Method for the Preparation of a Carbonated Mineral Component, Carbonated Mineral Component, and Method for the Preparation of a Binder Composition

Abstract

A method for preparing a carbonated mineral for use in cement is provided; wherein a mineral component with a (CaO+MgO)/SiO.sub.2 weight ratio of 1.2 to 5.0 is ground to a powder; mixed with water to form a paste; the paste is placed in a reactor in an atmosphere containing CO.sub.2; the paste is carbonated in the reactor; and the resulting material is dried to constant weight; or the mineral component is ground to a Blaine fineness between 3000 cm2/g and 10000 cm2/g to obtain a powder; during grinding a CO2 rich gas is injected so that the component carbonates; the powder is mixed with water at a weight ratio between 0.3 and 1.5 to obtain a paste, or pre-humidified by adding water at a weight ratio between 0.03 and 0.2; the resulting material is dried to constant weight at 60-85 C.; and the resulting material is deagglomerated and sieved.

Claims

1-20. (canceled)

21. A method for preparing a carbonated mineral component, comprising the steps of: providing a mineral component including CaO, MgO and SiO.sub.2 in a weight ratio (CaO+MgO)/SiO.sub.2 of about 1.2 to about 5.0 and having an amorphous content of at least about 66% by weight; carbonating the mineral component to form a hardened material using a first sequence of steps or, alternatively, a second sequence of steps; drying the hardened material to a constant weight; and deagglomerating and sieving the hardened material to form the carbonated mineral component; wherein the first sequence of steps comprises: grinding the mineral component to obtain a powder; mixing the powder with water to form a paste; placing the paste in a reactor in an atmosphere that includes a CO.sub.2 rich gas; and carbonating the paste in the reactor to form the hardened material; and the second sequence of steps comprises: grinding the mineral component in a mill; during grinding of the mineral component, injecting the CO.sub.2 rich gas into the mill to carbonate the mineral component, yielding a carbonated powder; and either a) mixing the carbonated powder with water at a solid to water weight ratio of about 0.3 to about 1.5, or b) pre-humidifying the carbonated powder using a solid to water ratio of about 0.03 to about 0.2, to obtain the hardened material.

22. The method of claim 21, wherein the step of drying the hardened material to the constant weight is preformed at a temperature of about 60 C. to about 85 C.

23. The method of claim 21, wherein the mineral component comprises at least about 35% by weight of the CaO.

24. The method of claim 21, wherein the CO.sub.2 rich gas is a combustion gas from a cement plant.

25. The method of claim 21, wherein the weight ratio of (CaO+MgO)/SiO.sub.2 is 1.26 to 5.0.

26. The method of claim 21, wherein, after grinding the mineral component, the powder or carbonated powder has a Blaine fineness between about 3000 cm.sup.2/g and about 10,000 cm.sup.2/g,

27. The method of claim 26, wherein the Blaine fineness is between 5000 cm.sup.2/g and 8000 cm.sup.2/g.

28. The method of claim 21, wherein the powder or carbonated powder is mixed with the water at a solid to water weight ratio between 0.3 and 1.5.

29. The method of claim 21, comprising the first sequence of steps, wherein the reactor is operated at atmospheric pressure, a temperature of 50-90 C., and a relative humidity of 56-95%.

30. The method of claim 21, comprising the first sequence of steps, wherein the paste is carbonated in the reactor for a duration between 12 and 52 hours.

31. The method of claim 30, wherein the duration is between 18 and 30 hours.

32. The method of claim 21, wherein the hardened material is sieved to particle sizes of 63 m or less to exclude coarse aggregates.

33. The method of claim 21, wherein the mineral component is selected from one or more of ground granulated blast-furnace slag, ground steel slag, fly ash, and ground concrete demolition waste.

34. A carbonated mineral including carbonated and non-carbonated constituents; the non-carbonated constituents including CaO, MgO and SiO.sub.2 in a weight ratio (CaO+MgO)/SiO.sub.2 of about 1.2 to about 5.0 and having an amorphous content of at least about 66% by weight.

35. The carbonated mineral of claim 34, wherein the carbonated mineral has a degree of carbonation of about 5% to about 20% by weight.

36. The carbonated mineral of claim 35, wherein the degree of carbonation is about 8% to about 16% by weight.

37. The carbonated mineral of claim 34, wherein the carbonated mineral has a Blaine fineness of 3000 cm.sup.2/g to 10,000 cm.sup.2/g.

38. A method of preparing a binder composition, comprising the steps of: providing a carbonated mineral component including CaO, MgO and SiO.sub.2 in a weight ratio (CaO+MgO)/SiO.sub.2 of about 1.2 to about 5.0; and mixing the carbonated mineral component with a cementitious component selected from the group consisting of a Portland cement, a Portland cement clinker, and combinations thereof.

39. The method of claim 38, wherein the carbonated mineral component is added to the cementitious component and ground together with the cementitious component to obtain the binder composition.

40. The method of claim 38, wherein the carbonated mineral component has a Blaine fineness of 3000 cm.sup.2/g to 10,000 cm.sup.2/g.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0084] The invention is further explained by way examples. The examples are shown in accompanying drawings, which show:

[0085] FIG. 1: a table showing the list of materials used;

[0086] FIG. 2: the fineness and the Blaine surface of the used materials;

[0087] FIG. 3: the relevant chemical composition of the components;

[0088] FIG. 4: the compressive strength of the materials and material admixtures without carbonation;

[0089] FIG. 5 the compressive strength of the materials and material admixtures with carbonation

[0090] FIG. 6: schematically the test device;

[0091] FIG. 7: the impact of the fineness of the mineral component;

[0092] FIG. 8: three comparative examples in which carbonated material is substituted by limestone.

DETAILED DESCRIPTION OF THE INVENTION

[0093] With reference to FIG. 5 samples of 10 g each are prepared from a mineral component and mixed with water with different water-cement ratios in sample pans.

[0094] The sample pans with the sample materials are introduced in a market available container which allows temperature control as well as a gas control. The gas control comprises the composition of the gas and the gas pressure wherein the container has respective gas connections (inlet/outlet) to provide for a gas flow.

[0095] The relative humidity is controlled by means of a tank of deionised water laid on the bottom of the container.

[0096] The temperature is set to 70-80 C. and the CO.sub.2-pressure at the inlet of the chamber is set to 1.02 bar and remain constant. The relative humidity which was set by means of the tank was measured as to be 80-85% in the reactor.

[0097] After a predetermined time in the container the carbonation and hydration amount of the respective materials were determined.

a) Total Mass Gain with Respect to Mineral Component

[0098] The total mass gain (m, see eq. (1)) is related to both bound water (m_H2O) and bound CO.sub.2 (m_CO.sub.2) with respect to the mineral component [g/g of mineral component].

[0099] After carbonation, the samples are dried at 80 C. to get the final dry mass noted m(f,dry), expressed in grams [g].

[0100] The mass of the samples after mixing and before carbonation is known, it is noted m(0,wet) and expressed in grams [g].

[0101] The mass of the solid, i.e. the dry mass, is calculated from initial mix composition, it is noted m(0,dry) and expressed in grams [g].

[00001]$\begin{array}{cc}m=\left(m\left(f,\mathrm{dry}\right)-m\left(0,\mathrm{dry}\right)\right)/m(0,\mathrm{dry}& \mathrm{Equation}1\end{array}$

b) CO.sub.2 Mass Gain with Respect to the Mineral Component:

[0102] The bound water content and bound CO.sub.2 content with respect to the mass of samples is also calculated from the measured mass of samples, respectively at 550 C. and 950 C. The mass difference of samples between 80 C. and 550 C. is related to bound water content (see eq. (2)) whereas the mass loss of samples between 550 C. and 950 C. is related to CO.sub.2 content (see eq. (3)).

[00002]$\begin{array}{cc}m\mathrm{\_H2O}=\left(\left(m\left(f,80\right)-m\left(f,550\right)\right)\right)/m\left(950\right)& \mathrm{Equation}2\end{array}$$\begin{array}{cc}m\mathrm{\_CO2}=\left(\left(m\left(f,550\right)-m\left(f,950\right)\right)\right)/m\left(950\right)& \mathrm{Equation}3\end{array}$

[0103] In this way prepared carbonated mineral components were used to prepare respective mortars and measuring the compressive strength according to the norm NF EN196-1 of September 2016.

[0104] In the tables according to the Figures the samples are shown, wherein all samples, which are marked 75/25 were made of a composition of a cement CEM I (A or B) and 25 wt.-% of the respective mineral component. Carbonated mineral components according to the invention were used as well as the same mineral components without the carbonation step to elaborate the differences in the strength development. The respective 75/25 admixtures were used to prepare a mortar and the compressive strength was determined as described above.

[0105] FIG. 2 and FIG. 3 lists the mineral components used in the examples. As will be confirmed in the results discussed further below, GGBFS C and the fly ash B are not suitable for the present invention.

[0106] The results related to the strength of the mortar and carbonation of the mineral component are presented in FIG. 4.

[0107] As a comparative example, sample 1 and sample 2 pertain to a pure CEM I (A and B) sample without an additional mineral component.

[0108] Samples 3-11 (FIG. 4) show the impact of the substitution of CEM I A and B with a non-carbonated mineral component on strength development. In all cases in comparison to a mortar made of the pure CEM I cement, the strength at 2 and 7 days is always reduced and the strength at 28 days is reduced, except in the case of ground blast-furnace slags B which contributes positively to the compressive strength at 28 days at a similar level as CEM I. This could be expected according to the latent hydraulic properties of this blast-furnace slag.

[0109] Samples 12-19 (FIG. 5) are examples with carbonated mineral components. The mineral components were carbonated for 24 hours in the already defined way. As it can be seen the samples 12 and 14 with CEM I A and CEM I B and blast-furnace slag A as the mineral component led to a compressive strength after 28 days in the range which can be achieved by the corresponding CEM I alone. A certain deviation occurs between samples 12 and 13, which is not significant.

[0110] A closer look to the impact of the fineness of the mineral component was made by grinding the blast-furnace slag to two different Blaine grades: 4710 cm.sup.2/g and 5920 cm.sup.2. Here too, these constituents were carbonated for 24 hours in the already defined way. The results can be seen in FIG. 7 wherein the weight gain after carbonation is higher with a higher fineness and more or less uniformly the carbonation weight gain is about 2%, wherein the weight gain by the introduction of water is 2.7%.

[0111] Sample 5 in FIG. 4 pertains to the use of CEM I A with a fly ash B without any carbonation wherein sample 18 pertains to the same CEM I A and carbonated fly ash. In comparison in particular of sample 18 showing a carbonated fly ash B with CEM I A and the same constituents but with a non-carbonated fly ash which is sample 5, it can be seen that the carbonation caused a 28-day compressive strength of 52.33 MPa and 55.25 MPa in sample 5.

[0112] As in sample 18 the carbonated fly ash B obviously does not contribute to a higher compressive strength than in comparison to sample 5 it can be concluded that according to the lower ratio of (CaO+MgO)/SiO.sub.2 of 1.02, this example is not working and therefore, outside of the inventive range. In this sample the dilution effect of the fly ash as a mineral component was not compensated by carbonation.

[0113] Another sample showing the lower limit is the ground concrete demolition waste (CDW) with a ratio of (CaO+MgO)/SiO.sub.2 of 0.53. A sample of CEM I A with CDW (sample 4) showed a remarkable drop of the 28 days compressive strength from over 60 to 45.38 MPa. The same situation but with a carbonated CDW (sample 15) did not lead to a higher compressive strength.

[0114] Samples 9 and 19 pertain to the use of GGBFS C as a non-carbonated (sample 9) and carbonated (sample 19) mineral component. This mineral component has a (CaO+MgO)/SiO.sub.2 ratio of 1.15. Example 19 shows that this slag GGBFS C did not carbonate efficiently, as the carbonation, expressed in wt.-% CO.sub.2, was only of 1 wt.-%. This example is therefore not working and therefore, outside of the inventive range.

[0115] Therefore, a (CaO+MgO)/SiO.sub.2 ratio under 1.20 is not suitable for the invention. A ratio above 1.26 is preferred.

[0116] Samples 7 and 17 pertain to the use of steel slag BOF, which has a (CaO+MgO)/SiO.sub.2 ratio of 4.47. When compared to the non-carbonated test (Sample 7), the carbonated sample (Sample 17) shows a particularly strong increase of the compressive strength at 28 days. This sample is therefore working and is within the inventive range.

[0117] The invention substitutes a cementitious material in a hydraulic binder composition with a selected group of mineral components with a (CaO+MgO)/SiO.sub.2 ratio between 1.20 and 5.0, in particular 1.20 and 2.0 in an advantageous manner.

[0118] It was surprisingly found that carbonating these mineral components and grinding them to a sufficient fineness does not lower the 28 compressive strength in comparison to the binder composition using pure cementitious material without the mineral component. It is thereby possible to lower the carbon footprint of such a hydraulic binder composition and the resulting concrete remarkably but avoiding any detrimental effect on the long term compressive strength.

[0119] To further characterize the advantages of the present invention, additional comparative tests have been carried out, in which 3 cement compositions have been tested: [0120] CT1: A CEM III/A cement, comprising 55 wt.-% CEM I LT, 42 wt.-% non-carbonated GGBFS A, and 3 wt.-% ground limestone filler [0121] CT2: A CEM III/A cement, comprising 55 wt.-% CEM I LT, 42 wt.-% carbonated GGBFS A, and 3 wt.-% ground limestone [0122] CT3: A CEM III/A cement, comprising 55 wt.-% CEM I LT, 35 wt.-% non-carbonated GGBFS A, and 10 wt.-% Durcal 10.

[0123] The GGBFS A carbonates to capture an equivalent of 8.2 wt.-% CO.sub.2, which corresponds to the formation of an amount of calcium carbonate of 7 wt.-% of the total weight of cement. CT2 then has the following full composition: is 55 wt.-% CEM I B, 35 wt.-% non-carbonated GGBFS A, and 10 wt.-% ground limestone.

[0124] CT3 was then prepared by replacing all sources of calcium carbonate in CT2 by Durcal 10. Durcal 10 is a fine ground calcium carbonate provided by Omya, having a Blaine value of 5000 cm.sup.2/g. The total amounts of CEM I B and non-carbonated GGBFS A in samples CT2 and CT3 are therefore the same. Furthermore, as the carbonation results in the formation of calcium carbonate in the mineral component, the total amount of calcium carbonate in samples CT2 and CT3 remains also the same.

[0125] The results of these three tests are provided in FIG. 8. When compared to CT1, CT2 shows a small reduction in strength and 2 days, 7 days, and 28 days. When compared to CT1, CT3 also shows a smaller reduction in strength at 2 days, and stronger decrease at 28 days. Interestingly, even though the total composition of CT2 and CT3 are the same, the compressive strength at 28 days of CT3 is significantly lower to that of CT2.