Method for eliminating the alkali-aggregate reaction in concretes and cement thereby obtained

Abstract

Method for eliminating the dangerous alkali-aggregate reaction in concretes which contain hydrated cement obtained by the alkaline activation of Portland cement. The formation in this concrete of a compound which can generate a soluble alkali aluminate is prevented by reacting a mineral composition by alkaline activation, the said compound consisting of a hydrated alumino-silicate whose Nuclear Magnetic Resonance .sup.27 Al MAS-NMR spectrum shows a resonance at 66.+-.5 ppm corresponding to a (Q.sub.3)(3Si)-type (AlO.sub.4) tetrahedron. The above-mentioned mineral composition contains: a) 100 parts by weight of the said calcium alumino-silicate; b) 10 to 30 parts by weight of powdered synthetic alumino-silicate belonging to the class of silicates whose mineralogical structure is lamellar and whose MAS-NMR for .sup.27 Al has at least one main resonance at 20.+-.5 ppm and/or 50.+-.5 ppm in relation to AlCl.sub.3. c) 0 to 10 parts by weight of a hydrated disilicate Ca(H.sub.3 SiO.sub.4).sub.2 whose (SiO.sub.4) tetrahedron polymerization degree is (Q.sub.1) as determined by the value of the MAS-NMR spectrum for .sup.29 Si. The mineral composition is a rapid-set geopolymeric cement characterized after alkaline activation by its .sup.27 Al MAS-NMR spectrum which shows a resonance at 55.+-.5 ppm in relation to AlCl.sub.3, corresponding to a (Q.sub.4)(4Si)-type (AlO.sub.4) tetrahedron, and a resonance at 0.+-.5 ppm in relation to AlCl.sub.3, corresponding to Al in VI-fold coordination (AlO.sub.6) in aluminum hydroxide and/or hydrated calcium sulfo-aluminate (ettringite). The ratio (AlO.sub.4)(4Si)/(AlO.sub.6) between the intensity of the (Q.sub.4)(4Si)-type (AlO.sub.4) resonance at 55.+-.5 ppm and the intensity of the (AlO.sub.6) resonance at 0 ppm is equal to or between 0.1 and 1.

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