Preparation method of chopped basalt fiber concrete by adopting twice dry stirring process

Abstract

The invention discloses a method for preparing chopped basalt fiber concrete by adopting a twice dry-mixing stirring process, which comprises the following steps: adding a first dry-mixing material into a stirring barrel of a stirrer, starting the stirrer to start stirring, in a stirring state, mixing a part of short-cut basalt fibers with the first dry mixing material, and stirring for T1 time to obtain a second dry mixing material; mixing the second part of short-cut basalt fiber with the second dry mixing material, and stirring for T2 time to obtain a third dry mixing material; mixing broken stone, sand and a gel material with a second particle size with the third dry mixed material, and stirring for T3 time to obtain a fourth dry mixed material; and adding water and an additive into the stirring barrel, mixing with the fourth dry mixing material, carrying out wet mixing, and stirring for T4 time to obtain the short-cut basalt fiber concrete. According to the invention, full dispersion and low fracture rate of fibers in a concrete matrix are realized, and the obtained basalt fiber concrete has excellent performance and stable quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete preparation, and in particular relates to a method for preparing chopped basalt fiber concrete using a double dry mixing process. Background Art

[0002] Basalt fiber, a new type of natural mineral fiber, boasts excellent properties such as high strength, high modulus, high and low temperature resistance, acid and alkali resistance, super insulation, low thermal conductivity, and radiation resistance. It is used in a variety of fields, including automotive, shipbuilding, aerospace, military, and construction, and is known as a green industrial material for the 21st century. In civil engineering, chopped basalt fiber is considered an ideal concrete reinforcement and is often incorporated into concrete to improve its properties. Chopped basalt fiber is evenly distributed throughout the concrete, inhibiting the growth of internal pores by filling and bridging the gaps, thereby improving related properties. Studies have shown that medium-length fibers (12mm-16mm) at a volume content of 0.1%-0.15% produce the most significant improvements in concrete performance.

[0003] However, due to the characteristics of chopped basalt fibers, such as their susceptibility to breakage, agglomeration, and difficulty in dispersion, they tend to aggregate in concrete, forming internal defects that affect concrete product performance and hinder the further promotion of chopped basalt fibers in civil engineering. Therefore, different mixing processes can significantly impact the improvement effect of basalt fibers. For example, improper mixing processes can fail to fully disperse the chopped basalt fibers or cause them to agglomerate. Undispersed or agglomerated fibers leave pores or weak points within the matrix, which can easily lead to stress concentrations under load, resulting in localized excessive stress within the concrete and localized failure. Furthermore, improper mixing processes can easily lead to extensive breakage of basalt fibers, preventing them from fully utilizing their bridging function within the concrete matrix. The breakage rate, dispersion characteristics, and bonding state of chopped basalt fibers with the matrix are key factors influencing the performance of basalt fiber-reinforced concrete. Summary of the Invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a method for preparing chopped basalt fiber concrete using a two-step dry mixing process, so as to solve the problems in the prior art of chopped basalt fiber being difficult to disperse, easy to agglomerate, and easy to break in concrete.

[0005] The object of the present invention is achieved like this:

[0006] A method for preparing chopped basalt fiber concrete using a two-step dry mixing process comprises the following steps:

[0007] Prepare the materials according to the ratio, and divide the chopped basalt fibers into the first part and the second part according to weight;

[0008] Adding a first dry mix into a mixing barrel of a mixer, and starting the mixer to begin mixing; wherein the first dry mix includes cement and gel powder of a first particle size;

[0009] The first dry mix is ​​performed according to the following steps: under stirring, the first portion of chopped basalt fibers is added to a mixing barrel, mixed with the first dry mix, and premixed for the first time, and stirred for T1 time to obtain a second dry mix; then, the second portion of chopped basalt fibers is immediately added to the mixing barrel, mixed with the second dry mix, and premixed for the second time, and stirred for T2 time to obtain a third dry mix;

[0010] Perform a second dry mix according to the following steps: add crushed stone, sand, and the gel material of the second particle size into a mixing bucket, mix with the third dry mix, and dry mix for T3 time to obtain a fourth dry mix;

[0011] After the second dry mix is ​​completed, wet mix is ​​performed according to the following steps: water and admixtures are added to a mixing bucket, mixed with the fourth dry mix and wet mixed, and stirred for T4 time to obtain chopped basalt fiber concrete.

[0012] Furthermore, the volume content of the chopped basalt fibers is 0.1%; the length of the chopped basalt fibers is 12 mm and the diameter is 7-14 μm.

[0013] Furthermore, the stirring time T1 is 1 min; the stirring time T2 is 2 min; the stirring time T3 is 10 s; and the stirring time T4 is 2 min.

[0014] Furthermore, the first part is 40%-60% of the total amount of the chopped basalt fibers, and the rest is the second part.

[0015] Furthermore, the first part and the second part are both 50% of the total amount of the chopped basalt fibers.

[0016] Furthermore, the ratios of the particle size of the cement, the first particle size and the diameter of the chopped basalt fibers are all 1-3.

[0017] Furthermore, the step of preparing the materials according to the ratio further includes the following steps: checking whether the chopped basalt fibers are dry, and drying the chopped basalt fibers if they are damp.

[0018] Furthermore, before adding the first portion of chopped basalt fibers into the mixing barrel and after adding the first dry mix into the mixing barrel of the mixer, the mixer is started to stir for T0 time, and the water absorption characteristics of the first dry mix are utilized to completely dry the internal mixing space of the mixing barrel.

[0019] Furthermore, the stirrer is a forced stirrer with a stirring rate of 25-35 rpm and a distance between the blade and the wall of the stirring barrel of 3-5 mm.

[0020] Furthermore, the gel powder of the first particle size includes quartz powder, fly ash, and fine dust mineral powder; the gel powder of the second particle size includes silica fume, fine dust-ultrafine dust mineral powder.

[0021] Compared with the prior art, the method for preparing chopped basalt fiber concrete using a two-step dry mixing process provided by the present invention has the following beneficial effects:

[0022] 1. The present invention adopts a mixing process of "two dry mixes followed by wet mix, and the first dry mix adopts a second premix", which solves the problems of short-cut basalt fibers being difficult to disperse, easy to agglomerate, and easy to break in concrete. The short-cut basalt fibers can be fully dispersed in the concrete matrix with a low breakage rate, ensuring the improvement effect of basalt fibers on concrete materials, thereby obtaining basalt fiber concrete with excellent performance and stable quality.

[0023] 2. The present invention can be applied to different types of concrete and has universal promotion significance in the field of civil engineering. It can also improve the performance utilization rate of basalt fiber, reduce the production cost of fiber concrete prefabricated components, and effectively promote the further application of chopped basalt fiber in the field of civil engineering.

[0024] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0026] Figure 1 This is a process flow chart of the method for preparing chopped basalt fiber concrete using a two-step dry mixing process provided by the present invention;

[0027] Figure 2The characteristics of dry-mixed basalt fibers with different particle sizes (basalt fiber volume parameter 0.1%, dry-mixing time 2 minutes); among them, a. chopped basalt fiber bundles (length 12 mm, single fiber diameter 7-15 μm) without stirring and dispersion; b. crushed stone (particle size > 5 mm); c. river sand (coarse sand, particle size 0.5-1 mm); d. 26-40 mesh quartz sand (particle size 0.42-0.7 mm); e. 40-70 mesh quartz sand (particle size 0.21-0.425 mm); f. 300 mesh quartz powder (particle size < 48 μm); g. cement (particle size 7-40 μm); h. silica fume (particle size 0.1-0.3 μm); i. river sand and cement dry-mixed with basalt fibers; j. crushed stone, river sand and cement dry-mixed with basalt fibers

[0028] Figure 3 The figure shows the mixing effect of the M-1 mixing process of the present invention; a, b show the characteristics of the fiber premixed cement obtained by the M-1 mixing process; c, d show the characteristics of the basalt fiber concrete mixture obtained by the M-1 mixing process;

[0029] Figure 4 The characteristics of concrete mixtures obtained by mixing processes M-2 to M-5 are as follows: a) basalt fibers dispersed by M-2 mixing process; b) bundled basalt fibers by M-2 mixing process; c) basalt fibers with different dispersion characteristics by M-3 mixing process; d) bundled basalt fibers by M-3 mixing process; e) basalt fibers with different dispersion characteristics by M-4 mixing process; f) dispersed basalt fibers by M-4 mixing process; g) medium-dispersed basalt fibers by M-5 mixing process; h) semi-bundled basalt fibers by M-5 mixing process

[0030] Figure 5 are the failure characteristics of the specimens; among them, a. failure characteristics of plain concrete; b. failure characteristics of fiber concrete using M-1 mixing process; c. failure cross-sectional characteristics of fiber concrete using M-2 mixing process; d. failure cross-sectional characteristics of fiber concrete using M-3 mixing process; e. failure cross-sectional characteristics of fiber concrete using M-4 mixing process; f. failure cross-sectional characteristics of fiber concrete using M-5 mixing process;

[0031] Figure 6 The ultimate load (28d) of fiber concrete and plain concrete specimens with different mixing processes;

[0032] Figure 7 The compressive strength variation characteristics of fiber concrete and plain concrete specimens with different mixing processes (28 days);

[0033] Figure 8Scanning electron microscope images of fiber concrete specimens obtained from different mixing processes from M-1 to M-5; a, M-1 mixing process; b, M-2 mixing process; c, M-3 mixing process; d, M-4 mixing process; e, f, M-5 mixing process;

[0034] Figure 9 Schematic diagram of the dispersion characteristics of basalt fibers in the matrix with different stirring processes from M-1 to M-5. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0036] To facilitate understanding of the embodiments of the present application, the following will be further explained with reference to specific embodiments in conjunction with the accompanying drawings. The embodiments do not constitute a limitation of the embodiments of the present application. In the accompanying drawings, the sizes and relative sizes of the components may be exaggerated for clarity and / or descriptive purposes. When the exemplary embodiments can be implemented differently, the specific process sequence may be performed in an order different from that described. For example, two consecutively described processes may be performed substantially simultaneously or in an order opposite to that described. In addition, the same reference numerals represent the same components.

[0037] The terms used herein are for the purpose of describing specific embodiments and are not intended to be restrictive. As used herein, unless the context clearly indicates otherwise, the singular forms "one (kind, person)" and "said (the)" are also intended to include plural forms. In addition, when the terms "comprise" and / or "include" and their variations are used in this specification, the features, integral bodies, steps, operations, parts, assemblies and / or their groups stated are explained, but the presence or addition of one or more other features, integral bodies, steps, operations, parts, assemblies and / or their groups is not excluded. It should also be noted that, as used herein, the terms "substantially", "approximately" and other similar terms are used as approximate terms and not as degree terms, so that they are used to explain the inherent deviations of the measured values, calculated values ​​and / or the values ​​provided that will be recognized by those of ordinary skill in the art.

[0038] Example 1

[0039] A specific embodiment of the present invention discloses a method for preparing chopped basalt fiber concrete using a double dry mixing process. The process flow is shown in Figure 1, including steps 1 to 9:

[0040] Step 1: Prepare the materials according to the ratio and divide the chopped basalt fibers into the first and second parts by weight. Preferably, the first and second parts each account for 50% of the total amount of the chopped basalt fibers. In addition, in this step, it is necessary to check whether the chopped basalt fibers are dry. If they are damp, they should be placed in a dryer to dry for more than 10 minutes or air-dried in advance. The chopped basalt fibers used are 12 mm in length and 7-14 μm in diameter. The volume content of the chopped basalt fibers is 0.1%-0.15%, preferably 0.1%.

[0041] Step 2: Clean the blender and keep the inside of the mixing bowl dry.

[0042] Step 3: Add the first dry mix into the mixing barrel of the mixer, start the mixer and start stirring; wherein, the first dry mix includes cement and gel powder of a first particle size, and the gel powder of the first particle size includes quartz powder, fly ash, fine dust mineral powder, etc. Preferably, the particle size of the cement and the first particle size are of the same level, and the ratio of the particle size of the cement, the first particle size and the diameter of the chopped basalt fiber are all 1-3. Specifically, add cement and gel powder of the same particle size level into the mixing barrel of the mixer, start stirring for T0=10 seconds, and utilize the water absorption characteristics of cement and other materials in the first dry mix to ensure that the inner wall of the mixing barrel, the blades and the bearings are completely dry, thereby ensuring that the internal stirring space of the mixing barrel is completely dry.

[0043] Follow steps 4 to 7 for the first dry mix, as follows:

[0044] Step 4: Keep the mixer running and add the first 50% of the chopped basalt fiber to the first dry mix in the mixing bucket. Add the first 50% of the chopped basalt fiber to the mixing bucket in small, multiple additions. Alternatively, add the fiber in 5-8 batches within 30 seconds.

[0045] Step 5: 50% of the chopped basalt fiber is mixed with the first dry mix and pre-mixed for the first time. The mixing is continued for T1 time, preferably T1 = 1 min, to obtain a second mixed material, which can also be called a fiber primary mix.

[0046] Step 6: Keep the mixer running and add the remaining 50% of the chopped basalt fiber to the second batch in the mixing bucket. Add the second 50% of the chopped basalt fiber to the mixing bucket in small, multiple additions. Alternatively, add the fiber in 5-8 batches within 30 seconds.

[0047] Step 7: The remaining 50% of the chopped basalt fiber is mixed with the second dry mix and pre-mixed for the second time, stirring for T2 time, preferably T2 = 2min, to obtain the third dry mix, which can also be called fiber premix. When the volume content of the chopped basalt fiber is greater than 0.15%, the stirring time T2 should be appropriately extended to no more than 4min. In this step, the characteristics of the fiber premix can be observed. After the fibers are completely broken up, they can be evenly dispersed in the gel material, such as Figure 2 f, Figure 2 As shown in g.

[0048] After completing the first dry mix, perform the second dry mix according to step 8, as follows:

[0049] Step 8: Add gravel, sand and gel material of the second particle size into a mixing barrel, mix with the third dry mix and dry mix, stir for T3 time, preferably T3=10s, to obtain a fourth dry mix, which can be called basalt fiber concrete mixture (dry); optionally, the stirring time in this step is appropriately increased according to the amount of concrete material stirred at one time, but T3 should not exceed 30 seconds.

[0050] After completing the second dry mix, proceed with the wet mix according to step 9, as follows:

[0051] Step 9: Add water and admixtures into a mixing barrel, mix with the fourth dry mix and perform wet mixing, stirring for T4 time, preferably T4=2min, to obtain a basalt fiber concrete mixture, that is, to obtain chopped basalt fiber concrete with uniformly dispersed fibers.

[0052] Since the stirring of basalt fiber primarily utilizes the mechanical shear force generated by the paddle stirring process to break down the bonds between the basalt fiber bundles, the mixer in this embodiment is a forced mixer, either single-shaft or multi-shaft, with spiral blades and a stirring rod within the mixing barrel. The distance between the paddles and the inner wall of the mixing barrel should not be too large, otherwise the stirring efficiency will be low. It is recommended that the distance between the paddles and the mixing barrel wall be less than 5 mm, preferably 3-5 mm. A stirring rate of 25-35 rpm is recommended; this parameter setting can achieve the effect of thoroughly stirring the basalt fiber. At a basalt fiber volume parameter of 0.1%, stirring time for stirring the basalt fiber at a conventional stirring speed is approximately 2 minutes. Increasing the stirring rate using a variable frequency mixer can shorten the stirring time, but excessive stirring speeds (>100 rpm) can cause the fiber dispersion rate to lag behind the agglomeration rate, resulting in a surge in the friction coefficient between the locally accumulated fibers and the stirring blades, leading to torque overload and resulting in seizure failure. When the rotation speed is higher than 120 rpm, the electrostatic effect on the cement surface will be promoted. In an alkaline environment, cement easily forms positive charges, which generate electrostatic attraction with the negative charge layer formed on the surface of basalt fiber, resulting in an imbalance of Coulomb repulsion between basalt fibers and aggravating fiber agglomeration.

[0053] Basalt fiber is formed by melting and drawing natural basalt. After contacting water, some soluble substances (Ca 2+ 、Na + ) Water migrates to the surface, forming a colloid-like substance that increases interfiber adhesion. Basalt fiber is also hydrophilic. Upon contact with water, it readily absorbs water, forming a hydrogen bond network on the fiber surface and promoting fiber aggregation. Although basalt fiber products used for concrete modification undergo surface modification with silane coupling agents during production, reducing their hydrophilicity, the relatively thin diameter of basalt fiber filaments, only 7-15 μm, results in a large surface area when in contact with water, easily absorbing large amounts of water and causing fiber adhesion. The surface tension of water forms a liquid film on the fiber surface, fostering adhesion between fibers. These characteristics dictate that water should not be added to basalt fiber during mixing. Experimental results also indicate that dry mixing facilitates fiber dispersion. Therefore, the purpose of steps 1 and 2 of the technical solution provided by this invention is to ensure that the basalt fiber and the inner wall of the mixing drum remain dry. Step 3 further ensures that areas of the mixer, such as the blades and bearings, which are difficult to dry manually, remain dry. Steps 4 through 8 involve dry mixing of the fibers with the materials, and the addition of water is not recommended during this process.

[0054] Concrete, as a composite material, typically contains coarse aggregate (crushed stone, pebbles, cementite, etc.), fine aggregate (river sand, machine-made sand, quartz sand, etc.), water, gelling materials (cement, fly ash, mineral powder, silica fume, etc.), and admixtures. The dry mix materials for basalt fiber can be selected from these aggregates and gelling materials of varying particle sizes. For example, the materials prepared according to the proportions in step 1 include chopped basalt fiber, cement, crushed stone, sand, gelling material, water, and admixtures. The gelling material includes gelling materials of a first particle size and gelling materials of a second particle size. The gelling powder of the first particle size includes quartz powder, fly ash, and fine mineral dust, while the gelling powder of the second particle size includes silica fume, fine to ultrafine mineral dust, etc. The basalt fibers are dispersed primarily by breaking the bonds of the basalt fiber bundles with mechanical shear force generated by the paddle mixing process. Aggregates with larger particle sizes often support each other during mixing, forming stress voids. This causes some basalt fibers to remain in a stress-protected state during mixing, preventing them from being properly mixed and leading to localized clumping. Materials with particle sizes significantly smaller than basalt fibers also fail to fully disperse the fibers during mixing. This is because ultrafine particles tend to form a "lubricating layer" during mixing, causing shear stress to rapidly decay between fiber bundles. The energy of collisions between particles that are too small is too low to disrupt the van der Waals forces between fiber bundles. Furthermore, ultrafine particles adhere to the fiber surface through surface electrostatic interactions, forming a "shielding layer" that inhibits direct shear forces from acting on the fiber bundles. Ultrafine particles also tend to form densely packed structures, raising the energy threshold required for fiber debundling.

[0055] This embodiment determines the dry mixing material of basalt fiber through experiments. Specifically, the experiment is conducted with the volume parameter of basalt fiber being 0.1% and the dry mixing time being 2 minutes. Figure 2 The characteristics of dry-mixed basalt fibers with different particle sizes are shown in the experimental results. The results show that the chopped basalt fiber bundles without stirring and dispersion are as follows: Figure 2 As shown in a, gravel with larger particle size (>5mm), coarse sand (0.5~1mm), 26~40 mesh quartz sand (0.42~0.7mm), 40-70 mesh quartz sand (0.21~0.42mm) are all unable to mix basalt fiber ( Figure 2 b to Figure 2 e). Even with smaller silica fume (0.42~0.7mm), it is not possible to effectively mix basalt fiber ( Figure 2 h). Gel materials with particle sizes similar to or slightly larger than basalt fibers (7-15μm), such as cement (7-40μm) and quartz powder (<48μm), have the best dispersion effect on basalt fibers ( Figure 2 f, Figure 2 g). When different particle sizes are mixed, such as cement and river sand dry-mixed with basalt fiber or crushed stone, river sand and cement dry-mixed with basalt fiber, the obtained basalt fiber still cannot be fully dispersed ( Figure 2 i, Figure 2 j). Therefore, the present invention recommends that the dry-mixed material for mixing basalt fibers should be a gel material with a particle size similar to or slightly larger than that of the basalt fibers, with the ratio of gel material particle size to basalt fiber diameter being 1 to 3.

[0056] From Steps 4 to 7, add chopped basalt fibers to the mixing barrel in two batches to prevent the fibers from agglomerating all at once and reducing the amount of stirring force. The second premixing in Step 7 should last for ≥ 2 minutes to ensure the fibers are fully mixed.

[0057] Based on the fiber premix obtained in step 7, step 8 involves a second dry mixing process, where crushed stone, sand, and a gel material of the second particle size are added and stirred to produce a dry basalt fiber concrete mixture. This means that the mixing process of this embodiment premixes cement, sand, stone, gel material, and other materials before adding water. Mechanical shear forces are used to achieve the initial formation of a dense skeleton structure, avoiding problems such as cement clumping and weakening of the interface transition zone that can occur with premature water addition. Furthermore, post-addition of water and admixtures facilitates precise control of the hydration process and allows for adjustment of the water-cement ratio based on actual conditions.

[0058] In step 8, the mixing time T3 is determined based on the amount of concrete material mixed in the first mixing. If the mixing volume is 60L, the mixing time T3 should not exceed 10 seconds, for example, T3 should be 6-10 seconds. Of course, it is understood that if the mixing volume is greater than 60L, the mixing time T3 can be appropriately extended, but the mixing time T3 should not exceed 30 seconds. Test results show that excessively long second dry mixing times can cause dispersed fibers to reagglomerate. This is because sharp gravel and sand easily form charge concentrations during mixing (skin effect), leading to an imbalance in the Coulomb repulsion between basalt fibers and fiber reagglomeration. Furthermore, the sharp edges of gravel and sand easily cut the fibers, significantly increasing the fiber breakage rate and negatively impacting the fiber bridging effect.

[0059] In this example, dry mixing using a gel material with a particle size similar to or slightly larger than the basalt fiber (gel material particle size / basalt fiber diameter = 1-3) fully disperses the basalt fiber, achieving a dispersion rate exceeding 95%. The dispersion rate is calculated by washing, separating, sampling, drying, and weighing the concrete mixture. The dispersion rate is calculated as 1 - undispersed fiber mass / total fiber mass. The environment and material dryness must be strictly controlled during the dispersion process.

[0060] Because the electrostatic effect of different materials during mixing is a key factor in preventing the dispersed basalt fibers from agglomerating again, in this example, during the first premixing process, the mixer speed was less than 120 rpm, and the second dry mixing time T3 = 10 seconds, the resulting fiber concrete showed no obvious agglomeration.

[0061] The shearing effect of coarse and fine aggregate on fibers is the primary factor leading to fiber breakage. To ensure a low breakage rate for basalt fibers, the duration of the second dry mix should be strictly controlled. In step 8 of this embodiment, the second dry mix time T3 is 10 seconds, which ensures a fiber breakage rate of less than 10%. (This breakage rate is obtained by cleaning and sampling the concrete mixture, drying it, and then counting it under a microscope: breakage rate = number of fibers less than 10 mm / total number of fibers.) Furthermore, replacing gravel with pebbles can further reduce the fiber breakage rate.

[0062] In step 9, the addition of water and a water-reducing agent followed by prolonged stirring has limited impact on the fiber breakage rate. This is because the addition of water forms a lubricating layer, effectively reducing the friction coefficient between the fiber and the aggregate and blades, thereby minimizing damage to the fiber caused by mechanical shear forces. Furthermore, the "Bingham fluid" formed by the water and gel material evenly coats the fibers, providing protection.

[0063] Compared with the existing technology, the method for preparing chopped basalt fiber concrete using a two-step dry mixing process provided in this embodiment optimizes the mixing process to ensure that the basalt fibers are better dispersed in the concrete matrix, have a lower breakage rate, and are less likely to agglomerate. The resulting basalt fiber concrete has significantly improved performance compared to plain concrete and has good performance stability.

[0064] Example 2 - Test Case

[0065] 1. Test Materials

[0066] The cement used in the experiment is P42.5 ordinary Portland cement. The river sand is medium sand with a density of 1650 kg / m 3 , fineness modulus is 2.5~2.9. Coarse aggregate nominal particle size is 5~20 mm, density is 2750 kg / m 3 The water reducer was a lignin sulfonate polycondensate superplasticizer produced by Shandong Wanshan Chemical Co., Ltd., with a water reduction rate of 8%. The experimental fibers were basalt fibers produced by Haining Anjie Composite Materials Co., Ltd., with a fiber length of 12 mm, a tensile strength of 3,000 to 4,800 MPa, and good dispersibility. Their physical and mechanical properties and chemical composition are shown in Tables 1 and 2.

[0067] Table 1 Physical and mechanical properties of basalt fiber

[0068]

[0069] Table 2 Chemical composition of basalt fiber

[0070]

[0071] 2. Sample design and testing

[0072] The experimental design employed a concrete strength grade of C50 and a water-cement ratio of 0.35. The mix proportions are shown in Table 3. To investigate the effects of different mixing processes on the mechanical properties of concrete, 15 cm × 15 cm × 15 cm fiber-reinforced concrete specimens were produced using various mixing methods. The specific mixing procedures are shown in Table 4. The fiber volume content was 0.1% throughout the experiment, and plain concrete specimens were also produced as a control group. A single-shaft forced mixer was used, which exhibits excellent mixing properties for basalt fiber. To minimize experimental error, five specimens were produced per group, and the curing period was 28 days. The mixing of plain concrete was conducted in accordance with GB / T 50080-2016, "Standard for Test Methods for Properties of Ordinary Concrete Mixtures."

[0073] Table 3 Concrete mix ratio (kg / m 3 )

[0074]

[0075] Table 4 Comparison of different mixing processes of basalt fiber concrete

[0076]

[0077] 3. Test results

[0078] 1. Dispersion characteristics of basalt fiber under different mixing processes

[0079] Figure 3 The figure shows the stirring effect of the M-1 stirring process of the present application; Figure 4 The characteristics of concrete mixes obtained by mixing processes M-2 to M-5 are shown.

[0080] The M-1 mixing process of this application adopts the cement premixing method, which adds dry basalt fiber to cement twice, and uses powdered cement to mix and disperse the fiber to obtain fiber premixed cement in a dry state ( Figure 3 a). After pre-mixing with cement, the basalt fiber has achieved a good dispersion effect, and most of the fibers are longer than 10mm ( Figure 3 b). Add sand, stone and other aggregates to the premixed fiber cement and dry mix to further enhance the fiber dispersion. Finally, add water reducer and water to obtain basalt fiber concrete mixture, which has the following characteristics: Figure 3 c, Figure 3 d. Under this process, the basalt fibers in the concrete mix are uniformly dispersed in a fibrous form within the concrete matrix. After cleaning and drying the concrete mix, statistically analyzed fiber breakage rates of approximately 5%-10%.

[0081] The M-2 mixing process uses a method where all materials are mixed at once. The process is simple and the characteristics of the concrete mixture obtained are as follows: Figure 4 As shown in a. The M-2 mixing process has a significantly weaker effect on the dispersion of basalt fibers than the M-1 process, although some fibers are dispersed in the concrete matrix ( Figure 4 b), but there are a large number of bundle-like basalt fiber aggregates unevenly distributed in the concrete matrix. The morphology of these aggregates is similar to that of unmixed chopped basalt fiber products, indicating that these fiber bundles were not subjected to significant external forces during the mixing process.

[0082] The M-3 process is similar to the M-2 process, except that the other materials are pre-mixed for 2 minutes before the basalt fiber is added, and the mixing time is shortened to 1 minute after the basalt fiber is added. The characteristics of the concrete mixture obtained are as follows Figure 4 c, Figure 4 As shown in Figure d, the characteristics of the concrete mix obtained under the M-3 process are similar to those under the M-2 process, but it contains more bundled fiber aggregates, and only a small amount of basalt fibers are broken up and extremely unevenly distributed.

[0083] The M-4 process first adopts the form of dry mixing, mixing 50% basalt fiber with aggregates of various particle sizes and cement under dry conditions, then adding 50% water and water reducer to wet mix the remaining fibers, and finally adding the remaining water and water reducer. The degree of dispersion of basalt fiber in the concrete mixture obtained under this process is significantly better than that of the M-2 process and M-3 process. A large number of basalt fibers are dispersed in the concrete matrix in a fibrous form, but the fiber length is significantly shortened (<10mm), indicating that some fibers are broken during the mixing process. At the same time, a small amount of incompletely broken up bundled fiber aggregates can still be seen in the matrix ( Figure 4 e). Compared with the unmixed chopped basalt fiber product, the diameter of the fiber bundles in the concrete matrix is ​​significantly smaller, indicating that these aggregates are the residues after partial dispersion ( Figure 4 f).

[0084] The M-5 process is similar to the M-4 process, except that 10% water is added at the beginning of mixing, and the remaining water is added after the fibers are fully mixed. The characteristics of the concrete mixture obtained are similar to those of the M-4 process, with most of the basalt fibers being broken up and evenly dispersed in the concrete matrix ( Figure 4 g), the presence of a small amount of water ensures a low fiber breakage rate. However, a large number of bundled fiber aggregates can still be seen. The diameter of these bundled aggregates is larger than the residual fiber bundles in the M-4 process, and they are partially scattered ( Figure 4 h).

[0085] 2. Destruction process

[0086] Plain concrete samples undergo axial compression and lateral expansion deformation under axial pressure. When the specimen reaches the limit deformation, longitudinal cracks appear on the concrete surface. Figure 5 The failure characteristics of the specimens under different mixing processes are shown. After the failure, the plain concrete specimens showed multiple vertical wide cracks, and the edges and corners of the specimens were crushed ( Figure 5 a). Fiber concrete specimens mixed using different processes showed similar crack characteristics after destruction. Compared with plain concrete, the fiber concrete specimens retained better appearance after destruction, with vertical cracks becoming thinner and shorter, and transverse cracks appearing ( Figure 5 b). During compression, the basalt fibers constrained the lateral expansion of the specimen, delaying its failure and changing the crack propagation path, thereby better maintaining its appearance. If the load were further increased, the fiber-reinforced concrete would begin to flake.

[0087] The surface of the M-1 process specimen is smooth and neat, with no bundled fiber distribution. All basalt fibers are dispersed in the matrix in a fibrous form, which is difficult to observe with the naked eye. Under the M-2 and M-3 processes, many bundled fiber aggregates can be seen on the surface and fractured sections of the specimens, and some fiber bundles show pull-out characteristics ( Figure 5 c, Figure 5 d). The fracture surface characteristics of the specimens under M-4 and M-5 processes are similar. Most basalt fibers are evenly distributed in the matrix, and a small amount of bundle-like aggregates can be seen ( Figure 5 e, Figure 5 f). The fiber aggregates in the M-5 process specimens are partially scattered, and the concrete often fails along these weak surfaces ( Figure 5 f).

[0088] 3. Compressive strength

[0089] Compressive tests were conducted on 28-day-old cubic specimens of basalt fiber concrete and plain concrete using different mixing processes. The test results showed that the ultimate load of the plain concrete specimens reached 1134.00-1185.70 kN, and the compressive strength was 50.40-52.70 MPa, meeting the C50 concrete strength standard. Compared with plain concrete, the ultimate load of the basalt fiber concrete specimens was significantly improved ( Figure 6 Among them, the ultimate load of basalt fiber concrete specimens under M-1 mixing process is 1337.60~1374.1 kN, with an average of 1357.28 kN, and the average compressive strength is 60.32 MPa, which is 17.6% higher than that of plain concrete specimens; the ultimate load of M-2 process specimens is 1294.63~1379.3 kN, with an average of 1336.76 kN, and the average compressive strength is 59.41 MPa, which is 15.83% higher than that of plain concrete specimens; the ultimate load of M-3 process specimens is 1073.42~1401.4 kN, with an average of 1263.14 kN, and the average compressive strength is 56.14 MPa, which is 9.45% higher than that of plain concrete specimens; the ultimate load of M-4 process specimens is 1253.98~1389.18 kN, with an average of 1354.24 kN, and the average compressive strength was 60.19 MPa, which was 17.34% higher than that of plain concrete specimens. The ultimate load of M-5 process specimens was 1304.68~1376.05 kN, with an average of 1336.56 kN, and the average compressive strength was 59.40 MPa, which was 15.81% higher than that of plain concrete specimens.

[0090] Comparison of compressive strength of fiber concrete specimens with different mixing processes ( Figure 7 ), the M-1 and M-4 process specimens showed the largest average strength increase, but the M-4 process specimens exhibited large fluctuations in ultimate load (135.2 kN), indicating poor performance stability. The M-1 and M-5 process specimens exhibited relatively concentrated compressive strength, demonstrating good performance stability. In contrast, the M-3 process specimens showed significant variability in test results, with ultimate load values ​​fluctuating by as much as 327.97 kN. The M-3-4 specimens achieved a compressive strength of 47.71 MPa, lower than the average for plain concrete specimens, demonstrating a negative strength growth effect.

[0091] 4. Results Analysis

[0092] Figure 8 Shown are the scanning electron microscope images of fiber concrete specimens obtained from different mixing processes from M-1 to M-5. Figure 9 Schematic diagram showing the dispersion characteristics of basalt fibers in the matrix with different stirring processes from M-1 to M-5.

[0093] The compressive strength of basalt fiber concrete test blocks obtained by different mixing processes has different degrees of improvement. The strength of the concrete test blocks under the M-1 process of this application has been the most significantly improved. This is because the M-1 process of this application adopts a dry mixing method, which uses micron-sized cement particles to fully break up the bundled fiber aggregates, so that the basalt fibers are evenly distributed in the concrete matrix ( Figure 3 , Figure 8 a). These fibers overlap with the aggregate within the concrete, effectively reducing the porosity and microcracks within the concrete. Furthermore, the evenly distributed fibers form a dense spatial network within the concrete, sharing the load with the concrete, improving its compressive properties and limiting its lateral expansion.

[0094] The concrete test blocks obtained by the M-1 mixing process of this application have high fiber dispersion, low fiber breakage rate and uniform fiber distribution (see Figure 8 a).

[0095] Both the M-2 and M-3 processes directly mix basalt fibers with other materials (including water) (wet mixing). The concrete mixtures obtained using both mixing processes exhibit a large number of undispersed bundled fiber aggregates. This is because the impact of aggregates of varying particle sizes during mixing in the M-2 and M-3 processes is the primary force that breaks up the basalt fibers. However, larger aggregates often support each other during mixing, forming stress voids. This leaves some basalt fibers in a stress-protected state during mixing, preventing proper mixing. Furthermore, the addition of water increases fiber adhesion and localized aggregation, preventing adequate mixing. Consequently, the basalt fibers obtained using the M-2 and M-3 processes exhibit two distinct states within the concrete matrix: dispersed fibers and bundled aggregates.

[0096] Compared with dispersed basalt fibers, bundled aggregates reduce the specific surface area of ​​the fiber material, affecting the interface performance between the fiber and the concrete matrix, and failing to effectively reduce the pores inside the concrete. At the same time, the fibers inside the bundled aggregates are not effectively wrapped by the cement mortar, which increases the internal defects of the concrete ( Figure 8 b). During the concrete failure process, although bundled fibers can also play a bridging role, their failure process is usually pull-out failure or spalling failure, and their mechanical properties are not fully utilized ( Figure 5 c, Figure 8c). Therefore, compared with the M-1 process, the strength improvement of the test blocks of the M-2 and M-3 processes is smaller. Compared with the M-2 process, the M-3 process premixed other materials for 2 minutes before adding the basalt fiber, and the basalt fiber mixing time was only 1 minute. The insufficient fiber mixing time resulted in a large proportion of bundled fiber aggregates in the concrete mixture, and the bundled fibers bonded together by water were unevenly distributed in the concrete matrix ( Figure 8 b and Figure 8 c), and thus the performance of the fiber concrete specimens obtained varies greatly.

[0097] Some specimens in the M-3 and M-4 processes showed a negative strength growth effect, which may be because the bundled fiber aggregates were locally concentrated and could not fully bond with the concrete matrix, thus forming pores or weak surfaces in the concrete matrix.

[0098] The M-4 process uses dry mixing to mix 50% of the basalt fiber, and the remaining 50% is wet mixing. The M-5 process first adds a small amount of water (10%) to pre-mix the fiber and other materials, and then adds the remaining water after the fiber is fully mixed. Both processes can break up some of the bundled fiber aggregates, but due to the supporting and protective effect of the large-size aggregate, a small amount of incompletely broken-up bundled fibers still remain ( Figure 4 h). The difference is that the residual bundled fibers of the M-4 process are either completely retained or partially broken up, while the M-5 process is characterized by one end of the fiber bundle being broken up or the whole bundle being broken up but still relatively clustered, forming a "fan-like" or "comb-like" distribution feature ( Figure 9 This is because the M-4 process uses a partially dry mixing method, and the fiber bundles are gradually broken up from the surface to the center, so the diameter of the remaining fiber bundles becomes thinner ( Figure 8 d) The dry stirring environment is conducive to dispersing the fibers that have been broken apart from the fiber bundles.

[0099] The M-5 process wet mixes all the fibers with a small amount of water. Due to the presence of water, the fibers stick together, which is not conducive to dispersion in the matrix, forming relatively aggregated residual fiber bundles. The results of the specimen compressive test show that the specimens of the M-4 and M-5 processes have a more obvious improvement than the plain concrete specimens. This is because both processes can break up some fiber bundles and disperse them in the matrix, and the strength enhancement mechanism is also the bridging effect of the fibers. The reason why the enhancement of the M-5 process is slightly lower than that of the M-4 may be that the residual "fan-shaped" or "comb-shaped" fiber bundles are more likely to form weak surfaces in the concrete matrix, and the specimens often crack along these weak surfaces during the compressive failure process ( Figure 3 f, Figure 8 e, Figure 8 f).

[0100] Table 5 shows the mixture characteristics, fiber characteristics, and concrete compressive strength improvement for different mixing processes. It can be seen that the concrete specimens obtained using mixing process M-1 in this application have a high degree of fiber fragmentation, a low fiber breakage rate, and uniform fiber distribution. They also exhibit the largest average strength improvement and relatively concentrated ultimate compressive strength values. The strength standard deviation and coefficient of variation are both minimized, indicating good specimen performance stability.

[0101] Table 5 Comparison of characteristic parameters of concrete produced by different mixing processes

[0102]

[0103] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of this application. It should be understood that the above description is only the specific implementation methods of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application should be included in the scope of protection of this application.

Claims

1. A method for preparing chopped basalt fiber concrete using a double dry mixing process, characterized in that: The steps include: Prepare the materials according to the ratio, and divide the chopped basalt fibers into the first part and the second part according to weight; Adding a first dry mix into a mixing barrel of a mixer, and starting the mixer to begin mixing; wherein the first dry mix includes cement and gel powder of a first particle size; The first dry mix is ​​performed according to the following steps: under stirring, the first portion of chopped basalt fibers is added to a mixing barrel, mixed with the first dry mix, and premixed for the first time, and stirred for T1 time to obtain a second dry mix; then, the second portion of chopped basalt fibers is immediately added to the mixing barrel, mixed with the second dry mix, and premixed for the second time, and stirred for T2 time to obtain a third dry mix; Perform a second dry mix according to the following steps: add crushed stone, sand, and the gel material of the second particle size into a mixing bucket, mix with the third dry mix, and dry mix for T3 time to obtain a fourth dry mix; After the second dry mix is ​​completed, wet mix is ​​performed according to the following steps: water and admixtures are added to a mixing bucket, mixed with the fourth dry mix and wet mixed, and stirred for T4 time to obtain chopped basalt fiber concrete.

2. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 1, characterized in that: The volume content of the chopped basalt fiber is 0.1%; The chopped basalt fibers have a length of 12 mm and a diameter of 7-14 μm.

3. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 2, characterized in that: The stirring time T1 is 1 min; the stirring time T2 is 2 min; the stirring time T3 is 10 s; and the stirring time T4 is 2 min.

4. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 3, characterized in that: The first part is 40%-60% of the total amount of the chopped basalt fibers, and the rest is the second part.

5. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 4, characterized in that: The first part and the second part are both 50% of the total amount of the chopped basalt fibers.

6. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to any one of claims 2 to 5, characterized in that: The ratios of the cement particle size, the first particle size and the diameter of the chopped basalt fibers are all 1-3.

7. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 1, characterized in that: The step of preparing materials according to the ratio also includes the following steps: Check whether the chopped basalt fiber is dry. If it is damp, dry it.

8. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 1, characterized in that: Before adding the first portion of chopped basalt fibers into the mixing barrel and after adding the first dry mix into the mixing barrel of the mixer, the mixer is started to stir for T0 time, and the water absorption characteristics of the first dry mix are used to completely dry the internal mixing space of the mixing barrel.

9. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 1, characterized in that: The stirrer is a forced stirrer with a stirring rate of 25-35 rpm and a distance between the blade and the wall of the stirring barrel of 3-5 mm.

10. The method for preparing chopped basalt fiber concrete using a double dry mixing process according to claim 1, characterized in that: The gel powder of the first particle size includes quartz powder, fly ash, and fine dust mineral powder; the gel powder of the second particle size includes silica ash, fine dust-ultrafine dust mineral powder.

Images