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 for improved compressive strength.

Claims

1. A method for producing high strength cementitious products comprising the step of: mixing raw fly ash with a lithium compound to produce a cement having a better than slag 100 performance.

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

3. The method of claim 2 wherein the amount of lithium compound by weight is an excess of 0.1%.

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

5. The method of claim 1 wherein the fly ash is Class F fly ash mixed to between 17.5 and 20% by weight using a of fly ash containing high calcium content containing minerals.

6. The method of claim 1 wherein the raw Class F fly ash is mixed with 30% by weight of fly ash containing high calcium content minerals.

7. The method of claim 5, wherein the high calcium content mineral includes high aluminum compounds found in Calcium aluminate cements.

8. The method of claim 5, wherein the high calcium content material includes Merwinite having a weight concentration of between 8 and 25%.

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

10. The method of claim 1, wherein the mixing of the lithium compound with the raw fly ash results in cementitious material having strengths that exceed 100 slag performance.

11. The method of claim 1, and further including mixing the lithium fly ash mixture to replace 60% of Ordinary Portland Cement for obtaining a minimum of grade 100 slag performance.

12. The method of claim 1, wherein the fly ash is Class F fly ash and wherein the Class F fly ash is mixed with subbituminous coal derived Class C fly ash.

13. The method of claim 12, wherein the Class F fly ash is lignite and wherein the lignite derived fly ash is mixed with subbituminous coal derived fly ash.

14. The method of claim 13, wherein the lignite is mixed with subbituminous coal in a 40%/60% ratio.

15. The method of claim 1, wherein the percent of fly ash having calcium containing minerals is between 17.5 and 20% or greater.

16. The method of claim 1, wherein the mixing of the lithium compound with raw fly ash results in cementitious material having strengths that exceed 120 slag performance.

17. A cementitious product made from raw fly ash mixed with a lithium compound and having a greater than 100 slag performance.

18. The cementitious product of claim 17, wherein the raw fly ash includes Class C fly ash.

19. The cementitious product of claim 17, wherein the raw fly ash includes Class F fly ash.

20. The cementitious product of claim 17, wherein the raw fly ash includes a blend of Class C fly ash and Class F fly ash.

21. The cementitious product of claim 17, wherein the compressive strength exceeds 5000 psi. in 7 days

22. 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.

Description

DETAILED DESCRIPTION

[0021] Key to the imparting of strength to raw fly ash is keeping percent 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.

[0022] 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.

[0023] As will be discussed, the range of lithium chloride in the fly ash can be from 0.05% to 0.25wt % of lithium in fly ash.

[0024] 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.

[0025] 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, when blended for instance with subbituminous coal which has a calcium rich mineral content considerably higher than other coals, then 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 to be activated in the raw fly ash to impart the aforementioned strength.

[0026] In general Class F fly ash is defined to have iron, silica, aluminum above 70% by weight, whereas if these elements are less than 70% one has a Class C fly ash.

[0027] 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 this 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.

[0028] 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 sub bituminous 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.

[0029] 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 2500F 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.

[0030] 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.