MXPA99001679A - Fibers having enhanced concrete bonding strength - Google Patents

Abstract

The bonding between concrete and fibers is enhanced by using a fiber coating material selected from certain glycol ethers, having at least three carbon atoms in an oxyalkylene group, and glycerol ethers. The present invention pertains to such coated fibers, a method for modifying a concrete using the coated fibers, and a cementitious composition containing the coated fibers.

Description

"FIBERS THAT HAVE IMPROVED RESISTANCE TO THE ACCESSION TO THE CONCRETE" FIELD OF THE INVENTION The present invention relates to fibers for reinforcing concrete and, more particularly, to the use of fibers coated with a material for improving resistance to adhesion to concrete such as glycol ethers and specific glycerol ethers.

BACKGROUND OF THE INVENTION Fibers made of metal, glass and synthetic materials, such as polyolefins, have been used in concrete, to provide additional tensile strength and to reinforce against impact damage and crack propagation, including self-induced cracks. Polyolefin fibers, such as polypropylene tend to be hydrophobic due to the nature of the material, and require a wetting agent to provide a surface tension characteristic that allows them to be more easily dispersed within an aqueous concrete mixture. U.S. Patent No. 5,399,195 (assigned to Danaklon A / S) described polyolefin fibers which were treated with a wetting agent by passing filament bundles through lubricating application rolls. The wetting agent can be selected from wetting agents normally applied to synthetic fibers to make them hydrophilic such as emulsifiers, surfactants, detergents and mixtures thereof. The examples in the '195 patent included fatty acid esters of glycerides, fatty acid amides, polyglycol esters, polyethoxylated amides, nonionic surfactants and cationic surfactants. Fiber coatings of the prior art, however, are believed by the present inventors, which presents some problems in concrete applications. Some coating formulations that are derived from ethylene oxide or that contain fatty residues can generate air or cause foaming which, adjacent to the surface of the fiber, can increase the tendency of the fiber to be extracted during the formation of cracks. Accordingly, a novel coated fiber, a fiber coating material and a method for modifying concrete properties using a novel coated fiber are necessary.

SUMMARY OF THE INVENTION Overcoming the disadvantages of the prior art, the present invention provides coated fibers having improved resistance to concrete adhesion and improved extraction resistance, and it is believed that they help to suppress the air retention capabilities of the Cement mixture, in which the coated fibers are mixed. The fibers, preferably made of polypropylene, are coated with a material that is selected from specific glycol ethers, having at least three carbon atoms in an oxyalkylene group, and glycerol ethers. A preferred glycol ether fiber coating material is dipropylene glycol-t-butyl ether; while a preferred glycerol ether fiber coating is di-t-butyl glycerol. An exemplary method of the invention for modifying the properties of a concrete comprises adding to the concrete, mortar or cement mixture, an amount of 0.05 percent to 10 percent by weight, and more preferably an amount of 0.1 percent to 5 percent by weight. percent based on the total dry weight of the cement, the fibers having a coating material that is mentioned above; and mixing the resulting mixture. The present invention also relates to cementitious compositions comprising the coated fibers described above.

DETAILED DESCRIPTION OF THE EXEMPLARY MODALITIES The terms "paste", "mortar" and "concrete" are technical terms: pastes are mixtures composed of a hydraulic cement binder (usually, but not exclusively, Portland cement, Masonry cement or Mortar cement, and also include limestone, hydrated lime, fly ash, blast furnace concrete and silica vapors or other materials commonly included in these cements) and water; mortars are pastes that also include a fine aggregate; and concretes are mortars that also include coarse aggregate. The "cementitious" compositions of the invention can be formed by mixing the required amounts of certain materials, e.g. a hydraulic cement, water and fine or coarse aggregate, as desired, with the coated fibers as will be described below. A method of the present invention for modifying the properties of a concrete comprises: adding to a concrete, mortar or cement mixture, in an amount of 0.05 percent to 10 percent by weight based on the total dry weight of the cement, fibers having a coating material that is selected from the group consisting of glycol ether and glycerol ether; mix the resulting mixture to obtain a concrete, mortar or paste mixture in which the individual fibers are distributed homogeneously; and molding the mixture in one configuration. Most preferably, the amount of addition of the coated fiber is from 0.1 percent to 5 percent, and most preferably, from 0.5 percent to 2 percent, based on the total dry weight of the cement. The term "configuration" means and refers to a wall, floor, panel, block, paver or other component of a building or civil engineering structure, such as a building, parking garage, bridge deck, tunnel and the like, which It is formed by molded concrete. The coated fibers of the invention can also be used in mortars. Exemplary fibers of the invention comprise steel, glass, carbon fiber, cellulose, rayon or synthetic materials such as polyolefins, nylon, polyester, and acrylics. Polyolefins such as polypropylene are preferred. The polypropylene fibers may be in the form of monofilament, confronted fibrillation, tape or other configurations and adhere in a formation of various sizes and dimensions. The fibers can also be packaged using mechanical or chemical means or can still be introduced into cementitious compositions using special packaging technology (See, e.g., North American Patent Number 5,224,774 to W. R. Grace). The fibers of the invention can be coated during or after the fiber manufacturing process, using known methods. Exemplary coated fibers of the present invention are coated with a glycol ether having the formula: RO (AO) n-H wherein R comprises an alkyl group of 1 to 7 carbon atoms or a cycloalkyl group of 5 to 7 carbon atoms; A comprises an alkylene group of 3 to 4 carbon atoms; Or is oxygen; n represents an integer from 1 to 10, and H is hydrogen. The AO groups (e.g., "oxyalkylene") which form the chain of these glycols may contain a single type of the alkylene ether group or a mixture of alkylene ether groups which may be in a block or random arrangement. The present invention proposes that an oxyalkylene group has at least three carbon atoms. Preferred glycol ethers are: di-propylene glycol t-butyl ether, having the formula CH3 H H H I I I I CH3-C-O-C-C-O-C-C-OH I I I I CH3 H CH3 H CH3 di-propylene glycol-n-butyl ether, having the formula H H H H l i l i CH3-CH2-CH2-CH2 -O-C-C-O-C-C-OH I I I H CH3 H CH3; Y di-propylene glycol-n-propyl ether having the formula H H H I I I I CH 3 -CH 2 -CH 2 -O-C-C-O-C-C-OH I I I I H CH 3 H CH 3 Other exemplary coated fibers of the present invention are coated with a glycerol ether having the formula: CH ~ (AO) and-OR2 CH2- (AO) z-OR3 wherein R] _, R2 and R3 are hydrogen or an alkyl group of 1 to 14 carbon atoms, at least one of R] _, R2 and R3 comprises an alkyl group of 1 to 14 carbon atoms; A is a group of 2 to 4 carbon atoms; and x, y and z are integers from 0 to 10.

A preferred glycerol ether is di-t-butylglycerol, which has the formula CH2 - 0 - C (CH3) 3 I CH2 - OH I CH2 - 0 - C (CH3) 3 The invention is further illustrated by the following non-limiting examples.

Example 1 This example illustrates the operation of relative air retention of an ethylene glycol, namely, triethylene glycol monobutyl ether (which can be obtained from Union Carbide under the name "butoxytriglycol"), which is chemically similar to a known wetting agent, the ether of polyethylene glycol lauryl (See, eg column 8, II.10-12, US Patent Number 5,399,195) as compared to the di-propylene glycol-t-butyl ether as proposed in the present invention. A control sample mortar was made using 2 weight percent of an air retention agent (based on the dry weight of the cement). The air retention agent can be obtained from W. R. Grace & Co.-Conn., Of Cambridge, Massachusetts, under the name of DARAVAIR® 1000. A second sample of triethylene glycol monobutyl ether mortar ("butoxytriglyc") was prepared in an amount of 2 percent (by weight). A third sample of mortar containing di-propylene glycol-t-butyl ether ("DPTB") was also prepared in an amount of 2 percent (by weight). The samples were mixed for nine minutes, and the air content was determined in accordance with Method C185 of the American Society for the Testing of Materials (1994). The results are summarized in the following table and show that ethylene glycol ("butoxitriglicol") retained the air in an amount similar to the control sample. However, sample 3 containing DPTB surprisingly showed almost two thirds less of retained air. Table 1 Sample Retained Air (Method C185-1994 of the American Society for the Testing of Materials) 1 Control 24% 2 Butoxytriglycol 20% 3 DPTB 7% Example 2 This test measured the resistance to the extraction of several coated fibers. Polypropylene fibers with a length of 5.08 centimeters and a diameter of .648 x 1.00 millimeters were used to elaborate the three samples. Sample 1 comprised polypropylene fibers having a coating comprising polyethylene glycol monolaurate ("PEG monolaurate"), an ester having a molecular weight of about 400 to 500. Sample 2 was prepared by coating another identical number of polypropylene fibers with butoxitriglicol. Sample 3 was prepared by coating another set of identical fibers with di-propylene glycol t-butyl ether ("DPTB"). The 5.08 centimeter fibers were coated by immersing in coating materials, allowing it to air dry, and then the coated portion was immersed in identical cement pastes (slurry) in such a way that the embedded length of the fibers was 2.54 centimeters. The cement was allowed to cure for 24 hours at 100 percent relative humidity. All three samples were tested on an Instron 1011 tester that measured the load (in kilograms) needed to displace the cement fibers. The resistance to extraction, or the resistance to adhesion (kilograms per square centimeter), was calculated by determining the average maximum load reed to displace the fibers, and dividing it by the average surface area of the fiber that comes into contact with the fiber. Cementitious matrix. The following table summarizes the relative adhesion strengths calculated for each of the three fiber samples. Table 2 Mués - Coating Material - Load Load Resistance Maximum Fiber Traction Average Adhesion (kgs) (kgs) (kgs per cm ^) PEG monolaurate 1.32 PEG monolaurate 0.91 PEG monolaurate 1.33 l.lí 877 Butoxitriglicol 1.09 Butoxitriglicol 1.18 Butoxitriglicol 1.27 Butoxitriglicol 1.00 Butoxitriglicol 1.77 1.23 915 DPTB 1.27 DPTB 1.63 DPTB 1.36 DPTB 1.54 1.45 1.077 Sample 1 demonstrated an adhesion strength of .872 kilogram per square centimeter (with a standard deviation of .037). Sample 2 demonstrated a similar adhesion strength of .915 kilogram per square centimeter (with a deviation of 0.038). However, Sample 3 involving dipropylene glycol butyl ether ("DPTB") as the coating material demonstrated a comparatively improved adhesion strength of 1077 kilograms per square centimeter (standard deviation of .026). The following examples are provided for illustration only and are not intended to limit the scope of the invention, as claimed.

Claims (11)

CLAIMS:

1. A method to modify the properties of concrete that includes: adding to a concrete, mortar or cement mixture, in an amount of 0.05 percent to 10 percent by weight based on the total dry weight of the cement, fibers that have a material of coating which is selected from the group consisting of a glycol ether and a glycerol ether, mixing the resulting mixture to obtain a concrete, mortar or paste mixture in which the individual fibers are homogeneously distributed, and molding the mixture in a; the glycol ether having the formula RO (AO) n-H wherein R comprises an alkyl group of 1 to 7 carbon atoms or a cycloalkyl group of 5 to 7 carbon atoms; A comprises an alkylene group of 3 to 4 carbon atoms; Or is oxygen; n represents an integer from 1 to 10, and H is hydrogen; and the glycerol ether has the formula: CH2- (AO) x-OR? I CH2- (AO) y-OR2 CH2- (AO) Z-0R3 wherein R] _, R2 and R3 are hydrogen or an alkyl group of 1 to 14 carbon atoms, at least one of R] _, R2 and R3 comprises an alkyl group of 1 to 14 carbon atoms; A is a group of 2 to 4 carbon atoms; and x, y and z are integers from 0 to 10. The method of claim 1, wherein the fibers comprise a material that is selected from the group consisting of steel, glass, acrylics and polyolefins. 3. The method of claim 1 wherein the fibers comprise polypropylene. 4. The method of claim 3, wherein the fiber coating material comprises a glycol ether selected from the group consisting of dipropylene glycol-t-butyl ether, di-propylene glycol-n-butyl ether and di-propylene glycol-n-propyl. The method of claim 4, wherein the glycol ether comprises di-propylene glycol-t-butyl ether. The method of claim 4, wherein the fiber coating material comprises glycerol ether having the formula: CH2- (AO) and-OR2 CH2- (AO) z-OR3 wherein R] _, R2 and R3 are hydrogen or an alkyl group of 1 to 14 carbon atoms, at least one of R] _, R2 and R3 comprises an alkyl group of 1 to 14 carbon atoms; A is a group of 2 to 4 carbon atoms; and x, y and z are integers from 0 to 10. The method of claim 6, wherein the glycerol ether is di-t-butylglycerol, and the fibers comprise polypropylene. 8. Coated fibers for modifying the properties of a concrete comprise: a plurality of fibers coated with a material selected from the group consisting of a glycol ether and a glycerol ether; the glycol ether has the formula RO (AO) n-H wherein R comprises an alkyl group of 1 to 7 carbon atoms or a cycloalkyl group of 5 to 7 carbon atoms; A comprises an alkylene group of 3 to 4 carbon atoms; Or is oxygen; n represents an integer from 1 to 10, and H is hydrogen; and the glycerol ether has the formula: CH2- (AO) and-OR2 CH2- (AO) z-OR3 wherein R] _, R2 and R3 are hydrogen or an alkyl group of 1 to 14 carbon atoms, at least one of R] _, R2 and R3 comprises an alkyl group of 1 to 14 carbon atoms; A is a group of 2 to 4 carbon atoms; and x, y and z are integers from 0 to 10. The coated fibers of claim 8, wherein the fiber coating material comprises a glycol ether selected from the group consisting of di-propylene glycol-t-butyl ether. of di-propylene glycol-n-butyl, and di-propylene glycol-n-propyl ether. 10. The coated fibers of claim 9, wherein the fiber comprises polypropylene and the fiber coating material is di-propylene glycol-t-butyl ether. 11. A cementitious composition comprising a hydraulic cementitious binder, water, a fine aggregate and a fiber coated with a material selected from the group consisting of a glycol ether and a glycerol ether; the glycol ether has the formula: RO (AO) n-H wherein R comprises an alkyl group of 1 to 7 carbon atoms or a cycloalkyl group of 5 to 7 carbon atoms; A comprises an alkylene group of 3 to 4 carbon atoms; Or is oxygen; n represents an integer from 1 to 10, and H is hydrogen; and the glycerol ether has the formula: CH2- (AO)? - OR] _ I CH2- (AO) y-OR2 I CH2- (AO) z-OR3 wherein R_, R2 and R3 are hydrogen or an alkyl group of 1 to 14 carbon atoms, at least one of R_, R2 and R3 comprises an alkyl group of 1 to 14 carbon atoms; A is a group of 2 to 4 carbon atoms; and x, y and z are integers from 0 to 10.