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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Formation of Silica gel During Carbonation of Cementitious Systems Containing Slag Cements
Author(s): TH. A. Bier J. Kropp, and H. K. Hilsdorf
Publication: Special Publication
Appears on pages(s): 1413-1428
Keywords: alkalinity; blast furnace slag; carbonation; silica gel; corrosion resistance; permeability; portland-slag cements; Materials Research
Abstract:During hydration of portland cement clinker and granulated slag in portland blast furnace slag cement, finely dispersed calcium silicate hydrates are formed as the major constituent of hydrated cement paste. With increasing slag content of cement, more C-S-H phases are formed, contributing to the well-known dense pore structure of pastes made of PBFS cements. Upon carbonation of the hydrated cement paste, all alkaline compounds are decomposed to form carbonates. Furthermore, the decomposition of CSH results in the formation of a porous silica gel. In an experimental investigation, different types of hydrated cement paste, mortars, and concretes manufactured with portland cement and portland blast furnace slag cements with different slag contents were subjected to carbonation and the resulting changes in the pore structure monitored. These tests demonstrated that the silica gel formed during carbonation shows pores in the range of approximately 300 nm pore radius. Where large quantities of silica gel are formed, carbonation leads to a coarser pore structure compared to the original structure. Permeability of these systems then increases significantly. The porous silica gel, however, proved to be reactive. Upon access of alkalies, new C-S-H phases may be rebuilt with a very fine port size distribution with pore radii ó 10 nm.
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