Green cementing material as well as preparation method and application thereof

Abstract

The invention relates to a green cementing material as well as a preparation method and application thereof, and the green cementing material comprises the following raw materials in parts by weight: 120-180 kg of a composite material, 120-180 kg of cement, 100-150 kg of water and 3-10 kg of a water reducing agent, the composite material is prepared from the following raw materials in parts by mass: 80 to 140kg of modified charcoal, 2 to 20kg of graphite-phase carbon nitride and 24 to 36kg of silica fume. Compared with the prior art, the graphite-phase carbon nitride and the biochar are used for replacing part of cement, the environmental pressure caused by the cement can be relieved, meanwhile, good adsorbability to carbon dioxide in the air is achieved, the carbon sequestration potential is extremely high, pollutants in the environment can be degraded by the cement-based material, and the cement-based material has the advantages of environmental protection, environmental protection and the like. And the method has positive significance in realizing green and healthy development.

Description

Technical Field

[0001] The present invention relates to the technical field of cementitious materials, and in particular to a green cementitious material, a preparation method thereof, and an application thereof. Background Art

[0002] As a widely used building material, concrete plays an important role in infrastructure construction. However, during the production and use of concrete, a large amount of carbon dioxide emissions will be generated, which exacerbates the trend of global warming. In addition, ordinary cement concrete lacks the ability to treat pollutants, and its surface is often covered by pollutants, resulting in damage to the appearance of buildings, reduction of performance, and even shortening of the service life of buildings. This has a serious negative impact on the environment and infrastructure on which we depend for survival.

[0003] Graphitic carbon nitride is a carbon material with a special microstructure, and its main component is a planar hexagonal structure composed of carbon atoms and nitrogen atoms. Graphitic carbon nitride has good thermochemical stability and visible-light photocatalytic performance. Compared with traditional metal oxide-based photocatalysts, its synthesis process is simple, and its thermal and chemical stability is excellent. It is considered a new high-performance material with broad application prospects. Graphitic carbon nitride can be incorporated into concrete raw materials to improve the performance of concrete. However, the application of graphitic carbon nitride in concrete also has many defects, such as small surface area, easy recombination of photogenerated carriers, low photocatalytic CO2 reduction performance, insufficient binding force with cement-based materials, etc. These problems limit the application of graphitic carbon nitride in concrete.

[0004] Biochar is a porous carbide made from organic matters such as biomass and municipal waste through pyrolysis or gasification technologies under anaerobic or oxygen-limited conditions. Biochar has a high specific surface area and strong affinity, and can adsorb substances such as water, nutrients, and heavy metals. At the same time, biochar can also be used as a substitute material for cement in the preparation of concrete, thereby reducing the use of cement in concrete, absorbing carbon dioxide in the atmosphere, alleviating the greenhouse effect, and reducing the impact on the environment. However, the content of active components in biochar is relatively low, and the porosity is relatively high. These characteristics limit its incorporation amount in concrete, making it difficult to apply biochar concrete on a large scale.

[0005] Therefore, how to efficiently mix and apply graphitic carbon nitride, biochar, and concrete materials, so as to achieve low carbon emissions and the self-cleaning and decontamination ability of concrete, while also significantly improving the various performances of concrete, has become an urgent problem to be solved. Summary of the Invention

[0006] The object of the present invention is to provide a green cementitious material, its preparation method and application. By using graphitic carbon nitride and biochar to replace part of the cement, the present invention can reduce the environmental pressure caused by cement. Meanwhile, it has good adsorption performance for carbon dioxide in the air, has extremely high carbon sequestration potential, and can enable cement-based materials to degrade pollutants in the environment, which has positive significance for environmental protection and realizing green and healthy development. The present invention also realizes the synergistic effect among graphitic carbon nitride, biochar and silica fume, and can significantly improve the strength and durability of concrete while showing high carbon sequestration performance and photocatalytic performance, with remarkable environmental benefits, and can provide new possibilities for the green development of the concrete industry.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A green cementitious material, comprising raw materials in the following parts by weight:

[0009]

[0010] Among them, the composite material comprises raw materials in the following parts by mass: 80-140 kg of modified biochar, 2-20 kg of graphitic carbon nitride, and 24-36 kg of silica fume.

[0011] Furthermore, the specific preparation steps of the modified biochar are as follows:

[0012] S1. Cut the biological agricultural waste, and then carry out pyrolysis, cooling and grinding in sequence, and obtain biological agricultural waste powder after screening;

[0013] S2. Add an alkali solution to the biological agricultural waste powder obtained in step S1, carry out alkali activation treatment, and obtain modified biochar after washing and carbonization.

[0014] As a preferred technical solution, in step S1, there are no special requirements for the source of the biological agricultural waste, and any biochar well-known in the art can be used.

[0015] Furthermore, in step S2, the alkali solution is a KOH solution, the concentration of the KOH solution is 1-3 g / L, and the alkali activation treatment time is 20-40 h;

[0016] The washing method is ultrasonic washing at 30-50 kHz, and the washing time is 10-30 min;

[0017] The carbonization temperature is 500-700 °C, and the carbonization is carried out in an induction cooker.

[0018] Furthermore, the modified biochar contains the following elements in the following mass contents:

[0019] The C content is 75.3 - 80.5%; the O content is 15.2 - 20.5%; the Si content is 1.1 - 3.3%; the K content is 0.4 - 0.7%; the Ca content is 0.1 - 0.2%; the Mg content is 0.1 - 0.2%; the Na content is 0.1 - 0.2%; the Fe content is 0.1 - 0.2%.

[0020] Further, the specific surface area of the modified biochar is 350 - 560 m 2 / kg; the pore volume is 0.008 - 0.3 cm 3 / g; the pore diameter is 0.5 - 40 nm.

[0021] Further, the specific preparation steps of the graphitic carbon nitride are as follows:

[0022] After being ground, melamine is heated, cooled and sieved to obtain graphitic carbon nitride.

[0023] As a preferred technical solution, the grinding time is 30 - 60 min;

[0024] The heating temperature is 500 - 600 °C, and the heating time is 3 - 6 h.

[0025] Further, the graphitic carbon nitride contains the following elements with the following mass contents:

[0026] The C content is 47 - 50%; the N element content is 50 - 53%.

[0027] Further, the specific surface area of the graphitic carbon nitride is 176 - 183 m 2 / g; the average pore volume is 0.005 cm 3 / g, and the average pore diameter is 30.65 nm.

[0028] Further, the silica fume contains the following elements with the following mass contents:

[0029] The SiO2 content is 99.0 - 99.3%; the Al2O3 content is 0.1 - 0.7%; the Fe2O3 content is 0.1 - 0.4%; the CaO content is 0.1 - 0.6%.

[0030] Further, the moisture content of the silica fume is 1.0 - 1.3%, and the loss on ignition is 2.5 - 2.6.

[0031] Further, the specific preparation steps of the composite material are as follows:

[0032] The silica fume, graphitic carbon nitride and modified biochar are mixed and ball-milled in a ratio of 1:(0.1 - 0.4):(3.6 - 3.9) to obtain the composite material.

[0033] Furthermore, the ball milling speed is 200 - 400 r / min, and the ball milling time is 1 - 2 h.

[0034] Furthermore, the silica fume model is SF90, purchased from Huaxin Cement Factory in Wuhan, Hubei;

[0035] The cement model is P·O 42.5, purchased from Huaxin Cement Factory in Wuhan, Hubei;

[0036] The water reducing agent is the high - performance water reducing agent of China State Construction New Materials.

[0037] In addition, the present invention also provides a preparation method of a green cementitious material, and the specific steps are as follows:

[0038] S1. Prepare the composite material;

[0039] S2. Weigh the composite material, cement, water and water reducing agent according to the mixing ratio;

[0040] S3. After mixing the composite material with cement, water and water reducing agent, stir to obtain the green cementitious material.

[0041] As a preferred technical solution, in step S3, the stirring time is 20 - 40 h.

[0042] In addition, the present invention also provides an application of the green cementitious material in the preparation of concrete.

[0043] Furthermore, the weight of the raw materials contained in each cubic meter of concrete is as follows:

[0044]

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] 1. Biochar has a carbon sequestration effect, and also provides nucleation sites for cement hydration reaction and graphitic carbon nitride, promoting the precipitation of cement hydration products and the progress of photocatalytic reaction, and improving the concrete strength and photocatalytic efficiency. Graphitic carbon nitride has filling and photocatalytic functions, which can degrade pollutants in the environment and promote the carbon sequestration reaction of biochar. Silica fume can fill the pores of biochar to make it denser, and silicon dioxide can be embedded in the pores of graphitic carbon nitride and react with calcium hydroxide generated by cement hydration to form C - S - H gel, solving the problem of weak bonding force between graphitic carbon nitride and cement.

[0047] 2. As a good adsorption material, biochar can construct a large number of reaction active sites and increase the specific surface area of graphite carbon nitride. At the same time, the hydroxyl groups on the surface of biochar will attract positively charged cement particles and produce nucleation clusters, promoting the precipitation of cement hydration products on the cluster surface; and biochar can also enhance the conductivity of graphite carbon nitride, accelerate the separation of photogenerated charges, optimize the energy band structure of graphite carbon nitride, and improve the photocatalytic efficiency of graphite carbon nitride.

[0048] 3. The high electrical conductivity of graphite-phase carbon nitride particles can accelerate electrochemical reactions on the biochar surface, promoting the reduction of carbon dioxide molecules and their embedding into the biochar pores. Furthermore, graphite-phase carbon nitride particles can catalyze the carbon fixation process in biochar, degrading air pollutants while reducing the activation energy of the biochar carbon fixation reaction and promoting its progress. Furthermore, graphite-phase carbon nitride can diffuse into the pores between the biochar and cement hydration products, filling them and reducing the porosity of the biochar.

[0049] Silica fume fills the pores of biochar, making it denser. The porous structure of biochar reduces the agglomeration of silica fume particles. Furthermore, the silica in silica fume can be embedded in the pores of graphite carbon nitride and react with calcium hydroxide generated by cement hydration to form a CSH gel, thereby combining with the graphite carbon nitride to form a CSH gel. This solves the problem of weak adhesion between graphite carbon nitride and cement.

[0050] 5. The present invention uses KOH solution alkaline activation treatment to remove natural oils and organic matter from biomass, enhance oxygen-containing functional groups on the biochar surface, and improve the biochar's adsorption rate. Simultaneously, ultrasonic treatment effectively strips away impurities such as incompletely oxidized carbon materials, minerals, and other insoluble particles in the biochar, allowing the alkaline solution to better penetrate the biochar interior and help it disperse evenly within the biochar micropores, further improving the biochar's adsorption capacity. The biochar, graphite-phase carbon nitride, and silica fume are mixed and ball-milled using ball milling technology to increase the specific surface area of the biochar and graphite-phase carbon nitride, impart more negative zeta potential and oxygen-containing functional groups to the biochar, thereby enhancing its adsorption capacity and improving its interfacial compatibility with the biochar, graphite-phase carbon nitride, and silica fume.

[0051] 6. The present invention gives full play to the balanced and synergistic effects of the ternary composite system of biochar, graphite-phase carbon nitride and silica fume in concrete, realizes the high-value utilization of biochar and graphite-phase carbon nitride in construction projects, enhances the carbon fixation and self-cleaning ability of concrete, and improves the durability and service life of concrete. DETAILED DESCRIPTION

[0052] The present invention will be described in detail below in conjunction with specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0053] In the following embodiments, the sources of raw materials are as follows:

[0054] The bio-agricultural waste is rice straw for waste recycling;

[0055] The water reducer is a high-performance water reducer from China State Construction New Materials;

[0056] The cement type is PO42.5, purchased from Huaxin Cement Factory in Wuhan, Hubei;

[0057] The silica fume type is SF90, purchased from Huaxin Cement Factory in Wuhan, Hubei;

[0058] Melamine is purchased from Sinopharm.

[0059] For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. All reagents used are conventional products that can be obtained through commercial purchase.

[0060] The following will describe some embodiments of the present invention in detail in conjunction with the attached table. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0061] Example 1

[0062] This embodiment provides a green cementitious material, including the following raw materials in parts by mass:

[0063]

[0064]

[0065] Among them, the composite material includes the following raw materials in parts by mass: 122 kg of modified biochar, 14 kg of graphitic carbon nitride, and 34 kg of silica fume.

[0066] In this embodiment, the modified biochar contains the following elements in the following mass contents:

[0067] The C content is 78.5%; the O content is 18.5%; the Si content is 2.1%; the K content is 0.5%; the Ca content is 0.1%; the Mg content is 0.1%; the Na content is 0.1%; the Fe content is 0.1%;

[0068] The average specific surface area of the modified biochar is 464 m 2 / kg; the average pore volume is 1.53 cm 3 / g; the average pore diameter is 22.6 nm.

[0069] In this embodiment, the graphite phase carbon nitride contains the following elements in mass content:

[0070] The C content is 49%; the N content is 51%;

[0071] The specific surface area of the graphite phase carbon nitride is 180m 2 / g; average pore volume 0.005cm 3 / g, average pore size 30.65nm.

[0072] In this embodiment, the silica fume contains the following elements by mass:

[0073] SiO2 content is 99.2%; Al2O3 content is less than 0.5%; Fe2O3 content is less than 0.1%; CaO content is less than 0.2%;

[0074] The moisture content of the silica fume is 1.05%, and the loss on ignition is 2.58.

[0075] In addition, this embodiment also provides a method for preparing a green gelling material, the specific steps of which are as follows:

[0076] (1) Preparation of modified biochar:

[0077] 1) chopping rice straw, pyrolyzing, cooling, and grinding the stalks, and sieving to obtain bio-agricultural waste powder;

[0078] 2) soaking the bio-agricultural waste powder obtained in step 1) in a 2 g / L KOH solution at a solid-liquid ratio of 1:3 for 24 hours, and drying the powder in an oven at 105° C. for 12 hours to obtain alkali-activated modified rice straw biochar;

[0079] 3) The modified rice straw biochar obtained after alkali activation in step 2) is placed in a cleaning tank, deionized water is added to cover the modified rice straw biochar after alkali activation by 2 mm, and then ultrasonically washed for 15 minutes using 40 kHz. After completion, the sewage in the cleaning tank is emptied, and the washing is repeated three times. Then, the biochar is placed in an oven at 105° C. and dried for 12 hours to obtain activated carbon after alkali activation and ultrasonic washing;

[0080] 4) After the activated carbon obtained in step 3) is dried after alkali activation and ultrasonic washing, it is placed in an induction cooker at 600° C. for carbonization for 30 minutes to obtain modified biochar.

[0081] (2) Preparation of graphite phase carbon nitride:

[0082] 1) Take a certain amount of melamine and grind it in a mortar for 30 min, then put it into a crucible and cover it to prevent steam volatilization;

[0083] 2) In a box-type atmosphere furnace, heat from room temperature to 550 °C at a heating rate of 2.5 °C·min -1 , and introduce argon as a protective gas during this process. Keep it at 550 °C for 4 h.

[0084] 3) After completion, take out the dried sample and let it cool naturally to room temperature. Then put it into an agate mortar, grind it finely, and sieve it through a 0.75 mm sieve to obtain graphitic carbon nitride.

[0085] (3) Preparation of composite material

[0086] Feed graphitic carbon nitride powder, silica fume, and modified biochar powder into a ball mill in a ratio of 0.4:1:3.5, and mix and ball mill at a rotation speed of 300 r / min for 1 h to obtain the solid product after ball milling, which is the composite material;

[0087] (4) Preparation of green cementitious material

[0088] Mix the composite material and cement in a mass ratio of 1:1 and stir for 30 min to obtain the green cementitious material.

[0089] Example 2

[0090] This example provides a green cementitious material, including the following raw materials in parts by mass:

[0091]

[0092] Among them, the composite material includes the following raw materials in parts by mass: 126 kg of modified biochar, 10 kg of graphitic carbon nitride, and 34 kg of silica fume.

[0093] In addition, this example also provides a preparation method of the green cementitious material, and the specific steps are as follows:

[0094] (1) Preparation of modified biochar:

[0095] 1) Cut the rice straw into pieces, then carry out pyrolysis, cooling, and grinding in sequence, and sieve to obtain the bio-agricultural waste powder;

[0096] 2) Soak the bio-agricultural waste powder obtained in step 1) with a 2 g / L KOH solution at a solid-liquid ratio of 1:3 for 24 h, and after the treatment, put it into an oven at 105 °C for drying treatment for 12 h to obtain the alkali-activated modified rice straw biochar;

[0097] 3) Place the alkali-activated modified rice straw biochar obtained in step 2) in a cleaning tank. Add deionized water to submerge the alkali-activated modified rice straw biochar by 2 mm, and then wash it with ultrasonic waves at 40 kHz for 15 min. After completion, drain the sewage in the cleaning tank, repeat the cleaning 3 times, and then place it in an oven at 105 °C to dry for 12 h to obtain the activated carbon after alkali activation and ultrasonic washing;

[0098] 4) After the drying treatment of the activated carbon after alkali activation and ultrasonic washing obtained in step 3) is completed, put it into an induction cooker at 600 °C for carbonization treatment for 30 min to obtain the modified biochar.

[0099] (2) Preparation of graphitic carbon nitride:

[0100] 1) Take a certain amount of melamine and grind it in a mortar for 30 min, and then put it into a crucible and cover it to prevent steam volatilization;

[0101] 2) In a box-type atmosphere furnace, heat from room temperature to 550 °C at a heating rate of 2.5 °C·min -1 . During this process, introduce argon as a protective gas and maintain it at 550 °C for 4 h.

[0102] 3) After completion, take out the dried sample and let it cool naturally to room temperature, and then put it into an agate mortar, grind it finely and sieve it through a 0.75 mm sieve to obtain graphitic carbon nitride.

[0103] (3) Preparation of composite material

[0104] Feed the graphitic carbon nitride powder, silica fume and modified biochar powder into a ball mill in a ratio of 0.4:1:3.5, and mix and ball mill at a rotation speed of 300 r / min for 1 h to obtain the solid product after ball milling, which is the composite material;

[0105] (4) Preparation of green cementitious material

[0106] Mix the composite material and cement in a mass ratio of 1:1 and stir for 30 min to obtain the green cementitious material.

[0107] Example 3

[0108] This example provides a green cementitious material, including the following raw materials in parts by mass:

[0109]

[0110] Among them, the composite material includes the following raw materials in parts by mass: 133 kg of modified biochar, 3 kg of graphitic carbon nitride, and 34 kg of silica fume.

[0111] In addition, this embodiment also provides a preparation method of a green gelling material, and the specific steps are as follows:

[0112] (1) Prepare modified biochar:

[0113] 1) Cut the rice straw into pieces and then pyrolyze, cool, and grind it in sequence. After sieving, obtain the bio-agricultural waste powder;

[0114] 2) Use a 2g / L KOH solution to soak the bio-agricultural waste powder obtained in step 1) for 24h according to a solid-liquid ratio of 1:3. After the treatment, put it into an oven at 105°C for drying treatment for 12h to obtain the alkali-activated modified rice straw biochar;

[0115] 3) Place the alkali-activated modified rice straw biochar obtained in step 2) in a cleaning tank. Add deionized water to submerge the alkali-activated modified rice straw biochar by 2mm, then wash it with 40kHz ultrasonic waves for 15min. After completion, drain the sewage in the cleaning tank, repeat the cleaning 3 times, and then place it in an oven at 105°C for drying for 12h to obtain the activated carbon after alkali activation and ultrasonic washing;

[0116] 4) After the drying treatment of the activated carbon after alkali activation and ultrasonic washing obtained in step 3), put it into an induction cooker at 600°C for carbonization treatment for 30min to obtain the modified biochar.

[0117] (2) Prepare graphitic carbon nitride:

[0118] 1) Take a certain amount of melamine and grind it in a mortar for 30min, then put it into a crucible and cover it to prevent steam volatilization;

[0119] 2) In a box-type atmosphere furnace, heat it from room temperature to 550°C at a heating rate of 2.5°C·min -1 and keep it at 550°C for 4h while introducing argon as a protective gas during this process.

[0120] 3) After completion, take out the dried sample and naturally cool it to room temperature, then put it into an agate mortar, grind it fine, and sieve it through a 0.75mm sieve to obtain graphitic carbon nitride.

[0121] (3) Prepare the composite material

[0122] Feed the graphitic carbon nitride powder, silica fume, and modified biochar powder into a ball mill according to a ratio of 0.4:1:3.5, and mix and ball mill at a rotation speed of 300r / min for 1h to obtain the solid product after ball milling, which is the composite material;

[0123] (4) Prepare the green gelling material

[0124] Mix the composite material and cement in a mass ratio of 1:1 and stir for 30 minutes to obtain the green cementitious material.

[0125] Comparative Example 1

[0126] This comparative example provides a cementitious material, including the following raw materials in parts by mass:

[0127]

[0128] Among them, the composite material includes the following raw materials in parts by mass: 122 kg of modified biochar, 14 kg of graphitic carbon nitride, and 34 kg of silica fume.

[0129] The average specific surface area of the modified biochar is 435 m 2 / kg; the average pore volume is 1.58 cm 3 / g; the average pore diameter is 24.2 nm.

[0130] In addition, this comparative example also provides a preparation method of the cementitious material. In this preparation method, the biochar is not activated. The specific steps are as follows:

[0131] (1) Prepare biochar:

[0132] 1) Cut the rice straw into pieces and then conduct pyrolysis, cooling, and grinding in sequence. After screening, obtain the bio-agricultural waste powder;

[0133] 2) Place the bio-agricultural waste powder obtained in step 1) in a cleaning tank. Add deionized water to submerge the bio-agricultural waste powder by 2 mm, and then use 40 kHz ultrasonic wave to wash for 15 minutes. After completion, drain the sewage in the cleaning tank, repeat the cleaning 3 times, and then place it in an oven at 105 °C to dry for 12 hours to obtain the activated carbon after ultrasonic wave washing;

[0134] 3) After the drying treatment of the activated carbon after ultrasonic wave washing obtained in step 2) is completed, put it into an induction cooker at 600 °C for carbonization treatment for 30 minutes to obtain the modified biochar.

[0135] (2) Prepare graphitic carbon nitride:

[0136] 1) Take a certain amount of melamine and grind it in a mortar for 30 minutes, and then put it into a crucible and cover it to prevent steam volatilization;

[0137] 2) In a box-type atmosphere furnace, heat from room temperature to 550 °C at a heating rate of 2.5 °C·min -1 During this process, introduce argon as a protective gas and maintain it at 550 °C for 4 hours.

[0138] 3) After completion, take out the dried sample and allow it to cool naturally to room temperature. Then, put it into an agate mortar, grind it finely, and sieve it through a 0.75 mm sieve to obtain graphitic carbon nitride.

[0139] (3) Preparation of composite material

[0140] Feed the graphitic carbon nitride powder, silica fume, and modified biochar powder into a ball mill in a ratio of 0.4:1:3.5, and perform mixing ball milling at a speed of 300 r / min for 1 h to obtain a solid product after ball milling, which is the composite material;

[0141] (4) Preparation of cementitious material

[0142] Mix the composite material and cement in a mass ratio of 1:1 and stir for 30 min to obtain the cementitious material.

[0143] Comparative Example 2

[0144] This example provides a cementitious material, including the following raw materials in parts by mass:

[0145]

[0146] Among them, the composite material includes the following raw materials in parts by mass: 122 kg of modified biochar, 14 kg of graphitic carbon nitride, and 34 kg of silica fume.

[0147] In addition, this example also provides a preparation method of the cementitious material. In this preparation method, the composite material is not subjected to ball milling treatment. The specific steps are as follows:

[0148] (1) Preparation of modified biochar:

[0149] 1) Cut and wash rice straw to obtain powder of biological agricultural waste;

[0150] 2) Soak the powder of biological agricultural waste obtained in step 1) with a 2 g / L KOH solution at a solid-liquid ratio of 1:3 for 24 h. After the treatment, put it into an oven at 105 °C for drying treatment for 12 h to obtain alkali-activated modified rice straw biochar;

[0151] 3) Place the alkali-activated modified rice straw biochar obtained in step 2) in a cleaning tank. Add deionized water to submerge the alkali-activated modified rice straw biochar by 2 mm, then use ultrasonic washing at 40 kHz for 15 min. After completion, drain the sewage in the cleaning tank, repeat the washing 3 times, and then place it in an oven at 105 °C for drying for 12 h to obtain the activated carbon after alkali activation and ultrasonic washing;

[0152] 4) After drying the activated carbon obtained in step 3) and washed ultrasonically, put it into an induction cooker at 600 °C for carbonization treatment for 30 min to obtain modified biochar.

[0153] (2) Preparation of graphitic carbon nitride:

[0154] 1) Take a certain amount of melamine, grind it in a mortar for 30 min, then put it into a crucible and cover it to prevent steam volatilization;

[0155] 2) In a box-type atmosphere furnace, heat from room temperature to 550 °C at a heating rate of 2.5 °C·min -1 , and introduce argon as a protective gas during this process. Keep it at 550 °C for 4 h.

[0156] 3) After completion, take out the dried sample, and cool it naturally to room temperature. Then put it into an agate mortar, grind it fine and sieve it through a 0.75 mm sieve to obtain graphitic carbon nitride.

[0157] (3) Preparation of composite material

[0158] Mix the graphitic carbon nitride powder, silica fume and modified biochar powder in a ratio of 0.4:1:3.5 to obtain a composite material;

[0159] (4) Preparation of cementitious material

[0160] Mix the composite material and cement in a mass ratio of 1:1 and stir for 30 min to obtain a cementitious material.

[0161] Comparative Example 3

[0162] This example provides a cementitious material, including the following raw materials in parts by mass:

[0163]

[0164] Among them, the composite material includes the following raw materials in parts by mass: 122 kg of modified biochar and 34 kg of silica fume.

[0165] In addition, this example also provides a preparation method of the cementitious material, and the specific steps are as follows:

[0166] (1) Preparation of modified biochar:

[0167] 1) Cut and wash rice straw to obtain powder of biological agricultural waste;

[0168] 2) Soak the bio - agricultural waste powder obtained in step 1) with a KOH solution of 2 g / L at a solid - to - liquid ratio of 1:3 for 24 h. After the treatment, place it in an oven at 105 °C for drying for 12 h to obtain the alkali - activated modified rice straw biochar;

[0169] 3) Place the alkali - activated modified rice straw biochar obtained in step 2) in a cleaning tank. Add deionized water to submerge the alkali - activated modified rice straw biochar by 2 mm, and then wash it with ultrasonic waves at 40 kHz for 15 min. After completion, drain the sewage in the cleaning tank, repeat the washing 3 times, and then place it in an oven at 105 °C for drying for 12 h to obtain the activated carbon after alkali activation and ultrasonic washing;

[0170] 4) After the drying treatment of the activated carbon after alkali activation and ultrasonic washing obtained in step 3), place it in an induction cooker at 600 °C for carbonization treatment for 30 min to obtain the modified biochar.

[0171] (2) Preparation of composite material

[0172] Feed silica fume and modified biochar powder into a ball mill at a ratio of 1:3.5, and carry out mixing ball - milling at a speed of 300 r / min for 1 h to obtain the solid product after ball - milling, which is the composite material;

[0173] (3) Preparation of cementitious material

[0174] Mix the composite material and cement and stir for 30 min to obtain the cementitious material.

[0175] Comparative Example 4

[0176] This example provides a cementitious material, which includes the following raw materials in parts by mass:

[0177]

[0178] Among them, the composite material includes the following raw materials in parts by mass: 122 kg of modified biochar and 14 kg of graphitic carbon nitride.

[0179] In addition, this example also provides a preparation method of the cementitious material, and the specific steps are as follows:

[0180] (1) Preparation of modified biochar:

[0181] 1) Cut and wash rice straw to obtain bio - agricultural waste powder;

[0182] 2) Soak the bio-agricultural waste powder obtained in step 1) with a 2 g / L KOH solution at a solid-liquid ratio of 1:3 for 24 h. After the treatment, place it in an oven at 105 °C for drying treatment for 12 h to obtain the alkali-activated modified rice straw biochar;

[0183] 3) Place the alkali-activated modified rice straw biochar obtained in step 2) in a cleaning tank. Add deionized water to submerge the alkali-activated modified rice straw biochar by 2 mm, and then wash it with ultrasonic waves at 40 kHz for 15 min. After completion, drain the sewage in the cleaning tank, repeat the cleaning 3 times, and then place it in an oven at 105 °C for drying for 12 h to obtain the activated carbon after alkali activation and ultrasonic washing;

[0184] 4) After the drying treatment of the activated carbon after alkali activation and ultrasonic washing obtained in step 3), place it in an induction cooker at 600 °C for carbonization treatment for 30 min to obtain the modified biochar.

[0185] (2) Preparation of graphitic carbon nitride:

[0186] 1) Take a certain amount of melamine and grind it in a mortar for 30 min, and then put it into a crucible and cover it to prevent steam volatilization;

[0187] 2) In a box-type atmosphere furnace, heat it from room temperature to 550 °C at a heating rate of 2.5 °C·min -1 . During this process, introduce argon as a protective gas and keep it at 550 °C for 4 h.

[0188] 3) After completion, take out the dried sample and let it cool naturally to room temperature. Then put it into an agate mortar, grind it finely and sieve it through a 0.75 mm sieve to obtain graphitic carbon nitride.

[0189] (3) Preparation of composite material

[0190] Feed the graphitic carbon nitride powder and the modified biochar powder into a ball mill at a ratio of 0.4:3.5 and mix and ball mill at a rotation speed of 300 r / min for 1 h to obtain the solid product after ball milling, which is the composite material;

[0191] (4) Preparation of cementitious material

[0192] Mix the composite material and cement and stir for 30 min to obtain the cementitious material.

[0193] Performance testing

[0194] Apply the green cementitious materials prepared in Examples 1 to 3 and the cementitious materials prepared in Comparative Examples 1 to 4 to prepare concrete. The water-binder ratio is taken as 0.45, and the raw materials and their masses are: cementitious material 500 kg / m3 , sand: 600 kg / m 3 , stone: 1100 kg / m 3 , water reducing agent: 10 kg / m 3 , water: 225 kg / m 3 ; among them, the fineness modulus of the sand is 2.4 and the MB value is 1.5; the stone uses ordinary crushed stone with a continuous gradation of 5 - 20 mm, and the crushing index is 8.7%; the water reducing agent uses a polycarboxylate-based water reducing agent, with a solid content of 20% and a water reducing rate of 25%.

[0195] At the same time, a cement-based concrete was set as the reference sample (all the cementitious materials are cement), and the workability, mechanical properties, carbon sequestration properties, and decontamination properties were tested respectively. The results are shown in Table 1. Among them, the slump and spread of the concrete mixture were tested in accordance with GB / T50080—2016 "Standard Test Method for Properties of Ordinary Concrete Mixtures"; the 3 / 28d compressive strength of the concrete specimens was tested in accordance with GB / T 50081-2019 "Standard Test Method for Physical and Mechanical Properties of Concrete".

[0196] The concretes prepared in Examples 1 - 3 and the concretes prepared in Comparative Examples 1 - 4 were cured in a photocatalytic reaction chamber for 2 h and NO X was introduced as the main pollutant for the photocatalytic degradation test to calculate the degradation efficiency of the concrete for NO X . The photocatalytic effect was evaluated, and the calcium carbonate content in the 28-day-old concrete was calculated using the thermogravimetric test results to evaluate the carbon sequestration performance of the concrete specimens.

[0197] Table 1 Test results of concrete performance

[0198]

[0199] Note: The spread of the concrete is feasible within a certain range. According to different construction scenarios, the spread of the concrete can be adjusted by adding a water reducing agent. Therefore, the spread is not a decisive factor for performance.

[0200] As shown in Table 1, compared with Example 1, the green cementitious material prepared in Comparative Example 1 did not modify the biochar at the same content, resulting in a decrease in the overall carbon sequestration and compressive strength of the concrete. Therefore, through the KOH solution alkali activation treatment, it helps to remove the natural oils and organic substances in the biomass, enhance the oxygen-containing functional groups on the surface of the biochar, and improve the adsorption rate of the biochar.

[0201] Compared with Example 1, in the composite material of Example 3, the content of modified biochar increases while the content of graphitic carbon nitride decreases. The content of biochar determines the carbon sequestration ability, and the content of graphitic carbon nitride determines the photocatalytic ability. If both increase simultaneously, it will lead to a decrease in the amount of cement used, thus affecting the strength of concrete. Therefore, in this application, the amounts of the composite material and cement are controlled to be 1:1 for research.

[0202] The slump and compressive strength of the concrete prepared from the green cementitious materials obtained in Examples 1 to 3 are significantly greater than those of the concrete prepared from the cementitious materials obtained in Comparative Examples 1 to 4. With the increase in the content of modified biochar, the carbon sequestration amount of the concrete is improved. With the increase in graphitic carbon nitride, the NOx degradation rate is improved. A high degradation efficiency represents a strong photocatalytic effect. In order to ensure the strength of the concrete, the amounts of the composite material and cement are controlled to be 1:1 in this invention. Experiments are carried out by adjusting the ratio of modified biochar and graphitic carbon nitride in the composite material. The final results show that a green cementitious material proposed in this invention has excellent workability, mechanical properties, carbon sequestration and photocatalytic properties. It can promote the resource utilization of biochar and graphitic carbon nitride, simultaneously greatly reduce the carbon emissions of the concrete industry, and improve the self-cleaning ability of the concrete.

[0203] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A green gelling material, characterized in that, Comprising the following raw materials in parts by weight: Among them, the composite material comprises the following raw materials in parts by mass: 80 - 140 kg of modified biochar, 2 - 20 kg of graphitic carbon nitride, and 24 - 36 kg of silica fume.

2. The green gelling material according to claim 1, characterized in that, The specific preparation steps of the modified biochar are as follows: S1. Cut the bio - agricultural waste, and then conduct pyrolysis, cooling, and grinding in sequence. After screening, obtain bio - agricultural waste powder; S2. Add an alkali solution to the bio - agricultural waste powder obtained in step S1, conduct alkali activation treatment, and obtain modified biochar after washing and carbonization.

3. A green gelling material according to claim 2, characterized in that, In step S2, the alkali solution is a KOH solution, the concentration of the KOH solution is 1 - 3 g / L, and the alkali activation treatment time is 20 - 40 h; The washing method is ultrasonic washing at 30 - 50 kHz, and the washing time is 10 - 30 min; The carbonization temperature is 500 - 700 °C, and the carbonization is carried out in an induction cooker.

4. A green gelling material according to claim 1, characterized in that, The modified biochar contains the following elements in mass content: C content is 75.3 - 80.5%; O content is 15.2 - 20.5%; Si content is 1.1 - 3.3%; K content is 0.4 - 0.7%; Ca content is 0.1 - 0.2%; Mg content is 0.1 - 0.2%; Na content is 0.1 - 0.2%; Fe content is 0.1 - 0.2%; The specific surface area of the modified biochar is 350-560 m 2 / kg; the pore volume is 0.008-0.3 cm 3 / g; the pore diameter is 0.5-40 nm.

5. A green gelling material according to claim 1, characterized in that, The specific preparation steps of the graphitic carbon nitride are as follows: Melamine is ground, heated, cooled, and screened to obtain graphitic carbon nitride.

6. A green gelling material according to claim 1, characterized in that, The graphitic carbon nitride contains the following elements in mass content: C content is 47 - 50%; N element content is 50 - 53%; The specific surface area of the graphitic carbon nitride is 176 to 183 m 2 / g; the average pore volume is 0.005 cm 3 / g, and the average pore diameter is 30.65 nm.

7. The green gelling material according to claim 1, characterized in that, The silica fume contains the following elements in mass content: SiO2 content is 99.0 - 99.3%; Al2O3 content is 0.1 - 0.7%; Fe2O3 content is 0.1 - 0.4%; CaO content is 0.1 - 0.6%; The moisture content of the silica fume is 1.0 - 1.3%, and the loss on ignition is 2.5 - 2.

6.

8. A green gelling material according to claim 1, characterized in that, The specific preparation steps of the composite material are as follows: Mix and ball - mill silica fume, graphitic carbon nitride, and modified biochar according to the ratio of 1:(0.1 - 0.4):(3.6 - 3.9) to obtain a composite material.

9. A preparation method of the green gelling material as described in any one of claims 1-8, characterized in that, The specific steps are as follows: S1. Prepare the composite material; S2. Weigh the composite material, cement, water, and water - reducing agent according to the mix ratio; S3. After mixing the composite material with cement, water, and water - reducing agent, stir to obtain a green cementitious material.

10. Use of a green cementitious material according to claim 9 in the preparation of concrete.

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