Microstructure of Concretes Made with and without Blast Furnace Slag after 40 Years of Immersion in Saturated Gypsum Solutions at 20” C

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Title: Microstructure of Concretes Made with and without Blast Furnace Slag after 40 Years of Immersion in Saturated Gypsum Solutions at 20” C

Author(s): A.C. Courault, A.K. Crumbie, D. Sorrentino and D. Damidot

Publication: Special Publication

Volume: 178

Issue:

Appears on pages(s): 955-974

Keywords: blast furnace slag; calcium silicates; concrete; ettringite; hydrogarnet; microstructure; slag.

Date: 6/1/1998

Abstract:
Concrete samples made with and without blast furnace slag (BFS) and stored in saturated gypsum solutions for 40 years have been studied. After this long period of time, there still remains small amounts of anhydrous cement and unreacted BFS grains. The reacted BFS are easily identified by EPMA analyses by considering the Mg concentration ; Mg does not diffuse away from the BFS grains. On the contrary Al diffuses away from the BFS grains towards the paste, whereas Ca tends to diffuse from the paste towards the BFS grains. The evolution of Ca, Al, Si and Mg concentrations from slag grains to the paste, or to cement grains, can be described by a succession of local equilibria defined in the CaO-Si02 -A12 03 -MgO-S03 -H2 0 system. The formation of different phase assemblages in the presence of BFS may account for the finer pore structure found despite similar total porosities for both concretes. Moreover a calcite layer has been formed : this layer limits sulfate ions ingress into the paste for both concretes.