NEW CONSTRUCTION MATERIAL PREPARED FROM A NEW POZZOLANIC MATERIAL

Abstract

A new construction material prepared from a new pozzolanic material.

Claims

1. A construction material in the form of a powder containing at least 1.5% of CaO and in which 1% to 80% of the particles having a diameter smaller than or equal to 150 m contain: at least 25% of Al.sub.2O.sub.3; less than 60% of CaO; and at least 5% of SiO.sub.2, the SiO.sub.2/Al.sub.2O.sub.3 weight ratio being less than 1.2.

2. The construction material according to claim 1 wherein it contains at least 3% of CaO.

3. The construction material according to claim 1, wherein the proportion of the considered particles is from 1% to 60%.

4. The construction material according to claim 1, wherein the diameter of the considered particles is smaller than or equal to 100 m.

5. The construction material according to claim 1, wherein the considered particles contain at least 30% of Al.sub.2O.sub.3.

6. The construction material according to claim 1, wherein the considered particles contain at most 50% of CaO.

7. The construction material according to claim 6, wherein the considered particles contain from 1% to 50% of CaO.

8. The construction material according to claim 1, wherein the considered particles contain SiO.sub.2, the SiO.sub.2/Al.sub.2O.sub.3 weight ratio being less than 1.

9. The construction material according to claim 1, wherein the considered particles contain at least 10% of SiO.sub.2.

10. The construction material according to claim 1, wherein the considered particles further contain up to 20% of Fe.sub.2O.sub.3.

11. The construction material according to claim 1, wherein the considered particles further contain up to 5% of TiO.sub.2.

12. A pozzolanic material or geopolymer precursor for the preparation of a construction material according to claim 1, comprising: from 10% to 95% of Al.sub.2O.sub.3; from 5% to 50% of SiO.sub.2; from 0% to 35% of CaO; from 0% to 25% of Fe.sub.2O.sub.3; and from 0% to 8% of TiO.sub.2.

13. The pozzolanic material or geopolymer precursor according to claim 12, wherein the pozzolanic material is a calcined bauxite.

Description

EXAMPLE 1

Calcination of Bauxite

[0094] A bauxite having the chemical composition reported in the following Table 1 is used:

TABLE-US-00001 TABLE 1 Chemical composition of bauxite before calcination SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Fe.sub.2O.sub.3 TiO.sub.2 K.sub.2O P.sub.2O.sub.5 Mn.sub.2O.sub.3 Loss on ignition 26.7% 37.7% 0.5% 0.2% 21.0% 1.6% 0.2% 0.2% 0.1% 11.8%

[0095] The bauxite described hereinabove is dried for 24 hours at 105 C. and then crushed in a ring roll mill to a median diameter of 25 m. The powder thus prepared is cooked in a laboratory furnace in batches of 200 g at 600 C. or 700 C. as the case may be for 1 hour with hot charging and drawing. Afterwards, the calcined bauxite thus obtained is again crushed slightly in a ring roll mill (15 seconds, 700 rpm) to deagglomerate it.

[0096] Bauxite calcined at 600 C. (hereinafter Bx-1) is analyzed. The chemical composition thereof is reported in Table 2 hereinbelow:

TABLE-US-00002 TABLE 2 Chemical composition of bauxite calcined at 600 C. - Bx-1 SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Fe.sub.2O.sub.3 TiO.sub.2 K.sub.2O P.sub.2O.sub.5 Mn.sub.2O.sub.3 Loss on ignition 31.0% 42.1% 0.2% 0.2% 20.9% 1.8% 0.3% 0.2% 0.1% 3.2%

[0097] Likewise, bauxite calcined at 700 C. (hereinafter Bx-2) is analyzed. The chemical composition thereof is reported in Table 3 hereinbelow:

TABLE-US-00003 TABLE 3 Chemical composition of bauxite calcined at 700 C. - Bx-2 SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Fe.sub.2O.sub.3 TiO.sub.2 K.sub.2O P.sub.2O.sub.5 Mn.sub.2O.sub.3 Loss on ignition 31.1% 43.1% 0.1% 0.2% 21.3% 1.9% 0.3% 0.2% 0.1% 1.7%

EXAMPLE 2

Analysis of the Composition of a Construction Material Prepared from Bx-1

[0098] Cement 1 Preparation

[0099] A cement 1 is prepared by mixing 75% of a Portland cement CEM I 52.5 R according to standard EN 196-1 and 25% of calcined bauxite Bx-1.

[0100] Characterization by SEM Coupled to an EDAX Probe

[0101] Cement 1 was sieved to 150 m, then the undersize was analyzed by scanning electron microscopy (SEM) coupled to an EDAX probe (X-ray fluorescence emission spectrum) according to the following protocol.

[0102] The 150 m undersize is included in resin in order to obtain a block in which the particles are dispersed. Afterwards, this block is progressively polished so as to obtain a mirror surface which reveals a large number of particle sections.

[0103] After metallization with carbon, this phase is observed using a scanning electron microscopy. It is thus possible to distinguish the different types of particles by their color (gray level) and their shape.

[0104] The EDAX probe coupled to the electron microscope makes it possible to determine the chemical composition locally and is used in two ways: [0105] for a point-in-time approach, an average measurement is made over the entire section of a particle; and [0106] for a statistical approach, a scan of the entire image (or mapping) is carried out enabling a chemical analysis of each pixel of the image. The software will then make it possible to visualize very clearly the richest in alumina or poorest in calcium areas. The software also makes it possible to group together the pixels having a similar chemistry and thus define areas of identical chemistry. This mapping not only allows determining the chemistry of the composition but also the percentage of pixels that the area represents in the image.

[0107] This approach based on image analysis to characterize a true property for spherical particles is conventionally used in the technical field of the invention.

[0108] Results

[0109] The mapping described hereinabove made it possible to obtain the results reported in the following Table 4.

TABLE-US-00004 TABLE 4 Identified Al.sub.2O.sub.3 SiO.sub.2 CaO area % of pixels (in % w/w) (in % w/w) (in % w/w) 1 2% 3.59 5.40 41.34 2 6% 23.24 26.89 30.78 3 8% 19.57 23.19 16.01 4 3% 17.09 14.15 0.69 5 0% 3.70 36.02 3.80 6 6% 17.50 13.10 19.92 7 5% 33.76 27.91 2.14 8 14% 43.82 45.58 1.10 9 16% 4.27 19.00 68.33 10 5% 31.96 29.58 12.83 11 13% 11.36 17.93 52.21 12 8% 53.64 35.17 0.67 13 6% 12.88 30.68 22.02 14 9% 11.63 17.78 37.70

[0110] In cement 1, 32% of particles with a diameter of less than 150 m contain [0111] at least 25% Al.sub.2O.sub.3; [0112] less than 60% of CaO; and [0113] at least 5% of SiO.sub.2;

[0114] and the SiO.sub.2/Al.sub.2O.sub.3 weight ratio is less than 1.

EXAMPLE 2

Mortar Compositions

[0115] Preparation of Mortars 1 to 7

[0116] 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: [0117] 450 g of CEM I 52.5 R cement; [0118] 1350 g of standardized sand; and [0119] 225 g of water.

[0120] Similarly, mortars 2 to 7 are prepared from a 75% mixture of CEM I 52.5 R with respectively: [0121] 25% of Bx-1 (mortar 2); [0122] 25% of Bx-2 (mortar 3); [0123] 25% of limestone filler from St Hilaire (mortar 4); [0124] 25% of commercial calcined clay (Argicem) (mortar 5); [0125] 25% of fly ash (mortar 6); and [0126] 25% of ground blast-furnace slag (mortar 7);

[0127] the other ingredients and their proportions remaining unchanged.

[0128] Mechanical Strength

[0129] The mechanical strength of the mortars is measured in accordance with standard EN 196-1 on prismatic mortar test specimens 4416 cm3 prepared at 20 C.

[0130] The activity index characterizes the performance of the pozzolanic material when it is used at 25% substitution. It is defined as the ratio of the compressive strengths (measured as indicated hereinabove) of a cement mortar constituted by 75% of a reference cement (CEM I) and 25% of the considered pozzolanic addition, and of a mortar prepared with 100% of reference cement.

[00001]$\mathrm{AI}.Math..Math.\left(\%\right)=\frac{\mathrm{CS}.Math..Math.\mathrm{cement}.Math..Math.\mathrm{substituted}.Math..Math.\mathrm{at}.Math..Math.25.Math.\%}{\mathrm{CS}.Math..Math.\mathrm{Reference}}$

[0131] The results of the compressive strength (CS) measurements are reported in the following Table 5.

TABLE-US-00005 TABLE 5 Mortar 1 Mortar 2 Mortar 3 Mortar 4 Mortar 5 Mortar 6 Mortar 7 (ref.) (Bx-1) (Bx-2) (Filler) (Argicem) (Fly ash) (Slag) Compressive 2 days 46.6 34 33.7 33.9 31.5 35.3 32.2 strength 7 days 55.9 48.6 51.1 42.2 45.9 44.8 43.7 (MPa) 28 days 60.5 58.9 61.4 47.8 54.6 51.5 53.2 Activity 2 days 73.0% 72.3% 72.7% 67.6% 75.8% 69.1% index 7 days 86.9% 91.4% 75.5% 82.1% 80.1% 82.1% 28 days 97.4% 101.5% 79.0% 90.2% 85.1% 87.9%

[0132] It appears that the mortars prepared from a Portland cement/calcined bauxite mixture (mortars 2 and 3) have a mechanical strength comparable to that of the mortar prepared from Portland cement alone (mortar 1) and a much better mechanical strength than the mortars prepared from conventional pozzolanic additions (mortars 5 to 7) or from filler-type additions (mortar 4).

EXAMPLE 3

Mortar Compositions

[0133] Preparation of Mortars 8 to 12

[0134] As in Example 2, mortars 6 to 10 are prepared from a CEM I 52.5 R/Bx-2 mixture in the following proportions: [0135] 90/10 (mortar 8); [0136] 80/20 (mortar 9); [0137] 70/30 (mortar 10); [0138] 60/40 (mortar 11); and [0139] 50/50 (mortar 12);

[0140] the other ingredients and their proportions remaining unchanged.

[0141] Mechanical Strength

[0142] The mechanical strength of the mortars is measured on prismatic mortar test specimens 4416 cm3 prepared at 20 C. according to standard EN 196-1.

[0143] The performance index of the material may be defined in a way comparable to the activity index but for a substitution rate different from 25%. In this case, this index 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 by a mortar prepared with 100% of reference cement.

[00002]$\mathrm{PI}.Math..Math.\left(\%\right)=\frac{\mathrm{CS}.Math..Math.\mathrm{cement}.Math..Math.\mathrm{substituted}.Math..Math.\mathrm{at}.Math..Math.X.Math..Math.\%}{\mathrm{CS}.Math..Math.\mathrm{Reference}}$

[0144] The results of the compressive strength (CS) measurements are reported in the following Table 6.

TABLE-US-00006 TABLE 5 Mortar 1 Mortar Mortar Mortar (ref.) Mortar 8 Mortar 9 10 11 12 Compressive 2 days 40.2 34.9 32.2 29.7 22.6 16.4 strength 7 days 51.6 52.6 53.1 48.5 40.2 31.8 (MPa) 28 days 60.5 65.0 63.5 61.7 56.8 50.1 Performance 2 days 86.8% 80.1% 73.8% 56.2% 40.8% index (PI) 7 days 101.9% 102.8% 94.0% 77.9% 61.6% 28 days 106.7% 104.3% 101.2% 93.3% 82.3%

[0145] It appears that the mortars prepared from a Portland cement/calcined bauxite mixture in proportions varying from 90/10 to 70/30 (mortars 6 to 8) have a mechanical strength comparable to or even greater than that of the mortar prepared from only Portland cement (mortar 1). Furthermore, the mortars containing large proportions of calcined bauxite in place of Portland cement (mortars 9 and 10) have a resistance at least comparable to that of the mortars prepared from conventional pozzolanic additions but in much lower proportions (mortars 5 to 7-example 2).

EXAMPLE 4

Concrete Compositions

[0146] Preparation of Concretes 1 and 2

[0147] A reference concrete (hereinafter Concrete 1) is prepared from a Portland cement CEM I 52.5 R. The composition of concrete 1 is as follows: [0148] 12.3 kg of CEM I 52.5 R cement; [0149] 28.9 kg of aggregates 0-4 mm; [0150] 13.6 kg of aggregates 4-11 mm; [0151] 22.6 kg of aggregates 11-22 mm; and [0152] 6.8 kg of mixing water (E.sub.eff/C=0.50).

[0153] Similarly, a concrete 2 is prepared from a Portland cement mixture CEM I 52.5 R/Bx-2 in a 85/15 proportion, the other ingredients and their proportions remaining unchanged.

[0154] Mechanical Strength

[0155] The mechanical strength of the concretes is measured on cylindrical concrete proof bodies (diameter 16 cm, height 32 cm) according to standard NF EN 12390-3.

[0156] The performance index of a pozzolanic material in a concrete may be defined as the ratio of the compressive strength (measured as indicated hereinabove) of two concretes formulated according to the same concrete formula, one being prepared from a cement constituted by reference cement substituted at X % by the pozzolanic material, and the other being prepared from a cement constituted by 100% of said reference cement.

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[0157] The results of the compressive strength (CS) measurements are reported in the following Table 7.

TABLE-US-00007 TABLE 7 Concrete 1 Concrete 2 (ref.) (15% Bx-2) Compressive 2 days 29.9 25.2 strength 7 days 42.4 41.6 (MPa) 28 days 49.4 51.6 Performance 2 days 84.3% Index (PI) 7 days 98.1% 28 days 104.5%

[0158] It appears that the concrete prepared from a Portland cement/calcined bauxite mixture (concrete 2) has a mechanical strength comparable to or even greater than that of the concrete prepared from Portland cement alone (concrete 1) after 7 days.

EXAMPLE 5

Geopolvmer Compositions

[0159] Preparation of Geopolymers

[0160] A geopolymer 1 is prepared from metakaolin (Argicem) and an activating solution constituted by 80 weight % of sodium silicate, 10 weight % of soda and 10 weight % of water. Geopolymer 1 is formulated from 100 g of metakaolin Argicem and 100 ml of activating solution.

[0161] Similarly, a geopolymer 2 is prepared from Bx-2 (instead of metakaolin), the other ingredients and their proportions remaining unchanged.

[0162] Mechanical Strength

[0163] The mechanical strength of the geopolymers is measured on geopolymer dough cubes with dimensions 2020 mm. The cubes are made in steel molds and then stored for 24 hours at 20 C. and 100% humidity. After demolding, the cubes are stored for 5 additional days at 20 C. in sealed bags containing a bottom of water in order to keep them at 100% humidity without completely immersing them.

[0164] The strength of the obtained samples is tested at 6 days

[0165] The maximum strengths of this type of material are reached in less than one week.

[0166] At 6 days, the geopolymer 1 leads to a compressive strength (CS) of 37 MPa while the geopolymer 2 leads to a compressive strength (CS) of 68 MPa, or almost the double.

[0167] The use of calcined bauxite as a geopolymer precursor therefore makes it possible to produce particularly high-performance geopolymers, which further have at 6 days strengths comparable to those of CEM I cement at 28 days.