Design and preparation method of high-ductility cement-based composite material

Abstract

The invention discloses a design method of a high-ductility cement-based composite material, which comprises the following steps: S1, carrying out mix proportion design by using Box-Behnken in a response surface method, and designing a three-factor three-response test, the three factors being a water-binder ratio, a sand-binder ratio and a fiber mixing amount; s2, mixing and proportioning the materials according to the three factors in S1, and preparing to obtain the high-ductility cement-based composite material, s3, maintaining the high-ductility cement-based composite material obtained in the S2, and testing the three-response mechanical properties in the S1, wherein the three responses are compressive strength Y1, breaking strength Y2 and equivalent bending toughness Y3; and S4, analyzing the influence of the interaction of the three factors in the S1 on the three responses in the S3, establishing a response surface model equation through variance analysis verification, and verifying and optimizing a result to obtain an optimal mix proportion. A Box-Behnke method in RSM is adopted to establish a regression model with the water-binder ratio, the sand-binder ratio and the fiber mixing amount as influence factors and the compressive strength, the breaking strength and the equivalent bending toughness as response values.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a design and preparation method of a high-ductility cement-based composite material. Background Art

[0002] With the rapid development of civil engineering construction, my country has made major breakthroughs in the fields of bridges, high-rise structures and large-span structures. Cement-based materials have the advantages of easy availability of raw materials, low production costs, high strength and good alkali resistance. They are one of the raw materials that are widely used in the field of civil engineering. However, they also have corresponding defects, such as poor crack resistance, low tensile strength, poor toughness, low fatigue resistance, etc., which affect the overall durability and service life of the structure. Since cement-based materials go through many different stages during the destruction process, it is urgent to overcome a variety of complex factors and optimize their mechanical properties. Fiber blending is a direct and effective way to improve the shortcomings of a single fiber reinforcement system and to make up for its shortcomings. How to design and prepare high-ductility cement-based composites with hybrid fibers to meet the material performance requirements of specific applications is of great significance for cement-based composites to achieve the goals of high strength, high toughness, and green sustainability. Summary of the Invention

[0003] The purpose of the present invention is to provide a design and preparation method of a high-ductility cement-based composite material. The specific technical solution is as follows:

[0004] A design method for high-ductility cement-based composite materials comprises: S1, using the Box-Behnken method in the response surface method to perform mix design and design a three-factor three-response experiment, wherein the three factors are water-binder ratio, sand-binder ratio and fiber content; S2, performing material mix proportioning and preparation according to the three factors in S1 to obtain a high-ductility cement-based composite material; S3, after curing the high-ductility cement-based composite material obtained in S2, testing the three-response mechanical properties in S1, wherein the three responses are compressive strength Y1, flexural strength Y2 and equivalent bending toughness Y3; S4, analyzing the influence of the interaction of the three factors in S1 on the three responses in S3, establishing a response surface model equation through variance analysis, and verifying and optimizing the results to obtain an optimal mix ratio.

[0005] The water-binder ratio can be set between 0.1 and 0.3. The sand-binder ratio can be set between 0.2 and 0.5. The fiber content can be set between 1.5% and 3%. The fiber content includes polyethylene fiber and basalt fiber. The polyethylene fiber content is 0.5% to 1.5%, and the basalt fiber content is 0.6% to 1.8%.

[0006] The response surface model equation in S3 is:

[0007] Y1=+105.19-8.74*A-0.51*B-0.005*C+2.44*AB-7.12AC-

[0008] 0.97*BC+1.72*A 2 -34.02*B 2 +0.28*C 2

[0009] Y2=+23.12+0.44*A-1.11*B+2.75C-1.40*AB+1.53*AC-1.42*BC+

[0010] 2.44*A 2 +0.49*B 2 -3.58*C 2

[0011] Y3=+103.69+3.14*A-0.29*B+13.20*C-5.43*AB+16.71*AC-

[0012] 1.47*BC-17.35*A 2 -12.31*B 2 -39.92*C 2

[0013] Among them: Y1 is compressive strength, Y2 is flexural strength, Y3 is equivalent bending toughness, A is water-binder ratio, B is sand-binder ratio, and C is basalt fiber content.

[0014] A method for preparing a high-ductility cement-based composite material, comprising: M1, adding a portion of mixing water, a cementitious material, and an admixture to a mixer, and stirring at a low speed for 1-3 minutes; M2, adding polyethylene fiber and basalt fiber, and stirring at a high speed for 1-3 minutes; M3, adding reserved mixing water, and further stirring at a high speed for 1-3 minutes;

[0015] M4. Cast the mixed composite material into a mold, vibrate for 30-90 seconds, and then smooth it into shape to obtain a mixed fiber high-ductility cement-based composite material. The water-to-material ratio of the partial mixing water and the reserved mixing water is 0.2-0.3.

[0016] The above-mentioned technical solution of the present invention has the following beneficial technical effects: A regression model is established using the Box-Behnke method in RSM, with water-binder ratio, sand-binder ratio, and fiber content as influencing factors, and compressive strength, flexural strength, and equivalent flexural toughness as response values. The established prediction model is highly accurate, verifying that the relative error between the RSM optimized value and the experimental value is less than 5%, providing more optimal model parameters for the preparation of hybrid fiber high-ductility cement-based materials. The resulting material has excellent mechanical properties, can improve the strength and durability of structures, and possesses high ductility and high strength. The material has a wide range of applications and can be used in high-rise, long-span structures, and structures subject to large deformation, such as connecting beams in high-rise buildings, bridge deck connection plates, and seismic structures. It is also suitable for repairing damaged concrete structures and improving overall structural strength. By using a synergistic blending method of polyethylene fiber and basalt fiber, the advantages of the high elastic modulus and high tensile strength of basalt fiber are utilized to significantly improve the compressive and flexural strength of cement-based materials. This material is a green and environmentally friendly material in the construction industry and is of great significance in achieving the goal of green and sustainable cement-based composites. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of compressive strength within the mix ratio range;

[0018] Figure 2 This is a 3D response surface diagram of the two-factor interaction of the independent variables on the compressive strength, where: (a) AB interaction; (b) AC interaction; (c) BC interaction;

[0019] Figure 3 It is a schematic diagram of flexural strength within the mix ratio range;

[0020] Figure 4 The 3D response surface diagram of the two-factor interaction of the independent variables on the flexural strength, where: (a) AB interaction; (b) AC interaction; (c) BC interaction;

[0021] Figure 5 It is a schematic diagram of equivalent bending toughness within the mix ratio range;

[0022] Figure 6 This is a 3D response surface diagram of the two-factor interaction of the independent variables on the equivalent bending toughness, including: (a) AB interaction; (b) AC interaction; (c) BC interaction. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0024] A design method for high-ductility cement-based composite materials includes: S1. Using the Box-Behnken method in the response surface methodology to perform mix design, designing a three-factor, three-response experiment, where the three factors are water-binder ratio, sand-binder ratio, and fiber content; S2. Preparing and preparing the materials according to the three factors in S1 to obtain a high-ductility cement-based composite material; S3. After curing the high-ductility cement-based composite material obtained in S2, testing the three-response mechanical properties in S1, where the three responses are compressive strength Y1, flexural strength Y2, and equivalent flexural toughness Y3; S4. Analyzing the effects of the three-factor interaction in S1 on the three responses in S3, establishing a response surface model equation through variance analysis, and verifying and optimizing the results to obtain the optimal mix ratio. The Box-Behnke method in the RSM is used to establish a regression model with water-binder ratio, sand-binder ratio, and fiber content as influencing factors and compressive strength, flexural strength, and equivalent flexural toughness as response values. The established prediction model has high accuracy, and it is verified that the relative error between the RSM optimization value and the experimental value is less than 5%, which provides more excellent model parameters for the preparation of hybrid fiber high-ductility cement-based materials. The resulting material has excellent mechanical properties, can improve the strength and durability of the structure, and has the characteristics of high ductility and high strength. The material has a wide range of applications and can be used for high-rise, large-span and large-deformation structures, such as connecting beams, bridge deck connection plates, and seismic structures of high-rise buildings. It is also suitable for repairing damaged concrete structures and improving the overall structural strength. A blending mode of polyethylene fiber and basalt fiber based on synergistic effect is adopted, and the advantages of high elastic modulus and high tensile strength of BF fiber are utilized to greatly improve the compressive and flexural strength of cement-based materials. It is a green and environmentally friendly material in the construction field and is of great significance to the realization of green and sustainable goals for cement-based composite materials.

[0025] The water-binder ratio can be set between 0.1 and 0.3. The sand-binder ratio can be set between 0.2 and 0.5. The fiber content can be set between 1.5% and 3%. The fiber content includes polyethylene fiber and basalt fiber. The polyethylene fiber content is 0.5% to 1.5%, and the basalt fiber content is 0.6% to 1.8%.

[0026] The response surface model equation in S3 is:

[0027] Y1=+105.19-8.74*A-0.51*B-0.005*C+2.44*AB-7.12AC-

[0028] 0.97*BC+1.72*A 2 -34.02*B 2 +0.28*C 2

[0029] Y2=+23.12+0.44*A-1.11*B+2.75C-1.40*AB+1.53*AC-1.42*BC+

[0030] 2.44*A 2 +0.49*B 2 -3.58*C 2

[0031] Y3=+103.69+3.14*A-0.29*B+13.20*C-5.43*AB+16.71*AC-

[0032] 1.47*BC-17.35*A 2 -12.31*B 2 -39.92*C 2

[0033] Among them: Y1 is compressive strength, Y2 is flexural strength, Y3 is equivalent bending toughness, A is water-binder ratio, B is sand-binder ratio, and C is basalt fiber content.

[0034] A method for preparing a high-ductility cement-based composite material, comprising: M1, adding a portion of mixing water, a cementitious material, and an admixture to a mixer, and stirring at a low speed for 1-3 minutes; M2, adding polyethylene fiber and basalt fiber, and stirring at a high speed for 1-3 minutes; M3, adding reserved mixing water, and further stirring at a high speed for 1-3 minutes;

[0035] M4. Cast the mixed composite material into a mold, vibrate for 30-90 seconds, and then smooth it into shape to obtain a mixed fiber high-ductility cement-based composite material. The water-to-material ratio of the partial mixing water and the reserved mixing water is 0.2-0.3.

[0036] In order to make the present invention easier to understand, the following is further described with reference to the accompanying drawings:

[0037] Using the Box-Behnken approach in the response surface methodology, a three-factor, three-response experiment was designed with PE as the primary fiber. The three independent variables were the water-binder ratio (A), the sand-binder ratio (B), and the BF dosage (C), and the three responses were the compressive strength (Y1), the flexural strength (Y2), and the equivalent flexural toughness (Y3). The independent variables were coded as -1, 0, and 1, with the water-binder ratio ranged from 0.15 to 0.25, the sand-binder ratio ranged from 0.3 to 0.4, and the BF dosage ranged from 0.9% to 1.5%. The details are shown in Table 1.

[0038]

[0039] Table 1

[0040] The specific materials are mixed in proportions by weight. Mix ratio 1: approximately 30 parts of silicate cement, approximately 24 parts of fly ash, approximately 6 parts of silica fume, approximately 21 parts of 70-100 mesh quartz sand, approximately 15 parts of water, approximately 0.7 parts of water reducer, approximately 0.01 parts of thickener, approximately 0.5 parts of polyethylene fiber and 1.7 parts of basalt fiber.

[0041] Mix ratio 2: 30 parts of Portland cement, 24 parts of fly ash, 6 parts of silica fume, 21 parts of 70-100 mesh quartz sand, 15 parts of water, 0.7 parts of water reducer, 0.01 parts of thickener, 0.5 parts of polyethylene fiber and 1.02 parts of basalt fiber.

[0042] Mix ratio three: 30 parts of Portland cement, 24 parts of fly ash, 6 parts of silica fume, 21 parts of 70-100 mesh quartz sand, 9 parts of water, 0.7 parts of water reducer, 0.01 parts of thickener, 0.5 parts of polyethylene fiber and 1.7 parts of basalt fiber.

[0043] Each mix ratio was prepared separately. A portion of the mixing water, cementitious materials, and admixtures were added to a mixer and stirred at low speed for 2 minutes, with a water-to-cement ratio of 0.27. Polyethylene and basalt fiber were then added and stirred at high speed for 2 minutes. The reserved mixing water was then added and stirred at high speed for 2 minutes. After this stage, the prepared composite material was cast in a mold and compacted using a layered vibration method, with each layer vibrated on a vibrating table for 60 seconds. The resulting material was then smoothed and formed to produce a highly ductile cementitious composite material.

[0044] The response surface model equation established was verified by variance analysis. The F value of the model was 124.13, with a probability of P < 0.0001 < 0.05. The model was extremely significant at the 95% confidence level (CL), and the F value of the lack-of-fit term was 2.97, with a probability of P = 0.16 > 0.05. As shown in Table 2, it can well describe the relationship between the response and the factors, and the experimental results are accurately fitted with the model.

[0045]

[0046] Table 2

[0047] The high ductility cement-based composite material obtained according to the above mix ratio and preparation method is cured for 28 days and its compressive strength Y1 is tested:

[0048] like Figure 1As shown, the highest value is 120.65 MPa. This mix has the lowest water-binder ratio and the highest basalt fiber content in the design, at 0.15 and 1.5%, respectively. The material has low internal porosity and is relatively dense. The lowest compressive strength is 60.64 MPa. This mix has the highest water-binder ratio and the lowest sand-binder ratio, at 0.25 and 0.3, respectively, and a fiber content of 1.2%. In comparison, the material has a more dispersed internal packing, resulting in lower compressive strength.

[0049] As shown in Table 2, the F value of the model is 124.13, with a probability of P < 0.0001 < 0.05, indicating that the model is extremely significant at the 95% confidence level (CL), and the F value of the lack-of-fit term is 2.97, with a probability of P = 0.16 > 0.05. The corresponding experimental data is not significant when they are unrelated to the model, indicating that the model error is small.

[0050] like Figure 2 As shown in the figure, under the same A, as B increases from 0.3 to 0.4, the compressive strength shows a trend of first increasing and then decreasing, which plays a controlling role in the compressive strength. When B is 0.35, it is easier to obtain higher compressive strength. The response surface diagram is obviously warped. In the joint effect of BC on the compressive strength, C has a weaker control over the compressive strength. At this time, the main factor affecting the compressive strength is B.

[0051] The high ductility cement-based composite material obtained according to the above mix ratio and preparation method was tested for its flexural strength Y2 after 28 days of curing:

[0052] like Figure 3 As shown in the figure, the flexural strength ranges from 17.1 to 28.6 MPa, with the highest flexural strength reaching 28.6 MPa. This mix has the highest water-binder ratio, the lowest sand-binder ratio, and a moderate fiber content. Increasing the fiber content from 0.9% to 1.5% increases the flexural strength by 14.2%.

[0053] As shown in Table 3, the F-value of the flexural strength model is 54.95, with a probability of P < 0.0001 < 0.05, indicating that the model is extremely significant at the 95% confidence level. The F-value of the lack-of-fit term is 3.57, with a probability of P = 0.1255 > 0.05, indicating that the lack-of-fit term is not significant and the model error is small.

[0054]

[0055] Table 3

[0056] like Figure 4As shown in the figure, the response surface of the interaction relationship between BC is obviously warped. When B remains fixed, the content of C has a significant effect on the flexural strength. With the increase of the content of C, the flexural strength shows a trend of first increasing and then decreasing. In the influence of the interaction between BC on the flexural strength, controlling the content of C at 1.1%-1.3% can easily achieve higher flexural strength.

[0057] The high ductility cement-based composite material obtained according to the above mix ratio and preparation method was tested for its equivalent bending toughness Y3 after 28 days of curing:

[0058] As shown in Table 4, the F value of the equivalent bending toughness model is 91.1, with a probability of P < 0.0001 < 0.05, and the F value of the lack-of-fit term is 3.88, with a probability of P = 0.1117 > 0.05. The experimental results and the model fit are highly accurate.

[0059]

[0060] Table 4

[0061] like Figure 5 As shown, the equivalent bending strength ranges from 22.81 to 106.39 KJ / m 3 , the mix M15 has the best performance in absorbing energy during the stress process. The mix has moderate water-binder ratio, sand-binder ratio and BF content in the design, which are 0.2, 0.35 and 1.2% respectively.

[0062] like Figure 6 As shown in the figure, in the interaction of two factors AB, when one of the factors is fixed, the bending toughness shows a trend of first increasing and then decreasing with the increase of the other factor, indicating that there is a good interaction between the two factors. When the water-binder ratio is 0.2 and the mortar-sand ratio is 0.35, the equivalent bending toughness is the largest.

Claims

1. A method for designing a high-ductility cement-based composite material, characterized in that: include: S1. Use the Box-Behnken method in the response surface method to conduct mix design and design a three-factor three-response experiment, where the three factors are water-binder ratio, sand-binder ratio and fiber content; S2. According to the three factors in S1, the materials are mixed and prepared to obtain a high-ductility cement-based composite material; S3, curing the high ductility cement-based composite material obtained in S2 and then testing the three-response mechanical properties in S1, wherein the three responses are compressive strength Y1, flexural strength Y2, and equivalent bending toughness Y3; S4. Analyze the effects of the three-factor interaction in S1 on the three responses in S3, establish a response surface model equation through variance analysis, and verify and optimize the results to obtain the optimal mix ratio.

2. The method for designing a high-ductility cement-based composite material according to claim 1, wherein: The setting range of the water-to-binder ratio is 0.1-0.

3.

3. The design method of high ductility cement-based composite material according to claim 1, characterized in that: The setting range of the sand-to-adhesive ratio is 0.2-0.

5.

4. The method for designing a high-ductility cement-based composite material according to claim 1, wherein: The setting range of the fiber content is 1.5%-3%.

5. The design method of high ductility cement-based composite material according to claim 4, characterized in that: The fiber content includes polyethylene fiber content and basalt fiber content. The polyethylene fiber content is 0.5%-1.5%, and the basalt fiber content is 0.6%-1.8%.

6. The method for designing a high-ductility cement-based composite material according to claim 5, wherein: The response surface model equation in S3 is: Y1=+105.19-8.74*A-0.51*B-0.005*C+2.44*AB-7.12AC- 0.97*BC+1.72*A 2 -34.02*B 2 +0.28*C 2 Y2=+23.12+0.44*A-1.11*B+2.75C-1.40*AB+1.53*AC-1.42*BC+ 2.44*A 2 +0.49*B 2 -3.58*C 2 Y3=+103.69+3.14*A-0.29*B+13.20*C-5.43*AB+16.71*AC- 1.47*BC-17.35*A 2 -12.31*B 2 -39.92*C 2 Among them: Y1 is compressive strength, Y2 is flexural strength, Y3 is equivalent bending toughness, A is water-binder ratio, B is sand-binder ratio, and C is basalt fiber content.

7. A method for preparing a high-ductility cement-based composite material, characterized in that: include: M1. Add part of the mixing water, gelling material and admixture into the mixer and stir at low speed for 1-3 minutes; M2, add polyethylene fiber and basalt fiber, stir at high speed for 1-3 minutes; M3. Add reserved mixing water and stir at high speed for 1-3 minutes; M4. Cast the mixed composite material into a mold, vibrate for 30-90 seconds, and then smooth it into shape to obtain a mixed fiber high-ductility cement-based composite material.

8. The method for preparing a high-ductility cement-based composite material according to claim 7, wherein: The water-to-material ratio of the partial mixing water and the reserved mixing water is 0.2-0.3.

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