Low-carbon environmentally friendly building cement and preparation method thereof

Abstract

The present application discloses a low-carbon and environmentally friendly building cement and its preparation method, belonging to the field of building materials technology. The cement comprises silicate cement clinker, fly ash, slag powder, steel slag powder, construction waste recycled powder, a composite activator, a biomineralization additive, and a nano-modifier. Based on the weight of the cement, the silicate cement clinker content is 15-25wt%, the fly ash content is 25-35wt%, the slag powder content is 20-30wt%, the steel slag powder content is 8-15wt%, the construction waste recycled powder content is 5-12wt%, the composite activator content is 2-6wt%, the biomineralization additive content is 1.5-3.5wt%, and the nano-modifier content is 1.5-4.5wt%.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and more specifically, to a low-carbon and environmentally friendly building cement and a preparation method thereof. Background Art

[0002] As the most widely used building cementitious material, Portland cement plays an irreplaceable role in infrastructure construction. However, the production of traditional Portland cement presents significant environmental and resource issues, which have become a major factor restricting the sustainable development of the building materials industry.

[0003] First, cement production emits high carbon emissions. According to statistics, producing one ton of Portland cement releases approximately 0.8 to 1.0 tons of carbon dioxide. Approximately 60% of this carbon emission comes from the decarbonization reaction during limestone calcination, while the remaining 40% comes from the combustion of fuel required for high-temperature calcination. This high carbon emission characteristic makes the cement industry one of the world's major carbon emitters. Second, traditional cement production relies heavily on natural mineral resources such as limestone and clay. Large-scale mining of these resources severely damages the geological structure and ecological environment, making it difficult to meet the requirements of resource recycling and ecological protection.

[0004] Furthermore, current industrial by-products such as fly ash, slag, and steel slag are not being efficiently utilized. Some solid wastes have even become sources of pollution, increasing disposal costs while failing to effectively alleviate the pressure on cement raw material resources. While traditional processes have attempted to incorporate some industrial solid wastes into cement systems as alternative materials, these processes are limited by factors such as insufficient activation, limited dosage, and unstable interface structures. The resulting products generally exhibit suboptimal early strength and durability, making them difficult to meet high-standard engineering requirements.

[0005] Furthermore, the firing of cement clinker requires a high temperature environment of 1450-1500°C, resulting in significant energy consumption and heavy reliance on non-renewable energy sources such as coal, exacerbating energy shortages and environmental pollution. While some existing technologies attempt to reduce carbon emissions by replacing clinker raw materials, a systematic and integrated low-carbon solution is still lacking. In particular, research on promoting the high-value utilization of solid waste resources and synergistic carbon sequestration remains insufficient.

[0006] In summary, how to develop an environmentally friendly construction cement with high performance, low carbon emissions and high solid waste utilization rate and its preparation method has become a technical problem that needs to be solved urgently. Summary of the Invention

[0007] In order to overcome a series of defects in the prior art, the purpose of the present application is to provide a low-carbon and environmentally friendly construction cement for the above-mentioned problems, including silicate cement clinker, fly ash, slag powder, steel slag powder, construction waste recycled powder, a composite activator, a biomineralization additive and a nano-modifier. Based on the weight of the cement, the content of the silicate cement clinker is 15-25wt%, the content of the fly ash is 25-35wt%, the content of the slag powder is 20-30wt%, the content of the steel slag powder is 8-15wt%, the content of the construction waste recycled powder is 5-12wt%, the content of the composite activator is 2-6wt%, the content of the biomineralization additive is 1.5-3.5wt%, and the content of the nano-modifier is 1.5-4.5wt%.

[0008] Furthermore, the fly ash is Class I fly ash with a specific surface area of ​​300-400m 2 / kg; the slag powder is S95 grade, with a specific surface area of ​​400-500m 2 / kg; the specific surface area of ​​the steel slag powder is 400-450m 2 / kg, free calcium oxide content ≤3wt%; the particle size of the construction waste recycled powder is <45μm, and the chloride ion content is ≤0.02wt%.

[0009] Furthermore, calculated by weight percentage, the fly ash includes the following components: 45-65wt% SiO2, 15-35wt% Al2O3, 4-20wt% Fe2O3, 1-12wt% CaO, 0.5-5wt% MgO, K2O+Na2O content ≤3wt%, loss on ignition ≤5wt%, and the total content of SiO2+Al2O3+Fe2O3 ≥70wt%.

[0010] Furthermore, calculated by weight percentage, the slag powder includes the following components: 32-42wt% CaO, 28-38wt% SiO2, 8-19wt% Al2O3, 5-15wt% MgO, no more than 1.5wt% Fe2O3, no more than 2.5wt% S, and the basicity coefficient (CaO+MgO) / (SiO2+Al2O3) is 0.9-1.4.

[0011] Furthermore, the composite activator includes an alkaline activator, a sulfate activator and an organic activator, the alkaline activator is a composite of sodium hydroxide and water glass, wherein the modulus of water glass is 1.2-1.5, and the alkaline activator accounts for 40-60% of the weight of the composite activator; the sulfate activator is a composite of dihydrate gypsum and anhydrous gypsum, with a weight ratio of 2:1-1:2, and the sulfate activator accounts for 35-55% of the weight of the composite activator; the organic activator is a composite of sodium citrate and triethanolamine, with a weight ratio of 1:1-2:1, and the organic activator accounts for 3-8% of the weight of the composite activator.

[0012] Furthermore, the biomineralization additive includes a Bacillus pasteurianus bacterial solution, a nutrient medium, and a pH buffer of potassium dihydrogen phosphate, wherein the viable cell count of the Bacillus pasteurianus bacterial solution is 1×10 8 -5×10 8 CFU / ml, accounting for 30-50% of the weight of the biomineralization additive; the nutrient medium includes urea and calcium chloride in a molar ratio of 1:1, accounting for 40-60% of the weight of the biomineralization additive; the pH buffer potassium dihydrogen phosphate accounts for 3-8% of the weight of the biomineralization additive.

[0013] Furthermore, the nano-modifier includes nano-silicon dioxide, nano-calcium carbonate and a surfactant, wherein the average particle size of the nano-silicon dioxide is 10-30 nm and the specific surface area is 150-300 m 2 / g, accounting for 60-80% of the weight of the nano modifier; the average particle size of the nano calcium carbonate is 20-50nm, accounting for 15-35% of the weight of the nano modifier; the surfactant is a polycarboxylic acid surfactant, accounting for 3-8% of the weight of the nano modifier.

[0014] Furthermore, the purity of the nano-silicon dioxide is ≥99% and is an amorphous structure; the purity of the nano-calcium carbonate is ≥97% and is a calcite or aragonite crystal type; the general structural formula of the polycarboxylic acid surfactant is R1-[OCH2CH2] x -[OCH(CH2R2)CH2] y -OSO3H, wherein: R1 is methyl or isobutylene, R2 is -COOH or -SO3H, x is 30-120, and y is 5-25; the polycarboxylic acid surfactant is a polycarboxylic acid water reducer, having a main chain molecular weight of 20,000-80,000, an acid equivalent of 2,000-5,000 g / mol, a water reduction rate ≥25%, and a solid content of 40-50 wt%.

[0015] In addition, the present application also provides a method for preparing low-carbon and environmentally friendly building cement, which includes the following steps.

[0016] Step 1: Raw material pretreatment, specifically including: roasting fly ash at 800-900℃ for 30-45 minutes and cooling to room temperature; grinding slag in a ball mill to make its specific surface area reach 450-500m 2 / kg; the steel slag is subjected to magnetic separation to remove iron, and then ball milled to a specific surface area of ​​400-450m 2 / kg, and the free calcium oxide content is controlled below 3wt%; the construction waste is sorted, crushed and sieved to obtain recycled powder with a particle size of <45μm, and the chloride ion content is controlled below 0.02wt%.

[0017] Step 2, preparing a composite activator, specifically: dissolving sodium hydroxide in water glass to prepare an alkaline activator solution with a modulus of 1.2-1.5; mixing dihydrate gypsum and anhydrous gypsum in a weight ratio of 2:1-1:2 to prepare a sulfate activator; mixing sodium citrate and triethanolamine in a weight ratio of 1:1-2:1 to prepare an organic activator; mixing the sulfate activator, sulfate activator and organic activator in a weight ratio to obtain a composite activator.

[0018] Step 3: Preparation of biomineralization additives: culturing Bacillus pasteurianus at 30±2°C and pH 9.0±0.2 for 24 hours until the viable cell count reaches 1×10 8 -5×10 8 CFU / ml; dissolve urea and calcium chloride in deionized water at a molar ratio of 1:1 to a concentration of 0.5-1.0 mol / L; mix the bacterial solution with the nutrient medium, add potassium dihydrogen phosphate to adjust the pH to 8.5-9.0, and pre-react at 25-30°C for 2-4 hours.

[0019] Step 4, preparation of nano-modifier, specifically: pre-dispersing nano-silica and surfactant in water for 30 minutes; using ultrasonic treatment with a power of 200-300W for 15-20 minutes to eliminate agglomeration; adding nano-calcium carbonate and continuing stirring for 10-15 minutes to obtain a nano-modifier dispersion.

[0020] Step 5: Cement preparation and molding, specifically: put silicate cement clinker, activated fly ash, treated slag powder, steel slag powder, and construction waste recycled powder into a V-type mixer according to the proportion, and mix for 15-20 minutes; according to the water-cement ratio of 0.28-0.35, first add 70wt% of water and all liquid additives and stir for 2 minutes, then add powder materials in batches and stir for 5-8 minutes, and finally add the remaining water and nano modifier dispersion and stir for 2 minutes; adopt vibration molding, with a vibration frequency of 50Hz, an amplitude of 2-3mm, a molding pressure of 2-3MPa, and a time of 30-60 seconds.

[0021] Step six, curing in stages, specifically: curing for 24-48 hours at a temperature of 20±2℃ and a relative humidity ≥95%; curing for 7-14 days at a temperature of 25±2℃ and a relative humidity ≥90% to promote microbial-induced carbonate precipitation reaction; and continuing curing to the design age under standard curing conditions of a temperature of 20±2℃ and a relative humidity ≥95%.

[0022] Furthermore, in the step 2, the concentration of the alkaline activator solution is 8-12 mol / L, the SO3 content in the sulfate activator is controlled at 4-6wt%, and the organic activator is prepared and used immediately; in the step 3, during the biomineralization pretreatment process, the pre-reaction is terminated when the CO2 conversion rate reaches more than 60%, and the conversion rate is detected by gas chromatography; in the step 5, the temperature is controlled below 35°C during the wet mixing process to ensure the activity of the strain; in the step 6, the pH value is detected every 2-3 days during the biomineralization maintenance period and maintained within the range of 8.0-9.5.

[0023] Compared with the existing technology, this application has the following beneficial effects: 1) Through the microbial induced carbonate precipitation (MICP) technology, CO2 is converted into stable calcium carbonate deposits, which significantly reduces carbon emissions compared to traditional Portland cement, and the emission reduction rate can reach more than 50%; 2) Synergistic utilization of various solid wastes such as fly ash, slag, steel slag and construction waste recycled powder, with a total solid waste content of more than 65%, effectively improving the level of resource utilization; 3) The process flow can be adapted and implemented on the basis of existing cement production lines, with strong technical compatibility and low transformation cost advantages; 4) The proportion of alternative raw materials is high, the energy consumption in the calcination link is low, and the overall raw material and energy consumption costs are significantly reduced, which has good economic benefits and application prospects. DETAILED DESCRIPTION

[0024] To make this application easier to understand, the following examples will be used to further illustrate this application. These examples are merely illustrative and do not limit the scope of application of this application. The raw materials or components used in this application can be purchased or prepared by conventional methods unless otherwise specified.

[0025] In a broad embodiment of the present application, a low-carbon and environmentally friendly construction cement includes silicate cement clinker, fly ash, slag powder, steel slag powder, construction waste recycled powder, a composite activator, a biomineralization additive and a nano-modifier. Based on the weight of the cement, the content of the silicate cement clinker is 15-25wt%, the content of the fly ash is 25-35wt%, the content of the slag powder is 20-30wt%, the content of the steel slag powder is 8-15wt%, the content of the construction waste recycled powder is 5-12wt%, the content of the composite activator is 2-6wt%, the content of the biomineralization additive is 1.5-3.5wt%, and the content of the nano-modifier is 1.5-4.5wt%.

[0026] Furthermore, the Portland cement clinker adopts ordinary Portland cement clinker of P·I 52.5 grade in accordance with GB175-2007 standard, and comprises the following components by weight percentage: tricalcium silicate 55-65wt%, dicalcium silicate 18-28wt%, tricalcium aluminate 6-12wt%, tetracalcium aluminoferrite 8-15wt%, free calcium oxide ≤1.0wt%, free magnesium oxide ≤5.0wt%, and a specific surface area of ​​320-380m 2 / kg.

[0027] Furthermore, the fly ash is Class I fly ash with a specific surface area of ​​300-400m 2 / kg; the slag powder is S95 grade, with a specific surface area of ​​400-500m 2 / kg; the specific surface area of ​​the steel slag powder is 400-450m 2 / kg, free calcium oxide content ≤3wt%; the particle size of the construction waste recycled powder is <45μm, and the chloride ion content is ≤0.02wt%.

[0028] Furthermore, calculated by weight percentage, the fly ash includes the following components: 45-65wt% SiO2, 15-35wt% Al2O3, 4-20wt% Fe2O3, 1-12wt% CaO, 0.5-5wt% MgO, K2O+Na2O content ≤3wt%, loss on ignition ≤5wt%, and the total content of SiO2+Al2O3+Fe2O3 ≥70wt%.

[0029] Furthermore, calculated by weight percentage, the slag powder includes the following components: 32-42wt% CaO, 28-38wt% SiO2, 8-19wt% Al2O3, 5-15wt% MgO, no more than 1.5wt% Fe2O3, no more than 2.5wt% S, and the basicity coefficient (CaO+MgO) / (SiO2+Al2O3) is 0.9-1.4.

[0030] Furthermore, the composite activator includes an alkaline activator, a sulfate activator and an organic activator, the alkaline activator is a composite of sodium hydroxide and water glass, wherein the modulus of water glass is 1.2-1.5, and the alkaline activator accounts for 40-60% of the weight of the composite activator; the sulfate activator is a composite of dihydrate gypsum and anhydrous gypsum, with a weight ratio of 2:1-1:2, and the sulfate activator accounts for 35-55% of the weight of the composite activator; the organic activator is a composite of sodium citrate and triethanolamine, with a weight ratio of 1:1-2:1, and the organic activator accounts for 3-8% of the weight of the composite activator.

[0031] Furthermore, the molecular formula of the water glass is Na2O·nSiO2·mH2O, wherein n is the modulus, m is the number of water molecules, the value of n is 1.2-1.5, and the value of m is 8-12; the purity of the sodium hydroxide is ≥96%.

[0032] Furthermore, the purity of the dihydrate gypsum is ≥85%; the purity of the anhydrous gypsum is ≥90%; the purity of the sodium citrate is ≥99%; and the purity of the triethanolamine is ≥85%.

[0033] Furthermore, the biomineralization additive includes a Bacillus pasteurianus bacterial solution, a nutrient medium, and a pH buffer of potassium dihydrogen phosphate, wherein the viable cell count of the Bacillus pasteurianus bacterial solution is 1×10 8 -5×10 8 CFU / ml, accounting for 30-50% of the weight of the biomineralization additive; the nutrient medium includes urea and calcium chloride in a molar ratio of 1:1, accounting for 40-60% of the weight of the biomineralization additive; the pH buffer potassium dihydrogen phosphate accounts for 3-8% of the weight of the biomineralization additive.

[0034] Furthermore, the purity of the urea is ≥99%; the purity of the calcium chloride is ≥95%; the purity of the potassium dihydrogen phosphate is ≥99%, and the pH buffer range is 6.0-7.5.

[0035] Furthermore, the nano-modifier includes nano-silicon dioxide, nano-calcium carbonate and a surfactant, wherein the average particle size of the nano-silicon dioxide is 10-30 nm and the specific surface area is 150-300 m 2 / g, accounting for 60-80% of the weight of the nano modifier; the average particle size of the nano calcium carbonate is 20-50nm, accounting for 15-35% of the weight of the nano modifier; the surfactant is a polycarboxylic acid surfactant, accounting for 3-8% of the weight of the nano modifier.

[0036] Furthermore, the purity of the nano-silicon dioxide is ≥99% and is an amorphous structure; the purity of the nano-calcium carbonate is ≥97% and is a calcite or aragonite crystal type; the general structural formula of the polycarboxylic acid surfactant is R1-[OCH2CH2] x -[OCH(CH2R2)CH2] y -OSO3H, wherein: R1 is methyl or isobutylenyl, R2 is -COOH or -SO3H, x is 30-120, and y is 5-25.

[0037] Furthermore, the polycarboxylic acid surfactant is a polycarboxylic acid water reducer with a main chain molecular weight of 20,000-80,000, an acid equivalent of 2,000-5,000 g / mol, a water reduction rate of ≥25%, and a solid content of 40-50 wt%.

[0038] In addition, a method for preparing low-carbon and environmentally friendly building cement is provided, which includes the following steps.

[0039] Step 1: Raw material pretreatment, specifically including: roasting fly ash at 800-900℃ for 30-45 minutes and cooling to room temperature; grinding slag in a ball mill to make its specific surface area reach 450-500m 2 / kg; the steel slag is subjected to magnetic separation to remove iron, and then ball milled to a specific surface area of ​​400-450m 2 / kg, and the free calcium oxide content is controlled below 3wt%; the construction waste is sorted, crushed and sieved to obtain recycled powder with a particle size of <45μm, and the chloride ion content is controlled below 0.02wt%.

[0040] Step 2, preparing a composite activator, specifically: dissolving sodium hydroxide in water glass to prepare an alkaline activator solution with a modulus of 1.2-1.5; mixing dihydrate gypsum and anhydrous gypsum in a weight ratio of 2:1-1:2 to prepare a sulfate activator; mixing sodium citrate and triethanolamine in a weight ratio of 1:1-2:1 to prepare an organic activator; mixing the sulfate activator, sulfate activator and organic activator in a weight ratio to obtain a composite activator.

[0041] Step 3: Preparation of biomineralization additives: culturing Bacillus pasteurianus at 30±2°C and pH 9.0±0.2 for 24 hours until the viable cell count reaches 1×10 8 -5×10 8 CFU / ml; dissolve urea and calcium chloride in deionized water at a molar ratio of 1:1 to a concentration of 0.5-1.0 mol / L; mix the bacterial solution with the nutrient medium, add potassium dihydrogen phosphate to adjust the pH to 8.5-9.0, and pre-react at 25-30°C for 2-4 hours.

[0042] Step 4, preparation of nano-modifier, specifically: pre-dispersing nano-silica and surfactant in water for 30 minutes; using ultrasonic treatment with a power of 200-300W for 15-20 minutes to eliminate agglomeration; adding nano-calcium carbonate and continuing stirring for 10-15 minutes to obtain a nano-modifier dispersion.

[0043] Step 5: Cement preparation and molding, specifically: put silicate cement clinker, activated fly ash, treated slag powder, steel slag powder, and construction waste recycled powder into a V-type mixer according to the proportion, and mix for 15-20 minutes; according to the water-cement ratio of 0.28-0.35, first add 70wt% of water and all liquid additives and stir for 2 minutes, then add powder materials in batches and stir for 5-8 minutes, and finally add the remaining water and nano modifier dispersion and stir for 2 minutes; adopt vibration molding, with a vibration frequency of 50Hz, an amplitude of 2-3mm, a molding pressure of 2-3MPa, and a time of 30-60 seconds.

[0044] Step six, curing in stages, specifically: curing for 24-48 hours at a temperature of 20±2℃ and a relative humidity ≥95%; curing for 7-14 days at a temperature of 25±2℃ and a relative humidity ≥90% to promote microbial-induced carbonate precipitation reaction; and continuing curing to the design age under standard curing conditions of a temperature of 20±2℃ and a relative humidity ≥95%.

[0045] Furthermore, in the step 2, the concentration of the alkaline activator solution is 8-12 mol / L, the SO3 content in the sulfate activator is controlled at 4-6 wt%, and the organic activator is prepared and used immediately.

[0046] Furthermore, in the step three, during the biomineralization pretreatment process, the pre-reaction is terminated when the CO2 conversion rate reaches 60% or more, and the conversion rate is detected by gas chromatography.

[0047] Furthermore, in step five, the temperature during the wet mixing process is controlled below 35° C. to ensure the activity of the strain.

[0048] Furthermore, in step six, the pH value is tested every 2-3 days during the biomineralization curing period and maintained within the range of 8.0-9.5.

[0049] The following lists the embodiments of the present application to further explain the present application in detail.

[0050] Example 1.

[0051] This embodiment provides a low-carbon and environmentally friendly building cement, which is composed of 20 wt% of Portland cement clinker; 30 wt% of Class I fly ash (specific surface area 350 m2); 2 / kg); 25wt% S95 grade slag powder (specific surface area 450m 2 / kg); 10wt% steel slag powder (specific surface area 420m 2 / kg, free CaO content 2.5wt%); 8wt% construction waste recycled powder (particle size <45μm, chloride ion content 0.015wt%); 4wt% composite activator; 2.5wt% biomineralization additive; 3wt% nano-modifier.

[0052] The method for preparing low-carbon and environmentally friendly building cement in this embodiment includes the following steps.

[0053] Raw material pretreatment: fly ash is calcined at 850℃ for 40 minutes; slag is ball-milled to a specific surface area of ​​450m 2 / kg; steel slag is magnetically separated to remove iron and then ball milled to a specific surface area of ​​420m 2 / kg; construction waste is sorted, crushed and screened to <45μm.

[0054] Preparation of composite activator: prepare alkaline activator (concentration 10 mol / L) with sodium hydroxide and water glass with a modulus of 1.3, prepare sulfate activator with dihydrate gypsum: anhydrous gypsum = 3:2, prepare organic activator with sodium citrate: triethanolamine = 3:2, and mix the three in a weight ratio of 2:2.5:0.3.

[0055] Preparation of biomineralization additives: Bacillus pasteurianus was cultured at 30°C and pH 9.0 for 24 h until the viable cell count reached 3×10 8 CFU / ml; urea and calcium chloride were prepared in a 1:1 molar ratio to prepare a 0.8 mol / L nutrient medium; after mixing, potassium dihydrogen phosphate was added to adjust the pH to 8.8, and the mixture was pre-reacted at 28°C for 3 hours, and the CO2 conversion rate reached 65%.

[0056] Preparation of nano-modifier: nano-SiO2 (particle size 20nm, specific surface area 200m 2 / g) was pre-dispersed with polycarboxylic acid surfactant for 30 minutes, ultrasonically treated for 18 minutes (250W), and nano-CaCO3 (particle size 30nm) was added and stirred for 12 minutes.

[0057] Cement preparation: dry mixing for 18 minutes, wet mixing with a water-cement ratio of 0.32, first add 70wt% water and liquid additives and stir for 2 minutes, add powder in batches and stir for 6 minutes, and finally add the remaining water and nano-modifier and stir for 2 minutes. The mixing temperature is controlled at 32℃.

[0058] Molding and curing: vibration molding (frequency 50 Hz, amplitude 2.5 mm, pressure 2.5 MPa, time 45 seconds), initial curing (20 ° C, RH > 95%, 36 hours), biomineralization curing (25 ° C, RH > 90%, 10 days), standard curing to the age.

[0059] The performance test results are: 3-day compressive strength is 28.5MPa; 28-day compressive strength is 56.2MPa; 90-day compressive strength is 68.7MPa; impermeability grade is P14; frost resistance grade is F350; carbon emission reduction rate is 53%; solid waste utilization rate is 68%.

[0060] Example 2.

[0061] Calculated by weight percentage, the composition of the low-carbon and environmentally friendly construction cement provided in this embodiment is: 18wt% of silicate cement clinker; 32wt% of Class I fly ash; 28wt% of S95 grade slag powder; 12wt% of steel slag powder; 10wt% of construction waste recycled powder; 5wt% of composite activator; 3wt% of biomineralization additive; and 4wt% of nano-modifier.

[0062] Compared with Example 1, the preparation process parameters were adjusted as follows: fly ash roasting temperature 880°C, time 35 minutes; bacterial count 4×10 8 CFU / ml; nutrient medium concentration 1.0 mol / L; pre-reaction temperature 30℃, time 2.5 hours, CO2 conversion rate 70%; nano-SiO2 particle size 15nm; water-binder ratio 0.30; biomineralization curing 12 days.

[0063] The performance test results are: 28-day compressive strength is 58.8MPa; 90-day compressive strength is 71.3MPa; the impermeability grade is P16, the carbon emission reduction rate is 56%; and the solid waste utilization rate is 70%.

[0064] Example 3.

[0065] Calculated by weight percentage, the composition of the low-carbon and environmentally friendly construction cement provided in this embodiment is: 22wt% of silicate cement clinker; 28wt% of Class I fly ash; 22wt% of S95 grade slag powder; 14wt% of steel slag powder; 6wt% of construction waste recycled powder; 3.5wt% of composite activator; 2wt% of biomineralization additive; and 2.5wt% of nano-modifier.

[0066] Performance test results: 28-day compressive strength is 54.1MPa; 90-day compressive strength is 66.8MPa; impermeability grade is P12; carbon emission reduction rate is 51%; solid waste utilization rate is 64%.

[0067] Comparative Example 1 (conventional Portland cement).

[0068] Ordinary Portland cement P.O52.5, prepared in standard proportion.

[0069] The performance test results are: 28-day compressive strength is 52.5MPa; 90-day compressive strength is 58.2MPa; impermeability grade is P8; carbon emissions are 850kg CO2 / t cement; solid waste utilization rate: 0%.

[0070] Comparative Example 2 (ordinary composite cement).

[0071] Portland cement clinker 70wt%, fly ash 20wt%, slag 10wt%, conventional preparation process.

[0072] The performance test results are: 28-day compressive strength is 45.2MPa; 90-day compressive strength is 52.8MPa; impermeability grade is P6; carbon emission reduction rate is 25%; solid waste utilization rate is 30%.

[0073] Comparison with the comparative examples shows that the low-carbon, environmentally friendly building cement of this application achieves significant carbon emission reduction and high solid waste utilization while maintaining excellent mechanical properties. Specifically, in terms of mechanical properties, the 28-day compressive strength is 3-12% higher than that of traditional Portland cement, and the 90-day compressive strength is 15-22% higher. In terms of durability, the impermeability grade is significantly improved from P8 to P12-P16. In terms of environmental performance, the carbon emission reduction rate reaches over 50%, and the solid waste utilization rate exceeds 65%. In terms of microscopic mechanism, SEM and XRD analysis show that CaCO3 crystals formed by microbial-induced carbonate precipitation effectively fill the pores, and the CSH gel and biomineralization products work synergistically to form a denser microstructure.

[0074] It should be noted that the embodiments described above are only used to explain the present application and do not constitute any limitation to the present application. The present application has been described with reference to the embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. Although the present application described therein relates to specific methods, materials and embodiments, it does not mean that the present application is limited to the specific examples disclosed therein. On the contrary, the present application can be extended to all other methods and applications with the same function.

Claims

1. A low-carbon and environmentally friendly building cement, characterized in that: The invention comprises silicate cement clinker, fly ash, slag powder, steel slag powder, construction waste recycled powder, a composite activator, a biomineralization additive and a nano-modifier. Based on the weight of the cement, the content of the silicate cement clinker is 15-25wt%, the content of the fly ash is 25-35wt%, the content of the slag powder is 20-30wt%, the content of the steel slag powder is 8-15wt%, the content of the construction waste recycled powder is 5-12wt%, the content of the composite activator is 2-6wt%, the content of the biomineralization additive is 1.5-3.5wt%, and the content of the nano-modifier is 1.5-4.5wt%. The composite activator includes an alkaline activator, a sulfate activator and an organic activator, wherein the alkaline activator is a compound of sodium hydroxide and water glass, wherein the modulus of the water glass is 1.2-1.5, and the alkaline activator accounts for 40-60% of the weight of the composite activator; the sulfate activator is a compound of dihydrate gypsum and anhydrous gypsum, with a weight ratio of 2:1-1:2, and the sulfate activator accounts for 35-55% of the weight of the composite activator; the organic activator is a compound of sodium citrate and triethanolamine, with a weight ratio of 1:1-2:1, and the organic activator accounts for 3-8% of the weight of the composite activator; The biomineralization additive comprises a Bacillus pasteurianus bacterial solution, a nutrient medium, and a pH buffer agent, potassium dihydrogen phosphate. The viable cell count of the Bacillus pasteurianus bacterial solution is 1×10 8 -5×10 8 CFU / ml, accounting for 30-50% of the weight of the biomineralization additive; the nutrient medium comprises urea and calcium chloride in a molar ratio of 1:1, accounting for 40-60% of the weight of the biomineralization additive; the pH buffer potassium dihydrogen phosphate accounts for 3-8% of the weight of the biomineralization additive; The nano-modifier comprises nano-silicon dioxide, nano-calcium carbonate and a surfactant. The average particle size of the nano-silicon dioxide is 10-30 nm, and the specific surface area is 150-300 m 2 / g, accounting for 60-80% of the weight of the nano modifier; the average particle size of the nano calcium carbonate is 20-50nm, accounting for 15-35% of the weight of the nano modifier; the surfactant is a polycarboxylic acid surfactant, accounting for 3-8% of the weight of the nano modifier.

2. The low-carbon and environmentally friendly building cement according to claim 1, characterized in that: The fly ash is Class I fly ash with a specific surface area of ​​300-400m 2 / kg; the slag powder is S95 grade, with a specific surface area of ​​400-500m 2 / kg; the specific surface area of ​​the steel slag powder is 400-450m 2 / kg, free calcium oxide content ≤3wt%; the particle size of the construction waste recycled powder is <45μm, and the chloride ion content is ≤0.02wt%.

3. The low-carbon and environmentally friendly building cement according to claim 2, characterized in that: Calculated by weight percentage, the fly ash includes the following components: 45-65wt% SiO2, 15-35wt% Al2O3, 4-20wt% Fe2O3, 1-12wt% CaO, 0.5-5wt% MgO, K2O+Na2O content ≤3wt%, loss on ignition ≤5wt%, and the total content of SiO2+Al2O3+Fe2O3 ≥70wt%.

4. The low-carbon and environmentally friendly building cement according to claim 2, characterized in that: Calculated by weight percentage, the slag powder includes the following components: 32-42wt% of CaO, 28-38wt% of SiO2, 8-19wt% of Al2O3, 5-15wt% of MgO, no more than 1.5wt% of Fe2O3, no more than 2.5wt% of S, and the basicity coefficient (CaO+MgO) / (SiO2+Al2O3) is 0.9-1.

4.

5. The low-carbon and environmentally friendly building cement according to claim 1, characterized in that: The purity of the nano-silicon dioxide is ≥99% and is an amorphous structure; the purity of the nano-calcium carbonate is ≥97% and is a calcite or aragonite crystal type; the general structural formula of the polycarboxylic acid surfactant is R1-[OCH2CH2] x -[OCH(CH2R2)CH2] y -OSO3H, wherein: R1 is methyl or isobutylenyl, R2 is -COOH or -SO3H, x is 30-120, and y is 5-25.

6. A method for preparing low-carbon and environmentally friendly building cement according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, raw material pretreatment, specifically comprising: roasting fly ash at 800-900°C for 30-45 minutes and cooling to room temperature; The slag is ground in a ball mill to a specific surface area of ​​450-500m 2 / kg; the steel slag is subjected to magnetic separation to remove iron, and then ball milled to a specific surface area of ​​400-450m 2 / kg, the free calcium oxide content is controlled below 3wt%; the construction waste is sorted, crushed and sieved to obtain recycled powder with a particle size of <45μm and a chloride ion content of less than 0.02wt%; Step 2, preparing a composite activator, specifically: dissolving sodium hydroxide in water glass to prepare an alkaline activator solution with a modulus of 1.2-1.5; mixing dihydrate gypsum and anhydrous gypsum in a weight ratio of 2:1-1:2 to prepare a sulfate activator; mixing sodium citrate and triethanolamine in a weight ratio of 1:1-2:1 to prepare an organic activator; mixing the alkaline activator, sulfate activator and organic activator in a weight ratio to obtain a composite activator; Step 3: Preparation of biomineralization additives: culturing Bacillus pasteurianus at 30±2°C and pH 9.0±0.2 for 24 hours until the viable cell count reaches 1×10 8 -5×10 8 CFU / ml; dissolve urea and calcium chloride in deionized water at a molar ratio of 1:1 to a concentration of 0.5-1.0 mol / L; mix the bacterial solution with the nutrient medium, add potassium dihydrogen phosphate to adjust the pH to 8.5-9.0, and pre-react at 25-30°C for 2-4 hours; Step 4, preparing the nano-modifier, specifically: pre-dispersing nano-silica and surfactant in water for 30 minutes; using ultrasonic treatment at a power of 200-300W for 15-20 minutes to eliminate agglomeration; adding nano-calcium carbonate and continuing stirring for 10-15 minutes to obtain a nano-modifier dispersion; Step 5, cement preparation and molding, specifically: Portland cement clinker, activated fly ash, treated slag powder, steel slag powder, and construction waste recycled powder are put into a V-type mixer according to a proportion and mixed for 15-20 minutes; according to a water-binder ratio of 0.28-0.35, 70wt% of water, a composite activator, and a biomineralization additive are first added and stirred for 2 minutes, then the powder materials are added in batches and stirred for 5-8 minutes, and finally the remaining water and nano-modifier dispersion are added and stirred for 2 minutes; vibration molding is adopted with a vibration frequency of 50Hz, an amplitude of 2-3mm, a molding pressure of 2-3MPa, and a time of 30-60 seconds; Step six, curing in stages, specifically: curing for 24-48 hours at a temperature of 20±2℃ and a relative humidity ≥95%; curing for 7-14 days at a temperature of 25±2℃ and a relative humidity ≥90% to promote microbial-induced carbonate precipitation reaction; and continuing curing to the design age under standard curing conditions of a temperature of 20±2℃ and a relative humidity ≥95%.

7. The method for preparing low-carbon and environmentally friendly building cement according to claim 6, characterized in that: In the step 2, the concentration of the alkaline activator solution is 8-12 mol / L, the SO3 content in the sulfate activator is controlled at 4-6wt%, and the organic activator is prepared and used immediately; in the step 3, during the biomineralization pretreatment process, the pre-reaction is terminated when the CO2 conversion rate reaches more than 60%, and the conversion rate is detected by gas chromatography; in the step 5, the temperature is controlled below 35°C during the wet mixing process to ensure the activity of the strain; in the step 6, the pH value is detected every 2-3 days during the biomineralization curing period and maintained within the range of 8.0-9.5.