GB2247453A - Spherosilicate cements - Google Patents

Abstract

Method for preparing a powdered cold setting spherosilicate-type cement which develops, after 4 hours at 20 DEG C, a compressive strength of at least 15 MPa with a water/binder ratio of 0.20-0.27, wherein the following three reactive elements are used: a) an alumino-silicate oxide (2SiO2,Al2O3) having the Al cation in (IV-V) co-ordination as determined by the MASS-NMR Nuclear Magnetic Resonance spectrum analysis for <27>Al; b) an alkaline sodium and/or potassium disilicate, (Na2,K2)(H3SiO4); c) calcium silicate characterized in that the mol ratios between the three reactive elements are the same or between (Na2,K2)(H3SiO4)2/(2SiO2,Al2O3) = 0,40 and 0,60, Ca<++>/(2SiO2,Al2O3) = 0.60 and 0.40 so that (Na2,K2)(H3SiO4)2 + Ca <++>/(SiO2,Al2O3) = 1,0 wherein Ca<++> designates the calcium belonging to a slightly basic calcium silicate with an Ca/Si atomic ratio of less than 1.

Description

Preparation method for a spherosilicate1 type cement and the cement thus obtained.

The present invention concerns a method for the preparation of a spherosilicate type cement which hardens rapidly at ambient temperature. The invention also concerns the cement obtained using tis method. Bore specifically, the mineral compositions described in the invention enable a spherosilicate type cement to be obtained with a setting time equal to or greater than 30 minutes at 20C, as well as a hardening rate giving compression resistances (Rc) equal to or greater than 15 MPa after just 4 hours at 20'C, when tested using the standards applied to binder mortar with a binder/sand ratio of 0.38 and a water/binder ratio of between 0.22 and 0.27.

The spherosilicate type mineral compositions subject of this invention allow rapid-hardening, spherosilicate type cement to be obtained, with an Re > 15 MPa after 4 hours at 20"C, and containing essentially three reactants The first reactant is an aluminosilicate oxide (2SiO2 Al203) with the Al cation being in tetrahedral (lav) and irregular (V) coordination2, i.e. AlIV-V, as determined from the analysis [or absorption] spectrum obtained using Nuclear Magnetic Resonance MASS-NE for 27A1.This aluminosilicate oxide (2Si02.A1203) is obtained by heat-treating naturally occurring hydrated aluminosilicates (in which the Al cation is in octahedral coordination as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance MASS-NMR for 27A1) in the presence of an oxidant. In a number of previous articles, the aluminosilicate oxide (2SiO2Al2o3) was only defined by the cation Al in tetrahedral coordination, which was consistent with the extent of previous scientific research. Today, the use of Nuclear Magnetic Resonance, or HSS-MR, has enabled the detection of Ally, or irregular, coordination.In effect, the MASS-NMR spectrum for zrAl shows two peaks, one around SO65 ppm which is characteristic of A1tY, and the second around 25-35 ppm which a number of scientists define as indicating AlV, whereas others prefer to consider it as distorted Allv (MacKenzie et al., Journal of the American Ceramic Society, Volume 68, pp. 293-297, 1985). The theory of AltVv mixed coordination for this oxide (2Si02.A1203) shall be used throughout.

The second reactant is a water-soluble sodium and/or potassium disilicate (Na2, ) (H3sio4)2. Potassium disilicate K2(H3SiO4)2 will be preferred over sodium disilicate Na2(H3SiO4)2 although the latter also enables the formation of spherosilicate type mineral compositions subject of this invention. A mixture of the two alkaline minerals may also be used.

The third reactant is a basic calcium silicate, i.e. one having a Ca/Si atomic ratio equal to or greater than 1. It will in essence be characterised by its ability to form, when attacked using an alkali, weakly basic calcium silicate, i,e.

having a Ca/Si atomic ratio of less than 1 and preferably closer to 0.5. This characterisation will be established using X-ray photoelectron spectromet (Xps) and by analysis of the Ca v Sib ratios (see M. Regourd, Phil. Trans. Royal Society, London, A.310, pp. 85-92, 19S3).

The mineral compositions of the invention are also called spherosilicate type mineral compositions as the spherosilicate type cement obtained results from a mineral polycondensation reaction unlike the standard binders where hardening results from the hydration of calcium aluminates and calcium silicates. Here again the spectra obtained using Nuclear Magnetic Resonance, NASS-NNR, for rA1 are used as investigative tools. The products resulting from the mineral polycondensation reaction, as advocated under this invention, possess a unique peak at 55 ppm which is characteristic of the Al coordination, whereas the compounds obtained from hydration in standard binders have a peak of 0 ppm, characteristic of the MVI coordination , i.e of calcium hydroxyalosminate.

The MASS-NMR spectrum for DSi also allows the spherosilicate type compounds to be very clearly distinguished from binders.

If the degree of polymerisation of the Sio4 tetrahedra is represented by Qn (where n = 0, 1, 2, 3 or 4), one may distinguish between monosilicates (QO), disilicates (Q1), silicate groups (Q2), grafted silicates (Q3) and silicates which are part of a three dimensional lattice (Q4). Using DSi MASS-NER, these degrees of polymerisation are characterised by the following peaks: (QO) from -68 to -76 ppm; (Q1) from -76 to -80 ppm (Q2) from -80 to -85 ppm; (Q3) from -85 to -90 ppm; (Q4) from -91 to -130 ppm. The peaks which characterise the spherosilicate type compounds are found in the -85 to -100 ppm zone and correspond to the (Q4) three dimensional lattice which corresponds to poly(sialates)5 and poly(sialatesiloxo6).On the other hand, the results of hydrating binders to produce hydrated calcium silicate C-S-H (as per the notation used by the cement chemical industry) show peaks within the -68 to -85 region, namely the monosilicate (QO) or the disilicate (Q1)(Q2) (see, for example, J. Hjorth, Cement and Concrete Research, Viol. 18, No. 4, 1988).

Using the current terminology for spherosilicate type compounds, the rapid-hardening mineral binder, with an Rc greater than 15 MPa after 4 hours at 20it, corresponds to a (Ca, K)-poly(sialate-siloxo) type spherosilicate compound with a formula varying between (O.EK + O.2ca) (-Si-O-Al-O-Si-0-) ,o and (0.4R + 0.3Ca) (-Si-O-Al-O-Si-O-),H2O.

In the past, binders and cements exhibiting rapid-hardening and based on mineral polycondensation reactions were proposed which bring into play the three reactants used in this invention. Some spherosilicate type compositions are thus known to give rapid-hardening mortar which develop a compression resistance Rc of 6.89 NPa after I hour at 65C and an Re of 41.34 MPa after 4 hours at 65 C. A spherosilicate type composition is also known which develops a compression resistance Rc of 24 SPa after 4 hours at 23 to 25 C Based on the eXperience acquired by cement experts, a compression resistance Rc of 15 NPa after 4 hours at 20 C is equivalent to an Rc of 22.5 MPa after 4 hours at 25'C.This composition consists of 840 g of what is termed a "standard" type reactant mixture to which has been added inert fillers and 220 g of ground blast furnace slag cement7. The spherosilicate type reactants are characterised by the molar ratios of the oxides: K2O/SiO2 0.32 sio2ttAl2o3) 4.12 FO/tAl203) 17.0 S20/ (A1203) 1.33 K2O/K2O 12.03 which, to enable comparison between the spherosilicate type mineral compositions subject of this invention, correspond to a spherosilicate type composition containing 1 mole of aluminosilicate oxide (2Si02-Al203), and either 222 g, 1.12 moles of potassium disilicate K2(H3SiO)2, or 300 g, 0.21 moles of R;o, corresponding to 28 g of 90% anhydrous KOH, and 290 g of water and 220 g of slag cement.

As can easily be observed, the molar ratio between K2(H3SiO4)2 and (2SiO2.Al2O3) equals 1.12 with respect to the aluminosilicate oxide (2SiO2A12O3). It was therefore very important to be able to reduce significantly the amount of this very costly product. This is the main aim of the present invention.

Within the scope of the invention, the spherosilicate type mineral compositions are characterised by the molar ratio of the three reactants being equal or situated between Na2, K2)(H3SiO4)2 0.40 and 0.60 (2SiO2.Al2Q3) 0.60 and 0.40 (2Si02.AI2O3) such that (Na2, X Bisio4L2 + Ca++ 1.0 (2Si02.AlaOs) with Ca++ being the calcium ion belonging to the weakly basic calcium silicate.

As can be observed, the quantity of alkaline disilicate is reduced by 200 to 300 compared to that obtained from previous research.

For this, it was not sufficient simply to lower the quantity of alkaline disilicate. It was in fact surprising to learn that it was bundamentally important to change the physical state of the constituents.

Thus the previously identified compositions mentioned above are in the liquid phase. The slag cement is added to an aqueous reaction mixture containing aluminosilicate oxide (2SiO2.Al2O3), the alkalis, water, and the potassium polysilicate in solution.

On the contrary, the spherosilicate type mineral compositions subject of this invention are in the solid phase, especially the second reactant; the sodium and/or potassium disilicate (Na2, K2)(H3SiOL)2 is a finely divided powder, with the water not being added until the final phase of mixing the mortar or binder.

In the earlier technique, powdered mineral compositions are also seen to occur, e.g. mineral compositions consisting of: 100 parts of vetakaolin 20 to 70 parts of slag cement 85 to 130 parts of fine filler (flue-ash, dead clay) 70 to 215 parts of amorphous silica 55 to 145 parts of a mixture containing potassium silicate (not less than 55 parts) and potassium hydroxide.

In this last composition the amorphous silica is essentially present to replace a proportion of the potassium silicate required for mineral polycondensation, i.e. the amorphous silica reacts with the potassium hydroxide to produce the desired quantity of potassium silicate within the mortar.

For the expert, the term "potassium silicate" means powdered industrial potassium silicate having the formula R20w3Sio2b3azol which is water soluble and allows binders and adhesives to be formed with the same properties as "water glass" or alkaline silicates in solution.

However, a composition having a formulation of this type does not harden at ambient temperature since, to obtain this rapidhardening, it is absolutely necessary to add Portland cement.

But, even with the addition of Portland cement, these compositions do not give an Roc greater than 15 XPa after 4 hours at 20c Thus, and as an example, the following mixture was recommended: 68 parts of metakaolin 36 parts of slag cement 60 parts of flue-ash 103 parts of microsilica8 44 parts of potassium silicate 22 parts of potassium hydroxide, and 423 parts of Portland cement.

For the mortar obtained, the compression resistance Rc after 4 hours at 23XC is only approximately 6.9 MPa, which is much less than the Rc claimed in this invention, namely greater than 15 NPa after 4 hours at 20 C. In another known example, Rc after 4 hours at 23iC is only equal to approximately 4.6 MPa, whereas in yet other examples only Rc values for approximately 65iC are provided, the Rc values obtained after 4 hours at 23 .C being too weak to be mentioned.

Assuming that the metakaolin corresponds to our aluminosilicate oxide (2Si02.Al2Q) and that the potassium hydroxide has allowed the potassium silicate K2o-3SiO2-3H2O to be transformed into the disilicate K2(H3SiO4)2, we obtain the following compositions expressed in moles: (2SiO2.Al2O3) 0.30 moles K2(H3SiO4)2 0.20 moles which equals a K2 (SiO)2/(2SiO2A12O3) ratio of 0.66. In fact this ratio is higher since, with the potassium hydroxide excess being 0.13 moles of O, this potassium has reacted with the microsilica to produce also 0.13 moles of K2(H3SiO4)2, thus giving a total K2(H3SiO4)2 concentration of 0,33 [moles] resulting in a K2(H3SiO4)2/(2SiO2#Al2O3) ratio of 1.10, i.e.

exactly that of the known compositions mentioned initially.

These examples clearly show that the simple replacement of silicate in solution with powdered silicate causes a very marked decrease in the rate of hardening as these known compositions require heat activation when rapid hardening is to be obtained within a few hours.

Within the scope of this invention and contrary to earlier techniques, the powdered alkaline disilicate allows a spherosilicate type cement to be obtained exhibiting rapid hardening at 20'C within a few hours, i.e. having an Rc greater than 15 MPa after 4 hours at 20 C.

It has also been suggested that all of the potassium silicate in solution be replaced with an amorphous silicate (microsilica) and potassium hydroxide mixture. Sere again, the rapid hardening requires the addition of Portland cement, and in the best cases the compression resistance Rc after 4 hours at 23 C is equal to approximately 7.5 XPa, which is much less than the Rc claimed in this invention, namely an Rc greater than 15 MPa after 4 hours at 20 C. Still with reference to the earlier techniques as illustrated in the above example, the spherosilicate type mineral composition consists of 24 to 28 parts of potassium hydroxide, 73 to 120 parts of silica vapour, and 18 to 29 parts of slag cement for 52 parts of metakaolin. The silica vapours react with the potassium hydroxide to produce, within the mixture, the potassium silicate, which reduces the cost price of this very expensive reactant. One therefore obtains in moles, using the same rationale as above: (2SiO2#Al2O3) 0.23 moles 4(B3sio4)2 from 0.215 to 0.25 moles Which gives a (Sio4)(2Si02Al203) ratio of between 0.93 and 1.08, again practically equalling the ratios mentioned earlier.

These examples of earlier techniques clearly show that by simply replacing silicate in solution with a mixture of microsilica and potassium hydroxide, the rate of hardening is reduced significantly as it requires heat activation to obtain rapid hardening within a few hours.

The known examples described above show that rapid hardening requires a temperature of between 40 and 60C. In other words, the mixtures claimed are endothermic and absorb heat.

The following tests clearly demonstrate that in earlier techniques, the endothermicity of the mixtures was too great to allow rapid hardening to occur at ambient temperature. It.

is known that the mineral polycondensation reaction is exothermic, with this exothermicity being well highlighted when hardening occurs at 40 to 60"C. The exothermicity of the mixtures, with and without amorphous silica such as microsilica, has been measured. The analysis method used was Differential Thermal Analysis.

Two powdered mixtures were prepared: mixture A: (2SiO2.Al3) oxide 400 g Micronized mica 100 g mixture B: (2SiOzA1203) oxide 400 g Nicrosilica 100 g together with two liquid mixtures: liquid 1: 40% potassium silicate solution 520 g 90% KOH 82 g liquid 2: 40% sodium silicate solution 1040 g powdered NaOR 120 g The powder and liquid are mixed in the proportions given in the table, and mineral polycondensation is followed by Differential Thermal Analysis. The values for the ratio J/g are compared, i.e. the quantity of energy measured in joules over the sample weight in grammes. Mineral polycondensation temperature equals 60'C.

Test no. Mixture J/g 1 powder A 55 g liquid 1 100 g 247 2 powder B 55 g liquid 1 100 g 53 3 powder B 55 g liquid 2 100 g 116 It is therefore seen that the addition of microsilica, i.e.

the formation of potassium silicate in the mixture, absorbs heat.

The exothermicity of test No. 2 (with microsilica) is one fifth that of test No. 1 (without microsilica) whilst test No.

3 is half that of test No. 1.

Thus one may explain why the mixtures used in earlier techniques do not show rapid hardening at ambient temperature.

On the contrary, in the case of the invention, amorphous silica such as microsilica or other silicas which transform readily into potassium or sodium silicate, at a moderate or even ambient temperature, will be added in a quantity such that the spherosilicate type mixture's natural exothermicity is not affected. Amorphous silica, such as - for example ticrosilica, rice ash, diatomite, silica smectites and certain pozzuolana with a high silica content (having a high percentage of volcanic allophane and glass) are considered as finely divided and reactive fillers. The reactivity of these fillers make them react on the surface with the spherosilicate type reactional medium, thus increasing the mechanical resistance of the mineral poly(;ialate-siloxo) binder.These silica compounds are not initially dissolved at ambient temperatures, i.e. within the scope of this invention.

However, as in the case of binders which contain them, their breakdown by the spherosilicate type matrix or by basic silicates still present within the matrix may be observed after 28 days or more.

The third of the invention's reactants is the weakly basic calcium silicate with a Ca/Si atomic ratio of less than 1.

This may be, for example, the calcium disilicate Ca(H3SiO4)2 or tobermbrite Ca10(Si12O31)(OH)6,8H2O. This third reactant is linked to the previous ones by the molar ratios between the three reactants being equal or within: (Na2, K2) (H3SiO4)2 0.40 and 0.60 (2SiO2#Al2O3) Ca++ 0.60 and 0.40 (2SiO2#Al2O3) In the case of calcium disilicate Ca(H3SiO4)2 and potassium disilicate K2(H3SiO4)2, the following ratios are obtained: (K2(H3SiO4)2/(2SiO2#Al2O3) of between 0.40 and 0.60 Ca(Sio)2/(2SiO2.M2O3) of between 0.60 and 0.40.

In other words, the sum of the number of moles of calcium disilicate, Ca(E3SiO4)2, and the number of moles of potassium disilicate, K2(H3SiO4)2, is equal to the number of moles of aluminosilicate oxide, (2SiO2'Al2). This aluminosilicate oxide (2SiO2*Al203) determines all the reaction conditions of the spherosilicate type mineral compositions.It will react with either an alkaline or alkaline-earth disilicate to form, after mineral polycondensation, a compound (Si2O5#Al2O2#Si2O5#(K2O#CaO)), i.e (K,Ca)-poly(sialate-siloxo) with a formula varying between (0.6K + 0.2Ca) (-Si-O-Al-O-Si-O-) and (0.4K + O.3Ca)(-Si-O-Al-O-Si-O-) The oxide (2SiO2#Al2O3) reacts firstly with the most soluble disilicate which is always the alkaline disilicate (XN, x 3SiO4)2. The quantity of calcium disilicate acting within the mineral polycondensation reaction is essentially determined by the quantity of alkaline disilicate.If the sum of the moles of these disilicates is greater than 1, the nonreacting proportion will be that which is the least soluble, i.e. the calcium disilicate.

However, it is the calcium ions Ca++ which determine the rate of hardening by mzking the mineral alkaline polycondensation gels less soluble, the optimal rate of hardening being attained when these CaZ ions are integrated within the spherosilicate type structure. If the quantity of alkaline Na+ and/or r is high, a larger amount of CaZ ions is required to result in the same rate of hardening. On the contrary, if the quantity of alkaline disilicate (Na2,Ri Sio4)2 is too weak, dissolution of the calcium disilicate Ca(H3SiO4)2 will be reduced, rapid hardening at 20'C will not occurs and mechanical resistances will be lower.

Thus we explain why for some compositions used in earlier techniques, for which the (Sio)2/(2Sio2,Al2o3) ratio was approximately equal to or greater than 1, the excessive solubility of the reaction medium slowed down the precipitation reaction of the Ca++ ions originating from, for example, the slag cement or the Portland cement.

The calcium disilicate Ca(H3SiO4)2 may be manufactured separately by, for example, hydrothermal metamorphosis/reaction between the limestone and the silica.

Rowever, using a method favoured by the invention, it will be produced, at the nascent state, within the binder after the addition of the necessary amount of water to dissolve the various powdered reactants. The starting material is a basic calcium silicate, i.e. with a Ca/Si atomic ratio greater than or equal to 1.This will be, for example, wollastonite Ca(SiO3), gehlenite (2CaO-z1203 SiO2), bicalcium silicate S (2Ca0.Sio2), tricalcium silicate S t3CaO-SiO2), and akermanite (2CaO2#MgO#2SiO2)9. When granules of these compounds are placed in contact with an alkaline solution (NaOH or KOH), CaO desorption rapidly occurs such that the Ca/Si atomic ratio becomes less than 1 and goes towards 0.5 for basic silicates initially having a Ca/Si ratio equal to or less than 2, such as wollastonite, qS, gehlenite and @kermanite.

The blast furnace slag cement primarily contains the basic silicates gehlenite, @kermanite and wollastonite and is therefore very suitable. In addition, as we are able to follow it using X-ray photoelectron spectrometry (Xps) as mentioned earlier, the alkaline attack on the basic silicate produces a weakly basic silicate with a Ca/Si atomic ratio of 0.5, equalling exactly the calcium disilicate Ca(H3SiO4)2.

This process occurs unifornly and may be completed within 30 minutes at ambient temperature. On the contrary, in the case of C2S, a high concentration of weakly basic silicate, with a Ca/Si ratio of less than 1, is produced in a few seconds, causing the attack to be halted and then to continue more uniformly. This is what is termed nflash-setn whereby the formation of a gel causes a false set. To prevent the sudden formation of calcium disilicate, in the case of C2SI it is necessary to employ setting retarders such as those currently in use in Portland cement mixtures.

The mineral polycondensation reaction used in this invention must not be confused with the simple alkaline activation of binders or with the alkali setting accelerator action on Portland cements and other binders.

In effect, the simple action of the alkalis NaOH and KO on Portland cements and blast furnace slag cement results in the production of hydrated calcium silicates, as mentioned above.

Unlike that which occurs under this invention, these hydrated silicates crystallise to form C-S-H, the main constituent of calcium type binder cements. C-S-E is a monosilicate and/or a disilicate, that is to say that the SiO4 tetrahedras forming it belong to the categories (QO), (Q1) and possibly (Q2). On the other hand, mineral polycondensation causes the formation of (Q4) type SiO, tetrahedras, as determined from the Nuclear Magnetic Resonance MASS-NER analysis spectra for 29Si.

Although the alkalis NaOB and KOH are setting accelerators, they are not hardening accelerators able to meet the aim of the invention, i.e they do not provide an Rc greater than 15 MPa after 4 hours at 20 C.

In the case of blast furnace slag cements, the alkalis are not setting accelerators, but develop the latent hydraulicity of the slag cements: The hardening accelerator is generally either temperature or added Fortland cement. One may, for example, use a slag-based cement, Portland or limestone cement, and an alkaline accelerator such as NaOH and sodium and/or potassium carbonates. All compression resistances are obtained after heating at 50'C or 7OC. Experience gained by experts indicates that these resistances of 30 MPa obtained after 6 hours at 70'C correspond to a maximum Rc of 1 to 3 MPa after 4 hours at 20'C.

Scientific analysis using Nuclear Magnetic Resonance MASS-NMR for 27Al shows that slag type binder cements result from hydration of calcium aluninates, silicates and silicoaluminates, with the formation of either hydrated gehlenite, 2 CaC Al203 S i02 8O, or hydrated calcium aluminate, 4CaOA1203-10E20, in which the Al cation is in octahedral coordination. The MASS-NER spectra for SSi show that most of the sio4 tetrahedras are of type (QO), (Q1) and (Q2) which is characteristic of C-S-H.

Similarly, a mixture comprising aluminosilicate oxide (2Si02.Al2o3), slag cement or cement, and KOR and NaOH alkalis does not constitute a mineral polycondensation mineral binder under this invention. It is known that a mortar made with this mixture and water will not harden at 20'C in less than 24 hours. Thus it is seen that if the oxide (2Si02.Al2O3) is not masked by a polysilicate solution against attack by strongly basic KOH and NaOH, a simple hydroxysodalite-type poly(sialate) is formed which precipitates without contributing any binding effect. It is known that hydroxysodalite can only act as a binder in compounded clay, using very little water and only when the material is compressed.

Within the scope of the invention, the third reactant of the mineral polycondensation composition is calcium silicate.

This may be accompanied with calcium silicate and aluininate complexes.

Thus the blast furnace slag cement is in part formed from a glass consisting of gehlenite 2CaO Al203 SiOz, akermanite 2CaO XgO-2SiO2, and wollastonite, amongst others.

Within the scope of the invention, the proportion of the above silicates not transformed into weakly basic calcium silicate during alkaline attack (or that part which is unable to participate in the mineral polycondensation reaction once R;(EiSiO)2 + Ca (H3SiO4)2 over 2(SiO2#Al2O3) equals 1) together with the silicates and aluminosilicates will all be hydrated as per the mechanism identified for calcium silicates forming binder cements. One then obtains, in addition to the spherosilicate type compound (K, Ca)(-Si-O-Al-Si-O-), the formation of hydrated gehlenite, of C-S-H, of hydrated calcium aluminate and other magnesium silicates.

Analysis using Nuclear Magnetic Resonance spectrometry shows, for 27Al MASS-NMR, the presence of peaks corresponding to both AltV and AlVi. In general, within the scope of this invention, the concentration of AlIV is four to six tines greater than that of AlVI. This could decrease if other silicoaluminous or aluminous fillers are added to the mixture, but even under these circumstances the AlIV/AlVI concentration ratio will be AlIV equal to or greater than 1 AlVI In the MASS-NMR spectrum for 29Si, these same basic calcium silicates will lead to the simultaneous presence of the SiO4 tetrahedras (Q4), (QO), (Q1) and (Q2).In general the concentration of the SiO4 tetrahedra (Q4) is four to six times greater than the sum of the concentrations of SiO4 tetrahedras (Q0) + (Ql) + (Q2), and, depending on the nature of the fillers, one obtains (Q4) equal to or greater than 1 (Q0) + (Q1) + (Q2) Blast furnace slag is an economical source of wollastonite, gehlenite and Akermanite. The mineral polycondensation compositions subject of this invention and containing blast furnace slag cement enable a powdered mineral polycondensation binder to be obtained containing:: a) 100 parts in weight of aluminosilicate oxide (2SiO2*Alz03) having the Al-V cation as determined using the analysis spectrum from Nuclear Magnetic Resonance MASS-NMR for rA1, and b) 48 to 72 parts of potassium disilicate (N3Sio4)2 and c) 50 to 70 parts of blast furnace slag cement with a mean size grading of 10 microns, consisting in part of gehlenite, akermanite and wollastonite.

The mortar obtained by adding an amount of water, such that the water/binder ratio is between 0.20 and 0.27, and an amount of ISO sand giving a binder/sand ratio of 0.38, cold hardens and develops after four hours at 20iC a compression resistance equal to or greater than 15 XPa.

When the manufacturing conditions do not allow the alkaline disilicate K2(H3SiO4)2 to be obtained, the 48 to 72 parts of potassium disilicate Ri SiO4)2 are replaced with a powdered mixture containing 35 to 40 parts of potassium silicate si0 3sio2 3H20 7 to 15 parts of 90% anhydrous potassium hydroxide RoB o to 65 parts of amorphous silica.

The comparison between the slag cement/water ratio (by weight) enables the essential differences between the mineral polycondensation compositions as per this invention and earlier techniques to be highlighted. The limit values of this ratio have been determined, above which it is no longer possible to use binders thus produced as the mixture hardens immediately within the mixer, setting being practically instantaneous. One must also note that a number of earlier formulations which use the maximum amount of slag cement also contain calcium fluoride F2Ca. However, it is known that fluorides have a retarding action on the formation of weakly basic calcium silicate and therefore on the precipitating action of CaZ ions, thus favouring a longer setting time and preventing flash-set.

On the contrary, under the scope of this invention, setting is considered as being slow as it occurs after more than thirty minutes without the addition of a retarder, allowing its utilisation with standard mixers by the industry. Any expert will appreciate the advantage of a setting time greater than 30 minutes at 20*C.

The table summarises the setting times for various slag cement/water ratios (by weight), the compositions of the alkaline silicate solutions and the mineral polycondensation compositions containing powdered alkaline disilicates, as per this invention.

slag cement/water ratio 1.0 0.85 0.70 0.55 0.42 start of set (at approx. 23'C) for an earlier composition 0 0 12 min 30 min 60 min start of set (at 200C) for this invention 30 min 60 min 90 min 3 hrs The expert knows that the lower the quantity of water contained in the basic cement mixture, the higher the mechanical resistance. In earlier techniques, the maximum slag cement/water ratio equalled 0.70. The workability of mortar and concrete generally require setting times of at least 30 minutes, thus forcing (for example) the selection of a slag cement/water ratio of 0.55 in previous compositions.

However, this high amount of water causes the compression resistance Rc to drop by approximately 30%. On the other hand, within this invention, the workability of the mortar is good even with a slag cement/water ratio of 1.0. Bigh mechanical resistance is thus obtained with, in addition, all the other physical characteristics which accompany a low water quantity, such as (for example) high densification and low porosity, whilst still having decreased the amount of disilicate (Naz, 4 SiO4) by more than 200% to 300t, this being the inmost expensive of all of the reactants.

One may also use 42 to 64 parts of sodium disilicate Na2tEiSiO4)2 instead of potassium disilicate (H3SiQ)2 or even a mixture of the two disilicates, This will allow impure alkali sources to be used containing both potassium and sodium. It is often the case for alkali-rich industrial waste such as Portland cement calcination oven filter dust or mineral or chemical industry alkaline washes.

The interest of this invention also lies in the fact that the use of powdered alkaline disilicate (Na2, ) (H3SiO4)2 allows cheap raw materials from industrial waste to be utilised. One interesting source of amorphous silica is microsilica, or more specifically smelting flux, recovered from filters above iron silicide steel smelting furnaces. These microsilicas contain 90 to 95% SiO2, carbon, and 0.5 to 1t of finely dispersed metallic silicon. The microsilicas enable alkaline disilicate to be manufactured at very low temperatures, even ambient temperature. Unlike silica (or glass) sand, it is generally necessary to use an autoclave when reacting with alkaline hydroxides, or a smelting oven when using alkaline carbonates.

One may also use naturally occurring amorphous silica such as diatomite, highly siliceous smectites or gaizes11, volcanic glass and highly siliceous pozzuolana. Silica-rich ash obtained from calcination of plants (e.g. rice) may also be used in this way.

Aluminosilicate oxide (2SiO2tAl203) is manufactured by heating kaolinitic clays to between 650it and 8OO.C. Kaolinitic sands may be used as raw materials as well as some clays containing kaolinite, montmorillionite and illite together. Similarly, lateritic soils and laterites, both containing kaolinite, may also be used. Tests carried out on pyrophillites show that these materials are suitable for mineral polycondensation.

The temperatures for the heat treatment of raw materials must be regulated such that they allow the maximum production of aluminosilicate oxide (2SiO2^Al24) having a higher concentration of AlIv.V as determined using MasS-NMR spectra for 27A1. The siliceous materials which for technical reasons must also be subject to calcination need to be heated to temperatures lower than the amorphous silica's cristobalite transition point when it is required as a raw material for the manufacture of powdered alkaline disilicate (Na2, Ki)(Eis104)2.

In general, this temperature is around 700etc.

The alkalis are generally sodium and/or potassium hydroxides industrially produced using electrolysis. they are also the result of the chemical reaction between an alkaline salt and calcium hydroxide or a compound producing the latter in situ.

The alkali salts are selected from sodium and potassium carbonates, potassium sulphates and potassium sulphites. One may thus use the dust collected from the Portland cement oven filters which is very rich in potassium sulphites and sulphates, transform this into carbonates as per beblanc's method, or react this with clinker to produce potassium hydroxide in situ. Powdered alkali disilicates obtained in this way from the reaction between the amorphous silica and alkalis such as in Example 1 below are more so double potassium and calcium disilicates. They also allow this invention to be implemented.

The following examples illustrate this invention. They do not in any way limit the full scope of the invention as provided in the claims. All parts indicated are by weight.

Example 1 Manufacture of the powdered alkaline disilicate K2(H3SiO4)2.

130 parts by weight of microsilica is mixed with 125 parts of 90% KOH to which is then added 30 parts of water. The mixture is exothermic after a period of time and begins to effervesce due to the action of the KOH on the metallic silicon. The mixture transforms into a paste which cools and hardens into a brittle cellular material. The product obtained is highly water soluble when cold and contains 86% of dry extract and 14% water, corresponding to technical potassium disilicate K2(H3SiO4)2 with 3 to 5% of impurities in the form of insoluble carbon and potassium silicoaluminate.

Example 2 222 g of oxide (2SiO2#Al2O3) and 28 g of 90% KOH are mixed together. A previously prepared liquid mixture of 310 g powdered disilicate from Example 1 and 290 g of water is then added to the mixture, followed by 220 g of blast furnace slag cement.

The binder thus obtained is used to make an ISO mortar with a binder/sand ratio of 0.38 in which the water/binder ratio equals 0.27.

The mortar then sets after 15 minutes and has a compression resistance Rc of 15 MPa after 4 hours at 20-C.

The (1SiO)2/(2Si02.AO3) molar ratio equals 1.12 and the ratio by weight of the slag cement/alkaline disilicate equals 0.73 for a slag cement/water ratio (by weight) of 0.75.

Example 3 22 parts of oxide (2SiO2Al203), 13 parts of slag cement, 18 parts of microsilica and 36 parts of a previously prepared liquid mixture (containing 12 parts of disilicate prepared as per Example 1, 4 parts of KOH and 20 parts of water) are mixed together A mortar is obtained as per Example 2. Setting occurs by the end of 3 hours and the Rc equals 2 MPa after 4 hours at 20'C.

The Xi(E45iO4)2/(2SiO2eAl203) molar ratio equals 0.43, the ratio byweight of the slag cement/alkaline disilicate equals 1.08 and the slag cement/water ratio (by weight) equals 0.65.

Example 4 22 parts of oxide t25iOZÁ1203), 15 parts of slag cement, 18 parts of microsilica and 40 parts of a previously prepared liquid mixture (containing 15 parts of disilicate prepared as per Example 1, 4 parts of KOH and 22 parts of water) are mixed together.

A mortar is obtained as per Example 2. Setting occurs after 150 minutes and the Rc equals 4 MPa after 4 hours at 20'C.

The water/binder ratio is 0.29.

The K2(H3SiO4)2/(2SiO2#Al2O3) molar ratio equals 0.56. The ratio by weight of the slag cement/alkaline disilicate equals 1.0 and the slag cement/water ratio (by weight) equals 0.68.

Example 5 22 parts of (2SiO2Al2O3), 15 parts of slag cement, 20 parts of microsilica and 11 parts of KOH are mixed together without the addition of any liquid. To this mixture is added firstly the sand and then 25 parts of water. A mortar is then obtained as per Example 2. No setting occurs even after 24 hours at 20 C.

Example 6 A dry mixture is prepared containing 27 parts of (2SiO2Al203), 21 parts of slag cement, 15 parts of microsilica and 19 parts of potassium disilicate K2(H3SiO4)2 prepared as per Example 1.

To this is added 215 parts of ISO sand followed by 21.5 parts of water.

[Setting] occurs after 35 minutes13 and the resistance Rc after 4 hours at 20 C equals 16 MPa. The water/binder ratio equals 0.26 and the (SiO4)2(/(2SiO2.Al203) molar ratio equals 0.5814. The ratio by weight of the slag cement/alkaline disilicate equals 1.10 and the slag cement/water ratio by weight equals 1.023 It is obviously understood that various modifications may be applied by an expert to the mineral polycondensation cements as well as to the process, both of which are described above solely as examples, whilst still remaining within the scope of the invention.

Claims (10)

1) A preparation process for a powdered spherosilicate type cement which is cold-hardening, which develops a compression resistance equal to or greater than 15 XPa by the end of 4 hours at 20iC and which has a water/binder ratio of between 0.20 and 0.27, the said cement containing the following three reactants: a) an aluminosilicate oxide (2SiO2eAl203) with the AlIV-V coordinated cation as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance MASS- NMR for 2tA1; b) an alkaline sodium and/or potassium disilicate, (Na2, K2) (H3SiO4)2; c) a calcium silicate characterised in that the molar ratio of the three reactants being either equal or situated between (Na2, K2) (H3SiO4)2 0.40 and 0.60 (2SiO2#Al2O3) Cav 0.60 and 0.40 (2SiO2#Al2O3) such that (Na2, K2) (H3SiO4)2 + Ca++ = 1.0 (2SiO2#Al2O3) with Ca++ being the calcium ion belonging to a weakly basic calcium silicate for.; which the Ca/Si atomic ratio is less than 1.

2) A process as per Claim 1, characterised in that the said weakly basic calcium silicate, with a Ca/Si atomic ratio of less than 1, being obtained at the nascent state by the alkaline attack of a basic, anhydrous calcium silicate having a Ca/Si atomic ratio equal to or greater than 1, and causing the in situ formation of hydrated calcium silicate with a Ca/Si ratio equal to 0.5 in the same way as the disilicate Ca(H3SiO4)2, or otherwise between 0.5 and 1 as in the case of tobermorite Ca10(Si12031) (OH)6SO, as determined by the CWSi ratio using Xps (X-ray photoelectron spectrometry).

3) A spherosilicate type cement prepared in accordance with the process in either Claim 1 or 2, characterised in that the said alkaline disilicate being potassium disilicate K2(SiO)2.

The spherosilicate type cement corresponds to the formation of a (Ca, K) -poly (sialate-siloxo) type mineral polycondensation compound having a formula varying between (0.6K + O.2Ca) (-Si-O-Al-O-Si-O-), H2O and (0.4K + O.3Ca) (-Si-O-Al-O-Si-O-), H2O.

4) A spherosilicate type cement prepared in accordance with the process in either Claim 1 or 2, characterised in that the Al cation being, after hardening, fully tetrahedrally coordinated as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance MASS-NMR for 27Al, and by the degree of polymerisation of the SiO4 tetrahedra being (Q4) as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance NASS-NMR for 29Si.

5) A spherosilicate type cement'prepared in accordance with the process in either Claim 1 or 2, in which the said basic, anhydrous calcium silicate is in solid solution with calcium aluminate or calcium aluminosilicate whereby the Al cation is tetrahedrally coordinated, and the said aluminosilicate oxide (2SiO2#Al2O3), in".which Al is irregularly coordinated (AlIV-V), is mixed with, natural or synthetic aluminous (Al2O3) or silicoaluminous (nSiO2A103) powders in which the Al cation is octahedrally coordinated, characterised in that the ratio between the tetrahedrally coordinated Al cation concentration and the octahedrally coordinated Al cation concentration being, after hardening:: AlIV equal to or greater than 1 AlVI as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance M2SS-NMR for 27Al, and the ratio between the concentration of the Sia4 tetrahedra (Q4) and the concentration of the Si04 tetrahedras (QO) + (Q1) + (Q2) is: (04) equal to or greater than 1: (QO) + (Q1) + (Q2) as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance MASS-NMR for 29Si.

6) A process as per Claim 2, characterised in that the said basic calcium silicate, with a Ca/Si atomic ratio equal to or greater than 1, and selected from amongst wollastonite Ca(SiO3), gehlenite (2CaO#Al2O3#SiO2)15, bicalcium silicate S (2CaO#SiO2)16, tricalcium silicate S (3CaO.SiO2), and ikermanite (2CaO2#MgO#2SiO2).

7) A powdered spherosilicate type cement containing: a) 100 parts by weight of aluminosilicate oxide (2SIO2#Al2O3) having the Al cation irregularly coordinated (AlIV'V), as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance MASS- NMR for 27M, b) 48 to 72 parts of potassium disilicate K2(H3SiO4)2, and c) 50 to 70 parts of blast furnace slag cement with a mean size grading of 10 microns, partly consisting of gehlenite, åkermanite and wollastonite, the mortar obtained on the addition of an amount of water such that the water/binder ratio is between 0.20 and 0.27, and the addition of a quantity of ISO sand such that the binder/sand ratio equals 0.38, cold hardens and develops a compression resistance equal to or greater than 15 MPa after 4 hours at 20 C.

8) A spherosilicate type cement as per Claim 7, characterised in that the 48 to 72 parts of potassium disilicate K2(H3SiO4)217 being replaced by a mixture containing 35 to 40 parts of potassium silicate K2O#3SiOH2#3H2O 7 to 15 parts of 90t anhydrous potassium hydroxide KOH and o to 65 parts of amorphous silica.

9) A powdered spherosilicate type cement containing: a) 100 parts by weight of aluminosilicate oxide (2Sio2Al203), having the Al cation irregularly coordinated (Al tv-v) , as determined from the analysis spectrum obtained using Nuclear Magnetic Resonance MASS-NMR for nAl, b) 42 to 64 parts of sodium disilicate Na2(S;;SiO4)z, and c) 50 to 70 parts of blast furnace slag cement with a mean size grading of 10 microns, consisting in part of gehlenite and akermanite, the mortar obtained on the addition of an amount of water such that the water/binder ratio is between 0.20 and 0.27, and the addition of a quantity of ISO sand such that the binder/sand ratio equals 0.3$, cold hardens and develops a compression resistance equal to or greater than 15 MPa after 4 hours at 20'C.

10) A spherosilicate type cement, which cold hardens and develops a compression resistance equal to or greater than 15 MPa after 4 hours at 20 C, obtained by adding 10 to 30 parts by weight of filler or fine filler selected from calcium carbonate, flue ash, calcinated clays, calcinated schists or calcinated smectites to 100 parts by weight of the spherosilicate type mineral binder, as per any one of the claims 7 to 9.