A mix ratio design method and preparation method of negative carbon lightweight aggregate concrete

Abstract

The present invention provides a negative carbon lightweight aggregate concrete mix design method and preparation method. Negative carbon lightweight aggregate concrete includes components by mass: 196-300 parts of negative carbon lightweight aggregate, 100-200 parts of regenerated sand, 30-50 parts of recycled micropowder, 30-50 parts of Bayer red mud powder, 30-50 parts of slag, 1-3 parts of sodium hydroxide, 5-10 parts of water glass, 25-45 parts of water, and 0.1-0.5 parts of water reducer; the negative carbon lightweight aggregate is made of sugarcane bagasse biochar as the core, and the shell material composed of recycled micropowder, Bayer red mud powder and slag is wrapped on the outside to improve the strength; the present invention develops negative carbon lightweight aggregate through sugarcane bagasse biochar, and its carbon emissions are negative compared to traditional stone, with obvious low-carbon advantages. At the same time, considering the carbon emissions of the whole process, the concrete mix ratio is designed with negative implicit carbon emissions as the target, and construction and industrial solid waste are used as raw materials to reduce manufacturing costs and reduce resource waste.

Description

Technical Field

[0001] The present invention relates to the technical field of low-carbon building materials, and in particular to a negative-carbon lightweight aggregate concrete mix ratio design method and a preparation method. Background Art

[0002] Globally, the construction industry is one of the largest carbon-emitting sectors, accounting for over one-fifth of global carbon emissions. In my country, the construction industry is a pillar of the national economy, and its carbon emissions are also significant, becoming a major environmental issue that demands urgent resolution. According to the "2023 China Building and Urban Infrastructure Carbon Emissions Research Report," my country's total carbon dioxide emissions from building materials production reached 1.7 billion tons in 2021, accounting for 16% of the nation's energy-related carbon emissions. Cement-based materials accounted for 250 million tons of carbon dioxide emissions, representing 15% of the total. Concrete and cement products contribute nearly 50% of the embodied carbon emissions in buildings. In response to this, the central and local governments have successively introduced a number of policies to promote energy conservation and carbon reduction in building materials. In particular, the "2024-2025 Energy Conservation and Carbon Reduction Action Plan" issued by the State Council explicitly calls for promoting energy conservation and carbon reduction in the building materials industry. Therefore, energy conservation and carbon reduction efforts for building materials like concrete are particularly urgent.

[0003] Currently, carbon reduction strategies for concrete materials primarily include the following: using low-carbon cement to reduce carbon emissions during cement production; increasing the resource utilization of solid waste, which not only helps reduce carbon emissions but also reduces the consumption of natural resources; and applying carbon sequestration technology to capture carbon dioxide and store it in concrete. Of these measures, the first two have been widely adopted. In the prior art, patent CN 118084406 A discloses a low-carbon concrete and its preparation method, which uses fly ash, slag powder, and other solid wastes as precursors and a mixture containing carbide slag alkali-activated powder and water glass as an alkali activator to prepare low-carbon concrete. Patent CN 118005358 A discloses a low-carbon concrete that uses coal gangue to replace cement to control strength, and its preparation method. By controlling the amount of coal gangue replaced, the carbon emissions of concrete are reduced. Patent CN 118005308 A discloses waste incineration fly ash-based composite admixtures, low-carbon cementitious materials, and preparation methods. These materials are prepared using processed solid wastes such as waste incineration fly ash, steel slag, red mud, and furnace slag. These patents focus on utilizing solid waste to reduce cement usage, thereby lowering carbon emissions from cementitious materials. While these methods have achieved some carbon reduction results, their CO2 accounting, performed after preparation, does not incorporate carbon emissions as a precondition, making effective carbon management difficult.

[0004] As for carbon dioxide capture and storage technology, the focus is on the carbonization of concrete materials. Patent CN117964270A discloses a method for preparing and applying a non-burning ultra-light, high-strength, carbon-fixing type recycled light aggregate. The recycled light aggregate is soaked in a Ca(OH)2 solution and then dried. It is further mixed with alkaline waste slag composed of solid waste electroslag powder and slag powder. After sufficient carbonization, a non-burning, carbon-fixing type light aggregate is obtained. However, this type of method has the problems of low carbonization efficiency and small carbon fixation amount. In addition, during the carbonization process, the alkalinity of the concrete material decreases, which will weaken the passivation film on the surface of the steel bar and promote steel corrosion. Therefore, it has not been widely promoted and applied in actual engineering.

[0005] In summary, traditional concrete design fails to consider carbon management, potentially leading to potential risks in later carbon accounting for construction projects. Furthermore, traditional low-carbon concrete preparation focuses on cement material replacement and carbonization, a perspective that is somewhat limited. Therefore, there is an urgent need to develop cost-effective low-carbon concrete design and preparation methods that proactively consider carbon emissions, in order to promote a green and low-carbon transition in the construction industry and achieve sustainable development. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention proposes a method for designing the mix proportion of negative carbon lightweight aggregate concrete and a method for preparing the same. From a broad perspective, the present invention defines the carbon contained in bagasse biochar as carbon dioxide that has been captured, mineralized, and sealed, giving it the characteristics of a negative carbon material. By using a shell-making and wrapping method, the bagasse biochar is modified to enhance its mechanical properties and ensure that the strength of the negative carbon lightweight aggregate meets the requirements. During the mix proportion design stage, the present invention aims to reduce carbon emissions to zero or lower, and adjusts the raw materials to meet the design requirements of both carbon emissions and strength. In addition, in order to further reduce carbon emissions and ensure negative carbon targets, the present invention uses solid wastes such as regenerated sand, regenerated micropowder, Bayer red mud powder and slag in concrete raw materials, which reduces carbon while also reducing costs, providing a feasible design approach for low-carbon concrete materials.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for designing a mix ratio of negative carbon lightweight aggregate concrete comprises the following steps:

[0009] Step A1: Determine the concrete strength grade based on actual project requirements, use negative carbon lightweight aggregate, recycled sand, solid waste cementitious materials, alkali activator, water reducer and water as raw materials, and determine the initial mix ratio;

[0010] Step A2: Obtain the carbon emission factors of each raw material and its transportation and preparation process, calculate the embodied carbon emissions of concrete under the initial mix ratio, and determine whether it is less than 0;

[0011] Step A3: Adjust the initial mix ratio so that the carbon emission is less than 0 to obtain the test mix ratio;

[0012] Step A4: Conduct test verification according to the test mix ratio to test the strength of the concrete and determine whether it meets the project requirements;

[0013] Step A5: Reduce the water-cement ratio according to the test results to ensure the concrete strength requirements and ultimately obtain a negative carbon concrete mix ratio.

[0014] Furthermore, the carbon-negative lightweight aggregate described in step A1 is a core-shell carbon-negative lightweight aggregate, which uses bagasse biochar as the core material and uses a shell material to seal the carbon in the biochar, thereby achieving a negative embodied carbon emission value; the preparation method is as follows:

[0015] Step B1: Weigh 20-50 parts by mass of recycled micropowder, 20-30 parts by mass of Bayer red mud powder, 25-50 parts by mass of slag, and 1-4 parts by mass of sodium silicate, place the mixture in a mixer, and mix them evenly to obtain a shell material;

[0016] Step B2: Using sugarcane bagasse biochar as the core material, weigh 10-20 parts by mass of the core material, place it in a granulator with the shell material obtained in step B1, and mix at a constant speed for 3 minutes to obtain a mixture;

[0017] Step B3: Continuous granulation for 15 minutes, during which 20-30 parts by weight of water are evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0018] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 7-28 days to obtain a negative carbon lightweight aggregate product;

[0019] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0020] Furthermore, the embodied carbon emissions of concrete under the initial mix ratio as described in step A2 are calculated using the following formula:

[0021] Total c =M c +T c +P c

[0022] Among them, Total c is the total embodied carbon emissions of concrete; M c is the carbon emission of raw materials; T c is the carbon emission during the transportation of raw materials; P cis the carbon emissions of each preparation process; the calculation methods for each are as follows:

[0023]

[0024] Among them, C m,i is the carbon emission factor of each raw material per unit mass; C t,i is the carbon emission factor of transportation; C p,i is the carbon emission factor of the process for preparing unit mass of concrete; m i is the quality of each raw material; i is the transport distance; m t For the quality of each raw material and.

[0025] Furthermore, the adjustment of the initial mix ratio described in step A3 is specifically as follows:

[0026] If Total c If Total is less than or equal to 0, no adjustment is made; c If it is greater than 0, then negative carbon lightweight aggregate is added, and the added mass is calculated as follows:

[0027] Total c =(C m,LA +C t,LA )m LA

[0028] Among them C m,LA is the carbon emission factor per unit mass of negative carbon lightweight aggregate; C t,LA is the carbon emission factor for transporting unit mass of carbon-negative lightweight aggregate; m LA is the mass of negative carbon lightweight aggregate.

[0029] Furthermore, the bagasse biochar is obtained by pyrolysis of bagasse, a solid waste of a sugar factory, and has a particle size range of 1.18-4.75 mm.

[0030] Furthermore, the embodied carbon emissions of the bagasse biochar are -2300kg CO2-eq / m 3 .

[0031] The present invention also provides a method for preparing negative carbon lightweight aggregate concrete, which uses the negative carbon lightweight aggregate concrete mix ratio design method to obtain a mix ratio, and performs the following steps:

[0032] Step C1: Immerse the carbon-free lightweight aggregate in water, pre-wet for 2 hours, then take it out and air dry it until the surface is dry;

[0033] Step C2: Weigh 1-3 parts of sodium hydroxide and 5-10 parts of water glass by mass, stir and mix them evenly, and cool to room temperature to obtain an alkaline activator;

[0034] Step C3: Weigh 30-50 parts of recycled micropowder, 30-50 parts of Bayer red mud powder, and 30-50 parts of slag by mass, mix them evenly as a solid waste cementitious material, then add 100-200 parts of regenerated sand, place them in a concrete mixer, mix for 30 seconds, then add 196-300 parts of pre-wetted negative carbon lightweight aggregate, stir for 60 seconds to mix evenly, finally add 25-45 parts of water, 0.1-0.5 parts of water reducer, and the alkali activator in step C2, and stir for 2-3 minutes to obtain a negative carbon concrete mixture;

[0035] Step C4: Pour the mixture into a mold, cast and shape it, vibrate and smooth it, and finally cure it for 28 days to obtain negative carbon concrete.

[0036] Furthermore, the recycled fine powder described in step C3 is obtained by crushing, screening and grinding waste concrete, and is tested with reference to "Fly Ash Used in Cement and Concrete" (GB / T 1596-2017), and the compressive strength ratio is greater than 0.65.

[0037] Furthermore, the regenerated sand described in step C3 is obtained by crushing, screening and particle shaping of mortar blocks in waste concrete, and is Class II or above.

[0038] The negative carbon lightweight aggregate concrete prepared by the preparation method of the present invention has a 28-day compressive strength of 27-40 MPa and an implicit carbon emission of less than 0, and is suitable for use in green and low-carbon buildings.

[0039] The present invention has the following beneficial effects:

[0040] 1. The present invention uses bagasse biochar produced by pyrolysis of sugarcane bagasse, a solid waste from a sugar refinery, to prepare negative carbon lightweight aggregate. By encapsulating the bagasse biochar with recycled micropowder, Bayer red mud powder, and slag, and adopting a combustion-free process, not only is the carbon content in the bagasse biochar effectively sealed, energy consumption during preparation is reduced, but the mechanical properties of the lightweight aggregate are also significantly improved. Compared with traditional lightweight aggregate, the negative carbon lightweight aggregate prepared by the present invention has the advantage of negative carbon emissions, providing new possibilities for low-carbon development in the concrete industry.

[0041] 2. This invention considers carbon emissions as a key factor during the concrete mix design phase, using both negative carbon emissions and strength as dual criteria for concrete mix design. This proactive carbon accounting facilitates carbon emission risk management and provides a new low-carbon development path for the entire construction industry.

[0042] 3. The carbon-negative concrete of the present invention is made from materials such as carbon-negative lightweight aggregate, reclaimed sand, reclaimed micropowder, and slag. The bagasse biochar in the carbon-negative lightweight aggregate is derived from bagasse, a solid waste product from sugar refineries. Therefore, the main raw materials of this concrete are solid waste, reducing the environmental burden. Furthermore, the use of solid waste as a raw material further reduces carbon emissions and economic costs, providing a new, low-carbon, and economical concrete material for the construction industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The present invention is a schematic flow chart of a method for designing a mix ratio of negative carbon lightweight aggregate concrete. DETAILED DESCRIPTION

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0045] First, the preparation method of negative carbon lightweight aggregate is further explained.

[0046] The sugarcane bagasse biochar in the examples of the present invention is produced by pyrolysis of sugarcane bagasse, a solid waste from a Guangxi sugar factory. After screening, the particle size range used is 1.18-4.75 mm. The chemical composition of the recycled micropowder, Bayer red mud powder, and slag used was tested, and the test results are shown in Table 1.

[0047] Table 1 Chemical composition of recycled micro powder, Bayer red mud powder and slag (mass fraction, %)

[0048] raw materials <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> <![CDATA[Na2O]]> <![CDATA[K2O]]> other Recycled micropowder 43.39 11.20 30.26 5.64 3.92 2.48 0.19 1.79 1.13 Bayer red mud powder 13.86 22.53 10.49 30.34 0.48 0.60 10.70 1.60 9.41 slag 35.50 15.60 36.41 0.43 8.24 1.03 0.46 0.65 1.68

[0049] The sodium silicate used was analytically pure sodium silicate nonahydrate powder with a Na2O content of 28.6-29.6% and a Na2O to SiO2 content ratio of 1.03±0.03.

[0050] Example 1

[0051] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0052] Step B1: Weigh 40 parts by mass of recycled micropowder, 30 parts by mass of Bayer red mud powder, 30 parts by mass of slag, and 2 parts by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0053] Step B2: Using sugarcane bagasse biochar as the core material, weigh 15 parts of the core material by mass, place it in a granulator with the above shell material, and mix it at a constant speed for 3 minutes to obtain a mixture; according to the statistics of biochar carbon footprint in the literature, the embodied carbon emissions of the sugarcane bagasse biochar are -2300kg CO2-eq / m 3 calculate;

[0054] Step B3: Continuous granulation for 15 minutes, during which 20 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0055] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 7 days to obtain a negative carbon lightweight aggregate product;

[0056] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0057] Example 2

[0058] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0059] Step B1: Weigh 40 parts by mass of recycled micropowder, 20 parts by mass of Bayer red mud powder, 40 parts by mass of slag, and 2 parts by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0060] Step B2: Using sugarcane bagasse biochar as the core material, weigh 15 parts of the core material by mass, place it in a granulator with the above shell material, and mix it at a constant speed for 3 minutes to obtain a mixture; the embodied carbon emission of the sugarcane bagasse biochar is -2300kgCO2-eq / m 3 ;

[0061] Step B3: Continuous granulation for 15 minutes, during which 20 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0062] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 7 days to obtain a negative carbon lightweight aggregate product;

[0063] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0064] Example 3

[0065] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0066] Step B1: Weigh 30 parts by mass of recycled micropowder, 30 parts by mass of Bayer red mud powder, 40 parts by mass of slag, and 2 parts by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0067] Step B2: Using sugarcane bagasse biochar as the core material, weigh 15 parts of the core material by mass, place it in a granulator with the above shell material, and mix it at a constant speed for 3 minutes to obtain a mixture; the embodied carbon emission of the sugarcane bagasse biochar is -2300kgCO2-eq / m 3 ;

[0068] Step B3: Continuous granulation for 15 minutes, during which 20 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0069] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 7 days to obtain a negative carbon lightweight aggregate product;

[0070] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0071] Example 4

[0072] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0073] Step B1: Weigh 40 parts by mass of recycled micropowder, 30 parts by mass of Bayer red mud powder, 30 parts by mass of slag, and 2 parts by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0074] Step B2: Using sugarcane bagasse biochar as the core material, weigh 15 parts of the core material by mass, place it in a granulator with the above shell material, and mix it at a constant speed for 3 minutes to obtain a mixture; the embodied carbon emission of the sugarcane bagasse biochar is -2300kgCO2-eq / m 3 ;

[0075] Step B3: Continuous granulation for 15 minutes, during which 20 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0076] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing them in water for 14 days to obtain a negative carbon lightweight aggregate product;

[0077] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0078] Example 5

[0079] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0080] Step B1: Weigh 40 parts by mass of recycled micropowder, 30 parts by mass of Bayer red mud powder, 30 parts by mass of slag, and 2 parts by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0081] Step B2: Using sugarcane bagasse biochar as the core material, weigh 15 parts of the core material by mass, place it in a granulator with the above shell material, and mix it at a constant speed for 3 minutes to obtain a mixture; the embodied carbon emission of the sugarcane bagasse biochar is -2300kgCO2-eq / m 3 ;

[0082] Step B3: Continuous granulation for 15 minutes, during which 20 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0083] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 28 days to obtain a negative carbon lightweight aggregate product;

[0084] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0085] Example 6

[0086] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0087] Step B1: Weigh 50 parts by mass of recycled micropowder, 25 parts by mass of Bayer red mud powder, 25 parts by mass of slag, and 1 part by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0088] Step B2: Using sugarcane bagasse biochar as the core material, 10 parts of the core material were weighed by mass, and placed in a granulator with the above shell material, and mixed at a constant speed for 3 minutes to obtain a mixture; the embodied carbon emission of the sugarcane bagasse biochar was -2300 kgCO2-eq / m 3 ;

[0089] Step B3: Continuous granulation for 15 minutes, during which 25 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0090] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 28 days to obtain a negative carbon lightweight aggregate product;

[0091] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0092] Example 7

[0093] A method for preparing negative carbon lightweight aggregate comprises the following steps:

[0094] Step B1: Weigh 20 parts by mass of recycled micropowder, 30 parts by mass of Bayer red mud powder, 50 parts by mass of slag, and 4 parts by mass of sodium silicate, place them in a mixer, and mix them evenly to obtain a shell material;

[0095] Step B2: Using sugarcane bagasse biochar as the core material, weigh 20 parts of the core material by mass, place it in a granulator with the above shell material, and mix it at a constant speed for 3 minutes to obtain a mixture; the embodied carbon emission of the sugarcane bagasse biochar is -2300kgCO2-eq / m 3 ;

[0096] Step B3: Continuous granulation for 15 minutes, during which 30 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact;

[0097] Step B4: curing the lightweight aggregate spheres for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing in water for 28 days to obtain a negative carbon lightweight aggregate product;

[0098] Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

[0099] Negative carbon lightweight aggregate was prepared according to the above embodiment, and its performance test results are shown in Table 2.

[0100] Table 2 7-day performance test results of negative carbon lightweight aggregate of Examples 1-7

[0101]

[0102] As shown in Table 2, the embodied carbon emissions of the negative carbon lightweight aggregates prepared in Examples 1-7 are all negative. This phenomenon is attributed to the lower carbon emission factors of recycled micropowder and Bayer red mud powder relative to slag, resulting in a corresponding increase in the embodied carbon emissions of the negative carbon lightweight aggregates as the recycled micropowder and Bayer red mud powder dosage decreases. Comparing Example 1 and Example 2, at a constant recycled micropowder dosage, increasing the slag dosage promotes geopolymerization within the negative carbon lightweight aggregate shell, thereby improving the 7-day cylinder compressive strength and reducing the 24-hour water absorption rate. Furthermore, when the slag dosage remains unchanged, increasing the Bayer red mud powder dosage increases the alkalinity of the system, thereby increasing the amount of dissolved silica-alumina phases. The increased number of reactants leads to an increase in reaction products, an increase in the 7-day cylinder compressive strength, and a decrease in the 24-hour water absorption rate. These results demonstrate that the preparation of negative carbon lightweight aggregates from solid wastes such as recycled micropowder, Bayer red mud powder, slag, and bagasse biochar has significant potential to promote green and low-carbon development in the construction industry.

[0103] Furthermore, the negative carbon lightweight aggregate obtained in Example 5 is used as raw material to illustrate the mix design method of negative carbon lightweight aggregate concrete.

[0104] When designing the mix proportion for negative carbon lightweight aggregate concrete, the recycled fine powder, Bayer red mud powder, slag, and water used are consistent with those used in the preparation of the negative carbon lightweight aggregate. Recycled fine powder is obtained by crushing, screening, and grinding waste concrete. Tested according to "Fly Ash for Cement and Concrete" (GB / T 1596-2017), the compressive strength ratio is greater than 0.65. Recycled sand is obtained by crushing, screening, and shaping mortar blocks from waste concrete. It is Class II or higher.

[0105] In addition, the sodium hydroxide used is analytically pure powdered solid with a NaOH content of ≥96%; the sodium silicate is industrial grade liquid sodium silicate, and the basic parameters are shown in Table 2.

[0106] Table 3 Main parameters of sodium silicate

[0107] Material Baume Modulus <![CDATA[Na2O / %]]> <![CDATA[SiO2 / %]]> Sodium silicate 38.2 3.37 8.8 28.4

[0108] Example 8

[0109] A method for designing a mix ratio of negative carbon lightweight aggregate concrete, comprising the following steps:

[0110] Step A1: Determine the concrete strength grade LC30 based on actual project requirements, use negative carbon lightweight aggregate, recycled sand, solid waste cementitious material, alkali activator, water reducer and water as raw materials, and determine the initial mix ratio as follows.

[0111] Ratio Regenerated sand Recycled micropowder Bayer red mud powder slag Sodium hydroxide water glass Negative carbon lightweight aggregate water Initial mix ratio 100 40 30 30 2 8 150 30

[0112] Step A2: Obtain the carbon emission factors of each raw material and its transportation and preparation process, and calculate the embodied carbon emissions of concrete under the initial mix ratio;

[0113] After literature review, the carbon emission factors of various raw materials and their transportation and preparation processes are shown in Table 5.

[0114] Table 5 Carbon emission factors during raw materials, transportation and preparation

[0115] Raw materials, transportation and preparation process Carbon emission factor Regenerated sand <![CDATA[3.678kg CO2-eq / t]]> Recycled micropowder <![CDATA[4kg CO2-eq / t]]> Bayer red mud powder <![CDATA[28kg CO2-eq / t]]> slag <![CDATA[83kg CO2-eq / t]]> Sodium hydroxide <![CDATA[860kg CO2-eq / t]]> water glass <![CDATA[1514kg CO2-eq / t]]> Negative carbon lightweight aggregate <![CDATA[-106.34kg CO2-eq / t]]> water <![CDATA[0.168kg CO2-eq / t <!-- 7 -->]]> water reducer <![CDATA[1064CO2-eq / t]]> transportation <![CDATA[0.078kg CO2-eq / (t·km)]]> Concrete preparation <![CDATA[5kg CO2-eq / t]]>

[0116] Under the initial mix ratio, the embodied carbon emissions of concrete are:

[0117] Total c =M c +T c +P c =4.47+2.34+5=11.81kg CO2-eq / t

[0118] Step A3: Adjust the initial mix ratio to meet the negative carbon emission target and obtain the test mix ratio;

[0119] Since the preparation of negative carbon lightweight aggregate is consistent with the concrete pouring site, C t,LA =0,

[0120] Right now Therefore, 46.55 parts of negative carbon lightweight aggregate are added. At this time, the implicit carbon emission is 0. The test mix ratio is as follows

[0121]

[0122] Step A4: Test verification was carried out according to the test mix ratio. The 28-day compressive strength of the lightweight aggregate concrete was 27.36 MPa, which is less than the LC30 design value of 28.33 MPa specified in the Technical Specification for Lightweight Aggregate Concrete (JGJ51-2002).

[0123] Step A5: Adjust the water-binder ratio according to the test results, that is, reduce the water consumption to obtain the following mix ratio.

[0124]

[0125] Testing showed that with this mix ratio, the lightweight aggregate concrete achieved a 28-day strength of 30.26 MPa and an embodied carbon emission of -0.18 kgCO₂-eq / t, meeting the design targets. This mix ratio is known as a negative carbon lightweight aggregate concrete mix ratio.

[0126] The method for preparing negative carbon lightweight aggregate concrete comprises the following steps:

[0127] Step C1: Immerse the carbon-free lightweight aggregate in water, pre-wet for 2 hours, then take it out and air dry it until the surface is dry;

[0128] Step C2: Weigh 2 parts of sodium hydroxide and 8 parts of water glass by mass, stir and mix them evenly, and cool to room temperature to obtain an alkaline activator;

[0129] Step C3: Weigh 40 parts of recycled micropowder, 30 parts of Bayer red mud powder, and 30 parts of slag by mass, mix them evenly as a solid waste cementitious material, then add 100 parts of regenerated sand, place them in a concrete mixer, mix for 30 seconds, then add 196.55 parts of pre-wetted negative carbon lightweight aggregate, stir for 60 seconds to mix evenly, finally add 28 parts of water, 0.1 part of water reducer, and the alkali activator in step C2, and stir for 2-3 minutes to obtain a negative carbon concrete mixture;

[0130] Step C4: Pour the mixture into a mold, cast and shape it, vibrate and smooth it, and finally cure it for 28 days to obtain negative carbon concrete.

[0131] The negative carbon ratios of the other examples are shown in Table 6

[0132] Table 6 Negative carbon mix ratio of Examples 9-14

[0133] Case Regenerated sand Recycled micropowder Bayer red mud powder slag Sodium hydroxide water glass Negative carbon lightweight aggregate water water reducer Example 9 150 40 30 40 2 6 200 25 0.3 Example 10 150 40 40 50 2 9 250 30 0.2 Example 11 200 30 50 30 1 7 250 28 0.5 Example 12 100 30 50 50 3 10 300 32 0.4 Example 13 150 50 30 40 1 5 200 25 0.4 Example 14 150 50 50 50 2 8 250 45 0.5

[0134] Intensity testing and carbon emission accounting were carried out on the above embodiment, and the results are shown in Table 7.

[0135] Table 7 28-day compressive strength and embodied carbon emissions

[0136] Case 28-day compressive strength (MPa) <![CDATA[Embodied carbon emissions (kg CO2-eq / t)]]> Example 8 27.36 -0.18 Example 9 32.52 -3.74 Example 10 40.31 -1.88 Example 11 31.95 -9.57 Example 12 28.68 -6.46 Example 13 38.82 -8.01 Example 14 35.40 -2.82

[0137] The above description is only a preferred specific embodiment of the present invention, and the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention within the technical scope disclosed in the present invention, and they should all be covered by the protection scope of the present invention.

Claims

1. A method for designing a mix ratio of negative carbon lightweight aggregate concrete, characterized in that: The steps include: Step A1: Determine the concrete strength grade based on actual project requirements, use negative carbon lightweight aggregate, recycled sand, solid waste cementitious materials, alkali activator, water reducer and water as raw materials, and determine the initial mix ratio; Step A2: Obtain the carbon emission factors of each raw material and its transportation and preparation process, calculate the embodied carbon emissions of concrete under the initial mix ratio, and determine whether it is less than 0; Step A3: Adjust the initial mix ratio so that the carbon emission is less than 0 to obtain the test mix ratio; Step A4: Conduct test verification according to the test mix ratio to test the strength of the concrete and determine whether it meets the project requirements; Step A5: Reduce the water-cement ratio based on the test results to ensure the concrete strength requirements and ultimately obtain a negative carbon concrete mix ratio; The embodied carbon emissions of concrete under the initial mix ratio as described in Step A2 are calculated using the following formula: ， Among them, Total c is the total embodied carbon emissions of concrete; M c is the carbon emission of raw materials; T c is the carbon emission during the transportation of raw materials; P c is the carbon emissions of each preparation process; the calculation methods for each are as follows: ， ， ， ， Among them, C m,i is the carbon emission factor of each raw material per unit mass; C t,i is the carbon emission factor of transportation; C p,i is the carbon emission factor of the process for preparing unit mass of concrete; m i is the quality of each raw material; i is the transport distance; m t For the quality of each raw material and; The adjustment of the initial mix ratio described in step A3 is specifically as follows: If Total c If Total is less than or equal to 0, no adjustment is made; c If it is greater than 0, then negative carbon lightweight aggregate is added, and the added mass is calculated as follows: ， Among them C m,LA is the carbon emission factor per unit mass of negative carbon lightweight aggregate; C t,LA is the carbon emission factor for transporting unit mass of carbon-negative lightweight aggregate; m LA is the mass of negative carbon lightweight aggregate.

2. A method for designing a mix ratio of negative carbon lightweight aggregate concrete according to claim 1, characterized in that: The carbon-negative lightweight aggregate described in step A1 is a core-shell carbon-negative lightweight aggregate, which uses sugarcane bagasse biochar as the core material and uses a shell material to seal the carbon in the biochar, thereby achieving a negative embodied carbon emission value. The preparation method is as follows: Step B1: Weigh 20-50 parts by mass of recycled micropowder, 20-30 parts by mass of Bayer red mud powder, 25-50 parts by mass of slag, and 1-4 parts by mass of sodium silicate, place the mixture in a mixer, and mix them evenly to obtain a shell material; Step B2: Using bagasse biochar as the core material, weigh 10-20 parts by mass of the core material and place it in a granulator with the shell material obtained in step B1, and mix them at a constant speed for 3 minutes to obtain a mixture; Step B3: Continuous granulation for 15 minutes, during which 20-30 parts by weight of water were evenly sprayed into the mixture for another 3 minutes to make the lightweight aggregate more compact; Step B4: curing the lightweight aggregate pellets for 1 day under the following carbon curing conditions: controlling the temperature at 25±2°C, the humidity at 50%±2%, and the CO2 concentration at 20%±2%, and then curing them in water for 7-28 days to obtain a negative carbon lightweight aggregate product; Step B5: Determine the embodied carbon emissions of the carbon-negative lightweight aggregate based on the material, transportation, and preparation process.

3. The method for designing a mix ratio of negative carbon lightweight aggregate concrete according to claim 2, wherein: The bagasse biochar is obtained by pyrolysis of bagasse, a solid waste from a sugar factory, and has a particle size range of 1.18-4.75 mm.

4. A method for designing a mix ratio of negative carbon lightweight aggregate concrete according to claim 2, characterized in that: The embodied carbon emissions of the bagasse biochar are -2300 kg CO2-eq / m 3 .

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