Basalt / polyethylene hybrid fiber reinforced cement-based composite material and anti-cracking preparation method thereof

Abstract

The invention provides a basalt / polyethylene hybrid fiber reinforced cement-based composite material and an anti-cracking preparation method thereof, and relates to the technical field of building materials, the basalt / polyethylene hybrid fiber reinforced cement-based composite material comprises Portland cement with the strength grade of 42.5, the compression strength of the cement is 38.8-52.6 MPa, fly ash with the density of 2.4 g / cm < 3 > and the doping amount of 10% of the total mass of a matrix, silica fume with the density of 2.1 g / cm < 3 > and the doping amount of 5% of the total mass of the matrix, and quartz sand with the density of 2.1 g / cm < 3 > and the doping amount of 0.5% of the total mass of the matrix. The particle size range is 0.09-0.15 mm, the density is 2.6 g / cm < 3 >, and the doping amount is 30% of the total mass of the matrix. According to the basalt / polyethylene hybrid fiber reinforced cement-based composite material and the anti-cracking preparation method thereof, the basalt fibers and the polyethylene fibers are mixed and matched, and reasonable fiber length proportion and mixing amount are combined, so that the anti-cracking performance and the toughness of the cement-based composite material are improved, and the anti-fatigue capability of the material in long-term use is also enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, in particular to a basalt / polyethylene hybrid fiber reinforced cement-based composite material and a crack-resistant preparation method thereof. Background Art

[0002] Cement, a traditional building material, is widely used in various civil engineering projects, including residential and commercial buildings, bridges, roads, and other infrastructure. Its main components include raw materials such as limestone, clay, and iron ore. These raw materials are calcined at high temperatures to form cement clinker, which is then ground into the final cement powder. Due to its high compressive strength and ease of construction, cement's production process is well-established and widely used in the production of building materials such as concrete and mortar.

[0003] As a fundamental building material, cement plays an indispensable role in building structures, particularly in large-scale engineering and infrastructure construction. Cement's advantages lie not only in its high strength and durability, but also in its relatively low cost, ease of transportation, and ease of construction, which have earned it a prominent position in the global construction industry. Through its hydration reaction, cement hardens and forms a strong structure, effectively withstanding various static loads.

[0004] While cement exhibits advantages in many applications, it also suffers from significant drawbacks. Cement suffers from poor toughness, low fatigue resistance, and poor crack resistance, which not only reduces the overall stability of structures but can also lead to further structural degradation. These drawbacks hinder cement's ability to meet demanding engineering requirements in applications such as those requiring earthquake resistance and crack resistance, hindering its further application in certain fields. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a basalt / polyethylene hybrid fiber reinforced cement-based composite material and a crack-resistant preparation method thereof. The technical problem to be solved by the invention is: how to optimize the mixing and vibration process through reasonable proportioning and fiber mixing design to improve the crack resistance, fatigue resistance and toughness of the composite material.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: basalt / polyethylene hybrid fiber reinforced cement-based composite material and its crack-resistant preparation method, comprising:

[0007] Cement, strength grade 42.5, the cement having a compressive strength of 38.8 MPa to 52.6 MPa;

[0008] Fly ash, density 2.4g / cm 3 , the dosage is 10% to 15% of the total mass of the matrix;

[0009] Silica fume, density 2.1g / cm 3 , the dosage is 5% to 8% of the total mass of the matrix;

[0010] Quartz sand, particle size range 0.09mm to 0.15mm, density 2.6g / cm 3 , the dosage is 30% to 35% of the total mass of the matrix;

[0011] Basalt fibers, with lengths of 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, and a content of 1.25%;

[0012] Polyethylene fiber, length 12mm, dosage 1%;

[0013] admixtures, including water reducers and thickeners, to improve the workability of the mixture;

[0014] Water, tap water.

[0015] Preferably, the mixing ratio of the basalt fibers of different lengths is 6mm:9mm:12mm:15mm:18mm=1:1:1:1:1.

[0016] Preferably, the ratio of the cement-based composite material is: water-binder ratio 0.2, sand-binder ratio 0.35.

[0017] Preferably, the amount of the water reducer is 0.5% to 2% of the mass of the cement, and the amount of the thickener is 0.05% to 0.3% of the mass of the cement.

[0018] Method for preparing crack-resistant basalt / polyethylene hybrid fiber reinforced cement-based composite materials: S1. Providing Portland cement with a strength grade of 42.5, as well as fly ash, silica fume, and quartz sand;

[0019] S2. The Portland cement, fly ash, silica fume and quartz sand were mixed in a water-binder ratio of 0.2 and a sand-binder ratio of 0.35 and stirred at low speed in a mixer for 2 minutes to ensure that the components were fully mixed;

[0020] S3. Basalt fibers were added to the mixture, the lengths of the basalt fibers being 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, and polyethylene fibers were added, the length of the polyethylene fibers being 12 mm and the amount being 1% of the total mass of the matrix;

[0021] S4. Adding a water reducer and a thickener to the mixture to improve the working properties of the mixture and ensure uniform dispersion of the fibers;

[0022] S5. Continue stirring the mixture at high speed for 2 minutes, add the remaining mixing water and stir at high speed again for 2 minutes to ensure that the mixture is fully homogenized;

[0023] S6. The uniformly stirred mixture is poured into a mold and vibrated by layering;

[0024] S7. The prepared cement-based composite material is cured at room temperature for 28 days to ensure that the cement matrix is fully hydrated and that the mechanical properties of the composite material reach an optimal state;

[0025] S8. The crack resistance, fatigue resistance, and toughness of the basalt / polyethylene hybrid fiber-reinforced cementitious composite material were evaluated through compression tests, flexural tests, four-point bending tests, and scanning electron microscopy analysis to ensure that it has good crack resistance, fatigue resistance, and high toughness, and is suitable for the long-term stability requirements of building structures.

[0026] Preferably, the layered compaction in S6 is performed for 60 seconds each time to ensure uniform distribution of the fibers, avoid fiber aggregation, remove bubbles, and improve the density and mechanical properties of the composite material.

[0027] Preferably, the compression test adopts GB / T 17671-2021 standard, the specimen size is 40mm×40mm×40mm, and the load is gradually applied until the specimen is destroyed to evaluate the change in compressive strength of the composite material at different ages to ensure the strength and durability of the cement matrix. The flexural test adopts the center load method, the specimen size is 40mm×40mm×160mm, and the load is applied to the middle of the specimen until a destructive crack appears, and the flexural strength is recorded to further evaluate the bridging effect of the fiber and the crack resistance of the composite material. The four-point bending test adopts a four-point loading method, and the specimen size is 40mm×40mm×160mm.

[0028] Preferably, the layered compaction method is to compact the mixture layer by layer with a thickness of 10 mm each time.

[0029] The present invention provides a basalt / polyethylene hybrid fiber reinforced cement-based composite material and a crack-resistant preparation method thereof. It has the following beneficial effects:

[0030] This basalt / polyethylene hybrid fiber-reinforced cement-based composite and its crack-resistant preparation method utilize a blend of basalt and polyethylene fibers, combined with a reasonable fiber length ratio and dosage, to not only enhance the cement-based composite's crack resistance and toughness, but also strengthen its fatigue resistance during long-term use. Optimized mixing and vibration processes ensure uniform fiber distribution within the cement matrix, preventing fiber agglomeration and improving the composite's overall performance and stability.

[0031] Through meticulous control of the curing process and scanning electron microscopy analysis, the full hydration of the cement matrix and the good adhesion between the fibers and the matrix were ensured, thereby improving the composite material's strength and crack resistance at a microscopic level. This technical solution effectively addresses the problems of traditional cement materials, such as poor toughness and low crack resistance, and has high application value, especially suitable for the long-term stability requirements of building structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram for calculating the equivalent bending strength for realizing the invention;

[0033] Figure 2 It is to realize the microscopic morphology of the transition zone of the BF fiber-matrix interface of the invention;

[0034] Figure 3 It is to realize the EDS analysis of the BF fiber-matrix interface transition zone of the invention;

[0035] Figure 4 The invention is to realize the compressive strength of BF / PE-ECC mixed with different length fibers at different ages;

[0036] Figure 5 The invention is to realize the flexural strength of BF / PE-ECC mixed with different length fibers at different ages;

[0037] FIG6 is a load-deflection curve of a BF / PE-ECC hybrid of fibers of different lengths according to the present invention;

[0038] Figure 7 It is to realize the equivalent bending strength of BF / PE-ECC fibers of different lengths of the invention;

[0039] Figure 8 It is to realize the equivalent bending toughness of BF / PE-ECC fibers of different lengths of the invention;

[0040] Figure 9 It is to realize the microscopic morphology of the PE fiber-matrix interface transition zone of the invention;

[0041] Figure 10 This is an EDS surface scan of the PE fiber-matrix interface transition zone implemented in the invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Example 1

[0044] like Figures 1-10 As shown, the embodiment of the present invention provides a basalt / polyethylene hybrid fiber reinforced cement-based composite material and a crack-resistant preparation method thereof, comprising: cement with a strength grade of 42.5 and a compressive strength of the cement of 38.8 MPa (3 days) to 52.6 MPa (28 days);

[0045] Fly ash, density 2.4g / cm 3 , the dosage is 10% of the total mass of the matrix;

[0046] Silica fume, density 2.1g / cm 3 , the dosage is 5% of the total mass of the matrix;

[0047] Quartz sand, particle size range 0.09mm to 0.15mm, density 2.6g / cm 3 , the dosage is 30% of the total mass of the matrix;

[0048] Basalt fibers have lengths of 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, with a dosage of 1.25%. The mixing ratio of basalt fibers of different lengths is 6 mm: 9 mm: 12 mm: 15 mm: 18 mm = 1:1:1:1:1. The mix ratio of cement-based composite materials is: water-binder ratio 0.2, sand-binder ratio 0.35.

[0049] Polyethylene fiber, length 12mm, dosage 1%;

[0050] Admixtures, including water reducers and thickeners, to improve the workability of the mixture, with the water reducer being added in an amount of 0.5% to 2% by weight of the cement and the thickener being added in an amount of 0.05% by weight of the cement;

[0051] Water, tap water.

[0052] S1. Provide Portland cement with a strength grade of 42.5, as well as fly ash, silica fume and quartz sand;

[0053] S2. Add Portland cement, fly ash, silica fume and quartz sand in a water-binder ratio of 0.2 and a sand-binder ratio of 0.35 and stir at low speed in a mixer for 2 minutes to ensure that all components are fully mixed;

[0054] S3. Basalt fibers were added to the mixture. The lengths of the basalt fibers were 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, respectively. At the same time, polyethylene fibers were added. The length of the polyethylene fibers was 12 mm and the addition amount was 1% of the total mass of the matrix.

[0055] S4. Adding a water reducer and a thickener to the mixture to improve the working properties of the mixture and ensure uniform dispersion of the fibers;

[0056] S5. Continue stirring the mixture at high speed for 2 minutes, add the remaining mixing water and stir at high speed again for 2 minutes to ensure that the mixture is fully homogenized;

[0057] S6. The stirred mixture is poured into a mold and vibrated by layering. In S6, the layers are vibrated for 60 seconds each time to ensure uniform distribution of the fibers, avoid fiber aggregation and remove bubbles, thereby improving the density and mechanical properties of the composite material.

[0058] S7. The prepared cement-based composite material is cured at room temperature for 28 days to ensure that the cement matrix is fully hydrated and that the mechanical properties of the composite material reach an optimal state;

[0059] S8. The crack resistance, fatigue resistance and toughness of basalt / polyethylene hybrid fiber reinforced cement-based composites were evaluated through compression tests, flexural tests, four-point bending tests and scanning electron microscopy analysis to ensure that they have good crack resistance, fatigue resistance and high toughness, and are suitable for the long-term stability requirements of building structures. The compression test adopts the GB / T17671-2021 standard, with a specimen size of 40mm×40mm×40mm. The load is gradually applied until the specimen is destroyed. The changes in the compressive strength of the composite material at different ages are evaluated to ensure the strength and durability of the cement matrix. The flexural test adopts the center load method, with a specimen size of 40mm×40mm×160mm. The load is applied to the middle of the specimen until it is destroyed. Cracks are detected and the flexural strength is recorded to further evaluate the bridging effect of the fiber and the crack resistance of the composite material. The four-point bending test adopts a four-point loading method, the specimen size is 40mm×40mm×160mm, the loading rate is 0.2mm / min, the specimen span is 150mm, and the equivalent flexural strength and equivalent flexural toughness are calculated to evaluate the flexural performance of the composite material. The four-point bending test can effectively evaluate the toughness of the composite material during crack propagation. Scanning electron microscopy analysis is used to analyze the microstructure of the composite material, especially the interface transition zone between the fiber and the matrix, showing the distribution of CSH gel and other hydration products, evaluating the bonding strength between the fiber and the cement matrix, and providing guidance for further improving the crack resistance of cement-based composites.

[0060] Example 2

[0061] like Figures 1-10 As shown, the embodiment of the present invention provides a basalt / polyethylene hybrid fiber reinforced cement-based composite material and a crack-resistant preparation method thereof, comprising: cement with a strength grade of 42.5 and a compressive strength of the cement of 38.8 MPa (3 days) to 52.6 MPa (28 days);

[0062] Fly ash, density 2.4g / cm 3, the dosage is 15% of the total mass of the matrix;

[0063] Silica fume, density 2.1g / cm 3 , the dosage is 8% of the total mass of the matrix;

[0064] Quartz sand, particle size range 0.09mm to 0.15mm, density 2.6g / cm 3 , the dosage is 35% of the total mass of the matrix;

[0065] Basalt fibers have lengths of 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, with a dosage of 1.25%. The mixing ratio of basalt fibers of different lengths is 6 mm: 9 mm: 12 mm: 15 mm: 18 mm = 1:1:1:1:1. The mix ratio of cement-based composite materials is: water-binder ratio 0.2, sand-binder ratio 0.35.

[0066] Polyethylene fiber, length 12mm, dosage 1%;

[0067] Admixtures, including water reducers and thickeners, to improve the workability of the mixture, with the water reducer being added in an amount of 0.5% to 2% by weight of the cement and the thickener being added in an amount of 0.3% by weight of the cement;

[0068] Water, tap water.

[0069] S1. Provide Portland cement with a strength grade of 42.5, as well as fly ash, silica fume and quartz sand;

[0070] S2. Add Portland cement, fly ash, silica fume and quartz sand in a water-binder ratio of 0.2 and a sand-binder ratio of 0.35 and stir at low speed in a mixer for 2 minutes to ensure that all components are fully mixed;

[0071] S3. Basalt fibers were added to the mixture. The lengths of the basalt fibers were 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, respectively. At the same time, polyethylene fibers were added. The length of the polyethylene fibers was 12 mm and the addition amount was 1% of the total mass of the matrix.

[0072] S4. Adding a water reducer and a thickener to the mixture to improve the working properties of the mixture and ensure uniform dispersion of the fibers;

[0073] S5. Continue stirring the mixture at high speed for 2 minutes, add the remaining mixing water and stir at high speed again for 2 minutes to ensure that the mixture is fully homogenized;

[0074] S6. The stirred mixture is poured into a mold and vibrated by layering. In S6, the layers are vibrated for 60 seconds each time to ensure uniform distribution of the fibers, avoid fiber aggregation and remove bubbles, thereby improving the density and mechanical properties of the composite material.

[0075] S7. The prepared cement-based composite material is cured at room temperature for 28 days to ensure that the cement matrix is fully hydrated and that the mechanical properties of the composite material reach an optimal state;

[0076] S8. The crack resistance, fatigue resistance and toughness of basalt / polyethylene hybrid fiber reinforced cement-based composites were evaluated through compression tests, flexural tests, four-point bending tests and scanning electron microscopy analysis to ensure that they have good crack resistance, fatigue resistance and high toughness, and are suitable for the long-term stability requirements of building structures. The compression test adopts the GB / T17671-2021 standard, with a specimen size of 40mm×40mm×40mm. The load is gradually applied until the specimen is destroyed. The changes in the compressive strength of the composite material at different ages are evaluated to ensure the strength and durability of the cement matrix. The flexural test adopts the center load method, with a specimen size of 40mm×40mm×160mm. The load is applied to the middle of the specimen until it is destroyed. Cracks are detected and the flexural strength is recorded to further evaluate the bridging effect of the fiber and the crack resistance of the composite material. The four-point bending test adopts a four-point loading method, the specimen size is 40mm×40mm×160mm, the loading rate is 0.2mm / min, the specimen span is 150mm, and the equivalent flexural strength and equivalent flexural toughness are calculated to evaluate the flexural performance of the composite material. The four-point bending test can effectively evaluate the toughness of the composite material during crack propagation. Scanning electron microscopy analysis is used to analyze the microstructure of the composite material, especially the interface transition zone between the fiber and the matrix, showing the distribution of CSH gel and other hydration products, evaluating the bonding strength between the fiber and the cement matrix, and providing guidance for further improving the crack resistance of cement-based composites.

[0077] Experimental Examples

[0078] 1.1 Experimental raw materials

[0079] In this study, silicate cement with a strength grade of 42.5 was selected. The physical properties of cement are shown in Table 1. The density of the first-grade fly ash and silica fume selected were 2.4 g / cm 3 and 2.1 g / cm 3 The average size of quartz sand ranges from 0.09mm to 0.12mm, the maximum particle size is 0.15mm, and the density is 2.6g / cm 3 The BF fibers used in the experiment had lengths of 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm. The PE fiber was 12 mm long. The physical and mechanical properties of the fibers are shown in Table 2. The admixtures used were a water reducer (SP) and a thickener (HPMC). Ordinary tap water was used.

[0080] 1.2 Test methods

[0081] 1.2.1 Test mix ratio

[0082] Based on relevant research results, this study used a water-binder ratio of 0.2, a sand-binder ratio of 0.35, a BF content of 1.25%, and a PE content of 1%. The fiber lengths were varied, with BF fibers of different lengths (6 mm, 9 mm, 12 mm, 15 mm, and 18 mm) mixed with PE (12 mm) fibers. The dispersion of the BF / PE-ECC fibers in the matrix during mixing was investigated.

[0083] The mixing process for this experiment was as follows: a portion of the mixing water, cementitious materials, and admixtures were added to the mixer and stirred at low speed for 2 minutes. 27% of the mixing water was reserved. BF and PE fibers were added and stirred at high speed for 2 minutes. The reserved mixing water was added and stirred at high speed for 2 minutes. After this stage, the prepared composite material was cast into a mold and compacted using a layered vibrating method, with each layer vibrated on a vibrating table for 60 seconds before being smoothed and formed.

[0084] 1.2.2 Compression and flexural strength test

[0085] Compression and flexural tests were conducted in accordance with GB / T 17671-2021. The flexural strength of the specimens was tested using the central load method, with three standard test pieces tested per mix. The compressive test load was applied to both sides of the forming surface, with a compression area of 40 × 40 mm². From the start of the test, the load was applied continuously and evenly until the specimen failed.

[0086] 1.2.3 Four-point bending test

[0087] The test uses a four-point loading method with a loading rate of 0.2mm / min. The specimen size is 40mm×40mm×160mm, and the span between the two supports is L=150mm. It is divided into three sections, and the middle section is a pure bending section. The equivalent bending strength is calculated according to formula (1) with an accuracy of 0.1MPa. The equivalent bending toughness Wu is calculated according to formula (2) with an accuracy of 0.1KJ / m 3 . Figure 1 The principle of specimen equivalent calculation is explained.

[0088]

[0089] Where: f u —Equivalent bending strength (N / mm 2 );

[0090] W u —Equivalent bending toughness (KJ / m 3 ).

[0091] b, h—section width and height (mm);

[0092] L—span of specimen (mm);

[0093] δ u —The deflection value corresponding to the load dropping to u times the peak load, where u is 0.85;

[0094] Ω u — is the mid-span deflection δ u The area under the load-deflection curve (N·mm).

[0095] 2 Experimental results and data analysis

[0096] 2.1 Compression test

[0097] Organize the test results, Figure 4 Figure 3 shows the compressive strength of BF / PE-ECC hybrids with different fiber lengths at various ages. Compared to the control group, PB0, the addition of PE and BF fibers of varying lengths to the cement matrix improved the compressive strength at all ages. However, as BF fiber length increased, the improvement showed an initial upward trend followed by a downward trend. Furthermore, the fibers' improvement was lower in the early stages of the specimen than in the later stages. This is attributed to the weak adhesion at the interface transition zone between the fibers and the cement matrix in the early stages. When the same proportion of BF fibers was incorporated into the matrix, the fiber counts in PB6 and PB9 were significantly higher than in PB15 and PB18. This is because, at younger ages, it's difficult for sufficient hydration products to form near the fibers and bond with them. With increasing age, the bond strength in the interfacial transition zone between the fiber and matrix increases as the cement fully hydrates. At 28 days, the compressive strength of PB12 increased by 16.42%, 10.55%, 2.71%, and 17.51% compared to PB6, PB9, PB15, and PB18, respectively. Longer fibers enhance their crack-bridging ability, resulting in a more pronounced improvement in mechanical properties. However, when the fiber length reaches 18 mm, its fluidity is 18.5 cm, indicating poor workability. At this point, the fibers aggregate within the matrix, making it difficult to disperse evenly, introducing defects and reducing compressive strength. At 60 days, secondary hydration products appear within the BF / PE-ECC due to the active effect of fly ash. At this point, the compressive strength growth rate of the specimen slows and gradually stabilizes.

[0098] 2.2 Flexural strength

[0099] Figure 5Figure 2 shows the flexural strength of BF / PE-ECC composites with different fiber lengths at different ages. Overall, as BF fiber length increases, the flexural strength of the specimens increases first and then decreases. The highest flexural strength is achieved at a fiber length of 15 mm, with a fluidity of 20.2 cm, indicating good performance. At 28 days, PB15 exhibits improvements of 35.44%, 24.55%, 8.98%, and 38.12% compared to PB6, PB9, PB12, and PB18, respectively. This is due to the fact that when a central load is applied to the specimen surface, the first microcracks gradually appear in the matrix, with the fibers acting as a direct bridge. As the load increases, the fibers begin to debond. During this phase, the displacement generated by the longer fiber embedding length is smaller than the pull-out displacement on the shorter side. For a given load borne by the bridging fibers, the embedded short fibers are unable to withstand the load. Therefore, the flexural strength enhancement effect of short and medium fibers is less than that of 15 mm BF fibers. Due to its excessive length, 18mmBF fibers tend to agglomerate within the matrix, resulting in a relatively weak improvement in flexural strength. At 60 days of age, the cement matrix is more fully hydrated than in specimens with younger ages, leading to a significantly improved bond strength in the fiber-matrix interface transition zone. This is demonstrated by the fibers' ability to control cracks, resulting in lower interfacial slip relative to the matrix and finer cracks.

[0100] 2.3 Equivalent bending toughness

[0101] After reaching 60 days of age, the four-point bending properties of BF / PE-ECC with different fiber lengths were tested. The load-deflection curves are shown in Figure 6. The control sample, PB0, exhibited complete brittle failure under the four-point bending load, as shown in Figure 6(a). Compared to PB0, specimens incorporating BF fibers of varying lengths all exhibited flexural hardening during loading. The load-deflection curves in Figure 6(b) show that the incorporation of medium and long fibers significantly improved toughness compared to short fibers. The reason for this is that, in ECC, the fiber embedment length in the matrix is generally considered to be between 0 and Lf / 2 (Lf / 2 is typically 9-15mm). When the matrix fails, the fibers are difficult to evenly distribute across the crack. In this case, the incorporation of longer fibers results in smaller displacement during the debonding phase. When the BF fibers in the mixed matrix are sufficiently long, they are more easily embedded at both ends of the crack, allowing the bridging fibers to withstand a higher load, resulting in higher toughness.

[0102] Figure 7 、 Figure 8 The equivalent bending strength and equivalent bending toughness bar graphs of BF / PE-ECC fibers of different lengths are shown. When BF short fibers are mixed into the BF / PE-ECC matrix, the equivalent bending strengths of PB6 and PB9 are 7.31 and 8.34 MPa, respectively, and the equivalent bending toughnesses are 76.55 and 79.35 kJ / m, respectively. 3, the mechanical properties of the two are not much different. When mixed with BF medium and long fibers, the equivalent bending strengths of PB12, PB15, and PB18 are 8.39, 9.12, and 10.31 MPa, respectively, and the equivalent bending toughness are 161.59, 182.11, and 159.23 kJ / m3, respectively. Among them, PB15 has the highest equivalent bending toughness, which is 12.7% higher than that of PB12. The reason is that the longer the length of the BF fiber, the greater the effective bonding length coefficient of the fiber in the matrix, and the tighter the bond with the matrix interface transition zone. In the four-point bending failure of the specimen, more fracture energy is consumed during fiber debonding and pulling off, thus showing better equivalent bending toughness. The equivalent bending toughness of PB18 is 12.6% lower than that of PB15, because fibers that are too long are prone to fiber agglomeration in the matrix, thereby forming excess pores and defects, resulting in reduced fiber bridging ability and weak crack control ability. However, PB18 has the highest equivalent bending strength because the fiber agglomeration produces a strengthening regional bridging effect, which is related to the bending stress generated per unit area. From the load-deflection curve in Figure 6(b), PB18 has the highest peak load under four-point bending and the deflection generated is relatively small. Therefore, compared with the PB6 to PB15 groups, it has increased by 41.0%, 23.6%, 22.9%, and 13.0%, respectively.

[0103] 2.4 Microstructure analysis

[0104] 2.4.1 PE fiber-matrix interface transition zone

[0105] Figure 9 This is the microscopic morphology of the transition zone between the PE fiber and the matrix interface. After the PE fiber is subjected to force, the surface is obviously damaged, showing a good ability to absorb energy. Figure 9 (a). When the specimen begins to bear the load, stress concentration appears at the crack tip inside the matrix, and microcracks begin to expand. The high tensile strength PE fiber bridges the cracks and shares the fracture energy of the matrix, thereby effectively suppressing the cracking and deformation of the matrix, allowing the matrix to bear a larger load and effectively improving the equivalent bending toughness of the matrix. Figure 9 (b) Since PE itself is a hydrophobic organic fiber, the transition zone between the fiber and the matrix has large pores and weak interfacial bonding. When the matrix is damaged, the PE fiber tends to be pulled out and damaged. From a macroscopic perspective, it manifests as multiple cracks in the matrix. At this time, the debonding of the fiber and matrix interface generates relative sliding friction, further consuming the energy generated during the loading process, such as Figure 9 (c).

[0106] Considering EDS surface scanning and fiber size, the experiment selected a 20μm area at the PE fiber-matrix interface and transition zone to analyze its hydration products. Previous studies have shown that in a cement matrix, when the calcium-silicon ratio in the matrix is less than 2.5, the cement hydration product is primarily CSH gel. When the calcium-silicon ratio in the matrix is greater than 2.5, the CSH gel content in the reaction product decreases, while the relative contents of AFm, Aft, and CH increase. When the (Al+Fe) / Ca ratio in the matrix region is greater than 0.4, the hydration product is primarily AFm. Figure 10 The EDS surface scan of the PE fiber-matrix interface transition zone is shown in Table 3. The EDS analysis of the PE fiber-matrix interface transition zone shows that the C content accounts for 87.63% at data 1 of the distribution diagram EDS, which indicates that the area is PE fiber. The EDS surface scan data in the analysis diagram shows that the calcium-silicon ratio at data 2 is 10.43, which is much greater than 0.5, and the ratio of the total amount of Al and Fe to the calcium content is 0.18, indicating that Figure 10 The primary hydration product at EDS scan point 2 in (b) is flake CH. Due to the low strength and stability of CH itself, this indicates weak adhesion at the interface transition zone between the PE fiber and the matrix. At EDS scan point 3, the calcium-silicon ratio decreases significantly, with (Al+Fe) / Ca being 0.08. The primary hydration product here is CSH gel.

[0107] 2.4.2BF fiber-matrix interface transition zone

[0108] Figure 2 The microscopic morphology of the transition zone between the BF fiber and the matrix interface. Since the density of BF fibers is similar to that of the cement matrix, they can be more evenly dispersed in the cement matrix. Some scholars have shown that the increase in the porosity of the cement matrix will reduce the mechanical properties of cement-based materials. BF is a hydrophilic inorganic fiber. During the hydration process of cement, it guides the migration of water molecules to the BF surface, accelerating the production of more CSH gel in the transition zone between the fiber and the matrix, thereby effectively filling the initial pores in the cement matrix and improving the compressive strength of the matrix. Figure 2 (b). In addition, BF is a fiber with a high elastic modulus. Due to the strong interfacial bonding between BF and the matrix, when the load continues to increase, the fiber is mainly broken by pulling out, and the cross section at the fiber fracture is smooth, which has an effect on improving the initial crack strength of the matrix. Figure 2 (c).

[0109] Figure 3 The EDS surface scan of the BF fiber-matrix interface transition zone is shown in Table 4. The EDS analysis of the BF fiber-matrix interface transition zone is shown in Table 4. The element content at data 4 in the analysis table is combined with Figure 3 (a), it is determined that this is a BF fiber. Figure 3The calcium-silicon ratios at locations 5 and 6 in the EDS data are 3.26 and 4.31, respectively, both greater than 2.5 and with little difference between the two. The (Al+Fe) / Ca values at locations 5 and 6 are 0.05 and 0.04, respectively, both less than 0.4. This indicates that the hydration products at locations 5 and 6 are mainly flocculent, granular CSH gels and a small amount of needle-like Aft, which act as a supporting skeleton in the cement matrix. Comparing the data at the interface transition zone between PE fibers and the matrix, it is shown that the BF fibers are more tightly bonded to the cement matrix. When the matrix is subjected to load, the BF fibers have a greater interfacial bonding force with the matrix, further demonstrating the strength-enhancing effect of BF fibers on the BF / PE-ECC.

[0110] Table 1 Physical properties of cement

[0111]

[0112] Table 2 Physical and mechanical properties of BF and PE fibers

[0113]

[0114] 6-9mm is defined as short fiber, 12mm is defined as medium fiber, and 15-18mm is defined as long fiber.

[0115] Table 3 EDS analysis of PE fiber-matrix interface transition zone

[0116]

[0117] Table 4 EDS analysis of BF fiber-matrix interface transition zone

[0118]

[0119]

[0120] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Basalt / polyethylene hybrid fiber reinforced cement-based composite material, characterized in that: include: Cement, strength grade 42.5, the cement having a compressive strength of 38.8 MPa to 52.6 MPa; Fly ash, density 2.4g / cm 3 , the dosage is 10% to 15% of the total mass of the matrix; Silica fume, density 2.1g / cm 3 , the dosage is 5% to 8% of the total mass of the matrix; Quartz sand, particle size range 0.09mm to 0.15mm, density 2.6g / cm 3 , the dosage is 30% to 35% of the total mass of the matrix; Basalt fibers, with lengths of 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, and a content of 1.25%; Polyethylene fiber, length 12mm, dosage 1%; admixtures, including water reducers and thickeners; Water, tap water.

2. The basalt / polyethylene hybrid fiber reinforced cement-based composite material according to claim 1, characterized in that: The mixing ratio of the basalt fibers of different lengths is 6mm:9mm:12mm:15mm:18mm=1:1:1:1:

1.

3. The basalt / polyethylene hybrid fiber reinforced cement-based composite material according to claim 1, characterized in that: The mix ratio of the cement-based composite material is: water-binder ratio 0.2, sand-binder ratio 0.

35.

4. The basalt / polyethylene hybrid fiber reinforced cement-based composite material according to claim 1, characterized in that: The amount of the water reducer is 0.5% to 2% of the mass of the cement, and the amount of the thickener is 0.05% to 0.3% of the mass of the cement.

5. A method for preparing crack-resistant basalt / polyethylene hybrid fiber reinforced cement-based composite materials, characterized by: S1. Provide Portland cement with a strength grade of 42.5, as well as fly ash, silica fume and quartz sand; S2. The Portland cement, fly ash, silica fume and quartz sand were mixed in a water-binder ratio of 0.2 and a sand-binder ratio of 0.35 and stirred at low speed in a mixer for 2 minutes to ensure that the components were fully mixed; S3. Basalt fibers were added to the mixture, the lengths of the basalt fibers being 6 mm, 9 mm, 12 mm, 15 mm, and 18 mm, and polyethylene fibers were added, the length of the polyethylene fibers being 12 mm and the amount being 1% of the total mass of the matrix; S4. Adding a water reducer and a thickener to the mixture; S5. Continue stirring the mixture at high speed for 2 minutes, add the remaining mixing water and stir at high speed again for 2 minutes to ensure that the mixture is fully homogenized; S6. The uniformly stirred mixture is poured into a mold and vibrated by layering; S7. The prepared cement-based composite material was cured at room temperature for 28 days to ensure that the cement matrix was fully hydrated; S8. Evaluate the crack resistance, fatigue resistance, and toughness of the basalt / polyethylene hybrid fiber-reinforced cementitious composite material through compression testing, flexural testing, four-point bending testing, and scanning electron microscopy analysis.

6. The method for preparing the crack-resistant basalt / polyethylene hybrid fiber reinforced cement-based composite material according to claim 5, characterized in that: The layers were compacted as described in S6, with each vibration lasting 60 seconds.

7. The method for preparing the crack-resistant basalt / polyethylene hybrid fiber reinforced cement-based composite material according to claim 5, characterized in that: The compression test adopts the GB / T 17671-2021 standard, the specimen size is 40mm×40mm×40mm, and the load is gradually applied until the specimen is destroyed to evaluate the change in the compressive strength of the composite material at different ages. The flexural test adopts the central load method, and the four-point bending test adopts the four-point loading method.

8. The method for preparing the crack-resistant basalt / polyethylene hybrid fiber reinforced cement-based composite material according to claim 5, characterized in that: The layered compaction method is to compact the mixture layer by layer with a thickness of 10 mm each time.

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