Alkaline activated slag cements. Determination of reaction degree

Abstract

The aim of the present work was to evaluate the validity of non-calorimetric different methods, used in the determination of reaction degree of alkaline activated slag pastes. The methods used were: (a) chemical separation by methanol-salicylic acid; (b) determination of the weight loss mass between 100-600°C in TG curves, associated to chemically combined water; (c) quantification of the -74 ppm signal in ²⁹Si MAS-NMR spectra. The parameters considered in the process were: nature of the alkaline activator (Waterglass, Na₂CO₃ and NaOH), activator concentration (4% and 3% Na₂O in mass with respect to the slag), curing temperature (25 and 45°C), slag specific surface (460 and 900 m²/kg) and time of reaction (from 7 days to 18 months). The results obtained indicate that none of the three methods is definitive but complementary and they provide to follow the reactive evolution of the alkaline activated slag cements. The method based on the quantification of the -74 ppm signal in the ²⁹Si MAS NMR is the most suitable method.