Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1992-07-29
1994-02-22
Group, Karl
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106739, 106746, C04B 736
Patent
active
052883213
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for eliminating the dangerous alkali-aggregate reaction in concretes. More specifically the mineral compounds described in this invention enable the production of a rapid-set geopolymeric cement comprising portland cement and alkali activation, the said geopolymeric cement preventing the formation in these concretes of a compound which can generate a soluble alkali aluminate, responsible for the deleterious alkali-aggregate reaction.
The accelerating properties of small quantities of alkali salts or of alkali hydroxides on the setting of ordinary hydraulic binders are well known. This particular setting or hardening acceleration of cement, is often called alkali activation. However, several drawbacks have limited its applications, for example the attack and destruction of concrete due to alkali-aggregate reaction. The present invention provides a remedy to these failures and enables advantage to be taken of the alkali activation properties without the said drawbacks.
In the present invention, alkali activation is performed with alkali salts, sodium and/or potassium carbonates, soluble alkali silicates or sodium and/or potassium hydroxides; in the resulting mineral composition, the amount of the said alkali ingredients involves an oxide molar ratio [M.sub.2 O]/[SiO.sub.2 ]<0,1, equivalent to the oxide weight ratio M2O/SiO2<0,15; in a preferred description of the invention, M is potassium and alkali activation is carried out with potassium carbonate. Any worker in the field knows about the rapid-set accelerating properties of potassium carbonate and the necessity of adding citric acid or potassium citrate in order to prevent any flash-set of cement.
To differentiate the cements described in the present invention from traditional alkali activated cements, the investigation tool used is Nuclear Magnetic Resonance spectroscopy (MAS-NMR). MAS-NMR spectra for geopolymers and hydraulic binders are disclosed in the publication Geopolymer '88, Volume 2, pages 149-197, published by the Geopolymer Institute, Universite de Technologie, Compiegne, France. MAS-NMR spectrography for .sup.27 Al for products yielded by a geopolymeric reaction show a single peak at 55.+-.5 ppm, characteristic of Al(IV) coordination and a tetrahedron (AlO.sub.4) of the Q.sub.4 (4Si) type, whereas the hydration products obtained with traditional hydraulic binders show a peak at 0 ppm, characteristic of Al(VI) coordination, i.e. of the hydroxy-aluminate of calcium.
In this invention, the portland cement based geopolymeric mineral compositions yielding a rapid-set geopolymeric cement after alkali activation [M.sub.2 O]/[SiO.sub.2 ]<0,1, comprise essentially three reactive constituents: x(CaO).y(Al.sub.2 O.sub.3).(SiO.sub.2), where "x" has a value between 2 and 3.5 and "y" has a value between 0 and 0.2, whose (SiO.sub.4) tetrahedron polymerization degree is (Q.sub.1) as determined by the MAS-NMR spectrum for .sup.29 Si, and whose MAS-NMR spectrum for .sup.27 Al has a main resonance equal to 75.+-.5 ppm in relation to AlCl.sub.3 corresponding to a Q.sub.0 (0Si)-type (AlO.sub.4) tetrahedron. 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. SiO.sub.4).sub.2 whose (SiO.sub.4) tetrahedron polymerization degree is (Q1) as determined by the value of the MAS-NMR spectrum for .sup.29 Si.
The inorganic compositions of the invention are also called inorganic geopolymeric compositions, since the geopolymeric cement obtained has resulted from an inorganic polycondensation reaction, a so-called geopolymerisation, unlike traditional hydraulic binders in which hardening is the result of the hydration of aluminates of calcium and silicates of calcium.
MAS-NMR spectrography of .sup.29 Si also shows a very clear difference between geopolymers and hydraulic binders. If the degree of polymerisation of SiO.sub.4 tetrahedron is represented by Q.sub.n (n=0,1,2,3,4), distinction can be m
REFERENCES:
S. Komarneni et al, "Selective Cation Exchange . . . Tobermorites", J. Am. Ceram. Soc. 72, 1668-74 (1989).
J. Davidovits, "Structural Characterization of Geopolymeric . . . Spectroscopy", Geopolymer '88, vo. 2, pp. 149-166, Universite de Technologie, Compiegne, France. (1988).
J. Skibsted, "High-Speed 29SiAND 27Al MAS NMR . . . Cements", Geopolymer '88, vol. 2, pp. 179-196, Universite de Technologie, Compiegne France (1988).
M. Regourd, "Microanalytical Studies (X-Ray Photoelectron Spectrometry) . . . Compounds", Phil. Trans. R. Soc. Lond. A 310, 85-92 (1983).
J. F. Young, "Investigations of Calcium Silicate Hydrate Structure . . . Resonance Spectroscopy", J. Am. Ceram. Soc., 71, C-118-120 (1988).
J. Sang et al, "Aluminum-27 abd Silico-29 Magic-Angle . . . Transformation", J. Am. Ceram. Soc., 71[10], C418-C421 (1988).
Proceedings of the 3rd International Conference, Table of Contents (1989).
Group Karl
Marcantoni Paul
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