MXPA06010288A - Cementitious material reinforced with purified cellulose fiber - Google Patents

Abstract

The present invention is directed to a cellulose fiber reinforced cementitious material having cement;optionally sand and/or aggregate;and chemically purified cellulose fibers with a Zero-Span Stability Ratio or percent cellulose content of about 90 percent or greater. The invention may also include one or more synthetic or natural fibers, and may also include latex.

Description

CEMENT-BASED MATERIAL REINFORCED WITH PURIFIED CELLULOSE FIBER REFERENCE TO RELATED REQUESTS This application claims priority, pursuant to 35 US C, section 119, of the United States Provisional Application Serial No. 60 / 552,338, filed on March 10, 2004, which is hereby incorporated in its entirety by means of this reference.

FIELD OF THE INVENTION The present invention relates to a cementitious material reinforced with a chemically purified cellulose fiber.

BACKGROUND OF THE INVENTION U.S. Patent Nos. 1,048,913, 1,349,901, 1,571,048, 1,633,219, 1,913,707, 2,377,484 and 2,677,955, refer to the use of various materials, including fibers, in concrete. Previous efforts were aimed at improving cracking resistance and improving energy absorption of concrete masses. U.S. Patent Nos. 4,188,454, 4,287,365, 4,287,020, 4,310,478, 4,369,201, 4,400.27, 4,483,727, 4,524,101, 4,524,101, 4,861,812, 4,985,119, 4,968,561, 5,000,824, 5,196,061, 5,362,562, 5,385,978, 5,399, 1 95 and 5,453,310, 5,643, 359, 5,897,701, all of which are incorporated herein in their entirety, by means of this reference, refers to various efforts to provide improved reinforced materials. It was recognized that cellulosic materials were widespread, abundant and relatively cheap. However, it was also recognized that cellulosic materials were of limited value in many compositions, due to the aggressive alkaline environment of many cementitious mixtures, which caused physical degradation of the cellulosic fibers when the mixture was cured. The US patent application serial number 1 0 / 638,274, filed August 8, 2003, under the title of Cementitious Material Reinforced with Chemically Treated Cellulose Fiber, which is incorporated herein in its entirety by way of this reference, describes chemically treated cellulose fibers, with high alkaline stability, and their use in cementitious materials. The United States Provisional Patent Application, Serial No. 60 / 498,782, filed on August 23, 2003, entitled System for Delivery of Fibers into Concrete, which is incorporated herein by reference. whole by means of this reference, it describes forms of fibrous sheet material, which can be easily mixed in compositions of building material, with rapid dispersion of the individual fibers.

BRIEF DESCRIPTION OF THE INVENTION It would be advantageous to be able to provide a cellulose fiber for mixing in cementitious materials, which is resistant to structural degradation in the aggressive alkaline environment of many cementitious mixtures and which, therefore, is effective in reinforcing the microenvironment around the individual fibers, and to prevent the beginning of microcracks. Additionally, it would be advantageous to be able to provide said fiber that does not require chemical treatment. This invention describes cellulose fibers of relatively high purity, which provide superior resistance to degradation and loss of resistance in the aggressive alkaline environment of cementitious materials. It has been found that, while hemicellulose and lignin contribute to reduced alkaline stability, of both, the deleterious effect of lignin appears to be greater.

DESCRIPTION OF THE DRAWINGS Figure 1 shows a graph of the percentage of ZSSR versus S1 0 or percentage of cellulose for bleached pulps that gives the same correlation. Figure 2 shows a graph of the percentage of ZSSR versus S1 0 or percentage of cellulose for bleached pulps that gives the same correlation. Figure 3 shows the percentage of ZSSR values for all the samples of Example 6, plotted against the S10 value. Figure 4 shows the percentage of the ZSSR values of all the samples of Example 6, plotted against the purity in which the percentage value of cellulose is determined by subtracting the S10 value and the percentage of lignin remaining in the pulp fibers.

DETAILED DESCRIPTION All patents, patent applications and publications cited in this description are incorporated herein in their entirety, by reference. In case of a conflict in terminology, the present description is in control. Reference is made here to several standard tests that have been published by the Technical Association for the Pulp and Paper Industry ("TAPPI"), 15 Technology Parkway South, Norcross, GA 30092, web site: www.tappi. org. The final test methods are promulgated by the TAPPI's Standards Advisory Review Group. Detailed descriptions of those tests can be obtained from the TAPPI. A typical designation of a test is, for example, T233 cm-95 for the length of pulp fiber, by classification. Reference is made here to several tests of the ASTM. ASTM I International is a nonprofit organization, formerly known as the American Society for Testing and Materials, ASTM International, which provides standards that are accepted and used in research and development, product testing, systems quality and in commercial transactions around the world. ASTM, 1 00 Bar Harbor Drive, West ConSchohocken PA, 19428-2959, USA A major problem in the current state of the art, which limits the effectiveness of cellulosic fibers as reinforcement for cementitious materials, is the aggressive alkaline environment of these materials . When unprotected cellulosic fibers are introduced in this alkaline environment, the degradation of the fibers in the cement mixture begins immediately, before it has an opportunity to set and cure. It is important that the reinforcing fibers maintain their physical integrity if they are to be effective in reinforcing the cementitious mixture and limiting the formation of microcracks during the curing stages of the cementitious mixture. The chemically purified cellulose fiber of the present invention shows stability in an aggressive alkaline environment, which is superior to that of the cellulose fiber produced by the same basic method, but which has lower purity. Because the cellulose fibers of the present invention, chemically purified, are well bonded within the cement matrix, most of the fibers are broken, rather than released. For this reason, the individual fiber strength of cellulose fibers is a very important consideration. Breaking really the individual fibers is very slow and gives extremely variable results. A standard method (Tappi T231) was developed to measure the average resistance of a large number of fibers, breaking strips of ordinary paper, where the separation between the clamping jaws approaches a distance "of zero extension", assuring that so that most of the fibers are broken, instead of coming out of the paper matrix. It is possible to determine the effect of exposing to an alkaline environment, on the strength of a single fiber in the cellulose fibers, by measuring the zero tensile strength of alkali treated and untreated (control) fibers. This effect is expressed as the "stability ratio to zero extension" (ZSSR, by its English designation: Zero-Span Stability Ratio), which is defined as follows: Zero-extension traction after alkaline treatment (1) ZSSR = Zero extension traction without alkaline treatment The ZSSR can be determined for various alkaline treatments and for various time intervals. A preferred method for the determination of tensile to zero extension and the ZSSR, which has been designated as the method D 6942-03 of the ASTM, is as follows: Procedure to determine the stability of fibers of cellulose in alkaline environments This procedure can be used to determine the effect of exposure to alkaline environments on the strength of cellulose fibers. An alkaline environment is defined as any matrix in which the pH is greater than 8, over a period of two hours or more. The references of the tests and procedures for the present procedure are as follows: ASTM D 1695: Terminology of cellulose and cellulose derivatives; see Annual Book of ASTM Standards, volume 6.03. ASTM D 1348 Standard test methods for pulp moisture. TAPPI T205"Formation of test sheets for physical pulp tests". TAPPI T 231"Resistance to breakage of pulp at zero extension (dry traction to zero extension.) This procedure can be used to compare different types of cellulose pulp, based on its response to a standard alkaline solution. defined below can be used to measure the effect of exposure to alkaline conditions on the strength of the fiber.The cellulose fibers are treated with a standard alkaline solution for a specified interval, washed until alkali-free, and then formed to standard test sheets to test the resistance Zero tensile tensile test is used to determine the effect of alkaline treatment on the strength of the fiber A stability ratio is defined based on the proportion of tensile to zero extension of the fibers treated with alkali, between the zero extension traction of the untreated control fibers. At 1 percent, in percentage terms, closer to 100 percent, indicates relatively greater stability in the alkaline environment; while a smaller number indicates a decrease in resistance. This method is intended to provide a generalized procedure to determine the stability of cellulose pulp fibers exposed to alkaline environments. Specifically, this method allows different types of pulp to be compared with respect to the effect of exposure to alkaline conditions, on the strength of individual cellulosic fibers, based on a tensile test at zero extension. The time intervals listed in the procedure are not critical, and more intervals of shorter or longer duration can be added. In addition, the procedure can be simplified by removing some of the intermediate intervals, as long as an interval scale is determined. An example of a simplified procedure would be to determine four intervals, such as one day, one week, two weeks, four weeks; or one day, three days, seven days, fourteen days. The specified solution, in 1 N NaOH, is strongly alkaline. Although this alkaline concentration is higher than some modalities that would be simulated by this test, the stronger pH provides better differentiation between different types of cellulose fiber. Although it could be determined by this method the alkaline stability based on other alkalis, such as KOH, Ca (OH) 2, etc. , at a different concentration, the 1 N NaOH will be considered as the standard solution. The results of alkaline stability can be reported from other treatments, in addition to the standard solution, if the additional solution (s) provides useful information. The required apparatus includes a test sheet forming apparatus, as defined in TAPPI T205; a tensile tester with zero extension, as described in TAPPI T231, a humidity balance and an analytical balance. Sodium hydroxide (NaOH) 1 N is a required reagent. The values indicated in the SI units should be considered as the norm. The values in parentheses are for information only. The starting cellulose fibers should be in the form of a dry sheet, such as folded dry pulp sheets, or in the form of a dry, low density volume. In this context, the term dry means a balanced moisture content, which is six to eight percent moisture in most pulps. Calibration and maintenance of zero tensile tensile tester shall be accomplished as prescribed in TAPPI T231. Additionally, a control chart of the instrument will be maintained, based on the breaking of strips of paper cut from the sheets of control paper. You can use a ream of paper copy for this purpose or any other paper with consistent ingredients, uniform base weight and uniform density. Control paper produced on a paper machine must be tested in the machine direction. The test sheets must be conditioned before testing, as described in TAPPI T205. For dry folded sheets, the pulp sheet is mechanically disintegrated to obtain 150 grams of individualized fibers for each sample to be tested. High density pulp sheets can also be formed into a thick slurry of low consistency; then they are air dried to provide a volumetric sample of low density. The volumetric air-dried sample can then be mechanically disintegrated, or it can be disintegrated by hand in order to provide individualized fibers. 20 grams, on a dry basis, of cellulose fibers, 46.7 grams of 1 N NaOH are added and allowed to remain for 24 hours. This corresponds to a consistency of 30 percent, which corresponds to 20 grams of pulp / 66.7 grams in total. The sample is then placed in an uncovered beaker to simulate an environment that is open to the atmosphere. It is repeated to prepare three more samples that will be aged for 7, 14 and 28 days, respectively. Once the time interval has been met, the composition of the samples is obtained by collecting fibers in a 325 mesh wire screen, washing with running water until the washings are neutral, with a pH of 7 to 7.5, and they are then rinsed overnight to form the test sheets. Two sets of normal test sheets are prepared, according to the Tappi method T205, "Formation of test sheets for physical pulp tests", for each time interval. A series of pulp will be made that has not been treated with sodium hydroxide and will be the control series. The other series will be prepared from fibers that had been exposed to alkali during the designated time interval. These two series of test sheets will be prepared on the same day. Each series of test sheets will be tested for zero tensile traction, according to the Tappi method T231"Resistance to pulp rupture at zero extension (dry traction to zero extension)".

The zero extension stability ratio, ZSSR is determined by dividing the tensile result to zero extension of the alkali treated sample, between the result of the zero extension tensile of the corresponding untreated control sample. The results are reported as a decimal proportion, such as 0.921, or as a percentage, such as 92.1 percent. It is recommended to report three significant figures. The zero extension stability ratios will be reported individually for each time slice sample and / or as an average value of all the time interval samples tested. Note that higher proportions will be observed for pulps that have higher resistance stability in the alkaline environment. ZSSR zero extension stability ratios, determined for each time slice sample, are reported as a decimal fraction or as a percentage, together with the average zero extension stability ratio, determined from all the interval samples weather. Since 1 N NaOH is the standard test solution, it is not necessary to specify it, except if another test solution is used in addition to the standard solution; in which case its composition must be specified. Accuracy and deviations are given for the tensile test to zero extension in TAPPI T231. The repeatability within a laboratory is 3 to 5 percent, and the reproducibility between laboratories, for thirty samples in three laboratories, was 10 percent. The repeatability of zero tensile tensile tests, used to calculate stability ratios, was found to be 5 percent, based on 14 sets of control test sheets, made at different times by two operators; where each series was tested four times to cut two test strips of two test sheets of each series, for a total of 64 tractions. The repeatability of the stability ratio depends partly on the type of fibers tested, such as, for example, SSK, NSK, sulfite, mechanical, etc. , and the duration of the test, for example, one day, one week, four weeks. For certain samples in uncovered beakers, the repeatability, expressed as a percentage coefficient of variation, was 5 to 8 percent. This invention is a cement or fiber reinforced cementitious material, wherein the reinforcing fiber is a chemically purified cellulose fiber. As used herein, the phrase "chemically purified cellulose fiber" means a cellulose fiber that has been processed to produce fibers that had not been chemically treated, such as in U.S. Patent Application Serial No. 10 / 638,274, and which have not been mineralized but which, however, exhibit an alkaline stability value (ZSSR) as defined in ASTM D6942-03, which is about 90 percent or more, preferably about 95 percent or more and, more preferably , approximately 97 percent or more. It is shown in the experimental section that obtaining a ZSSR value of more than 90 percent requires the purification of the fibers at levels above 90 percent cellulose. Thus, the chemically purified cellulose fibers useful in the practice of this invention have a cellulose content of about 90 percent or more; more conveniently about 93 percent or more, preferably about 95 percent or more and, most preferred, about 97 percent or more. Cellulosic fibrous materials, suitable for use in the present invention, include softwood fibers and hardwood fibers. See MJ Kocurek and CFB Stevens, Pulp and Paper Manufacture - Vol. 1: Properties of Fibrous Raw Materials and Their Preparation for Pulping, THE JOI NT TEXTBOOK COMMITTEE OF THE PAPER I NDUSTRY, 1983, 1 82 pages, which is incorporated here in its totality through this reference. The types of softwood pulps of example, although not exclusive, are derived from Pinus elliotti, Pinus banksiana, Pinus radiata, Pinus taeda, white spruce, broadleaf pine, sequoia and Oregon pine. Softwoods from southern North America and softwoods from northern North America, as well as softwoods from other regions of the world, can be used. Hardwood fibers of oak, Quercus, maples, Acer, poplar, Populus genus or other species commonly used for pulp can be obtained. In general, softwood fibers are preferred due to their greater fiber length, when measured by T233 cm-95, and those that are most preferred with softwood fibers from the south, due to a greater thickness when measured by T234 cm-84, which leads to greater intrinsic fiber resistance, when measured by breaking load in relation to soft northern wood or hardwood fibers.

The fibrous material can be prepared from its natural state by any pulping process. These industrial processes are described in detail in R. G. Macdonald and J. N. Franklin, Pulp and Paper Manufacture in three volumes, 2a. edition, volume 1: The pulping of wood, 1969; Volume 2: Control, secondary fiber, structural board, coating, 1 969, volume 3: Papermaking and paperboard making, 1 970; THE JOI NT TEXTBOOK COMM ITTEE OF THE PAPER IN DUSTRY, and in MJ Kocurek and CFB Stevens, Pulp and Paper Manufacture, Volume I: Properties of Fibrous Raw Materials and Their Preparation for Pulping, THE JOI NT TEXTBOOK COM M ITTEE OF THE PAPER IN DUSTRY, 1983, 182 pages; both works incorporated here in their entirety by means of this reference. Preferably, the fibrous material is prepared by a chemical pulping process, such as a Kraft or sulphite process. In particular, the Kraft process is especially preferred. The pulp prepared from a soft southern wood, by means of a Kraft process, is often called SSK. Similarly, southern hardwood pulp, northern softwood and northern hardwood are designated SHK, NSK and NHK, respectively. Bleached pulp, consisting of fibers that have been delignified at very low levels of lignin, is preferred; although unbleached Kraft fibers may be preferred for some applications, due to the lower cost, especially if the alkaline stability does not matter. Conveniently, the chemically treated cellulose fiber has been derived from a source that is one or more of the following: Southern softwood kraft, Northern softwood kraft, hardwood, eucalyptus, mechanical, recycling and rayon, preferably kraft of soft southern wood, northern softwood kraft or mixtures thereof, more preferable, southern softwood kraft. In addition to the high purity cellulose fibers obtained from cotton linters, high purity cellulose fibers can be prepared from wood. The two main processes for manufacturing these high purity cellulose fibers are the acid sulphite process and the prehydrolyzed kraft process. Detailed descriptions of the acid sulphite process can be found in Pulping Processes, Rydholm, ed. , pages 439-576, 1965, Interscience Publishers, New York, E. U. A., and in Pulp and Paper Manufacture, volume 4 - Sulfile Science & Technology, O. V. Ingruber, M. J. Kocurek and A. Wong, eds., Pages 229-243, 1985, Technical Section of the Canadian Pulp and Paper Association, Montreal, Quebec, Canada. In a typical example, wood chips are subjected to a solution of sulfur dioxide dissolved in water at temperatures up to 150 ° C, in a digester under pressure, for 4 to 6 hours. At the end of that period, the contents of the digester are opened to the atmosphere, until they reach atmospheric pressure, which allows the digested chips to move through a tube driven by pressure higher than atmospheric pressure, to a container receiver. While in transit, the chips are defibrated to individualized fibers. These fibers, or unbleached wood pulp, are washed with fresh water to remove residual chemicals and wood components separated from the fibers during the sulfite process. After washing, residual lignin and non-cellulose materials present in the fibers are removed in a multi-stage bleaching process, using in the individual steps: chlorine, sodium hydroxide, sodium hypochlorite and chlorine dioxide. The end products are cellulose fibers with purity greater than 98 percent. Detailed descriptions of the prehydrolized Kraft process can be found in Pulping Processes, S. A. Rydholm, etc. , pages 576-649 and 655-672, 1965, Interscience Publishers, New York, E. U. A., and in Pulp and Paper Manufacture, volume 5 - Alkaline Pulping, T. M. Grace, EW Malcom and MJ Kocurek, eds, page 1 989, THE JO INT TEXTBOOK COMMITTEE OF THE PAPER I NDUSTRY, CPPA: Montreal, Quebec, Canada, and TAPPI, Atlanta, Georgia, USA In a typical example, wood chips are subjected to steam in a pressure digester, at temperatures up to 1 76 ° C (350 ° F) for 30 minutes. This prehydrolysis extracts a large part of the hemicelluloses present in the wood, which are resistant to alkali. The steam condensate from this stage, from the digester, is drained and the prehydrolyzed wood chips are subjected to an aqueous solution of sodium hydroxide, sodium sulfite and sodium hydrosulfide, in a digester under pressure, at temperatures up to 1 75 °. C for 90 minutes. At the end of that period the contents of the digester are discharged by opening into a large tube that is at atmospheric pressure, which leads to a receiving vessel. While in transit, the chips are defibrated to individual fibers. Unbleached pulp fibers are washed with fresh water to remove residual chemicals and water-soluble components of the wood. The unbleached fibers are subjected to individual steps of bleaching and purification using chlorine, chlorine dioxide, sodium hydroxide and sodium hypochlorite. The final products are cellulose fibers with more than 98 percent purity. The purity of the cellulose fibers is specified based on their percentage by weight of cellulose. The most common designation of cellulose is the alpha-cellulose content. For example, a pulp with alpha = 95 has a cellulose content of 95 percent. The procedure for measuring the alpha-cellulose content is based on the insolubility in aqueous sodium hydroxide. Alpha-cellulose is that fraction of cellulose fibers that is insoluble in both aqueous sodium hydroxide at 17.5 percent and insoluble in 9.75 percent aqueous sodium hydroxide. The procedure is described in the TAPPl T203 standard. A second method frequently used to specify the purity of cellulose is the solubility in alkali, in 1 0 percent aqueous sodium hydroxide, known as S10, and which can also be indicated as S-10 or S10. These S10 data are a measure of the solubility of hemicellulose in the aqueous alkali. Subtracting S10 from 1 00 gives approximately the same figure as the alpha-cellulose content of the sample. The S10 procedure is described in the TAPPl T235 standard. As used herein for bleached pulp, "percentage of cellulose" means 100-S10. In one embodiment, the cellulose fibers suitable for use in this invention are chemically purified, individualized cellulose fibers having a length of about 0.1 to about 10 mm, a diameter of about 0.001 to about 0.1 mm, and having length to diameter ratios of from about 30 to about 3000. The cellulosic fiber reinforced cementitious material of this invention is produced by combining the fibers with cement, water and sand, aggregate, or sand and aggregate. Cellulose fibers are derived from chemical, mechanical or thermal means or their combinations; of plants that do not contain wood, of plants that have wood and of products of recycled paper, reducing the process of individualization the union between the fibers, so that they can be dispersed in conventional mixtures of concrete using conventional mixing equipment, at relatively low doses from about 0.1 kg / m3 to about 30 kg / m3 of chemically purified cellulose fiber. The affinity of the individualized pulp fibers towards water facilitates their dispersion in the concrete. The new concrete mixtures that incorporate fibers of plant pulp, have possibility of convenient work, resistance to segregation and outcrop, ability to be pumped, ability to be finished, resistance to the formation of cracks by plastic shrinkage, and reduced rebound when they are pneumatically applied. Some embodiments of this invention require that a substantial weight percent of the cementitious material be chemically purified fiber; while other modalities use a very small weight percentage of fiber. In general, the content of chemically purified cellulose fiber, of the cementitious material, is from about 0.01 weight percent to about 20 weight percent, based on the weight of the cementitious material; more often, from about 0.01 weight percent to about 10 weight percent, based on the weight of the cementitious material; conveniently about 0.01 weight percent to about 3 weight percent, based on the weight of the cementitious material; more convenient, from about 0.01 weight percent to about 1 weight percent, based on the weight of the cementitious material, preferably from about 0.01 weight percent to about 0.5 weight percent, based on in the weight of the cementitious material; more preferably, from about 0.01 weight percent to about 0.1 weight percent, based on the weight of the cementitious material. Inorganic binders useful for the present invention include inorganic water-curable substances, which form a matrix upon setting; such as cement-based materials, calcium silicate materials and mixtures thereof. The chemistry of such compositions is described in P. K. Mehta and P. J.M. Monteiro, Concrete Structure, Properties and Materials, Prentice Hall, 1993 [548 pp], and in P.C. Hewlett, Lea 's Chemistry of Cement and Concrete, 4a. edition, Butterworth-Heinemann, 1998 [1056 pp], both incorporated herein in their entirety by means of this reference. When used herein, the term "cement-based materials or cementitious materials" refers to compositions that generally comprise lime, alumina, silica and iron oxide. Applicable cement-based materials include: Portland cement, aluminous cement, blast furnace cement and mixtures thereof. Portland cement is contemplated especially for use with the present invention. In general, Portland cement is composed primarily of tetracalcium aluminoferrate (4 CaO AI2O3 Fe2O3), tricalcium aluminate (3 CaO AI2O3), tricalcium silicate (3 CaO SiO2) and dicalcium silicate (2CaO SiO2). Each of the five conventional types of Portland cement and white Portland cement can be used as an inorganic binder. These include moderate heat setting cement, known in the art as type II, early high strength cement (HES), known as type III, low heat cement, known as type IV and cement of chemical resistance, known as type V. It is contemplated in particular the type I cement, which is commonly used for a variety of construction purposes in general. It is within the ability of anyone with ordinary experience in the field to modify and adjust the relative proportions of the Portland Cement components, in order to increase a particular property or to prepare any of the conventional types of Portland cement., including white Portland cement, from the list above. The preparation of the chemically purified cellulose fibers can be easily achieved for use in the cement mixture. Method 1: Chemically purified cellulose fibers are supplied in the form of typical sheet rolls, with approximate physical sheet properties, on the basis of weight, of about 710 g / m2 and density of approximately 0.59 g / cm3. The sheet is fed to a pulp sheet disintegrator, such as, for example, a Kamas Mili, so that the sheet form is converted to the fluff form of much lower density, which is between about 0.05 g / cm 3 and around 0.25 g / cm3. Then the fluff fibers are dosed to specified weights and packaged as they are in small bags, made of degradable material, which disintegrates when put in contact with water. These small bags are supplied to the concrete manufacturer, where they are simply emptied into the concrete mixture, the bag and the individualized, chemically treated cellulose fibers, at the appropriate time to be evenly distributed throughout the concrete load. Based on the desired fiber load, for example, in kilograms of fiber per m3 of concrete, the appropriate weight and the appropriate number of bags are used. Method 2: Typical cellulose fibers in the form of sheet bale are supplied, with approximate physical sheet properties for the base weight of approximately 710 g / m2 and density of approximately 0.59 g / cm3, to a concrete manufacturing site . The pulp sheets are then loaded into a tank containing water and a suitable stirrer, so that the sheets are mixed with the water to form a uniform slurry of individual pulp fibers, with a consistency varying from 0.1 percent. at 3.0 percent by weight. During the concrete mixing process, the appropriate volume of fibers and thick aqueous suspension are pumped to the concrete mixer truck to supply the necessary water and fiber content for the concrete loading, and to allow its uniform distribution. The chemically purified cellulose fibers of the present invention can be made of laminated cellulose, in the form of twisted dies of laminated fibrous material, where the twisted die has a generally rectangular shape, with an uncrossed length of about 10 mm at around 1 00 m; a width of about 2 mm to 15 mm, and a thickness of about 1 mm to about 6 mm; an approximate density of 0.1 g / cc to about 0.5 g / cc, and where the die has one or more twists of 45 degrees or more, the full length thereof, or a rectangular die shape of sheet fibrous material, wherein the rectangular die has a generally rectangular shape with a length of about 4 mm to about 10 mm, a width of about 3 mm to about 8 mm, and a thickness of about 1 mm to about 2 mm; a density of approximately 0.5 g / cc to approximately 0.6 g / cc. In an alternative embodiment of this invention, the chemically purified cellulose fibers are used to produce a non-woven material, for example, by an air-laying process, and the non-woven material is used as a reinforcement in a cementitious mixture. In another embodiment of this invention the chemically purified cellulose fibers, described above, are used in a cementitious material, in the form of a reinforcing mixture or combination comprising one or more other reinforcing materials. These can be one or more fibers which are synthetic or natural fibers, such as, for example: thermoplastic fibers, polyolefin fibers, polyethylene fibers, polyester fibers, nylon fibers, polyamide fibers, polyacrylonitrile, polyacrylamide, viscose, wool , silk, polyvinyl chloride, polyvinyl alcohol, metal fibers, carbon fibers, ceramic fibers, steel fibers (straight, curled, twisted, deformed, with hooked or flattened ends), glass fibers, carbon fibers, fibers Natural organic and mineral (Manila hemp, asbestos, bamboo, coconut, cotton, jute, henequen, wood, rock wool), polypropylene fibers (flat, twisted, fibrillated, with button-shaped ends), kevlar, rayon. In another embodiment of this invention, chemically purified cellulose fibers, described above, are used in a cementitious material, either alone or in admixture with other fibers; where the cementitious material contains a latex or a latex mixture. The cementitious materials of this invention are useful for forming a wide variety of poured structures, structures that anyone looks at every day, such as, for example: highways, roads, sidewalks, accesses, parking lots, concrete buildings, bridges and the like.

TEST METHODS Purity measurements are usually based on what is called the alpha-cellulose content. Pulp fibers contain three basic types of polymers: cellulose, hemicellulose and lignin. Bleached fibers have had almost all of the lignin polymer removed during processing. The alpha-cellulose content of the bleached samples is determined by extracting the pulp with 10 percent sodium hydroxide. The hemicelluloses and the degraded cellulose are dissolved in the alkaline solution, and the amount eliminated is called the S10 value in percentage. (See Tappi standard T235). If that value of 100 percent is subtracted, a good estimate of the alpha-cellulose content is obtained. For unbleached pulps, such as impure materials, the alpha-cellulose content is determined by subtracting both the Sio value in percent and the percentage value of lignin of 1 00 percent. The percentage value of lignin is calculated from the number K of the impure material. And, accordingly, when used here for bleached pulp, the "percentage of cellulose" means 100-S 0, and for the impure material, the "percentage of cellulose" means 100-S10-percentage of lignin. The consistency of the pulp is a specific term in the pulp industry, which is defined as the amount of totally dry fiber divided by the total amount that includes fiber, water, other solids, etc. , and multiplied by 1 00. Therefore, for a thick suspension of 12 percent consistency, every 1 00 kilograms of slurry will contain 12 dry kilograms of fiber.

EXAMPLE The following examples illustrate the invention, but do not limit it.

EXAMPLE 1 Preparation of impure and whitened soft southern wood kraft (SSK) Pulp of wood chips of Pinus elliotti was formed predominantly, by means of a kraft process, up to a permanganate number (number K) of around 17 mL, when determined by the procedure described in the TAPPl method T214, and the value S10 (Tappi T-235) measured was 9.34 percent. The fibers were washed and screened for quality, and then bleached with a D-E0p-D-EPD process, at an ISO brightness of about 86 percent. The viscosity, when measured by T230 was approximately 16 cP. S10, when measured by T235, was 12.78 percent. In this process D is a chlorine dioxide stage, E0p is an extraction step with addition of oxygen and hydrogen peroxide, and Ep is an extraction step with added hydrogen peroxide. These bleached cellulose fibers were diluted with water to form a slurry consisting of 0.9 parts of fiber per 1000 parts of slurry, at a pH of 6.5. The resulting slurry was continuously dehydrated with a machine in which a sheet was formed at a rate of 1 .0 influx / drag, laid, then pressed and densified using three wet pressing steps up to 48 parts of fiber per 100 parts in total. The sheet was dried using conventional drum dryers, at a solids content of 94 percent. The flat pulp was then processed to individual rolls. This fiber is commercially available as FOLEY FLUFFS® from Buckeye Technologies, Memphis, Tennessee, E. U. A.

Samples of the SSK pulp were subjected before bleaching FFbs) and after the bleaching sequence described above (FF) to the alkaline stability test described below (see example 6).

EXAMPLE 2 Northern softwood kraft pulp (NSK) Alkaline stability tests were also carried out on commercial samples of impure and wholly bleached kraft pulp from northern softwood, prepared from northern pine and spruce shavings, similar to the process described above. The number K of the impure sample was 25 and its viscosity with chlorite was 37 cP.

EXAMPLE 3 Dissolution of previously hydrolysed SSK pulps Commercial samples of kraft pulps of purified and fully bleached southern pine were subjected to the alkaline stability test. These samples differ from the sample of Example 1 in that they received a prior hydrolysis treatment to reduce the amount of hemicellulose present in the pulp. The sample designated V-60 is less pure than sample V-5, because it received a less severe previous hydrolysis treatment, and because it did not receive a cold caustic extraction. The caustic extraction process that received the V-5 product increases its purity by eliminating more hemicellulose and degraded cellulose present in the pulp. The samples of these previously hydrolysed SSK pulps, designated V-60 and V-5, were subjected to the alkaline stability test described below (see Example 6), as described above.

EXAMPLE 4 Mercerized SSK Pulp Samples of the SSZ-derived HPZ pulp described above were subjected to the alkaline stability test described below (see Example 6).

EXAMPLE 5 Purified cotton wool pulps Two pulps of purified cotton linters were subjected to the alkaline stability test. A sample, grade 505, is used to prepare fine paper, and receives a more severe treatment of pulp formation with sodium hydroxide and a more severe bleaching, at lower viscosity, 9.4 cP (Tappi T230) and 90 percent more brightness . The other sample, HVE, is a degree of dissolution intended for the preparation of high viscosity ethers, and has a brightness of 75.5 percent and a viscosity of more than 13,000 ACS seconds (see ASTM D6188). This viscosity is equivalent to about 330 cP (see Tappi T230). The pulp samples of the cotton linings described above were subjected to the alkaline stability test described below (see Example 6).

EXAMPLE 6 Determination of the alkaline stability (ZSSR) of cellulose fibers This test method is described in detail in the ASTM method D6942-03. This test method can be used to compare different types of cellulose pulp fiber, based on their response to standard alkaline solutions. The stability factor defined below can be used to measure the effect of exposure to alkaline conditions on the strength of the fiber. Reference is made in this method to other methods for forming test sheets and for the determination of traction to zero extension, which are included here. At 20 g (dry basis) of FOLEY FLUFFS® fibers in an uncovered beaker, 46.7 g of 1 N NaOH was added and left to remain in the beaker for 24 hours. Additional samples were allowed to age for 7, 14 and 28 day time intervals. When the time interval had passed, the treatment of the samples was obtained by collecting the fibers on a wire mesh, washing with running water until the washes are substantially neutral (pH = 7 to 7.5), and then air drying. Control samples were prepared using the above procedure, with replacement of the distilled water by 1 N sodium hydroxide. Two sets of standard test sheets were prepared according to TAPPl T205 for each sample. A series is prepared from fibers that had been exposed to alkali. These series of test sheets were prepared on the same day. Each series of test sheets was tested for zero tensile traction, in accordance with TAPPl T231. The zero extension stability ratio (ZSSR) was calculated by dividing the tensile result at zero extension of the alkali treated sample between the tensile to zero extension result of the corresponding untreated sample (control). The results are reported as a percentage, such as 92.1 percent. The stability proportions at zero extension are reported individually for each sample time interval, and as an average value for all samples of time interval tested. The procedure described above was used to test each of the pulp samples. Table 1 gives a summary of the data.

TABLE 1 ZSSR test against purity The average results at the bottom of the table have less variability than the individual days. The samples are listed in the order of purity estimated, from left to right. It is clear that the ZSSR values increase from left to right, which demonstrates a direct relationship in which a high ZSSR correlates with high purity of the cellulose. Table 2 shows all the data for purity and ZSSR. } TABLE 2 ZSSR. S-10 AND PERCENTAGE OF CELLULOSE A plot of the percentage of ZSSR versus S10 or the percentage of cellulose for bleached pulps, gives the same correlation shown in figures 1 and 2. The results are somewhat different when the two impure samples are included, as shown in figures 3 and 4. In figure 3, the percentage values ZSSR of all the samples are plotted against the value S10- In figure 4 the percentage values ZSSR of all the samples are plotted against the purity, where the percentage value of cellulose subtracting the S10 value and the percentage of lignin remaining in the pulp fibers. The correlation improves, but it is still lower than for bleached pulps. This suggests that residual lignin is more harmful to alkaline stability than hemicellulose. In general, these data clearly show that the purification of the cellulosic fibers results in improved alkaline stability, as measured by the ASTM method D6942-03. The present invention is not limited in scope by the specific embodiments described herein. In fact, various modifications of the invention, in addition to those already described herein, will be apparent to those of ordinary skill in the art, from the foregoing description and the appended figures. It is intended that said modifications fall within the scope of the claims that follow. The patents, the patent applications, the publications, the product descriptions and the protocols cited throughout that description are hereby incorporated into their descriptions by means of this reference, in their entirety, for any purpose.

Claims (8)

REIVIN DICACIONES

1 .- A cementitious material reinforced with cellulose fiber, characterized in that it comprises: (A) cement; (B) optionally, sand, aggregate, or sand and aggregate; and (C) chemically purified cellulose fibers, which have a ZSSR of about 90 percent or more.

2. The material according to claim 1, further characterized in that the chemically purified cellulose fibers have a ZSSR of about 93 percent or more.

3. The material according to claim 2, further characterized in that the chemically purified cellulose fibers have a ZSSR of about 95 percent or more.

4. A cementitious material reinforced with cellulose fiber, characterized in that it comprises: (A) cement; (B) optionally, sand, aggregate, or sand and aggregate; and (C) chemically purified cellulose fibers, which have a cellulose percentage content of about 90 percent or more.

5. The material according to claim 4, further characterized in that the chemically purified cellulose fibers have a percentage content of cellulose around 93 percent or more.

6. The material according to claim 5, further characterized in that the chemically purified cellulose fibers have a cellulose percentage content of about 95 percent or more.

7. A cementitious material reinforced with cellulose fiber, characterized in that it comprises: (A) cement; (B) optionally, sand, aggregate, or sand and aggregate; (C) chemically purified cellulose fibers, having a ZSSR of about 90 percent or more; and (D) one or more synthetic or natural fibers, which are chemically treated cellulose fibers, thermoplastic fibers, polyolefin fibers, polyethylene fibers, polyester fibers, nylon fibers, polyamide fibers, polyacrylonitrile fibers, polyacrylamide fibers , viscose fibers, wool fibers, silk fibers, polyvinyl chloride fibers, polyvinyl alcohol fibers, metal fibers, carbon fibers, ceramic fibers, straight steel fibers, crimped, twisted, deformed, with ends in hooked or flattened shape; glass fibers, abaca fibers, asbestos fibers, bamboo fibers, coconut fibers, cotton fibers, jute fibers, henequen fibers, wood fibers, rock wool fibers, normal polypropylene fibers, twisted, fibrillated , with ends in the form of a button; kevlar fibers or rayon fibers.

8. The material according to claim 7, further characterized in that it additionally comprises a latex.