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 108 MPa were achieved for Ms = 1–1.5 after 720 d of curing at 20°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 Å 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.

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The Mechanical and chemical properties of inorganic polymers based on metakaolin activated by alkaline blends of sodium silicate and sodium hydroxide were characterized. Twenty-four formulations were elaborated with variable molar composition SiO 2 /Al 2 O 3 (2.6-3.0), Na 2 O/Al 2 O 3 (0.55-0.7), and H 2 O/Solids (0.53-0.57). The effect of the chemical composition on the compressive strength development was first investigated. Infrared spectroscopy showed that the condensed reaction products were formed by bonds of T-O-T (T = Si and/or Al) and water retained.Two formulations of highest strength were chosen to evaluate their chemical resistance after immersion for 10 days in 0.5 N HCl solutions at 60°C; the compressive strength and microstructural changes were characterized. Before the acid exposure the strengths reached up tõ 80 MPa, and after acid attack, the loss of strength was a function of the SiO 2 /Al 2 O 3 ratio. Infrared spectroscopy and electron microscopy suggested that the deterioration was due to the destruction of the polymeric network with migration of Na and Al toward the solution and the incorporation of H 3 O + and ingress of Cl À ions in the corroded structure; however, the chemical resistance was good considering the aggressiveness of the acid solutions.G. Scherer-contributing editor Manuscript No. 30685. J ournal 0.5 N HCl, in deionized water, were used for tests of chemical durability for selected geopolymeric formulations.

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