M. Murat

Hydration reaction and hardening of calcined clays and related minerals V. Extension of the research and general conclusions

Abstract For a comparison between the behaviour of pure metakaolinite and other clays or related minerals thermally activated at 750°C, the research has been extended to different calcined raw-materials, e.g. montmorillonite, illite, muscovite and phlogopite, impure natural clays, laterites and tropical soils, black colliery spoil and slate waste. The more reactive solids obtained by thermal activation are pure kaolinite and kaolinitic minerals such as tropical soils and laterites: the hydration of samples added with calcium hydroxyde and gauged at normal consistency leads to optimal 28 days strength from 15 to 27 MPa. Montmorillonite and illite lead to lower 28-days strength. Pure muscovite and phlogopite, black colliery spoil and slate waste do not present any interest in this field when thermally activated at 750°C. Some recommendations are given for a practical application of the research.

Effect of large additions of Cd, Pb, Cr, Zn, to cement raw meal on the composition and the properties of the clinker and the cement

Abstract The addition of important quantities of Cd, Pb, Cr, Zn to raw meals of Portland and calcium aluminate cement modifies the mineralogical composition and the properties of the final cement. Portland cement can absorb a large amount of Cd, and Zn. This absorption leads to an increase of setting time and a decrease of strengths of the cement. It also can trap chromium with a short setting time and high strengths. Calcium aluminate cements easily trap Cd and Cr with a delayed setting and good strength but also Pb with normal setting time and strengths. Large quantities of zinc oxide have a deleterious effect on calcium aluminate strengths.

Hydration reaction and hardening of calcined clays and related minerals. IV. Experimental conditions for strength improvement on metakaolinite minicylinders

Abstract For metakaolinite cements activated by calcium hydroxide, the more convenient curing process to optimize 28 days compressive strengths on pure paste minicylinders was defined as follows: samples are removed from the molds at 7 days, then cured in liquid water and tested after drying for one day at 50°C. In such conditions, strength values, which are about 10% lower than those measured on 4×4×16cm standardized prisms cured in the same way, become optimal with a metakaolinite/calcium hydroxide ratio of 3. They attain 26–27 MPa and 32–33 MPa when samples are gauged at normal consistency and at the limit of workability, respectively. The strength improvement depends on the nature of hydrates which form during the hardening, then on the curing process. It is essentially correlated to CSHI formation during the hydration reaction, the correlation becoming linear only at ages higher than 28 days. In one other hand, the hydration of metakaolinite with chemical activators other than hydrated lime (calcite, gypsum) has been investigated without any success.

Chemical reactivity of thermally activated clay minerals estimation by dissolution in hydrofluoric acid

The rapid estimation of the chemical reactivity of transitory phases (TACK synthetic pozzolanic binders) obtained by Thermal Activation of Clay Minerals between 500°C and 1000°C, can be obtained in less than one hour, using the σ = f(t) conductimetric curve associated to the congruent dissolution in dilute hydrofluoric acid at 25°C. Investigations on thermally activated kaolinite and montmorillonite has allowed to point out sensitive differences in the dissolution process according to the structure of the raw-material the recorded σ = f(t) curve is a two steps and a continous one for kaolinite and montmorillonite, respectively. Two different specific parameters can be measured either the conductivity variation associated to the first dissolution step, or the slope of the curve at time t=0 (initial dissolution rate). These parameters can be correlated to the short-time strength development of calcium hydroxyde-activated TACK binder, and have their maximal values for the thermal activation temperature which leads to the optimum disorganization state of the solid.

Stabilite thermodynamique des phases dans le systeme CaOAl2O3CO2H2O

Abstract The paper presents a theoretical investigation on the nature of thermodynamical stable precipitating phases in the CaOAl 2 O 3 CO 2 H 2 O system when monocalcium aluminate (CA) with or without an excess of lime or alumina is mixed with water in equilibrium with gaseous carbon dioxide. Basing on the nature of ions in solution (A10 2 − , Ca ++ , CO 3_ −− , OH − and H + ). and supposing that only C C , AH 3 , CH, CAH 10 , C 2 AH 8 and C 4 ACH 11 are the possible stable phases, the system was mathematically described taking into account the values of solubility products, the equilibrium between atmospheric carbon dioxide and the solution, ionic dissociation constant of water, matter balance of calcium and aluminate ions and condition of the solution electroneutrality. For a given system of initial parameters, computer calculation has allowed to determine the only possible solid-liquid system among the 22 theoretically possible cases (zero, one or two solids in equilibrium with the solution). So, varying the initial parameters has led to draw isobaric and isosteric phase diagramms, what shows that, in the conditions of the study, CAH 10 is the only stable phase at 21°C. The result suggests that the precipitation of C 2 AH 8 and C 4 A C H 11 can only be a consequence of saturations of the solution with respect to CAH 10 .

Caractérisation des fibres par amélioration de l'essai sur mèche avec mesure directe de la déformation

The statistical variation in mechanical properties of E-glass fibres has been studied using loose bundles containing N ≥ 1 000 fibres. Particular care has been taken for preparation of these bundle specimens so as to he able to measure the direct sample deformation with a mechanical extensometer. The direct measure of the bundle strain during a tensile test allows us to obtain a reliable determination of the intrinsic ‘load-strain’ behaviour law and of the following characteristics of the bundle: number of initially intact fibres in the bundle; Weibull shape parameter, strength and failure strain of the bundle and mean strength of the fibres.

Kinetics of non-congruent dissolution of E-glass fiber in saturated calcium hydroxide solution

Abstract The kinetics of non-congruent dissolution of long E-glass fiber in saturated calcium hydroxide solution has been investigated at 25°C in a closed reactor adopting the rotating disc method for the sample holder. The fiber dissolution rate (α), measured from the relative loss weight of the fiber after selective dissolution of the attack layer in acetic acid, is a linear function of time, what implies an interfacial dissolution process. However, the kinetics does not stay regular for a long time due to local detachment of the attack layer. The comparison between α = f (t) and α′ = f (t) curves, where α′ is the formation rate of the attack layer, shows that the formation of the layer does not only imply the deposit of a bad-crystalline hydrated calcium silicate but the nucleation and growth of solid calcium hydroxide and calcium carbonate resulting from the transfert, to the interface, of ions coming from the liquid phase. This phenomenon was precedently observed by some other authors in the case of glass-fiber reinforced cement matrix.

Investigation on some factors affecting the reactivity of synthetic orthorhombic anhydrite with water. I. role of foreign cations in solution

Abstract The hydration kinetics of pure synthetic orthorhombic anhydrite, obtained by calcination of synthetic Merck Gypsum, depends on the temperature of preparation, on the mechanical activation by grinding and of the nature of foreign cations in solution, used as chemical activators. Concerning this last factor, it is shown that the higher the “z/r” parameter, characterizing the foreign cation (z the charge and r the ionic radius), the higher the reactivity of the solid. Nucleation is the more concerned step in the dissolution-nucleation-growth process involved in the hydration and hardening of anhydrite. A theoretical model, taking into account the electrical potential created by the cation around the forming dihydrate nucleus is proposed.

The polarizing microscope: A tool of interest for investigation on concrete; application to carbonation

Abstract Polarizing microscope is the technique the more commonly used by geologists whereas it is not so much used in concrete or mortar studies. But nevertheless this technique can be very interesting in petrographic field for the determination of aggregates (mineralogy, state of alteration, regularity of composition, size of grain…) and for cement paste investigation. This paper treats the study of the carbonation of concrete by polarizing microscope.

Strength development and hydrate formation rate. Investigation on anhydrite binders

Abstract It does not seem possible to obtain an accurate correlation between the strength development and the rate of calcium sulfate dihydrate formation in anhydrite binders. Investigations on the hydration and hardening of anhydrite samples from different origins allows us to point out that the representation of strength versus the calcium sulfate dihydrate content of the hardened material leads to a diagramm with very scattered experimental points. That is due to a large variation in both the porosity and the crystal habit of dihydrate crystal which are directly connected to the nucleation rate during the hydration reaction. This observation is certainly not limited to anhydrite binders.