Chemical Activation of Lime-Slag Blends


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Title: Chemical Activation of Lime-Slag Blends

Author(s): C. Shi and R. L. Day

Publication: Special Publication

Volume: 153


Appears on pages(s): 1165-1178

Keywords: blast furnace slag; chemical analysis; free lime; hydration; lime; porosity; strength; Materials Research

Date: 6/1/1995

Ground granulated blast furnace slag may show very high strength in the presence of proper alkaline activators. However, the high cost and short supply of alkalies restrict the application of such cementitious materials. This paper reports on an investigation of some practical ways to increase the reactivity of blast furnace slag. Experimental results indicate that for moisture curing at 50 C, the addition of either four percent Na 2SO 4 or four percent flake calcium chloride can significantly increase the strength of lime- slag mixtures consisting of 80 percent slag and 20 percent hydrated lime. The measurements of change in Ca(OH) 2 content with times in the hardened pastes show that the addition of activators accelerates the early reaction, but does not affect overall reactivity. Strength improvement in Na 2SO 4 pastes is due to the formation of ettringite (AFt), while the presence of CaCl 2 favors the formation of C 3A.Ca(OH) 2.12H 2O. At the same time CaCl 2 partially replaces the Ca(OH) 2 in C 3A.Ca(OH) 2.12H 2O and forms a solid solution of C 3A.Ca(OH) 2.12H 2O - C 3A.CaCl 2.10H 2O in CaCl 2 pastes.