the carbonation depth after 1 or 2 years and compressive strength after 28 days and, even better, after 7 days for each type of cement. This relation might cover all types of cements when the lime content of the binder is involved.