USE OF A CLAY FOR PRODUCING A POZZOLANIC MATERIAL

Abstract

The use of a clay including: less than 25% of kaolinite; and at least 20% of muscovite and/or illite; the muscovite and/or illite/kaolinite weight ratio being greater than 1, for the preparation of a pozzolanic material.

Claims

1.-11. (canceled)

12. A method for preparing a pozzolanic material, comprising calcination of a clay, wherein the clay comprises: less than 25% by weight of kaolinite; and at least 20% by weight of at least one of muscovite and illite, wherein a weight ratio of the at least one of muscovite and illite to the kaolinite is greater than 1.

13. The method according to claim 12, wherein the clay contains less than 22% by weight of kaolinite.

14. The method according to claim 13, wherein the clay contains less than 20% by weight of kaolinite.

15. The method according to claim 12, wherein the clay contains at least 1% by weight of kaolinite.

16. The method according to claim 12, wherein the clay contains at least 25% by weight of the at least one of muscovite and illite.

17. The method according to claim 16, wherein the clay contains 25% to 50% by weight of the at least one of muscovite and illite.

18. The method according to claim 12, wherein the weight ratio of the at least one of muscovite and illite to the kaolinite is greater than 2.

19. The method according to claim 12, wherein the clay further contains at least 1% by weight calcite.

20. The method according to claim 12, wherein the clay further contains an amorphous phase containing one or more of silica, alumina and calcium.

21. The method according to claim 12, wherein the clay further contains one or more of chlorite, quartz, dolomite, microcline, hematite and smectite.

22. The method according to claim 12, the method further comprising, prior to the calcination, drying the clay.

23. The method according to claim 22, the method further comprising, following the drying, grinding the clay until the clay has a median diameter less than or equal to 25 μm.

24. The method according to claim 12, the method further comprising disagglomeration of the calcined clay until a median diameter of 10 μm to 20 μm is reached.

25. The method according to claim 12, wherein the calcination is conducted at a temperature of from 650° C. to 900° C.

26. The method according to claim 12, wherein the calcination is conducted in a rotary calciner for about 30 to 90 minutes.

27. The method according to claim 12, wherein the calcination is conducted in a flash calciner for about 2 seconds or less.

Description

EXAMPLE 1—CALCINATION OF CLAY

1.1—Composition of Clay

[0077] A crude clay having the mineralogical composition reported in the following Table 1 is used.

TABLE-US-00001 TABLE 1 Mineralogical composition of the clay before calcination Category Phase % (w/w) Clays Muscovite/Illite 39.8 Kaolinite 14.9 Chlorite 5.6 Smectite 7.9 Carbonates Calcite 4.1 Dolomite 5.4 Others Quartz 12.2 Hematite 1 Albite 0.4 Anatase 2.1 Microcline 2.3 Amorphous 4.3

[0078] The above clay has the chemical composition (in % (w/w)) reported in Table 2 below.

TABLE-US-00002 TABLE 2 Chemical composition of the clay before calcination Loss on SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 K.sub.2O Na.sub.2O SrO TiO.sub.2 P.sub.2O.sub.5 MnO ignition 47.79 20.94 6.16 4.24 2.90 0.08 2.75 0.26 0.02 0.99 0.08 0.04 13.83

[0079] The clay used also has the physical characteristics reported in Table 3 below.

TABLE-US-00003 TABLE 3 Physical characteristics of the clay before calcination Density (in g/cm.sup.3) 2.6 Specific surface Blaine (in cm.sup.2/g) 2300 BET (in m.sup.2/g) 43.9

1.2—Calcination of Clay

1.2.1—in a Laboratory Furnace

[0080] The clay described above is dried for 12 hours at 105° C. and then ground in a ring roll mill to a median diameter of 30 to 40 μm. The powder thus prepared is cooked in a laboratory furnace in batches of 200 g at 800° C. for 1 hour with hot charging and drawing. The calcined clay thus obtained (calcined clay AC-1) is again ground slightly in a in a planetary mill (15 seconds, 700 rpm) to deagglomerate it and obtain a median diameter of 20 μm.

1.2.2—in a Flash Calciner

[0081] The clay described above is dried for 72 hours at 105° C. and then crushed in a jaw crusher until 100% passing to 2 mm is obtained. The powder thus prepared is then calcined in a flash calciner at 625° C. (calcined clay ACF-1), 780° C. (calcined clay ACF-2), 870° C. (calcined clay ACF-3) or 875° C. under atmosphere reducing agent (calcined clay ACF-4) with an average residence time of 1 to 2 seconds. The calcined clay thus obtained is then ground again in a vertical mill to deagglomerate it and obtain a median diameter of 10-11 μm.

[0082] The calcined clays thus obtained are analyzed. The mineralogical composition (in % (w/w)) thereof is reported in Table 4 below.

TABLE-US-00004 TABLE 4 Mineralogical composition of calcined clays ACF-1 to ACF-4 Category Phase ACF-1 ACF-2 ACF-3 ACF-4 Clays Muscovite/Illite 26.4 24.8 17.6 17.2 Kaolinite 5.8 2.5 — — Chlorite 3.1 — — — Carbonates Calcite 3.3 3 1.7 2.1 Dolomite 1.1 0.2 — — Others Quartz 10.7 11.8 12.1 11.9 Hematite 1.7 1.8 1.9 1.6 Microcline 4.2 3.5 2.3 2.3 Free lime — 0.5 0.5 0.4 Periclase — 0.5 0.4 0.4 Amorphous 43.8 51.3 63.4 64

EXAMPLE 2—MORTAR COMPOSITIONS

Preparation of Mortars 1 to 16

[0083] A reference mortar (hereinafter Mortar 1) is prepared from Portland cement CEM I 52.5 R according to standard EN 196-1. The composition of mortar 1 is as follows: [0084] 450 g of CEM I 52.5 R cement; [0085] 1350 g of standardized sand; and [0086] 225 g of water.

[0087] Similarly, mortars 2 to 15 are respectively prepared from a mixture: [0088] 90% of CEM I 52.5 R/10% of AC-1 (mortar 2); [0089] 80% of CEM I 52.5 R/20% of AC-1 (mortar 3); [0090] 70% of CEM I 52.5 R/30% of AC-1 (mortar 4); [0091] 60% of CEM I 52.5 R/40% of AC-1 (mortar 5); [0092] 83% of CEM I 52.5 R/17% of AC-1 (mortar 6); [0093] 83% of CEM I 52.5 R/(8.5% of AC-1 and 8.5% of limestone filler) (mortar 7); [0094] 83% CEM I 52.5 R/17% limestone filler (mortar 8); [0095] 75% of CEM I 52.5 R/25% of AC-1 (mortar 9); [0096] 75% CEM I 52.5 R/25% limestone filler (mortar 10); [0097] 50% of CEM I 52.5 R/50% of AC-1 (mortar 11); [0098] 50% of CEM I 52.5 R/(33% of AC-1 and 17% of limestone filler) (mortar 12); [0099] 50% of CEM I 52.5 R/(25% of AC-1 and 25% of limestone filler) (mortar 13); [0100] 50% of CEM I 52.5 R/(17% of AC-1 and 33% of limestone filler) (mortar 14); and [0101] 50% CEM I 52.5 R/50% limestone filler (mortar 15);
the other ingredients and their proportions remaining unchanged.

[0102] Finally, mortar 16 is prepared from a mixture of 75% CEM I 52.5 R/25% commercial calcined clay (Argicem®), the other ingredients and their proportions remaining unchanged.

Mechanical Strength

[0103] The mechanical strength of the mortars is measured in accordance with standard EN 196-1 on prismatic mortar test specimens 4×4×16 cm.sup.3 prepared at 20° C.

[0104] The activity index characterizes the performance of the pozzolanic material when it is used at x % substitution. It is defined as the ratio of the compressive strengths (measured as indicated hereinabove) of a cement mortar constituted by 100-x % of a reference cement (CEM I) and x % of the considered pozzolanic addition, and of a mortar prepared with 100% of reference cement.

[00001]$\mathrm{AI}\left(\%\right)=\frac{\mathrm{CS}\mathrm{cement}\mathrm{substituted}\mathrm{at}x\%}{\mathrm{CS}\mathrm{Reference}}$

[0105] The results of the compressive strength (CS) measurements are reported in the following Tables 5 and 6.

TABLE-US-00005 TABLE 5 Compressive strengths Mortar 1 (ref.) Mortar 2 Mortar 3 Mortar 4 Mortar 5 Mortar 6 Mortar 7 Mortar 8 Compressive 2 days 46.6 42.5 36.5 32.6 27.8 38.7 39.5 40.1 strength 7 days 55.9 51.6 46.2 42.7 38.0 50.1 52.4 49.1 (MPa) 28 days  60.5 57.6 56.6 51.2 46.4 58.0 59.1 57.6 Activity 2 days — 91.3 78.3 69.9 59.8 83.0 84.8 86.1 index 7 days — 92.3 82.6 76.3 67.9 89.6 93.7 87.8 (in %) 28 days  — 95.2 93.6 84.6 76.7 95.9 97.7 95.2

TABLE-US-00006 TABLE 6 Compressive strengths Mortar 9 Mortar 10 Mortar 11 Mortar 12 Mortar 13 Mortar 14 Mortar 15 Mortar 16 Compressive 2 days 34.6 35.8 21.1 22.4 22.3 21.0 19.4 31.5 strength 7 days 44.7 45.0 32.7 36.1 33.6 31.3 25.4 45.9 (MPa) 28 days  54.6 50.4 40.0 41.1 39.5 36.9 27.8 54.6 Activity 2 days 74.2 76.8 45.3 48.1 47.9 45.1 41.6 67.6 index 7 days 80.0 80.5 58.5 64.6 60.1 56.0 45.4 82.1 (in %) 28 days  90.2 83.3 66.1 67.9 65.3 61.0 46.0 90.2

[0106] It appears that the mortar prepared from a binary mix Portland cement/calcined clay in a laboratory furnace (mortars 2 to 6, 9 and 11) have a mechanical strength at 28 days comparable to that of the mortar prepared from the Portland cement alone (mortar 1) and comparable or even higher than that of the mortar prepared from a mixture of Portland cement/commercial calcined clay to 25% substitution. In addition, it appears that the addition of calcined clay in laboratory furnace has a dilution effect by lowering the mechanical strength at 28 days.

[0107] The results obtained for the mortars prepared from a binary mix Portland cement/limestone filler (mortar 8, 10 and 15) or from a ternary mixture of Portland cement/(calcined clay in a laboratory furnace+limestone filler) (mortars 7 and 12 to 14) highlight the positive effect to the presence of the calcined clay on the mechanical strength at 28 days, especially at the higher degree of substitution.

EXAMPLE 3—MORTAR COMPOSITIONS

Preparation of Mortars 17 to 21

[0108] As in Example 2, mortars 17 to 21 are prepared from a mixture CEM I 52.5 R/clay in the following proportions: [0109] 75% CEM I 52.5 R/25% ACF-1 (mortar 17); [0110] 75% CEM I 52.5 R/25% ACF-2 (mortar 18); [0111] 75% CEM I 52.5 R/25% ACF-3 (mortar 19); [0112] 75% CEM I 52.5 R/25% ACF-4 (mortar 20); and [0113] 55% CEM I 52.5 R/(30% ACF-4 and 15% limestone filler) (mortar 21);
the other ingredients and their proportions remaining unchanged.

Mechanical Strength

[0114] The mechanical strength of mortars is measured on prismatic mortar test specimens 4×4×16 cm.sup.3 prepared at 20° C. in accordance with standard EN 196-1.

[0115] The activity index characterizes the performance of the pozzolanic material when it is used at x % substitution. It is defined as the ratio of the compressive strengths (measured as indicated hereinabove) of a cement mortar constituted by 100-x % of a reference cement (CEM I) and x % of the considered pozzolanic addition, and of a mortar prepared with 100% of reference cement.

[00002]$\mathrm{AI}\left(\%\right)=\frac{\mathrm{CS}\mathrm{cement}\mathrm{substituted}\mathrm{at}x\%}{\mathrm{CS}\mathrm{Reference}}$

[0116] The results of the compressive strength (CS) measurements are reported in Table 7 below.

TABLE-US-00007 TABLE 7 Compressive strengths Mortar 1 (ref.) Mortar 16 Mortar 17 Mortar 18 Mortar 19 Mortar 20 Mortar 21 Compressive 2 days 43.9 31.5 30.8 33.7 33.4 33.5 24.7 strength 7 days 53.6 45.9 43.7 46.4 47.5 47.5 46.0 (MPa) 28 days  61.8 54.6 52.5 56.2 62.0 64.7 56.0 Activity 2 days — 67.6 70.2 76.8 76.1 76.3 56.3 index 7 days — 82.1 81.5 86.6 88.6 88.6 85.8 (in %) 28 days  — 90.2 85.0 90.9 100.3 104.7 90.6

[0117] It appears that the mortars prepared from a binary mixture of 75% Portland cement/25% calcined clay in a flash calciner (mortars 17 to 20) have a mechanical strength at 28 days comparable or even higher (depending on the calcination temperature) than that of the mortar prepared from Portland cement alone (Mortar 1) or from a Portland cement/commercial calcined clay mixture.

[0118] The results obtained for the mortar prepared from a ternary mixture of Portland cement/(clay calcined in a flash calciner+limestone filler) (mortar 21) show that it is possible to reduce the amount of Portland cement used by 45% with less 10% loss of compressive strength at 28 days.