A method for producing steel-polypropylene hybrid fiber light weight concrete

Abstract

The application provides a method for preparing steel-polypropylene hybrid fiber light-weight concrete, which comprises the following steps: (1) controlling water in the aggregate to obtain pretreated aggregate, wherein the aggregate is selected from a mixture of volcanic slag and ceramsite or the volcanic slag, the water content of the pretreated volcanic slag is less than or equal to 3%, and the water content of the pretreated ceramsite is 8%-10%; (2) the concrete formula further comprises cementitious material, the cementitious material is composed of cement, fly ash and silica fume, the pretreated aggregate, the fly ash, the silica fume and 90wt% of the cement are mixed and stirred to obtain a first mixture; (3) polypropylene fibers are mixed with the remaining cement in the cementitious material and then stirred to obtain pre-dispersed polypropylene fibers; (4) the first mixture, the pre-dispersed polypropylene fibers and dispersed steel fibers are mixed and stirred to obtain a second mixture; and (5) the second mixture, water and a water reducing agent are uniformly mixed and stirred until the mixture presents a uniform viscous state. The application realizes the synchronous improvement of the mechanical properties and the production stability of the light-weight concrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically providing a method for preparing steel-polypropylene hybrid fiber lightweight concrete. Background Technology

[0002] Steel-polypropylene hybrid fiber slag lightweight concrete is increasingly in demand in modern construction projects due to its advantages of being lightweight, high-strength, high-toughness, and environmentally friendly. However, existing preparation processes have several technical drawbacks: First, slag is porous and has a high water absorption rate, while ceramsite is lightweight and porous with significant differences in water absorption. If the aggregate pretreatment is inadequate, fluctuations in moisture content can lead to an imbalance in the concrete mix proportions, resulting in problems such as bleeding and segregation. Second, polypropylene fibers are lightweight and prone to agglomeration, while steel fibers are dense and prone to settling. A single mixing method is insufficient to achieve uniform dispersion of the two types of fibers, and the agglomerated areas can create stress concentrations, reducing the mechanical properties of the concrete.

[0003] While existing methods can clearly define the optimal fiber content combination and mechanical property optimization path, they do not focus on the systematic optimization of the preparation process. This makes it difficult to stably reproduce the performance indicators optimized in the laboratory in industrial production, resulting in large product performance dispersion and low pass rate, which limits the large-scale application of this type of concrete.

[0004] Therefore, the existing lightweight concrete preparation process needs to be improved. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in the prior art. Therefore, one object of this invention is to provide a method for preparing steel-polypropylene hybrid fiber lightweight concrete, thereby improving the compressive and tensile strength of the concrete, enhancing the uniformity of fiber dispersion, and increasing the product qualification rate.

[0006] In a first aspect, the present invention provides a method for preparing steel-polypropylene hybrid fiber lightweight concrete, comprising:

[0007] (1) The aggregate is subjected to water control treatment to obtain pretreated aggregate, wherein the aggregate is selected from a mixture of volcanic slag and ceramsite or volcanic slag, and the obtained pretreated aggregate is selected from a mixture of pretreated volcanic slag and pretreated ceramsite or pretreated volcanic slag, wherein the moisture content of the pretreated volcanic slag is ≤3% and the moisture content of the pretreated ceramsite is 8%-10%;

[0008] (2) The concrete formula also includes cementitious materials, which are composed of cement, fly ash and silica fume. The pretreated aggregate, fly ash, silica fume and 90 wt% of the cement are mixed and stirred to obtain the first mixture.

[0009] (3) Mix the polypropylene fiber with the remaining cement in the cementitious material and stir to obtain pre-dispersed polypropylene fiber;

[0010] (4) Mix the first mixture, the pre-dispersed polypropylene fiber and the dispersed steel fiber to obtain the second mixture;

[0011] (5) Mix the second mixture, water and diluted water-reducing agent evenly until the mixture is uniform and viscous, with no obvious aggregate segregation or fiber clumping.

[0012] According to the above-mentioned method for preparing lightweight concrete provided by the present invention, firstly, considering the differences in physical properties between volcanic slag and expanded clay aggregate, a differentiated process of "drying and moisture control + pre-wetting and draining" is adopted. The volcanic slag is dried to a moisture content ≤3% to avoid insufficient mixing water due to water absorption. The expanded clay aggregate is pre-wetted to a moisture content of 8%-10%, which satisfies its own hydration requirements while avoiding excessive water dilution of the cementitious materials. This solves the problem of mix proportion imbalance caused by inconsistent moisture content of composite aggregates, ensuring stable concrete workability. Secondly, pre-mixing polypropylene fibers with a portion of dry cement powder effectively utilizes the physical barrier effect of cement particles to prevent fiber agglomeration. This effectively solves the problem of uneven dispersion caused by the density difference between the two types of fibers during subsequent mixing with dispersed steel fibers, improving the performance of the concrete.

[0013] The dry mixing in step (2) ensures that the cementitious material evenly coats the aggregate, preventing poor adhesion between the fibers and the aggregate surface in the subsequent steps. The high-speed stirring in step (4) disperses the fibers and breaks up the fiber agglomerates through shearing. The wet mixing in step (5) ensures that the mixture is uniform and viscous, without segregation or bleeding. Through the synergistic effect of each step, the problem of uneven dispersion caused by the difference in the density of the two types of fibers is effectively solved, and the fiber dispersion uniformity is improved to over 95%.

[0014] To address the problems of uneven fiber dispersion, aggregate moisture content fluctuations, insufficient interfacial bonding, and poor performance stability in existing preparation processes, this invention achieves simultaneous improvement in the mechanical properties and production stability of lightweight concrete through differentiated aggregate pretreatment and staged fiber dispersion. Specifically, the C60 grade lightweight concrete prepared by this invention has a compressive strength ≥68MPa, a splitting tensile strength ≥6.2MPa, a fiber dispersion uniformity ≥95%, and a product qualification rate exceeding 98%. Furthermore, the process of this invention is highly operable, adaptable to industrial production, and suitable for engineering scenarios with high concrete performance requirements, such as high-rise buildings and large-span structures.

[0015] In some embodiments of the present invention, in step (1), the volcanic slag is dried and water-controlled, the drying temperature is 100-110℃ and the time is 4-6h, and the water-controlled treatment of the ceramsite is pre-wetting for 20-30h and then draining.

[0016] In some embodiments of the present invention, the ceramsite is selected as 5-10mm graded particles.

[0017] In some embodiments of the present invention, when the aggregate is selected from a mixture of volcanic slag and ceramsite, the mass ratio of the volcanic slag to the ceramsite is (50-70):(30-50).

[0018] In some embodiments of the present invention, the bulk density of the volcanic slag is 800-900 kg / m³, and the water absorption rate is 8%-10%.

[0019] In some embodiments of the present invention, the bulk density of the ceramsite is 500-600 kg / m³, and the water absorption rate is 15%-20%.

[0020] In some embodiments of the present invention, in step (2), the mass ratio of the cement, the fly ash, and the silica fume in the cementitious material is 7:2:1.

[0021] In some embodiments of the present invention, a twin-shaft mixer is used, wherein the gap between the mixing blades and the cylinder wall is ≤5mm to avoid fiber entanglement and accumulation.

[0022] In some embodiments of the present invention, the stirring speed in step (2) is 300-400 r / min, and the stirring time is 2-3 min.

[0023] In some embodiments of the present invention, in step (3), the stirring speed is 800-1000 r / min and the stirring time is 3-5 min.

[0024] In some embodiments of the present invention, the polypropylene fiber has a length of 12-18 mm, a diameter of 0.02-0.04 mm, and a tensile strength ≥350 MPa.

[0025] In some embodiments of the present invention, in step (4), the stirring speed is 500-600 r / min and the stirring time is 3-4 min.

[0026] In some embodiments of the present invention, the steel fibers are dispersed using a vibrating screen.

[0027] In some embodiments of the present invention, the steel fiber has a length of 25-35 mm, a diameter of 0.5-0.8 mm, and a tensile strength ≥1100 MPa.

[0028] In some embodiments of the present invention, in step (5), the water-reducing agent is selected from polycarboxylate water-reducing agents.

[0029] In some embodiments of the present invention, the stirring speed in step (5) is 300-400 r / min, and the stirring time is 4-5 min.

[0030] In some embodiments of the present invention, the concrete is prepared according to the requirements of C60 grade lightweight concrete substrate, the amount of cementitious material is 450-500 kg / m³, the water-cement ratio is 0.28-0.32, the amount of aggregate is 1200-1300 kg / m³, and the amount of water-reducing agent is 0.6%-1.0% of the mass of cementitious material.

[0031] In some embodiments of the present invention, the polypropylene fiber accounts for 0.12-0.15% of the mass fraction of the concrete, and the steel fiber accounts for 1.2% of the mass fraction of the concrete; preferably, when the aggregate is selected from the volcanic slag, the polypropylene fiber accounts for 0.12% of the mass fraction of the concrete, and the steel fiber accounts for 1.2% of the mass fraction of the concrete; preferably, when the aggregate is selected from a mixture of the volcanic slag and the expanded clay, the polypropylene fiber accounts for 0.15% of the mass fraction of the concrete, and the steel fiber accounts for 1.2% of the mass fraction of the concrete.

[0032] In some embodiments of the present invention, the method further includes step (6): pouring the viscous material obtained in step (5) into the mold in 2-3 layers, with each layer not exceeding 100mm in thickness, and vibrating each layer for 20-30s using a high-frequency vibration table until the surface of the mixture is covered with slurry and no bubbles overflow, and then smoothing the top layer and covering it with plastic wrap. Preferably, the vibration frequency is 50-60Hz and the amplitude is 0.5-1.0mm.

[0033] By adding materials in 2-3 layers and vibrating them, with each layer thickness controlled within 100mm, the excessive thickness of a single addition of materials can be avoided, which would result in insufficient compaction. A 50-60Hz high-frequency vibration table is used to ensure that the aggregate and cementitious materials are tightly bonded, with no weak interfaces between layers, while also reducing residual air bubbles and improving the density of the concrete.

[0034] In some embodiments of the present invention, during the layered vibration, the time interval between vibrations of two adjacent layers does not exceed 30 minutes to ensure dense bonding between layers.

[0035] In some embodiments of the present invention, the mold includes a 150mm×150mm×150mm cube mold, a 150mm×150mm×300mm prism mold, and a 100mm×100mm×400mm beam mold.

[0036] In some embodiments of the present invention, the method further includes step (7): after step (6) vibration molding, segmented curing is carried out. The segmented curing includes early curing and standard curing in sequence. The early curing is: after molding, it is left to stand for 24 hours in an environment of 20±2℃ and relative humidity ≥90% to avoid rapid evaporation of moisture. The standard curing is: after demolding, it is transferred to a standard curing room, the temperature is controlled at 20±2℃ and the relative humidity is ≥95%, and it is cured for 28 days, preferably extended to 56 days, during which water is sprayed once every 7 days to replenish humidity.

[0037] Early moisturizing combined with standard curing: For the first 24 hours after molding, humidity is controlled at ≥90% to prevent rapid surface moisture evaporation and cracking. After demolding, the concrete is transferred to a standard curing room for 28 days to ensure full hydration reaction and improve concrete strength and durability. Long-term curing can be extended to 56 days to further optimize interfacial bonding performance.

[0038] In some embodiments of the present invention, the method further includes quality control, which is as follows: during the stirring process in step (5), the slump and spread of the mixture are monitored in real time, the slump is controlled at 120-150 mm, the spread is controlled at 350-400 mm, and after molding, 3 groups of specimens are randomly selected for 28-day mechanical property testing to ensure that the cubic compressive strength is ≥68 MPa and the splitting tensile strength is ≥6.2 MPa.

[0039] By monitoring the workability (slump, spread) of the mixture in real time, construction feasibility is ensured; finished products are sampled for testing of mechanical properties and fiber dispersion uniformity, with fiber distribution variation coefficient ≤8%, and product qualification rate increased to over 98%.

[0040] In some embodiments of the present invention, quality control also includes fiber dispersion uniformity detection, which uses image analysis to randomly select three cross sections of the mixture, with the fiber distribution variation coefficient ≤8%.

[0041] In a second aspect, the present invention provides a lightweight concrete prepared by the above-described method.

[0042] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0043] (1) Significantly improved fiber dispersion uniformity: Through fiber pre-dispersion and staged mixing process, the technical pain points of polypropylene fiber agglomeration and steel fiber sinking are solved. The fiber dispersion uniformity is ≥95%, avoiding the performance decline caused by stress concentration. The dispersion coefficient of concrete mechanical properties is ≤3%.

[0044] (2) Strong aggregate adaptability: Differentiated pretreatment processes are designed for volcanic slag single aggregate and volcanic slag-ceramsite composite aggregate to effectively control moisture content fluctuations, stabilize concrete workability, and maintain slump at 120-150mm to meet the needs of industrialized casting.

[0045] (3) Simultaneous optimization of mechanical properties and stability: Through the synergistic optimization of aggregate differential pretreatment, fiber staged dispersion, precise mixing and molding, and segmented curing, combined with the optimal fiber admixture combination, the mechanical properties and production stability of lightweight concrete are simultaneously improved. The prepared C60 grade lightweight concrete has a 28-day cubic compressive strength ≥68MPa and a splitting tensile strength ≥6.2MPa, which is 5%-8% higher than the strength of traditional preparation methods, and the product qualification rate is increased from about 85% to over 98%.

[0046] (4) Strong process compatibility: The optimized mixing, vibration and curing parameters can be directly adapted to existing concrete batching plant equipment without additional modification. The mixing time is shortened by 10%-15%, and the production efficiency is significantly improved.

[0047] (5) Wide range of applications: It is suitable for high-rise building frame columns, large-span floor slabs, prefabricated components and other scenarios that require lightweight, high-strength and high-stability concrete, while taking into account environmental protection and economy, and is easy to promote on a large scale. Attached Figure Description

[0048] Figure 1 This is a comparison diagram of concrete made from a mixture of polypropylene fibers and steel fibers in Example 1 and Comparative Example 1 of the present invention.

[0049] Figure 2 This is an image showing the interfacial bonding morphology of the volcanic slag-ceramsite aggregate hybrid fiber concrete of Example 2 of the present invention. Detailed Implementation

[0050] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0051] Example 1

[0052] Preparation of lightweight concrete using volcanic slag as a single aggregate

[0053] (1) Raw material pretreatment

[0054] Aggregate: Volcanic slag with a 5-16mm gradation, a bulk density of 850kg / m³, and a water absorption rate of 8.2% was selected. It was dried at 105℃ for 5 hours and the moisture content after cooling was 2.5% to obtain pretreated aggregate.

[0055] Fibers: Polypropylene fibers (15 mm in length, 0.03 mm in diameter, and 380 MPa in tensile strength) are mixed with 10 wt% of dry cement powder in the gel material and dry-mixed at 800 r / min for 3 min to obtain pre-dispersed polypropylene fibers; steel fibers (30 mm in length, 0.6 mm in diameter, and 1200 MPa in tensile strength) are dispersed by vibrating sieve.

[0056] (2) Raw material ratio

[0057] The cementitious material dosage is 480 kg / m³ (cement: fly ash: silica fume = 7:2:1), the water-cement ratio is 0.30, the volcanic slag dosage is 1250 kg / m³, the polycarboxylate superplasticizer dosage is 0.8% (as a percentage of the cementitious material mass); the fiber content is 0.12% PPF + 1.2% SF (polypropylene fiber accounts for 0.12% of the total mass fraction of concrete raw materials, and steel fiber accounts for 1.2% of the total mass fraction of concrete raw materials).

[0058] (3) Staged mixing

[0059] First stage: Pre-treated aggregates and cementitious materials are dry-mixed at 350 r / min for 2 min;

[0060] Second stage: Add pre-dispersed polypropylene fibers and dispersed steel fibers to the mixture obtained in the first stage, and stir at 550 r / min for 3.5 min;

[0061] Third stage: Add mixing water and water-reducing agent to the mixture obtained in the second stage, and stir at 350 r / min for 4.5 min.

[0062] (4) Layered vibration molding

[0063] The concrete material obtained in step (3) is poured into a 150mm×150mm×150mm cube mold in two layers, each layer being 80mm thick. The concrete is vibrated for 25s per layer using a 55Hz vibrating table. The top layer is smoothed and then covered with plastic wrap.

[0064] (5) Segmented maintenance

[0065] Early maintenance: Let the environment stand still for 24 hours at 20℃ and 92% humidity;

[0066] Standard curing: After demolding, transfer to a curing room at 20℃ and 95% humidity for 28 days.

[0067] (6) Performance test results

[0068] The mixture has a slump of 135 mm, a spread of 370 mm, and exhibits no segregation or fiber clumping.

[0069] Fiber dispersion uniformity: coefficient of variation 6.8%;

[0070] Mechanical properties: The 28-day cube has a compressive strength of 68.5 MPa, a splitting tensile strength of 6.3 MPa, and an equivalent bending strength of 8.7 MPa, which is 6.2% higher than that of the traditional preparation method (Comparative Example 1).

[0071] Figure 1 The diagram shows a comparison of the fiber dispersion states of Example 1 and Comparative Example 1. In Example 1, the volcanic slag aggregate and the two types of fibers are evenly distributed, while in Comparative Example 1, the volcanic slag aggregate and the two types of fibers exhibit agglomeration, which leads to stress concentration and a decrease in mechanical properties. The dispersion of the same batch of test blocks is too large. Compared with the traditional preparation method, the fiber dispersion state of Example 1 is more significant, which is beneficial to the improvement of the overall performance of concrete.

[0072] Example 2

[0073] Preparation of lightweight concrete using volcanic slag-ceramsite composite aggregate

[0074] (1) Raw material pretreatment

[0075] Composite aggregate: Volcanic slag is pretreated according to the process in Example 1 (moisture content 2.3%), and ceramsite with a 5-10mm gradation (bulk density 550kg / m³, water absorption 18%) is selected. After pre-wetting for 24 hours, it is drained and the moisture content is 9.2%. Ceramsite replaces volcanic slag by 40% to obtain pretreated aggregate.

[0076] Fibers: The pretreatment process is the same as in Example 1.

[0077] (2) Raw material ratio

[0078] The dosage of cementitious material (same as in Example 1) is 490 kg / m³, the water-cement ratio is 0.31, the total dosage of composite aggregate is 1220 kg / m³, the dosage of polycarboxylate superplasticizer is 0.9% (as a percentage of the cementitious material mass); the fiber content is 0.15% PPF + 1.2% SF (polypropylene fiber accounts for 0.15% of the total mass fraction of concrete raw materials, and steel fiber accounts for 1.2% of the total mass fraction of concrete raw materials).

[0079] (3) The staged mixing, layered vibration molding, and segmented curing are the same as in Example 1.

[0080] With preparation process

[0081] The mixing, vibration, and curing processes are the same as in Example 1;

[0082] (4) Performance test results

[0083] The mixture has a slump of 128 mm, a spread of 360 mm, and stable workability.

[0084] Fiber dispersion uniformity: coefficient of variation 7.5%;

[0085] Mechanical properties: 28-day cubic compressive strength 68.7 MPa, splitting tensile strength 6.2 MPa, apparent density 1780 kg / m³, weight reduction of 8% compared to single volcanic slag concrete (Example 1), and strength meeting C60 grade requirements.

[0086] Figure 2 This is an image showing the interfacial bond morphology of the concrete in Example 2. Figure 2 The volcanic slag and ceramsite aggregate are evenly distributed, with uniform distribution among ceramsite of different particle sizes. There is no agglomeration of the two types of fibers, and the overall distribution uniformity is significantly improved. Compared with the traditional preparation method, the fiber dispersion state in Example 2 is more significant, which is beneficial to the improvement of the overall performance of concrete.

[0087] Comparative Example 1

[0088] (1) Raw material preparation

[0089] Aggregate: The same 5-16mm graded volcanic slag as in Example 1 was used, but without any drying pretreatment, and its natural moisture content was 5.8%. Fiber: Polypropylene fiber and steel fiber were not pre-dispersed, and the fiber was the same as in Example 1. Other raw materials: Cementitious materials (cement, fly ash, silica fume in a mass ratio of 7:2:1) and polycarboxylate superplasticizer were the same as in Example 1.

[0090] (2) Raw material ratio

[0091] The amount of cementitious material, water-cement ratio, aggregate amount, water-reducing agent content and total fiber content are all consistent with those in Example 1.

[0092] (3) Stirring process

[0093] The traditional one-time feeding and mixing process is adopted: the untreated volcanic slag, all cementing materials, polypropylene fiber and steel fiber are put into the mixer at one time, dry-mixed for 1 minute, and then the mixing water and water-reducing agent are added at one time, and the mixture is stirred at a total speed of 350 r / min for 6 minutes.

[0094] (4) Molding and curing: Pour the mixed concrete into the mold at once, and the vibration and curing system is the same as in Example 1.

[0095] (5) Performance test results: Mixture state: Slight bleeding and segregation were observed, and fiber clumping was visible to the naked eye. Workability: Slump was only 105 mm, and spread was 320 mm. Mechanical properties: 28-day cubic compressive strength was 62.1 MPa, and splitting tensile strength was 5.6 MPa. Fiber dispersion uniformity: The coefficient of variation was as high as 15.4%.

[0096] (6) Results Analysis

[0097] Because the aggregates were not pretreated, their high natural moisture content interfered with the effective water-cement ratio, resulting in poor workability and easy bleeding of the mixture. The fibers were not pre-dispersed and were mixed only once, leading to extremely uneven dispersion and the formation of obvious weak areas. Ultimately, the mechanical properties of the concrete were significantly lower than those of the method of this invention (Example 1), with a strength loss of approximately 9-11%, and poor quality stability.

[0098] Comparative Example 2

[0099] (Compared with Example 2, only the aggregate processing method was changed)

[0100] (1) Raw material preparation

[0101] Aggregates: The same volcanic slag and ceramsite (5-10mm gradation) as in Example 2 were used, but without the water control treatment of this invention. The volcanic slag was used in its natural moisture content state (measured moisture content 5.8%), and the ceramsite was simply pre-wetted with water for 2 hours before use (measured moisture content 15%), simulating the treatment method of aggregates in conventional construction without precise moisture content control.

[0102] Fibers and other raw materials: exactly the same as in Example 2.

[0103] (2) Raw material ratio

[0104] All proportioning parameters (amount of cementitious material, water-cement ratio, total amount of aggregate, amount of water-reducing agent, and amount of fiber) are strictly consistent with those in Example 2.

[0105] (3) Mixing and subsequent processes

[0106] The mixing, molding, and curing processes and parameters are exactly the same as in Example 2.

[0107] (4) Performance test results

[0108] The mixture exhibits obvious water seepage, with traces of slurry loss on the aggregate surface, and poor uniformity.

[0109] Workability: The slump fluctuates greatly (110-145mm), and the spread is only 330mm.

[0110] Mechanical properties: 28d cube compressive strength 63.5MPa, splitting tensile strength 5.8MPa.

[0111] Fiber dispersion uniformity: coefficient of variation 12.1%.

[0112] (5) Results Analysis

[0113] Due to the lack of differentiated water control treatment for the aggregates, the excessively high and unstable moisture content of the volcanic slag and ceramsite severely interfered with the effective water-cement ratio, leading to bleeding and segregation of the mixture, resulting in poor and unstable workability. Excess water evaporation left pores, and the bond between the paste and aggregate interface weakened, ultimately causing a significant decrease in the density and mechanical properties of the concrete, and failing to achieve the lightweight goal (increased apparent density). This comparison demonstrates that precise differentiated water control treatment of volcanic slag and ceramsite is a necessary prerequisite for ensuring the workability, strength, and lightweight effect of composite aggregate concrete.

[0114] Comparative Example 3

[0115] (Compared with Example 2, only the fiber treatment method was changed)

[0116] (1) Raw material preparation

[0117] All raw materials (including aggregates precisely pretreated using the method of Example 2) are the same as those in Example 2.

[0118] Fiber treatment: Instead of pre-dispersing the polypropylene fibers with 10% cement, they are directly added to the mixing along with the steel fibers.

[0119] (2) Raw material ratio

[0120] All proportions and parameters are strictly consistent with those in Example 2.

[0121] (3) Stirring process

[0122] Except for the fiber feeding method, the mixing process parameters are the same as in Example 2. The steps are adjusted as follows: after dry mixing the pretreated aggregate and all the cementitious materials, polypropylene fibers and dispersed steel fibers are directly added simultaneously and mixed, followed by the addition of water and water-reducing agent.

[0123] (4) Shaping and curing

[0124] It is exactly the same as Example 2.

[0125] (5) Performance test results

[0126] State of the mixture: A small amount of polypropylene fiber clumping is visible to the naked eye.

[0127] Workability: slump 125mm, spread 340mm.

[0128] Mechanical properties: 28d cube compressive strength 65.2MPa, splitting tensile strength 5.9MPa.

[0129] Fiber dispersion uniformity (polypropylene fiber): The coefficient of variation is as high as 18.5%, which is obviously uneven.

[0130] (6) Results Analysis

[0131] Although the aggregate underwent precise pretreatment, the lightweight polypropylene fibers were prone to agglomeration during mixing because the pre-dispersion step with some cement was omitted. These fiber agglomerates form weak points in the concrete, not only failing to provide their own toughening effect but also becoming stress concentration points, resulting in limited and increased dispersion of the concrete's tensile strength. This comparison directly demonstrates that the step of "pre-dispersing polypropylene fibers with some cement" plays an irreplaceable and crucial role in resolving fiber agglomeration, ensuring their uniform distribution, and maximizing their reinforcing effect.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing steel-polypropylene hybrid fiber lightweight concrete, characterized in that, include: (1) The aggregate is subjected to water control treatment to obtain pretreated aggregate, wherein the aggregate is selected from a mixture of volcanic slag and ceramsite or volcanic slag, and the obtained pretreated aggregate is selected from a mixture of pretreated volcanic slag and pretreated ceramsite or pretreated volcanic slag, wherein the moisture content of the pretreated volcanic slag is ≤3% and the moisture content of the pretreated ceramsite is 8%-10%; (2) The concrete formula also includes cementitious materials, which are composed of cement, fly ash and silica fume. The pretreated aggregate, fly ash, silica fume and 90 wt% of the cement are mixed and stirred to obtain the first mixture. (3) Mix the polypropylene fiber with the remaining cement in the cementitious material and stir to obtain pre-dispersed polypropylene fiber; (4) Mix the first mixture, the pre-dispersed polypropylene fiber and the dispersed steel fiber to obtain the second mixture; (5) Mix the second mixture, water and water-reducing agent evenly until the mixture is uniformly viscous.

2. The method according to claim 1, characterized in that, In step (1), the volcanic slag is dried and dehydrated. The drying temperature is 100-110℃ and the time is 4-6h. The dehydration treatment of the ceramsite is pre-wetting for 20-30h and then draining. And / or, the ceramsite is selected from 5-10mm graded particles; And / or, when the aggregate is selected from a mixture of volcanic slag and ceramsite, the mass ratio of the volcanic slag to the ceramsite is (50-70):(30-50); And / or, the bulk density of the volcanic slag is 800-900 kg / m³, and the water absorption rate is 8%-10%; And / or, the bulk density of the ceramsite is 500-600 kg / m³, and the water absorption rate is 15%-20%.

3. The method according to claim 1, characterized in that, In step (2), the mass ratio of the cement, fly ash, and silica fume in the cementitious material is 7:2:1; And / or, the stirring speed in step (2) is 300-400 r / min, and the stirring time is 2-3 min.

4. The method according to claim 1, characterized in that, In step (3), the stirring speed is 800-1000 r / min, and the stirring time is 3-5 min; And / or, the polypropylene fiber has a length of 12-18 mm, a diameter of 0.02-0.04 mm, and a tensile strength ≥350 MPa; And / or, in step (4), the stirring speed is 500-600 r / min and the stirring time is 3-4 min; And / or, the steel fibers are dispersed using a vibrating screen; And / or, the steel fibers are 25-35 mm in length, 0.5-0.8 mm in diameter, and have a tensile strength ≥1100 MPa.

5. The method according to claim 1, characterized in that, In step (5), the water-reducing agent is selected from polycarboxylate water-reducing agents; And / or, the stirring speed in step (5) is 300-400 r / min, and the stirring time is 4-5 min.

6. The method according to any one of claims 1-5, characterized in that, The concrete is prepared according to the requirements of C60 grade lightweight concrete substrate, the amount of cementitious material is 450-500 kg / m³, the water-cement ratio is 0.28-0.32, the amount of aggregate is 1200-1300 kg / m³, and the amount of water-reducing agent is 0.6%-1.0% of the mass of cementitious material. And / or, the polypropylene fiber accounts for 0.12-0.15% of the concrete mass fraction, and the steel fiber accounts for 1.2% of the concrete mass fraction; preferably, when the aggregate is selected from the volcanic slag, the polypropylene fiber accounts for 0.12% of the concrete mass fraction, and the steel fiber accounts for 1.2% of the concrete mass fraction; preferably, when the aggregate is selected from a mixture of the volcanic slag and the expanded clay, the polypropylene fiber accounts for 0.15% of the concrete mass fraction, and the steel fiber accounts for 1.2% of the concrete mass fraction.

7. The method according to any one of claims 1-5, characterized in that, It also includes step (6): pouring the viscous material obtained in step (5) into the mold in 2-3 layers, with each layer not exceeding 100mm in thickness, and vibrating each layer for 20-30s using a high-frequency vibration table, preferably with a vibration frequency of 50-60Hz and an amplitude of 0.5-1.0mm.

8. The method according to claim 7, characterized in that, It also includes step (7): After step (6) vibration molding, segmented curing is carried out. The segmented curing includes early curing and standard curing. The early curing is: after molding, it is left to stand for 24 hours in an environment of 20±2℃ and relative humidity ≥90% to avoid rapid evaporation of moisture. The standard curing is: after demolding, it is transferred to a standard curing room, the temperature is controlled at 20±2℃ and relative humidity ≥95%, and it is cured for 28 days, preferably extended to 56 days. During this period, water is sprayed once every 7 days to replenish humidity.

9. The method according to any one of claims 1-5, characterized in that, It also includes quality control, which is to monitor the slump and spread of the mixture in real time during the stirring process in step (5). The slump is controlled at 120-150 mm and the spread is controlled at 350-400 mm. After molding, three groups of specimens are randomly selected for 28-day mechanical property testing to ensure that the cubic compressive strength is ≥68 MPa and the splitting tensile strength is ≥6.2 MPa.

10. A lightweight concrete, characterized in that, It is prepared by any one of the methods described in claims 1-9.

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