Low-carbon cement-based ultra-high performance concrete and preparation method thereof

Abstract

The present invention discloses a low-carbon cement-based ultra-high performance concrete, which comprises the following components, by weight: 500-600 parts of low-carbon cement, 350-500 parts of a siliceous-calcium reinforcing component, 150-250 parts of modified recycled construction waste powder, 1,100 parts of fine aggregate, 1.8-2.5 parts of a retarding component, 9.5-11.5 parts of a water-reducing component, and 240-250 parts of water; steel fiber is added, accounting for 1.5-2.5% of the volume of the low-carbon cement-based ultra-high performance concrete; the modified recycled construction waste powder is obtained by acidolysis, coprecipitation, and alkali activation of the construction waste powder; the obtained product has an expansion of 600 mm or more, a 28-day compressive strength of 120 MPa or more, and a chloride ion permeability coefficient of less than 17.0×10 ‑14 m 2 ·s ‑1 Moreover, during the entire low-carbon cement-based ultra-high performance concrete preparation process, the CO2 storage rate can reach more than 20%; while ensuring the high density requirements of ultra-high performance concrete, the carbonization effect of low-carbon cement is taken into account, and at the same time, the resource utilization of construction waste fine powder can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a low-carbon cement-based ultra-high performance concrete and a preparation method thereof. Background Art

[0002] Ultra-high-performance concrete (UHPC) is typically designed and prepared using the closest packing theory. Its high density makes it a fiber-reinforced cementitious composite material with exceptional mechanical properties, durability, and toughness. It is widely used in the production of large-span pedestrian bridges, highway and railway bridges, thin-walled silos, nuclear waste tanks, cable anchor reinforcement plates, and ATM protective casings. With the implementation of the national "dual carbon" policy, the development of new green and low-carbon building materials has become a major research focus. Ultra-high-performance concrete, due to its high specific strength and durability, is considered an important low-carbon engineering structural material.

[0003] Currently, ultra-high-performance concrete (UHPC) is typically produced using ordinary Portland cement and / or Portland cement as the primary binder. The primary mineral compositions of ordinary Portland cement and / or Portland cement are C2S, C3S, C3A, and C4AF. These mineral compositions are primarily derived from limestone, which produces significant amounts of CO2 upon pyrolysis, contradicting China's dual carbon policy. Low-carbon cement, a cement product that significantly reduces carbon emissions, emits 40%-80% less CO2 than ordinary cement during its production process. Common raw materials include steel slag, fly ash, slag, and silicates. Its primary mineral composition is 5%-40% C3S2, 20%-50% γ-C2S, and 10%-50% CS. The application of low-carbon cement in the production of ultra-high-performance concrete would have significant environmental implications.

[0004] However, although low-carbon cement production has lower carbon emissions, its own hydration activity is low, and the products need to be carbonized for reinforcement. During the carbonization process of low-carbon cement products, the denser the product, the worse the carbonization reinforcement effect. However, the preparation of ultra-high performance concrete often requires the product to have a higher density in order to have excellent mechanical properties, durability and toughness. Therefore, when using low-carbon cement for the preparation of ultra-high performance concrete, how to balance the carbonization effect of low-carbon cement and the high density requirements of ultra-high performance concrete is an urgent problem that needs to be solved.

[0005] At the same time, construction waste fine powder is an issue that cannot be ignored when recycling waste concrete. It accounts for about 5%-20% of the total waste concrete. Its main mineral components are silica, calcium hydroxide, calcium aluminoferrite, and calcium aluminosilicate, which are potentially active ingredients. However, when construction waste fine powder is used in concrete preparation, especially ultra-high performance concrete with a low water-binder ratio (usually 0.12-0.18), due to the high water absorption rate and low hydration activity of construction waste fine powder, the mix workability is poor when concrete is prepared with construction waste fine powder. The mechanical properties and durability after hardening are also poor, which greatly limits its resource utilization. If construction waste fine powder can be successfully used in the preparation of ultra-high performance concrete, it will not only provide a new direction for the resource utilization of construction waste fine powder, but also increase the low-carbon emission reduction significance of ultra-high performance concrete. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention provides a low-carbon cement-based ultra-high performance concrete, which takes into account the carbonization effect of low-carbon cement while ensuring the high density requirements of ultra-high performance concrete, and at the same time can realize the resource utilization of construction waste fine powder.

[0007] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0008] A low-carbon cement-based ultra-high performance concrete comprising the following components in parts by weight:

[0009] 500-600 parts of low-carbon cement, 350-500 parts of silicon-calcium reinforcing component, 150-250 parts of modified recycled construction waste powder, 1100 parts of fine aggregate, 1.8-2.5 parts of retarding component, 9.5-11.5 parts of water-reducing component, and 240-250 parts of water; steel fiber accounting for 1.5-2.5% of the volume of the low-carbon cement-based ultra-high performance concrete is added; the modified recycled construction waste powder is obtained by acidolysis, coprecipitation, and alkali activity activation of construction waste powder.

[0010] The present invention transforms unstable hydration products in the construction waste micropowder into calcium-aluminum hydrotalcite with strong adsorption properties by subjecting it to acid hydrolysis, coprecipitation, and alkali activation treatment. This process stimulates the hydration activity of the construction waste micropowder, synergizing with the calcium-silicon reinforcement component to compensate for the low activity of low-carbon cement, which leads to low strength in the formulated low-carbon ultra-high performance wave-absorbing concrete. Furthermore, the present invention modulates the hydration process of the calcium-silicon reinforcement component and the modified recycled construction waste micropowder by adding a retarding component, synergizing with the calcium-aluminum hydrotalcite in the modified recycled construction waste micropowder. While ensuring good working performance in the formulated low-carbon UHPC, the present invention provides sufficient carbonation channels for the low-carbon cement, absorbing more CO2, and improving the mechanical properties of the formulated low-carbon UHPC. Furthermore, based on the above-mentioned material system, the present invention adopts a high water-cement ratio (0.20-0.22) to improve the problem of excessive viscosity of the slurry caused by the high adsorption of the modified recycled construction waste micropowder, which in turn affects its CO2 absorption efficiency, providing favorable conditions for enhancing the strength of low-carbon UHPC. In addition, the present invention reasonably adjusts the usage ratio of each component, so that the carbonation of low-carbon cement and the hydration of ordinary Portland cement / Portland cement develop synergistically, further improving the mechanical properties of the entire system.

[0011] Optionally, the modified recycled construction waste powder is prepared by the following method:

[0012] (1) Grind the construction waste powder to a specific surface area of ​​≥300m 2 / kg, then acid hydrolyze at 50-60℃ and filter to obtain the Ca 2+ 、Al 3+ Solution A and solid B; in this step, the acid hydrolysis solution may preferably be 15-20% by mass of hydrochloric acid, and the mass ratio of the recycled construction waste powder to the acid hydrolysis solution may preferably be 1: (2-3);

[0013] (2) adding an alkaline solution to the solution A, adjusting the pH of the solution A to 10-11, carrying out a coprecipitation reaction at 80-90° C., followed by crystallization at 100-110° C., cooling, filtering, washing, and drying to obtain a calcium aluminum hydrotalcite and a filtrate C; in this step, the alkaline solution may preferably be a sodium hydroxide solution, and the molar concentration of the sodium hydroxide solution may preferably be 0.1-0.2 mol / L;

[0014] (3) mixing the solid B and the filtrate C, reacting with alkali at 40-60° C. for 3-5 hours, filtering, and drying to obtain fine powder D;

[0015] (4) The calcium aluminum hydrotalcite and the fine powder D are mixed to obtain modified recycled construction waste fine powder.

[0016] The present invention uses an acid hydrolysis method to decompose the unstable hydration products in the recycled construction waste powder, and then uses a co-precipitation method to separate the Ca2+ 、Al 3+ It is converted into calcium-aluminum hydrotalcite, wherein the calcium-aluminum hydrotalcite, as a layered structure material, can adsorb water and gas, and can not only serve as a CO2 scavenger, but also provide a carbonization channel for CO2, providing enhanced protection for the application of low-carbon cement in ultra-high performance concrete. At the same time, the present invention makes full use of the filtrate (alkaline solution) produced by the co-precipitation reaction and the filtrate (solid B) produced by the acid hydrolysis reaction. The alkaline filtrate can stimulate the chemical activity of solid B, thereby effectively improving the reaction activity of recycled construction waste micropowder and cement, thereby effectively ensuring the mechanical properties of low-carbon ultra-high performance wave-absorbing concrete.

[0017] Optionally, the silica-calcium reinforcement component consists of ordinary Portland cement or Portland cement and silica fume; the mass ratio of the ordinary Portland cement or Portland cement to the silica fume is 1:(0.2-0.3).

[0018] The present invention uses ordinary Portland cement or Portland cement and silica fume as reinforcing components of the entire system. The hydration rate of ordinary Portland cement or Portland cement and silica fume is faster than that of low-carbon cement, which can make up for the problem that when low-carbon cement is used to prepare pouring concrete, the slurry hardens and solidifies slowly due to its low hydration activity, and the demoulding period is long. In addition, the calcium hydroxide produced by the hydration of ordinary Portland cement or Portland cement can balance the overall alkalinity of the slurry, avoiding the significant reduction in slurry alkalinity caused by carbonization of low-carbon cement, which leads to steel fiber rust and affects the durability and conductive wave-absorbing properties of the low-carbon ultra-high-performance absorbing concrete.

[0019] Optionally, the grade of the ordinary Portland cement or Portland cement is not less than grade 42.5.

[0020] Optionally, the water demand ratio of the silica fume is not greater than 125%, and the 28d activity index is not less than 105%.

[0021] Optionally, the retarding component is prepared by mixing sodium gluconate and tartaric acid in a mass ratio of 1:(0.1-0.3).

[0022] Optionally, the water-reducing component is a polycarboxylate water-reducing agent with a water-reduction rate of not less than 25%.

[0023] Optionally, the steel fiber has a diameter of 0.18-0.22 mm, a length of 13-15 mm, and an aspect ratio of 60-70.

[0024] Optionally, the fine aggregate is one or more of quartz sand, river sand, and machine-made sand, wherein the quartz sand preferably has a fineness modulus of 1.8-2.0, and the river sand and machine-made sand preferably have a fineness modulus of 2.3-2.5.

[0025] Optionally, the main components of the low carbon cement include 23.5-25.5% C3S2, 31.5-34.5% C2S, 19.5-22.5% CS, and 20.0-24.0% C3S by mass percentage, and the specific surface area of ​​the low carbon cement is not less than 300m 2 / kg.

[0026] A second object of the present invention is to provide a method for preparing the above-mentioned low-carbon cement-based ultra-high performance concrete, the preparation method comprising the following steps:

[0027] 1) uniformly mixing the low-carbon cement, the siliceous-calcium reinforcing component, the modified recycled construction waste powder, the fine aggregate, the retarding component, and the water-reducing component, adding the water and stirring to form a slurry, then adding the steel fiber to the slurry and continuing to stir for 1-2 minutes to obtain a low-carbon cement-based ultra-high performance concrete slurry precursor;

[0028] 2) In a closed environment, a certain amount of CO2 gas is charged into the low-carbon cement-based ultra-high performance concrete paste precursor while stirring, and the mixture is poured, formed, demolded, and cured to obtain low-carbon cement-based ultra-high performance concrete, wherein the amount of CO2 gas charged can preferably be 4-6% of the mass of the cementitious material.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention innovatively uses low-carbon cement and construction waste powder simultaneously in the preparation of ultra-high performance concrete, solving the problem that low-carbon cement and construction waste powder are difficult to use in the preparation of ultra-high performance concrete, greatly improving the environmental significance of ultra-high performance concrete, and also facilitating its promotion and application.

[0031] The low-carbon cement-based ultra-high performance concrete prepared by the present invention has good working performance, mechanical properties, and durability. Its expansion is ≥600mm, its 28d compressive strength can reach above 120MPa, and its chloride ion permeability coefficient can be less than 17.0×10 -14 m 2 ·s -1 Moreover, during the entire preparation process of low-carbon cement-based ultra-high performance concrete, the CO2 storage rate can reach more than 20%. DETAILED DESCRIPTION

[0032] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0033] The specific embodiment provides a modified recycled construction waste powder:

[0034] The construction waste powder is ball-milled to a specific surface area of ​​350m 2 / kg, the ball-milled recycled construction waste powder was placed in 15% hydrochloric acid at a mass ratio of 1:2, and acid-hydrolyzed at 50 ° C. After the acid hydrolysis was completed, it was filtered to obtain the Ca-containing 2+ 、Al 3+ Solution A and solid B;

[0035] A sodium hydroxide solution with a molar concentration of 0.15 mol / L was added to solution A, the pH of solution A was adjusted to 10, a coprecipitation reaction was carried out at 85° C., followed by crystallization at 100° C., cooling, filtering, washing, and drying to obtain calcium aluminum hydrotalcite and filtrate C;

[0036] The solid B and the filtrate C were mixed, and the reaction was alkali-induced at 50°C for 3 h, filtered, and dried to obtain micropowder D;

[0037] The calcium aluminum hydrotalcite and the micropowder D are mixed to obtain modified recycled construction waste micropowder.

[0038] In the specific implementation mode, raw materials are used:

[0039] The main mineral composition of low carbon cement is calculated by mass percentage, including: 24.8% C3S2, 33.2% C2S, 21.0% CS, 21.0% C3S. The specific surface area of ​​the low carbon cement is 325m 2 / kg. The siliceous-calcium reinforcement component consists of P·O52.5 ordinary Portland cement and silica fume in a mass ratio of 1:0.2. The silica fume has a water demand of 115% and a 28-day activity index of 118%. The fine aggregate is quartz sand with a fineness modulus of 1.9. The retarding component is a mixture of sodium gluconate and tartaric acid in a mass ratio of 1:0.2. The water-reducing component is a powdered polycarboxylate water-reducing agent with a water-reducing efficiency of 25%. The steel fibers have an average diameter of 0.20 mm, an average length of 14 mm, and an average aspect ratio of 70. All other raw materials, unless otherwise specified, were commercially available.

[0040] Example 1

[0041] A low-carbon cement-based ultra-high performance concrete comprises, by weight, 500 parts of low-carbon cement, 500 parts of a siliceous-calcium reinforcing component, 150 parts of modified recycled construction waste fine powder, 1,100 parts of fine aggregate, 2.5 parts of a retarding component, 9.5 parts of a water-reducing component, 250 parts of water, and steel fiber accounting for 2.0% of the volume of the low-carbon cement-based ultra-high performance concrete.

[0042] The low-carbon cement-based ultra-high performance concrete is specifically prepared by the following method:

[0043] 1) low carbon cement, calcium silicate reinforcement component, modified recycled construction waste powder, fine aggregate, retarding component, and water reducing component are uniformly mixed according to the above-mentioned dosage ratio, and water is added to stir into a slurry. Then, steel fiber is added to the slurry and stirring is continued for 2 minutes to obtain a low carbon cement-based ultra-high performance concrete slurry precursor;

[0044] 2) In a closed environment, CO2 gas (concentration of 99.9%) at 5% by mass of the cementitious material is charged into a low-carbon cement-based ultra-high performance concrete paste precursor while stirring for 90 seconds. The mixture is then poured, formed, and demolded. The demolded specimens are then subjected to standard curing to a specified age to obtain low-carbon cement-based ultra-high performance concrete.

[0045] Example 2

[0046] The low-carbon cement-based ultra-high performance concrete of this embodiment comprises the following components, by weight: 550 parts low-carbon cement, 450 parts calcium-silicon reinforcement component, 200 parts silicon-modified recycled construction waste fine powder, 1100 parts fine aggregate, 2.2 parts retarding component, 10 parts water-reducing component, 245 parts water, and steel fiber accounting for 2.0% of the volume of the low-carbon cement-based ultra-high performance concrete. The preparation method is the same as that of Example 1.

[0047] Example 3

[0048] The difference between this embodiment and Example 1 is that the low-carbon cement-based ultra-high performance concrete of this embodiment includes the following components, by weight: 550 parts of low-carbon cement, 400 parts of cement reinforcing component, 250 parts of modified recycled construction waste fine powder, 1100 parts of fine aggregate, 2.0 parts of retarding component, 11.5 parts of water-reducing component, 240 parts of water, and steel fiber accounting for 2.0% of the volume of the low-carbon cement-based ultra-high performance concrete.

[0049] Example 4

[0050] The low-carbon cement-based ultra-high performance concrete of this embodiment comprises the following components, by weight: 600 parts low-carbon cement, 350 parts siliceous-calcium reinforcing component, 150 parts modified recycled construction waste fine powder, 1100 parts fine aggregate, 1.8 parts retarding component, 9.5 parts water-reducing component, 245 parts water, and steel fiber accounting for 2.0% of the volume of the low-carbon cement-based ultra-high performance concrete. The preparation method is the same as that of Example 1.

[0051] Comparative Example 1

[0052] In the low-carbon cement-based ultra-high performance concrete of this comparative example, unmodified recycled construction waste powder is used, and the construction waste powder is only ball-milled to a specific surface area of ​​350m 2 / kg, and the rest is the same as in Example 1.

[0053] The low-carbon cement-based ultra-high performance concrete is specifically prepared by the following method:

[0054] 1) low carbon cement, calcium silicate reinforcement component, construction waste powder, fine aggregate, retarding component, and water reducing component were mixed uniformly according to the above-mentioned dosage ratio, and water was added to stir into a slurry. Then, steel fiber was added to the slurry and stirred for 2 minutes to obtain a low carbon cement-based ultra-high performance concrete slurry precursor;

[0055] 2) In a closed environment, CO2 gas (concentration of 99.9%) at 5% by mass of the cementitious material is charged into a low-carbon cement-based ultra-high performance concrete paste precursor while stirring for 90 seconds. The mixture is then poured, formed, and demolded. The demolded specimens are then subjected to standard curing to a specified age to obtain low-carbon cement-based ultra-high performance concrete.

[0056] Comparative Example 2

[0057] The low-carbon cement-based ultra-high performance concrete of this comparative example does not contain any retarding component, and the rest is the same as in Example 1.

[0058] The low-carbon cement-based ultra-high performance concrete is specifically prepared by the following method:

[0059] 1) low carbon cement, calcium silicate reinforcement component, modified recycled construction waste powder, fine aggregate, and water-reducing component were uniformly mixed according to the above-mentioned dosage ratio, and water was added to stir into a slurry. Then, steel fiber was added to the slurry and stirred for 2 minutes to obtain a low carbon cement-based ultra-high performance concrete slurry precursor;

[0060] 2) In a closed environment, CO2 gas (concentration of 99.9%) at 5% by mass of the cementitious material is charged into a low-carbon cement-based ultra-high performance concrete paste precursor while stirring for 90 seconds. The mixture is then poured, formed, and demolded. The demolded specimens are then subjected to standard curing to a specified age to obtain low-carbon cement-based ultra-high performance concrete.

[0061] Comparative Example 3

[0062] The retarding component in the low-carbon cement-based ultra-high performance concrete of this comparative example is only sodium gluconate, and the rest is the same as in Example 1.

[0063] The low-carbon cement-based ultra-high performance concrete is specifically prepared by the following method:

[0064] 1) low carbon cement, calcium silicate reinforcement component, modified recycled construction waste powder, fine aggregate, retarding component, and water reducing component are uniformly mixed according to the above-mentioned dosage ratio, and water is added to stir into a slurry. Then, steel fiber is added to the slurry and stirring is continued for 2 minutes to obtain a low carbon cement-based ultra-high performance concrete slurry precursor;

[0065] 2) In a closed environment, CO2 gas (concentration of 99.9%) at 5% by mass of the cementitious material is charged into a low-carbon cement-based ultra-high performance concrete paste precursor while stirring for 90 seconds. The mixture is then poured, formed, and demolded. The demolded specimens are then subjected to standard curing to a specified age to obtain low-carbon cement-based ultra-high performance concrete.

[0066] Comparative Example 4

[0067] The low-carbon cement-based ultra-high performance concrete of this comparative example does not contain any cement reinforcing component, and uses low-carbon cement to replace the cement reinforcing component. The rest is the same as in Example 1.

[0068] The low-carbon cement-based ultra-high performance concrete is specifically prepared by the following method:

[0069] 1) low carbon cement, modified recycled construction waste powder, fine aggregate, retarding component, and water reducing component are uniformly mixed according to the above-mentioned dosage ratio, and water is added to stir into a slurry. Then, steel fiber is added to the slurry and stirring is continued for 2 minutes to obtain a low carbon cement-based ultra-high performance concrete slurry precursor;

[0070] 2) In a closed environment, CO2 gas (concentration of 99.9%) at 5% by mass of the cementitious material is charged into a low-carbon cement-based ultra-high performance concrete paste precursor while stirring for 90 seconds. The mixture is then poured, formed, and demolded. The demolded specimens are then subjected to standard curing to a specified age to obtain low-carbon cement-based ultra-high performance concrete.

[0071] According to the standard specification of ultra-high performance concrete, the working performance, mechanical properties and durability performance of the low-carbon cement-based ultra-high performance concrete of Examples 1-4 of the present invention and Comparative Examples 1-4 were tested. The test results are shown in Table 1.

[0072] The mass loss of the specimen between 400 and 900°C was tested by differential scanning calorimetry, and the mass loss was recorded as the CO2 absorption amount. The CO2 storage rate was then calculated by the CO2 absorption amount and the CO2 charging amount. CO2 storage rate = CO2 absorption amount / CO2 charging amount × 100%. The calculation results are shown in Table 1.

[0073] As can be seen from Table 1, the low-carbon cement-based ultra-high performance concrete prepared in the present invention has good working performance, its 28d compressive strength can reach more than 120 MPa, and its chloride ion permeability coefficient is no more than 17.0×10 -14 m 2 ·s -1At the same time, compared with comparative example 1, after the construction waste powder is modified in embodiment 1 of the present invention, the mechanical properties and durability are greatly improved, among which the 28d compressive strength is increased by 27.7%, and the flexural strength is increased by 71.7%; compared with comparative example 2, the addition of an appropriate amount of retarder in embodiment 1 of the present invention can greatly improve the initial working performance of the slurry after CO2 is introduced, and the addition of the retarder is beneficial to the carbonization and hardening efficiency of the slurry, and further to the improvement of the mechanical properties and durability of the hardened slurry, among which the 28d compressive strength is increased by 27.7%, and the flexural strength is increased by 71.7%. The results show that the 28d compressive strength of the slurry is 20.0% higher and the flexural strength is 52.8% higher than that of the comparative example 3. Compared with the comparative example 3, the embodiment 1 of the present invention uses the mixture of ammonium gluconate and tartaric acid as the retarding component, which can improve the initial fluidity of the slurry, and the 28d compressive strength can be increased by 16.8%, and the flexural strength is increased by 31.1%; Compared with the comparative example 4, the embodiment 1 of the present invention adds the cement reinforcing component, which can greatly improve the mechanical properties of the hardened slurry, among which the 28d compressive strength is increased by 250.1%, the flexural strength is increased by 198.5%, and the durability is also significantly improved.

[0074] Table 1

[0075]

[0076]

[0077] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A low-carbon cement-based ultra-high performance concrete, characterized in that The following components are included by weight: 500-600 parts of low-carbon cement, 350-500 parts of silica-calcium reinforcing component, 150-250 parts of modified recycled construction waste powder, 1,100 parts of fine aggregate, 1.8-2.5 parts of retarding component, 9.5-11.5 parts of water-reducing component, and 240-250 parts of water; steel fiber accounting for 1.5-2.5% of the volume of the low-carbon cement-based ultra-high performance concrete is added; the modified recycled construction waste powder is obtained by acid hydrolysis, coprecipitation, and alkali activation of the construction waste powder; The modified recycled construction waste powder is prepared by the following method: (1) Grind the construction waste powder to a specific surface area of ​​≥300m 2 / kg, then acid hydrolyze at 50-60℃ and filter to obtain the Ca 2 + 、Al 3+ Solution A and solid B; (2) adding an alkaline solution to the solution A, adjusting the pH of the solution A to 10-11, carrying out a coprecipitation reaction at 80-90° C., followed by crystallization at 100-110° C., cooling, filtering, washing, and drying to obtain calcium aluminum hydrotalcite and a filtrate C; (3) Mixing the solid B and the filtrate C, reacting with alkali at 40-60°C for 3-5 hours, filtering, and drying to obtain micropowder D; (4) mixing the calcium aluminum hydrotalcite and the fine powder D to obtain modified recycled construction waste fine powder; The silica-calcium reinforcement component is composed of ordinary Portland cement or Portland cement and silica fume; the mass ratio of the ordinary Portland cement or Portland cement to the silica fume is 1: (0.2-0.3); The retarding component is prepared by mixing sodium gluconate and tartaric acid in a mass ratio of 1:(0.1-0.3).

2. The low-carbon cement-based ultra-high performance concrete according to claim 1, characterized in that The grade of the ordinary Portland cement or Portland cement is not less than 42.5; the water requirement ratio of the silica fume is not greater than 125%, and the 28d activity index is not less than 105%.

3. The low-carbon cement-based ultra-high performance concrete according to claim 1, characterized in that The water-reducing component is a polycarboxylic acid water-reducing agent with a water-reducing rate of not less than 25%.

4. The low-carbon cement-based ultra-high performance concrete according to claim 1, characterized in that The steel fiber has a diameter of 0.18-0.22 mm, a length of 13-15 mm, and an aspect ratio of 60-70.

5. The low-carbon cement-based ultra-high performance concrete according to claim 1, characterized in that The fine aggregate is one or more of quartz sand, river sand, and machine-made sand.

6. The low-carbon cement-based ultra-high performance concrete according to claim 1, characterized in that The main components of the low carbon cement include 23.5-25.5% C3S2, 31.5-34.5% C2S, 19.5-22.5% CS, and 20.0-24.0% C3S by mass percentage. The specific surface area of ​​the low carbon cement is not less than 300m 2 / kg.

7. The method for producing low-carbon cement-based ultra-high performance concrete according to any one of claims 1 to 6, characterized in that The steps include: 1) uniformly mixing the low-carbon cement, the silica-calcium reinforcing component, the modified recycled construction waste powder, the fine aggregate, the retarding component, and the water-reducing component, adding water and stirring to form a slurry; adding the steel fiber to the slurry and continuing to stir for 1-2 minutes to obtain a low-carbon cement-based ultra-high performance concrete slurry precursor; 2) In a closed environment, CO2 gas is introduced into the low-carbon cement-based ultra-high performance concrete slurry precursor while stirring, and the mixture is poured, formed, demolded, and cured to obtain the low-carbon cement-based ultra-high performance concrete.

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