AMORPHOUS LOW-CALCIUM CONTENT SILICATE HYDRAULIC BINDERS AND METHODS FOR THEIR MANUFACTURING

Abstract

The invention relates to a hydraulic binder consisting essentially in a hydraulically active amorphous calcium silicate phase, having in its constitution less than 20% in weight of a crystalline material. The said hydraulically active amorphous calcium silicate phase is a continuous matrix that may contain embedded fractions of crystalline material, being the overall C/S molar ratio of this hydraulic binder comprised between 0.8 and 1.25. The crystalline fraction of this material is essentially composed by wollastonite in both of its polymorphic structures, α and β. Furthermore, the invention relates to methods of producing the hydraulic binder by liquefying the raw materials, in a specified C/S molar ratio, followed by fast cooling to room temperature. Finally, the invention relates to a building material made by setting the binder or a mixture containing this binder with water and subsequent hardening. The invention enables the production of a hydraulic binder with a significant reduction of CO2 emissions, when compared to OPC clinker, by reducing the amount of limestone in the raw materials while obtaining competitive overall values of compressive strength of the hardened material.

Claims

1. A hydraulic binder comprising in a continuous amorphous calcium silicate matrix containing less than 20% in weight of a wollastonite crystalline phase in any of its a or 3 polymorphs, with an overall C/S molar ratio in the range from 0.8 to 1.25.

2. The hydraulic binder of any of claim 1, wherein a part of the calcium or silicon of the hydraulically active amorphous silicate phase is substituted by a metal selected from Al, Fe, Mgr B, S, P, K, Na, or any combination thereof, in particular from 1% to 20%.

3. A mixture containing at least 10% in weight of the hydraulic binder of claim 1 and wherein a part of the calcium or silicon of the hydraulically active amorphous silicate phase is substituted by a metal selected from Al, Fe, Mgr B, S, P, K, Na, or any combination thereof, in particular from 1% to 20%.

4. A method for the production of the hydraulic binder of claim 1 comprising the steps of: A. Heating raw material, containing at least calcium and silicon in an overall C/S molar ratio in the range from 0.8 to 1.25, to a temperature Ti wherein Ti is within the liquid (L) region in the CaO-SiOj phase diagram for the specific chemical composition; and B. Optionally maintaining at that temperature Ti until homogenization of the heated material; and C. Fast cooling to room temperature.

5. The method of claim 4 further comprising a grinding stage after cooling to a Blaine specific surface above 3000 cm2/g, in particular above 3500 cm2/g.

6. A building material obtainable by setting the hydraulic binder of claim 1 with water and subsequent hardening.

7. The hydraulic binder of claim 1 which upon hydration do not produce any portlandite.

8. The building material of claim 6 wherein a part of the calcium or silicon of the hydraulically active amorphous silicate phase is substituted by a metal selected from Al, Fe, Mgr B, S, P, K, Na, or any combination thereof, in particular from 1% to 20%.

9. The building material of claim 6 comprising a mixture containing at least 10% in weight of the hydraulic binder and wherein a part of the calcium or silicon of the hydraulically active amorphous silicate phase is substituted by a metal selected from Al, Fe, Mgr B, S, P, K, Na, or any combination thereof, in particular from 1% to 20%.

10. The hydraulic binder of claim 2 which upon hydration do not produce any portlandite.

Description

[0035] Preferred embodiments of the invention are described in the description hereinafter (including examples), the claims and the figures.

[0036] FIG. 1a) shows a temperature versus time diagram indicating the temperature course for the process according to the invention.

[0037] FIG. 1b) shows the CaO—SiO.sub.2 phase diagram indicating the amount of silica with the balance being calcium oxide and the range of the C/S molar ratio in the silicate relevant to the invention.

[0038] FIG. 1c) shows a XRD diffractogram and corresponding Rietveld refinement of an anhydrous hydraulic binder, with an overall C/S molar ratio of 1.1, obtained by the process described in FIG. 1a). The blue diamonds indicate the presence of pseudowollastonite while the black circles are referred to corundum phase used as internal standard for the determination of the weight percentage of amorphous phase.

[0039] FIG. 1d) shows a XRD diffractogram and corresponding Rietveld refinement of an anhydrous hydraulic binder, with an overall C/S molar ratio of 1.25, obtained by the process described in FIG. 1a). The black circles are referred to corundum phase used as internal standard for the determination of the weight percentage of amorphous phase. In this, case a fully amorphous hydraulic binder was produced.

[0040] FIG. 2) shows a SEM image of a paste produced by mixing the described amorphous calcium silicate phase, with a C/S molar ratio of 1.1, with water after 28 days. It is also shown the distribution of Ca and Si atoms, as determined by EDS, along the yellow line represented in the figure.

[0041] FIG. 3) shows the XRD diffractogram of a paste produced by mixing the described amorphous calcium silicate phase, with a C/S molar ratio of 1.25, with water after 28 days. Green triangles indicate the corresponding peaks of tobermorite-like structures in the C—S—H formed. It is also possible to conclude that no formation of portlandite has occurred, since its main peak at around 18° (28) is not present.

[0042] FIG. 4) is a .sup.29Si MAS-NMR spectra showing the structural evolution with respect to the silicon coordination as the hydration develops for 28 days in a paste produced by mixing the described amorphous calcium silicate phase, with a C/S molar ratio of 1.25, with water. It is possible to observe polymerization of lower Q.sup.n coordinated units as the spectra dislocates to higher chemical shifts with hydration time, as well as it can be easily identified the development of tobermorite-like C—S—H structures by the presence of its typical peaks at chemical shifts around −80 and −85 ppm.

[0043] In the CaO—SiO.sub.2 phase diagram, as to be seen from FIG. 1b), when starting from alite (C.sub.3S), a decrease in calcium leads first to the formation of belite (C.sub.2S), in one of its five allotropic forms α,α′.sub.H, α′.sub.L, β and γ, then to rankinite (C.sub.3S.sub.2) and finally to wollastonite (CS), the latter with two allotropic forms α and β.

[0044] Considering the previous path of analysis in the CaO—SiO.sub.2 phase diagram, from the point of view of the Q.sup.n structural units, the connectivity increases as the amount of calcium decreases leading to a structural evolution from Q.sup.0 units with some free oxygen, in the case of alite, to belite with only Q.sup.0 units, then to rankinite constituted by dimers (Q.sup.1 structural units) and finally to wollastonite whose crystalline structure consists of infinite linear silicate chains or Q.sup.2 units.

[0045] It is well established in the art that belite shows a weak and slow hydraulic activity and both rankinite and wollastonite show no hydraulic activity at all, however the present invention provides amorphous silicates around the wollastonite chemical composition that are hydraulically active.

[0046] The process of the invention utilizes a selected region of the CaO—SiO.sub.2 phase diagram, combined with specific heating and cooling operations, to produce amorphous “low calcium” silicates.

[0047] The hydraulic binders comprise one amorphous hydraulic active silicate phase or combinations with other external hydraulic active or latent hydraulic crystalline and/or amorphous silicate phases.

[0048] In preferred embodiments of the hydraulic binder of the invention, a part of the calcium or silicon of the hydraulic active amorphous phase is substituted by a metal selected from Al, Fe, Mg, B, S, P, K, Na, or any combination thereof. The percentage of substitution is preferably from 1% to 20%, in particular from 5% to 15%.

[0049] The hydraulic binder of the invention can be produced by processes using the common clinkerization process but necessarily obtaining full liquefaction of the materials. The process comprises one heating step and one single cooling step. First, the raw materials are heated to a temperature T.sub.1 which is within the temperature range of the liquid (L) silicate phase. From the phase diagram, e.g. FIG. 1b), the skilled person can determine suitable values for T.sub.1. In FIG. 1b) the rectangle indicates the range of process temperatures (T.sub.1) being suitable for the production of the preferred fully amorphous calcium silicates.

[0050] Suitable values for T.sub.1 can be taken from e.g. FIG. 1b). Depending on the composition used, preferably, the temperature T.sub.1 is within the range of from 1300° C. to 1600° C., more preferably from 1450° C. to 1550° C., most preferably from 1500° C. to 1550° C. The heating is carried out at a suitable rate R.sub.1, which is similar to, or the same, as the heating rate used in the BAT. The rate R.sub.1 depends on the quantity of material used and the heat source. A suitable and preferred value for R.sub.1 is 25° C./min.

[0051] The raw materials used are raw materials common in the art, e.g. limestone, clays and other argillaceous materials, marls, sandstone, fly ash, natural and artificial pozzolanic materials, mineral industrial residues, slags or diatomites. The raw materials contain at least limestone and silica (amorphous or in quartz form).

[0052] In the production of the hydraulically active amorphous silicate object of the invention, the overall C/S molar ratio is in the range of 0.8 to 1.25, preferably from 1.0 to 1.25 and the cooling from T.sub.1 is carried out in one single step.

[0053] Depending on the amount of material used and the heating conditions, optionally the heated materials are maintained at the temperature T.sub.1±ΔT for a time t.sub.1 until homogenization of the heated material is obtained. Preferably, ΔT=50° C., and the time t.sub.1 is in the range of from 5 min to 100 min, in particular of from 10 min to 60 min.

[0054] A most preferred process is described in FIG. 1a).

[0055] FIG. 1.a) shows a production cycle which comprises the following steps: [0056] A. Heating raw material containing at least calcium oxide and silica in an overall C/S molar ratio in the range of from 0.8 to 1.25, preferably from 1.0 to 1.25, to a temperature T.sub.1, wherein T.sub.1 is within the liquid (L) range in the CaO—SiO.sub.2 phase diagram; and [0057] B. Optionally maintaining at that temperature T.sub.1 until homogenization of the heated material; and [0058] C. Cooling rapidly, in a single step, to ambient temperature.

[0059] Suitable values for the temperature T.sub.1 can be determined by the skilled person from the phase diagram, e.g. from FIG. 1b). Also, suitable times for maintaining the material at T.sub.1 and suitable cooling conditions can be determined by the skilled person aiming at the achievement of a fully amorphous silicate.

[0060] Preferably, the processes of the invention further comprise grinding the material obtained after cooling to a Blaine specific surface above 3000 cm.sup.2/g, in particular above 3500 cm.sup.2/g. Such a grinding step is known in the art and can be carried out by conventional procedures.

[0061] The invention further comprises a hydraulic binder prepared, obtained or obtainable by a process as described herein.

[0062] For preparing a building material, the hydraulic binder is mixed with water. Preferably, the amount of water added does not exceed 50% of weight based on 100% of weight of hydraulic binder, preferably, of from 10% to 40% by weight. Upon water addition, the hydraulic binder hydrates and hardens. In a preferred embodiment, the hydrated material comprises substantially no portlandite (calcium hydroxide), in particular less than 1% by weight.

[0063] The following examples illustrate the invention without restricting the scope of protection.

EXAMPLE 1

Production of a Hydraulic Binder Consisting Essentially of an Amorphous Calcium Silicate with an Overall C/S Molar Ratio Equal to 1.1

[0064] A hydraulic binder with C/S molar ratio of 1.1 was obtained in a three-steps procedure comprising: [0065] A. Heating the raw mixture described in table 1 to a temperature T.sub.1 of 1500° C., at a heating rate of 25° C./min, in the liquid region of CaO—SiO.sub.2 diagram for this composition; [0066] B. Maintaining T.sub.1 for a t.sub.1 of 60 minutes; [0067] C. Cooling to room temperature in air, at a cooling rate around 300° C./min.

[0068] The obtained hydraulic binder, consisting in over 95% of an amorphous calcium silicate and some residual pseudowollastonite (as determined by Rietveld analysis and shown in FIG. 1c), was then ground to fineness below 30 μm and mixed with water to a water/binder ratio of 0.375 in weight.

[0069] The paste was poured in into proper molds to produce test pieces of dimensions 20×20×40 mm.

[0070] The compressive strength of this hydraulic binder after 28 days is more than 30 MPa and after 90 days goes over 45 MPa. FIG. 2 shows a SEM image of a 28 days hydrated paste with a linear EDS mapping of Ca and Si elements.

TABLE-US-00001 TABLE 1 Raw material composition and mixture proportions for the production of said hydraulic binder, with an overall C/S molar ratio of 1.1. The theoretical composition of the final product is shown in the last column. Weight % 2.28% 32.93% 2.12% 62.67% Raw-Mat. Theoretical Fly-ash Sand Slag Limestone Clinker L.O.I. 4.54 0.37 −3.00 43.34 0.00 SiO.sub.2 57.07 97.30 13.90 1.62 46.85 Al.sub.2O.sub.3 23.91 1.29 8.26 0.30 1.70 Fe.sub.2O.sub.3 8.68 0.16 43.54 0.23 1.75 CaO 3.96 0.00 21.18 96.77 48.03 MgO 1.56 0.02 6.06 0.39 0.43 SO.sub.3 0.12 0.00 0.40 0.02 0.02 K.sub.2O 1.84 0.52 0.00 0.02 0.30 Na.sub.2O 0.62 0.11 0.00 0.12 0.13 TiO.sub.2 0.00 0.00 0.46 0.00 0.01 Cr.sub.2O.sub.3 0.00 0.00 1.98 0.00 0.06 P.sub.2O.sub.5 0.00 0.00 0.46 0.00 0.01 MnO 0.00 0.00 3.76 0.00 0.11

EXAMPLE 2

Production of a Hydraulic Binder Consisting of a Fully Amorphous Calcium Silicate with an Overall C/S Molar Ratio Equal to 1.25

[0071] The hydraulic binder with an overall C/S molar ratio of 1.25 was obtained in a three-step procedure comprising: [0072] A. Heating the raw mixture described in table 2 to a temperature T.sub.1 of 1500° C., at a heating rate of 25° C./min, in the liquid region of CaO—SiO.sub.2 diagram for this composition; [0073] B. Maintaining T.sub.1 for a t.sub.1 of approximately 60 minutes; [0074] C. Cooling to room temperature in air, at a cooling rate of about 300° C./min.

[0075] The obtained hydraulic binder, consisting in a fully amorphous calcium silicate (as determined by Rietveld analysis and shown in FIG. 1d) was then ground to fineness below 30 μm and mixed with water to a water/binder ratio of 0.375 in weight.

[0076] The paste was poured in into proper molds to produce test pieces of dimensions 20×20×40 mm.

[0077] The compressive strength of this hydraulic binder after 28 days is higher than 25 MPa and after 90 days goes over 35 MPa.

[0078] FIG. 3 shows a diffractogram of a 28 days paste produced with this fully amorphous hydraulic binder, where it is possible to observe the development of peaks related to the presence of tobermorite-like structures (identified by the green triangles). The presence of these structures was also confirmed by .sup.29Si MAS NMR, as it is shown in FIG. 4 by the spectra obtained for an anhydrous and a 28 days hydrated sample. The chemical shifts of the Tobermorite-like structures are identified by the green triangles in the spectra of FIG. 4.

TABLE-US-00002 TABLE 2 Raw material composition and mixture proportions for the production of a fully amorphous calcium silicate, with a C/S molar ratio of 1.25. The theoretical composition of the final product is shown in the last column. Weight % 2.24% 30.11% 2.08% 65.56% Raw-Mat. Theoretical Fly-ash Sand Slag Limestone Clinker L.O.I. 4.54 0.37 −3.00 43.34 0.00 SiO.sub.2 57.07 97.30 13.90 1.62 43.84 Al.sub.2O.sub.3 23.91 1.29 8.26 0.30 1.66 Fe.sub.2O.sub.3 8.68 0.16 43.54 0.23 1.75 CaO 3.96 0.00 21.18 96.77 51.07 MgO 1.56 0.02 6.06 0.39 0.44 SO.sub.3 0.12 0.00 0.40 0.02 0.02 K.sub.2O 1.84 0.52 0.00 0.02 0.28 Na.sub.2O 0.62 0.11 0.00 0.12 0.13 TiO.sub.2 0.00 0.00 0.46 0.00 0.01 Cr.sub.2O.sub.3 0.00 0.00 1.98 0.00 0.06 P.sub.2O.sub.5 0.00 0.00 0.46 0.00 0.01 MnO 0.00 0.00 3.76 0.00 0.11

EXAMPLE 3

Production of a Hydraulic Binder by Mixing Alite Rich Clinker with an Amorphous Calcium Silicate, with an Overall C/S Molar Ratio Equal to 1.1, as Described in Example 1

[0079] A highly amorphous calcium silicate with an overall C/S molar ratio of 1.1 was obtained in a three-step procedure, as described in Example 1.

[0080] The obtained hydraulic binder with an overall C/S molar ratio of 1.1 was then ground to fineness below 30 μm and mixed with 10% in weight of alitic clinker.

[0081] This mixture was used to produce a paste with a water/binder ratio of 0.375 in weight.

[0082] The paste was poured in into proper molds to produce test pieces of dimensions 20×20×40 mm.

[0083] After 28 days, the compressive strength of the described blend was higher than 35 MPa due to the addition of 10% of alitic clinker.

EXAMPLE 4

Production of a Hydraulic Binder by Mixing an Amorphous Calcium Silicate, with an Overall C/S Molar Ratio Equal to 1.1, as Described in Example 1, with a Sulphated Activator

[0084] A highly amorphous calcium silicate with a C/S molar ratio of 1.1 was obtained in a three-step procedure, as described in Example 1.

[0085] The obtained amorphous calcium silicate with a C/S molar ratio of 1.1 was then ground to fineness below 30 μm and mixed with 2% in weight of SO.sub.3 in the forms of Na.sub.2SO.sub.4 or CaSO.sub.4.

[0086] These mixtures were used to produce pastes with a water/binder ratio of 0.375 in weight.

[0087] The pastes were poured in into proper moulds to produce test pieces of dimensions 20×20×40 mm.

[0088] After 28 days, the compressive strength of the described blends was higher than 35 MPa for the addition of CaSO.sub.4 and higher than 40 MPa for the addition of Na.sub.2SO.sub.4, while after 90 days the compressive strengths were about 65 MPa for the mixture with CaSO.sub.4 and higher than 68 MPa for the mixture with Na.sub.2SO.sub.4.

[0089] The Examples illustrate the production of a low-calcium silicate hydraulic binder comprising the presence of a new hydraulically active amorphous calcium silicate and a full range of possible combinations with other hydraulically active phases and/or latent hydraulic phases and/or other activators such as alkaline silicates, sulphates, carbonates, phosphates, nitrates, hydroxides, fluorides or chlorides, in the anhydrous or in the hydrated form.

[0090] The concept of obtaining a highly amorphous hydraulic binder with C/S molar ratio below 1.25, preferably between 1.25 and 1.0 object of this invention contributes positively for a further significant reduction of CO.sub.2 emissions while obtaining competitive overall values of compressive strength of the hardened material.