CONCRETE COMPOSITIONS AND PROCESSES FOR CONTROLLING ALKALI-SILICA REACTION IN SAME

Abstract: Processes for making concrete stabilized against alkali-silica reactivity (ASR) from alkali containing components. The process includes adding lithium bearing ore treated to release lithium to a fluid concrete mixture comprising cement, aggregate, and water in an amount sufficient to minimize ASR. Concrete stabilized against alkali-silica reactivity (ASR) is also provided.

Description: CONCRETE COMPOSITIONS AND PROCESSES FOR CONTROLLING ALKALI-SILICA REACTION IN SAME Cross-Reference to Related Applications This application is related to commonly owned copending Provisional Application Serial No. 60/003,475, filed September 8, 1995. Field of the Invention This invention relates generally to concrete compositions and processes for controlling alkali- silica reaction in the same, and more particularly to the use of lithium bearing ores as components of concrete. Background of the Invention Concrete is a conglomerate of aggregate (such as gravel, sand, and/or crushed stone) , water, and hydraulic cement (such as portland cement) , as well as other components and/or additives. Concrete is generally fluidic when it is first made, enabling it to be poured or placed into shapes, and then later hardens, and is never again fluidic, in the general sense. Typically, moisture present in normal concrete is basic (that is, has a high pH) . Alkali materials can be supplied by the cement, aggregate, additives, and even from the environment in which the hardened concrete exists (such as salts placed on concrete to melt ice) . Silica compounds are typically found in the aggregate components of concrete. Silica which is present in aggregates used to make concrete and mortars is subject to attack and dissolution by hydroxide ions present in basic solutions. Generally, the higher the pH (i.e., the more basic the solution) , the faster the attack. Different forms of silica show varying degrees of susceptibility to this dissolution. If there is sufficient alkali metal ion also present in this solution (such as sodium or potassium ions) , the alkali metal ions can react with the dissolved silica and form an alkali-silica gel. Under certain conditions, the resultant alkali-silica gel can absorb water and swell. The swelling can exert pressures greater than the tensile strength of the concrete and thus cause the concrete to swell and crack. This process (hydroxide attack of silica, followed by reaction with alkali such as sodium and potassium) is referred to generally in the art as an "alkali-silica reaction" or "ASR" . ASR has caused the failure of concrete structures, although rarely. Further, ASR can weaken the ability of concrete to withstand other forms of attack. For example, concrete that is cracked due to this process can permit a greater degree of saturation and is therefore much more susceptible to damage as a result of "freeze-thaw" cycles. Similarly, cracks in the surfaces of steel reinforced concrete can compromise the ability of the concrete to keep out salts when subjected to de-icers, thus allowing corrosion of the steel it was designed to protect. ASR is a common chemical process in many concretes around the world. As an indication of its importance to the concrete industry, by 1991 over 1,450 research articles had been published on the subject. See S. Diamond, Alkali -aggrega te reactions in concrete ; an annotated bibliography 1939 -1991 , Washington, D.C : National Research Council, Strategic Highway Research Program, SHRP-C/UWP-92-601 :470 (1992) . In 1987, Congress authorized a $150 million, five-year research program to be administered by the National Research Council to study and develop improvements in highway construction materials and construction practices. This program was called the Strategic Highway Research Program (SHRP) . One of the areas addressed by this program was ASR mitigation. Four recommendations resulted from the SHRP research for preventing ASR in concrete. D. Stark, et al . , Eliminating or minimizing alkali -silica reactivi ty, Washington, D.C. :National Research Council, Strategic Highway Research Program, SHRP-C-343 (1993) (the "SHRP report") . One recommendation was the use a low alkali cement, which is defined as a cement with a sodium equivalent of 0.60% or less. The sodium equivalent of a cement is the weight percent of sodium, reported as sodium oxide, plus 0.658 times the weight percent of potassium, reported as potassium oxide. Sodium equivalent (Na 2 O e ) can be represented generally by the formula Na0 2 + 0.658 x K 2 0 = Na 2 O e . While the use of a low alkali cement can have some effectiveness, it is not a guarantee of ASR prevention. Low alkali cement is not always available on a local basis, can have limited availability, and can be more expensive than high alkali cement. Further, if the raw feed for the cement production contains high levels of alkali, then the production of low alkali cement from such feed can generate much greater waste than would otherwise be the case. Generally, "fines" are a waste product of cement production and are normally recirculated into the cement kiln. However, when the raw feed has a high alkali level, the fines must be removed from the process and constitute a waste material. These fines are called cement kiln dust. Still further, using a low alkali cement is no guarantee of ASR control, as the cement is not the sole source of the alkalies in concrete that can contribute to the problem. Alkalies also can be supplied by pozzolans that are either admixed in or part of the blended cement. Alkalies can be supplied by the mix water, admixtures used in the concrete, the aggregate itself, including recycled concrete used as aggregate, and/or deicers applied in snow and ice removal . Another recommendation set forth by the SHRP report is the use a non-reactive aggregate. This, however, is not always possible. There are limited aggregates with no potential for reactivity, since all silica has some potential for reaction and most aggregates contain significant amounts of silica. Recycled concrete when used as aggregate can also be reactive, particularly if it had already had ASR occurring before it was recycled. There are environmental reasons to use recycled glass as aggregate, but this is very reactive material. Also, transporting aggregates over long distances instead of using locally available materials adds significantly to the cost of concrete production. Another recommendation is the use of appropriate levels of a suitable pozzolan. A pozzolan is a siliceous material that can combine with lime and water to harden, similar to a cement with just water. Since the hydration of cement produces lime as a byproduct (resulting in its basic nature) , pozzolans can work well with cements. The pozzolan may be added as a mineral admixture at the time of concrete production, blended with the cement, or interground with the cement during the final production step of cement. The end result is about the same, as neither the cement nor the pozzolan is substantially changed as a result of the blending. However, sources of suitable pozzolans are not always available locally, and the supplies are limited. Also, many pozzolans used for this purpose are waste products, and thus are quite variable in composition. An example is fly ash, which is the end result of coal burned for electric generation. Further, sufficient amounts of the pozzolan must be used, or the protection is short lived, or the ASR can actually be made worse. This is particularly true of pozzolans with significant lime contents, such as many fly ashes. In a cementitious system, the Ca:Si ratio is very important to its stability with regard to ASR. The higher the Ca:Si ratio, the less capable the system is of tying up alkali present, and there is more susceptibility to ASR. A low lime content pozzolan will reduce the ratio and give more protection from increased alkalies. However, a high lime content pozzolan will not give this protection, and further, since pozzolans carry their own alkalies into the system, this can easily make the situation worse. Still another recommendation is the use a lithium-based admixture. Use of lithium was shown to be effective in ASR inhibition in 1951 (see W.J. McCoy and A.G. Caldwell, "New approach to inhibiting alkali- aggregate expansion," J " .Amer. Concrete Institute, 22:693-706 (1951)) . See also Y. Sakaguchi, et al . , "The inhibiting effect of lithium compounds on alkali- silica reaction, " Proceedings , 8th international conference, alkali aggregate reaction, Kyoto, Japan: 229-234 (1989) , and the SHRP report. For example, lithium salts, such as lithium hydroxide monohydrate, have been added to cement at the grinding stage of the cement production. J. Gajda, Development of a cement to inhibi t alkali -silica reactivi ty, Skokie, IL, Portland Cement Association Research and Development Bulletin RD115T (1996) . As with the pozzolan blended cements mentioned above, the net effect is basically the same as if the lithium salt were admixed into the concrete separately at the time the concrete was batched. That is, by adding the lithium salt to the cement at the time of grinding, neither the cement nor the lithium salt is changed during the process. Rather, the lithium salt and cement are merely blended. Despite the effectiveness of cement produced in this manner to mitigate ASR, using relatively pure lithium compounds can result in substantial amounts of the lithium (about 50%, as reported in the SHRP Report) being "locked up" in the hydration products of the early hydration reactions of the cement. A substantial portion of the lithium ions, therefore, is unavailable for use in controlling ASR. This generally happens within the first few days of hydration. Still further, the concentration of hydroxyl ion can increase when lithium salts are admixed into concrete and mortars (see the SHRP Report) . This can make the job of the lithium ion that much more difficult, and requires more lithium than would otherwise be the case. In addition, lithium salts, such as lithium carbonate, lithium nitrate, lithium hydroxide and lithium fluoride, can be expensive relative to other concrete additives. Summary of the Invention The present invention provides a process for producing concrete and mortars which are stabilized against alkali-silica reactivity from alkali containing components. In the invention, lithium bearing ores and ore concentrates are treated to impart lithium release properties thereto and added as a component of concrete. The use of treated lithium bearing ores can mitigate (minimize and/or substantially eliminate) ASR that can occur in the resultant concrete. This is turn can minimize and/or prevent deterioration of concrete from ASR. Lithium is relatively slowly released initially upon addition of the treated lithium bearing ores to a fluidic concrete mixture of cement, aggregate and water. Preferably, the treated lithium bearing ores initially release less than about 10 percent of the available lithium over the course of about 14 days. This can prevent or minimize the ASR mitigating lithium compounds being bound in the hydration compounds, and thus loss of the ASR mitigating component, during cement hydration, which occurs early in the age of concrete. The majority of cement hydration typically occurs within twenty-four hours of initiating the process, and by one month, the bulk of the hydration that the concrete will experience has occurred. Since ASR is generally a relatively slow reaction that can develop over a period of months and even years, releasing lithium slowly after much of the hydration has occurred is a significant advantage. Although lithium is initially slowly released into the concrete, over time, sufficient lithium is released to provide an ASR mitigating effect. Preferably, after about 60 days, about 25 to about 40% of the available lithium is released. This is contrast to the lithium release properties of untreated lithium bearing ores, which, after about 60 days, release essentially no lithium, or lithium salts, which immediately release lithium. Further, lithium-bearing ores include siliceous materials which are pozzolanic by nature. In addition, lithium bearing ores are less expensive than lithium salts (which require extracting and purifying lithium from the ores) . Still further, less lithium is required to inhibit ASR in the resultant concrete than purified forms of lithium because, as discussed above, the lithium is released slowly and after much of cement hydration has occurred. The present invention also includes mineral admixtures, concrete and mortar which include the treated lithium bearing ore as a component. Detailed Description of the Invention Lithium bearing ores and ore concentrates useful in practicing the invention include, but are not limited to, lithium aluminum silicates, such as spodumene (Li 2 0-A1 2 0 3 - 4Si0 2 ) , petalite (Li 2 0-Al 2 0 3 - 8Si0 2 ) , eucryptite (Li 2 0- Al 2 0 3 - 2Si0 2 ) , lithium aluminum phosphate ores, such as amblygonite (LiF-AlP0 4 ) , montrebrasite, lepidolite, lithium-bearing clays, and mixtures thereof. As the skilled artisan will appreciate, the term "lithium bearing ore concentrate" refers to lithium bearing ores which have been treated (beneficiated) to concentrate the lithium bearing mineral. For ease of reference, as used herein the term "lithium bearing ores" refers to both beneficiated and non-beneficiated lithium bearing ores. The lithium bearing ore is treated to impart lithium release properties to the ore when the ore is included as a component of concrete. In contrast, untreated lithium bearing ores do not exhibit lithium release properties, as demonstrated by the examples below. Preferably, the lithium bearing ore is heated to effect a phase change in the structure of the ore, referred to generally in the art as "decrepitating." In this regard, naturally occurring lithium bearing ore generally exists in an "alpha" configuration (for example, "alpha-spodumene" ) . When heated, such ores undergo an irreversible phase change to a "beta" configuration ("beta-spodumene" ) . Lithium bearing ores can be decrepitated by heating the ore at a temperature sufficient and for a time sufficient to produce the phase change, for example, for spodumene, at a temperature of at least about 900°C, preferably at least about 1000°C, for at least about an hour, or longer. As the skilled artisan will appreciate, the lithium bearing ore can be decrepitated at varying temperatures and times, depending upon factors such as elements present in the ore other than lithium, the crystalline structure of the ore, and the like, and such conditions can be readily determined by the skilled artisan. Other techniques also can be used to treat the lithium bearing ore to impart lithium release properties thereto. The inventors have found that addition of treated lithium bearing ore to a fluid concrete mixture or composition can result in the slow release of lithium into the concrete over time. Preferably, the treated lithium bearing ores initially release less than about 10 percent of the available lithium (total amount of lithium present in the ore) over the course of about 14 days. However, although lithium is initially slowly released into the concrete, over time, sufficient lithium is released to provide an ASR mitigating effect. Preferably, after about 60 days, about 25% to about 40% of the available lithium is released. The treated lithium bearing ores are added to the concrete mixture in an amount effective to mitigate the detrimental effects of ASR. Preferably, lithium bearing ores are added to a concrete mixture in an amount between about 0.1% to about 60%, more preferably about 1% to about 40%, and most preferably about 5% to about 25%, by weight, based on the dry weight of the cement component of the concrete. Stated differently, the treated lithium bearing ores are added to the concrete mixture in an amount sufficient to provide molar ratios of lithium to sodium equivalent (Na 2 O e = Na0 2 + 0.658 x K 2 0) of about 0.01:1 to about 10:1 in the concrete mixture, preferably about 1:10 to about 5:1, and more preferably about 0.5:1 to about 2:1. The concrete compositions of the invention generally include cement, aggregate, water and treated lithium bearing ores. As used herein, the term "cement" refers to, but is not limited to, hydraulic and alite cements, such as Portland cement; blended cements, such as Portland cement blended with fly ash, blast-furnace slag, pozzolans, and the like, and mixtures thereof; masonry cement; oil well cement; natural cement; alumina cement; expansive cements, and the like, and mixtures thereof. The cement is present in the fluid concrete mixture in an amount between about 5% to about 20% by weight based on the total weight of the concrete mixture. Aggregates can include, but are not limited to natural and crushed quarried aggregate, sand, recycled concrete aggregate, glass, and the like, as well as mixtures thereof. Aggregate is present in the fluid concrete mixture in an amount between about 75% to about 95% by weight, based on the total weight of the concrete mixture. The fluid concrete mixture also includes water, in an amount ranging from about 2% to about 10% by weight based on the total weight of the mixture. The fluid concrete mixture also can include other materials as known in the art for imparting various properties to concrete, including, but not limited to, air-entraining admixtures, water reducing admixtures, accelerating admixtures, pozzolans, such as, but not limited to, fly ash, metakaolin, and silica fume, and the like. These agents can be present in conventional amounts . Although reference has been made to the components of concrete, it will be appreciated that the present invention also includes mortar compositions, which generally are similar in composition to concrete, except that mortar is typically made with sand as the sole aggregate, in contrast to concrete which includeε larger aggregates. Sand in this sense is aggregate of about 3/8" and smaller in diameter. Still further, although the process of making concrete has been described above with regard to the addition of treated lithium bearing ores to a fluid concrete mixture, the present invention also provides for the addition of such treated lithium bearing ores to cement, which is in turn mixed with other suitable components to form concrete. The treated lithium bearing ores can be added to the cement for example by blending or intergrinding the treated ore with cement . The present invention will be further illustrated by the following non-limiting examples. Example 1 To simulate what happens inside the pore solution in concrete, spodumene ore concentrate and decrepitated spodumene ore concentrate were placed in a simulated concrete pore solution at room temperature and samples analyzed for lithium for two months. The simulated pore solution was as follows (weight %) : 0.2% Ca(OH) 2 , 1.0% NaOH, 2.45% KOH, and 96.35% deionized water. The following table gives the results in ppm lithium: Days Ore Concentrate Decrepitated Ore Concentrate 1 0.05 0.70 4 0.11 1.30 7 0.08 2.17 14 0.11 3.35 60 0.40 18.0 As can be seen from the table, about fifty times as much lithium was available from the decrepitated spodumene as from the untreated concentrate. The amounts used in the experiment were ten grams each of the untreated ore concentrate and the decrepitated material placed in four liters of solution. Both samples included 5% Li 2 0 by weight (about 58 ppm total lithium available, if all of the lithium were released) . At the end of two months, about one third of the lithium from the decrepitated material had been released, whereas less than one percent of the lithium from the untreated ore concentrate was released. Example 2 To demonstrate the release of lithium ion from these treated ores in cementitious systems, pastes with low and high alkali cement and 5% and 10% decrepitated spodumene ore concentrate were made and the pore solutions extracted over time and analyzed for lithium. For the high alkali case (results are molarity of lithium) : Age Control 5% 10% 1 0 0.005 0.005 30 0 0.022 0.039 90 0 0.050 0.092 And for the low alkali case: Age Control 5% 10% 1 0 0.004 0 . 004 30 0 0.012 0 . 024 90 0 0.045 0 . 086 In both cases, at all ages, the hydroxyl ion was near the original, but slightly less. Thus it was demonstrated that not only was there a slow but significant release, but that there was no extra demand placed on the system by an increase in pH, as would be the case for lithium salts tested under the SHRP program. .Example 3 As an example of more direct demonstration of the ability of the material to control ASR in concrete, concrete prisms were made according to Canadian Standards Association (CSA) A23.2-14A standard for alkali aggregate reactivity testing. Results for two highly reactive materials are given below. The first one from a quarry in New Mexico, "NM, " is a reactive aggregate containing andesites and rhyollites, and has demonstrated severe reactivity even with low alkali cements. The second one from a quarry in Ontario, "SP, " is a limestone with cherty inclusions, and also has an extensive and well documented history of severe reactions in the field. Results (% linear expansions) are shown for controls and for 10% replacement of the cement with decrepitated spodumene ore concentrate: Age NM SP (weeks) Control NM 10% Control SP 10% 0 0 0 0 0 4 0.05 0.03 0.01 0 8 0.11 0.04 0.04 0.01 13 0.15 0.05 0.10 0.02 18 0.18 0.07 0.13 0.02 26 0.20 0.08 0.16 0.03 Significant reductions with highly reactive aggregates are thus demonstrated; greater dosages yield greater control of the ASR. U.S. Patent No. 3,331,695 reports intergrinding spodumene with a portland cement to produce a cement that has accelerated strength gain. The pozzalonic effect reported in the ' 695 patent is believed to result from siliceous materials which are present in spodumene (about 60% silica) , which are known it the art to be pozzolonic in nature. Little lithium is released by this type of usage, and thus does not contribute to the pozzolonic effect. JP 62278151 reports reducing ASR by admixing lithium ores into concrete. Again, however, the effect is due to the pozzolanic nature of the material, not to its lithium release. Neither U.S. Patent No. 3,331,695 nor JP 62278151 teach or recognize the importance of the delayed release of lithium into concrete systems with regard to ASR inhibition. As the above examples demonstrate, essentially none of the lithium from untreated ores is actually released into the concrete. Accordingly, the process of JP 62278151 is a pozzolanic effect, which is second in effectiveness to a true lithium based control. More than an order of magnitude more lithium can be made to release by treatments such as decrepitation. The foregoing examples are illustrative of the present invention and are not to be construed as limiting thereof.

Claims: THAT WHICH IS CLAIMED IS: 1. A process for making concrete stabilized against alkali-silica reactivity (ASR) from alkali containing components, the process comprising adding lithium bearing ore treated to release lithium to a fluid concrete mixture comprising cement, aggregate, and water in an amount sufficient to minimize ASR. 2. The process of Claim 1, wherein said lithium bearing ore is decrepitated lithium bearing ore. 3. The process of Claim 1, wherein said lithium bearing ore is selected from the group consisting of spodumene, petalite, eucryptite, amblygonite, montrebrasite, lepidolite, lithium-bearing clays, and mixtures thereof. 4. The process of Claim 1, further comprising prior to said adding step the step of heating lithium bearing ore under conditions sufficient to impart lithium release properties thereto. 5. The process of Claim 4, wherein said heating step comprises heating lithium bearing ore under conditions sufficient to effect a phase change in the structure of the ore. 6. The process of Claim 4, wherein said heating step comprises heating lithium bearing ore at a temperature of at least about 900°C for at least about an hour. 7. The process of Claim 1, wherein said adding step comprises adding lithium bearing ore to the fluid concrete composition in an amount between about 0.1% to about 60% by weight based on the dry weight of the cement . 8. The process of Claim 1, wherein said adding step comprises adding lithium bearing ore to the fluid concrete composition in an amount between about 1% to about 40% by weight based on the dry weight of the cement . 9. The process of Claim 1, wherein said adding step comprises adding lithium bearing ore to the fluid concrete composition in an amount between about 5% to about 25% by weight based on the dry weight of the cement . 10. The process of Claim 1, wherein the treated lithium bearing ore releases less than about 10 percent of lithium present in the ore after about 14 days . 11. The process of Claim 1, wherein the treated lithium bearing ore releases at least about 25% of lithium present in the ore after about 60 days. 12. A process for making concrete stabilized against alkali-silica reactivity (ASR) from alkali containing components, the process comprising adding decrepitated spodumene to a fluid concrete mixture comprising cement, aggregate, and water. 13. The process of Claim 12, further comprising prior to said adding step the step of heating naturally occurring spodumene at a temperature of at least about 900°C for at least about an hour. 14. The process of Claim 12, wherein said adding step comprises adding decrepitated spodumene to the fluid concrete composition in an amount between about 0.1% to about 60% by weight based on the dry weight of the cement . 15. A process for making concrete stabilized against alkali-silica reactivity (ASR) from alkali containing components, the process comprising adding cement comprising lithium bearing ore treated to release lithium to a fluid concrete mixture comprising aggregate and water in an amount sufficient to minimize ASR. 16. The process of Claim 15, further comprising prior to said adding step the step of blending or intergrinding cement with treated lithium bearing ore. 17. The process of Claim 16, further comprising prior to said blending or intergrinding step the step of heating lithium bearing ore under conditions sufficient to impart lithium release properties thereto. 18. The process of Claim 17, wherein said heating step comprises heating the lithium bearing ore at a temperature of at least about 900°C for at least about an hour. 19. Concrete prepared according to the process of Claim 1. 20. Concrete prepared according to the process of Claim 12. 21. Concrete prepared according to the process of Claim 15. 22. Concrete comprising cement, aggregate, and lithium bearing ore treated to release lithium to a fluid concrete mixture in an amount sufficient to minimize alkali-silica reactivity (ASR) from alkali containing components thereof . 23. The concrete of Claim 22, wherein said lithium bearing ore is decrepitated lithium bearing ore. 24. The concrete of Claim 22, wherein said lithium bearing ore is selected from the group consisting of spodumene, petalite, eucryptite, amblygonite, montrebrasite, lepidolite, lithium-bearing clays, and mixtures thereof. 25. The concrete of Claim 22, wherein said lithium bearing ore is decrepitated spodumene. 26. The concrete of Claim 22, wherein said treated lithium bearing ore is present in an amount between about 0.1% to about 60% by weight. 27. The concrete of Claim 22, wherein said treated lithium bearing ore is present in an amount between about 1% to about 40% by weight. 28. The concrete of Claim 22, wherein said treated lithium bearing ore is present in an amount between about 5% to about 25% by weight. 29. Concrete comprising cement, aggregate, and decrepitated spodumene in an amount sufficient to minimize alkali-silica reactivity (ASR) from alkali containing components thereof. 30. A mineral admixture for making concrete stabilized against alkali-silica reactivity (ASR) from alkali containing components, comprising lithium bearing ore treated to release lithium to a fluid concrete mixture comprising cement, aggregate, and water.

Inventors: FOLTZ GARY E, MANISSERO CLAUDIO E, STOKES DAVID B, FOLTZ, GARY, E., MANISSERO, CLAUDIO, E., STOKES, DAVID, B.
Applicants: FMC CORP, FMC CORPORATION
Application year: 1996
Main classification: C04B14
IPC codes: C04B14, C04B28