High stress-strain ultra high performance concrete and method of making same

Abstract

The application discloses a high stress-strain super high performance concrete, and the components are as follows in percentage by weight: 500-1200 parts of PO52.5 cement, 100-280 parts of silica ash, 50-120 parts of superfine mineral powder, 130-350 parts of fly ash, 700-1500 parts of quartz sand, 10-24 parts of polycarboxylic acid water reducing agent, 180-300 parts of water, and 100-400 parts of composite steel fiber; the composite steel fiber is a mixture of long straight steel fiber and point contact type steel fiber; the application uses specific point contact type steel fiber and long straight steel fiber to improve the toughness of the super high performance concrete material, overcomes the problem that special-shaped steel fibers are easily overlapped and gathered and cannot be dispersed in the concrete slurry, and obtains a high stress-strain super high performance concrete building material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a kind of super high performance concrete and its preparation method. BACKGROUND

[0002] Due to the high strength and high toughness provided by the fiber reinforcement mechanism and its own durability, super high performance concrete has great potential in engineering application and economy, and is often used in fields such as long-span bridges, high-rise buildings, and marine engineering. However, most fiber-reinforced super high performance concrete only has higher toughness than ordinary concrete, and its absolute stress-strain performance is still poor. This is because the interfacial bonding force between the matrix and the steel fiber is weak, far less than the tensile strength of the steel fiber itself. Therefore, when the specimen is subjected to tensile stress, the ordinary steel fiber slips and breaks, and the steel fiber is pulled out from the matrix before it reaches the yield state, resulting in low utilization efficiency of the steel fiber and severely limiting the improvement of the stress-strain performance of super high performance concrete.

[0003] Therefore, using various shaped steel fibers to improve the mechanical anchoring ability between the steel fiber and the matrix can effectively improve the utilization efficiency of the steel fiber and thus improve the toughness of super high performance concrete. CN108585689B and CN202626044U disclose spiral steel fibers of different sizes, which are used to improve the toughness of concrete. CN214361039U discloses a hook-end wave steel fiber that can also increase the tensile capacity of the steel fiber end face. However, for most shaped steel fibers, the mechanical anchoring mechanism may have additional negative effects. On the one hand, shaped steel fibers are prone to overlap and agglomerate, and cannot be dispersed in the concrete slurry. Agglomerated steel fibers can introduce a large number of pores in the matrix, reducing the mechanical properties. On the other hand, when the shaped steel fiber is pulled out from the matrix, it can damage the matrix, often resulting in low strain performance. CN202310233254 discloses a super high performance concrete reinforced by micro-diameter fibers, which has an ultimate tensile strain of ≥0.2%. CN201710516645 discloses a normal temperature curing type super high performance concrete, which has an ultimate tensile strain of ≥3000με and a tensile strength of not less than 8MPa. Although the stress-strain performance is improved compared to ordinary concrete, it is still insufficient for use in harsh environments. SUMMARY

[0004] The present application aims to provide a high stress-strain super high performance concrete and its preparation method, which improves the toughness of super high performance concrete material by using specific point-touch steel fibers and long straight steel fibers, overcoming the problem of shaped steel fibers that are prone to overlap and agglomerate and cannot be dispersed in the concrete slurry, and obtaining a high stress-strain super high performance concrete building material.

[0005] To achieve the above object, the technical scheme is as follows:

[0006] A high stress strain ultra high performance concrete, its composition is as follows in weight fraction:

[0007] PO52.5 cement 500-1200 parts, silica fume 100-280 parts, superfine mineral powder 50-120 parts, fly ash 130-350 parts, quartz sand 700-1500 parts, polycarboxylic acid water reducer 10-24 parts, water 180-300 parts, composite steel fiber 100-400 parts;The composite steel fiber is a mixture of long straight steel fiber and point touch type steel fiber.

[0008] According to the above scheme, the point touch type steel fiber content is 50-200 parts, the long straight steel fiber content is 50-300 parts, and the total content of the two is not more than 400 parts.

[0009] According to the above scheme, the long straight steel fiber cross section is circular, the diameter is 0.1-0.25mm, the length is 10-25mm, the length-diameter ratio is >80, and the tensile strength is ≥2800MPa.

[0010] According to the above scheme, the point touch type steel fiber cross section is circular, the diameter is 0.15-0.25mm, the length is 10-25mm, the length-diameter ratio is ≥60, and the tensile strength is ≥2800MPa;The point touch type steel fiber is provided with 3-8 folding points, and the included angle at the folding point is 135°-180°.

[0011] According to the above scheme, the specific surface area of the silica fume is 20-32m 2 / g, the SiO2 content in the silica fume is ≥95%.

[0012] According to the above scheme, the particle size of the superfine mineral powder is 0.05-20μm.

[0013] According to the above scheme, the specific surface area of the fly ash is 2.0-3.0m 2 / g, wherein the SiO2 content is ≥55%.

[0014] According to the above scheme, the particle size of the quartz sand is 100μm-400μm.

[0015] According to the above scheme, the mechanical index of the ultra high performance concrete is that the compressive strength is ≥160MPa, the tensile strength is ≥12MPa, and the ultimate tensile strain is ≥1.0%.

[0016] The preparation method of the above high stress strain ultra high performance concrete comprises the following steps:

[0017] (1) Mix and stir PO52.5 cement, silica fume, superfine mineral powder, fly ash, quartz sand, polycarboxylic acid water reducer uniformly;

[0018] (2) add water and continue stirring for 10-15 min to obtain concrete mortar;

[0019] (3) add long straight steel fibers and point-touch steel fibers into the concrete mortar using a 9.5 mm aperture square hole sieve, and stir for 5-8 min to obtain high stress-strain ultra-high performance concrete.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] Compared with the use of long straight steel fibers alone, the point-touch steel fibers have a stronger mechanical anchoring effect with the concrete matrix and higher resistance to pullout performance.

[0022] Compared with other special-shaped steel fibers such as end-hook steel fibers and spiral steel fibers, the point-touch steel fibers have a relatively smooth shape and do not have the problem of mutual lapping and agglomeration, so the slurry also has good fluidity.

[0023] In addition, compared with other forms of special-shaped steel fibers, the point-touch steel fibers cause less damage to the matrix when pulled out, greatly improving the use efficiency of the steel fibers.

[0024] The point-touch steel fibers are used in combination with long straight steel fibers, which not only further reduces the risk of agglomeration of the steel fibers, but also forms a multi-interlaced three-dimensional network structure in the concrete matrix, and the combination of multiple forms and sizes of steel fibers is beneficial to bridging cracks of different sizes in the matrix, improving the cracking resistance.

[0025] The above effects reduce the internal porosity caused by the formation of a three-dimensional network of steel fibers, prolong the strain hardening stage of the ultra-high performance concrete, and improve the stress-strain performance of the test piece. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The figure is a schematic diagram of the structure of the point-touch steel fibers of the present application.

[0027] Figure 2 The figure is an axial tensile stress-strain curve of the high stress-strain ultra-high performance concrete of the present application.

[0028] Figure 3 The figure is a schematic diagram of a fiber pullout test.

[0029] Figure 4 The figure is a fiber pullout load-slip graph. DETAILED DESCRIPTION

[0030] The following examples further illustrate the technical solutions of the present application, but do not limit the scope of protection of the present application.

[0031] The embodiment provides a high stress-strain ultra-high performance concrete, and the concrete is prepared according to the following weight proportions:

[0032] PO52.5 cement 500-1200 parts, silica fume 100-280 parts, superfine mineral powder 50-120 parts, fly ash 130-350 parts, quartz sand 700-1500 parts, polycarboxylic acid water reducer 10-24 parts, water 180-300 parts, and composite steel fiber 100-400 parts.

[0033] The composite steel fiber is composed of long straight steel fiber and point-touch steel fiber; wherein the content of the point-touch steel fiber is 50-200 parts, the content of the long straight steel fiber is 50-300 parts, and the total content of the two is not more than 400 parts.

[0034] Specifically, the long straight steel fiber has a circular cross section, a diameter of 0.1-0.25 mm, a length of 10-25 mm, a length-diameter ratio of >80, and a tensile strength of >2800 MPa.

[0035] Specifically, the point-touch steel fiber has a circular cross section, a diameter of 0.15-0.25 mm, a length of 10-25 mm, a length-diameter ratio of >60, a tensile strength of >2800 MPa, 3-8 folding points arranged on the point-touch steel fiber, and an included angle of 135°-180° at the folding points. Figure 1

[0036] Specifically, the silica fume has a specific surface area of 20-32 m 2 / g, and the SiO2 content in the silica fume is >95%.

[0037] Specifically, the superfine mineral powder has a particle size of 0.05-20 μm.

[0038] Specifically, the fly ash has a specific surface area of 2.0-3.0 m 2 / g, and the SiO2 content is >55%.

[0039] Specifically, the quartz sand has a particle size range of 100 μm-400 μm.

[0040] The mechanical index of the ultra-high performance concrete is as follows: compressive strength >160 MPa, tensile strength >12 MPa, and ultimate tensile strain >1.0%.

[0041] The embodiment further provides a preparation method of the high stress-strain ultra-high performance concrete.

[0042] (1) adding PO52.5 cement, silica fume, superfine mineral powder, fly ash, quartz sand, polycarboxylic acid water reducer into a stirring pot, mixing for 5-10 min, and uniformly mixing the components;

[0043] ​(2) Add water into the stirring pot, stir for 10-15 min to obtain well-stirred concrete mortar;

[0044] (3) Add long straight steel fibers and point-touch steel fibers into the stirring pot using a 9.5 mm aperture square hole sieve, stir for 5-8 min to obtain high stress-strain ultra-high performance concrete products; the mechanical indexes of the obtained ultra-high performance concrete are compressive strength ≥ 160 MPa, tensile strength ≥ 12 MPa, and ultimate tensile strain ≥ 1.0%.

[0045] Example 1

[0046] The high stress-strain ultra-high performance concrete of the present example comprises PO52.5 cement, silica fume, ultra-fine mineral powder, fly ash, quartz sand, polycarboxylic acid water reducer, water, and steel fibers. A total of 5 groups of ultra-high performance concrete materials with different proportions are designed, numbered as 1-1, 1-2, 1-3, 1-4, and 1-5. The content of each component is given in Table 1 in parts by mass, wherein the long straight steel fibers include Φ0.2 mm × 20 mm and Φ0.15 mm × 12 mm, and the proportion of the two is fixed at 2:1; the point-touch steel fibers are Φ0.2 mm × 13 mm, with 3-8 random folds, and the angles at the folds are randomly distributed at 135°-180°.

[0047] In addition, all the steel fibers in Comparative Example 1 are point-touch steel fibers; Comparative Example 2 uses Φ0.2 mm × 20 mm long straight steel fibers; Comparative Example 3 uses Φ0.15 mm × 12 mm long straight steel fibers; and Comparative Example 4 uses end-hook steel fibers Φ0.2 mm × 20 mm.

[0048] Table 1

[0049]

[0050] In the present example, the specific molding process is as follows:

[0051] a) Add PO52.5 cement, silica fume, ultra-fine mineral powder, fly ash, quartz sand, and polycarboxylic acid water reducer in the raw materials into the stirring pot, mix for 8 min to mix them uniformly;

[0052] b) Add water into the stirring pot, stir for 12 min to obtain well-stirred concrete mortar;

[0053] c) Add long straight steel fibers and point-touch steel fibers into the stirring pot using a 9.5 mm aperture square hole sieve, stir for 7 min to obtain high stress-strain ultra-high performance concrete products.

[0054] The high stress-strain ultra-high performance concrete prepared in Example 1 is subjected to 2d steam curing and then performance detection, and the compressive strength, ultimate tensile strength, and ultimate tensile strain are detected according to GB / T50081-2019.

[0055] The stress-strain results for different mix proportions are shown in the appendix. Figure 2 As shown, the results indicate that the ultimate strain of each group exceeded 1.0% and the ultimate tensile strength exceeded 12 MPa. The ultimate strain of group 1-1 reached the highest at 1.49%, while the ultimate tensile strengths of groups 1-4 and 1-5 both exceeded 18 MPa. The specific performance test results of the high-stress-strain ultra-high-performance concrete obtained in Example 1 are shown in Table 2.

[0056] Table 2

[0057]

[0058] As shown in the above data and figures, the composite method of long straight steel fibers and point-contact steel fibers can effectively improve the ultimate stress-strain of ultra-high performance concrete. This is because the composite of steel fibers with different shapes and aspect ratios leads to the formation of an interwoven three-dimensional network structure within the matrix. Furthermore, the mechanical anchoring characteristics of the point-contact steel fibers and their minimal damage to the matrix during pull-out also play a significant role. In Example 2, increasing the total steel fiber content is beneficial to improving compressive strength and ultimate tensile strength, but has no significant effect on ultimate tensile strain. Therefore, it can be reasonably inferred that, under the premise of free dispersion of steel fibers, increasing the total steel fiber content proportionally according to the steel fiber combination is expected to further improve ultimate tensile strength and compressive strength while maintaining excellent strain performance.

[0059] The high-stress-strain ultra-high performance concrete prepared in Comparative Examples 1, 2, 3, and 4 were subjected to performance testing after 2 days of steam curing. The main focus was on comparing the ability of different steel fibers to resist pull-out from the ultra-high performance concrete matrix. A schematic diagram of the fiber pull-out test is shown below. Figure 3 As shown, its load-slip results are as follows: Figure 4 As shown, for Figure 4 Integrating the curve yields the fiber pullout energy, and the maximum pullout load is also calculated. max ) Fiber bond strength can be calculated The calculation results are shown in Table 3.

[0060] Table 3

[0061]

[0062] From the above data, the point contact steel fiber shows the best resistance to pull-out capacity, not only in its highest pull-out capacity and bond strength, but also in its better load decay curve. Although the end hook steel fiber has the highest pull-out load, the load decays cliff-like after reaching the peak, which means that the pull-out process causes greater damage to the matrix. In contrast, the point contact steel fiber shows a similar load decay curve to the long straight steel fiber, indicating that its pull-out behavior does not damage the matrix itself, which is an important reason for its best stress-strain curve.

[0063] The above examples are only for illustration and do not limit the embodiments. Any equivalent modifications and alternatives made by those skilled in the art to the present application are also within the protection scope of the inventive claims.

Claims

1. A high-stress-strain ultra-high-performance concrete, characterized in that The components are as follows in parts by weight: PO52.5 cement 500-1200 parts, silica fume 100-280 parts, superfine mineral powder 50-120 parts, fly ash 130-350 parts, quartz sand 700-1500 parts, polycarboxylic acid water reducer 10-24 parts, water 180-300 parts, and composite steel fiber 100-400 parts; the composite steel fiber is a mixture of long straight steel fiber and point-touch steel fiber; The point-touch steel fiber content is 50-200 parts, the long straight steel fiber content is 50-300 parts, and the total content of the two is not more than 400 parts; The long straight steel fiber has a circular cross section, a diameter of 0.1-0.25 mm, a length of 10-25 mm, an aspect ratio of >80, and a tensile strength of ≥2800 MPa; The point-touch steel fiber has a circular cross section, a diameter of 0.15-0.25 mm, a length of 10-25 mm, an aspect ratio of ≥60, and a tensile strength of ≥2800 MPa; the point-touch steel fiber is provided with 3-8 folding points, and the included angle at the folding points is 135°-180°; The mechanical index of the ultra-high performance concrete is a compressive strength of ≥160 MPa, a tensile strength of ≥12 MPa, and a limit tensile strain of ≥1.0%.

2. The high-stress strain ultra-high performance concrete according to claim 1, wherein The specific surface area of the silica fume is 20-32 m 2 / g, the SiO2 content in the silica fume is ≥ 95%.

3. The high-stress strain ultra-high performance concrete according to claim 1, wherein The superfine mineral powder has a particle size of 0.05-20 μm.

4. The high-stress strain ultra-high performance concrete according to claim 1, wherein said fly ash has a specific surface area of 2.0 to 3.0 m 2 / g, wherein the SiO2 content is > 55%.

5. The high-stress strain ultra-high performance concrete according to claim 1, wherein The quartz sand has a particle size range of 100 μm-400 μm.

6. The method of producing high-stress strain ultra-high performance concrete according to claim 1, characterized in that The method comprises the following steps: (1) mixing and stirring PO52.5 cement, silica fume, superfine mineral powder, fly ash, quartz sand, and polycarboxylic acid water reducer uniformly; (2) adding water and continuing to stir for 10-15 min to obtain concrete mortar; (3) adding long straight steel fiber and point-touch steel fiber into the concrete mortar using a 9.5 mm aperture square hole sieve, and stirring for 5-8 min to obtain high stress strain ultra-high performance concrete.

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