Ultrahigh-performance seawater and sea sand concrete and preparation method thereof

Abstract

The invention relates to ultrahigh-performance seawater and sea sand concrete and a preparation method thereof, and belongs to the technical field of building materials. The ultrahigh-performance seawater sea sand concrete is prepared by taking the seawater sea sand concrete as a base material, the silica fume, the fly ash and the metakaolin as auxiliary cementing materials and the stainless steel fibers as fiber reinforced materials, the optimal substitution rate of the auxiliary cementing materials is 20-30%, and the optimal mixing amount of the stainless steel fibers is 2%. Due to the mixing amount, the compressive strength value of the UHPSSC can be improved by 17.35%, the breaking strength value is improved by 46.32%, and in addition, the mechanical property of the seawater sea sand concrete is improved through the modified stainless steel fiber.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to an ultra-high performance seawater sand concrete and its preparation method. Background Technology

[0002] Ultra-High Performance Seawater and Sea-sand Concrete (UHPSSC) is an ideal building material for marine engineering construction. Its dense structure and excellent mechanical and durability properties mitigate the corrosive damage caused by chloride ions in the marine environment and also solve the problem of scarce resources such as freshwater river sand.

[0003] In the prior art, CN111635195B discloses a seawater sand concrete and its preparation method, belonging to the field of concrete materials technology. This invention uses sea sand as aggregate and reef powder as the main cementitious material to improve the compressive strength of the concrete, and seawater as the hydration reaction water. Simultaneously, a water-reducing agent is added to improve the density of the concrete, which effectively prevents chloride ion erosion, thereby enhancing the concrete's resistance to chloride ion penetration. Silica powder and slag are used to fill the gaps between cementitious materials, further enhancing the density of the concrete, supplemented by fiber reinforcement, and a concrete corrosion inhibitor is used to further prevent chloride ion corrosion of the reinforcing steel. By controlling the specifications and proportions of the raw materials, this invention produces seawater sand concrete with high density, which can reduce chloride ion erosion of the reinforcing steel and improve the durability of the concrete structure.

[0004] CN112982062B discloses a fiber-reinforced seawater sand pavement structure, comprising a crushed stone subbase, a roller-compacted concrete base course, a seawater sand concrete layer, and an asphalt concrete surface layer, wherein the crushed stone subbase, roller-compacted concrete base course, seawater sand concrete layer, and asphalt concrete surface layer are laid in layers from bottom to top. The fiber-reinforced seawater sand pavement structure provided by this invention utilizes a fiber-reinforced concrete mold frame structure, improving the strength and durability of the pavement structure. Using seawater sand to prepare the concrete offers superior economic efficiency. The use of a novel porous material (MOF) to dechlorinate the seawater sand increases the strength of the seawater sand concrete layer from 40.6 MPa to 62.7 MPa, significantly improving the strength and durability of the pavement structure. The use of high-strength fiber-reinforced concrete to replace steel reinforcement in the seawater sand concrete overcomes the limitation that seawater sand cannot be used in reinforced concrete structures.

[0005] CN108409246B discloses a C30 concrete material resistant to marine erosion, comprising continuously graded crushed stone, medium-coarse river sand, composite mineral powder, ordinary Portland cement or Portland cement, and a high-efficiency water-reducing agent. This C30 concrete material is produced by adding water, mixing, compacting, and standard curing. The composite mineral powder accounts for 70% of the total mass of the cementitious materials; the total electrical conductivity (C-value) is less than or equal to 600 coulombs; the strength loss rate after 100 sulfate wet-dry cycles is less than or equal to 18%; the mass loss rate is less than or equal to 4%; the impermeability grade is greater than P18; there is no potential alkali-aggregate reaction hazard; it has excellent reinforcement protection and strong crack resistance, effectively addressing the shortcomings and defects of traditional concrete materials.

[0006] Although the above-mentioned prior art partially mentions the use of seawater and sea sand, it does not address the purpose of improving concrete performance when using seawater and sea sand.

[0007] This invention uses seawater sand concrete as the matrix material, silica fume, fly ash and metakaolin as auxiliary cementing materials, and stainless steel fiber as fiber reinforcement material to prepare ultra-high performance seawater sand concrete. Summary of the Invention

[0008] The purpose of this invention is to provide an ultra-high performance seawater sand concrete and its preparation method, in order to solve the problems mentioned in the background art.

[0009] The objective of this invention can be achieved through the following technical solutions: Firstly, this invention provides an ultra-high performance seawater sand concrete, comprising the following raw materials in parts by weight: cement 500-1100 kg / m³. 3 Silica fume 100-120 kg / m³ 3 Fly ash 50-300 kg / m³ 3 Metakaolin 50-300 kg / m 3 Seawater 200-240 kg / m 3 Polycarboxylate superplasticizer 10-30 kg / m 3 Sea sand 800-1100 kg / m 3 Stainless steel fiber 60-280 kg / m 3 ; In some embodiments, silica fume, fly ash, and kaolinite are configured as auxiliary gelling materials, which partially replace the raw material cement. The amount of the auxiliary gelling material replacing the raw material cement is 10%-40% of the mass percentage of the cement, preferably 20%-30%. In some embodiments, the stainless steel fiber content accounts for 1%-3% of the concrete volume, preferably 2%-3%.

[0010] In some embodiments, the specific surface area of ​​the silica fume is not less than 15000 m². 2 / kg, preferably with the following chemical composition: SiO2 94.85%, CaO 0.85%, Al2O3 0.97%, Fe2O3 0.71%, SO3 0.53%, and loss on ignition 2.1%.

[0011] In some embodiments, the specific surface area of ​​the fly ash is not less than 450 m². 2 / kg, preferably with the following chemical composition: SiO2 49.26%, CaO 6.53%, Al2O3 30.14%, Fe2O3 5.16%, SO3 2.16%, and loss on ignition 3.34%.

[0012] In some embodiments, the specific surface area of ​​the metakaolin is not less than 12000 m². 2 / kg, preferably with the following chemical composition: SiO2 53.5%, CaO 0.15%, Al2O3 42.00%, Fe2O3 1.8%, SO3 0.65%, and loss on ignition 3.45%.

[0013] In some embodiments, the seawater contains 18-20 g / L of chloride ions, 10-12 g / L of sodium ions, 2-3 g / L of sulfate ions, 1-2 g / L of magnesium ions, 0.2-0.5 g / L of calcium ions, and 0.2-0.5 g / L of potassium ions.

[0014] In some embodiments, the apparent density of the sea sand is 2600-2700 kg / m³. 3 The moisture content is not higher than 1.6%, the mud content is not higher than 0.78%, the particle size is not greater than 5mm, and the fineness modulus is 2.5-2.6.

[0015] In some embodiments, the stainless steel fibers are 13 cm long and have an apparent density of 7850 kg / m³. 3 Tensile strength 2200MPa, elastic modulus 206Gpa, elongation ratio 1.8.

[0016] In some embodiments, the water-reducing agent has a water reduction rate of 47%, a solid content of 25.2%, an alkali content of 1.8%, and a chloride ion content not exceeding 0.03%.

[0017] In some embodiments, the water-cement ratio is 0.20, the sand-binder ratio is 0.80, and the amount of polycarboxylate superplasticizer is 2-3% of the total mass of the gel material.

[0018] In some embodiments, the liquidity test shall not be less than 230 mm.

[0019] In some embodiments, the ultra-high performance seawater sand concrete has a 7-day compressive strength of 89.51-132.9 MPa and a 28-day compressive strength of 95.07-155.82 MPa.

[0020] In some embodiments, the stainless steel fiber is modified by the following technical means: before impregnation, the stainless steel fiber is first impregnated with a 10%-20% sodium hydroxide solution at 50-60°C for 10-20 minutes; then it is activated by acid washing, the acid being sulfuric acid with a concentration of 5-8%, and washed at room temperature for 1-2 minutes; then it is washed with pure water and dried at room temperature.

[0021] In some embodiments, the stainless steel fibers are sequentially impregnated with water glass of modulus 3.2-3.5, water glass of modulus 2.6-3.0, and water glass of modulus 2.0-2.5. After each impregnation, the stainless steel fibers are centrifuged to control the thickness of the impregnation layer. The centrifugation speed is 1000-2000 rpm and the centrifugation time is 10-20 seconds. After each impregnation, pre-curing is performed by pre-curing the impregnated stainless steel fibers at 60-80°C for 1-2 minutes.

[0022] In some embodiments, pre-cured stainless steel fibers that have been gradient-impregnated with water glass are sprayed with quartz sand with an average particle size of 100-120 μm.

[0023] Secondly, the present invention also provides a method for preparing ultra-high performance seawater sand concrete, the method being used to prepare the ultra-high performance seawater sand concrete of the first aspect, comprising the following steps: Step 1): According to the raw material percentage of the ultra-high performance seawater sand concrete in the first aspect, put cement, silica fume, fly ash and metakaolin powder into the mixer and dry mix for 2-5 minutes, then put sea sand into the mixer and dry mix for 3-10 minutes. Step 2) Pre-stir the seawater and polycarboxylate superplasticizer to obtain a mixture, and then add the mixture into the mixer in two equal portions and stir for 5-10 minutes each time. Step 3) Divide the fiber into two equal portions and add them into the mixer. Mix for 5-10 minutes each time.

[0024] Thirdly, the present invention also provides an application of ultra-high performance seawater sand concrete as described in the first aspect, for construction applications in marine engineering environments.

[0025] The beneficial effects of this invention are: 1) This invention studies how the synergistic use of silica fume, fly ash, and metakaolin as auxiliary cementitious materials can improve the mechanical properties of seawater sand concrete, increase the density of the matrix, and enhance its crack resistance. The optimal substitution rate of the auxiliary cementitious materials is 20%-30%. 2) Stainless steel fibers, as a fiber reinforcement material, can solve the problem of excessive brittleness caused by the ultra-high strength of UHPSSCs and avoid the corrosion problem of steel fibers caused by the presence of chloride ions in seawater and sea sand. The incorporation of stainless steel fibers can improve the compressive and flexural strength of UHPSSCs and enhance their fracture toughness.

[0026] 3) The composite incorporation of different types of auxiliary cementitious materials can optimize the particle size distribution. The ultrafine spherical particles have good micro-aggregate effect and morphological effect, thereby improving the fluidity of freshly mixed composite slurry.

[0027] 4) The addition of stainless steel fibers can improve the mechanical properties and fracture toughness of UHPSSC. Its excellent crack-resistant and bridging effects can effectively delay the generation and propagation of concrete cracks, thereby improving the compressive and flexural strength of UHPSSC.

[0028] 5) Through gradient reaction impregnation with sodium silicate, the inner layer has a high-modulus silica network, and the outer layer has a low-modulus sodium silicate network. + The outer layer material is activated, and good contact between the gel material and stainless steel fiber is achieved through the silica fume, fly ash and kaolin on the surface. The chemical bonding ability is improved due to the spraying modification of quartz sand, thus realizing the dual role of CSH and improving the mechanical properties of seawater sand concrete. Attached Figure Description

[0029] Figure 1 Test apparatus: (a) Flowability test; (b) Cubic compressive strength test; (c) Axial compressive strength test; (d) Bending loading diagram; (e) Bending test apparatus; Figure 2 Flowability results of UHPSSC samples; Figure 3 Compressive strength of UHPSSC specimens: (a) after 7 days of curing; (b) after 28 days of curing; (c) Strength growth index from 7 to 28 days; Figure 4Failure modes of axially compressed specimens: (a) SCM1-SSF1, (b) SCM2-SSF1, (c) SCM3-SSF1, (d) SCM4-SSF1, (e) SCM5-SSF1, (f) SCM1-SSF2, (g) SCM2-SSF2, (h) SCM3-SSF2, (i) SCM4-SSF2, (g) SCM5-SSF2, (k) SCM1-SSF3, (l) SCM2-SSF3, (m) SCM3-SSF3, (n) SCM4-SSF3, (o) SCM5-SSF3; Figure 5 Stress-strain curves of UHPSSC specimens: (a) SSF1, (b) SSF2, (c) SSF3; Figure 6 Axial compressive strength of UHPSSC specimen; Figure 7 Elastic modulus of UHPSSC specimen; Figure 8 Peak strain of the UHPSSC specimen; Figure 9 Poisson's ratio of the UHPSSC sample; Figure 10 (a) Flexural strength of UHPSSC specimen; (b) Strength growth index of UHPSSC specimen Figure 11 Brittleness coefficient of UHPSSC specimens. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1

[0031] An ultra-high performance seawater sand concrete is prepared using the following method, comprising the following steps: Based on cement 1087.55 kg / m³ 3 Silica fume 120.84 kg / m³ 3 0 kg / m³ of fly ash 3 Metakaolin 0 kg / m 3 Seawater 223.94 kg / m 3 Polycarboxylate superplasticizer 24.17 kg / m 3966.71 kg / m³ of sea sand 3 Stainless steel fiber 78.50 kg / m 3 Cement, silica fume, fly ash, and metakaolin powders were added to a mixer and dry-mixed for 2 minutes. Sea sand was then added and dry-mixed for 3 minutes. Seawater and water-reducing agent were pre-mixed evenly, and then the mixture was added to the mixer in two equal portions and mixed for 5 minutes each. Fiber was then added to the mixer in two equal portions and mixed for 5 minutes each. A portion of the freshly mixed slurry was then used for flowability testing. The remaining portion was placed into Ø100mm × 200mm cylindrical axial compressive strength specimen molds, 100mm × 100mm × 100mm cubic compressive strength specimen molds, and 100mm × 100mm × 400mm prism flexural strength specimen molds for mechanical experiments. The specimens were compacted by vibration, and then smoothed and covered with a film to retain moisture. The specimens were then placed in a standard curing room (curing conditions: temperature 20±2°C, relative humidity greater than 95%) for curing. The mold was removed 24 hours later and numbered SCM1-SSF1.

[0032] According to standard GB / T 2419-2005, the fluidity of freshly mixed cement mortar was determined using a cement mortar flow tester. The composite mortar was poured into the mold twice, and insertion and compaction were performed according to the specified procedure. The mold was then gently lifted vertically, and the instrument was turned on to complete 25 vibrations within 25 seconds. The diameters in two perpendicular directions were measured with calipers, and the average value was taken as the fluidity of the freshly mixed mortar.

[0033] The cubic compressive strength of the specimens was determined according to standard GB / T 50081-2019. The specimens were 100 mm in size and the loading rate was fixed at 1.2 MPa / s. Three specimens were tested for each concrete mix proportion.

[0034] Axial compression tests were conducted according to standard ASTM C39 / C39M-2018 using an Italian MATEST high-performance material testing machine. The specimens were Ø100mm × 200mm concrete cylinders, with three specimens per mix design. Before loading, two longitudinal strain gauges and one circumferential strain gauge were symmetrically placed on either side of the specimen's mid-section, and the cylindrical specimen was secured with a clamp. Two linear displacement gauges (LVTDs) were symmetrically placed on either side of the clamp, corresponding to the positions of the longitudinal strain gauges, to measure the average strain in the central region of the concrete column. During the test, a TDS-540 data acquisition system was used to collect load, displacement, and strain data. Displacement loading was employed, with a displacement control rate of 0.18mm / min. The test principle and apparatus are as follows: Figure 1 As shown.

[0035] The flexural strength of the specimens was determined according to the four-point loading test scheme of standard GB / T 50081-2019 using a DDL300 material testing machine. The specimen span was 300 mm, and the two loading points were located at two equal division points of the span. The loading method was as follows: Figure 1 As shown. The test adopted a load-controlled loading mechanism, with continuous and uniform loading during the test at a loading rate of 0.10 MPa / s. The specimen size for the flexural strength test was a 100 mm × 100 mm × 400 mm concrete prism, and the number of specimens for each concrete mix design test was 3. Example 2-15

[0036] The main difference between Examples 2-15 and Example 1 is the composition of the raw materials. For specific differences, please refer to Table 1 below.

[0037] Table 1 Example <![CDATA[Cement (kg / m 3 )]]> <![CDATA[Silica fume (kg / m 3 )]]> <![CDATA[Fly ash (kg / m 3 )]]> <![CDATA[Metakaolin (kg / m 3 )]]> <![CDATA[Seawater (kg / m 3 )]]> <![CDATA[Polycarboxylate superplasticizer (kg / m 3 )]]> <![CDATA[Seawater sand (kg / m 3 )]]> <![CDATA[Stainless steel fiber (kg / m 3 )]]> SCM2-SSF1 954.05 119.26 59.63 59.63 221.00 23.85 954.04 78.50 SCM3-SSF1 823.99 117.71 117.71 117.71 218.15 23.54 941.71 78.50 SCM4-SSF1 697.27 116.21 174.32 174.32 215.36 23.24 929.69 78.50 SCM5-SSF1 573.73 114.75 229.49 229.49 212.65 22.95 917.97 78.50 SCM1-SSF2 1076.56 119.62 0.00 0.00 221.67 23.92 956.94 157.00 SCM2-SSF2 944.41 118.05 59.03 59.03 218.77 23.61 944.41 157.00 SCM3-SSF2 815.67 116.52 116.52 116.52 215.94 23.30 932.20 157.00 SCM4-SSF2 690.22 115.04 172.56 172.56 213.19 23.01 920.30 157.00 SCM5-SSF2 567.94 113.59 227.17 227.17 210.50 22.72 908.70 157.00 SCM1-SSF3 1065.58 118.40 0.00 0.00 219.41 23.68 947.18 235.50 SCM2-SSF3 934.77 116.85 58.42 58.42 216.54 23.37 934.77 235.50 SCM3-SSF3 807.35 115.34 115.34 115.34 213.74 23.07 922.68 235.50 SCM4-SSF3 683.18 113.86 170.79 170.79 211.01 22.77 910.91 235.50 SCM5-SSF3 562.14 112.43 224.86 224.86 208.35 22.49 899.42 235.50 Example 16

[0038] Compared to Example 8, Example 16 further includes modification of stainless steel fibers: Before impregnation, the stainless steel fibers are first immersed in a 10% sodium hydroxide solution at 60°C for 10 minutes; then they are activated by acid pickling, with sulfuric acid selected as the acid and an acid concentration of 5%, and washed at room temperature for 1 minute; finally, they are washed with pure water and dried at room temperature.

[0039] The stainless steel fibers were sequentially impregnated with water glass of modulus 3.2, modulus 2.6, and modulus 2.0, respectively, after being washed with pure water and dried at room temperature. After each impregnation, the stainless steel fibers were centrifuged to control the thickness of the impregnation layer. The centrifugation speed was 2000 rpm and the centrifugation time was 20 seconds. After each impregnation, pre-curing was performed by holding the impregnated stainless steel fibers at 80°C for 1 minute.

[0040] Pre-cured stainless steel fibers were sprayed with quartz sand with an average particle size of 120μm.

[0041] All other experimental conditions were the same as those in Example 8.

[0042] Compared with Example 8, Example 16 showed a 6.3% increase in 7-day compressive strength and a 5.4% increase in 28-day compressive strength.

[0043] By impregnating sodium silicate with a gradient reaction, an inner layer with a high-modulus silica network and an outer layer with a low-modulus sodium silicate are formed. +The outer layer material is activated, and good contact between the gel material and stainless steel fiber is achieved through the silica fume, fly ash and kaolin on the surface. The chemical bonding ability is improved due to the spraying modification of quartz sand, thus realizing the dual role of CSH and improving the mechanical properties of seawater sand concrete. Example 17

[0044] Compared to Example 8, Example 17 further includes modification of the stainless steel fibers: Before impregnation, the stainless steel fibers are first immersed in a 10% sodium hydroxide solution at 60°C for 10 minutes; then they are activated by acid pickling, with sulfuric acid selected as the acid and an acid concentration of 5%, and washed at room temperature for 1 minute; finally, they are washed with pure water and dried at room temperature.

[0045] The stainless steel fibers were sequentially impregnated with water glass of modulus 3.2, washed with pure water, and dried at room temperature. After each impregnation, the stainless steel fibers were centrifuged to control the thickness of the impregnation layer. The centrifugation speed was 2000 rpm and the centrifugation time was 20 s. After each impregnation, pre-curing was performed by pre-curing the impregnated stainless steel fibers at 80°C for 1 min.

[0046] Pre-cured stainless steel fibers were sprayed with quartz sand with an average particle size of 120μm.

[0047] All other experimental conditions were the same as those in Example 8.

[0048] Compared with Example 8, Example 17 showed a 1.5% increase in 7-day compressive strength and a 0.6% increase in 28-day compressive strength.

[0049] Modification using only sodium silicate solution has a limited effect on improving the mechanical properties of concrete.

[0050] Table 2 Results of static axial compression performance parameters of UHPSSC Example Axial compressive strength (MPa) Elastic modulus (GPa) <![CDATA[Peak strain (10 -3 )]]> Poisson's ratio SCM1-SSF1 108.52 34.34 3.375 0.228 SCM2-SSF1 127.35 38.39 4.063 0.210 SCM3-SSF1 111.54 33.24 3.188 0.220 SCM4-SSF1 103.98 32.06 3.501 0.233 SCM5-SSF1 96.31 31.18 2.813 0.234 SCM1-SSF2 122.49 35.75 4.688 0.216 SCM2-SSF2 136.59 47.32 5.938 0.176 SCM3-SSF2 136.72 41.17 4.563 0.212 SCM4-SSF2 109.27 33.82 4.188 0.226 SCM5-SSF2 99.96 32.83 4.015 0.228 SCM1-SSF3 126.65 36.26 5.003 0.216 SCM2-SSF3 127.93 42.91 5.750 0.185 SCM3-SSF3 120.10 35.33 4.313 0.207 SCM4-SSF3 108.64 33.93 4.688 0.218 SCM5-SSF3 103.48 32.71 4.063 0.220 According to the instruction manual Figure 1-11 Analysis: from Figure 2 It was observed that as the stainless steel fiber content gradually increased, the fluidity of the fresh cement paste gradually decreased, indicating that the fiber incorporation significantly reduced the fluidity of UHPSSC. Cement pastes with various auxiliary cementitious materials exhibited the same trend: when the stainless steel fiber content increased from 1% to 2%, the fluidity of UHPSSC decreased by approximately 8.6%. However, when the fiber content continued to increase to 3%, the fluidity of UHPSSC decreased by approximately 9.4%. This is because the increased fiber content in the fresh cement paste leads to an increase in fiber clusters, which also increases the surface area in contact between the fibers and the cement paste. This requires more cement paste to coat the fiber surface, reducing the fluidity of the fresh cement paste.

[0051] As the amount of auxiliary cementitious materials used to replace cementitious materials gradually increases, the fluidity of freshly mixed cementitious slurry gradually increases. This is because most of these auxiliary cementitious materials are ultrafine spherical particles with low fineness, exhibiting good micro-aggregate and morphological effects. This releases free water between the slurry particles, thereby improving the fluidity of the freshly mixed cementitious slurry.

[0052] Cement pastes with various auxiliary cementitious materials all exhibited the same pattern: when the stainless steel fiber content increased from 1% to 2%, the fluidity of UHPSSC decreased by approximately 8.6%. However, when the fiber content continued to increase to 3%, the fluidity of UHPSSC decreased by approximately 9.4%.

[0053] from Figure 3 It can be observed that the compressive strength of UHPSSC generally increases with the gradual increase of stainless steel fiber content. This indicates that the increase in fiber content improves the compressive strength of UHPSSC. When the stainless steel fiber content increases from 1% to 2%, the compressive strength of each group of samples gradually increases. The increase in fiber content reduces the average spacing of fibers in the slurry, allowing more fibers to share the load on the stress-bearing failure surface.

[0054] With the gradual increase in the amount of auxiliary cementitious materials, the compressive strength values ​​of each sample group showed a trend of first increasing and then decreasing. Silica fume and metakaolin have high specific surface area and reactivity, which can fill and compact the UHPSSC matrix. They exert a nucleation effect, promote the hydration process of cement paste, and improve the compressive strength value of UHPSSC.

[0055] Silica fume, fly ash, and metakaolin all possess high pozzolanic activity, which can promote secondary hydration reactions in cement paste, generating more hydration products. This improves the structural density of UHPSSC paste, thereby increasing its later-stage compressive strength. As the age increased from 7 days to 28 days, at fiber content of 1% and 3%, the growth rate of compressive strength in each sample group gradually decreased with increasing SCM substitution. However, for the sample with 2% fiber content, the growth rate of compressive strength gradually increased. This indicates that at this fiber content, increasing SCM substitution promotes the improvement of later-stage compressive strength in UHPSSC.

[0056] See appendix Figure 4During compression, the cylindrical specimen underwent axial deformation as the load increased. Upon reaching the ultimate load, vertical cracks appeared from the middle of the specimen and gradually propagated towards both ends along the axial deformation direction. The crack width gradually increased, eventually forming a longitudinally penetrating main crack, leading to specimen failure. In terms of failure mode, the gradual increase in the substitution of different auxiliary cementitious materials led to an increase in the inclination angle of the diagonal cracks developing from both ends of the specimen, gradually transforming into vertical tensile cracks. When the fiber content in the specimen was 1%, a longitudinally penetrating main crack began to form on the surface after axial loading, with the crack width gradually increasing, and numerous microcracks were observed around the main crack. When the peak load was reached, the specimen surface began to peel off, accompanied by a crisp cracking sound; large concrete blocks were found peeling off the surface of the failed specimen. As the fiber content gradually increased, the failure mode of the specimen shifted to a more ductile failure. When the loading continued to approach the ultimate load, the waist of the specimen bulged slightly, and microcracks appeared from the middle, propagating towards both ends. At this point, a large number of fibers act as bridging links within the concrete matrix. As the crack extends longitudinally, the fibers provide lateral restraint. This allows the specimen to gradually maintain its integrity after compressive failure, exhibiting a "cracked but not broken" morphology, with the crack width confined to a relatively small range. When the fiber content is 3%, numerous fiber connections are clearly visible at the cracks in the failed specimens, and some specimens show bulging failure or crushing at one end.

[0057] See appendix Figure 5 As observed from the stress-strain curves, when the fiber content remains constant, the curvature of the stress-strain curves is similar and the slope is relatively large in the elastic stage. In this stage, the load is mainly borne by the UHPSSC matrix, and the incorporation of SCM can improve the load stress borne by the UHPSSC specimen in the elastic stage. As the load value gradually increases, the specimen enters the plastic development stage, the curve curvature decreases, and the rate of strain increase is greater than the rate of stress increase. At this point, the load begins to be borne jointly by the bond between the UHPSSC matrix and the fiber. The fiber plays a bridging role, increasing the ductility of the concrete. With the increase of fiber content, the descending segment of the stress-strain curve gradually flattens and lengthens, improving the toughness of the concrete.

[0058] When the stainless steel fiber content increased from 1% to 2%, the axial compressive strength of all UHPSSC sample groups showed an upward trend. The SCM1, SCM2, SCM3, SCM4, and SCM5 groups increased by 12.88%, 7.26%, 22.57%, 5.08%, and 3.79%, respectively. The increased fiber content within the UHPSSC matrix, along with the crack-resistant and bridging effects of the numerous fibers, promoted the increase in axial compressive strength. However, when the fiber content continued to increase from 2% to 3%, the axial compressive strength of the SCM2 and SCM3 experimental groups showed a downward trend, decreasing by 6.34% and 12.16%, respectively.

[0059] When the fiber content is constant, the axial compressive strength of each sample group shows a trend of first increasing and then decreasing with the increase of the amount of auxiliary cementitious material substitution. When an appropriate amount of SCM is added, all types of SCM are active materials with high pozzolanic activity, which can promote the formation of more hydration products in cement paste, improve the structural density of UHPSSC paste, and increase the compressive strength of UHPSSC. However, as the SCM content gradually increases, the "dilution effect" of SCM becomes dominant, and the amount of paste participating in hydration in UHPSSC paste decreases, leading to a decrease in the strength of UHPSSC.

[0060] The above provides a detailed description of an ultra-high performance seawater sand concrete and its preparation method provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combination method. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the invention. In particular, as long as there is no structural conflict, the features in the embodiments disclosed in the present invention can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A high-performance seawater sand concrete, comprising the following raw materials in parts by weight: cement 500-1100 kg / m³ 3 Silica fume 100-120 kg / m³ 3 Fly ash 50-300 kg / m³ 3 Metakaolin 50-300 kg / m 3 Seawater 200-240 kg / m 3 Polycarboxylate superplasticizer 10-30 kg / m 3 Sea sand 800-1100 kg / m 3 Stainless steel fiber 60-280 kg / m 3 ; Its features are: Silica fume, fly ash, and metakaolin are configured as auxiliary gelling materials, wherein the auxiliary gelling materials at least partially replace the raw material cement, and the amount of the raw material cement replaced is 10%-40% of the mass percentage of the cement, preferably 20%-30%. The stainless steel fiber content accounts for 1%-3% of the concrete volume, preferably 2%-3%.

2. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The specific surface area of ​​the silica fume is not less than 15000 m². 2 / kg, preferably with the following chemical composition: SiO2 94.85%, CaO 0.85%, Al2O3 0.97%, Fe2O3 0.71%, SO3 0.53%, and loss on ignition 2.1%.

3. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The specific surface area of ​​the fly ash is not less than 450 m². 2 / kg, preferably with the following chemical composition: SiO2 49.26%, CaO 6.53%, Al2O3 30.14%, Fe2O3 5.16%, SO3 2.16%, and loss on ignition 3.34%.

4. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The specific surface area of ​​the metakaolin is not less than 12000 m². 2 / kg, preferably with the following chemical composition: SiO2 53.5%, CaO 0.15%, Al2O3 42.00%, Fe2O3 1.8%, SO3 0.65%, and loss on ignition 3.45%.

5. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The seawater contains 18-20 g / L chloride ions, 10-12 g / L sodium ions, 2-3 g / L sulfate ions, 1-2 g / L magnesium ions, 0.2-0.5 g / L calcium ions, and 0.2-0.5 g / L potassium ions.

6. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The apparent density of the sea sand is 2600-2700 kg / m³. 3 The moisture content is not higher than 1.6%, the mud content is not higher than 0.78%, the particle size is not greater than 5mm, and the fineness modulus is 2.5-2.

6.

7. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The stainless steel fibers are 13cm in length and have an apparent density of 7850 kg / m³. 3 Tensile strength 2200MPa, elastic modulus 206Gpa, elongation ratio 1.

8.

8. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The water-reducing agent has a water reduction rate of 47%, a solid content of 25.2%, an alkali content of 1.8%, and a chloride ion content not exceeding 0.03%.

9. The ultra-high performance seawater sand concrete according to claim 1, characterized in that, The water-cement ratio is 0.20, the sand-binder ratio is 0.80, and the dosage of polycarboxylate superplasticizer is 2-3% of the total mass of the gel material.

10. The ultra-high performance seawater sand concrete according to any one of claims 1-9, characterized in that, The liquidity level in the liquidity test is no less than 230mm.

11. The ultra-high performance seawater sand concrete according to any one of claims 1-9, characterized in that, The ultra-high performance seawater sand concrete has a 7-day compressive strength of 89.51-132.9 MPa and a 28-day compressive strength of 95.07-155.82 MPa.

12. A method for preparing ultra-high performance seawater sand concrete according to any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1): Add cement, silica fume, fly ash and metakaolin powder to the mixer according to the raw material percentage and dry mix for 2-5 minutes. Then add sea sand to the mixer and dry mix for 3-10 minutes. Step 2) Pre-stir the seawater and polycarboxylate superplasticizer to obtain a mixture, and then add the mixture into the mixer in two equal portions and stir for 5-10 minutes each time. Step 3) Divide the fiber into two equal portions and add them into the mixer. Mix for 5-10 minutes each time.

13. An application of ultra-high performance seawater sand concrete, characterized in that, The ultra-high performance seawater sand concrete as described in any one of claims 1 to 11 is used in marine engineering environment construction applications.

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