A kind of concrete with C70 strength grade and preparation method thereof

Abstract

The present invention provides a C70 strength grade concrete and a preparation method thereof, belonging to the technical field of concrete and resource recycling. The C70 strength grade concrete provided by the present invention is prepared from raw materials including the following mass percentages: 18-19.56% cementitious material, 74-75% aggregate, 0.07-0.1% water reducer and the balance water; the cementitious material includes cement, stainless steel slag and mineral powder; the mass of the stainless steel slag accounts for 20-30% of the total mass of the cementitious material; the water-cement ratio of the C70 strength grade concrete is 0.3-0.35. The C70 strength grade concrete provided by the present invention not only has high strength, but also has ultra-high durability and stability, and can also efficiently realize the resource recycling of stainless steel slag.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete and resource recycling, and in particular to concrete with a C70 strength grade and a preparation method thereof. Background Art

[0002] The main components of stainless steel slag include CaO, SiO2, MgO, Al2O3, and Fe2O3, along with some heavy metals such as Cr, Pb, and Cu. Chromium is primarily found in calcium chromite (CaCrO4), metallic phases, and chromium spinel. The chromium in calcium chromite is hexavalent chromium, which is highly toxic, corrosive to plants and animals, and harmful to the ecological environment. Furthermore, when stainless steel slag accumulates excessively, hexavalent chromium can seep into the ground, causing soil and water pollution. Long-term human exposure to hexavalent chromium can be harmful to the skin, digestive tract, lungs, and other areas, and in severe cases, can be carcinogenic. Therefore, the harmless treatment of stainless steel slag is a top priority for resource recycling.

[0003] Currently, the chromium in solidified stainless steel slag is usually stabilized using cement, thermoplastic materials, lime, etc., which confines the hexavalent chromium within the matrix and prevents it from dissolving. In actual applications, cement solidification is the main method. After cement solidification, the toxic heavy metals are confined in the cement matrix and are not easily dissolved, which can better achieve the purpose of detoxification. In actual cement solidification, stainless steel slag mainly includes EAF slag and AOD slag. The two differ in composition and mineral phase, but their mineral phase is mainly dicalcium silicate (C2S), which has very low hydration activity. When used as a concrete admixture, it is difficult to make the concrete obtain a high compressive strength. Invention patent CN115448659A discloses a solid waste stainless steel slag recycled concrete based on the coupling effect of early carbonization and early dry-wet cycle. Although stainless steel slag is added together with cement, mineral powder, fly ash and titanium dioxide powder as a cementing material, the 28d strength of the concrete can reach up to 80.6MPa. However, the mass proportion of stainless steel slag in the cementing material is only 7.04%, which does not achieve efficient utilization of stainless steel slag.

[0004] Therefore, providing a concrete that efficiently utilizes stainless steel slag as a cementitious material while enabling the concrete to have a higher strength grade has become a difficult problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The present invention aims to provide a C70 strength grade concrete and a method for preparing the same. The C70 strength grade concrete provided by the present invention has a high utilization rate of stainless steel slag and can reach a strength grade of C70, thereby not only having high workability but also enabling efficient reuse of stainless steel slag resources.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a C70 strength grade concrete, which is prepared from raw materials including the following mass percentages: 18-19.56% of cementitious material, 74-75% of aggregate, 0.07-0.1% of water reducing agent and the balance of water;

[0008] The cementitious material comprises cement, stainless steel slag and mineral powder; the mass of the stainless steel slag accounts for 20-30% of the total mass of the cementitious material;

[0009] The water-cement ratio of the C70 strength grade concrete is 0.3 to 0.35.

[0010] Preferably, the stainless steel slag comprises the following components in mass percentage: 28-30% SiO2, 27-29% CaO, 23.5-25% Al2O3, 11.5-13% MgO, 1.5-2% Fe2O3, 1.5-2% SO3, 0.5-1% Na2O and 0.1-0.5% K2O.

[0011] Preferably, the particle size distribution of the stainless steel slag is: D(0.1)≤4.0 μm, D(0.5)≤25.0 μm, D(0.9)≤90.0 μm.

[0012] Preferably, the mass of the cement accounts for 50-60% of the total mass of the cementitious material.

[0013] Preferably, the cement includes PO42.5 cement, PI-type silicate cement or PII-type silicate cement; the PO42.5 cement, PI-type silicate cement or PII-type silicate cement independently includes cement clinker with a mass percentage of ≥80%; the cement clinker includes 30-50% by mass of high-activity dicalcium silicate; the activity index of the high-activity dicalcium silicate is: when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa.

[0014] Preferably, the mass of the mineral powder accounts for 10-20% of the total mass of the cementitious material.

[0015] Preferably, the particle size distribution of the mineral powder is: D(0.1)≤3.0 μm, D(0.5)≤22.0 μm, D(0.9)≤100 μm.

[0016] Preferably, the cementitious material further comprises fly ash; the mass of the fly ash accounts for 0 to 10% of the total mass of the cementitious material.

[0017] Preferably, the particle size distribution of the fly ash is: D(0.1)≤4.1 μm, D(0.5)≤25.0 μm, D(0.9)≤75.0 μm.

[0018] The present invention also provides a method for preparing concrete with a strength grade of C70 as described in the above technical solution, comprising: mixing a cementitious material, an aggregate, a water reducer and water to obtain concrete with a strength grade of C70.

[0019] The present invention provides a C70 strength grade concrete, prepared from the following raw materials by weight: 18-19.56% cementitious material, 74-75% aggregate, 0.07-0.1% water reducer, and the balance water; the cementitious material includes cement, stainless steel slag, and mineral powder; the mass of the stainless steel slag accounts for 20-30% of the total mass of the cementitious material; and the water-cement ratio of the C70 strength grade concrete is 0.3-0.35. The present invention adds stainless steel slag, which, together with mineral slag, acts as an auxiliary cementitious material to stimulate higher hydration activity, enhance the early hydration reaction rate, and generate hydration products such as CSH gel, thereby partially replacing cement as a cementitious material, achieving higher utilization rate and imparting higher compressive strength to the concrete. Furthermore, by controlling the water-cement ratio and the amount of water reducer, the present invention ensures that the cementitious material is fully hydrated while maintaining better fluidity of the concrete, resulting in a higher density after hardening and drying, thereby imparting higher compressive strength and durability to the concrete.

[0020] The results of the examples show that the 3d strength of the C70 strength grade concrete provided by the present invention is between 30 and 38 MPa, the 7d strength is between 53 and 64 MPa, and the 28d strength is between 71 and 83 MPa, all of which meet the C70 strength grade requirements. At the same time, the later strength maintains a strong growth, not only does the 91d strength all meet the C80 strength grade requirements, but the 91d strength reaches a maximum of 95 MPa. The electric flux of the C70 strength grade concrete is less than 321 coulombs, which can be ignored; the chloride ion permeability coefficient is less than 2.14×10 -12 m 2 / s, meeting the 100-year chloride ion penetration resistance durability design requirements specified in GB / T50476-2019 "Concrete Durability Design Standard"; the carbonization depth is no more than 2mm, which meets the protection effect on steel bars; the autoclave stability test results show that the test blocks are intact and there is no cracking. In addition, the proportion of stainless steel slag added to the C70 strength grade concrete provided by the present invention in the cementitious material can reach 20-30%, which is significantly higher than the amount of stainless steel slag used as a cementitious material in the prior art. Therefore, the concrete of the C70 strength grade concrete not only has high strength, but also has ultra-high durability and stability, and can also efficiently realize the resource recycling of stainless steel slag. DETAILED DESCRIPTION

[0021] The present invention provides concrete with a strength grade of C70, which is prepared from raw materials including the following percentages by mass: 18-19.56% of a cementitious material, 74-75% of an aggregate, 0.07-0.1% of a water reducer, and the balance being water; the cementitious material includes cement, stainless steel slag, and mineral powder; the mass of the stainless steel slag accounts for 20-30% of the total mass of the cementitious material; and the water-cement ratio of the concrete with a strength grade of C70 is 0.3-0.35.

[0022] By mass percentage, the raw materials for preparing the C70 strength grade concrete of the present invention include 18 to 19.56% cementitious material, preferably 18.5 to 19.56%, and more preferably 19 to 19.56%. By controlling the cementitious material content within the above range, the present invention can fully bond the aggregate with the cementitious material, resulting in a higher density of the concrete, thereby achieving higher strength and durability.

[0023] In the present invention, the cementitious materials include cement, stainless steel slag and mineral powder. The present invention uses stainless steel slag and mineral slag as auxiliary cementitious materials for cement, which not only can make concrete have higher compressive strength and durability, but also can replace part of the cement, thereby improving resource recycling rate.

[0024] In the present invention, the mass of the cement preferably accounts for 50-60% of the total mass of the cementitious material. By using cement as the main cementitious material and controlling its amount within the above range, the present invention can ensure that the concrete has higher compressive strength and durability.

[0025] In the present invention, the cement preferably includes PO42.5 cement, PI-type Portland cement or PII-type Portland cement; the PO42.5 cement, PI-type Portland cement or PII-type Portland cement independently preferably includes cement clinker with a mass percentage of ≥80%; the cement clinker preferably includes 40-50% by mass of high-activity dicalcium silicate, more preferably includes 35-45% by mass of high-activity dicalcium silicate; the activity index of the high-activity dicalcium silicate is preferably: when the Portland cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the Portland cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa. In the present invention, the 3d compressive strength of the cement is preferably ≥18MPa, and the 28d compressive strength of the cement is preferably ≥65MPa. The present invention selects the above-mentioned type of cement and can utilize the highly active dicalcium silicate in the cement clinker to make the cement have higher hydration activity and higher strength, thereby ensuring a higher utilization rate of the stainless steel slag and making the concrete have higher strength and durability.

[0026] In the present invention, the mass of the stainless steel slag accounts for 20-30%, preferably 22-28%, of the total mass of the cementitious material. By using stainless steel slag as a cementitious material and controlling its amount within the aforementioned range, the present invention, together with slag, acts as an auxiliary cementitious material, thereby stimulating higher hydration activity, enhancing the early hydration reaction rate, and generating hydration products such as CSH gel. This allows the slag to partially replace cement as a cementitious material, achieving higher utilization rates while also imparting higher compressive strength and durability to the concrete.

[0027] In the present invention, the particle size distribution of the stainless steel slag is preferably: D(0.1) ≤ 4.0 μm, D(0.5) ≤ 25.0 μm, and D(0.9) ≤ 90 μm. By controlling the particle size of the stainless steel slag within this range, the present invention can achieve a high specific surface area, allowing sufficient contact with the mineral powder and cement to undergo hydration reactions, thereby effectively improving the strength and durability of concrete.

[0028] In the present invention, the stainless steel slag preferably comprises the following components by mass percentage: 28-30% SiO2, 27-29% CaO, 23.5-25% Al2O3, 11.5-13% MgO, 1.5-2% Fe2O3, 1.5-2% SO3, 0.5-1% Na2O, and 0.1-0.5% K2O. By controlling the composition and content of the stainless steel slag within the above ranges, the present invention can achieve higher hydration activity, improve utilization, and further enhance the strength and durability of concrete.

[0029] In the present invention, the mass of the mineral powder preferably accounts for 10-20% of the total mass of the cementitious material. By controlling the amount of the mineral powder within the above range, the present invention can better cooperate with the stainless steel slag to stimulate its hydration activity, thereby improving the strength and durability of the concrete.

[0030] In the present invention, the particle size distribution of the mineral powder is preferably: D(0.1) ≤ 3.0 μm, D(0.5) ≤ 221.0 μm, and D(0.9) ≤ 100 μm. By controlling the particle size of the mineral powder within this range, the present invention can provide it with a higher specific surface area, allowing for sufficient contact with stainless steel slag and cement, resulting in a higher hydration reaction rate, thereby achieving higher strength and durability in the concrete.

[0031] In the present invention, the cementitious material preferably further comprises fly ash. In addition to the cementitious material comprising cement, stainless steel slag and slag, the present invention can further stimulate the hydration activity of the stainless steel slag and effectively improve the strength and durability of the concrete.

[0032] In the present invention, the fly ash preferably accounts for 0-10% of the total mass of the cementitious material, and more preferably 1-8%. By controlling the amount of fly ash within the above range, the present invention can better cooperate with stainless steel slag and mineral powder to stimulate higher hydration activity, effectively improving the strength and durability of concrete.

[0033] In the present invention, the fly ash preferably has a particle size distribution of: D(0.1) ≤ 4.1 μm, D(0.5) ≤ 25.0 μm, and D(0.9) ≤ 75.0 μm. By controlling the fly ash particle size within this range, the present invention can provide it with a higher specific surface area, allowing for sufficient contact with stainless steel slag, mineral powder, and cement, thereby promoting a better hydration reaction and further improving the strength and durability of concrete.

[0034] Calculated by mass percentage, the raw materials for preparing the C70 strength grade concrete of the present invention include 74-75% aggregate, preferably 74-74.8%, and more preferably 74-74.5%.

[0035] In the present invention, the aggregate preferably includes river sand and gravel; the mass of the river sand preferably accounts for 42.78-44% of the total mass of the aggregate; the mass of the gravel preferably accounts for 56-57.22% of the total mass of the aggregate. By controlling the amount of river sand and gravel in the aggregate within the above range, the present invention can better exert their coordination effect, improve the density of the concrete, and thus make the concrete have higher strength and durability.

[0036] In the present invention, the river sand is preferably medium sand from Zone 2; the fineness modulus of the river sand is preferably 2.4 to 2.8. The present invention has no particular requirements for the source of the river sand; commercially available materials known in the art can be used. By selecting the aforementioned river sand, the present invention ensures sufficient contact with the gravel, improving the density of the concrete, thereby imparting greater strength and durability to the concrete.

[0037] In the present invention, the stone particle size is preferably ≤25 mm; the stone gradation is preferably continuous gradation. The present invention has no particular requirements for the source of the stone; commercially available materials known in the art can be used. By controlling the stone particle size within the above range, the present invention ensures sufficient contact with the river sand, improving the density of the concrete, thereby imparting higher strength and durability to the concrete.

[0038] The raw materials for preparing the C70 strength grade concrete of the present invention include, by mass percentage, 0.07-0.1%, preferably 0.08-0.09%, of a water reducer. By adding a water reducer and controlling its amount within the above range, the present invention can ensure high fluidity of the concrete while reducing water consumption, further facilitating the setting of the concrete and reducing cracks caused by water evaporation, thereby achieving high early strength and ensuring high durability of the concrete.

[0039] In the present invention, the water reducer preferably comprises a polyester polycarboxylic acid water reducer. The present invention has no special requirements on the source of the water reducer, and commercially available materials well known in the art can be used.

[0040] Calculated by mass percentage, the raw materials for preparing the C70 strength grade concrete of the present invention include the balance water.

[0041] The present invention has no special requirements on the source of the water, and concrete mixing water well known in the art can be used.

[0042] In the present invention, the water-binder ratio of the C70 strength grade concrete is 0.3 to 0.35, preferably 0.31 to 0.34, and more preferably 0.32 to 0.33. By controlling the water-binder ratio within the above range, the present invention ensures that the cementitious material and water undergo a sufficient hydration reaction while maintaining the workability of the concrete. Furthermore, the volatilization of water during the early hardening of the concrete prevents the formation of cracks, thereby providing the concrete with higher strength and durability.

[0043] The stainless steel slag added to the C70 strength grade concrete provided by the present invention has a high proportion in the cementitious material, which not only can efficiently realize the resource recycling of the stainless steel slag, but also has high strength and ultra-high durability and stability.

[0044] The present invention also provides a method for preparing C70 strength grade concrete described in the above technical solution, comprising: mixing a cementitious material, an aggregate, a water reducer and water to obtain C70 strength grade concrete.

[0045] The present invention has no special requirements for the mixing operation, and it is sufficient to use a concrete mixing method well known in the art to ensure that the concrete is mixed evenly.

[0046] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] Example 1

[0048] A C70 strength grade concrete is prepared from the following raw materials in percentage by weight: 19.55% cementitious material, 74.06% aggregate, 0.087% water reducer and the balance water;

[0049] The cementitious materials are cement, stainless steel slag, mineral powder and fly ash; wherein the cement is PI type Portland cement (wherein the mass percentage of cement clinker is 97.5%, the mass percentage of high-activity dicalcium silicate in the cement clinker is 45%, and the activity index of the high-activity dicalcium silicate is: when the Portland cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the Portland cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa); the 3d compressive strength of the cement is 20MPa, and the 28d compressive strength is 68MPa. The mass of the cement accounts for 60% of the total mass of the cementitious materials; the mass of the stainless steel slag accounts for 20% of the total mass of the cementitious materials. The particle size of the stainless steel slag is D(0.1)=2.760μm, D(0.5)=17.414μm, and D(0.9)=77.342μm. The chemical composition and content of the stainless steel slag are shown in Table 1, and the results of the strength and activity index testing of the stainless steel slag are shown in Table 2. The mass of the mineral powder accounts for 10% of the total mass of the cementitious material. The particle size of the mineral powder is D(0.1)=1.972μm, D(0.5)=18.290μm, and D(0.9)=87.908μm. The mass of the fly ash accounts for 10% of the total mass of the cementitious material. The particle size of the fly ash is D(0.1)=3.095μm, D(0.5)=19.604μm, and D(0.9)=66.552μm.

[0050] The water-cement ratio of the C70 strength grade concrete is 0.32.

[0051] The aggregates are river sand and gravel; the mass of the river sand accounts for 43.34% of the total mass of the aggregate, and the river sand is selected from the medium sand in the second zone, and its fineness modulus is 2.60; the mass of the gravel accounts for 56.66% of the total mass of the aggregate, and the particle size of the gravel is ≤20mm, and is continuously graded.

[0052] The water reducer is selected from polyester polycarboxylic acid water reducer.

[0053] The C70 strength grade concrete is prepared by mixing cementitious materials, aggregate, water-reducing agent, and water in a forced mixer for 3 minutes to obtain C70 strength grade concrete. The concrete is then poured into a 10×10×10 cm test mold and cured at room temperature of 20±0.5°C for 24 hours before removal. The mold is then removed and performance tested for 3, 7, 28, 56, and 91 days under standard conditions (temperature 20±0.5°C, relative humidity above 95%).

[0054] Example 2

[0055] A C70 strength grade concrete is prepared from the following raw materials in percentage by weight: 19.56% cementitious material, 74.04% aggregate, 0.087% water reducer and the balance water;

[0056] The cementitious materials are cement, stainless steel slag, mineral powder and fly ash; wherein the cement is PII type silicate cement (wherein the mass percentage of cement clinker is 92.5%, the mass percentage of high-activity dicalcium silicate in the cement clinker is 45%, and the activity index of the high-activity dicalcium silicate is: when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa); the 3d compressive strength of the cement is 23MPa, and the 28d compressive strength is 65MPa. The mass of the cement accounts for 55% of the total mass of the cementitious materials; the mass of the stainless steel slag accounts for 20% of the total mass of the cementitious materials, and the stainless steel slag accounts for 20% of the total mass of the cementitious materials. The particle size distribution of the slag is D(0.1)=1.360μm, D(0.5)=14.430μm, and D(0.9)=72.354μm. The chemical composition and content of the stainless steel slag are shown in Table 1, and the results of the strength and activity index testing of the stainless steel slag are shown in Table 2. The mass of the mineral powder accounts for 15% of the total mass of the cementitious material, and the particle size distribution of the mineral powder is D(0.1)=1.972μm, D(0.5)=18.290μm, and D(0.9)=87.908μm. The mass of the fly ash accounts for 10% of the total mass of the cementitious material, and the particle size distribution of the fly ash is D(0.1)=2.192μm, D(0.5)=17.612μm, and D(0.9)=61.541μm.

[0057] The water-cement ratio of the C70 strength grade concrete is 0.32.

[0058] The aggregates are river sand and gravel; the mass of the river sand accounts for 43.28% of the total mass of the aggregate, the particle size of the river sand adopts zone two medium sand, and its fineness modulus is 2.70; the mass of the gravel accounts for 56.72% of the total mass of the aggregate, the gravel is ≤25mm, and is continuously graded.

[0059] The water reducer is selected from polyester polycarboxylic acid water reducer.

[0060] The preparation method and curing method of the C70 strength grade concrete are the same as those in Example 1.

[0061] Example 3

[0062] A C70 strength grade concrete is prepared from the following raw materials in percentage by weight: 19.58% cementitious material, 74.02% aggregate, 0.087% water reducer and the balance water;

[0063] The cementitious materials are cement, stainless steel slag, mineral powder and fly ash; wherein the cement is PO42.5 cement (wherein the mass percentage of cement clinker is 80%, the mass percentage of high-activity dicalcium silicate in the cement clinker is 45%, and the activity index of the high-activity dicalcium silicate is: when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa); the mass of the cement accounts for 50% of the total mass of the cementitious materials; the mass of the stainless steel slag accounts for 20% of the total mass of the cementitious materials, and the particle size distribution of the stainless steel slag is D(0.1)=2.7 60μm, D(0.5)=17.414μm, D(0.9)=77.342μm, the chemical composition and content of the stainless steel slag are shown in Table 1, and the results of the strength and activity index detection of the stainless steel slag are shown in Table 2; the mass of the mineral powder accounts for 20% of the total mass of the cementitious material, and the particle size distribution of the mineral powder is D(0.1)=1.972μm, D(0.5)=18.290μm, D(0.9)=87.908μm; the mass of the fly ash accounts for 10% of the total mass of the cementitious material, and the particle size distribution of the fly ash is D(0.1)=4.060μm, D(0.5)=21.655μm, D(0.9)=68.576μm.

[0064] The water-cement ratio of the C70 strength grade concrete is 0.32.

[0065] The aggregates are river sand and gravel; the mass of the river sand accounts for 43.37% of the total mass of the aggregate, and the river sand adopts zone two medium sand with a fineness modulus of 2.65; the mass of the gravel accounts for 56.63% of the total mass of the aggregate, and the particle size of the gravel is ≤20mm, with continuous grading.

[0066] The water reducer is selected from polyester polycarboxylic acid water reducer.

[0067] The preparation method of the C70 strength grade concrete is the same as that in Example 1.

[0068] Example 4

[0069] A C70 strength grade concrete is prepared from the following raw materials in percentage by weight: 19.41% cementitious material, 74.16% aggregate, 0.086% water reducer and the balance water;

[0070] The cementitious material is cement, stainless steel slag and mineral powder; wherein the cement is PO42.5 type cement (wherein the mass percentage of cement clinker is 80%, the mass percentage of high-activity dicalcium silicate in the cement clinker is 45%, and the activity index of the high-activity dicalcium silicate is: when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa); the 3d compressive strength of the cement is 25MPa, and the 28d compressive strength is 60MPa, and the mass of the cement accounts for 10% of the cementitious material. The mass of the stainless steel slag accounts for 60% of the total mass of the cementitious material; the mass of the stainless steel slag accounts for 30% of the total mass of the cementitious material, and the particle size distribution of the stainless steel slag is D(0.1)=1.873μm, D(0.5)=15.440μm, D(0.9)=72.552μm. The chemical composition and content of the stainless steel slag are shown in Table 1, and the results of the strength and activity index testing of the stainless steel slag are shown in Table 2; the mass of the mineral powder accounts for 10% of the total mass of the cementitious material, and the particle size distribution of the mineral powder is D(0.1)=1.642μm, D(0.5)=16.880μm, and D(0.9)=81.654μm.

[0071] The water-cement ratio of the C70 strength grade concrete is 0.33.

[0072] The aggregates are river sand and gravel; the mass of the river sand accounts for 42.91% of the total mass of the aggregate, and the river sand is selected from the medium sand in the second zone, and its fineness modulus is 2.60; the mass of the gravel accounts for 57.09% of the total mass of the aggregate, and the particle size of the gravel is ≤25mm, and is continuously graded.

[0073] The water reducer is selected from polyether polycarboxylic acid water reducers.

[0074] The preparation method and curing method of the C70 strength grade concrete are the same as those in Example 1.

[0075] Example 5

[0076] A C70 strength grade concrete is prepared from the following raw materials in percentage by weight: 19.43% cementitious material, 74.14% aggregate, 0.086% water reducer and the balance water;

[0077] The cementitious material is cement, stainless steel slag and mineral powder; wherein the cement is PII type silicate cement (wherein the mass percentage of cement clinker is 92.5%, the mass percentage of high-activity dicalcium silicate in the cement clinker is 45%, and the activity index of the high-activity dicalcium silicate is that when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa and the 28d compressive strength is ≥60MPa); the 3d compressive strength of the cement is 23MPa, the 28d compressive strength is 65MPa, and the mass of the cement accounts for 1.5% of the total mass of the cement clinker. The mass of the stainless steel slag accounts for 55% of the total mass of the cementitious material; the mass of the stainless steel slag accounts for 30% of the total mass of the cementitious material, the particle size distribution of the stainless steel slag is D(0.1)=2.964μm, D(0.5)=19.486μm, D(0.9)=87.390μm, the chemical composition and content of the stainless steel slag are shown in Table 1, and the results of the strength and activity index detection of the stainless steel slag are shown in Table 2; the mass of the mineral powder accounts for 70% of the total mass of the cementitious material, and the particle size distribution of the mineral powder is D(0.1)=2.374μm, D(0.5)=20.560μm, D(0.9)=91.918μm.

[0078] The water-cement ratio of the C70 strength grade concrete is 0.33.

[0079] The aggregates are river sand and gravel; the mass of the river sand accounts for 42.85% of the total mass of the aggregate, and the river sand is selected from the medium sand in the second zone, and its fineness modulus is 2.55; the mass of the gravel accounts for 57.15% of the total mass of the aggregate, and the particle size of the gravel is ≤20mm, and is continuously graded.

[0080] The water reducer is selected from polyether polycarboxylic acid water reducers.

[0081] The preparation method and curing method of the C70 strength grade concrete are the same as those in Example 1.

[0082] Example 6

[0083] A C70 strength grade concrete is prepared from the following raw materials in percentage by weight: 19.44% cementitious material, 74.12% aggregate, 0.086% water reducer and the balance water;

[0084] The cementitious material is cement, stainless steel slag and mineral powder; wherein the cement is PI type silicate cement (wherein the mass percentage of cement clinker is 97.5%, the mass percentage of high-activity dicalcium silicate in the cement clinker is 45%, and the activity index of the high-activity dicalcium silicate is: when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa); the 3d compressive strength of the cement is 22MPa, and the 28d compressive strength is 70MPa), and the mass of the cement accounts for 10% of the cement. The mass of the stainless steel slag accounts for 55% of the total mass of the cementitious material; the mass of the stainless steel slag accounts for 30% of the total mass of the cementitious material, the particle size distribution of the stainless steel slag is D(0.1)=3.980μm, D(0.5)=19.498μm, D(0.9)=79.587μm, the chemical composition and content of the stainless steel slag are shown in Table 1, and the results of the strength and activity index detection of the stainless steel slag are shown in Table 2; the mass of the mineral powder accounts for 70% of the total mass of the cementitious material, and the particle size of the mineral powder is D(0.1)=2.954μm, D(0.5)=21.300μm, D(0.9)=98.131μm.

[0085] The water-cement ratio of the C70 strength grade concrete is 0.33.

[0086] The aggregates are river sand and gravel; the mass of the river sand accounts for 42.78% of the total mass of the aggregate, and the river sand adopts zone two medium sand with a fineness modulus of 2.70; the mass of the gravel accounts for 57.22% of the total mass of the aggregate, and the particle size of the gravel is ≤20mm, with continuous grading.

[0087] The water reducer is selected from polyether polycarboxylic acid water reducers.

[0088] The preparation method and curing method of the C70 strength grade concrete are the same as those in Example 1.

[0089] The stainless steel slag used in Examples 1 to 6 was selected from the same source and had the same composition and properties. The composition and content are shown in Table 1. The strength was tested and the hydration activity of the stainless steel was evaluated according to GB / T 20491-2017 "Steel Slag Powder for Cement and Concrete". The strength and activity index test results are shown in Table 2.

[0090] Table 1 Chemical composition and content of stainless steel slag in Examples 1 to 6 (mass percentage / %)

[0091] type CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> <![CDATA[Na2O]]> <![CDATA[K2O]]> stainless steel slag 27.88 28.68 23.92 1.74 11.99 1.73 0.71 0.31

[0092] Table 2 Activity index test results of stainless steel slag in Examples 1 to 6

[0093]

[0094] Note: The benchmark cement mentioned above is a special cement for testing activity indicators.

[0095] Concrete performance testing:

[0096] 1. Compressive strength test: The compressive strength of the concrete prepared in Examples 1 to 6 after curing for 3 days, 7 days, 28 days, 56 days, and 91 days was tested in accordance with GBT50081-2019 "Test methods for physical and mechanical properties of concrete". The test results are shown in Table 3.

[0097] Test results of compressive strength of concrete prepared in Examples 1 to 6 at 3d, 7d, 28d, 56d and 91d

[0098]

[0099] As can be seen from Table 3, the 3d strength of the C70 strength grade concrete provided by Examples 1 to 6 of the present invention is between 30 and 38 MPa, the 7d strength is between 53 and 64 MPa, and the 28d strength is between 71 and 83 MPa, all of which meet the C70 strength grade requirements. At the same time, the later strength maintains strong growth, and not only does the 91d strength all meet the C80 strength grade requirements, but the 91d strength reaches a maximum of 95 MPa.

[0100] 2. Durability Test: The durability of the C70 strength grade concrete provided in Examples 1 to 6 was evaluated based on the chloride ion permeability coefficient, electrical flux, sulfate corrosion resistance, carbonation resistance, and autoclave stability according to GBT50082-2009 "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete". The evaluation results are shown in Table 4.

[0101]

[0102]

[0103] It can be seen from Table 4 that the electric flux of the C70 strength grade concrete provided by Examples 1 to 6 of the present invention is less than 321 coulombs, which can be ignored; the chloride ion permeability coefficient is less than 2.14×10 -12 m 2 / s, meeting the 100-year durability design requirements for chloride ion penetration resistance specified in GB / T50476-2019 "Concrete Durability Design Standard"; the carbonization depth is no more than 2mm, which meets the protection effect for steel bars; the autoclave soundness test results show that the test blocks are intact and have no cracks.

[0104] In addition, the proportion of stainless steel slag added to the C70 strength grade concrete provided by the present invention in the cementitious material can reach 20-30%, which is significantly higher than the amount of stainless steel slag used as a cementitious material in the prior art.

[0105] In summary, concrete with a strength grade of C70 not only has high strength, but also has ultra-high durability and stability, and can also efficiently realize the resource recycling of stainless steel slag.

[0106] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A concrete with a strength grade of C70, characterized in that: It is prepared from the following raw materials in the following mass percentages: Cementitious materials 18~19.56%, aggregate 74~75%, water reducer 0.07~0.1% and balance water; The cementitious material includes cement, stainless steel slag and mineral powder; the mass of the stainless steel slag accounts for 20-30% of the total mass of the cementitious material; The water-binder ratio of the C70 strength grade concrete is 0.3-0.35; The stainless steel slag comprises the following components in percentage by mass: 28-30% SiO2, 27-29% CaO, 23.5-25% Al2O3, 11.5-13% MgO, 1.5-2% Fe2O3, 1.5-2% SO3, 0.5-1% Na2O and 0.1-0.5% K2O; The mass of the cement accounts for 50-60% of the total mass of the cementitious material; The cementitious material further comprises fly ash; the mass of the fly ash accounts for 0-10% of the total mass of the cementitious material.

2. The concrete according to claim 1, characterized in that The particle size distribution of the stainless steel slag is: D(0.1)≤4.0μm, D(0.5)≤25.0μm, and D(0.9)≤90.0μm.

3. The concrete according to claim 1, wherein The cement includes PO42.5 cement, PI-type silicate cement or PII-type silicate cement; the PO42.5 cement, PI-type silicate cement or PII-type silicate cement independently includes cement clinker with a mass percentage of ≥80%; the cement clinker includes 40-50% by mass of high-activity dicalcium silicate; the activity index of the high-activity dicalcium silicate is: when the silicate cement clinker contains 75±5% by mass of high-activity dicalcium silicate, the 3d compressive strength of the silicate cement clinker is ≥15MPa, and the 28d compressive strength is ≥60MPa.

4. The concrete according to claim 1, wherein The mass of the mineral powder accounts for 10-20% of the total mass of the cementitious material.

5. The concrete according to claim 1 or 3, characterized in that The particle size distribution of the mineral powder is: D(0.1)≤3.0μm, D(0.5)≤22.0μm, D(0.9)≤100μm.

6. The concrete according to claim 1, wherein The particle size distribution of the fly ash is: D(0.1)≤4.1μm, D(0.5)≤25.0μm, and D(0.9)≤75.0μm.

7. The method for preparing concrete according to any one of claims 1 to 6, wherein: include: Cementitious materials, aggregates, water reducing agent and water are mixed to obtain concrete of strength grade C70.

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