Fly ash-slag-based alkali-activated cementing material as well as preparation method, strength regulation and control method and application thereof

Abstract

The invention belongs to the technical field of low-carbon building materials, and particularly relates to a fly ash-slag-based alkali-activated cementing material as well as a preparation method, a strength regulation and control method and application thereof. The cementing material comprises, by mass, 64%-68% of powder, 21%-30% of a composite alkali activator and 5%-12% of additional water, and in the powder, slag powder accounts for 0-50% of the mass of the powder, and fly ash accounts for 50-100% of the mass of the powder. The initial setting time of the cementing material is larger than or equal to 60 minutes, the 28-day compressive strength is 30.0-100.0 MPa, the breaking strength is 4.0-7.0 MPa, the cementing material has good mechanical performance, meanwhile, the strength of the cementing material can be regulated and controlled through the powder mixing ratio, the regulation and control range is large, the cementing material is suitable for application scenes with different strength requirements, and the cementing material has wide application prospects in the field of civil engineering.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-carbon building materials, and in particular relates to a fly ash-slag based alkali-activated cementitious material, a preparation method thereof, and a strength control method and application thereof. Background Art

[0002] my country's construction industry has high carbon emissions, and cement, the main material of cement concrete, is known as a "three highs industry" of "high pollution, high energy consumption, and high water consumption."

[0003] Alkali-activated cementitious materials refer to potentially active raw materials that become hydraulically active when activated by alkaline activators. Slag powder and fly ash, as new energy-saving and environmentally friendly building materials, offer properties such as acid and alkali resistance, high temperature resistance, fire resistance, and low carbon content. However, they also suffer from drawbacks such as low strength and the inability to control activation strength. Consequently, their application and widespread adoption are limited by both mechanical properties and the manufacturing process.

[0004] In terms of improving the mechanical properties of materials, Chinese patent CN109880056A discloses a high-performance cement-based composite material and its preparation method. The raw materials include 200-300 parts of cement, 50-100 parts of silica fume, 300-400 parts of quartz sand, 50-150 parts of fly ash, 20-40 parts of steel fiber, 3-5 parts of water reducer, and 80-120 parts of water. The raw materials are put into the mixer in order and fully stirred. The invention significantly improves the mechanical properties of cement-based composite materials such as compression and flexural strength by adding steel fiber and utilizing its strengthening and toughening effect; Chinese patent CN110734724A discloses an ultra-high-strength concrete and its preparation method. The materials include 450-550 parts of cement, 80-120 parts of silica fume, and slag powder. 100-150 parts, quartz sand 600-700 parts, coarse aggregate 1000-1100 parts, water reducer 8-12 parts, water 140-160 parts. The invention improves the strength and other mechanical properties of concrete by rationally allocating the proportions of raw materials, making it suitable for projects with extremely high strength requirements; Chinese patent CN111454126A discloses a high-strength lightweight concrete and a preparation method thereof. The raw materials include 300-350 parts of cement, 100-150 parts of fly ash, 100-200 parts of polystyrene particles, 500-600 parts of sand, 3-5 parts of water reducer, and 150-180 parts of water. The invention utilizes the lightweight characteristics of polystyrene particles to reduce the dead weight of concrete while ensuring a certain strength, thereby improving its overall mechanical properties.

[0005] The above inventions all address the problem of insufficient mechanical properties of existing materials by improving the materials through doping, but do not involve the regulation of the mechanical properties of the materials, which to a certain extent limits the application scenarios and scope of the materials. Summary of the Invention

[0006] The present invention aims to address the aforementioned existing technical problems by providing an alkali-activated cementitious material and its preparation method, which features high strength, low carbon emissions, stable performance, easy manufacture, and adjustable properties. By formulating a composite alkali activator based on modulus and alkali equivalent, and controlling the quality of the powder blend, the physical and mechanical properties of the alkali-activated cementitious material can be adjusted to suit the specific applications and requirements of different concretes.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The present invention provides a fly ash-slag based alkali-activated cementitious material. Calculated by mass percentage, the raw material components of the alkali-activated cementitious material include: 64%-68% of powder, 21%-35% of a composite alkali activator, and 0-12% of added water, with the sum of the mass fractions of the components being 100%. The powder is formed by uniformly mixing slag powder and fly ash, and the mass percentages of the components of the powder are: 0%-50% of slag powder, 50%-100% of fly ash, and the sum of the mass fractions of the slag powder and fly ash being 100%.

[0009] Preferably, the specific surface area of ​​the slag powder is 400m 2 / kg~480m 2 / kg, the slag powder meets the S95 grade requirements in GB / T18046-2017, and more preferably, its main components are CaO, SiO2, Al2O3 and MgO; the CaO content is 30-50%, the SiO2 content is 20%-40%, the Al2O3 content is 10-25%, and the MgO content is 5-15%; more preferably, the CaO content is 35-42%, the SiO2 content is 25%-32%, the Al2O3 content is 13-18%, and the MgO content is 6-12%;

[0010] And / or, the fly ash meets the requirements for Class F fly ash in GB / T 1596-2017 "Fly ash for cement and concrete", has a sieve residue of no more than 10% after passing through a 45 μm square hole sieve, a loss on ignition of less than 5%, and main components of the fly ash are SiO, Al2O3, and Fe2O3; the SiO2 content is 45-55%, the Al2O3 content is 24-31%, and the Fe2O3 content is 7-11%.

[0011] Preferably, the composite alkali activator comprises sodium water glass solution (sodium silicate aqueous solution) and solid sodium hydroxide, and the composite alkali activator has a modulus of 1.2 and an alkali equivalent of 0.07;

[0012] and / or, the solid content is 31.97-45.55%,

[0013] And / or, the sodium water glass solution has a modulus n of 3.25, more preferably wherein the SiO2 content is 17.81%-26.87%, the Na2O content is 5.67%-8.53%, and the water content is 76.52%-64.67%; more preferably, the SiO2 content is 26.8%, the Na2O content is 8.53%, and the water content is 64.67%;

[0014] And / or, the purity of the main component of the solid sodium hydroxide, NaOH, is ≥96%;

[0015] And / or, the components of the composite alkali activator and the mass percentage of each component are: sodium water glass solution 84.19%, sodium hydroxide 0-15.80%;

[0016] The modulus refers to the ratio of the amounts of SiO2 and Na2O contained in the solution. When preparing the composite alkali activator, solid sodium hydroxide is added to the sodium water glass solution. Since the addition of sodium hydroxide increases the amount of Na2O in the solution, the alkalinity of the solution is enhanced, thereby adjusting the modulus from 3.25 to 1.2. The alkali equivalent refers to the mass ratio of the powder contained in the alkali-activated cementitious material to the Na2O contained in the composite alkali activator.

[0017] Preferably, the 28-day compressive strength of the fly ash-slag based alkali-activated cementitious material is 30.0-100.0 MPa, and the flexural strength is 4.0-7.0 MPa; more preferably, when the slag powder content is 50%, its initial setting time is ≥60 minutes, the 28-day compressive strength reaches 90-100 MPa, and the flexural strength reaches 6.0-6.2 MPa.

[0018] The present invention also provides a method for preparing any of the above-mentioned fly ash-slag based alkali-activated cementitious materials, comprising the following steps:

[0019] S1. Preparing a composite alkali activator: mixing a sodium water glass solution with solid sodium hydroxide to obtain a composite alkali activator;

[0020] S2. Mixed powder: Weigh slag powder and fly ash according to mass fraction and mix them at a low speed to obtain a mixed powder;

[0021] S3. Preparation of an alkali-activated gelling material: A composite alkali activator is added to the mixed powders and water is added. The mixture is stirred at a low speed for a specified period of time. The mixture is then stirred at a high speed until the solid and liquid phases are fully integrated, forming a viscous liquid with gelling properties. The gelling material is thus prepared. Low-speed stirring facilitates uniform mixing of the raw materials, while subsequent high-speed stirring further accelerates the reaction rate, allowing the gelling properties to develop more quickly, resulting in a uniform and stable gelling material.

[0022] Preferably, the low-speed stirring speed is 100-200 rpm; the high-speed stirring speed is 300-500 rpm;

[0023] And / or, in step S2, stirring at a low speed for ≥20 s, until the fly ash and slag powder are uniformly mixed; more preferably, 30 s;

[0024] And / or, in step S3, stirring at a low speed for 1-5 minutes, stopping for 1-30 seconds, and stirring at a high speed for 1-5 minutes; more preferably, stirring at a low speed for 2 minutes, stopping for 15 seconds, and stirring at a high speed for 2 minutes.

[0025] Preferably, the preparation method comprises the following specific steps:

[0026] S1. Preparation of composite alkali activator: Pour the sodium water glass solution into an alkali-resistant plastic beaker, slowly and evenly pour in a quantitative amount of sodium hydroxide solid while stirring and dissolving with a stirring rod. When the sodium hydroxide solid is completely dissolved in the solution, the solution becomes transparent and slightly white and continues to release heat. Cover the mouth of the composite alkali activator beaker with a single layer of plastic wrap and let it stand for 4-12 hours to cool the solution to room temperature.

[0027] S2. Mixing powders: Weigh slag powder, fly ash, and water according to mass fractions, pour the dry slag powder and fly ash powder into a mixing pot and mix them. Set the stirrer to manual mode and stir at low speed for 30 seconds to evenly mix the two powders.

[0028] S3. Preparation of alkali-activated gelling material: Add the composite alkali activator prepared in S1 and a corresponding amount of water, stir at a low speed for 2 minutes, stop stirring for 15 seconds, during which time use a scraper to scrape off the residual powder from the stirring blade and the pot wall into the pot, then stir at a high speed for 2 minutes until the solid and liquid phases in the stirring pot are fully integrated to present a viscous liquid with gelling characteristics, thus preparing the gelling material.

[0029] Preferably, the prepared alkali-activated gelling material is also subjected to flexural strength and compressive strength tests of the slurry specimens, and the specific steps are as follows:

[0030] S4. Prepare slurry test blocks: pour the alkali-activated cementitious material prepared in S3 into molds of 40mm×40mm×100mm and 40mm×40mm×40mm, and cover the mold surface with plastic wrap; remove the mold 24-96 hours after pouring, depending on the mass percentage of the powder: the powder composition is fly ash accounting for 90%-100% (including 100%), and slag powder accounting for 0%-10% (including 0%). When the fly ash content is 80%-90% (including 90%) and the slag powder content is 10%-20% (including 10%), the formwork should be removed 72 hours after pouring; when the fly ash content is 70%-80% (including 80%) and the slag powder content is 20%-30% (including 20%), the formwork should be removed 48 hours after pouring; when the fly ash content is not more than 70% and the slag powder content is not less than 30%, the formwork should be removed 24 hours after pouring. After demolding, the alkali-activated cementitious material slurry test block is prepared by curing at 25°C and 95% humidity for 28 days.

[0031] The present invention also provides a strength control method for the fly ash-slag based alkali activated cementitious material, which relies on the quantitative relationship between the mechanical performance index and the powder ratio. The specific strength control method includes the following:

[0032] S1. Determine the quantitative relationship: Set the slag powder content x, flexural strength y1, and compressive strength y2; under fixed conditions, change the slag powder content x to obtain the flexural strength y1 and compressive strength y2 of the corresponding material; use linear regression formulas to fit the quantitative relationship between the slag powder content x and the flexural strength y1, and the quantitative relationship between the slag powder content x and the compressive strength y2;

[0033] S2. Set target values: Set target flexural strength y1 and compressive strength y2 according to project requirements;

[0034] S3. Calculate the slag powder content x under the conditions: Substitute the target value into the quantitative relationship formula for flexural strength and / or the quantitative relationship formula for compressive strength to calculate the slag powder content x;

[0035] S4. Adjust the powder ratio according to the calculated slag powder dosage, and prepare a cementitious material of target strength according to the preparation method of claims 5-7.

[0036] Preferably, under the conditions that the composite base activator modulus is 1.2 and the base equivalent is 0.07, the quantitative relationship is as follows:

[0037] Quantitative relationship formula for flexural strength: y1 = 0.034x + 4.53 (0 ≤ x ≤ 50);

[0038] And / or, the quantitative relationship formula for compressive strength is: y2=1.28x+32(0≤x≤50).

[0039] More preferably, the specific intensity control method includes the following:

[0040] S1. Clear strength requirements: In actual engineering applications, the target values ​​of the flexural strength y1 (unit: MPa) and compressive strength y2 (unit: MPa) of the required alkali-activated cementitious materials shall be clearly defined according to the design requirements and use environment of the specific project;

[0041] S2. Determine the powder ratio using quantitative relationships: Given that the mass percentage of slag powder in the powder is x (x ranges from 0 to 50), the relationship between the powder ratio and the flexural strength and compressive strength of the cementitious material is as follows:

[0042] Flexural strength: y1 = 0.034x + 4.53 (0 ≤ x ≤ 50)

[0043] Compressive strength: y2=1.28x+32(0≤x≤50)

[0044] Based on the above quantitative relationship, if the target flexural strength y1 is known, the required slag powder mass percentage x can be calculated using the formula. Similarly, if the target compressive strength y2 is known, the slag powder mass percentage x can be calculated using the formula. When both the flexural strength and compressive strength target values ​​are known, the two x values ​​can be calculated separately. Taking into account the actual project conditions (such as material costs, construction technology, etc.), the appropriate x value can be selected, and the mass percentage of fly ash can be determined as (100-x)%.

[0045] S3. Based on the calculated mass percentages of slag powder and fly ash, the powder ratio is accurately adjusted when preparing the alkali-activated cementitious material. At the same time, the alkali-activated cementitious material of the target strength is prepared strictly according to the established preparation process.

[0046] More preferably, the 28-day flexural strength y1 is 4.0-7.0 MPa, and the 28-day compressive strength y2 is 30.0-100.0 MPa.

[0047] The present invention also provides an application of the fly ash-slag based alkali activated cementitious material in the field of construction.

[0048] Compared with alkali-activated gelling materials, the advantages and beneficial effects of the present invention are:

[0049] (1) Strong mechanical properties: The present invention provides a set of excellent compound alkali activator ratios based on the modulus and alkali equivalent of the compound alkali activator, constructs a high alkalinity activation environment, and can also avoid local weakness caused by excessive pH efflorescence of the cementitious material. The compound alkali activator activates the hydrolysis of the slag powder-fly ash system to produce more [Al(OH)4]- groups and participates in the geopolymerization reaction. Therefore, the resulting alkali-activated cementitious material has high mechanical strength. When the slag powder content relative to the powder is 50%, the strength can reach 90MPa to 100MPa.

[0050] (2) Precise strength control: One of the core innovations of this invention is to establish a quantitative linear relationship model between slag powder content (x) and mechanical properties (y1, y2), namely, flexural strength y1 = 0.034x + 4.53 (0 ≤ x ≤ 50) and compressive strength y2 = 1.28x + 32 (0 ≤ x ≤ 50). This model can be used to directly reverse-calculate the required slag powder content according to engineering requirements, achieving a precise mapping from theory to practice.

[0051] (3) Large space for strength control: The fly ash-slag based alkali-activated cementitious material prepared by the present invention has an initial setting time of ≥60 minutes, a 28-day compressive strength that can be controlled between 30.0 and 100.0 MPa, and a flexural strength that can be controlled between 4.0 and 7.0 MPa. According to the different material proportions of fly ash and slag powder in the selected powder, the strength control range shows a large span. Therefore, the present cementitious material can be applied to various engineering scenarios with different strength requirements. Whether it is general buildings with low strength requirements or large bridges, high-rise buildings and other projects with extremely high strength requirements, the needs can be met by reasonably adjusting the powder ratio, adapting to application scenarios with different strength requirements, effectively expanding the application range of the material, and having broad application prospects.

[0052] (4) Low carbon emissions: Compared with P·O42.5 cement, CO2 emissions are reduced by 80% to 85%, which meets the national "dual carbon" requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Attachment Figure 1 This is a schematic diagram of the preparation process of the alkali-activated gelling material of the present invention;

[0054] Attachment Figure 2 Graph showing the flexural test results of the alkali-activated gelling material paste specimens of Examples 1-6;

[0055] Attachment Figure 3 This is a graph showing the compressive test results of the alkali-activated cementitious material slurry specimens of Examples 1-6. DETAILED DESCRIPTION

[0056] In order to better clarify and understand the purpose, process scheme and advantages of the present invention, the technical scheme and implementation method of the present invention are further clearly, completely and in detail described below through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to illustrating and explaining the present invention and do not limit the present invention. Based on the embodiments in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0057] The experimental methods and conditions used in the embodiments of the present invention are conventional methods and conventional conditions unless otherwise specified. The materials, reagents, instruments, devices, etc. used in the embodiments are conventional substances or equipment known to those skilled in the art and can be obtained from commercial channels or prepared by conventional methods unless otherwise specified. The reaction conditions embodied in the summary of the invention of the present invention are all capable of achieving the described reactions and obtaining products with the desired effects. Due to space limitations, some examples are listed below to further illustrate the advantages of the technical solutions of the present invention.

[0058] Example 1-6: Preparation and performance testing of fly ash-slag based alkali activated cementitious materials

[0059] An alkali-activated gelling material is made of the following raw materials, calculated by mass percentage: powder: 66.08% (slag powder + fly ash), composite alkali activator: 23.81%, and added water: 10.11%.

[0060] The composite alkali activator is configured with an alkali equivalent of 0.07 and a composite alkali activator modulus of 1.2. The composite alkali activator comprises a sodium water glass solution and solid sodium hydroxide. The composite alkali activator is made from the following raw materials, calculated by mass percentage: 84.19% sodium water glass solution (modulus 3.25, SiO2 content 26.8%, Na2O content 8.53%, water content 64.67%) and 15.80% solid NaOH (purity ≥96%).

[0061] The fly ash and slag powder used were tested by XRF analysis, and their composition contents are as follows:

[0062] Chemical composition analysis of fly ash (unit: %)

[0063]

[0064] Chemical composition analysis of slag powder (unit: %)

[0065]

[0066] Preparation steps:

[0067] S1. Preparation of a composite alkali activator: Place a sodium water glass solution in an alkali-resistant plastic container. Slowly add solid sodium hydroxide (purity ≥96%) at a uniform rate under mechanical stirring (100-200 rpm), stirring continuously until completely dissolved to form a uniform, transparent, slightly white solution. The container is then sealed and allowed to mature for 4-12 hours, depending on the amount of activator used, allowing the solution temperature to naturally cool to room temperature. This yields a composite alkali activator with a modulus of 1.2, a solids content of 45.55%, and an alkali equivalent of 0.07. The solids content is the percentage of the mass of Na2O·nSiO2, the main component in the activator, to the total mass of the composite alkali activator solution.

[0068] S2. Powder mixing pretreatment: Weigh slag powder and fly ash according to mass percentage, put the dry powder into a planetary mixer, and stir at low speed (100-150 rpm) for 30 seconds to make the slag powder (specific surface area 400-480 m 2 / kg, S95 grade) and fly ash (45μm sieve residue ≤10%, loss on ignition <5%) are fully mixed.

[0069] S3. Preparation of gelling material: The composite alkali activator prepared in S1 and 10.11% of added water were added to a stirring pot at the same time. The mixture was stirred at a low speed (100-200 rpm) for 2 minutes, then stopped and allowed to stand for 15 seconds while using a scraper to clean the powder adhering to the stirring blades and the pot wall. The mixture was then switched to a high-speed mode (300-500 rpm) and stirred for 2 minutes until a thixotropic viscous gel was formed.

[0070] S4. Preparation of slurry test blocks: Cast the S3 alkali-activated cementitious material into molds measuring 40 mm × 40 mm × 100 mm and 40 mm × 40 mm × 40 mm, and cover the mold surfaces with plastic wrap. Remove the molds 24 to 96 hours after casting, depending on the mass percentage of the powder, and cure at 25°C and 95% humidity for 28 days to obtain slurry test blocks of the alkali-activated cementitious material.

[0071] The demolding time is stipulated as follows: when the powder composition is 90%-100% (including 100%) of fly ash and 0%-10% (including 0%) of slag powder, the mold shall be removed 96 hours after pouring; when the fly ash accounts for 80%-90% (including 90%) and the slag powder accounts for 10%-20% (including 10%), the mold shall be removed 72 hours after pouring; when the fly ash accounts for 70%-80% (including 80%) and the slag powder accounts for 20%-30% (including 20%), the mold shall be removed 48 hours after pouring; when the fly ash accounts for no more than 70% and the slag powder accounts for no less than 30%, the mold shall be removed 24 hours after pouring.

[0072] The flexural strength and compressive strength of alkali-activated cementitious materials were tested according to the national standard GB / T50107-2010 "Concrete Strength Test and Assessment Standard". The powder composition and strength performance results of Examples 1-6 are shown in the following table:

[0073]

[0074] Comparative Example (P·O42.5 Cement)

[0075] 28-day compressive strength: ≥42.5MPa (according to GB 175-2007 "General Portland Cement")

[0076] 28-day flexural strength: ≥6.5MPa (according to GB 175-2007 "General Portland Cement")

[0077] Carbon emissions: 842 kg CO2 / t (the carbon emissions of the system of the present invention are reduced by 80%-85% compared with the comparative example).

[0078] Result Analysis

[0079] Based on the data in the table and the attached Figure 2 and attached Figure 3 , we can see that:

[0080] (1) Mechanical property improvement rule: It can be seen from Examples 1-6 and their results that as the slag powder content increases from 0% to 50%, the compressive strength increases from 32 MPa to 95.95 MPa, and the flexural strength increases from 4.5 MPa to 6.2 MPa. The strength can be adjusted over a large span. The concrete prepared with this cementitious material can accurately control the material strength. This is attributed to the fact that the CaO in the slag powder and the silicon-aluminum components in the fly ash generate C-(A)-SH and NASH composite gels under the action of the composite activator, forming a dense network structure, which varies with the change in the content of the two powders.

[0081] (2) Synergistic effect of activator: The composite activator with a modulus of 1.2 promotes the depolymerization of slag powder glass and the reaction of fly ash pozzolana by regulating the pH value and ion concentration of the solution, so that the 28-day compressive strength of the G50-proportioned cementitious material reaches 2.26 times that of traditional P·O42.5 cement.

[0082] (3) Optimal setting time: The slag powder content is controlled to no more than 50% so that the initial setting time of the alkali-activated cementitious material meets the requirement of ≥45 minutes in the current standard GB 175-2007 "General Portland Cement". When the slag powder content is higher, the initial setting time is too short, which is not conducive to practical engineering application.

[0083] (4) Low carbon characteristics: Taking G50 as an example, compared with the comparative example P·O42.5 cement, CO2 emissions are reduced by 82% (based on production energy consumption conversion), which meets the national "dual carbon" requirements.

[0084] The calculation method is as follows:

[0085] Carbon emissions comparison table

[0086]

[0087] The calculation formula for carbon emissions from the fly ash-slag based alkali activated cementitious materials is:

[0088]

[0089] Where C represents the carbon emissions during the cementitious material production stage, in kgCO2 / t; Represents the unit carbon emission of the i-th raw material, in kgCO2 / t; m i It represents the percentage of the amount of the i-th raw material relative to the cementitious material, in %;

[0090] The carbon emissions of various raw materials are as follows:

[0091] Carbon emissions from fly ash-slag based alkali activated cementitious materials

[0092]

[0093] Among them, the carbon emission data of cement and water refer to the paper "The Impact of Mix Design Methods on Life Cycle Assessment of Recycled Concrete" published by Zhang Yurong, Xu Yaqin, Yao Zeyang, etc. in the Journal of Zhejiang University of Technology in 2020, Volume 48 (Issue 6); the emission data of fly ash and slag powder refer to the paper "Calculation and Comparison of Carbon Emission Factors of Four Commonly Used Mineral Admixtures" published by Lin Zuojiang, etc. in the second issue of Concrete World in 2025; the carbon emission data of sodium silicate and sodium hydroxide refer to the paper "Comprehensive Evaluation of the Performance and Environmental Impact of Mineralized Curing Alkali Activated Solid Waste Cementitious Materials" published by Wang Yixiao, etc. in the Silicate Bulletin, Volume 43 (Issue 3) in 2024.

[0094] The raw material sodium silicate is the main solid component of sodium water glass solution, Na2O·nSiO2, accounting for 33.33% of the solution mass.

[0095] According to the above carbon emission calculation formula, we can get:

[0096] An alkali-activated gelling material is made of the following raw materials, calculated by mass percentage: powder: 66.08% (50% slag powder + 50% fly ash), composite alkali activator: 23.81%, and added water: 10.11%.

[0097] The composite alkali activator is configured with an alkali equivalent of 0.07 and a composite alkali activator modulus of 1.2. The composite alkali activator comprises a sodium water glass solution and solid sodium hydroxide. The composite alkali activator is made from the following raw materials, calculated by mass percentage: 84.19% sodium water glass solution (modulus 3.25, SiO2 content 26.8%, Na2O content 8.53%, water content 64.67%) and 15.80% solid NaOH (purity ≥96%).

[0098]

[0099] C=150.06(kgCO2 / t)

[0100] Reduce carbon emissions by:

[0101]

[0102] In one embodiment of the present invention, a strength control method for an alkali-activated gelling material is provided. The method relies on the quantitative relationship between the mechanical performance index and the powder ratio. The specific strength control method is as follows:

[0103] S1. Clear strength requirements: In actual engineering applications, the target values ​​of the flexural strength y1 (unit: MPa) and compressive strength y2 (unit: MPa) of the required alkali-activated cementitious materials shall be clearly defined according to the design requirements and use environment of the specific project;

[0104] S2. Determine the powder ratio using a quantitative relationship: Given a mass percentage of slag powder in the powder as x (x ranges from 0 to 50), with a composite alkali activator modulus of 1.2 and an alkali equivalent of 0.07, the relationship between the powder ratio and the flexural and compressive strengths of the cementitious material is obtained by fitting a linear regression formula based on a large amount of experimental data in the early stage.

[0105] Flexural strength: y1 = 0.034x + 4.53 (0 ≤ x ≤ 50)

[0106] Compressive strength: y2=1.28x+32(0≤x≤50)

[0107] Based on the above quantitative relationship, if the target flexural strength y1 is known, the required slag powder mass percentage x can be calculated using the formula. Similarly, if the target compressive strength y2 is known, the slag powder mass percentage x can be calculated using the formula. When both the flexural strength and compressive strength target values ​​are known, the two x values ​​can be calculated separately. Taking into account the actual project conditions (such as material costs, construction technology, etc.), the appropriate x value can be selected, and the mass percentage of fly ash can be determined as (100-x)%.

[0108] S3. Based on the calculated mass percentages of slag powder and fly ash, accurately adjust the powder ratio when preparing the alkali-activated cementitious material. At the same time, use a composite alkali activator with a modulus of 1.2 and an alkali equivalent of 0.07, and strictly follow the established preparation process to prepare the alkali-activated cementitious material.

[0109] In the present invention, the quantitative relationship between the mechanical performance index and the powder ratio is fitted using a linear regression formula. The fitting process under the conditions of a composite alkali activator modulus of 1.2 and an alkali equivalent of 0.07 is as follows:

[0110] Assume that the flexural strength is y1 (unit: MPa), the compressive strength is y2 (unit: MPa), and the mass percentage of slag powder in the powder is x% (x ranges from 0 to 50).

[0111] Assume that the flexural strength y1 = ax + b

[0112] in

[0113]

[0114]

[0115] a=5.38-0.034×25=4.53

[0116] Within a given powder ratio range, the flexural strength and the slag content are approximately linearly positively correlated, and the relationship is y1=0.034x+4.53(0≤x≤50).

[0117] Assume compressive strength y2 = ax + b

[0118] in

[0119]

[0120] a=32-0×1.28=32

[0121] Within a given powder ratio range, the compressive strength and the slag content are approximately linearly positively correlated, and the relationship is y2=1.28x+32(0≤x≤50).

[0122] in conclusion:

[0123] The present invention achieves the synergistic optimization of mechanical properties and low-carbon characteristics by adjusting the raw material ratio (powder 64%-68%, composite alkali activator 21-35%, added water 0-12%), based on the optimization of the alkali activator modulus and alkali equivalent, and regulating the slag powder dosage. The compressive strength of the G50 formula reaches 95.95MPa, which is 199.8% higher than G0 and 125.76% higher than P·O42.5 cement (42.5MPa). Based on the quantitative linear model of slag powder dosage (x) and flexural strength y1=0.034x+4.53 (0≤x≤50) and compressive strength y2=1.28x+32 (0≤x≤50), the mechanical properties of cementitious materials can be regulated according to the powder mix ratio, and it has excellent engineering application potential.

[0124] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A fly ash-slag based alkali activated cementitious material, characterized in that: The raw material components of the alkali-activated cementitious material include, by mass percentage, 64%-68% powder, 21-35% composite alkali activator, and 0-12% added water; wherein, the powder includes, by mass percentage, 0-50% slag powder and 50%-100% fly ash.

2. The fly ash-slag based alkali activated cementitious material according to claim 1, characterized in that: The specific surface area of ​​the slag powder is 400-480m 2 / kg, meeting the S95 grade requirements in GB / T 18046-2017; and / or, the fly ash meets the requirements of Class F fly ash in GB / T 1596-2017 "Fly ash for cement and concrete", with a sieve residue of 45μm square hole sieve ≤10% and a loss on ignition <5%.

3. The fly ash-slag based alkali activated cementitious material according to claim 1, characterized in that: The composite alkali activator includes sodium water glass solution and solid sodium hydroxide, and the composite alkali activator has a modulus of 1.2 and an alkali equivalent of 0.07; and / or, the solid content is 31.97-45.55%, And / or, the sodium water glass solution has a modulus n of 3.25; and / or, the sodium water glass solution has an SiO2 content of 17.81%-26.87%, an Na2O content of 5.67%-8.53%, and a water content of 76.52%-64.67%; And / or, the purity of the main component of the solid sodium hydroxide, NaOH, is ≥96%; And / or, the components of the composite alkali activator and their mass percentages are: sodium water glass solution 84.19%, sodium hydroxide 0-15.80%.

4. The fly ash-slag based alkali activated cementitious material according to claim 1, characterized in that: The fly ash-slag based alkali activated cementitious material has a 28-day compressive strength of 30.0-100.0 MPa and a flexural strength of 4.0-7.0 MPa.

5. A method for preparing a fly ash-slag based alkali activated cementitious material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Preparing a composite alkali activator: mixing a sodium water glass solution with solid sodium hydroxide to obtain a composite alkali activator; S2. Mixed powder: Weigh slag powder and fly ash according to mass fraction and mix them at a low speed to obtain a mixed powder; S3. Preparation of alkali-activated gelling material: adding a composite alkali activator to the mixed powder and adding external water, stirring at a low speed for a certain period of time, stopping, and stirring at a high speed until the solid and liquid phases are fully integrated to present a viscous liquid with gelling characteristics, thereby preparing the gelling material.

6. The preparation method according to claim 5, characterized in that: The low-speed stirring speed is 100-200rpm, and the high-speed stirring speed is 300-500rpm; and / or, in step S2, stirring at a low speed for ≥20 s until the fly ash and slag powder are uniformly mixed; And / or, in step S3, stirring at a low speed for 1-5 minutes, stopping for 1-30 seconds, and stirring at a high speed for 1-5 minutes.

7. The preparation method according to claim 5, characterized in that: After the preparation of the cementitious material, the flexural strength and compressive strength test steps are also included to prepare the pure slurry test blocks: the alkali-activated cementitious material prepared by S3 is poured into 40mm×40mm×100mm and 40mm×40mm×40mm molds, and the mold surface is covered with plastic wrap; the mold is removed 24-96 hours after pouring, and the material is cured at 25°C and 95% humidity for 28 days.

8. A method for controlling the strength of fly ash-slag based alkali activated cementitious materials according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Determine the quantitative relationship: Set the slag powder content x, flexural strength y1, and compressive strength y2; under fixed conditions, change the slag powder content x to obtain the flexural strength y1 and compressive strength y2 of the corresponding material; use linear regression formulas to fit the quantitative relationship between the slag powder content x and the flexural strength y1, and the quantitative relationship between the slag powder content x and the compressive strength y2; S2. Set target values: Set target flexural strength y1 and compressive strength y2 according to project requirements; S3. Calculate the slag powder content x under the conditions: Substitute the target value into the quantitative relationship formula for flexural strength and / or the quantitative relationship formula for compressive strength to calculate the slag powder content x; S4. Adjust the powder ratio according to the calculated slag powder dosage, and prepare a cementitious material of target strength according to the preparation method of any one of claims 5 to 7.

9. The method for controlling the strength of fly ash-slag based alkali activated cementitious materials according to claim 8, characterized in that: Under the conditions of a composite base activator modulus of 1.2 and a base equivalent of 0.07, the quantitative relationship is as follows: Quantitative relationship formula for flexural strength: y1 = 0.034x + 4.53 (0 ≤ x ≤ 50); And / or, the quantitative relationship formula for compressive strength is: y2=1.28x+32(0≤x≤50).

10. Use of the fly ash-slag based alkali-activated cementitious material according to any one of claims 1 to 4, or the fly ash-slag based alkali-activated cementitious material prepared by the preparation method according to any one of claims 5 to 7, or the fly ash-slag based alkali-activated cementitious material prepared by the strength control method according to any one of claims 8 to 9 in the field of construction.

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