CN115677301B - Low-shrinkage high-carbon-fixation 3D printing cement-based building material utilizing agricultural waste and preparation and application methods thereof - Google Patents
Low-shrinkage high-carbon-fixation 3D printing cement-based building material utilizing agricultural waste and preparation and application methods thereof Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 19
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 28
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- 239000004035 construction material Substances 0.000 claims description 3
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- RAFRTSDUWORDLA-UHFFFAOYSA-N phenyl 3-chloropropanoate Chemical compound ClCCC(=O)OC1=CC=CC=C1 RAFRTSDUWORDLA-UHFFFAOYSA-N 0.000 claims description 3
- 229920003171 Poly (ethylene oxide) Polymers 0.000 claims description 2
- 239000006004 Quartz sand Substances 0.000 claims description 2
- 240000008042 Zea mays Species 0.000 claims description 2
- 235000005824 Zea mays ssp. parviglumis Nutrition 0.000 claims description 2
- 235000002017 Zea mays subsp mays Nutrition 0.000 claims description 2
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- 125000001033 ether group Chemical group 0.000 claims description 2
- PSZYNBSKGUBXEH-UHFFFAOYSA-M naphthalene-1-sulfonate Chemical compound C1=CC=C2C(S(=O)(=O)[O-])=CC=CC2=C1 PSZYNBSKGUBXEH-UHFFFAOYSA-M 0.000 claims description 2
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- DCNHVBSAFCNMBK-UHFFFAOYSA-N naphthalene-1-sulfonic acid;hydrate Chemical compound O.C1=CC=C2C(S(=O)(=O)O)=CC=CC2=C1 DCNHVBSAFCNMBK-UHFFFAOYSA-N 0.000 description 4
- 229910052625 palygorskite Inorganic materials 0.000 description 4
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- PSZYNBSKGUBXEH-UHFFFAOYSA-N naphthalene-1-sulfonic acid Chemical class C1=CC=C2C(S(=O)(=O)O)=CC=CC2=C1 PSZYNBSKGUBXEH-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
Abstract
The invention discloses a 3D printing cement-based building material with low shrinkage and high carbon fixation by utilizing agricultural wastes and a preparation and application method thereof, and relates to a 3D printing cement-based building material. The method aims to solve the technical problems of difficult rheological control, large shrinkage deformation and high carbon emission of the existing 3D printing cement-based material. The cement-based building material comprises modified agricultural waste particles, silicate cement, nano-silica micropowder, aggregate, tap water, a high-efficiency water reducer and anti-cracking fibers. The preparation method comprises the following steps: and (3) after pyrolysis of the wood waste, soaking and absorbing the hydration accelerator, uniformly mixing the wood waste with other raw materials to obtain a 3D printing cement-based building material, and extruding and molding to obtain the cement-based building body. Compared with the traditional material, the shrinkage rate of the 3D printing cement-based building material is reduced by more than 50%, the static yield stress growth speed is improved by more than 1 time, the static yield stress value after 2 hours is more than 1000Pa, the carbon emission is low, and the 3D printing cement-based building material can be used in the field of buildings.
Description
Technical Field
The invention relates to the technical field of building materials, in particular to a low-shrinkage high-carbon-fixation 3D printing cement-based building material utilizing agricultural wastes and a preparation method thereof.
Background
In view of the problems of large resource consumption, high dependence on labor force and the like in the building industry, the traditional building mode is deeply transformed, and in recent years, the new 3D printing (additive manufacturing) technology is valued and developed in the civil engineering field. Although 3D printing construction has the remarkable advantages of rapidness, high efficiency, resource saving, suitability for complex building curved surfaces and the like, a plurality of problems still exist in practical application and are needed to be solved.
The first difficulty is thixotropic regulation of the material, the ideal 3D printing mixture needs to have good fluidity in the conveying and extrusion processes, and enough static yield stress can be formed quickly after extrusion so as to ensure the stability of the stacked shape of the structure to resist deformation; the time-dependent change in the rheological behaviour of such slurries is known as "thixotropic", and the desired printable mix should have a high thixotropic behaviour. The second difficulty is that the early shrinkage deformation is large, the early shrinkage deformation refers to the volume reduction phenomenon of the cement-based material in the initial stage of coagulation or in the hardening process, and can be concretely classified into plastic shrinkage, drying shrinkage, self-shrinkage, carbonization shrinkage and the like, and if the shrinkage deformation is too large, the material is easy to crack; it is generally considered that shrinkage deformation mainly occurs in cement paste composed of cement and water, and shrinkage of river sand, fine stone portion as aggregate is almost negligible; the amount of cementing material in the 3D printed cementitious material mix is generally higher and the amount of aggregate is lower than in conventional cementitious concretes, so shrinkage deformation is greater than in conventional cementitious materials, and the rate of moisture evaporation is faster due to the lack of formwork coverage, which causes greater early shrinkage deformation of the material and is prone to induced cracking.
On the other hand, although the carbon emission during construction can be reduced by the 3D printing technique, a large amount of carbon dioxide gas is discharged during cement production and the ecological environment is destroyed due to the variation of the mixing ratio and the increase of the amount of the cementing material, and the carbon emission of the material itself is rather increased. In combination with the strategy of double carbon, the existing 3D printing cement-based material is necessary to be innovatively upgraded, the carbon emission in the life cycle is reduced, and the environmental-friendly social benefit is fully exerted.
Disclosure of Invention
The invention aims to solve the technical problems of difficult rheological control, large shrinkage deformation and higher carbon emission of the existing 3D printing cement-based material, and provides a low-shrinkage high-carbon-fixation 3D printing cement-based building material utilizing agricultural wastes, and a preparation and application method thereof.
The low-shrinkage high-carbon-fixation 3D printing cement-based building material utilizing agricultural waste comprises, by mass, 100-300 parts of modified agricultural waste particles, 700-900 parts of silicate cement, 0-100 parts of sulphoaluminate cement, 50-200 parts of nano silica micropowder, 800-2000 parts of aggregate, 200-600 parts of tap water, 5-30 parts of high-efficiency water reducer, 0-5 parts of viscosity improver and 1-3 parts of anti-cracking fiber.
Further, the preparation method of the modified agricultural waste particles comprises the following steps:
and (3) a step of: preparing an agricultural waste primary material: drying the wooden waste at 40-80 ℃, and then pyrolyzing the wooden waste for 2-6 hours in an anaerobic environment at 300-700 ℃ to obtain strip or sheet biochar; after natural cooling, crushing the biochar to a particle size of 1-5 mm by using a crusher to obtain blocky biochar particles; wherein the wood waste is one or the combination of a plurality of straw, fallen leaves, shells and dried branches;
and II: modification of agricultural waste particles: drying the blocky biochar particles, placing the dried blocky biochar particles in a container, adding a hydration accelerator solution, sealing the container, vacuumizing the container to ensure that the internal pressure of the container is reduced to below 0.2MPa and maintained for 1-3 hours, and continuously oscillating the container during the period to ensure that the particles are fully impregnated and absorbed; filtering to remove redundant solution, drying the solid phase, and grinding to obtain modified agricultural waste particles with the particle size of less than 150 mu m.
The hydration accelerator solution is an aluminum sulfate solution with the mass percentage concentration of 10% -20% or a calcium nitrite solution with the mass percentage concentration of 20% -40%;
the drying step two is to dry the solid phase at 40-60 ℃ for 24-48 hours;
further, the strength grade of the Portland cement is more than or equal to 42.5, the content of the mixed material is less than or equal to 20 percent, and the specific surface area of the Portland cement is less than or equal to>300m 2 /kg; the volcanic ash activity index of the nano silicon micro powder is more than or equal to 105%, the silicon dioxide content is more than or equal to 90%, and the granularity distribution index D 90 <10 μm; the index can lead the silica fume and the silicate cement to form idealThe grain composition fully exerts the filling effect and chemical activity of the silica fume, reduces the internal pores of the material and improves the early strength.
Furthermore, the aggregate is quartz sand or river sand with the grain diameter of less than 2.5mm, and the stacking repose angle of the aggregate is more than 35 degrees, so that the inside of the loose aggregate is ensured to have larger internal friction force, and the mixture has certain static yield stress in an initial state.
Further, the high-efficiency water reducing agent is ether polycarboxylate or naphthalene sulfonate; both ether polycarboxylates and naphthalene sulfonates are not combinable; the purpose is to ensure that the mixture has better fluidity in the conveying process.
Further, the viscosity improver is one or a combination of more than one of redispersible emulsion powder, hydroxypropyl methyl cellulose and polyethylene oxide; the viscosity improver ensures that the mixture has certain viscosity in the extrusion process so as to ensure continuous and uninterrupted discharging.
Furthermore, the anti-cracking fiber is chopped polypropylene fiber or polyvinyl alcohol fiber, so that the interface tensile strength of the 3D printing cement-based material is enhanced, and the generation of cracks in the material interface and the matrix is inhibited.
The preparation method of the 3D printing cement-based building material with low shrinkage and high carbon fixation by utilizing the agricultural waste comprises the following steps:
1. weighing 100-300 parts of modified agricultural waste particles, 700-900 parts of silicate cement, 0-100 parts of sulphoaluminate cement, 50-200 parts of nano silicon micro powder, 800-2000 parts of aggregate, 200-600 parts of tap water, 5-30 parts of high-efficiency water reducer, 0-5 parts of viscosity improver and 1-3 parts of anti-cracking fiber according to the mass parts;
2. and (3) uniformly mixing the modified agricultural waste particles with silicate cement, sulphoaluminate cement, nano silicon micropowder and aggregate, adding tap water, a high-efficiency water reducing agent and a viscosity improver, stirring for 3-5 minutes, and adding anti-cracking fibers in batches during stirring to uniformly disperse the anti-cracking fibers, so as to obtain the 3D printing cement-based building material.
The application method of the 3D printing cement-based building material with low shrinkage and high carbon fixation by utilizing the agricultural waste comprises the following steps: extruding the 3D printed cement-based building material by a 3D printer, and pre-curing for 6-24 hours in an environment with the temperature of 20+/-1 ℃ and the humidity of 60+/-5%; and then transferring the mixture into an environment with the temperature of 20+/-1 ℃ and the humidity of 60+/-5% and the carbon dioxide concentration of more than 99% for curing for 12-24 hours to obtain the cement-based building.
Compared with the prior art, the invention has the beneficial effects that:
1. the modified agricultural waste particles have a large number of nanoscale pores and surface active functional groups, moisture can be fully adsorbed in the mixing stage, the adsorbed moisture can be released along with the reduction of internal humidity in the material hardening process, and an internal curing effect is achieved, so that the drying shrinkage rate of the 3D printing cement-based material after the modified agricultural waste particles are doped can be reduced by more than 50%, and the risk of early deformation and cracking is greatly reduced.
2. The modified agricultural waste particles are used as a carrier of the hydration accelerator, and account for 10% -30% of the mass of the cementing material, so that the dissolution and diffusion rate of the cementing material are effectively slowed down, the mixture still keeps good fluidity in the early conveying and extrusion processes, the hydration accelerator gradually plays a role after printing is finished, the static yield stress of the mixture is rapidly increased at the moment and reaches more than 1000Pa within 2 hours after mixing, the stacking and shape stability of the material are greatly improved, the modified agricultural waste particles have an internal curing function on the cement-based material, and shrinkage cracking phenomenon is greatly reduced. Compared with the traditional 3D printing cement-based building material, the shrinkage rate of the 3D printing cement-based building material prepared by utilizing the modified agricultural waste particles is reduced by more than 50%, the growth rate of static yield stress is improved by more than 1 time, and the static yield stress value after 2 hours is more than 1000Pa.
3. A large amount of biomass charcoal in the modified agricultural waste is fixedly sealed inside the 3D printing cement-based material, so that carbon dioxide is prevented from being generated and circulated into an atmosphere, and the carbon emission in the life cycle of the material is reduced.
4. The carbon dioxide is captured and reused in the material maintenance process.
The invention can be used in the field of construction.
Detailed Description
The following examples are used to demonstrate the benefits of the invention:
example 1: the preparation method of the 3D printing cement-based building material with low shrinkage and high carbon fixation by utilizing agricultural wastes in the embodiment comprises the following steps:
preparing modified agricultural waste particles:
(1) 1kg of waste corn stalks are collected, dried at 60 ℃, pyrolyzed for 4 hours at 600 ℃ in an anaerobic environment and naturally cooled to obtain strip-shaped biochar, and the strip-shaped biochar is processed by a crusher to form blocky particles with the size of about 3 mm;
(2) Weighing 260g of massive particles, placing the massive particles in a container, adding 1.0kg of calcium nitrite solution with the mass percentage concentration of 30%, sealing the container, vacuumizing to ensure that the internal pressure is reduced to 0.1MPa, and maintaining for 2 hours, and continuously oscillating the container at the frequency of 60Hz during the period to ensure that the particles are fully impregnated and absorbed; then filtering to remove redundant solution, and drying the residue of the solid phase at 60 ℃ to obtain blocky particles with the mass of 292.8 g; further grinding the massive particles by using an electric powder grinding machine, and passing through a 140-mesh screen to obtain modified agricultural waste particles with the particle size of less than 150 mu m;
2. weighing 280g of modified agricultural waste particles, 800g of silicate cement, 60g of sulphoaluminate cement, 50g of nano silicon micropowder, 800g of aggregate, 300g of tap water, 5.0g of ether polycarboxylate water reducer, 1.0g of redispersible emulsion powder and 2g of chopped polypropylene fiber;
wherein the silicate cement has a strength grade of 42.5, a mixed material content of 20% and a specific surface area of 350m 2 /kg；
Nanometer silica micropowder with volcanic ash activity index of 110%, silica content of 93% and particle size distribution index D 90 5.6 μm; the aggregate is river sand with the particle size of 0.15-2.5 mm, and the stacking repose angle of the river sand is 38.6 degrees;
3. uniformly mixing modified agricultural waste particles, silicate cement, sulphoaluminate cement, nano-silica micropowder and aggregate, adding tap water, an ether polycarboxylate water reducer and redispersible emulsion powder, stirring for 3 minutes, and adding chopped polypropylene fibers in batches during stirring to uniformly disperse the mixture, so as to obtain the 3D printing cement-based building material.
Extruding the 3D printing cement-based building material prepared in the embodiment by a 3D printer, and pre-curing for 12 hours in an environment with the temperature of 20 ℃ and the humidity of 60%; and then the mixture is moved into an environment with the temperature of 20 ℃ and the humidity of 60 percent and the carbon dioxide concentration of 99.5 percent for curing for 24 hours, and the cement-based building body is obtained. The cement-based building body was transferred to an environment with a temperature of 20 ℃ and a humidity of 60% for storage.
In the embodiment, ideal particle grading is formed between the nano-silica micropowder and the silicate cement, so that the filling effect and chemical activity of the nano-silica micropowder are fully exerted, and the particle fineness of the nano-silica micropowder is far smaller than that of the cement, so that the porosity of the nano-silica micropowder after the nano-silica micropowder is combined is greatly reduced, and the filling effect and early strength are improved.
The static yield stress value, i.e., the initial static yield stress value, of the 3D printed cementitious building material prepared in this example was tested after the preparation was completed. The static yield stress value, the shrinkage at 7 days of age, the shrinkage at 28 days of age, and the theoretical carbon sequestration amount calculation were performed on the cement-based construction body obtained after 3D printing for 2 hours and are listed in table 1.
Example 2: the preparation method of the 3D printing cement-based building material with low shrinkage and high carbon fixation by utilizing agricultural wastes comprises the following steps:
1. preparing modified agricultural waste particles:
(1) Collecting 800g of waste dried branches, drying at 70 ℃, pyrolyzing at 500 ℃ in an anaerobic environment for 6 hours, naturally cooling to obtain strip-shaped biochar, and processing the biochar by a crusher to form blocky particles with the size of about 2 mm;
(2) Weighing 200g of massive particles, placing the massive particles in a container, adding 1.2kg of aluminum sulfate solution with the mass percentage concentration of 20%, sealing the container, vacuumizing to ensure that the internal pressure is reduced to 0.1MPa, and maintaining the internal pressure for 2 hours, and continuously oscillating the container at the frequency of 100Hz during the period to ensure that the particles are fully impregnated and absorbed; then filtering to remove redundant solution, and drying the residue of the solid phase at 60 ℃ to obtain massive particles with the mass of 217.3 g; further grinding the massive particles by using an electric powder grinding machine, and passing through a 140-mesh screen to obtain modified agricultural waste particles with the particle size of less than 150 mu m;
2. weighing 190g of modified agricultural waste particles, 900g of silicate cement, 60g of nano-silica micropowder, 1300g of aggregate, 400g of tap water, 12g of naphthalene sulfonate water reducer, 1.0g of hydroxypropyl methyl cellulose and 2g of polyvinyl alcohol fiber;
wherein the silicate cement has a strength grade of 42.5, a mixed material content of 20% and a specific surface area of 350m 2 /kg；
Nano silicon micropowder, its volcanic ash activity index is 123%, silicon dioxide content is 98% and grain size distribution index is D 90 3.7 μm; the aggregate is river sand with the particle size of 0.075-2.5 mm, and the stacking repose angle of the river sand is 37.1 degrees;
3. and (3) uniformly mixing the modified agricultural waste particles, the silicate cement, the nano-silica micropowder and the aggregate, adding tap water, the naphthalene sulfonate water reducer and the hydroxypropyl methyl cellulose, stirring for 3 minutes, and adding polyvinyl alcohol fibers in batches during stirring to uniformly disperse the polyvinyl alcohol fibers, so as to obtain the 3D printing cement-based building material.
Extruding the 3D printing cement-based building material prepared in the embodiment by a 3D printer, and pre-curing for 18 hours in an environment with the temperature of 20 ℃ and the humidity of 60%; and then the mixture is moved into an environment with the temperature of 20 ℃ and the humidity of 60 percent and the carbon dioxide concentration of 99.5 percent for curing for 18 hours, and the cement-based building body is obtained. The cement-based building body was transferred to an environment with a temperature of 20 ℃ and a humidity of 60% for storage.
In the embodiment, ideal grain composition is formed between the nano-silica micropowder and the silicate cement, so that the filling effect and chemical activity of the nano-silica micropowder are fully exerted, the internal pores of the material are reduced, and the early strength is improved. The static yield stress value, i.e., the initial static yield stress value, of the 3D printed cementitious building material prepared in this example was tested after the preparation was completed. The static yield stress value, the shrinkage at 7 days of age, the shrinkage at 28 days of age, and the theoretical carbon sequestration amount calculation were performed on the cement-based construction body obtained after 3D printing for 2 hours and are listed in table 1.
Comparative example 1: the comparative example is a traditional 3D printed cementitious building material, and the preparation method thereof is as follows:
1. weighing 800g of silicate cement, 140g of granulated blast furnace slag powder, 90g of limestone powder, 10g of attapulgite, 1300g of aggregate, 380g of tap water, 6g of ether polycarboxylate water reducer and 5g of polypropylene fiber;
wherein the strength grade of the Portland cement is 52.5, the content of the mixed material is 0, and the specific surface area is 370m 2 /kg；
The fineness of the attapulgite is 2000 meshes, and the palygorskite mineral content is 70%;
the aggregate is machine-made sand with the grain diameter of 0.075-2.5 mm, and the stacking repose angle of the machine-made sand is 39.2 degrees;
and (3) uniformly mixing the Portland cement, the granulated blast furnace slag powder, the limestone powder, the attapulgite and the aggregate, then adding tap water and an ether polycarboxylate water reducer, stirring for 3 minutes, and adding polypropylene fibers in batches during stirring to uniformly disperse the mixture, so as to obtain the traditional 3D printing cement-based building material.
Extruding the traditional 3D printing cement-based building material prepared in the comparative example 1 through a 3D printer, and pre-curing for 18 hours in an environment with the temperature of 20 ℃ and the humidity of 60%; and then the mixture is moved into an environment with the temperature of 20 ℃ and the humidity of 60 percent and the carbon dioxide concentration of 99.5 percent for curing for 18 hours, and the traditional 3D printing cement-based building body is obtained. The cement-based building body was transferred to an environment with a temperature of 20 ℃ and a humidity of 60% for storage.
The static yield stress value after the completion of the preparation of the conventional 3D printed cement-based construction material prepared in this comparative example 1, i.e., the initial static yield stress value was tested. The static yield stress value, the shrinkage at 7 days of age, the shrinkage at 28 days of age, and the theoretical carbon sequestration amount calculation were performed on the cement-based construction body obtained after 3D printing for 2 hours and are listed in table 1.
Comparative example 2: this comparative example differs from example 2 in that no modified agricultural waste was added, and the specific method is as follows:
1. weighing 900g of silicate cement, 60g of nano-silica micropowder, 1300g of aggregate, 400g of tap water, 12g of naphthalene sulfonate water reducer, 1.0g of hydroxypropyl methylcellulose and 2g of polyvinyl alcohol fiber;
wherein the silicate cement has a strength grade of 42.5, a mixed material content of 20% and a specific surface area of 350m 2 /kg；
Nano silicon micropowder, its volcanic ash activity index is 123%, silicon dioxide content is 98% and grain size distribution index is D 90 3.7 μm; the aggregate is river sand with the particle size of 0.075-2.5 mm, and the stacking repose angle of the river sand is 37.1 degrees;
3. and (3) uniformly mixing the Portland cement, the nano-silica micropowder and the aggregate, adding tap water, a naphthalene sulfonate water reducer and hydroxypropyl methyl cellulose, stirring for 3 minutes, and adding polyvinyl alcohol fibers in batches during stirring to uniformly disperse the polyvinyl alcohol fibers to obtain the contrast 3D printing cement-based building material.
Extruding the comparative 3D printing cement-based building material prepared in comparative example 2 by a 3D printer, and pre-curing for 18 hours at the temperature of 20 ℃ and the humidity of 60%; and then the mixture is moved into an environment with the temperature of 20 ℃ and the humidity of 60 percent and the carbon dioxide concentration of 99.5 percent for curing for 18 hours, and the comparative cement-based building body is obtained. The comparative cement-based building body was transferred to an environment with a temperature of 20 ℃ and a humidity of 60% for storage.
The static yield stress value after the preparation of the comparative 3D printed cement-based construction material prepared in comparative example 2 was tested, i.e., the initial static yield stress value. The static yield stress value, the shrinkage at 7 days of age, the shrinkage at 28 days of age test and the theoretical carbon sequestration amount calculation were performed on the comparative cement-based construction body obtained after 3D printing for 2 hours and are listed in table 1.
Static yield stress and shrinkage tests for examples 1, 2 and comparative examples 1, 2, wherein the static yield stress value test was run at 0.01s -1 Constant shear rate; the shrinkage test was performed as specified in JGJ/70-2009 Standard for basic Property test of construction mortar, and the test piece was aged for 36 hours to begin measuring the initial length. The carbon sequestration amount is measured and calculated by a life cycle assessment method to verify the improvement effect of the carbon sequestration amount on shrinkage and carbon sequestration capacity. The results are shown in Table 1.
Table 1 shrinkage and carbon sequestration of materials
As can be seen from the results in table 1, the 3D printed cement-based building material mixture prepared in example 1 had a lower static yield stress before printing, with an initial static yield stress measured value of 307.5Pa; the static yield stress rapidly increased after printing, and the static yield stress test value was 1983.1Pa after 2 hours.
The 3D printed cementitious building material mix prepared in example 2 had a lower static yield stress prior to printing, an initial static yield stress measured value of 280.1Pa; the static yield stress rapidly increased after printing, and the static yield stress test value was 2217.9Pa after 2 hours.
The 3D printing cement-based building materials prepared by using the modified agricultural waste particles in the embodiment 1 and 2 can reduce the shrinkage rate by more than 50%, increase the growth rate of static yield stress by more than 1 time, and have the static yield stress value of more than 1000Pa after 2 hours and obvious carbon sealing effect.
Therefore, the 3D printing cement-based building material utilizing the modified agricultural waste can greatly reduce the risk of shrinkage cracking, improve the early performance of the material and further improve the green degree of the building engineering.
Claims (8)
1. The 3D printing cement-based building material with low shrinkage and high carbon fixation by utilizing agricultural wastes is characterized by comprising, by mass, 100-300 parts of modified agricultural waste particles, 700-900 parts of silicate cement, 0-100 parts of sulphoaluminate cement, 50-200 parts of nano silica micropowder, 800-2000 parts of aggregate, 200-600 parts of tap water, 5-30 parts of high-efficiency water reducer, 0-5 parts of viscosity improver and 1-3 parts of anti-cracking fiber;
the preparation method of the modified agricultural waste particles comprises the following steps:
(1) 1kg of waste corn stalks are collected, dried at 60 ℃, pyrolyzed for 4 hours at 600 ℃ in an anaerobic environment and naturally cooled to obtain strip-shaped biochar, and the strip-shaped biochar is processed by a crusher to form blocky particles with the size of about 3 mm;
(2) Weighing 260g of massive particles, placing the massive particles in a container, adding 1.0kg of calcium nitrite solution with the mass percentage concentration of 30%, sealing the container, vacuumizing, and continuously oscillating the container at the frequency of 60Hz during the period to fully impregnate and absorb the particles; then filtering to remove redundant solution, and drying the residue of the solid phase at 60 ℃ to obtain blocky particles with the mass of 292.8 g; further grinding the massive particles by using an electric powder grinding machine, and passing through a 140-mesh screen to obtain modified agricultural waste particles with the particle size of less than 150 mu m;
or the preparation method of the modified agricultural waste particles comprises the following steps:
(1) Collecting 800g of waste dried branches, drying at 70 ℃, pyrolyzing at 500 ℃ in an anaerobic environment for 6 hours, naturally cooling to obtain strip-shaped biochar, and processing the biochar by a crusher to form blocky particles with the size of about 2 mm;
(2) 200g of massive particles are weighed and placed in a container, 1.2kg of aluminum sulfate solution with the mass percentage concentration of 20% is added, the container is closed and then vacuumized, and the container is continuously oscillated at the frequency of 100Hz during the period to fully impregnate and absorb the particles; then filtering to remove redundant solution, and drying the residue of the solid phase at 60 ℃ to obtain massive particles with the mass of 217.3 g; further grinding the block-shaped particles by using an electric grinding machine, and passing through a 140-mesh screen to obtain modified agricultural waste particles with the particle size of less than 150 mu m.
2. The 3D printing cement-based building material with low shrinkage and high carbon content by utilizing agricultural wastes according to claim 1, wherein the silicate cement has the strength grade of more than or equal to 42.5, the content of the mixed material of less than or equal to 20 percent and the specific surface area>300m 2 /kg; the volcanic ash activity index of the nano silicon micro powder is more than or equal to 105%, the silicon dioxide content is more than or equal to 90%, and the granularity distribution index D 90 <10μm。
3. The 3D printed cement-based construction material of claim 1, wherein the aggregate is quartz sand or river sand with a grain size of less than 2.5mm, and the stacking repose angle is more than 35 °.
4. The 3D printing cement-based building material with low shrinkage and high carbon fixation by using agricultural wastes according to claim 1, wherein the high-efficiency water reducing agent is ether polycarboxylate or naphthalene sulfonate.
5. The 3D printing cement-based building material with low shrinkage and high carbon content by using agricultural wastes according to claim 1, wherein the viscosity improver is one or a combination of a plurality of redispersible latex powder, hydroxypropyl methylcellulose and polyethylene oxide.
6. The 3D printed cementitious building material of claim 1 or 2 wherein the crack resistant fibers are chopped polypropylene fibers or polyvinyl alcohol fibers.
7. A method for preparing a low shrinkage high carbon content 3D printed cementitious building material utilizing agricultural waste as defined in claim 1, the method comprising the steps of:
1. weighing 100-300 parts of modified agricultural waste particles, 700-900 parts of silicate cement, 0-100 parts of sulphoaluminate cement, 50-200 parts of nano silicon micro powder, 800-2000 parts of aggregate, 200-600 parts of tap water, 5-30 parts of high-efficiency water reducer, 0-5 parts of viscosity improver and 1-3 parts of anti-cracking fiber according to the mass parts;
2. and (3) uniformly mixing the modified agricultural waste particles with silicate cement, sulphoaluminate cement, nano silicon micropowder and aggregate, adding tap water, a high-efficiency water reducing agent and a viscosity improver, stirring for 3-5 minutes, and adding anti-cracking fibers in batches during stirring to uniformly disperse the anti-cracking fibers, so as to obtain the 3D printing cement-based building material.
8. The method for using the 3D printing cement-based building material with low shrinkage and high carbon fixation by using agricultural wastes as claimed in claim 1, which is characterized by comprising the following steps:
extruding the 3D printed cement-based building material by a 3D printer, and pre-curing for 6-24 hours in an environment with the temperature of 20+/-1 ℃ and the humidity of 60+/-5%; and then transferring the mixture into an environment with the temperature of 20+/-1 ℃ and the humidity of 60+/-5% and the carbon dioxide concentration of more than 99% for curing for 12-24 hours to obtain the cement-based building.
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