MXPA97008237A - Method to increase the regime of gain of resistance to compression in hard mixes containing ash vola - Google Patents

Abstract

The present invention relates to concrete, mortar and hardenable mixtures comprising cement and volatile ash for use in construction, the invention provides a method for increasing the resistance gain rate of a hardened mixture containing volatile ash by exposing the volatile ash to an aqueous paste of calcium oxide (lime) before its incorporation into the hardenable mixture, the invention further relates to curable mixtures, v. gr. concrete and mortar containing volatile ash that has previously reacted calcium oxide, in particular volatile ash is added to the calcium oxide paste, the hardenable mixture can be concrete mortar, in a specific embodiment, the mortar containing volatile ash treated by exposure to an aqueous lime paste is prepared and tested for compressive strength at earlier time points

Description

METHOD TO INCREASE THE GAIN OF RESISTANCE TO COMPRESSION IN ENDURECBLE MIXTURES CONTAINING ASHES VOLATILE The investigation that led to the present invention was carried out with governmental support, under contract No. DE-FG22--90PC90299, granted by the Department of Energy. The government has certain rights over this invention ..

FIELD OF THE INVENTION The present invention relates to concrete, mortar and other hardening mixtures comprising cement and fly ash, for use in construction. The invention provides a method to increase the rate of resistance gain in a hardened mixture containing fly ash, by exposing the fly ash to a suspension of calcium oxide or other suspension of alkaline material, before its incorporation into the mixture. The invention further relates to said hardened mixtures, for example concrete and mortar, containing fly ash, previously reacted with an alkaline material, for example, a suspension of calcium oxide (lime).

BACKGROUND OF THE INVENTION Fly ash, a byproduct of a coal-burning plant, is produced worldwide in large quantities, every year. In 1988, approximately 84 million tons of coal ash were produced in the United States in the form of fly ash (60.7%), bottom ash (16.7%), boiler slag (5.9%) and combustion gas desulfurization ( 16.7%) (Tyson, 1990, Coal Cornóustion By-Product utilization Seminar, Pittsboro, 15 pages). Of the approximately 50 million tons of fly ash generated each year, only about 10 percent is used in concrete (ACI Corn itee 226, 1987, Use of Fly Ash In Concrete, ACI 226.3R-87, ACI 3. Proceedings 84 : 381-409), while the remaining portion is disposed primarily as a waste in landfills. It is usually more expensive for an installation to sell its ash, even at an exorbitant price, than to dispose of it in a landfill, since this will avoid the cost of discarding it. In the 1960s and 1970s the cost of disposing of the ash was typically less than one dollar per ton. However, due to the stricter environmental regulations, which began in the late 1970s, the cost of disposing of the ash has risen rapidly to $ 2 to $ 5 per ton, and is still rising (Bahor and Golden, 1984, Proceedings , 2nd International Conference on Technology and Marketing of Ash, London, pages 133-136). The lack of landfill due to environmental concerns has further escalated the cost of disposal. The United States Environmental Protection Agency (EPA) estimated in 1987 that the total cost of disposing of waste in coal-fired thermoelectric plants ranged from 11.00 to 20.00 dollars per ton of fly ash and bottom ash (Courst, 1991, Proceedmgs: 9th International Symposium on the use of ash, 1: 21-1 to 21-10). This increasing trend in the cost of discarding has caused many concerns and researchers are urgently looking for ways to improve the use of fly ash. A potential outlet for fly ash is its incorporation into concrete or mortar mixtures. Fly ash is used in concrete in two different ways: one, as a replacement for the cement and the other as a load. The first use takes advantage of the pozzolana properties of fly ash that. when it reacts with lime or with calcium hydroxide, it can increase the strength of the cementitious compositions. However, fly ash is relatively inert and the increase in compressive strength can take up to 90 days to materialize. In addition, since fly ash is simply a byproduct of the electrical industry, the quality of fly ash has always been a major concern for end users in the concrete industry.

The incorporation of fly ash in the concrete improves the working capacity and thus reduces the water requirement with respect to conventional concrete. This is extremely beneficial when the concrete is pumped into place. Among the numerous other beneficial effects are reduced exudation, reduced segregation, reduced permeability, increased plasticity, decreased heat of hydration and increased setting times (ACI Cornnitee 226, 1987, supra). Settlement is greater when flying ash is used (Ukita and coauthors, 1989, P-114, American Concrete Institute, Detroit, pp. 219-240). However, the use of fly ash in particular has many drawbacks. For example, the addition of fly ash to concrete results in a product with low air entrainment and early development of early resistance.

As noted before, a critical drawback of the use of fly ash in concrete is that essentially fly ash significantly reduces the compressive strength of concrete. The tests carried out by Ravindrarajah and Tarn (1989, Fly Ash, Silica Fume, Slag and Natural Pozzolans m Concrete, SP-114, American Concrete Institute, Detroit, pp. 139-155) showed that the compressive strength of fly ash concrete, at younger ages, is lower than that of control concrete, which is a general property of concrete or mortar when flying ash is added. Most reported studies tend to show less concrete strength, due to the presence of fly ash; However, no one has suggested a solution to actually increase the property of the concrete in an economical way. However, for fly ash to be used as a replacement for cement, it must be used for cement in terms of resistance to a useful point in construction. As a practical matter, this means that the concrete with fly ash must reach an acceptable compressive strength in about two weeks. Swarny (1984, Proceedmgs, 2nd International Conference on Technology and Marketing of Ash, London, pp. 359-367) showed that a 30% by weight replacement, and the inclusion of a high dose of a superplasticizer, produced concrete with material properties and structural behavior almost identical to those of concrete of similar strength, without fly ash. However, due to the high cost of the superplasticizer, the proportions of the mixture were not economical. U.S. Patent No. 3,852,084 refers to a cement composition containing a mixture of fly ash. The lime and a portion of the fly ash in the mixture are mechanically treated to reduce the particle size and increase the total reactivity. The described activation process is a dry process that uses only a portion of the fly ash component of the overall composition. U.S. Patent 2,564,690 to Havelm refers to the use of fly ash and hydrated lime, which is a powder obtained from quick lime, treated with sufficient water to produce a greater state of hydration of lime, ash as cement in mortar for lime and ridge . The combination of fly ash and hydrated lime is described to obtain a higher early compression strength compared to hydrated lime cement, without fly ash. U.S. Patent 4,877,453, to Loggers, refers to a process for increasing the pozzolania properties of a pozzolan material, such as fly ash, by mixing the fly ash with lime and water and heating the mixture, which results in a greater degree of resistance after hardening. US Patent 2,803,556 to Carlsson relates to the grinding of fly ash, lime and cement, so that 95% passes through a screen having an operating size of 0.063 mm. It is critically important in the construction to have concrete or mortar that obtains in a predictable way the required functional characteristics, for example, a minimum resistance to compression in the term of 14 days. However, prior art concrete or mortar mixtures containing fly ash and cement generally have lower compressive strength than concrete or mortar mixtures lacking fly ash. Consequently, there has been a lack of incentives in the use of fly ash in such hardened mixtures. Accordingly, there is a need in the art for a method for increasing the early rate of gain in the compressive strength of hardenable fly ash containing mixtures. There is a further need in the art for such hardenable mixtures that demonstrate an early rate of gain in compressive strength. There is additionally another need in the art, for the use of fly ash generated during coal combustion. The citation or identification of any reference in this application should not be construed as the admission that said reference is available as a prior art for the present invention.

BRIEF DESCRIPTION OF THE INVENTION It has now been discovered that the rate of gain in strength of a toughened mixture comprising fly ash can be increased. Accordingly, the invention provides a method for increasing the early rate of gain in the compressive strength of a hardened mixture containing fly ash, which comprises exposing the fly ash to an aqueous suspension of alkaline material, for example, calcium oxide ( CaO), before adding the mud to cement or other components of the hardening mixture. In particular, the fly ash is added to a suspension of calcium oxide in water, before incorporating the fly ash into a hardened mixture. The present invention also relates to said hardened mixtures comprising cement and a preformed suspension of fly ash, alkaline material, such as calcium oxide and water; wherein the fly ash and the alkaline material together are approximately 5% to 60%, preferably from 10% to 50%, approximately, and better still, about 30%, by weight of the cement materials present in the hardened mixture; and the cement is about 95% to 40% by weight of the cement materials present in the hardening mixture; and wherein the percentage of alkaline material, by weight of the alkaline material and the fly ash, varies from 5% to 50%, approximately. In a specific modality, the hardening mixture is concrete; in another specific modality, the hardened mixture is mortar. Preferably the alkaline material is calcium oxide. The invention additionally takes advantage of a recent discouragement made by the inventors here not in use, in particular that the compressive strength of a hardened mixture containing fly ash can be predicted reliably by measuring the fineness modulus of the fly ash. In addition, hardened mixtures containing fly ash demonstrate a significantly higher compressive strength, compared to those mixtures lacking fly ash, when using a fly ash fraction having a fine particle size distribution, ie , diameter smaller. This invention is the subject of the pending United States patent application, by the same successor, Serial No. 08 / 246,875, filed May 20, 1994, by the inventors mentioned herein, and entitled Improved Compressive Strength Concrete And Mortar Containing Fly Ash (Concrete and mortar of improved compressive strength, containing fly ash), which is incorporated here as a reference in its entirety. Thus, the invention relates to a method for increasing the early rate of gain in the compressive strength of said mixtures, which comprises exposing fractionated fly ash, which has a modulus of fineness of less than 600, to calcium oxide. , before incorporating the fly ash into a hardenable mixture; where the fineness modulus is calculated as the sum of the fly ash percentage retained in sieves of 0, 1, 1.5, 2, 3, 5, 10, 20, 45, 75, 140 and 300 microns. Preferably the fly ash is wet, boiler bottom fly ash, which has a fineness modulus of less than about 350, when calculated as stated above. The invention further relates to curable compositions comprising fractionated fly ash that has been treated by exposure to a lime slurry, prior to its incorporation into a hardenable mixture. It is a first object of the present invention to provide a method for increasing the rate or early rate of gain in the compressive strength of a hardenable mixture comprising fly ash. It is another object of the invention to provide hardenable mixtures characterized in that they have fly ash which has been treated by exposing it to a suspension of lime or to another suspension of alkaline material. Yet another objective of the present invention is to provide hardenable mixtures having highly increased functional characteristics of early and late compressive strength, using finer fractions of fractionated fly ash, in the method and composition of this invention. These and other objects of the present invention will become more apparent by reference to the following figures and the detailed description of the invention that is attached.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 presents graphs showing the particle size distribution of fractionated fly ash and cement particles (inverted triangles, 98% of which have a diameter of 75 μr or less). (A) dry boiler bottom fly ash (filled square, where 92% of the particles have a diameter of 75 μm or less) and fractions 1C (filled triangle, 95% less than 150 μm); 11F (filled diamond, 96% less than 30 μrn), 10F (blank box, 94% less than 20 μm); 6F (blank diamond, 99% less than 15 μm), 5F (X, 98% less than 10 μm) and 3F (blank triangle, 90% less than 5 μm). (B) Wet boiler bottom fly ash (white square, 95% less than 75 μm), and fractions 18C (blank triangle, 90.2% less than 75 μm), 18F (X, 100% less than 30 μm) , 16F (blank diamond, 99% lower than 20μm), 15F (99% less than 15μ), 14F, (filled diamond, 100% less than 10μrn) and 13F (filled square, 93% less than 5μ ). The fly ash from dry or wet bottom boilers was collected and fractionated into six fractions of different size distribution, as described in the examples that follow.

DETAILED DESCRIPTION As described above, the present invention relates to a method for increasing the early rate of gain in the compressive strength of hardenable mixtures comprising fly ash. The method comprises exposing the fly ash to an aqueous suspension of alkaline material, such as calcium oxide (CaO), before mixing the fly ash alkaline suspension with other components of the hardenable mixture. The term "lime" means CaO powder. The invention further relates to curable mixtures comprising fly ash which has been treated by exposure to aqueous alkaline material, for example, lime, as a replacement of the cement in the cementitious materials; hardenable mixtures that obtain an early compressive strength that is approximately equal to or greater than the compressive strength of similar hardenable mixtures that do not contain aqueous lime in place of the cementitious materials. Preferably, the fly ash is fractionated fly ash, of a defined fineness modulus, as defined below. In the preferred embodiment, a first step in the method of the invention is to prepare a suspension by mixing calcium oxide (CaO) powder in water for at least about 2 to 10 minutes. In the preferred embodiment, a second step consists of adding fly ash to the suspension of calcium oxide (CaO) in water, forming a fly ash suspension-CaO, where the calcium oxide contains the fly ash. Preferably, the fly ash-CaO suspension is allowed to react for about 2 to 10 minutes, before adding other materials. A third step is to mix the fly ash suspension ~ CaO-water with cement, fine aggregate and any other materials of a hardenable mixture, such as concrete or mortar. The percentage of fly ash-CaO is around 5% to 60% of the cement materials of the hardened mixture. The percentage of calcium oxide present in the hardenable mixture is about 5% to 50% of the amount of fly ash in the hardenable mixture, by weight. As noted above, the fly ash and calcium oxide, together, constitute about 5% to 60% by dry weight of the cement materials in the hardened mixture. That is, those proportions exclude the water in the suspension. Preferably the fly ash and the CaO together are approximately 10% to 50% of the cement materials present in the hardened mixture. In a preferred embodiment, fly ash and calcium oxide together are about 30% of the cement materials present in the hardened mixture. As a result, cement, for example, portland cement, it is approximately 95% to 40% by weight of the cement materials present in the hardening mixture. As used herein, the term "about" or "about", in reference to an amount of material present in the mixture, means that proportion of a component of the mixture, within an error scale that is acceptable to or common practices in an industry that uses such hardened mixtures. In the absence of such a standard, the term "approximately" or "around" should be considered to mean ± 20% of the indicated amount of material; preferably, the variation indicated by the said term is about ± 10% of the amount of material indicated. In particular embodiments, the hardenable mixture may be concrete or mortar, as defined below. Throughout this description, when specific relationships, percentages or proportions are mentioned, they are determined by weight and not by volume. The present invention is based, in part, on the observation that, regardless of the source and chemical composition of the fly ash, pretreatment of the fly ash by sure to an aqueous suspension of CaO increases the early rate of gain in the compressive strength of the hardened mixture containing the fly ash. The "early rate of gain in compressive strength" is the rate of increase in compressive strength with respect to the first seven to fourteen days of healing. If it is not intended to follow any particular theory or particular hypothesis, it is believed that this prior treatment produces a chemically distinct form of fly ash. The fly ash treated by sure to a lime slurry exhibits increased pozzolanic properties compared to untreated fly ash, when detected by the increased early rate of gain in the compressive strength of hardened mixtures containing treated fly ash. This modification of the early rate of gain in compressive strength is evidenced by the fact that the treated fly ash is chemically distinct from the untreated fly ash. As used herein, the term "fly ash" refers to a solid material having a chemical composition similar to or equal to the composition of the material that is produced during coal dust commotion. In a specific aspect, the solid material is the material that remains after combustion of the hard coal. The ACI Commitee 166 (1990, ACI 116-85, ACI Manual of Concrete Practice, Part I, American Concrete Institute, Detroit, defines fly ash as "the finely divided residue resulting from the commotion of ground or pulverized coal, which is transported from the cornóustión chamber, by means of the comóustión gases ", and the term" flying ash ", as it is used here, implies that definition In general, the flying ash derived from diverse coals has differences in the chemical composition , but the main components of fly ash are: Si? 2 (25% to 60%, AI2O3 (10% to 30%) and Fe2? 3 (5% to 25%). The MgO content of the fly ash generally Thus, the term fly ash generally refers to solid powders comprising approximately 25% to 60% of silica, approximately 10% to 30% of AI2O3, of 5% a 25%, approximately, of Fß2? 3, from 0% to around 20% CaO and from 0% to 5%, approximately, of MgO. The term "fly ash" additionally contemplates synthetic fly ash, which can be prepared so that it has the same functional characteristics as the fly ash described herein. Fly ash is currently classified primarily into two groups: Class C and Class F, in accordance with ASTM C 618 (1990, ASTM C 618-89a, Annual Book of ASTM Standards, volume 04.02). Class F is generally produced by burning anthracite or hard coal; and class C is the result of sudorituminous or lignite coal. In general, fly ash from the combustion of sulfur-containing ash contains more CaO and less Fß2 ?3 than flying ash from gray coal (Berry and Malhotra, 1980, ACI 3. Proceedings 77: 59-73). Thus, the CaO content of fly ash class C is usually greater than 10%, the sum of the oxides SIO2, AI2O3 and Fß2? 3 being not less than 50%. For fly ash of class F, the CaO content is normally less than 10% and the sum of the aforementioned oxides is not less than 70%. The vitreous phase of the fly ash depends essentially on the conditions of combustion and the type of boiler. Non-fractionated fly ash, supplied from different boilers, such as dry bottom boilers or .1.7 boilers with a humid bottom, has been found with a different behavior. Boilers that reach higher temperatures produce fly ash with a vitreous phase that is more developed or pronounced. Alternatively, the combustion in the presence of a fluxing agent, which reduces the melting temperature of the fly ash, may increase the vitreous phase of the fly ash produced by combustion for lower temperature boilers. The compressive strength of a hardened mixture containing fly ash may depend, in part, on the vitreous phase of the fly ash, so that generally the fly ash produced for higher temperature boilers, or produced in the presence of a fluxing agent, or oas, may be preferred. However, as demonstrated herein, the fineness modulus is the most important parameter for the compressive strength after the early healing period, ie, until day 7, and the fly ash, in particular the ash Fractionated flywheel having a defined fineness modulus, coming from any source, can be used according to the invention. Although fly ash generally arrives in a dry and finely divided form, in many cases, due to weather conditions and transportation processes, fly ash is wet and often forms lumps. Said flying ash may be less reactive. Pozzolan (or pozolana), as defined by ASTM C 593 (1990, ASTM C 593-89, Annual Book of ASTM Standards, lathe 04.02) is "a siliceous or alumino-silicon material that possesses little or no value by itself cementitious, but which, in a finely divided form and in the presence of moisture, will react chemically with alkaline and alkaline earthy hydroxides at ordinary temperatures to form or help form compounds that have cementitious properties ". In a preferred aspect, the present invention relates to the determination of the fineness modulus of the fractionated fly ash. As used herein, the term "fineness modulus" refers to a measure of the distribution of the flying ash particle volumes, or to the particle size distribution of the fly ash. In accordance with the present invention, the fineness module is a distribution analysis that is much more informative than a determination of average or average particle diameter, or the determination of the total surface area. The value of the fineness modulus corresponds to the fineness of a flying ash fraction or unfractionated fly ash. Thus, a fraction of the fly ash containing a distribution of smaller sized particles, for example, a mean diameter that falls within a smaller scale setting, will have a fineness modulus value that is lower than a fraction of fly ash containing a distribution of particles that have a larger size, eg, a mean diameter that is within a larger scale setting, or unfractionated fly ash. In accordance with the present invention, lower values of fineness modulus are preferred, since hardened mixtures containing fractions having a lower fineness modulus, ooten more quickly gains in compressive strength. In another embodiment, higher values of fineness modulus may be preferred, when a lower rate of gain in compressive strength may be desired. It should be noted that the invention includes inverse values of fineness module, obtained by turning the reciprocal or the residue after subtracting a greater number of the fineness module, as discussed above. Such inverse values, of course, will have an inverse relationship between the "modulus of fineness" and the scale of particle sizes. Thus, the present invention is directed, in part, to the use of fractionated fly ash, wherein the fly ash particles in any given fraction, have a more uniform distribution of volumes or sizes, than in the unfractionated fly ash. Preferably, the fineness modulus is determined as the sum of the fly ash percentage remaining in each of a series of sieves of different sizes. Consequently, the term "fineness module" refers to a relative value, which may vary depending on the selected series of screens. Since, in accordance with the present invention, fly ash particles of smaller size or diameter are preferred for use in hardenable mixtures, fine determinations of the fineness modulus are available if a series of smaller sieves are selected. Preferably, the size of the sieves is predominantly less than 10 μm, for example, the sieves may be 0.5, 1, 2, 3, 4, 5, 6, 7, 8 and 10 microns, the sieves being useful They vary up to 300 microns. The number of sieves of the size of 10 microns or less must be at least one more than the number of sieves with sizes of more than 10 microns. In a preferred embodiment, the number of sieves with size of 10 microns or less is therefore five. While dry sieves are used in a specific mode to calculate a value for the fineness modulus, other methods, such as wet sieving, can also be used. The greater the number of sieves of size of 10 microns or less, the greater the absolute value of the fineness module. Consequently, when sieves of 0.5, 1, 2, 3, 4, 5, 6, 7, 8 and 10 microns are used, the fineness module will be an absolute greater number, which reflects the greater degree of precision of the determination of that value for fly ash particles of smaller diameter or smaller size. The pozzolanic reaction of the fly ash in a hardenable mixture comprising cement is the reaction between the constituents of the fly ash and the calcium hydroxide. It is generally assumed that it takes place on the surface of the flying ash particles, between the silicates and aluminates of the vitreous phase of the fly ash and the hydroxide ion present in the pore solution (Plo man, 1984, Proceedinge, 2nd Conference International on Technology and Marketing of Ash, London, pages 437-443). However, the result of the investigation that led to the present invention indicates that the pozzolanic reactions of the ash depend on the volume of the fly ash particles: the lower the particle volume, the faster it completes its reaction with the cement to provide the resistance to compression. The solubility regime and the reactivity of these vitreous phases in different types of fly ash depends on the vitreous phase of the fly ash which, in turn, depends on the combustion temperature of the boiler that produced the fly ash and the presence or absence of fluxing reagents during combustion. In addition to the effect of the combustion conditions on the vitreous phase of the fly ash, different fly ash of one kind may behave differently, depending on the content of SiO2, AI2O3 and Fe2Ü3, as well as other factors such as the particle size distribution and storage conditions of the ash (see Aitcin and co-authors, 1986, Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, SP-91, American Concrete Institute, Detroit, pages 91-113; Liskowitz and co-authors, 1983, Sórbate Characteristics of Fly Ash, Final Report, US Department of Energy, Morgantown Energy Technology Center, page 211).

During hydration, portland cement produces an excess of lime (CaO) that is released into the pore spaces. It is the presence of that lime that allows the reaction between the siliceous components of fly ash and calcium hydroxide to form more calcium silicate hydrate (C-S-H). He and coauthors (1984, Cement and Concrete Research, 14: 505-511) demonstrated that the content of crystalline calcium hydroxide in the fly ash-portland cement pastes decreased as a result of the addition of the fly ash; probably as a result of a reaction of calcium with the alumina and silica of the fly ash to form more C-S-H. This procedure stabilizes the concrete, reduces permeability and increases the resistance to attacks by chemical substances. However, the production of lime from cement to react with fly ash in pore spaces occurs relatively slowly, compared to the reaction of lime with portiand cement components. Thus, the present invention provides for the increase in the rate of reactivity of the fly ash, early in the curing process, by pretreating the fly ash with aqueous CaO, ie, with a lime slurry. This allows a faster in early compressive strength, compared to hardenable mixtures containing fly ash that has not been treated by exposure to a lime slurry. While lime (CaO) is the preferred alkaline material for the suspension to treat fly ash, before its incorporation into a hardenable mixture, such as mortar or cement, whoever is ordinarily skilled in the art will recognize that it can be used in place from it other alkaline materials. Among these alternative alkaline materials for the preparation of a suspension are cement kiln dust (which is generally considered as waste material), sodium hydroxide, potassium hydroxide and the like. Therefore, it should be understood that whenever the term CaO is used, any of the alkaline materials mentioned above may be used instead. The fractionation of the fly ash can be achieved by any means known in the art. Preferably the fractionation proceeds with a pneumatic classifier system. In a specific modality, which appears later, a MICRO-SIZER pneumatic classifier system was used to split fly ash into six different particle size scales. In another embodiment, the fly ash can be fractionated by sieving. For example, a sieve of 45 μm or smaller can be used to select particles of a defined maximum size. In another embodiment, the fly ash can be milled to a desired size or fineness. The term "cement", as used herein, refers to a powder comprising alumina, silica, lime, iron oxide and magnesium oxide, burned together in an oven and finely pulverized; which, when mixed with water, agglutinate or bind to other materials present in the mixture, to form a hard mixture. The hardenable mixtures of the invention comprise cement. In general, the term cement refers to hydraulic cements, such as, but not limited to, portland cement, particularly portland cement types I, II, III, IV and V. As used herein, the term " "cementitious materials" or "cementitious materials" refers to the portion of a hardenable mixture that provides bonding or bonding to the other materials present in the mixture and, thus, includes cement and pozzolanic fly ash, treated by exposure to a lime suspension. The pretreated fly ash and CaO present in the suspension may comprise from 5% to 50%, approximately, of the cement materials present in a hardenable mixture of the invention, on the basis of dry weight; preferably, the fly ash-CaO mixture comprises from 10% to 35%, approximately, of the cement materials. The rest of the materials will generally be cement, particularly portland cement. In a specific embodiment, below, the hardenable mixtures of the invention comprise portland type I cement. The term "concrete" refers to a hardenable mixture comprising cement materials, a fine aggregate, such as sand, an aggregate coarse, such as, but not limited to, coarse aggregate of crushed basalt, and water.

The concrete of the invention additionally comprises fly ash treated by exposure to aqueous calcium oxide. In a specific modality, fly ash-CaO constitutes from 10% to 50%, approximately, of cement materials. In another aspect, additional fly ash is used as a fine aggregate, in a ratio of 4: 1 to 1: 1 with respect to the sand. In another form, fly ash is an additive in addition to a cement replacement, or a replacement of cement and fine aggregate. In specific embodiments, the concrete of the invention comprises about 1 part by weight of cement materials, about 1 to 3 parts by weight of fine aggregate, about 1 to 5 parts by weight of coarse aggregate and about 0.35 to 0.6 parts. in weight of water; so that the ratio of cement materials to water varies from approximately 3: 1 to 1.5: 1; preferably the ratio of cement materials to water is around 2: 1. The water for the concrete of the invention is provided, in part, by introduction of the aqueous fly ash: CaO. In a specific modality, the concrete comprises a part of cementitious materials, 2 parts of river siliceous sand or Ottawa sand, 3 parts of coarse aggregate of crushed basalt, of 9.52 m and 0.5 parts of water. The term "mortar" refers to a hardenable mixture comprising cement materials, a fine aggregate, such as sand, and water. The mortar of the invention additionally treated fly ash treated by exposure to aqueous calcium oxide. In a specific modality, fly ash-CaO constitutes from 10% to 50%, approximately, of cement materials. In another aspect, additional fly ash is used as a fine aggregate, in an approximate ratio of 4: 1 to 1: 1, with r-spice to the sand. In another form, fly ash is an additive in addition to a cement replacement, or a replacement of cement and fine aggregate. In specific embodiments, the mortar of the invention comprises about 1 part by weight of cement materials, about 1 to 3 parts by weight of fine aggregate and about 0.5 parts by weight of water, such that the proportion of cement materials to water is approximately 2: 1. The water for the concrete of the invention is provided, in part, by the introduction of the aqueous fly ash suspension-CaO. In a specific modality, the mortar comprises 1 part of cement materials, 2.75 parts of Ottawa sand and 0.5 parts of water. As noted above, fly ash can be used as a fine aggregate in concrete or mortar, in addition to having a role as a cement material. Said fly ash may be treated fly ash by exposure to an aqueous suspension of CaO; alternatively, untreated fly ash can be used. It has been found that substituting fly ash for a conventional fine aggregate, such as sand, gives the advantages of increased compressive strength in concrete or mortar, since the total amount of fly ash in the hardenable composition is the same, with a faster rate of increase in the resistance to the contract, because the amount of cement in the cement materials is greater. According to the present invention, the hardenable mixture may further comprise one or more of the following: kiln powder, for example, the powder generated in the manufacture of cement; silica fume, which is a by-product of the industrial silicon metal, which consists essentially of about 95% to 98% of reactive SiO2, and which generally comes in fine particle sizes, less than 1 miera; superplasti ficante, such as Daracern-100 (U. R. Grace), a coetious but common additive for concrete, used to decrease the need for water to mix the concrete; and a dispersing agent, such as sodium hexametaphosphate (NaP 3). Particularly preferred is the use of a dispersing agent when weathering fly ash is incorporated into the hardenable mixture. The addition of silica fume can improve the early rate of resistance gain in a hardenable mixture and, therefore, it can be a desirable component of the hardenable mixtures of the invention. In a specific embodiment, a hardenable mixture of the invention may also contain glass fibers as reinforcement. The use of glass fibers in the hardenable mixtures of the invention, for reinforcement, can be achieved because the fly ash, particularly the finer fractions of the fly ash, reacts more easily than the glass fibers with the reactive components of the fly ash. cement, for example, with Ca (0H) 2. thus preventing the long-term reaction of the glass fibers with these reactive components, which would otherwise degrade the glass fibers. The most inert hardenable mixtures are the result of those that contain approximately equal amounts of fly ash or fly ash and silica fume (as discussed below) and cement. The ability of fly ash to neutralize reactive agents in cement is discussed in greater detail in United States Patent Application Serial No. 08 / 246,861, filed May 20, 1994, entitled "Sulfate and Acid Resietant Concrete and Mortar". Concrete and mortar resistant to sulfate and acid) of the present inventors. In another specific embodiment, a hardenable mixture of the invention additionally comprises glass fibers and silica fume. Silica fume reacts more readily with the reactive components of the cement than glass fibers and, thus, can provide desirable early protection of the glass fibers against degradation, as well as early gains in compressive strength. Subsequently, the fly ash will react with said reactive components, thereby preventing early reactivity and delayed reactivity of the glass fibers. As noted above, the reaction of the glass fibers with alkaline and alkaline earth compounds can lead to the degradation of the glass fibers and the loss of tensile strength of the hardenable mixture. When the hardenable mixture of the invention comprises glass fibers, the amount of CaO used to treat the fly ash is reduced, in order to leave more reactive fly ash with the cement components than it would otherwise react with, and would degrade the glass fibers. A desirable amount of CaO for use in a suspension for treating fly ash can be determined empirically. Concrete beam of the invention can be used, with dimensions of 7.62 x 15.24 x 68.58 cm to evaluate the flexural strength of concrete with fly ash, for example, using a simple beam with load in third point. Preferably, said test procedures are in accordance with ASTM C 78 (1990, STM C 78-84 Ann? Al Book of STM Standards, volume 04.02). The present invention will be better understood by reference to the following example, which is given by way of illustration and in no way as limitation.

EXAMPLE The fly ash used in this study was collected from a facility in the northeastern section of the United States. Fly ash from different sources, called DH, H, M and P, was used in this program. The last sample was obtained both in dry and in the open state, as previously described here. Cubic samples of 5.08 x 5.08 x 5.08 cm and cylindrical 7.62 x 15.24 cm were used, for the ASTM standard, in order to study the compressive strength of mortar and concrete, respectively. Beam samples of 7.62 x 15.24 x 68.58 c were selected to study the bending or flal strength of the concrete. All the tests were carried out in a hydraulic test machine with servomotor, in closed circuit, MTS.

MATERIALS The materials used in this study consisted of portland cement type I, common and current; Ottawa sand, siliceous sand (river sand), coarse aggregate, fly ash, kiln dust, silica fume, superplasticizer, dispersing agent and water. Two kinds of sand were used. Classified sand was used, predominantly classified among the sieve No. 300 (0.06 nm) and sieve No. 100 (0.150 nm), in accordance with ASTM C-778 (1990, Specification for Standard Sand, Annual Book of ASTM Standards, volume 04.08). Another local siliceous sand (river sand) that passed through sieve No. 4 (aperture size 4.75 nm) was also used to make mortar and concrete. A crushed basalt aggregate of 9.52 mrn was used to make concrete. Fly ash from wet bottom boiler and dry bottom boiler was selected for the study. These two types of fly ash were fractionated additionally to different particle sizes for further study. Silica fume (produced in the manufacture of icroelectronic wafers) of very fine particles, with size less than 1 miera, and 96 to 98% of reactive SiO 2 in pulverized form was used. The addition of silica fume was intended to produce high strength concrete. Superplasticizer (Daracem-100, U. R. Grace) was used according to the cornunee and corrientee procedures. Sodium hexametaphosphate (NaP03) was commonly used as the dispersing agent. The addition of dispersing agent in the mixture of fly ash and concrete was to ensure that fly ash clumps were dispersed to fine particles and, as a result, could be more reactive. Tap water was used in all studies.

The chemical composition of fly ash and cement was determined by X-ray fluorescence (ASTM D-4326 1990, "Test Method for Major and Minor Elernents in Coal and Coke Aeh by X-Ray Fl? Orescence", Annual Book of ASTM Standards, volume 05.05).

FINANCE OF THE FLYING ASH The fineness of fly ash was measured using two different common and current methods: Blaine's air permeability and fineness through 45 micron sieve (sieve No. 325). Fineness was also determined as the fineness modulus, as described. For Blaine's air permeability (Blaine fineness, the fineness was expressed in terms of the specific surface area, expressed as the total surface area, in square centimeters per gram, or square meters per kilogram, of fly ash. The Blaine method was a measure of relative fineness rather than absolute fineness.The test procedure followed ASTM C 204 (1990, "Test Method for Fineness of Portland Cement", ASTM C 204-89, Ann? Book of ASTM Standards, lathe 04. 01). The fineness of fly ash retained in the sieve of 45 microns (sieve No. 325) was determined by the amount of fly ash retained when wet sieved in No. 325 sieve, according to ASTM C 430 (1990). , "Test Method for Fineness of Hydraulic Cement by the 45-Micron (No. 325) Sieve", ASTM C 430-89, Annual Book of ASTM Standards, volume 04.01), a test method for hydraulic cement. The fineness modulus was determined by adding the percentage of flying ash that was retained in the following sieve year: 0, 1, 1.5, 2, 3, 5, 10, 20, 45, 75, 150 and 300 micrae.

THE MORTAR WITH ASH FLYING DH, H, dry and outdoor fly ash was mixed with Ottawa cement and sand. The replacement of a portion of portland cement by fly ash varied by 0%, 15%, 25% and 35% by weight of the cement materials (cement + fly ash). sample was mixed and cast in accordance with ASTM C 109 (1990, "Test Method for Strength of Hydraulic Cement Compreseive Mortare ...", ASTM C 109-88 Annual Book of ASTM Standards, around 04.01). All samples were cured in water saturated with lime and were tested at the ages of 1, 3, 7, 14, 28, 56 and 90 days.

CONCRETE AND MORTAR WITH ASH FRACTIONED STEERING WHEEL The dry bottom and wet bottom boiler fly ash was separated into two different particle sizes using the Micro-Sizer air sorting system. Flying ash was fractionated into six particle size distributions. The fractionated fly ash and the fly ash originally fed were used to replace 15%, 25%, 35% and 50% of the cement, by weight of the cement materials. The compressive strength of the concrete was tested with fractionated fly ash, from day 1 to day 180. The particle size effect of 0-5, 0-10, 0-15, 0-20, 0-30 was investigated. , 0-44 microns, and the original feed fly ash, and compared with the control concrete. The cylinder of 7.62 x 15.24 crn was used to determine the compressive strength of the fractionated fly ash. The normal size cube of 5.08 x 5.08 x 5.08 c was used to determine the compressive strength of mortars with fractionated fly ash. The mixing ratio of the mortar with fractionated fly ash is shown in table 1. The mixing ratio of the mortar with fractionated fly ash is shown in table 1.

BOX LJ, PROPORTION OF MIXTURE OF THE MORTAR WITH ASH FRACTIONED STEERING WHEEL Ingredients Fractionated fly ash (boiler with dry bottom and wet bottom) by weight % 25% 50% Cement 1.00 0.85 0.75 0.50 Flying ash 0.15 0.25 0.5 0 Arena 2.75 2.75 2.75 2.75 Water 0.50 0.50 0.50 0.5 0 Water / (Cernento + FA) 0.50 0.50 0.50 0.50 CHEMICAL COMPOSITION OF THE FRACTIONED FLYING ASHES The chemical composition of the fractionated fly ash is shown in Table 3. The CEM sample is the cement sample used in this study. The SECA and HUMID samples are the fly ash from the original feed of boiler ash with a dry bottom and wet bottom, respectively. 3F is the finest fly ash sample of the dry bottom boiler ash and 13F is the finest sample of the wet bottom boiler ash. The thickest fly ash samples of the dry bottom and wet bottom boiler ash are 1C and 18C, respectively. Both fly ash wet bottom boiler as dry bottom,? Sadae here were classified as Class F fly ash according to flSTM C-618 (1990, supra). Most of the fractionated fly ash varied slightly in the oxide composition, with changes in particle size. It is reported that the separation of fly ash class F (high calcium) to size fractions does not result in a chemical, morphological and important mineralogical specification between the particles (I ming and Berry, 1986? Ymposium Proceedmgs, Fly ñsh and Coal Conversion By -Products: Characterization, Utiiization and Disposal II, Material Research ociety 65: 91-130). The S1O2 content tends to be lower when the particle size is larger. Differences were observed in the chemical compositions of the two fly ash in the contents of S1O2, Fß2Ü2 and CaO. Samples of the dry bottom boiler fly ash were approximately 10% richer in? 1O2 than the wet bottom boiler fly ash. The CaO content of the dry-bottomed boiler fly ash varied from 1.90% to 2.99%, while for the humid bottom boiler fly ash, the CaO varied from 6.55% to 7.38%. The content of wet-bottomed boiler fly ash was about twice as high in the wet-bottomed fly ash as in the dry-bottom boiler fly ash. The maximum concentration of Fß2? of each type of fly ash was observed in the thickest particles, ie, 1C and 18C. The chemical composition of the fly ash is shown in table 2. TABLE 2 CHEMICAL COMPOSITION OF FRACTIONED FLYING ASHES AND CEMENT Chemical coposition (Z) Sai LOl S02 Si02 f.1203 Fe203 CaO K20 flOg Na20 CEU 0.73 2.53 20.07 8.84 1.41 60.14 0.86 2.49 0.28 3F0 4.97 1.69 49.89 26.94 5.43 2.99 0.99 0.33 5F 4.10 1.53 50.27 26.74 5.30 2.95 0.93 0.33 IF 3.12 1.09 51.40 26.54 4.91 2.72 0.74 0.31 10F 2.52 0.72 51.98 26.23 4.44 2.28 0.54 0.29 0.29 11F 2.84 0.53 51.27 26.28 4.42 2.02 0.49 0.26 1C 1.46 0.39 53.01 26.50 5.66 1.90 0.56 0.24 DRY 2.75 0.98 52.25 26.72 5.43 2.41 0.69 0.28 13F 2.Í7 3.81 38.93 24.91 12.89 6.85 1.55 1.31 14F 1.94 3.47 39.72 25.09 13.02 6.71 1.25 1.55 1.31 15F 1.88 3.33 40.25 25.02 13.12 6.12 1.60 1.47 16F 2.06 3.05 40.55 24.92 13.26 6.55 2.09 1.41 1.26 18F 1.94 2.94 41.56 24.47 14.21 6.50 2.01 1.40 1.17 lSC 2.55 2.48 43.25 23.31 17.19 7.38 2.00 1.30 0.85 HUItEDfl 2.05 3.13 41.54 24.74 14.83 6.89 2.07 1.43 1.17 It is interesting to note that, after the fly ash was split into different sizes, the ignition loss (LOl) of the finer particle was greater than that for the larger particles. In other words, the LO1 content gradually decreased as the particle size increased. Ravina (1980, Cernent and Concrete Research, 10: 573-80) also reported that the finest particle of fly ash has the highest LOl values. Ukita and coauthors (1989, Fly flsh, Silica Fume, Slag and Natural Pozzolans in Concrete, SP-114, American Concrete Institute, Detroit, pp 219-40) also showed that, although the chemical composition did not change when the average diameter decreased of the fly ash from 17.6 microns to 3.3 microns, the LOI increased from 2.7B to 4.37. The observations of the inventors and these previous reports are in conflict with the report of ACI Cornmitee 226 (1987, Use of Fly Ash in Concrete, ACI 226.3R-87, ACI 3. Proceedings 84: 381-409) and Sheu and co-authors (1990, Symposium Proceedings, Fly Aeh and Coal Conversion By-Products: Characterization, Utilization and Disposal VI, Materials Research Society 178: 159-166), which indicate that the coarse fraction of fly ash usually has a LOl higher than that of the fine fraction.

ANALYSIS OF THE TAMAKO OF PARTICLE OF FLYING ASHES FRACTIONAL The particle size distributions of the fractionated fly ash from dry bottom and wet bottom boilers are shown in Figures IA and IB, respectively. The curves for the original feed fly ash are not as pronounced as others, since the original, unfractionated feed ash includes the full scale of sizes and, thus, a larger scale of size distributions than the samples fractioned. The percentage of fly ash of each fraction that has size smaller than a particular size is indicated in parentheses in each curve. For example, in the case of 3F fly ash, the finest dry bottom boiler fly ash, 3F (90% -5 μ) means that 90% of the fly ash particles are less than 5 microns. From the original feed, each type of fly ash was divided into six layers. As shown in Figures IA and IB, the particle size of fly ash varied from 0-5.5 microns to 0-600 microns. The average diameter of the particles of each fraction was determined from the curves in Figures IA and IB, extrapolating from 50% of the finest percentage value. The mean diameters of 3F and 13F were 2.11 and 1.84 microns, respectively, while the mean diameters of the coarsest particle size, 1C and 18C, were 39.45 and 29.23 microns, respectively. For the humid bottom boiler fly ash, 13F was the finest fraction and 18C was the thickest.

It was found that the original feed of the wet bottom boiler ash was finer than the original feed of the dry bottom boiler fly ash. The original feed particle sizes of dry bottom boiler ash varied from 1 miera to 600 micras, approximately, with an average particle size of 13.73 microns. The original feed of the humid bottom boiler fly ash included particles up to 300 microns, with an average diameter of 6.41 microns. Particles of smaller fractions tend to have a more spherical shape (Hernning and Berry, 1986, supra). The density of the fly ash of different electricity generating plants varies from 1.97 to 2.89 g / cm3 per-o normally varies between 2.2 and 2.7 g / cm3, approximately (Lane and Best, 1982, supra). The work carried out by McLaren and Digiolm (1990, Coal Combustion and By-Product Utilization Seminar, Pittsburgh, p.15) reported that Class F fly ash had an average specific density value of 2.40. The specific density of fractionated fly ash varies from 2.28 for coarse fly ash to 2.54 for finer fly ash, for dry bottom boiler ash, and 2.22 for coarse fly ash to 2.75 for the finer fly ash. , of humid bottom boiler. Differences in density between the dry bottom boiler fly ash and the wet bottom boiler fly ash suggest that the very fine particles of the wet bottom boiler fly ash are thick walled, void-free, or are composed of crystals and crystalline components more dense than dry bottom boiler ash (Hernrning and Berry, 1986, Syrnposium Proceedings, Fly physical and Coal Conversion By-Products: Characterization, Utilization and Disposal II, Material Research Society (65: 91-103).

EFFECT OF CALCIUM OXIDE (CaO) ON THE RESISTANCE OF MORTAR WITH FRENCH FROSTED ASH The fractionated fly ash 6F, 16F, 1C, 18C and the fly ash of dry bottom and wet bottom, non-fractionated, to form cement mortar were used. Calcium oxide was added to the mixture in proportions of 10%, 20% and 30% by weight of the weight of fly ash + calcium oxide. First, the calcium oxide was allowed to absorb the mixing water for 3 to 5 minutes, and then the CaO-water suspension was mixed. Flying ash, either unfractionated or fractionated, was then added to the mixer and mixed with the calcium oxide suspension. The fractionated fly ash mortar was slipped with calcium oxide, cured and tested for its compressive strength for a period of 180 days. The mixing ratio of the fractionated fly ash mortar with calcium oxide is shown in table 3.

TABLE 3 PROPORTIONS OF ASH MORTAR MIXTURE STEERING WITH SUSPENSION OF CaO Do not . of Type of. Mixing ratio C * Q (fly ash) shows fly ash ash (Cement CAO vol ant CAO 1.00 DCAO Seto 0.65 - 0.350 0 DCA10 Dry 0.65 0.035 0.315 10 DCA20 Dry 0.65 0.700 0.280 20 DCA30 Dry 0.65 0.105 0.245 30 WCAO Wet 0.65. 0.350 0 CA10 Moist 0.65 0.035 0.315 10 WCA20 Moist 0.65 0.700 0.280 20 CA30 Moist 0.65 0.105 0.245 30 6CA0 6F 0.65 - 0.350 0 6CA10 6F 0.65 0.035 0.315 10 6CA20 6F 0.65 0.700 0.280 20 6CA30 6F 0. 65 0.105 0.245 30 16 CAO 18F 0.65 0.350 0 15CA10 18F 0.65 0.035 0.315 10 16CA20 18F 0.65 0.700 0. 280 20 1SCA30 18F 0.65 0.105 0.245 30 1CA0 1C 0. 65 0.350 0 1CA10 1C 0. 65 0.035 0.315 10 1CA20 1C 0.65 0.700 0.280 20 1CA30 1C 0.65 0.105 0.245 30 13CA0 18C 0.65 0.350 0 18CA10 18C 0.65 0.035 0.315 10 18CA20 18C 0.65 0.700 0.280 20 18CA30 18C 0.65 0.105 0.245 30 CA10 0.965 0.035 0 CA20 0.930 0.070 0 CA30 0.985 0.105 0 Note: Water / (Cement + CaO + Fly Ash) = 0.50 (Cement + Ash Flywheel + CaO) = Sand Ratio = - 1: 2 .75 RESULTS In this example the objective was to accelerate the early resistance of the mortar with fly ash, treating the fly ash with an aqueous suspension of calcium oxide (CaO) before adding the fly ash suspension-CaO to the other components of the mortar. The calcium oxide, in the powder form, with a purity of more than 98%, was used to increase the calcium oxide content of the fly ash. The percentage of fly ash plus calcium oxide in the mixture was kept constant at 35% by weight of the cement materials (cement + fly ash + calcium oxide). However, the percentage of CaO between 10% and 30% of the fly ash-CaO portion of the cementitious materials was varied. The mixing ratios of cement, CaO and fly ash, of the various samples prepared for testing in this experiment, are summarized in Table 3. CAO, which was the mortar sample with cement, without any fly ash or rust. calcium, was the control sample. DCAO and UCAO were samplers of mortar with fly ash, mixed with non-fractionated fly ash, dry bottom boiler and wet bottom boiler, respectively. The numbers at the end of the sample, ie "0", "10", "20" and "30", represent the percentage of calcium oxide in the mixture, by weight of fly ash + calcium oxide.

The CA10, CA20 and CA30 control samples were prepared by replacing cement with calcium oxide at 3.5%, 7.0% and 10.5%, respectively, by weight of the cement materials, ie, cement + calcium oxide. These samples did not contain fly ash. The amounts of calcium oxide used to replace the cement in samples CA10, CA20 and CA30 were the same as in the samples containing fly ash, where the content of fly ash-CaO was 10%, 20% and 30%, respectively. In this case, cement was used instead of fly ash in the final composition (the cement was not treated by mixing with the equivalent portion in the lime slurry). The results of this experiment are reported in Table 4. The compressive strength of various mortar samples was determined in times ranging from 1 day to 28 days of healing. The data in Table 4 is given as the percentage of the compressive strength of a sample, with respect to the control sample, CAO. As expected, the early values of compressive strength of the untreated fly ash samples (CaO = 0) were lower than the compressive strength of the control sample, for all times tested. The pretreatment of the fly ash with the aqueous CaO, however, greatly increased the early values of the compressive strength, in comparison with the samples to be treated.

TABLE 4 RESISTANCE TO COMPRESSION OF MORTAR WITH ASH FLYING TREATED WITH CAO No. Percentage of resistance to compression (%) shows 1 day 3 days 7 days 14 days 28 days CAO * 156.3 391.2 533.2 596.6 647.8 DCAO 43.6 52.7 58.2 61.7 73.9 DCA10 54.5 60.8 61.9 65.3 75.5 DCA20 76.3 66.9 66.7 73.1 78.6 DCA30 89.6 76.4 72.1 73.9 81.4 UCAO 46.4 63.6 62.6 70.0 83.3 UCA10 60.1 69.8 68.8 71.6 84.3 UCA20 93.3 75.7 70.3 75.0 85.1 UCA30 103.1 82.6 76.6 76.2 86.8 6CA0 45.5 55.7 59.1 64.7 79.5 6CA10 67.3 62-9 63.9 70.7 80.9 6CA20 67.7 66.3 66.7 72.9 81.2 6CA30 81.5 71.8 69.1 73.8 82.2 16CA0 52.2 65.3 65.3 71.3 81.7 16CA10 72.4 68.4 69.0 72.5 83.4 16CA20 91.0 75.2 70.8 76.1 83.3 16CA30 105.3 84.4 78.0 79.3 87.8 1CA0 36.5 47.8 51.9 57.1 61.6 1CA10 59.3 56.2 56.4 60.3 65.5 TABLE 4 (continued) * The values for the control sample, CAO, are the actual compressive strength, in kg / cm2. These values represent 100% in the table. These results are illustrated by examining particular data points. In the samples containing dry bottomless boiler fly ash, the compression strength on day 1 of DCAO (fly ash mortar without calcium oxide) was 68.19 kg / cnv *; this value increased to 140.10 kg / crn * in sample DCA30, which contains fly ash and 30%. Thus, the treatment of fly ash (a lower amount, since the fly ash is replaced with CaO) with aqueous CaO, increases the compressive strength of dry bottom, unfractioned, boiling ash mortar of 43.6% to 89.6% of control resistances. Similar results were observed for the unfractionated wet bottom boiler fly ash. For those samples, resistance on day 1 increased from 10.73 for UCAO (0% CaO) to 161.26 kg / cm for the UCA30 sample, (containing 30% calcium oxide, as a percentage of fly ash and Ca ). Thus, the treatment of fly ash with aqueous CaO increased the compressive strength on day 1 approximately twice, compared to that of the sample without the addition of calcium oxide. These results were also observed with the samples prepared with samples of fractionated fly ash. The tested fractions were fly ash 6F, 16F, 1C and 18C (see table 1 above). The increase in the compressive strength for the fly ash mortar, obtained by treating the fly ash with an aqueous suspension of calcium oxide was more evident in the early healing times, that is, until day 14. At 28 days, the differences between the compressive strength of the samples prepared with and without the addition of calcium oxide were not significant. For example, the compressive strength values at 28 days for the DCAO and DCA30 samples (prepared with dry bottomless boiler fly ash) were 478.95 and 527.67 kg / cm, respectively, or 73.9% and 81.4%, respectively, of the resistance of the control. For mortars with fractionated fly ash, prepared with fractions 6F, 16F, 1C and 18C, the strength of the mortar with fly ash, prepared with fly ash treated with the calcium oxide suspension, where the amount of CaO as a percentage of fly ash + CaO ranged from 10% to 30% by weight, was slightly higher than that of the mortar samples prepared without calcium oxide. Control samples containing CaO but without fly ash were also evaluated. Sample CA10 (replacement of cement by calcium oxide, where CaO is 3.5% by weight of cement + calcium oxide) produced a compressive strength on day 1 of 174.69 kg / crn2 or 111.7% of the control mortar. The other samples, CA20 and CA30, also produced resistances higher than the resistance of the control. The percentage of resistance to co-compression of CA20 and CA30 was 134.4% and 153.8%, respectively, compared to the control mortar. The rate of gain in the compressive strength, in this case, decreased after 3 days: on the seventh day of the cure, the compression resistance of the samples containing CaO was lower than that of the control. The compressive strengths of samples CA10, CA20 and CA30, at 7 days, were 91.7%, 95.1% and 96.0%, respectively, of the resistance of the control. At 28 days, the values of the compressive strength of the samples in which the cement was replaced by calcium oxide were around 90% of that of the control mortar. An increased early compressive strength was observed in the samples in which the fly ash was treated by mixing in a CaO suspension before mixing the mortar. The presence of reactive lime soothing accelerates the reaction rate of the fly ash and results in a gain in the early strength of the fly ash-lime-cement slurry mixtures. In addition, during the mixing period of calcium oxide and water, the chemical reaction between calcium oxide and water releases energy in the form of heat. That heat can accelerate the hydration process of the cement, thus giving greater resistance in the early stages, than the sample without the added calcium oxide. It was also found that, with a constant proportion of water to cementitious materials, a higher content of calcium oxide in the mixture made the sample less workable than the cement-mortar control mixture. Based on the above results, it can be concluded that the use of calcium oxide to replace cement can accelerate the rate of gain in compressive strength on day 1, but has no effect, or even a slightly negative effect, after of 7 days, when compared to the resistance of the control mortar. The present invention is not limited in scope by the specific embodiments described herein. In fact, it will be apparent to those skilled in the art of various modifications of the invention, in addition to those described herein, from the foregoing description and the appended figures. It is intended that said modifications fall within the scope of the claims that follow. It cites here divereae publications, whose description is incorporated here as a reference in its entirety.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. - A method to increase the early rate of gain in the strength of a hardened mixture containing fly ash, characterized in that I understand to expose the fly ash to an aqueous suspension of an alkaline material before incorporating the fly ash into a hardenable mixture.

2. The method according to claim 1, further characterized in that the alkaline material coats the fly ash.

3. The method according to claim 1, further characterized in that the exposure of the fly ash to the alkaline material comprises adding fly ash to a suspension of alkaline material in water, thereby forming a suspension of fly ash-alkaline material. Water.

4. The method according to claim 3, further characterized in that it comprises additionally mixing the suspension of fly ash-alkaline-water material with cement and fine aggregate, < So mortar is formed.

5. The method according to claim 3, further characterized in that it comprises mixing the suspension of fly ash-alkaline-water material with cement, fine agr-egado and coarse aggregate, so that concrete is formed.

6. - The method according to claim 1, further characterized in that the percent alkaline-to-fly ratio-alkaline material is from 5% to 60% by weight, approximately, with respect to < ? the materials of cerne -t or present in the mixture ripple. ? . - The method according to claim 1, characterized in that the amount of alkaline material present in the mixture hardens approximately 5% to 50% by weight of the amount of fly ash present in the mixture. endu ecíMe. 8. The method according to claim 3, further characterized in that the suspension is prepared by mixing the alkaline material in water at least about 1 m 2 at a time for about 10 minutes. 9. The method according to claim 1, further characterized in that the flywheel has a width defined by a modulus of fineness of less than about 600, where the module is calculated ("wall as sum of the fly ash percentage retained on sieves of 0, 1, 1.4, 2, 3, 5, 10, 20, 45, 75, 150 and 300 microns .. The method according to claim 9, further characterized because the fly ash is humid bottom boiler fly ash, which has a fineness modulus of less than about 1 of 350. 11. The method according to claim 1, further characterized in that the alkaline oxidized material of 1) 3. c l cío ,. 12, .- The method in accordance with the rei indication 2, further characterized in that the alkaline material is lime oxide c o. 13.- r-l rnetodo of conf rmi ad with the rei indication 3, further characterized in that the alkaline material is calcium oxide. 14. A hardened mixture comprising cement and a reinforced suspension of flywheel, alkaline material and water, where the flywheel and the alkaline material together, account for approximately 5% to .08 by weight of the materials of cement present in the mixture, hardenable; and wherein the percentage by weight of calcium oxide with respect to calcium oxide and fly ash, varies between 5% and 50%, approximately. Ib.- the hardenable mixture according to claim 14, further characterized in that the fly ash and the alkaline material together are approximately 30% of the cementitious inatepals present in the hardenable mixture. 16. The hardened mixture according to claim 14, further characterized in that the fly ash has a fineness defined by a fineness modulus of less than about 600; where the modulus of fineness is calculated as the sum of the fly ash percentage retained in sieves of 0, 1, 1.5, 2, 3, 5, 10, 20, 45, 75, 150 and 300 mi eras. 17.- The hardening mixture in accordance with the rediiication 16, further characterized in that the fly ash is humid bottom boiler fly ash, which has a fineness modulus of less than about 350. IB.- The hardenable mixture according to claim 14, further characterized by the fact that the mixture It is concrete. 19. The hardened mixture according to claim 14, further characterized in that the mixture is mo tero. 20. The hardenable mixture according to claim 14, further characterized in that the alkaline material is oxy or calcium.