CEMENT REPLACEMENT MIXTURE

Abstract

The invention relates to a pozzolan mixture comprising between 5 and 80% of magnesium-iron solid solution silicates; between 5 and 80% of MgCOs X H20 where X=0-10; and between 2 and 30% of reactive silica; and having a free water content of at most 10% by total weight of mixture. The invention further relates to a method of making a cement slurry with a pozzolan mixture including the steps of: (i) reacting a magnesium-iron solid solution silicate with an acid and adding any extra magnesium-iron solid solution silicate to the products of the reaction to produce a pozzolan mixture comprising between 5 and 80% of magnesium-iron solid solution silicates: between 5 and 80% of MgCOs X H20, where X=0-10; between 2 and 30% of reactive silica: (ii) adding the products of step (i) to a slurry of cementitious material and water in a ratio of between 1:1.5 and 10:1 of cementitious material to the pozzolan mixture.

Claims

1. A pozzolan mixture comprising between 5 and 80% of magnesium-iron solid solution silicates; between 5 and 80% of MgCO.sub.3.Math.X H.sub.2O where X=0-10; and between 2 and 30% of reactive silica; and having a free water content of at most 10% by total weight of mixture.

2. The mixture according to claim 1, wherein the mixture comprises between 30 and 60% of magnesium-iron solid solution silicates.

3. The mixture according to claim 1, wherein the mixture comprises between 30 and 60% of MgCO.sub.3.Math.X H.sub.2O where X=0-10.

4. The mixture according to claim 1, wherein the mixture comprises between 10 and 30% of reactive silica.

5. The mixture according to claim 1, wherein the mixture has a free water content of at most 5% by total weight of mixture.

6. The mixture according to claim 1, wherein the mixture has a free water content of at most 1% by total weight of mixture.

7. The mixture according to claim 1, wherein the reactive silica is amorphous silica.

8. The mixture according to claim 1, wherein the magnesium-iron solid solution silicate is selected from the group of minerals consisting of olivines, orthopyroxenes, amphiboles, and serpentines.

9. The mixture according to claim 1, wherein the magnesium-iron solid solution silicate is olivine.

10. The mixture according to claim 1, further comprising a cementitious material, and the ratio of the cementitious material to the pozzolan mixture is between 1.5:1 and 5:1, preferably between 2:1 and 4:1.

11. The mixture according to claim 1, wherein the cementitious material is an alkaline cement.

12. The mixture according to claim 1, wherein the cementitious material is an alkali-activate binder.

13. The mixture according to claim 1, wherein the reactive silica is produced through one or more of the following: mechanical activation, temperature treatment, pressure treatment.

14. A method of making a cement slurry with a pozzolan mixture comprising the steps of: (i) reacting a magnesium-iron solid solution silicate with an acid containing a CO.sub.3.sup.2ion and adding any extra magnesium-iron solid solution silicate to the products of the reaction to produce a pozzolan mixture comprising between 5 and 80% of magnesium-iron solid solution silicates; between 5 and 80% of MgCO3.Math.X H.sub.2O, where X=0-10; between 2 and 30% of reactive silica; (ii) adding the products of step (i) to a slurry of cementitious material and water in a ratio of between 1:1.5 and 10:1 of cementitious material to the pozzolan mixture.

15. The method according to claim 14, wherein the mixture comprises between 30 and 60% of magnesium-iron solid solution silicates.

16. The method according to claim 14, wherein the mixture comprises between 30 and 60% of MgCO.sub.3.Math.X H.sub.2O where X=0-10.

17. The method according to claim 14, where the mixture comprises between 10 and 30%, of reactive silica.

18. The method according to claim 14, comprising adding the products of step (i) to a slurry of cementitious material and water in a ratio of between 1.5:1 and 5:1, preferably between 2:1 and 4:1, of cementitious material to the pozzolan mixture.

19. The method according to claim 14, wherein the reactive silica is produced by a reaction between the magnesium-iron solid solution silicate and an acid.

20. The method according to claim 14, wherein the MgCO.sub.3.Math.X H.sub.2O and the magnesium-iron solid solution silicate in the products are produced by a chemical reaction between the magnesium-iron solid solution silicates and H.sub.2CO.sub.3.

21. The method according to claim 14, wherein all the MgCO.sub.3.Math.X H.sub.2O in the products is produced by a chemical reaction between the magnesium-iron solid solution silicates and H.sub.2CO.sub.3.

22. The method according to claim 14, wherein all of the MgCO.sub.3.Math.H.sub.2O and all of the magnesium-iron solid solution silicates in the products are produced by a chemical reaction between the magnesium-iron solid solution silicates and H.sub.2CO.sub.3.

23. The method according to claim 14, wherein the acid is carbonic acid.

24. The method according to claim 14, wherein the carbonic acid is produced by a reaction of CO.sub.2 (g, l, sc) and water.

25. The method according to claim 14, wherein the carbonic acid is produced by a reaction of a bicarbonate with an acid and/or water.

26. The method according to claim 14, wherein the magnesium-iron solid solution silicate is selected from the group of minerals consisting of olivines, orthopyroxenes, amphiboles, and serpentines.

27. The method according to claim 14, wherein the magnesium-iron solid solution silicate is olivine.

28. The method according to claim 14, wherein the cementitious material is an alkaline cement.

29. The method according to claim 14, wherein the cementitious material is an alkali-activate binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0061] Reference will now be made in detail to the present invention and embodiments thereof. Alternative embodiments will also be presented. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided by way of illustration only. Several further embodiments, or combinations of the presented embodiments, will be within the scope of one skilled in the art.

[0062] Provided that magnesium-iron solid solution silicates are well known to not have significant pozzolanic properties, they are not thought as suitable to replace cementitious material in a dry mixture (that later be mixed with water to make a slurry with the desired pourability and strength characteristics).

[0063] We have discovered a synergetic pozzolanic effect of the combination of minerals:

Mg-Fe solid solution silicate+MgCO.sub.3.Math.X H.sub.2O+silica

in a mixture of 5-80%, preferably 30-60%, of magnesium-iron solid solution silicates, between 5-80%, preferably 30-60%, of MgCO.sub.3.Math.X H.sub.2O (hydromagnesite and magnesite), and between 2 and 30%, preferably between 10 and 30% of silica by total weight of the mixture. For a mixture that is suitable for sale in a bag of cement, it is preferable to have a free water content of at most 10% by total weight of the mixture. The mixture comprises the magnesium-iron solid solution silicates, MgCO.sub.3.Math.X H.sub.2O (hydromagnesite and magnesite), silica and water in the above-mentioned percentages (%) which preferably are percentages by weight (% by weight). The free water content is preferably at most 10% by total weight of mixture, or at most 10% by weight, based on the total weight of the mixture. Preferably the free water content is at most 5% by weight. Ideally, the free water content is less than 1% by weight. These allow the produced mixture, to be a smooth mixture and that the water content is low enough that it does not have to be taken into consideration when making a slurry to a desired water to binder ratio.

[0064] In a dry mixture form, the silica will be amorphous silica (SiO.sub.2). Amorphous silica is important as it already has a strong and documented pozzolanic effect (K) and may therefore work as a gel former in the cement.

[0065] When in a blended slurry, reactive silica refers to SiO.sub.4.sup.4 (aq). Also, when in a slurry, it could refer to amorphous silica mass that is in the solid part of the solution (normally as undissolved precipitate).

[0066] The reactive silica can also be formed by a reaction between the magnesium-iron solid solution silicate and an acid to produce an SiO.sub.4.sup.4 ion. This can be done by reacting the magnesium-iron solid solution silicate with an acid or water (example shown is olivine):

Mg.sub.2SiO.sub.4+4 HA(aq).fwdarw.2 MgA.sub.2+SiO.sub.4.sup.4 (aq)+4 H.sup.+

[0067] A is the conjugate base (XOH.sup.x). The acid may be an organic acid such as formic acid or acetic acid. It can also be a strong acid such as HCl or H.sub.2SO.sub.4.

[0068] When the magnesium-iron solid solution silicate reacts with H.sub.2CO.sub.3 (aq) (i.e. carbonic acid), both the reactive silica and MgCO.sub.3 is generated. This is preferable as only a single reaction is needed to produce the pozzolan mixture desired.

Mg.sub.2SiO.sub.4(s)+2H.sub.2CO.sub.3(aq).fwdarw.2 MgCO.sub.3(s)+H.sub.4SiO.sub.4(aq).fwdarw.2 MgCO.sub.3(s)+SiO.sub.4.sup.4(aq)+4 H.sup.+ (aq)

[0069] Note that since the carbonic acid dissociates in water, the above reaction can also be written as:

Mg.sub.2SiO.sub.4(s)+4H.sup.+(aq)+2CO.sub.3.sup.2 (aq).fwdarw.2 MgCO.sub.3(s)+SiO.sub.4.sup.4(aq)+4H.sup.+(aq)

[0070] There are several ways to produce H.sub.2CO.sub.3. The preferred method is to react CO.sub.2 with water:

CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3.fwdarw.2 H.sup.++CO.sub.3.sup.2

[0071] This allows further absorption of CO.sub.2 in addition to that from the process of curing cement that contains a magnesium-iron solid solution silicate.

[0072] Another way of producing H.sub.2CO.sub.3 is to react a bicarbonate with an acid (HCl is disclosed as an example of an acid):

CO.sub.3.sup.2+2 HCl.fwdarw.H.sub.2CO.sub.3+Cl.sub.2(g)

[0073] Note that the chlorine gas produced is quickly reacted with the iron in the magnesium-iron solid solution silicate, so from a practical perspective the chlorine gas is not released to the atmosphere. Another way of producing H.sub.2CO.sub.3 is to react a bicarbonate with water:

CO.sub.3.sup.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3

[0074] Note that in the previous reactions of olivine to produce MgCO.sub.3 and H.sub.2CO.sub.3 there are other products that are produced (for example H.sub.2SiO.sub.4) that are not relevant for understanding the pozzolanic mixture.

[0075] The above are examples pertaining to olivine. However, as magnesium-iron solid solution silicates are dominated by magnesium (Mg), their chemical reactions will be similar to the above. For example: the minerals olivine, orthopyroxenes, amphiboles, and serpentines are all desirable for this process. Our preferred magnesium-iron solid solution silicate is olivine.

[0076] The pozzolan mixture can replace between 10 and 70%, preferably between 20-50%, of cementitious mixture. This is a ratio, preferably weight ratio, of between 1.5:1 and 10:1, preferably between 1.5:1 and 4.5:1, most preferably between 2:1 and 4:1 of cementitious material to pozzolan mixture by weight of cementitious material. The properties of the finished product will be different for each of these ratios.

[0077] As it is desired that the cured cement has self-healing properties and absorption of CO.sub.2 occurs even after the slurry is hardened, an excess of the magnesium-iron solid solution silicate is used for these blends.

EXAMPLES

[0078] The invention is further illustrated in the following examples which, however, are not intended to limit the same. Parts, % and ratios relate to parts by weight, % by weight, and weight ratios, respectively, unless otherwise stated.

[0079] Multiple experiments were performed to assess the pozzolanic properties of a mixture of 41.3% olivine, 41.3% MgCO.sub.3.Math.4 H.sub.2O, and 17.3% (reactive) SiO.sub.2 was combined with cement and water. Samples with a cement to pozzolanic mixture ratio of between 2:1 and 4:1 were tested. The k factor, pozzolanic activity factor, was measured.

[0080] The total k factor for the mixture is given by the formula:

[00001]$k^{\mathrm{total}}=\%\mathrm{olivine}*k^{\mathrm{olivine}}+\%{\mathrm{MgCO}}_3{H}_{2}O*k^{\mathrm{MgCO}3.Math.\mathrm{XH}2O}+\%{\mathrm{SiO}}_2*k^{\mathrm{SiO}2}$

[0081] MgCO.sub.3.Math.4 H.sub.2O is assumed to have a k factor of 0 and SiO.sub.2 (amorphous silica) has a k factor of 2. Substitution of these factors into the above equation and solving for the k factor of olivine yields:

[00002]$k^{\mathrm{olivine}}=\left(k^{\mathrm{total}}-0.346\right)/0.413$

[0082] If we assume olivine and hydromagnesite both have a k factor of 0 then k.sup.total should be 0.346. However, in this mixture, the total K factor was measured to be 0.625. This gives a k.sup.olivine=0.675. This surprising result clearly shows that olivine in combination with MgCO.sub.3.Math.X H.sub.2O and SiO.sub.2 behaves synergistically as a pozzolan.