A method for modifying steel fibers and their use in concrete

Abstract

The application belongs to the technical field of building, and discloses a modification method of steel fiber and application of the steel fiber in concrete. The preparation method comprises the following steps: weighing polyallylamine hydrochloride (PAH) and dissolving the PAH in a phosphate buffered saline (PBS) solution and fully stirring to obtain a PAH solution with a specific concentration, and preparing a sodium silicate solution with a certain concentration for standby; immersing steel fiber in the PAH solution for a specific time, then taking out and cleaning with clean water; further immersing the cleaned steel fiber in a sodium silicate (Na2SiO3) solution with a certain concentration for a specific time; taking out the immersed steel fiber, and cleaning with clean water; and step five: drying the cleaned steel fiber until a constant weight is obtained, and cooling to room temperature for standby. The application can further improve the quality of the steel fiber, significantly enhance the strength and durability of the concrete, and has a very positive effect on prolonging the service life of the concrete and reducing the service life maintenance cost of the concrete structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of building technology, and particularly relates to a steel fiber modification method and application thereof in concrete. BACKGROUND

[0002] Steel fiber reinforced concrete is a multi-phase composite material composed of hardened cement stone, aggregate, cement stone-aggregate interface and steel fiber-cement stone interface. The random distribution of steel fibers in the cement matrix can effectively hinder the formation and development of internal micro-cracks in concrete, significantly improve the tensile, bending, impact and fatigue resistance of concrete, and has been widely used in subway tunnels, railway bridges, water conservancy projects and military protection projects.

[0003] However, the surface of the steel fiber is smooth, and after the rust-proof treatment of the plating layer, the surface has a certain hydrophobicity, and the interface combination with the concrete is relatively weak. Since the strength and toughness of the steel fiber are much higher than those of the concrete, there is a certain relative slip between the steel fiber and the concrete during the stress and damage process, which reduces the performance of the composite cement-based material. Through the modification of the surface of the steel fiber, it is an effective way to improve the bonding strength between the steel fiber and the concrete matrix. At present, there are mainly surface coating method, sol-gel method, EDTA (ethylenediamine tetraacetic acid) electrolysis method, sandpaper polishing method, etc. Among these methods, the surface coating method improves the compatibility between the steel fiber and the cement matrix, and realizes the improvement of the performance of the steel fiber reinforced concrete, which has attracted widespread attention. However, the above-mentioned methods require high requirements for the concentration of chemical solution, temperature and humidity, etc., which restricts the practical application in this aspect. SUMMARY

[0004] Based on the above, in order to improve the bonding performance between the steel fiber and the cement matrix and better play the ability of the steel fiber, the present application provides a steel fiber modification method and application thereof in high-strength concrete.

[0005] The object of the present application can be achieved by the following technical solutions:

[0006] A steel fiber modification method and application thereof in high-strength concrete, comprising the following steps: step one: a certain mass of PAH is dissolved in a certain mass of PBS buffer solution and fully stirred to obtain a PAH solution with a specific concentration, and a Na2SiO3 solution with a certain concentration is prepared for standby; step two: a certain mass of steel fiber is immersed in the PAH solution for a specific time, and then taken out and washed with clean water; step three: the steel fiber after washing is immersed in a Na2SiO3 solution with a certain concentration for a specific time; step four: the steel fiber after immersion treatment is taken out and washed with clean water; step five: the steel fiber after washing is dried to constant weight, and cooled to room temperature for standby.

[0007] The mass ratio of PAH to PBS buffer solution in the step one is 0.1:1000-1.4:1000, and the concentration of Na2SiO3 is 0.1mol / L-0.3mol / L.

[0008] Further, the purity of PAH and Na2SiO3 in the step one is analytical pure.

[0009] Further, the mass ratio of steel fiber to PAH solution in the step two is 1:3.

[0010] Further, the specific time of immersion in the step two and step three is 3-6h.

[0011] Further, the drying temperature in the step five is controlled at 60℃-80℃, and the processing time is 6-12h.

[0012] Further, the judgment method of constant weight in the step five is that the mass of steel fiber is weighed every 2 hours until the difference between the last two weights is not more than 0.01g, that is, the steel fiber has been dried to constant weight.

[0013] Further, the steel fiber in the steps one, two, three, four and five is flat, end hook and wavy, the length is 8-30mm, the diameter is 0.1-0.4mm, the length-diameter ratio is 50-120, and the tensile strength is greater than or equal to 2800MPa.

[0014] The present application utilizes the principle of biomineralization, focuses on the process of cell silicification, and uniformly coats amorphous SiO2 on the surface of steel fiber in a neutral aqueous solution environment at normal temperature and pressure, changes the physicochemical properties of the steel fiber surface, promotes the deposition of hydration products on the surface of steel fiber by the induction effect of SiO2 on secondary hydration reaction, and thus increases the bonding strength between steel fiber and cement matrix. For this purpose, the present application proposes to use polyallylamine hydrochloride (PAH) as a mineralization template, and sodium silicate as a mineralization object, to uniformly deposit amorphous SiO2 on the surface of steel fiber, to improve the degree of secondary hydration reaction at the interface between steel fiber and cement, and to improve the interfacial bonding strength.

[0015] The application relates to a steel fiber modification method and application thereof in high-strength concrete. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced.

[0017] Figure 1 is an electron microscope image of the steel fiber used by the reference group;

[0018] Figure 2 is an electron microscope image of the steel fiber used by the reference group;

[0019] Figure 3 is an EDS analysis image of the steel fiber used by the reference group;

[0020] Figure 4 is an EDS analysis image of the steel fiber used by the reference group;

[0021] Figure 5 is a pull-out load-slippage curve of the steel fiber used by the reference group and the steel fiber used in example 1;

[0022] Figure 6 is the bending strength of the concrete of the example and the reference group. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0024] Reference group 1

[0025] The steel fiber modification method and application thereof in high-strength concrete are characterized by comprising the following steps:

[0026] Step one: 657 parts of cement, 1313 parts of sand, 105 parts of untreated steel fiber are added into the cement mortar stirring pot in turn, dry stirring for 3 minutes;

[0027] Step two: then 5 parts of water reducing agent are added into 230 parts of water and stirred uniformly, then poured into the stirring pot, continue to stir for 3 minutes, further pour the newly mixed steel fiber mortar into the mold of 40mm*40mm*160mm, and place it in the constant temperature box with humidity of 95% and temperature of 20℃ for curing.

[0028] Further, the steel fiber in steps one and two is straight and has no hooks, the length is 13mm, the diameter is 0.2mm, the length-diameter ratio is 65, and the tensile strength is 2800MPa.

[0029] Example 1

[0030] A steel fiber modification method and its application in high-strength concrete, characterized in that it comprises the following steps:

[0031] Step one: 0.6 parts of PAH are dissolved in 1000 parts of PBS buffer and stirred thoroughly to obtain a PAH solution, and a 0.2mol / L Na2SiO3 solution is prepared for standby;

[0032] Step two: 333.3 parts of steel fiber are immersed in 1000 parts of PAH solution for 3h, then taken out and washed with clean water;

[0033] Step three: the washed steel fiber is immersed in a 0.2mol / L Na2SiO3 solution for 3h;

[0034] Step four: the steel fiber treated by immersion is taken out and washed with clean water;

[0035] Step five: the washed steel fiber is dried in a 60℃ oven to constant weight, and then cooled to room temperature for standby. Then 657 parts of cement, 1313 parts of sand, 105 parts of treated steel fiber are added into the cement mortar stirring pot in turn, dry stirring for 3 minutes, then 5 parts of water reducing agent are added into 230 parts of water and stirred uniformly, then poured into the stirring pot, continue to stir for 3 minutes, further pour the newly mixed steel fiber mortar into the mold of 40mm*40mm*160mm, and place it in the constant temperature box with humidity of 95% and temperature of 20℃ for curing.

[0036] Further, the purity of PAH, PBS and Na2SiO3 in step one is analytical pure.

[0037] Further, the mass ratio of steel fiber to PAH solution in step two is 1:3.

[0038] Further, the immersion time in steps two and three is 3h.

[0039] Furthermore, the drying temperature in step 5 is controlled at 60° C., and the treatment time is 8 hours.

[0040] Furthermore, the method for judging the constant weight in step 5 is: weighing the mass of the modified steel fiber every 2 hours until the difference between the last two weights does not exceed 0.01 grams, and it can be determined that the steel fiber has been dried to a constant weight.

[0041] Furthermore, the steel fibers in steps 1, 2, 3, 4, and 5 are straight and endless hooks with a length of 13 mm, a diameter of 0.2 mm, an aspect ratio of 65, and a tensile strength of 2800 MPa.

[0042] Baseline Group 2

[0043] A steel fiber modification method and its application in high-strength concrete, characterized by comprising the following steps:

[0044] Step 1: Add 657 parts of cement, 1313 parts of sand, and 210 parts of untreated steel fiber into the cement mortar mixing pot in sequence and dry-mix for 3 minutes;

[0045] Step 2: Then add 5 parts of water-reducing agent to 230 parts of water, stir evenly and pour into the mixing pot, continue stirring for 3 minutes, and further inject the freshly mixed steel fiber mortar into a 40mm×40mm×160mm mold, and place it in a constant temperature box with a humidity of 95% and a temperature of 20°C for curing.

[0046] Furthermore, the steel fiber in steps 1 and 2 is a straight endless hook with a length of 13 mm, a diameter of 0.2 mm, an aspect ratio of 65, and a tensile strength of 2800 MPa.

[0047] Example 2

[0048] A steel fiber modification method and its application in high-strength concrete, characterized by comprising the following steps:

[0049] Step 1: Weigh 0.6 parts of PAH and dissolve it in 1000 parts of PBS buffer, and stir thoroughly to obtain a PAH solution. Prepare 0.2 mol / L Na2SiO3 solution for later use.

[0050] Step 2: immerse 333.3 parts of steel fiber in 1000 parts of PAH solution for 3 hours, then remove and rinse with clean water;

[0051] Step 3: After cleaning, the steel fiber is immersed in a 0.2 mol / L Na2SiO3 solution for 3 h;

[0052] Step 4: Take out the impregnated steel fiber and wash it with clean water;

[0053] Step five: After the cleaning, the steel fiber is dried in an oven at 60℃ until the constant weight, and then cooled to room temperature for standby. Then 657 parts of cement, 1313 parts of sand, 210 parts of treated steel fiber are added into the cement mortar stirring pot in turn, dry stirring for 3 minutes, then 5 parts of water reducing agent is added into 230 parts of water and stirred evenly, then poured into the stirring pot, continue to stir for 3 minutes, further pour the newly mixed steel fiber mortar into the 40mm*40mm*160mm mold, and place it in the constant temperature box with humidity of 95% and temperature of 20℃ for curing.

[0054] Further, the purity of the PAH, PBS, and Na2SiO3 in step one is analytical pure.

[0055] Further, the mass ratio of steel fiber to PAH solution in step two is 1:3.

[0056] Further, the specific time for immersion in steps two and three is 3h.

[0057] Further, the drying temperature in step five is controlled at 60℃, and the treatment time is 8h.

[0058] Further, the method for determining the constant weight in step five is that the mass of the modified steel fiber is weighed every 2 hours until the difference between the last two weights is not more than 0.01g, which means that the steel fiber has been dried to a constant weight.

[0059] Further, the steel fiber in steps one, two, three, four, and five is flat and has no end hook, with a length of 13mm, a diameter of 0.2mm, a length-diameter ratio of 65, and a tensile strength of 2800MPa.

[0060] Reference group 3

[0061] A steel fiber modification method and its application in high-strength concrete, characterized in that it comprises the following steps:

[0062] Step one: 657 parts of cement, 1313 parts of sand, and 315 parts of untreated steel fiber are added into the cement mortar stirring pot in turn, dry stirring for 3 minutes.

[0063] Step two: then 5 parts of water reducing agent is added into 230 parts of water and stirred evenly, then poured into the stirring pot, continue to stir for 3 minutes, further pour the newly mixed steel fiber mortar into the 40mm*40mm*160mm mold, and place it in the constant temperature box with humidity of 95% and temperature of 20℃ for curing.

[0064] Further, the steel fiber in the step one and step two is straight and has no hook, the length is 13mm, the diameter is 0.2mm, the length-diameter ratio is 65, and the tensile strength is 2800MPa.

[0065] Example 3

[0066] A steel fiber modification method and its application in high-strength concrete, characterized in that it comprises the following steps:

[0067] Step one: weigh 0.6 parts of PAH dissolved in 1000 parts of PBS buffer and stir well to obtain a PAH solution, and prepare a 0.2 mol / L Na2SiO3 solution for use;

[0068] Step two: immerse 333.3 parts of steel fiber in 1000 parts of PAH solution for 3 hours, then take out and wash with clean water;

[0069] Step three: after washing, the steel fiber is immersed in a 0.2 mol / L Na2SiO3 solution for 3 hours;

[0070] Step four: take out the steel fiber after immersion treatment and wash with clean water;

[0071] Step five: after washing, the steel fiber is dried in an oven at 60°C to constant weight, and then cooled to room temperature for standby. Then 657 parts of cement, 1313 parts of sand and 315 parts of treated steel fiber are added into a cement mortar mixer in turn, and stirred for 3 minutes. Then 5 parts of water reducing agent is added into 230 parts of water and stirred evenly, and then poured into the mixer, and continue to stir for 3 minutes. Further, the freshly mixed steel fiber mortar is poured into a 40mm x 40mm x 160mm mold, and placed in a constant temperature box with humidity of 95% and temperature of 20°C for curing.

[0072] Further, the purity of PAH, PBS and Na2SiO3 in the step one is analytical pure.

[0073] Further, the mass ratio of steel fiber to PAH solution in the step two is 1:3.

[0074] Further, the immersion time in the step two and step three is 3 hours.

[0075] Further, the drying temperature in the step five is controlled at 60°C, and the treatment time is 8 hours.

[0076] Further, the judgment method of constant weight in the step five is that the weight of the modified steel fiber is weighed every 2 hours until the difference between the last two weights is not more than 0.01 grams, that is, the steel fiber has been dried to constant weight.

[0077] Further, the steel fibers in steps one, two, three, four, five are straight and have no hooks, with a length of 13 mm, a diameter of 0.2 mm, an aspect ratio of 65, and a tensile strength of 2800 MPa.

[0078] Table 1 is the test result of the steel fiber used in the reference group and the steel fiber used in the example

[0079]

[0080] Table 2 is the specific mix ratio of the concrete in the example and the concrete in the reference group

[0081]

[0082] After the steel fiber is surface-modified by the method, the surface microstructure of the steel fiber before and after modification is analyzed by using an electron scanning microscope (SEM), and the results show that after modification, the mineral coating can be uniformly deposited on the surface. The surface element composition of the steel fiber before and after modification is analyzed by using scanning electron microscope energy spectrum analysis (EDS), and the results show that after modification, the surface of the steel fiber in the example not only has C, O, Fe and Cu elements, but also has Na and Si elements. This shows that Na2SiO3 can be deposited on the steel fiber with the assistance of PAH. According to the “Cement Mortar Strength Test Method (ISO Method)” (GB / T 17671-2021), the compressive and flexural strength of the mortar specimen with a size of 40mm x 40mm x 160mm is analyzed by using a 300KN universal testing machine, and the results show that the compressive strength of the example can be as high as 77.3MPa, and the flexural strength can be as high as 21.12MPa, which can be improved by 71.4% compared with the reference group. According to the “Standard for Test Methods of Fiber Reinforced Concrete” (CECS13), the single fiber pull-out test is performed on the reference steel fiber and the steel fiber used in the example, and the results show that the maximum force that can be borne by the single steel fiber in the reference group is about 29N, and the maximum force that can be borne by the single steel fiber in the example is 58N. The single fiber pull-out energy of the reference group is 57.2N·mm, and the single fiber pull-out energy of the example is 113.9N·mm. The bonding strength of the steel fiber in the reference group and the single steel fiber in the example is 1.62MPa and 3.59MPa, respectively. The results show that the pull-out energy of the steel fiber treated by the method provided by the application can be improved by 99.125%, and the bonding strength can be improved by 121.60%. The above test results show that the method provided by the application can use the adsorption capacity of PAH to deposit Na2SiO3 on the steel fiber, form a SiO2 coating, effectively improve the degree of secondary hydration reaction between the steel fiber and the cement, and significantly improve the bonding strength between the steel fiber and the cement.

[0083] In the description of the specification, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples. The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A steel fiber modification method, characterized in that: The following steps are involved: Step 1: Weigh a certain amount of PAH and dissolve it in a certain amount of PBS buffer, and stir it thoroughly to obtain a PAH solution, and then prepare a certain concentration of Na2SiO3 solution for use; Step 2: a certain mass of steel fiber is immersed in PAH solution for a specific time, then taken out and washed with clean water; Step 3: The cleaned steel fiber is immersed in the Na2SiO3 solution prepared in step 1 for a specific period of time; Step 4: Take out the impregnated steel fiber and wash it with clean water; Step 5: After cleaning, the steel fiber is dried to constant weight, cooled to room temperature and the modification is completed; The mass ratio of PAH to PBS buffer solution in step 1 is 0.1:1000-1.4:1000, and the concentration of Na2SiO3 is 0.1mol / L-0.3mol / L; In the second step, the mass ratio of steel fiber to PAH solution is 1:3; The specific dipping time in step 2 and step 3 is 3-6 hours; In step 5, the drying temperature is 60° C.-80° C., and the treatment time is 6-12 hours.

2. A steel fiber modification method according to claim 1, characterized in that: The steel fibers may be straight, hooked or wavy, with a length of 8-30 mm, a diameter of 0.1-0.4 mm, an aspect ratio of 50-120, and a tensile strength of ≥2800 MPa.

3. Use of the steel fiber prepared by the steel fiber modification method according to claim 1 or 2 in the preparation of high-strength concrete.

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