Effect of Granulated Blast Furnace Slag on the Transition Zone in Concrete


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Title: Effect of Granulated Blast Furnace Slag on the Transition Zone in Concrete

Author(s): Rachel Detwiler, Kosalram Krishnan, and P. Kumar Mehta

Publication: Special Publication

Volume: 100


Appears on pages(s): 63-72

Keywords: aggregates; blast furnace slag; calcium hydroxides; concretes; cement pastes; permeability; portland cements; stress-strain relationships; Materials Research

Date: 4/1/1987

The properties of concrete--stress-strain behavior and permeability, for example--differ significantly from those of hydrated cement paste having the same water-cement ratio. The explanation for the difference lies mainly in the existence of a transition zone between the hydrated cement paste and the coarse aggregate particles. Results from a previous study at the University of California show that improvements in the mechanical and permeability characteristics of concrete brought about by the addition of pozzolans can be attributed largely to their effect on the transition zone. Results of a study on the transition zone as affected by the addition of varying amounts of granulated blast furnace slag to portland cement are reported. It is found that with a cement containing 10 percent slag, the thickness of the transition zone, as determined by the thickness of the region in which calcium hydroxide crystals showed a preferred orientation parallel to the aggregate surface, was not significantly different from that of a portland cement paste of the same water-cement ratio and curing conditions. For the cement with 30 percent slag, however, no preferred orientation was observed at or near the paste-aggregate interface. Since 30 percent slag is not sufficient to combine with all of the calcium hydroxide produced by portland cement hydration, the lack of preferred orientation can be attributed largely to the nucleation of numerous randomly oriented calcium hydroxide crystals on the fine particles of slag, with the pozzolanic reaction having a secondary effect.