C200 ultra-high performance concrete and preparation method thereof

Abstract

The invention discloses C200 ultra-high performance concrete which comprises the following components: a cementing material, fine aggregate, a polycarboxylic acid water reducer, steel fibers, carbon fibers and water, the cementing material is prepared from the following components in parts by weight: 64 to 68 parts of Portland cement, 10 parts of fly ash microbeads, 14 to 16 parts of silica fume and 6 to 10 parts of carbide slag; the addition amount of the polycarboxylic acid water reducer is 1.5-1.7% of the total weight of the cementing material; the mixing amount of the steel fibers is 2.0-3.0% of the total volume of the concrete, and the mixing amount of the carbon fibers is 0.3-1.0% of the total volume of the concrete; the water-binder ratio of the concrete is 0.14 to 0.18; the weight ratio of the cementing material to the fine aggregate is (0.9-1.1): 1. Through the synergistic effect of excitation of the high-activity carbide slag, hybrid reinforcement of the steel fiber and the recycled carbon fiber and gradation of the aggregate, the 7d strength which is larger than or equal to 200 MPa is successfully prepared, the concrete further has excellent toughness which is difficult to achieve by single steel fiber ultra-high performance concrete, and unification of ultra-high strength and ultra-high toughness is achieved.

Description

A C200 ultra-high performance concrete and its preparation method Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a C200 ultra-high performance concrete and its preparation method. Background Technology

[0002] Ultra-High Performance Concrete (UHPC), as a new generation of building materials, is characterized by its ultra-high strength, high toughness, and ultra-high durability. These characteristics make it widely used in ultra-long-life infrastructure, high-end prefabricated structures, and extreme environment engineering. In existing technologies, to achieve strength grades of 180–200 MPa and above, it is usually necessary to use high-volume admixtures such as silica fume and fly ash, combined with high-volume steel fibers and high-temperature steam curing to accelerate the reaction process of cementitious materials and obtain a dense microstructure. However, steel fiber reinforced concrete has poor alkali and acid resistance. Furthermore, steel fibers often agglomerate and settle during concrete mixing. Concrete strength has always been a key performance indicator for concrete as an important structural material, and the quality of existing steel fiber reinforced concrete is difficult to improve; it is prone to cracking. Therefore, although steel fibers can enhance the strength of concrete, further increases in steel fiber content do not necessarily lead to a significant increase in strength.

[0003] Therefore, how to obtain C200 ultra-high performance concrete through reasonable raw material ratios, activation methods, and curing systems is an urgent problem to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing ultra-high performance concrete with a strength grade of C200 by combining carbide slag activation with fiber hybrid technology.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a C200 ultra-high performance concrete, comprising the following components: cementitious materials, fine aggregates, polycarboxylate superplasticizer, steel fibers, carbon fibers and water; the cementitious materials, by weight, comprise the following components: 64-68 parts of silicate cement, 10 parts of fly ash microspheres, 14-16 parts of silica fume, and 6-10 parts of carbide slag;

[0006] The amount of the polycarboxylate superplasticizer added is 1.5 to 1.7% of the total weight of the cementitious material;

[0007] The steel fiber content is 2.0-3.0% of the total concrete volume, and the carbon fiber volume content is 0.3-1.0% of the total concrete volume.

[0008] The water-cement ratio of the concrete is 0.14 to 0.18;

[0009] The weight ratio of the cementitious material to the fine aggregate is 0.9 to 1.1:1.

[0010] Furthermore, the fine aggregate is three-graded quartz sand, and the theoretical densest packing target curve is determined by the MAA model. The MAA model calculates the particle volume ratio of each grade of fine aggregate, and the theoretical dense packing target curve is determined by the following formula:

[0011]

[0012] Among them: U t (X i The theoretical closely packed target curve calculated for this model, X i X represents the particle size (mm). max X represents the maximum particle size (mm). min denoted as the minimum particle size (mm), and m is the distribution modulus, with a value of 0.22 to 0.25.

[0013] Furthermore, with m = 0.25, the volume ratio of the three-graded quartz sand is: 10-26 mesh quartz sand : 26-40 mesh quartz sand : 40-70 mesh quartz sand = 6:1:3.

[0014] Furthermore, the calcium carbide slag is obtained by drying wet-process calcium carbide slag produced in the acetylene industry to constant weight at 80–105°C, followed by mechanical grinding and activation, with a specific surface area of ​​450–500 m². 2 / kg.

[0015] Furthermore, the steel fiber is a hook-shaped copper-plated steel fiber with a fiber length of 12-15 mm and a fiber diameter of 0.20-0.25 mm.

[0016] Furthermore, the fiber is a recycled fiber with a length of 9-15 mm and a single filament tensile strength ≥3000 MPa.

[0017] Furthermore, the cement is P·Ⅱ52.5R cement, with a 28-day compressive strength of 62.6 MPa.

[0018] Furthermore, the 3-day thermal curing activity index of the silica fume is 150%, and the 3-day thermal curing activity index of the fly ash microspheres is 122%.

[0019] The preparation method of C200 ultra-high performance concrete according to any one of the above-mentioned methods includes the following steps:

[0020] (1) Determination of the mix proportions of each raw material in C200 ultra-high performance concrete;

[0021] (2) Premix the cementitious material, fine aggregate and carbon fiber at 200-300 rpm for 100-150 s to obtain a carbon fiber-powder mixture;

[0022] (3) Add polycarboxylate superplasticizer to water and stir evenly, then add it to carbon fiber-powder mixture and increase the speed to 500-800 rpm and stir for 3-5 minutes to obtain a uniform slurry;

[0023] (4) Add steel fibers to the slurry and stir evenly to obtain C200 ultra-high performance concrete.

[0024] The beneficial effects of this invention are: through the synergistic effect of high-activity carbide slag activation, steel fiber and recycled carbon fiber hybrid reinforcement and aggregate gradation, this invention successfully prepared a 7-day strength ≥200MPa, and it also has excellent toughness that is difficult to achieve with single steel fiber ultra-high performance concrete, thus achieving the unity of ultra-high strength and ultra-high toughness.

[0025] This invention enables the high-value utilization of industrial solid waste carbide slag and recycled carbon fiber, significantly reducing the cost of raw materials and carbon emissions of products, and has good economic and environmental benefits, which is in line with the development direction of green and low-carbon building materials. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments.

[0027] The cement has a 28-day compressive strength of 62.6 MPa, the fly ash microspheres have a 3-day thermal curing activity index of 122%, and the silica fume has a 3-day thermal curing activity index of 150%. The activated calcium carbide slag is wet-process calcium carbide slag produced in the acetylene industry, dried to constant weight at 80–105°C, and then mechanically ground and activated to achieve a specific surface area of ​​450–500 m². 2 / kg, its main component is Ca(OH)2; the steel fiber is a hook-type copper-plated steel fiber with a fiber length of 13mm and a fiber diameter of 0.22mm; the recycled carbon fiber has a length of 13mm and a single filament tensile strength of 3100Mpa; the fine aggregate is prepared by mixing 10-26 mesh, 26-40 mesh and 40-70 mesh quartz sand in a ratio of 6:1:3 when m=0.25.

[0028] Example 1:

[0029] A method for preparing C200 ultra-high performance concrete includes the following steps:

[0030] (1) Determination of the mix proportions of each raw material in C200 ultra-high performance concrete:

[0031] Prepare the following raw materials in parts by weight: 770 parts P·Ⅱ52.5R cement, 154 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​480 m². 2 / kg of active carbide slag powder 66 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0032] (2) Add cementitious materials, fine aggregates and carbon fibers into a mixer and dry mix at 260 rpm for 120 s to obtain carbon fiber-powder mixture;

[0033] (3) Add polycarboxylate-based high-performance water-reducing agent to water and stir evenly. Then add it to carbon fiber-powder mixture and stir at 650 rpm for 5 minutes to obtain a uniform slurry.

[0034] (4) Add steel fibers to the slurry and stir evenly to obtain C200 ultra-high performance concrete;

[0035] (5) The obtained C200 ultra-high performance concrete was poured into a 100mm×100mm×100mm cube mold, vibrated to compact it, and then left to stand in a standard curing room (20℃, humidity>95%) for 24 hours before demolding. After demolding, the following two hot water curing regimes were used for curing:

[0036] A: Increase the temperature to 80℃ at a rate of 5℃ per hour, maintain the temperature at 80℃ for 72 hours, and then decrease the temperature to 20℃ at a rate of 5℃ per hour.

[0037] B: Increase the temperature to 80°C at a rate of 10°C per hour, maintain the temperature at 80°C for 72 hours, and then decrease the temperature to 20°C at a rate of 10°C per hour.

[0038] After hot water curing, all specimens were transferred to a standard curing room (20℃, humidity >95%) for continued curing for 7 days before being tested.

[0039] Example 2:

[0040] A method for preparing C200 ultra-high performance concrete includes the following steps:

[0041] (1) Determination of the mix proportions of each raw material in C200 ultra-high performance concrete:

[0042] Prepare the following raw materials in parts by weight: 748 parts P·Ⅱ52.5R cement, 176 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​450 m². 2 / kg of active carbide slag powder 66 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0043] (2) Add cementitious materials, fine aggregates and carbon fibers into a mixer and dry mix at 220 rpm for 150 s to obtain carbon fiber-powder mixture;

[0044] (3) Add polycarboxylate-based high-performance water-reducing agent to water and stir evenly. Then add it to the carbon fiber-powder mixture and stir at 550 rpm for 5 minutes to obtain a uniform slurry.

[0045] (4) Add steel fibers to the slurry and stir evenly to obtain C200 ultra-high performance concrete;

[0046] (5) The obtained C200 ultra-high performance concrete was poured into a 100mm×100mm×100mm cube mold, vibrated to compact it, and then left to stand in a standard curing room (20℃, humidity>95%) for 24 hours before demolding. After demolding, the following two hot water curing systems were used for curing, and the curing methods were the same as in Example 1.

[0047] Example 3:

[0048] A method for preparing C200 ultra-high performance concrete includes the following steps:

[0049] (1) Determination of the mix proportions of each raw material in C200 ultra-high performance concrete:

[0050] Prepare the following raw materials in parts by weight: 704 parts P·Ⅱ52.5R cement, 198 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​486 m². 2 / kg of active carbide slag powder 66 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0051] (2) Add cementitious materials, fine aggregates and carbon fibers into a mixer and dry mix at 280 rpm for 110 s to obtain carbon fiber-powder mixture;

[0052] (3) Add polycarboxylate-based high-performance water-reducing agent to water and stir evenly. Then add it to carbon fiber-powder mixture and stir at 750 rpm for 3 minutes to obtain a uniform slurry.

[0053] (4) Add steel fibers to the slurry and stir evenly to obtain C200 ultra-high performance concrete;

[0054] (5) The obtained C200 ultra-high performance concrete was poured into a 100mm×100mm×100mm cube mold, vibrated to compact it, and then left to stand in a standard curing room (20℃, humidity>95%) for 24 hours before demolding. After demolding, the following two hot water curing systems were used for curing, and the curing methods were the same as in Example 1.

[0055] Example 4:

[0056] A method for preparing C200 ultra-high performance concrete includes the following steps:

[0057] (1) Determination of the mix proportions of each raw material in C200 ultra-high performance concrete:

[0058] Prepare the following raw materials in parts by weight: 726 parts P·Ⅱ52.5R cement, 176 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​480 m². 2 / kg of active carbide slag powder 88 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0059] Everything else is the same as in Example 1.

[0060] Example 5:

[0061] A method for preparing C200 ultra-high performance concrete includes the following steps:

[0062] (1) Determination of the mix proportions of each raw material in C200 ultra-high performance concrete:

[0063] Prepare the following raw materials in parts by weight: 704 parts P·Ⅱ52.5R cement, 176 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​480 m². 2 / kg of active carbide slag powder 110 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0064] Everything else is the same as in Example 1.

[0065] Comparative Example 1:

[0066] Comparative Example 1 did not use activated carbide slag powder, but instead used silicate cement of equal mass to replace the activated carbide slag powder, and the rest was the same as in Example 4.

[0067] Comparative Example 2:

[0068] Comparative Example 2 used raw, dried calcium carbide slag powder without grinding, and had a specific surface area of ​​280 m². 2 / kg, other details are the same as in Example 4.

[0069] Comparative Example 3:

[0070] Prepare the following raw materials in parts by weight: 770 parts of P·Ⅱ52.5R cement, 176 parts of silica fume, 110 parts of fly ash microspheres, 44 parts of activated carbide slag powder (total cementitious materials 1100 parts), 1100 parts of fine aggregate, 9 parts of recycled carbon fiber (volume admixture 0.5%), 200 parts of steel fiber (volume admixture 2.5%), 1.6% of the total weight of cementitious materials of polycarboxylate-based high-performance water-reducing agent, and 161 parts of water (water-cement ratio 0.15);

[0071] Everything else is the same as in Example 1.

[0072] Comparative Example 4:

[0073] Prepare the following raw materials in parts by weight: 693 parts P·Ⅱ52.5R cement, 176 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​480 m². 2 / kg of active carbide slag powder 121 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0074] Everything else is the same as in Example 1.

[0075] Comparative Example 5:

[0076] Prepare the following raw materials in parts by weight: 682 parts P·Ⅱ52.5R cement, 220 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​480 m². 2 / kg of active carbide slag powder 88 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent at 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0077] Everything else is the same as in Example 1.

[0078] Comparative Example 6:

[0079] Prepare the following raw materials in parts by weight: 792 parts P·Ⅱ52.5R cement, 110 parts silica fume, 110 parts fly ash microspheres, and a specific surface area of ​​480 m². 2 / kg of calcium carbide slag powder 88 parts (total cementitious material 1100 parts), fine aggregate 1100 parts, recycled carbon fiber 9 parts (volume admixture 0.5%), steel fiber 200 parts (volume admixture 2.5%), polycarboxylate-based high-performance water-reducing agent of 1.6% of the total weight of cementitious material, and water 161 parts (water-binder ratio 0.15).

[0080] Everything else is the same as in Example 1.

[0081] Comparative Example 7:

[0082] Comparative Example 7 did not use recycled carbon fiber, but instead used steel fiber cement of equal mass to replace recycled carbon fiber, and otherwise it was the same as Example 4.

[0083] Comparative Example 8:

[0084] Comparative Example 8 involves adding recycled carbon fiber and steel fiber to the slurry simultaneously in step (4), with the rest being the same as in Example 4.

[0085] Comparative Example 9:

[0086] Comparative Example 9 only replaced the fine aggregate with two types of quartz sand with particle sizes of 26-40 mesh and 40-70 mesh, in a ratio of 1:1, and the rest was the same as in Example 4.

[0087] The concrete specimens obtained in the examples and comparative examples were tested. The workability of the concrete was tested according to GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The compressive strength of the concrete was tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The results are shown in Table 1.

[0088] Table 1

[0089] Expansion (mm) T500(s) 7d compressive strength (MPa) corresponding to A curing Example 1 650 7.9 201 Example 2 670 6.8 205 Example 3 640 8.2 208 Example 4 685 5.5 218 Example 5 655 5.2 210 Comparative Example 1 670 6.5 186 Comparative Example 2 650 8.6 196 Comparative Example 3 610 9.5 195 Comparative Example 4 670 6.7 186 Comparative Example 5 630 9.6 179 Comparative Example 6 640 9.0 194 Comparative Example 3 680 5.8 210 Comparative Example 4 640 7.2 200 Comparative Example 5 660 7.1 195 surface

[0090] The 7-day compressive strength corresponding to different curing methods in the examples is shown in Table 2.

[0091] Table 2

[0092] 7-day compressive strength (MPa) corresponding to curing method A; 7-day compressive strength (MPa) corresponding to curing method B. Example 1: 201183; Example 2: 205188; Example 3: 208189; Example 4: 218208; Example 5: 210185 surface

[0093] The flexural toughness of the concrete specimens obtained in Example 4 and Comparative Examples 3 and 4 were tested. The flexural test was conducted in accordance with the "Standard for Test Methods of Fiber Reinforced Concrete" (CECS13-2009). The results are shown in Table 3.

[0094] Table 3

[0095] Equivalent bending strength (MPa) I5I 10 I 20 R 5,10 R 10,20 Example 4: 45.25.811.419.7116.779.8; Comparative Example 7: 741.24.78.113.191.970.4; Comparative Example 8: 35.63.65.48.269.263.6 surface

[0096] It can be seen that the strength of Comparative Example 2 is lower than that of Example 4. The untreated carbide slag has reduced the working performance and mechanical properties of UHPC, proving that it is necessary to mechanically grind and activate the carbide slag to improve its specific surface area and reactivity.

[0097] The strength and workability of Comparative Example 3 were lower than those of Example 4, indicating that the amount of modified carbide slag was too low, which was insufficient to activate fly ash microspheres and silica fume, and was also detrimental to workability.

[0098] The strength of Comparative Example 4 was lower than that of Example 4, indicating that the excessive amount of modified carbide slag resulted in a low amount of cement, which was not conducive to strength development.

[0099] The strength of Comparative Example 5 was lower than that of Example 4, indicating that the excessive amount of silica fume resulted in a low amount of cement, which was not conducive to strength development.

[0100] Comparative Example 6 showed lower strength and workability than Example 4, indicating that when the amount of silica fume used is too low, the viscosity-reducing effect of silica fume is not obvious, and the secondary hydration effect is weak.

[0101] Comparative Example 7 achieved a strength of 200 MPa, but toughness tests showed that its equivalent flexural strength and toughness index (I5, I) were significantly lower. 10 I 20 The results were all lower than in Example 4, demonstrating that the recycled carbon fibers, through effective bridging at the microcrack scale, form a multi-level toughening synergy with the steel fibers.

[0102] Comparative Example 8 showed deterioration in workability (decreased spread, fiber clumping) and a significant reduction in strength, with a decrease in equivalent flexural strength and toughness index. This demonstrates that the "dry mixing and wrapping of recycled carbon fibers followed by wet mixing" stirring process described in this invention is a key process step in ensuring the uniform dispersion of recycled carbon fibers and thus guaranteeing the workability and mechanical properties of UHPC.

[0103] Comparative Example 9 shows that when a two-stage fine aggregate is used, the workability and compressive strength of the mixture are reduced to varying degrees compared to Example 4. The experimental results further demonstrate that a three-stage fine aggregate designed based on the MAA model is necessary to achieve the technical effects of this invention.

Claims

1. A C200 ultra-high performance concrete, comprising the following components: cementitious materials, fine aggregates, polycarboxylate superplasticizer, steel fibers, carbon fibers, and water; characterized in that: The cementitious material, by weight, comprises the following components: 64-68 parts silicate cement, 10 parts fly ash microspheres, 14-16 parts silica fume, and 6-10 parts carbide slag; the polycarboxylate superplasticizer is added at 1.5-1.7% of the total weight of the cementitious material; the steel fiber content is 2.0-3.0% of the total volume of concrete, and the carbon fiber volume content is 0.3-1.0% of the total volume of concrete; the water-cement ratio of the concrete is 0.14-0.18; and the weight ratio of the cementitious material to fine aggregate is 0.9-1.1:

1.

2. The C200 ultra-high performance concrete according to claim 1, characterized in that: The fine aggregate is three-graded quartz sand. The theoretical densest packing target curve is determined by the MAA model. The MAA model calculates the particle volume ratio of each grade of fine aggregate, and the theoretical dense packing target curve is determined by the following formula: Among them: U t (X i The theoretical closely packed target curve calculated for this model, X i X represents the particle size (mm). max X represents the maximum particle size (mm). min denoted as the minimum particle size (mm), and m is the distribution modulus, with a value of 0.22 to 0.

25.

3. The C200 ultra-high performance concrete according to claim 2, characterized in that: m = 0.25, the volume ratio of the three-grade quartz sand is: 10-26 mesh quartz sand: 26-40 mesh quartz sand: 40-70 mesh quartz sand = 6:1:

3.

4. The C200 ultra-high performance concrete according to claim 1, characterized in that: The calcium carbide slag is obtained by drying wet-process calcium carbide slag produced in the acetylene industry to constant weight at 80-105℃, followed by mechanical grinding and activation, with a specific surface area of ​​450-500 m². 2 / kg.

5. The C200 ultra-high performance concrete according to claim 1, characterized in that: The steel fiber is a copper-plated steel fiber with a hook-shaped end, a fiber length of 12-15 mm, and a fiber diameter of 0.20-0.25 mm.

6. The C200 ultra-high performance concrete according to claim 1, characterized in that: The fiber is a recycled fiber with a length of 9-15 mm and a single filament tensile strength ≥3000 MPa.

7. The C200 ultra-high performance concrete according to claim 1, characterized in that: The cement is P·Ⅱ52.5R cement, with a 28-day compressive strength of 62.6 MPa.

8. The C200 ultra-high performance concrete according to claim 1, characterized in that: The 3-day thermal curing activity index of the silica fume is 150%, and the 3-day thermal curing activity index of the fly ash microspheres is 122%.

9. A method for preparing C200 ultra-high performance concrete according to any one of claims 1 to 8, characterized in that, The process includes the following steps: (1) Determining the proportion of each raw material in C200 ultra-high performance concrete; (2) Premixing cementitious materials, fine aggregates, and carbon fibers at a speed of 200-300 rpm for 100-150 s to obtain a carbon fiber-powder mixture; (3) Adding polycarboxylate superplasticizer to water and stirring evenly, then adding it to the carbon fiber-powder mixture and increasing the speed to 500-800 rpm and stirring for 3-5 min to obtain a uniform slurry; (4) Adding steel fibers to the slurry and stirring evenly to obtain C200 ultra-high performance concrete.

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