Parameters affecting the properties and microstructure of quicklime (CaO) - Activated slag cement pastes

This research presents results of compressive strength and microstructural characterization of granulated blast furnace slag (BFS) cement pastes activated with quicklime (CaO) at concentrations of 6, 8 and 10 %wt. relative to the slag mass. The investigated variables that influenced the compressive strength were the % CaO, curing temperature, water/binder ratio and Blaine fineness; their effect was analyzed by the signal to noise ratio by a Taguchi experimental design. The statistically defined optimal activation conditions were: 10%CaO; temperature of 20 degrees C; water to binder ratio of 0.3; and surface area of the BFS of 450 m(2)/kg. Pastes cured at 20 degrees C, reached 28 MPa at 90 days, while samples at 40 degrees C and 60 degrees C 24 h showed strengths of 11-20 MPa at similar age of curing. The characterization by DRX, FTIR, SEM and NMR showed the formation of C-(A)-S-H, hydrotalcite and monocarboaluminate phases, but increased curing temperatures, lead to higher formation of Ca(OH)(2) and CaCO3 reducing considerably the strength of the pastes by a lower condensation of C-(A)-S-H gel.