Structure, Mechanisms of Reaction, and Strength of an Alkali-Activated Blast-Furnace Slag

This research examines the chemical activation of blast-furnace slag pastes with alkaline solutions by means of various characterization techniques. Pastes were activated using sodium silicate solutions with modulus (Ms) of 0, 1, 1.5, 2, and Na2O at 5%, 10%, and 15%. Compressive strengths of up to 108MPa were achieved for Ms=1-1.5 after 720d of curing at 20 degrees C. The addition of Na2O>10% resulted in the formation of hydrotalcite and carbonated pastes with low compressive strength. X-ray diffraction, microanalysis of outer products (OP), and nuclear magnetic resonance (NMR) results showed that the main reaction products in the activated cements with Ms=1 and 5%Na2O had an average ratio Ca/Si=0.71-0.9 and consisted of a mixture of two kinds of C-S-H; one similar to a 9 angstrom tobermorite-type calcium silicate hydrate (Ca5Si6O16(OH)(2) and other amorphous related to a cross-linked structure of C-N-(A)-S-H gel. Both were intermixed with hydrotalcite and cross-linked structures of silica gel.