Lithium infused raw fly ash for the production of high strength cementitious products

Abstract

A method of producing high-strength cementitious product from raw fly ash by mixing the raw fly ash with a lithium compound, whereby milling of the raw fly ash to achieve requisite strength is unnecessary. It has now been found that by adding as little as 0.1% of lithium chloride to raw untreated Class C fly ash, one can achieve improved seven-day and twenty-eight-day compressive strength. At the very least, raw lithium treated Class C fly ash may be used at lower total cementitious content per yard of concrete as opposed to Ordinary Portland Cement (OPC) for improved compressive strength.

Claims

1. A method for producing a cementitious product having a greater than Grade 100 slag performance, the method comprising: mixing raw fly ash with a lithium compound to produce the cementitious product, wherein 17.5% or greater of the raw fly ash includes calcium-containing minerals.

2. The method of claim 1, wherein the amount of the lithium compound is between 0.05-0.25% by weight of the raw fly ash.

3. The method of claim 1, wherein the amount of the lithium compound is in excess of 0.1% by weight of the raw fly ash.

4. The method of claim 1, wherein the raw fly ash is designated as Class C fly ash.

5. The method of claim 1, wherein the raw fly ash is Class F fly ash mixed with a fly ash including calcium-containing minerals.

6. The method of claim 5, wherein the fly ash including calcium-containing minerals is 30% by weight of the raw fly ash.

7. The method of claim 1, wherein the calcium-containing minerals include at least one of: an aluminum compound; and Merwinite having a weight concentration of between 8 and 25%.

8. The method of claim 1, wherein the lithium compound is selected from the group consisting of lithium hydroxide, lithium chloride, and lithium carbonate.

9. The method of claim 1, further comprising: mixing the raw fly ash and lithium compound mixture with Ordinary Portland Cement at a ratio of 60% raw fly ash and lithium compound mixture to 40% Ordinary Portland Cement.

10. The method of claim 1, wherein the raw fly ash is Class F fly ash derived from combustion of at least one of lignite and subbituminous coal.

11. The method of claim 10, wherein the Class F fly ash is derived from combustion of both lignite and subbituminous coal and is mixed at a ratio of 40% lignite ash to 60% subbituminous coal ash.

12. The method of claim 1, wherein the cementitious product has a greater than Grade 120 slag performance.

13. A cementitious product having a greater than Grade 100 slag performance, the cementitious product comprising: raw fly ash, wherein 17.5% or greater of the raw fly ash includes calcium-containing minerals; and a lithium compound.

14. The cementitious product of claim 13, wherein the raw fly ash includes either Class C fly ash or Class F fly ash.

15. The cementitious product of claim 13, wherein the raw fly ash includes a blend of Class C fly ash and Class F fly ash.

16. The cementitious product of claim 13, wherein the amount of the lithium compound is between 0.05-0.25% by weight of the raw fly ash.

17. The cementitious product of claim 13, wherein the amount of the lithium compound is in excess of 0.1% by weight of the raw fly ash.

18. The cementitious product of claim 13, wherein the lithium compound is selected from the group consisting of lithium hydroxide, lithium chloride, and lithium carbonate.

19. The cementitious product of claim 13, wherein the raw fly ash is Class F fly ash derived from combustion of at least one of lignite and subbituminous coal.

20. The cementitious product of claim 19, wherein the Class F fly ash is derived from combustion of both lignite and subbituminous coal and is mixed at a ratio of 40% lignite ash to 60% subbituminous coal ash.

21. The cementitious product of claim 13, wherein the calcium-containing minerals include at least one of: an aluminum compound; and Merwinite having a weight concentration of between 8 and 25%.

22. The cementitious product of claim 13, wherein the raw fly ash is Class F fly ash mixed with a fly ash including calcium-containing minerals.

23. The cementitious product of claim 22, wherein the fly ash including calcium-containing minerals is 30% by weight of the raw fly ash.

Description

DETAILED DESCRIPTION

(1) Key to the imparting of strength to raw fly ash is keeping the percentage of the fly ash having calcium-containing minerals between 17.5 and 20% or greater. Class C fly ash, by itself, meets these requirements. If the presence of this fly ash exceeds 20%, there may be problems with ASR. Ordinarily, it is desirable to keep the percentage of calcium below 20% to eliminate ASR problems. However, with the addition of lithium and its proven ASR remediation, high percentages of calcium do not become problematic.

(2) As mentioned above, calcium-rich minerals can exist in fly ash through the presence of Merwinite, and this mineral can react with Lithium to produce varying amounts of reactive amorphous glass. It has been found that most Class C fly ash has Merwinite and, when reacted with lithium compounds with water, appears to convert 35-50% of the Merwinite to a reactive glass. It is believed the net result of the existence of this mineral is that lithium reacts with this mineral in fly ash to activate the raw fly ash to achieve high strength.

(3) As will be discussed, the range of lithium chloride in the fly ash can be from 0.05 to 0.25 wt % of lithium in fly ash.

(4) As to raw Class F fly ash, raw Class F fly ash, for instance, from lignite is not high enough in calcium-rich minerals to be activated by lithium for providing the requisite strength. Thus, Class F fly ash, in general, does not lithium activate because the amount of calcium-rich mineral does not typically exceed 11-13% when the coal being fired is a lignite, bituminous, or anthracite, or combinations of such.

(5) On the other hand, Powder River basin fuel, which is a relatively young coal and comes from Wyoming, has a calcium-rich mineral content of between 22 to 45% when burned. With lignite having no more than about 14% calcium-rich mineral content, when blended, for instance, with subbituminous coal, which has a calcium-rich mineral content considerably higher than other coals, the blending of the Class F fly ash from, for instance, lignite with subbituminous coal at a ratio of, for instance, 40% lignite to 60% subbituminous coal, results in a blended fuel that, when burned, produces a fly ash having a sufficient amount of calcium-rich mineral content to be activated in the raw fly ash to impart the aforementioned strength.

(6) In general, Class F fly ash is defined to have iron, silica, and aluminum above 70% by weight, whereas if these elements are less than 70%, one has a Class C fly ash.

(7) Thus, while the subject invention is described in terms of treating raw Class C fly ash with lithium chloride or other lithium compound, it is possible to create a blended mixture of Class C and Class F fly ash to achieve the strengths associated with the Class C fly ash. Moreover, in some cases, at certain power stations, just the blending of Powder River Basin coal with other coal before it is pulverized and then burned in the boiler may create a hybrid ash that, in itself, is reactive to lithium while being defined as a Class F fly ash.

(8) The amount of lithium compound, be it lithium hydroxide, lithium fluoride, or lithium carbonate, is on the order of 0.1% to 0.2%. More than 0.2% of a lithium additive can make the process more expensive such that the practical limit for the amount of lithium compound is less than 0.2% by weight of fly ash. As mentioned hereinabove, raw fly ash from the Powder River basin fuel comes from a relatively young coal, generally available in Wyoming, which has a calcium-rich mineral content of between 22 and 45%. The Powder River basin coal may be subbituminous coal which has a greater percentage of calcium-rich mineral content than is found in all other coals. Thus, Powder River basin fuel fly ash can be mixed with raw Class F fly ash and lithium added to provide the required strength.

(9) Note that fly ash need not come from coal-fired boilers; it can come from industrial boilers or similar coal-fired boilers. The fly ash in question can come from any source in which the minerals are milled down and end up in the mineral matter that the coal becomes once it is burned, with some burned pieces agglomerated at 2,500 F. or higher into raw fly ash. In short, while pure raw Class F fly ash from lignite coal is not high enough in calcium-rich mineral content, blends with raw Class C fly ashes can result in a total calcium-rich mineral content measured as CaO content exceeding 17.5% that results in sufficient strength for the raw fly ash blend. Moreover, because of the use of lithium and its ASR remediation, the amount of Class C fly ash is somewhat unrestricted.

(10) While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended Claims.