CN115286301A

CN115286301A - Multi-scale fiber reinforcement alkali-activated cementing material and preparation method thereof

Info

Publication number: CN115286301A
Application number: CN202210902195.3A
Authority: CN
Inventors: 王桥; 张思凡; 周伟; 常晓林; 田文祥
Original assignee: Wuhan University WHU
Current assignee: Wuhan University WHU
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2022-11-04
Anticipated expiration: 2042-07-29
Also published as: CN115286301B

Abstract

The invention provides a preparation method of a multi-scale fiber reinforced alkali-activated cementing material, which comprises the following steps: firstly, dissolving filter paper fibers to obtain a nanofiber solution; secondly, adding sodium hydroxide to obtain alkali-activated solution of the nano-fibers; thirdly, adding the mixture of the cementing material precursor powder and the fine sand into the nanofiber alkali-activated solution; and finally, adding the micron fibers, uniformly mixing, filling into a mold, vibrating, and curing to obtain the multi-scale fiber reinforced alkali-activated cementing material. The gel material contains a nano-fiber woven network with self-assembly performance inside, and forms a unique multi-scale structure of a wolf tooth rod together with micro-fibers. The interaction of the two fibers with different scales improves the compactness of a microstructure and enhances the crack resistance of a matrix. The hydrophilic groups on the surface of the nanofibers improve the interface bonding between the microfiber and the matrix of the alkali-activated binding material, improve the mechanical properties of the alkali-activated binding material, and the prepared binding material has the advantages of high folding resistance, high shrinkage resistance and the like.

Description

Multi-scale fiber reinforcement alkali-activated cementing material and preparation method thereof

Technical Field

The invention belongs to the field of inorganic non-metallic materials, and particularly relates to a multi-scale fiber reinforced alkali-activated cementing material and a preparation method thereof.

Background

Alkali-activated cements are inorganic non-metallic cements comprised of aluminosilicates, which are produced by mixing waste or natural sources of aluminosilicates with high concentrations of alkali metal hydroxides. After mixing, the alkali activator dissolves the aluminosilicate precursor to release aluminate and silicate monomers, and then a polycondensation reaction is carried out to form a unique silicon-aluminum three-dimensional network structure. Thus, the production process has potential for low CO ₂ And (4) footprint. Depending on the mixing design and processing conditions, the activated cementitious material may exhibit different properties, such as high early compressive strength, acid resistance, and fire resistance. In addition, the alkali-activated cementing material also has the characteristics of solidifying heavy metals, stabilizing harmful chemical substances, purifying water quality and the like.

However, alkali-activated cements suffer from relatively significant brittleness defects, and exhibit relatively low tensile strength and cracking under adverse mechanical loads. At present, the alkali-activated cementing material is toughened by using fibers, but the fibers have the phenomena of uneven distribution and agglomeration in the doping process; meanwhile, in the multi-scale fiber toughening alkali-activated cementing material related in other patents, the nano fibers and the micro fibers cannot interact with each other, so that the multi-scale toughening effect cannot be exerted to the maximum extent, the interface combination of the fibers and a matrix is influenced, and the mechanical property of the alkali-activated cementing material is influenced.

In addition, the problem of drying shrinkage of alkali-activated cementitious materials is severe, and surface cracks and even through cracks can occur under the force of shrinkage. At present, internal curing agents such as water-absorbent resin and the like are generally used, and water is absorbed in advance before mixing to slow down drying shrinkage cracking, but no fiber can give consideration to both internal curing effect and bridging cracking, and the existing internal curing agents have little effect of improving the interface bonding between the micron fibers and the matrix.

Based on the above, on the basis of high durability and high compressive strength of the alkali-activated cementing material, the problems of high drying shrinkage rate, low toughness and the like of the alkali-activated cementing material are solved, and an inorganic material with uniformly distributed fibers and high shrinkage resistance and high fracture resistance is provided, so that the inorganic material can better meet the application requirements in the repair work of hydraulic building structures, and the technical problem to be solved is urgently needed.

Disclosure of Invention

The invention aims to provide a preparation method of a multi-scale fiber reinforcing alkali-activated cementing material capable of improving the shrinkage resistance and the high fracture resistance of a product.

The invention also aims to provide a multi-scale fiber reinforced alkali-activated cementing material with uniformly distributed fibers, high shrinkage resistance and high fracture resistance.

The technical scheme adopted by the invention for realizing one of the purposes is as follows: the preparation method of the multi-scale fiber reinforced alkali-activated cementing material comprises the following steps:

s1, placing filter paper fibers in a mixed solvent of sodium hydroxide, urea and deionized water, freezing for 6-12 hours at the temperature of minus 45-minus 35 ℃, and then unfreezing to obtain a nanofiber solution;

s2, adding sodium hydroxide into the nanofiber solution to adjust the concentration, and obtaining a nanofiber alkali-activated solution;

s3, dry-mixing the geopolymer precursor powder and the fine sand to obtain a mixture, adding the nanofiber alkali-activated solution into the mixture, and uniformly mixing to obtain a first product;

and S4, adding the micron fibers into the first product, uniformly mixing to obtain a second product, filling the second product into a mold, vibrating, and curing at the temperature of 55-65 ℃ for 6-8 days to obtain the multi-scale fiber-reinforced alkali-activated cementing material.

The preparation method is adopted to prepare the multi-scale fiber reinforced alkali-activated cementing material, and the general idea is as follows:

firstly, appropriate nanofibers are selected to be dispersed in the alkali-activated solution, so that the nanofibers can be uniformly distributed on the alkali-activated gelling material. Secondly, the alkali content of the nanofiber solution is adjusted according to the type and the dosage of the cementing material precursor powder so as to obtain better excitation effect. And thirdly, sequentially adding a mixture of the cementing material precursor powder and the fine sand into the nanofiber alkali-activated solution, and then adding the micro-fibers, so that the nanofibers are uniformly distributed on the alkali-activated cementing material along with the solution and are effectively distributed on the micro-fibers. And finally, maintaining the product at a proper temperature to ensure that the crosslinking reaction of the nano-fibers and the polymerization reaction of the alkali-activated cementing material are carried out simultaneously, so that the nano-fibers can be self-assembled into a nano-fiber woven network and can be attached to the micro-fibers and the fine sand to form a wolf tooth rod-shaped multi-scale fiber structure. By means of the structure, the control of the drying shrinkage rate and the anti-folding performance of the product is realized, and then the gel material with high shrinkage resistance and high anti-folding performance is prepared.

In the invention, the nano-fiber is selected from filter paper fiber, the cellulose content in the filter paper fiber is more than 90%, and a purer nano-fiber solution can be obtained; in addition, compared with other cellulose fibers (such as cotton linters and the like), the filter paper fibers have high crystallinity (1000-1500), longer nanofibers are easier to form, the viscosity of the obtained cellulose solution is higher, the obtained cellulose solution has better water retention performance, the filter paper fibers can play an internal curing role on the matrix of the alkali-activated binding material, the stored water is released during the early reaction of the alkali-activated binding material, the drying shrinkage cracking caused by too fast water loss is prevented, the reaction is promoted, and the compactness of the matrix is improved.

Furthermore, the filter paper fiber and other raw materials cannot be directly dissolved, and the cellulose molecular solution can be formed only by freezing and thawing at a specific temperature and then further polymerized into the nanofiber. The conventional freezing-thawing technology used in combination with NaOH/urea solution is usually precooled to-5 to-10 ℃. However, the filter paper fibers were completely insoluble under the above temperature conditions, and were only slightly soluble even if the dissolution time was prolonged. Through a great deal of exploration, the optimal freezing temperature of the filter paper fiber is-35 to-45 ℃, and the freezing time is 6 to 12 hours. Under the conditions of the temperature and the time, the filter paper fiber can be completely dissolved, and the cellulose exists in the solution in the form of tiny nano-fibers; if the temperature is further reduced, gel can be generated while the nano-fibers are completely dissolved, the nano-fibers are formed by crosslinking, the uniform distribution of the nano-fibers in the alkali-activated solution is not facilitated, and the free water content in the solution is reduced, so that the uniform distribution of the nano-fibers in the cementing material and the slurry fluidity in the mixing process are influenced.

In addition, in terms of the preparation method, it is necessary to control the order of addition of raw materials: dry-mixing the fine sand and the matrix powder, and adding the dry mixture into a fiber alkali excitation solution to obtain flowing slurry; if directly add the fiber alkali excitation solution into the dry mixture, the solution can take place local quick reaction with the matrix powder that contacts in the moment of adding, leads to the matrix reaction not enough for intensity distributes unevenly, and the structural weak face increases. The micron fibers need to be added into the flowing slurry in the last step, if the micron fibers are added into the solution, a large number of cellulose molecules can be gathered due to hydrophilic groups and high surface energy on the surfaces of the micron fibers, the obtained nano fibers in the matrix are few, and the water-retaining effect of the nano fibers on the matrix is further influenced.

The curing temperature is set to be 55-65 ℃, and the curing time is set to be 6-8 d. Under the conditions of the temperature and the time, the polymerization reaction speed of the alkali-activated cementing material and the crosslinking reaction speed of the nano-fibers can be kept consistent, so that the polymerization reaction speed and the crosslinking reaction speed of the nano-fibers are synchronously carried out. The nanofibers are not only present in the matrix voids, but also inside the matrix of the cementitious material. The nano-fiber is regenerated from the inside of the matrix gel, deeply implanted into the matrix gel at the other end, and finally covered and wrapped by the matrix gel generated by further reaction from the outside. On one hand, the nano-fibers form a woven network and exist in the gelled material matrix, so that the nano-fibers play a role in connecting micro-cracks and pores of the matrix in series; on the other hand, the nano-fiber exists on the surfaces of the micro-fiber and the fine sand to form a wolf tooth rod multi-scale structure, so that the interface bonding strength of the micro-fiber and the matrix is improved, the energy required by the extraction of the micro-fiber under the action of load is improved, the control of the drying shrinkage rate of the product is comprehensively realized, and the toughness of the product is improved.

Furthermore, in the multi-scale fiber reinforced alkali-activated cementing material, the content of the nano fibers is 0.25 to 1 weight percent, and the volume ratio of the micro fibers is 0.5 to 2 percent. Under the condition of the content range, the nano fibers can be uniformly distributed on the matrix and the micro fibers, the slurry has certain fluidity, and materials with controllable fluidity and different anti-bending properties can be obtained by controlling the addition amount of the micro fibers.

Preferably, in the multi-scale fiber reinforced alkali-activated cementing material, the content of the nano fibers is 0.5wt%, and the volume ratio of the micro fibers is 2%. Research shows that under the above conditions, the bending resistance of the product reaches a peak value, and beyond the range, the bending resistance tends to be reduced to a certain extent.

Further, in the step S1, the mass ratio of the sodium hydroxide, the urea and the deionized water is (6-8): (8-14): (76 to 88). Preferably, in the step S1, the mass ratio of sodium hydroxide, urea and deionized water is 7.

Furthermore, in the nanofiber solution, the diameter of the nanofiber is 20-100 nm, and the length of the nanofiber is 180-2000 nm.

Further, in the step S2, the amount of sodium hydroxide added depends on the type and amount of the cement precursor powder in the step S3.

Further, the geopolymer precursor powder is selected from one or more of metakaolin, fly ash and slag.

Further, the micro fibers are selected from polyvinyl alcohol fibers, polyethylene fibers, polypropylene fibers or a combination of a plurality of the fibers. Preferably, the diameter of the micro fiber is 30 to 60 μm, and the length is 6 to 12mm.

Further, in the step S4, the time for stirring and mixing after adding the micron fibers is not too long, and is preferably controlled to be about 5min, when the stirring time is too short, the micron fibers are not uniformly distributed and easily exist on the surface layer of the slurry, and when the stirring time is too long, fiber aggregation occurs. Preferably, the stirring time for uniformly mixing to obtain the second product is 4-6 min.

The second technical scheme adopted by the invention for realizing the purpose is as follows: the invention provides a multi-scale fiber reinforced alkali-activated cementing material prepared by the preparation method based on one of the purposes of the invention.

In the multi-scale fiber alkali-increasing activated cementing material, nano fibers are uniformly dispersed in a cementing material matrix and self-assembled to form a fiber woven network, and meanwhile, the nano fibers are reduced and polymerized on the surfaces of the micro fibers and fine sand to form a wolf tooth rod-shaped multi-scale structure.

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the preparation method of the multi-scale fiber-reinforced alkali-activated cementing material, provided by the invention, the nano fibers are uniformly dispersed in the alkali-activated cementing material along with the solution, the water loss rate of the matrix of the alkali-activated cementing material is improved through the water retention property, the bridging and filling effects of gel pores are provided, the compactness of a microstructure is promoted, the cracking risk is reduced, and the internal maintenance and the fiber bridging are combined into a whole.

(2) According to the preparation method of the multi-scale fiber reinforced alkali-activated cementing material, the multi-scale fibers are adopted to reinforce the alkali-activated cementing material, the hydrophilic groups on the surfaces of the nanofibers improve the interface bonding between the micro fibers and the alkali-activated cementing material matrix, the mechanical property of the alkali-activated cementing material is improved, and the multi-scale fiber reinforced alkali-activated cementing material with high bending resistance and shrinkage resistance is obtained.

(3) In the multi-scale fiber reinforced alkali-activated cementing material prepared by the invention, the cross-linking reaction of the nano fibers and the polymerization reaction of the alkali-activated cementing material are simultaneously carried out, on one hand, the nano fibers are uniformly dispersed in a matrix through in-situ polymerization to form a self-assembled nano fiber woven network, and on the other hand, the nano fibers are also attached to the micro fibers and the fine sand to form a wolf tooth rod-shaped multi-scale fiber structure. The existence of the structure can effectively control the drying shrinkage rate of the product and improve the toughness.

Drawings

FIG. 1 is a schematic flow chart of a method for preparing a multi-scale fiber-reinforced alkali-activated cementitious material according to an embodiment of the present invention;

FIG. 2 is a 2000 Xscanning electron microscope image of the multi-scale fiber reinforced alkali-activated cementing material prepared in example 1 of the present invention with a resolution of 2 μm;

FIG. 3 is a 7-day flexural strength profile of a multi-scale fiber reinforced alkali-activated cementitious material made in accordance with example 1 of the present invention.

FIG. 4 is a 5000 Xscanning electron micrograph of the non-fibrous alkali-activated cement of comparative example 1 at a resolution of 1 μm;

FIG. 5 is a 7-day flexural strength profile for the fiber-free alkali-activated cement of comparative example 1;

FIG. 6 is a 2000X scanning electron microscope image of a comparative example 2 micron fiber reinforced alkali-activated cement material with a resolution of 2 μm;

FIG. 7 is a 7-day flexural strength profile of a comparative example 2-micron fiber-reinforced alkali-activated cementitious material.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive efforts based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.

Example 1

A preparation method of a multi-scale fiber reinforced alkali-activated cementing material comprises the following steps:

step 1: 70g of NaOH is dissolved in 810g of deionized water, 120g of urea is added after cooling to room temperature, and the mixture is allowed to stand for 24 hours to obtain 1000g of the pre-solution for dissolving the filter paper fibers, wherein the dissolving step is shown in figure 1. Breaking the filter paper fibers by using a wall breaking machine, weighing filter paper fiber fragments accounting for 0.5% of the mass of the solution, adding the filter paper fiber fragments into the solution, and uniformly distributing the fragments by ultrasonic waves. The product was frozen in a refrigerator at-40 ℃ for 8 hours, and then thawed at 25 ℃ at room temperature to obtain a nanofiber solution.

And 2, step: and (2) slowly adding 23g of sodium hydroxide into the nanofiber solution obtained in the step (1) by 5 times to adjust the alkali concentration of the solution, and standing for 24 hours for later use.

And step 3: pouring 800g of metakaolin and 160g of fine sand into a stirrer, uniformly stirring, adding 1000g of nanofiber solution, and uniformly mixing.

And 4, step 4: and (4) adding polyvinyl alcohol fiber with the volume fraction of 2% into the product obtained in the step (3), stirring for 5 minutes, then filling a mold and vibrating for 2 minutes. And controlling the temperature in a constant-temperature constant-humidity curing box to be 60 ℃, curing for 12 hours, demolding, and then continuously curing for 7 days to finally obtain the multi-scale fiber reinforced alkali-activated cementing material.

FIG. 2 is a scanning electron microscope image of the multi-scale fiber reinforced alkali-activated cement prepared in example 1. It can be seen from fig. 2 that the nanofibers are polymerized in situ on the surface of the polyvinyl alcohol fibers to form a unique wolf tooth rod-shaped multi-scale structure, the presence of the nanofibers improves the interface bonding between the microfibers and the matrix, and the energy required for pulling out the microfibers is increased.

FIG. 3 is a 7-day flexural strength curve of the multi-scale fiber reinforced alkali-activated cementitious material prepared in example 1, and it can be seen from FIG. 3 that the multi-scale fiber reinforced alkali-activated cementitious material exhibits a multi-stage cracking mode, the nano-fibers promote matrix reaction at the nano-scale to improve first cracking strength, and the micro-fibers provide fiber bridging at the micro-scale to improve final cracking strength.

Example 2

step 1: 70g of NaOH is dissolved in 810g of deionized water, 120g of urea is added after cooling to room temperature, and the mixture is left standing for 24 hours to obtain 1000g of the preposed solution for dissolving the filter paper fibers, wherein the dissolving step is shown in figure 1. Breaking the filter paper fibers by using a wall breaking machine, weighing filter paper fiber fragments accounting for 1% of the mass of the solution, adding the filter paper fiber fragments into the solution, and uniformly distributing the fragments by ultrasonic waves. The product was frozen in a refrigerator at-35 ℃ for 12 hours, and then thawed at 25 ℃ at room temperature to give a nanofiber solution.

And 4, step 4: and (3) adding polyvinyl alcohol fiber with the volume fraction of 1% into the product obtained in the step (3), stirring for 5 minutes, then filling into a mold and vibrating for 2 minutes. And (3) controlling the temperature in a constant-temperature constant-humidity curing box to be 60 ℃, curing for 12 hours, demolding, and then continuing curing for 7 days to finally obtain the multi-scale fiber reinforced alkali-activated cementing material.

Example 3

step 1: 70g of NaOH is dissolved in 810g of deionized water, 120g of urea is added after cooling to room temperature, and the mixture is allowed to stand for 24 hours to obtain 1000g of the pre-solution for dissolving the filter paper fibers, wherein the dissolving step is shown in figure 1. Breaking the filter paper fibers by using a wall breaking machine, weighing filter paper fiber fragments accounting for 0.5 percent of the mass of the solution, adding the filter paper fiber fragments into the solution, and uniformly distributing the fragments by ultrasonic waves. And putting the product into a refrigerator with the temperature of-45 ℃ for freezing for 6 hours, and then unfreezing at the room temperature of 25 ℃ to obtain the nanofiber solution.

Step 2: and (3) slowly adding 23g of sodium hydroxide into the nanofiber solution obtained in the step (1) in 5 times to adjust the alkali concentration of the solution, and standing for 24 hours for later use.

And 3, step 3: pouring 800g of metakaolin and 160g of fine sand into a stirrer, uniformly stirring, adding 1000g of nanofiber solution, and uniformly mixing.

And 4, step 4: and (3) adding polyvinyl alcohol fiber with the volume fraction of 1.5% into the product obtained in the step (3), stirring for 5 minutes, then filling a mold and vibrating for 2 minutes. And controlling the temperature in a constant-temperature constant-humidity curing box to be 60 ℃, curing for 12 hours, demolding, and then continuously curing for 7 days to finally obtain the multi-scale fiber reinforced alkali-activated cementing material.

Example 4

step 1: 70g of NaOH is dissolved in 810g of deionized water, 120g of urea is added after cooling to room temperature, and the mixture is left standing for 24 hours to obtain 1000g of the preposed solution for dissolving the filter paper fibers, wherein the dissolving step is shown in figure 1. Breaking the filter paper fibers by using a wall breaking machine, weighing filter paper fiber fragments accounting for 1% of the mass of the solution, adding the filter paper fiber fragments into the solution, and uniformly distributing the fragments by ultrasonic waves. The product was frozen in a refrigerator at-40 ℃ for 8 hours, and then thawed at 25 ℃ at room temperature to give a nanofiber solution.

And 4, step 4: and (3) adding polyvinyl alcohol fiber with the volume fraction of 0.5% into the product obtained in the step (3), stirring for 5 minutes, then filling a mold and vibrating for 2 minutes. And (3) controlling the temperature in a constant-temperature constant-humidity curing box to be 55 ℃, curing for 12 hours, demolding, and then continuing curing for 8 days to finally obtain the multi-scale fiber reinforced alkali-activated cementing material.

Example 5

step 1: 70g of NaOH is dissolved in 810g of deionized water, 120g of urea is added after cooling to room temperature, and the mixture is left standing for 24 hours to obtain 1000g of the preposed solution for dissolving the filter paper fibers, wherein the dissolving step is shown in figure 1. Breaking the filter paper fibers by using a wall breaking machine, weighing filter paper fiber fragments accounting for 0.5% of the mass of the solution, adding the filter paper fiber fragments into the solution, and uniformly distributing the fragments by ultrasonic waves. The product was frozen in a refrigerator at-40 ℃ for 8 hours, and then thawed at 25 ℃ at room temperature to give a nanofiber solution.

Step 2: and (2) slowly adding 23g of sodium hydroxide into the nanofiber solution obtained in the step (1) by 5 times to adjust the alkali concentration of the solution, and standing for 24 hours for later use.

And 3, step 3: and pouring 800g of fly ash and 160g of fine sand into a stirrer, uniformly stirring, adding 400g of nanofiber solution, and uniformly mixing.

And 4, step 4: and (3) adding polyvinyl alcohol fiber with the volume fraction of 2% into the product obtained in the step (3), stirring for 5 minutes, then filling a mold and vibrating for 2 minutes. And (3) controlling the temperature in a constant-temperature constant-humidity curing box to be 65 ℃, curing for 12 hours, demolding, and then continuing curing for 6 days to finally obtain the multi-scale fiber reinforced alkali-activated cementing material.

Comparative example 1

Based on example 1, adjustment was performed, except that no filter paper fiber was added in step 1, no polyvinyl alcohol fiber was added in step 4, and other conditions and steps were not changed, to prepare a conventional alkali-activated cementitious material without fiber reinforcement.

The scanning electron micrograph of the alkali-activated cement prepared in comparative example 1 is shown in FIG. 4. As can be seen from fig. 4, no fiber was present inside the matrix of the product obtained in comparative example 1. The 7-day flexural strength curve is shown in FIG. 5, which is typical of brittle fracture. By comparison, the product obtained by adopting the technical scheme of multi-scale fiber reinforcement modification in example 1 has the first cracking strength improved by 129% and the final cracking strength improved by 280% compared with the cement without fiber reinforcement in comparative example 1.

Comparative example 2

Based on example 1, adjustment was performed, except that no filter paper fiber was added in step 1, polyvinyl alcohol fiber with a content of 2% was added in step 4, and other conditions and steps were not changed, to obtain a conventional alkali-activated gelling material reinforced with micro-fibers.

The scanning electron micrograph of the alkali-activated binding material prepared in comparative example 2 is shown in FIG. 6, and the surface of the polyvinyl alcohol fiber is smooth, and the interfacial fracture with the alkali-activated binding material matrix is neat. The 7-day flexural strength curve of the microfiber-reinforced alkali-activated cementitious material is shown in fig. 7, a multi-stage cracking mode is also presented due to the presence of the microfiber, but the first cracking strength and the final cracking strength of the product are not high due to the lack of nanofiber reinforcement and the combined action of multi-scale fibers, and the first cracking strength is improved by 106% and the final cracking strength is improved by 65% in example 1 compared with that of comparative example 2.

The alkali-activated cement obtained in example 1 and comparative examples 1 and 2 was put under the same curing conditions (60 ℃ C.), and the mass loss ratios after curing for 3 days and 7 days were measured, and the results are shown in Table 1 below.

TABLE 1

Group of	3d mass loss rate/%)	7d mass loss rate/%)
			Example 1	13.06	16.78
Comparative example 1	24.7	24.70
			Comparative example 2	21.2	22.65

As can be seen from the above table,

the mass loss rate in inventive example 1 was much less than comparative examples 1 and 2, the mass loss after 3 days and 7 days of curing was the same in comparative example 1, indicating that it was maximum at 3 days, and the presence of the microfibers in comparative example 2 slightly alleviated the mass loss, but not as well as the multi-scale fibers of example 1. The water retention property of the nano-fibers can be fully exerted by the multi-scale fiber alkali-enhanced alkali-activated cementing material prepared by the method, the water quality loss of the alkali-activated cementing material in the early reaction stage is greatly reduced, the water loss rate is controlled, and the early cracking risk of the material is further reduced.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

1. A preparation method of a multi-scale fiber reinforced alkali-activated cementing material comprises the following steps:

s1, placing filter paper fibers in a mixed solvent composed of sodium hydroxide, urea and deionized water, freezing for 6-12 hours at the temperature of minus 45-minus 35 ℃, and then unfreezing to obtain a nanofiber solution;

s3, dry-mixing the cementing material precursor powder and the fine sand to obtain a mixture, adding the nanofiber alkali-activated solution into the mixture, and uniformly mixing to obtain a first product;

and S4, adding the micron fibers into the first product, uniformly mixing to obtain a second product, filling the second product into a mold, vibrating, and curing at the temperature of 55-65 ℃ for 6-8 days to obtain the multi-scale fiber reinforced alkali-activated cementing material.

2. The preparation method of claim 1, wherein the multi-scale fiber-reinforced alkali-activated cementitious material contains 0.25-1 wt% of nano fibers and 0.5-2% of micro fibers by volume.

3. The preparation method according to claim 1, wherein in the step S1, the mass ratio of sodium hydroxide, urea and deionized water is (6-8): (8-14): (76 to 88).

4. The method of claim 3, wherein the nanofiber solution has a diameter of 20 to 100nm and a length of 180 to 2000nm.

5. The method according to claim 1, wherein the amount of sodium hydroxide added in step S2 is determined by the type and amount of the cement precursor powder in step S3.

6. The method according to claim 1, wherein the cementitious material precursor powder is selected from the group consisting of metakaolin, fly ash, slag, and combinations thereof.

7. The method of claim 1, wherein the microfibers are selected from the group consisting of polyvinyl alcohol fibers, polyethylene fibers, polypropylene fibers, and combinations thereof.

8. The method of claim 7, wherein the micro fiber has a diameter of 30 to 60 μm and a length of 6 to 12mm.

9. The preparation method according to claim 1, wherein in the step S4, the stirring time for uniformly mixing to obtain the second product is 4-6 min.

10. A multi-scale fiber-reinforced alkali-activated cementitious material produced according to the method of manufacture of any one of claims 1 to 9,