Method for preparing and testing fiber reinforced concrete fracture sample with prefabricated cracks

Abstract

The invention provides a method for preparing and testing a fiber reinforced concrete fracture sample with prefabricated cracks, and belongs to the technical field of performance testing of building materials. The crack prefabricating mold comprises a crack forming column and a pressing plate provided with a longitudinal through hole. The gap forming column is in clearance fit with the longitudinal through hole of the pressing plate, and the maximum fit clearance is 0.1 mm; the fracture forming column is a cuboid, the length of the cuboid is 95-105 mm, the width of the cuboid is 2.5-3.5 mm, and the height of the cuboid is equal to the sum of the thickness of the pressing plate and (15-25) mm. The method comprises the following steps: compacting a forming mold poured with slurry, covering a pressing plate, inserting a crack-making column into a longitudinal through hole of the pressing plate, enabling the top end of the crack-making column to be flush with the upper surface of the pressing plate, and pulling out the crack-making column after the slurry is hardened, so that a prefabricated crack is formed in a fiber reinforced concrete fracture sample. Compared with a pre-embedding method in the prior art, the precision of the size and the position of the prefabricated crack is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building material performance testing, and particularly relates to a method for preparing and testing a fiber-reinforced concrete fracture specimen with a prefabricated crack. Background Art

[0002] The concrete fracture specimen is an important experimental means for studying the fracture performance of concrete materials, and is usually used to measure parameters such as fracture toughness and fracture energy and analyze the crack propagation law. In the prior art, a metal sheet or a plastic sheet is usually embedded at the bottom of the mold, and then concrete is cast to form a prefabricated crack. However, the size and position accuracy of the prefabricated crack prepared by this method are poor, which has a great impact on subsequent analysis and testing. Therefore, how to improve the accuracy of the size and position of the prefabricated crack has become a difficult problem in this field. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing and testing a fiber-reinforced concrete fracture specimen with a prefabricated crack. The prefabricated crack prepared by using the prefabricated crack mold provided by the present invention has higher accuracy.

[0004] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a prefabricated crack mold, which includes a crack-forming column and a pressing plate provided with a longitudinal through hole; the crack-forming column and the longitudinal through hole of the pressing plate form a clearance fit, and the maximum fit clearance is 0.1 mm; the crack-forming column is a cuboid, the length of the cuboid is 95 - 105 mm, the width is 2.5 - 3.5 mm, and the height is the thickness of the pressing plate + (15 - 25) mm.

[0006] Preferably, a positioning part is fixedly provided at the top end of the crack-forming column; one transverse dimension of the positioning part is larger than the corresponding transverse dimension in the crack-forming column.

[0007] Preferably, the pressing plate is a cuboid, and the center point of the longitudinal through hole is located at the center point of the pressing plate.

[0008] The present invention also provides a method for preparing a fiber-reinforced concrete fracture specimen, including the following steps:

[0009] (1) Mix fibers with part of the aggregate to obtain a fiber mixture;

[0010] (2) Mix the fiber mixture obtained in step (1) with cement, the remaining aggregate, a water reducing agent and water to obtain a slurry;

[0011] (3) Pour the slurry obtained in the step (2) into a forming mold, and then use the prefabricated crack mold described in the above technical solution to create cracks to obtain a fiber-reinforced concrete fracture specimen; the crack creation includes: after vibrating the forming mold filled with slurry, covering the pressing plate, and then inserting the crack creation column into the longitudinal through-hole of the pressing plate so that the top end of the crack creation column is flush with the upper surface of the pressing plate.

[0012] Preferably, in the step (1), the mass of part of the aggregate is 20-40% of the total mass of the aggregate.

[0013] Preferably, in the step (1), the diameter of the fiber is 10-15 μm and the length of the fiber is 10-15 mm.

[0014] Preferably, in the step (2), the mass ratio of the fiber to the volume of the slurry is (1-12) kg: 1 m 3 .

[0015] Preferably, in the step (2), the mass ratio of water to cement is (0.3-0.4): 1.

[0016] The present invention also provides a fiber-reinforced concrete fracture specimen prepared by the preparation method described in the above technical solution; the width of the crack in the fiber-reinforced concrete fracture specimen is 2.5-3.5 mm and the height is 15-25 mm.

[0017] The present invention also provides a testing method, including: performing a three-point bending test on the fiber-reinforced concrete fracture specimen described in the above technical solution, and collecting digital image correlation technology and acoustic emission technology during the three-point bending test.

[0018] The present invention provides a prefabricated crack mold, including a crack creation column and a pressing plate provided with a longitudinal through-hole; the crack creation column and the longitudinal through-hole of the pressing plate form a clearance fit, and the maximum fit clearance is 0.1 mm; the crack creation column is a cuboid, the length of the cuboid is 95-105 mm, the width is 2.5-3.5 mm, and the height is the thickness of the pressing plate + (15-25) mm. When the prefabricated crack mold provided by the present invention is used to prepare a fiber-reinforced concrete fracture specimen, after vibrating the forming mold filled with slurry, covering the pressing plate, and then inserting the crack creation column into the longitudinal through-hole of the pressing plate so that the top end of the crack creation column is flush with the upper surface of the pressing plate, and pulling out the crack creation column after the slurry hardens, so as to form a prefabricated crack in the fiber-reinforced concrete fracture specimen. Compared with the embedded method in the prior art, the accuracy of the size and position of the prefabricated crack is improved. The results of the examples show that the width accuracy of the prefabricated crack prepared by using the prefabricated crack mold provided by the present invention reaches 0.1 mm ± 0.02 mm (the deviation of the embedded method > 0.5 mm), the height error is ±2% (the embedded method > 10%), and the deviation of the central axis of the crack position < 1 mm. Description of the Drawings

[0019] Figure 1 It is the plan view of the pressure plate in the prefabricated crack mold for Example 1;

[0020] Figure 2 It is the perspective view of the pressure plate in the prefabricated crack mold for Example 1;

[0021] Figure 3 It is the plan view of the crack - forming column in the prefabricated crack mold for Example 1;

[0022] Figure 4 It is the perspective view of the crack - forming column in the prefabricated crack mold for Example 1;

[0023] Figure 5 It is the SEM images of the specimens in Example 4 after curing and being placed in different environments (basic group, water - soaking treatment, acid - soaking treatment, and alkali - soaking treatment);

[0024] Figure 6 It is the position diagram of the loading head and supports and the specimen during the three - point bending test in Example 6;

[0025] Figure 7 It is the detection schematic diagram for real - time monitoring using acoustic emission and digital image correlation techniques while conducting the three - point bending test in Example 6;

[0026] Figure 8 It is the flexural strength of the specimens in Examples 2 - 5 and Comparative Example 1 after curing and being placed in different environments (basic group G1, water - soaking treatment G2, acid - soaking treatment G3, and alkali - soaking treatment G4);

[0027] Figure 9 It is the P - CMOD curves of the specimens in Examples 2 - 5 and Comparative Example 1 after curing and being placed in different environments (basic group G1, water - soaking treatment G2, acid - soaking treatment G3, and alkali - soaking treatment G4);

[0028] Figure 10 It is the evolution process of the strain nephogram of the specimens in Examples 2 - 5 and Comparative Example 1 during different loading processes after curing;

[0029] Figure 11 It is the evolution process of the displacement nephogram of the specimens in Examples 2 - 5 and Comparative Example 1 during different loading processes after curing;

[0030] Figure 12 It is the three - dimensional acoustic emission damage location map of the specimens in Example 3 after curing and being placed in different environments (basic group G1, water - soaking treatment G2, acid - soaking treatment G3, and alkali - soaking treatment G4). Detailed Description of the Invention

[0031] The present invention provides a prefabricated crack mold, which includes a crack - creating column and a pressing plate provided with a longitudinal through - hole; the crack - creating column and the longitudinal through - hole of the pressing plate form a clearance fit, and the maximum clearance fit is 0.1 mm; the crack - creating column is a cuboid, the length of the cuboid is 95 - 105 mm, the width is 2.5 - 3.5 mm, and the height is the thickness of the pressing plate+(15 - 25)mm.

[0032] The prefabricated crack mold provided by the present invention includes a crack - creating column.

[0033] In the present invention, the crack - creating column is a cuboid; the length of the cuboid is 95 - 105 mm, preferably 100 mm; the width of the cuboid is 2.5 - 3.5 mm, preferably 3 mm; the height of the cuboid is the thickness of the pressing plate+(15 - 25)mm, preferably the thickness of the pressing plate + 20 mm.

[0034] In the present invention, a positioning part is preferably fixedly provided at the top of the crack - creating column; one transverse dimension of the positioning part is preferably greater than the corresponding transverse dimension in the crack - creating column. The present invention has no special limitation on the specific transverse dimension of the positioning part, as long as it is greater than the corresponding transverse dimension of the crack - creating column.

[0035] As an implementation manner, the crack - creating column can specifically be a T - shaped crack - creating column; the length of the longitudinal part of the T - shaped crack - creating column is 100 mm, the width is 3 mm, and the height is 30 mm; the length of the transverse part (i.e., the positioning part) of the T - shaped crack - creating column is 150 mm, the width is 3 mm, and the height is 10 mm.

[0036] In the present invention, the material of the crack - creating column is preferably metal or plastic, more preferably metal. The present invention has no special limitation on the type of the metal, and any metal well - known to those skilled in the art can be used. As an implementation manner, the material of the crack - creating column can specifically be iron.

[0037] The prefabricated crack mold provided by the present invention further includes a pressing plate provided with a longitudinal through - hole.

[0038] In the present invention, the material of the pressing plate is preferably metal or acrylic plate. The present invention has no special limitation on the type of the metal, and any metal well - known to those skilled in the art can be used. As an implementation manner, the metal material of the pressing plate can specifically be iron.

[0039] In the present invention, the crack - creating column and the longitudinal through - hole of the pressing plate form a clearance fit, and the maximum clearance fit is 0.1 mm.

[0040] In the present invention, the pressing plate is preferably a cuboid; the center point of the longitudinal through - hole is preferably located at the center point of the pressing plate.

[0041] In the present invention, the length of the pressing plate is preferably ≥400 mm; the width of the pressing plate is preferably >100 mm.

[0042] As an embodiment, the length of the pressing plate is 400 mm, the width is 150 mm, and the height (i.e., thickness) is 10 mm.

[0043] When the prefabricated crack mold provided by the present invention is used to prepare a fiber-reinforced concrete fracture specimen, after the molding mold filled with the slurry is vibrated solid, the pressing plate is covered, and then the seam-forming column is inserted into the longitudinal through-hole of the pressing plate so that the top end of the seam-forming column is flush with the upper surface of the pressing plate. After the slurry hardens, the seam-forming column is pulled out, thereby forming a prefabricated crack in the fiber-reinforced concrete fracture specimen. Compared with the pre-buried method in the prior art, the accuracy of the size and position of the prefabricated crack is improved.

[0044] The present invention also provides a method for preparing a fiber-reinforced concrete fracture specimen, comprising the following steps:

[0045] (1) Mix the fibers with part of the aggregate to obtain a fiber mixture;

[0046] (2) Mix the fiber mixture obtained in step (1) with cement, the remaining aggregate, water reducer and water to obtain a slurry;

[0047] (3) Pour the slurry obtained in step (2) into a molding mold, and then use the prefabricated crack mold described in the above technical solution to form a crack to obtain a fiber-reinforced concrete fracture specimen; the crack formation includes: after the molding mold filled with the slurry is vibrated solid, covering the pressing plate, and then inserting the seam-forming column into the longitudinal through-hole of the pressing plate so that the top end of the seam-forming column is flush with the upper surface of the pressing plate.

[0048] The present invention mixes the fibers with part of the aggregate to obtain a fiber mixture.

[0049] The present invention does not have special limitations on the type of the fibers, and the fiber types well-known to those skilled in the art can be used. As an embodiment, the fibers are glass fibers.

[0050] In the present invention, the diameter of the fibers is preferably 10 - 15 μm; the length of the fibers is preferably 10 - 15 mm. As an embodiment, the diameter of the fibers can be specifically 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm; the length of the fibers can be specifically 10 mm, 11 mm, 12 mm, 13 mm, 14 mm or 15 mm. By controlling the diameter and length of the fibers within the above ranges, the present invention can further improve the uniformity of the fibers.

[0051] In the present invention, the aggregate is preferably fine aggregate or a mixture of coarse aggregate and fine aggregate.

[0052] In the present invention, the mass percentage content of fine aggregate in the aggregate is preferably 40-100%. As an implementation manner, the mass percentage content of fine aggregate in the aggregate can specifically be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0053] In the present invention, the particle size of the fine aggregate is preferably 0.075-4.75 mm, more preferably 0.25-0.5 mm. By using the fine aggregate with the above particle size in the present invention, the wrapping property of the paste and the dispersibility of the fiber can be further improved.

[0054] In the present invention, the fine aggregate preferably includes at least one of natural sand, manufactured sand, recycled fine aggregate and special sand; the natural sand preferably includes at least one of river sand, lake sand and mountain sand; the mud content of the natural sand is preferably < 3 wt%; the material of the manufactured sand preferably includes one or more of limestone, granite and basalt; the recycled fine aggregate is preferably waste concrete; the special sand preferably includes at least one of quartz sand, tailings sand and lightweight sand; the content of silicon dioxide in the quartz sand is preferably ≥ 95 wt%; the tailings sand is preferably iron ore tailings sand and / or copper ore tailings sand; the lightweight sand preferably includes ceramsite and / or expanded perlite.

[0055] In the present invention, when the fine aggregate includes manufactured sand, the mass of the manufactured sand is preferably 5-10% of the total mass of the fine aggregate.

[0056] In the present invention, the particle size of the coarse aggregate is preferably 4.75-25 mm, more preferably 5-25 mm. By using the coarse aggregate with the above particle size in the present invention, the interference of the aggregate with the crack propagation path is avoided, and at the same time, the entanglement of the fiber with the aggregate is avoided.

[0057] In the present invention, the coarse aggregate preferably includes at least one of natural crushed stone, river pebble, recycled coarse aggregate and lightweight aggregate; the natural crushed stone preferably includes one or more of granite, basalt and limestone; the crushing value of the natural crushed stone is preferably ≤ 15%; the recycled coarse aggregate is preferably the demolished concrete; the lightweight aggregate preferably includes ceramsite and / or pumice; the bulk density of the lightweight aggregate is preferably ≤ 1000 kg / m 3 。

[0058] In the present invention, the mass of the partial aggregate is preferably 20-40% of the total mass of the aggregate, more preferably 25-35% of the total mass of the aggregate, and further preferably 30% of the total mass of the aggregate.

[0059] In the present invention, the mixing time of the fiber and part of the aggregate is preferably 30 to 120 s. As an implementation manner, the mixing time of the fiber and part of the aggregate can specifically be 30 s, 60 s, 90 s or 120 s.

[0060] As an implementation manner, the mixing of the fiber and part of the aggregate is carried out in a mixer.

[0061] After obtaining the fiber mixture, the present invention mixes the fiber mixture with cement, the remaining aggregate, a water reducing agent and water to obtain a slurry.

[0062] In the present invention, the cement preferably includes one or more of ordinary portland cement, slag portland cement and fly ash portland cement.

[0063] In the present invention, the slag in the slag portland cement is preferably blast furnace slag; the mass content of the slag in the slag portland cement is preferably 20 to 70%. As an implementation manner, the mass content of the slag in the slag portland cement can specifically be 20%, 30%, 40%, 50%, 60% or 70%. The present invention adopts slag portland cement, which has a lower alkalinity (pH value 10.5 to 11.5) and can reduce fiber corrosion.

[0064] In the present invention, the mass content of fly ash in the fly ash portland cement is preferably 20 to 40%. As an implementation manner, the mass content of fly ash in the fly ash portland cement can specifically be 20%, 30% or 40%. The present invention adopts fly ash portland cement, which has a low heat of hydration and can improve the durability of the fiber-reinforced concrete fracture specimen.

[0065] In the present invention, the ratio of the mass of the cement to the total mass of the aggregate is preferably 460:(1500 - 2000), and more preferably 460:1845.

[0066] In the present invention, the water reducing agent is preferably a polycarboxylate superplasticizer. The present invention has no special limitation on the source of the polycarboxylate superplasticizer, and commercially available products well-known to those skilled in the art can be used.

[0067] In the present invention, the mass ratio of the water reducing agent to the cement is preferably (1 - 2):100, and more preferably 1.5:100.

[0068] In the present invention, the mass ratio of the water to the cement is preferably (0.3 - 0.4):1, and more preferably 0.35:1.

[0069] In the present invention, the mass of the fiber in the slurry and the volume ratio of the slurry are preferably (1 - 12) kg:1 m 3。As an implementation manner, the mass ratio of the fiber in the slurry to the volume of the slurry may specifically be 3 kg: 1 m 3 、6 kg: 1 m 3 、9 kg: 1 m 3 or 12 kg: 1 m 3 。

[0070] By controlling the dosages of the components within the above ranges, the present invention can further improve the mechanical properties of the fiber-reinforced concrete fracture specimens.

[0071] In the present invention, the mixing of the fiber mixture, cement, remaining aggregate, water reducer and water is preferably as follows: Mix water and the water reducer to obtain a water reducer solution, and then sequentially add cement, remaining aggregate and the water reducer solution to the fiber mixture, and stir for 1 - 3 min. The present invention has no special limitation on the mixing method and rate, and the mixing technical solutions well-known to those skilled in the art can be adopted.

[0072] After obtaining the slurry, the present invention pours the slurry into a forming mold, and then uses the prefabricated crack mold described in the above technical solution to create cracks to obtain fiber-reinforced concrete fracture specimens; the crack creation includes: After vibrating and compacting the forming mold filled with the slurry, cover the pressing plate, and then insert the crack creation column into the longitudinal through hole of the pressing plate so that the top end of the crack creation column is flush with the upper surface of the pressing plate.

[0073] As an implementation manner, the forming mold is a cuboid mold; the length of the forming mold is 400 mm, the width is 100 mm, and the height is 100 mm.

[0074] The present invention has no special limitation on the vibrating and compacting operation, and the vibrating and compacting technical solutions well-known to those skilled in the art can be adopted. As an implementation manner, the vibrating and compacting frequency is 50 Hz, the amplitude is 1 mm, the vibrating and compacting is stratified vibrating and compacting, the single-layer thickness is 3 mm, the vibrating and compacting time is 30 s / layer, and the vibrating and compacting method is vertical vibrating and compacting.

[0075] In the present invention, the surface of the crack creation column is preferably coated with a release agent. The present invention has no special limitation on the type and dosage of the release agent, and the type and dosage of the release agent well-known to those skilled in the art can be adopted. As an implementation manner, the release agent is a silicone release agent. The present invention has no special limitation on the source of the silicone release agent, and commercially available products well-known to those skilled in the art can be adopted.

[0076] After the crack creation is completed, the present invention preferably allows the concrete after crack creation to stand for 20 - 25 h, then withdraws the crack creation column, and then demolds to obtain fiber-reinforced concrete fracture specimens.

[0077] The present invention has no special limitation on the operation of extracting and demolding the crack - forming column, and the technical solutions well - known to those skilled in the art can be adopted.

[0078] The present invention first mixes fibers with part of the aggregate to reduce the electrostatic adsorption between the fibers, and then mixes with other components, which can avoid the phenomenon of fiber agglomeration, improve the dispersion of the fibers, and achieve the uniform distribution of the fibers in the fractured specimen.

[0079] The present invention also provides a test method, including: performing a three - point bending test on the fiber - reinforced concrete fractured specimen described in the above - mentioned technical solution, and collecting digital image correlation technology and acoustic emission technology simultaneously during the three - point bending test.

[0080] The present invention has no special limitation on the operation of the three - point bending test, and the technical solutions of the three - point bending test well - known to those skilled in the art can be adopted.

[0081] The present invention has no special limitation on the operation of collecting digital image correlation technology and acoustic emission technology, and the technical solutions of collecting digital image correlation technology and acoustic emission technology well - known to those skilled in the art can be adopted.

[0082] By using the three - point bending test, recording the load - displacement curve and the crack opening displacement curve, calculating the fracture energy, simultaneously collecting the surface strain field and displacement field of the test fracture area by using digital image correlation technology (DIC) during the loading of the three - point bending test, and collecting the acoustic emission signals generated during the fracture of the specimen during the fracture process by using acoustic emission technology (AE) to perform energy quantification of the fracture behavior, so as to analyze the crack propagation rate and the energy of the fracture of the fractured specimen. The present invention combines digital image correlation technology and acoustic emission technology with the three - point bending test to achieve synchronous acquisition of multiple parameters.

[0083] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0084] Embodiment 1

[0085] A pre - fabricated crack mold is composed of a crack - forming column and a pressing plate provided with a longitudinal through - hole;

[0086] The crack - forming column and the longitudinal through - hole of the pressing plate form a clearance fit, and the maximum fit clearance is 0.1 mm;

[0087] The crack - creating column is a T - shaped crack - creating column (made of iron); the longitudinal part of the T - shaped crack - creating column has a length of 100 mm, a width of 3 mm, and a height of 30 mm; the transverse part (i.e., the positioning part) of the T - shaped crack - creating column has a length of 150 mm, a width of 3 mm, and a height of 10 mm.

[0088] The pressing plate is a cuboid. The pressing plate has a length of 400 mm, a width of 150 mm, and a height (thickness) of 10 mm. The pressing plate is made of iron, and the center point of the longitudinal through - hole is located at the center point of the pressing plate.

[0089] In Example 1, the plan view of the pressing plate is as shown in Figure 1 shown, and the perspective view of the pressing plate in Example 1 is as shown in Figure 2 shown.

[0090] In Example 1, the plan view of the crack - creating column is as shown in Figure 3 shown, and the perspective view of the crack - creating column in Example 1 is as shown in Figure 4 shown.

[0091] Example 2

[0092] A method for preparing a fiber - reinforced concrete fracture specimen:

[0093] (1) Mix glass fibers (diameter 13 μm, length 12 mm) with a part of the aggregate (30% of the total mass of the aggregate) in a mixer for 30 s to obtain a fiber mixture; the aggregate consists of coarse aggregate and fine aggregate, and the percentage content of fine aggregate in the aggregate is 45%; the particle size of the fine aggregate is 0.25 - 0.5 mm, and the fine aggregate is river sand; the particle size of the coarse aggregate is 5 - 25 mm, and the coarse aggregate is natural crushed granite.

[0094] (2) Mix the fiber mixture obtained in step (1) with cement (ordinary Portland cement P.O 42.5), the remaining aggregate, water - reducing agent (polycarboxylate superplasticizer), and water and stir for 2 min to obtain a slurry; the mass ratio of cement to the total mass of the aggregate is 460:1845, the mass ratio of the water - reducing agent to cement is 1.5:100, the mass ratio of water to cement is 0.35:1, and the mass - to - volume ratio of fibers in the slurry is 3 kg:1 m 3 ;

[0095] (3) Pour the paste obtained in step (2) into a forming mold (a rectangular mold with a length of 400 mm, a width of 100 mm, and a height of 100 mm), and then use the prefabricated crack mold in Example 1 to create cracks to obtain fiber-reinforced concrete fracture specimens; the crack creation is as follows: Compact the forming mold filled with the paste (the compaction frequency is 50 Hz, the amplitude is 1 mm, the compaction is in layers, the single-layer thickness is 3 mm, the compaction time is 30 s / layer, and the compaction method is vertical compaction), cover the pressure plate, then insert the crack-creation column into the longitudinal through-hole of the pressure plate so that the top of the crack-creation column is flush with the upper surface of the pressure plate. Apply a release agent (silicone release agent) to the surface of the crack-creation column, and after standing and hardening for 24 h, pull out the crack-creation column and then demold.

[0096] Example 3

[0097] Replace the mixing time in step (1) of Example 2 with 60 s, and replace the mass-to-volume ratio of fibers in the paste in step (2) with 6 kg: 1 m 3 , and other parameters are the same as those in Example 2.

[0098] Example 4

[0099] Replace the mixing time in step (1) of Example 2 with 90 s, and replace the mass-to-volume ratio of fibers in the paste in step (2) with 9 kg: 1 m 3 , and other parameters are the same as those in Example 2.

[0100] Example 5

[0101] Replace the mixing time in step (1) of Example 2 with 120 s, and replace the mass-to-volume ratio of fibers in the paste in step (2) with 12 kg: 1 m 3 , and other parameters are the same as those in Example 2.

[0102] Comparative Example 1

[0103] Omit the glass fiber in step (1) of Example 2, and other parameters are the same as those in Example 2.

[0104] Use the cross-sectional image analysis method to test that the fiber agglomeration rate in the fiber-reinforced concrete fracture specimens of Examples 2 to 5 is <5% (the one-step mixing method is >15%), and the fiber distribution uniformity (coefficient of variation) is <8% (the one-step mixing method is 20%).

[0105] The width control accuracy of the prefabricated cracks in the fiber-reinforced concrete fracture specimens of Examples 2 to 5 reaches 0.1 mm ± 0.02 mm (the deviation of the traditional pre-embedding method is >0.5 mm), the depth error is ±2% (the traditional pre-embedding method is >10%), the deviation of the central axis of the crack position is <1 mm, and the repeatability error of the crack morphology is <3%.

[0106] The specimens in Examples 2-5 and Comparative Example 1 were cured in a constant environment of 20 °C and 95% humidity for 28 days, and then the cured specimens were placed in different environments, namely the basic group (placed in a conventional environment), soaking treatment (soaked in pure water for 30 days, and the amount of pure water only needs to cover the specimen), pickling treatment (soaked in 0.1 mol / L sulfuric acid solution for 30 days, and the amount of sulfuric acid solution only needs to cover the specimen), and soaking in alkali treatment (soaked in 0.1 mol / L NaOH solution for 30 days, and the amount of NaOH solution only needs to cover the specimen).

[0107] The SEM images of the specimen of Example 4 after curing and after being placed in different environments (basic group, soaking treatment, pickling treatment, and soaking in alkali treatment) are as Figure 5 shown. It can be seen from Figure 5 that in the basic group, a dense physical-chemical bonding interface was formed between the glass fiber and the cement matrix, and the fiber surface was tightly wrapped by continuously distributed calcium silicate hydrate gel (C-S-H gel). In the soaking treatment environment, after 30 days of water soaking treatment, small crystals appeared on the fiber surface, mainly because the long-term hydration reaction caused the penetration of water molecules, triggering the dissolution and recrystallization of the gel. In the pickling treatment environment, the acidic environment causes a dual damage mechanism to the material. In the 0.1 mol / L sulfuric acid solution soaking, the cement matrix first undergoes dissolution, and the matrix shows a honeycomb-like corrosion morphology in the figure. At the same time, the SiO2 in the glass fiber reacts with H + in sulfuric acid, resulting in a reduction in fiber strength and a decrease in the bonding force with the matrix. In the soaking in alkali treatment environment, after soaking in 0.1 mol / L NaOH solution, a silica gel layer with a certain thickness covers the surface of the glass fiber. This is an alkali-silica reaction triggered in an alkaline environment, resulting in volume expansion at the interface and damage to the structural strength. Through the analysis of the microscopic structure of the interface in different treatment environments, it is confirmed that the deterioration of the microscopic structure is the fundamental reason for the decline of macroscopic properties.

[0108] Example 6

[0109] The specimens in Examples 2 to 5 and Comparative Example 1 after curing and being placed in different environments (basic group G1, soaking treatment G2, pickling treatment G3, and caustic soda treatment G4) were subjected to a three-point bending test. During the three-point bending test, acoustic emission and digital image correlation techniques were used for real-time monitoring. A total of 8 acoustic emission sensors were installed, 4 on the front of the specimen (placed in two rows, 2 in each row) and 4 on the back (placed in two rows, 2 in each row). The acoustic emission sensors were circular with a diameter of 18 mm. The centers of the acoustic emission sensors were 20 mm away from the upper and lower edges of the specimen and 50 mm away from the left and right edges of the specimen. The acoustic emission sensors were successively connected to an acoustic emission preamplifier (signal gain 40 dB (100 times), bandwidth 20 - 1500 KHz, AST function: having an automatic sensor test function, input impedance > 10 MΩ, output impedance 50 Ω, output noise: 2.1 mv 26.4 dB (100 times), output dynamic range > 73.5 dB), an acoustic emission instrument (model DS5-16B), and an acoustic emission monitoring display; the digital image correlation technique included an LED light source, an industrial camera, and a DIC detection display. A size of 60 mm * 100 mm (with the prefabricated crack as the midline) was selected as the digital image acquisition area, and white paint was evenly sprayed and speckles were randomly drawn on the surface of the specimen (i.e., the DIC speckle area).

[0110] During the three-point bending test in Example 6, the positions of the loading head (P) and the supports relative to the specimen were as Figure 6 shown.

[0111] During the three-point bending test in Example 6, the detection schematic diagram of real-time monitoring using acoustic emission and digital image correlation techniques was as Figure 7 shown.

[0112] The flexural strength of the specimens in Examples 2 to 5 and Comparative Example 1 after curing and being placed in different environments (basic group G1, soaking treatment G2, pickling treatment G3, and caustic soda treatment G4) was as Figure 8 shown, Figure 8 where 0 represents Comparative Example 1, 3 represents Example 2, 6 represents Example 3, 9 represents Example 4, and 12 represents Example 5. It can be seen from Figure 8 that different environmental actions have significant differences in the damage mechanism of glass fiber concrete. In an erosive environment, an appropriate amount of glass fiber can improve the fracture performance, but an excessive amount of fiber cannot be evenly and randomly distributed, resulting in the generation of pores and weak interfaces, thereby weakening the bonding strength and the reinforcing effect of the glass fiber.

[0113] The P-CMOD curves of the specimens in Examples 2 to 5 and Comparative Example 1 after curing and being placed in different environments (basic group G1, soaking treatment G2, pickling treatment G3, and caustic soda treatment G4) were as Figure 9 shown, Figure 9In this, PC represents Comparative Example 1, GF3 represents Example 2, GF6 represents Example 3, GF9 represents Example 4, and GF12 represents Example 5.

[0114] The evolution process of the strain contour maps of the specimens in Examples 2 to 5 and Comparative Example 1 during different loading processes after curing is as Figure 10 shown, Figure 10 in which (a) represents Comparative Example 1, (b) represents Example 2, (c) represents Example 3, (d) represents Example 4, and (e) represents Example 5.

[0115] The evolution process of the displacement contour maps of the specimens in Examples 2 to 5 and Comparative Example 1 during different loading processes after curing is as Figure 11 shown, Figure 11 in which (a) represents Comparative Example 1, (b) represents Example 2, (c) represents Example 3, (d) represents Example 4, and (e) represents Example 5. It can be seen from Figures 10 - 11 that adding fibers can enhance the toughness of concrete.

[0116] The three-dimensional acoustic emission damage location map of the specimens in Example 3 after curing and placement in different environments (basic group G1, water immersion treatment G2, acid immersion treatment G3, and alkali immersion treatment G4) is as Figure 12 shown, Figure 12 in which (a) represents the basic group G1, (b) represents the water immersion treatment G2, (c) represents the acid immersion treatment G3, and (d) represents the alkali immersion treatment G4. It can be seen from Figure 12 that under the action of the load, the sound source signals inside the specimen are mainly concentrated in the middle of the specimen. The test results show that during the loading process, the failure mechanism of the specimen is that fine cracks start to appear in the center of the specimen and then continue to extend until failure. Figure 12 In (d), some acoustic emission signals are dispersed in other areas of the specimen. The reason may be that after soaking in the NaOH solution, the internal structure of the specimen expands and the structure is not dense, and the internal damage during loading cannot be concentrated in the mid-span area.

[0117] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A prefabricated crack mold, comprising a seam-forming column and a pressing plate provided with a longitudinal through-hole; the seam-forming column and the longitudinal through-hole of the pressing plate form a clearance fit, and the maximum fit clearance is 0.1 mm; the seam-forming column is a cuboid, the length of the cuboid is 95 - 105 mm, the width is 2.5 - 3.5 mm, and the height is the thickness of the pressing plate + (15 - 25) mm.

2. The prefabricated crack mold according to claim 1, characterized in that, A positioning part is fixedly arranged at the top end of the seam-forming column; one transverse dimension of the positioning part is larger than the corresponding transverse dimension in the seam-forming column.

3. The prefabricated crack mold according to claim 1 or 2, characterized in that, The pressing plate is a cuboid, and the center point of the longitudinal through-hole is located at the center point of the pressing plate.

4. A method for preparing a fiber-reinforced concrete fracture specimen, comprising the following steps: (1) Mix fibers with part of the aggregates to obtain a fiber mixture; (2) Mix the fiber mixture obtained in step (1) with cement, the remaining aggregates, a water reducer and water to obtain a slurry; (3) Pour the slurry obtained in step (2) into a forming mold, and then use the prefabricated crack mold according to any one of claims 1 - 3 to form a crack to obtain a fiber-reinforced concrete fracture specimen; the crack formation includes: after vibrating the forming mold filled with the slurry, covering the pressing plate, and then inserting the seam-forming column into the longitudinal through-hole of the pressing plate so that the top end of the seam-forming column is flush with the upper surface of the pressing plate.

5. The preparation method according to claim 4, characterized in that, In step (1), the mass of part of the aggregates is 20 - 40% of the total mass of the aggregates.

6. The preparation method according to claim 4, characterized in that, In step (1), the diameter of the fibers is 10 - 15 μm, and the length of the fibers is 10 - 15 mm.

7. The preparation method according to claim 4, characterized in that The mass of the fiber in the slurry in step (2) and the volume ratio of the slurry is (1-12) kg: 1 m 3 .

8. The preparation method according to claim 4, characterized in that, In step (2), the mass ratio of water to cement is (0.3 - 0.4):

1.

9. A fiber-reinforced concrete fracture specimen prepared by the preparation method according to any one of claims 4 - 8; the width of the crack in the fiber-reinforced concrete fracture specimen is 2.5 - 3.5 mm, and the height is 15 - 25 mm.

10. A testing method, comprising: Perform a three-point bending test on the fiber-reinforced concrete fracture specimen according to claim 9, and simultaneously collect digital image correlation technology and acoustic emission technology during the three-point bending test.

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