CN115259705A - Environment-friendly portland cement and preparation method thereof - Google Patents

Abstract

The invention discloses environment-friendly portland cement and a preparation method thereof. The preparation method of the environment-friendly portland cement comprises the following steps: adopting tetraethoxysilane, isobutyl triethoxysilane and graphene oxide for copolymerization grafting, and then adsorbing sodium p-dimethylaminoazobenzene sulfonate on the graphene oxide to prepare a reinforcing agent; portland cement clinker, limestone, bentonite, fly ash, slag, calcined clay, gypsum, titanium dioxide and a reinforcing agent are selected as raw materials, and the environment-friendly Portland cement is prepared by grinding and calcining processes. Compared with the prior art, the environment-friendly silicate cement prepared by the invention has the characteristics of water saving and environmental protection, and the mortar prepared by the cement has good fluidity and high strength.

Description

Environment-friendly portland cement and preparation method thereof

Technical Field

The invention relates to the field of building materials, in particular to environment-friendly portland cement and a preparation method thereof.

Background

Reducing carbon dioxide emissions from human activities has become a leading problem worldwide, and in addition to global warming, the problem of inhalable particles is one of the most serious environmental problems of international social concern, wherein the Portland Cement (PC) industry has a strong impact on the environment, and ordinary portland cement is the most produced man-made material, and the production thereof accounts for about 8% of the total amount of human carbon dioxide emissions due to the high amount of carbon dioxide generated during the calcination of cement clinker and the large energy consumption.

With the development of cement industry, cement-based materials are one of the most widely used building materials in engineering at present, environment-friendly cement is an important component of green building materials, and the environment-friendly cement is prepared by making full use of wastes generated in the urban development process, such as industrial wastes, waste residues, urban garbage and the like, to serve as raw materials for producing the environment-friendly cement, and processing and producing the environment-friendly cement. The cement can consume a large amount of urban waste, is energy-saving and environment-friendly, realizes harmony of human beings and natural environment, and becomes a key direction for cement development in a new period. In order to meet the requirements of people on living environment, the development of novel environment-friendly cement is a key research point.

With the expansion of the application range and the increase of the dosage, the problems of poor toughness, insufficient durability and the like of the traditional cement-based materials become more and more prominent, and the method for improving the performance of the cement by adding other types of mineral admixtures or clinkers such as volcanic ash, clay, fly ash, blast furnace slag, silica fume and other materials with low emission becomes an effective method gradually. The cement composite material prepared by using part of mineral admixture to replace cement can solve the problem of increasing shortage of cement resources for construction, reduce the problems of environmental pollution and large land occupation caused by tailing storage, and has good economic benefit and social benefit.

Patent No. CN109437621A discloses an environment-friendly portland cement and a preparation method thereof, belonging to the technical field of cement, wherein the environment-friendly portland cement comprises raw materials of portland cement clinker, microbial sludge, phosphogypsum, fly ash, slag, limestone, dihydrate gypsum, silicon dioxide and additives, and the additives comprise maleic anhydride modified triethanolamine, maleic anhydride, acetic acid, trimellitic anhydride glyceride, isopentenol polyoxyethylene ether, sodium fatty acid, dodecylamine polyoxyethylene ether, calcium lignosulfonate and molasses. The environment-friendly portland cement has high breaking strength and compressive strength, the application range is enlarged, the production cost is reduced, the additive has a good reinforcing effect on the portland cement, the adverse effect of the additive on the compatibility of the cement and a water reducing agent is reduced, meanwhile, the recycling of wastes is realized by adding the microbial sludge and the phosphogypsum, and the production cost of the environment-friendly portland cement is reduced. However, the microbial sludge added in the environment-friendly portland cement is easily weathered and degraded in the long-term wind-blowing and sun-drying process, potential safety hazards exist, most of other components are other components except cement in the concrete, a large amount of cement needs to be used in the later preparation process of the concrete, resources are wasted, and the environment protection is not facilitated.

CN110482885A discloses a portland cement raw material formula, which comprises the following components in parts by weight: 70-73 parts of limestone, 10-12 parts of sandstone, 9-10 parts of carbide slag, 2-3 parts of iron raw material, 2-3 parts of filter residue and 2-3 parts of shale; ca (OH) in the carbide slag₂The content is more than or equal to 80 percent, and the filter residue contains SiO₂30-40％、Al₂O₃45-50%, caO7-15% and impurities. Mixing and grinding raw materials in a specific ratio to prepare raw material powder; after the raw material powder is calcined into clinker particles, a retarder is added to prepare the Portland cement with higher structural strength. The carbide slag is used as the raw material of the raw material powder, so that the consumption of the carbide slag is improved, and the carbide slag can be rapidly and efficiently recycled. However, the components in the invention have the defects of difficult mixing and calcination, high processing requirement, easy generation of cement agglomeration, influence on the performance of concrete, great pollution and environmental protection.

Patent No. CN110282886A discloses a process for preparing portland cement by using solid waste and corresponding portland cement, which comprises the following steps: 1) 0.60 to 0.80 portion of white mud residue or alkali white mud residue, 0.050 to 0.07 portion of aluminum ash, 0.2 to 0.25 portion of tailing slag and 0.02 to 0.04 portion of iron correction raw material are sent to a raw material grinding machine to be ground into raw material powder with the water content of less than 1.5 percent through a proportioning machine and an electronic belt scale according to the weight portion ratio; 2) Homogenizing raw material powder and then feeding into a rotary kiln for calcination; 3) After calcining, cooling the calcined dry material balls by a cooling machine; 4) After the dry material balls in the step 3) are cooled, 5.0-7.0% of gypsum and 15.0-29.0% of mixed material are added into the cooled dry material balls and sent into a ball mill for grinding to prepare the silicate cement with different grades. The process for preparing the portland cement and the corresponding portland cement improve the resource recycling on one hand and solve the problem of serious life, property and ecology threats caused by long-term stockpiling of wastes on the other hand. However, the production process of the Portland cement is complex, and the prepared concrete structure has low strength.

Disclosure of Invention

The environment-friendly portland cement in the prior art has the defects of complex preparation process, high energy consumption, high pollution and low performance of prepared concrete. In order to solve the defects, the invention adopts partial wastes and conventional cement materials, and adds a reinforcing agent to construct the environment-friendly portland cement.

The environment-friendly portland cement comprises the following components in parts by weight: 30 to 45 portions of portland cement clinker, 10 to 20 portions of limestone, 5 to 15 portions of bentonite, 5 to 10 portions of fly ash, 1 to 5 portions of slag, 5 to 10 portions of calcined clay, 1 to 5 portions of gypsum, 1 to 5 portions of titanium dioxide and 10 to 20 portions of reinforcing agent.

The invention also provides a preparation method of the environment-friendly portland cement, which comprises the following steps:

step 1, weighing raw materials according to a formula; mixing and grinding limestone, bentonite, slag, gypsum and titanium dioxide until the particle size is 20-50 mu m, preparing a fine powder mixed material, and calcining the fine powder mixed material at high temperature to prepare a fine powder clinker;

and 2, respectively grinding the portland cement clinker and the calcined clay until the particle size is 50-100 mu m, mixing the portland cement clinker and the calcined clay to prepare powder, adding the fine powder clinker prepared in the step 1, fly ash and a reinforcing agent into the powder, and uniformly mixing to prepare the portland cement.

Preferably, the high-temperature calcination temperature in the step 1 is 1300-1700 ℃, and the calcination time is 20-80 min.

The preparation steps of the reinforcing agent are as follows, and the parts are all parts by weight:

s1, adding graphene oxide, polydopamine and tris (hydroxymethyl) aminomethane hydrochloride into a 60-80 wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 10-40 wt% ammonia solution into the uniform solution, adjusting the pH value to 8-9, and performing ultrasonic dispersion treatment for 0.3-2 hours to prepare a suspension;

s2, mixing the suspension prepared in the step S1, tetraethoxysilane, isobutyl triethoxysilane, a nonionic surfactant, a dispersing agent and water; reacting for 1-3 h under the conditions of stirring and heating, wherein the stirring speed is 100-500 r/min, the heating temperature is 30-50 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing the modified graphene silane solution prepared in the step S2, sodium p-dimethylaminoazobenzene sulfonate, a polycarboxylate ether water reducing agent and 60-80 wt% of ethanol water solution, and stirring for reaction for 0.3-2 h at the stirring speed of 100-400 r/min to obtain a suspension; centrifuging the suspension for 20-60 min at the rotating speed of 10000-15000 r/min, collecting the centrifuged precipitate, and washing the precipitate for 1-3 times by using water and absolute ethyl alcohol respectively; drying and grinding the collected precipitate to obtain the reinforcing agent.

Preferably, the components in the step S1 are calculated by weight: 10-20 parts of graphene oxide, 1-3 parts of polydopamine, 1-5 parts of tris (hydroxymethyl) aminomethane hydrochloride and 300-600 parts of 60-80 wt% ethanol aqueous solution.

Preferably, the components in the step S2 are calculated by weight: 20 to 30 parts of the suspension prepared in the step S1, 5 to 10 parts of ethyl orthosilicate, 5 to 15 parts of isobutyl triethoxysilane, 0.1 to 2 parts of nonionic surfactant, 0.1 to 1 part of dispersant and 100 to 300 parts of water.

Preferably, the nonionic surfactant in step S2 is composed of the following substances by mass: the mass ratio of the fatty alcohol-polyoxyethylene ether to the polysorbate 80 is 1: (1-2).

Preferably, the dispersing agent in step S2 is composed of one or more of polyethylene glycol, polyethylene wax, magnesium stearate, and glyceryl tristearate.

Preferably, the components in the step S3 are calculated by weight: 40-80 parts of modified graphene silane solution, 1-5 parts of sodium p-dimethylamino azobenzene sulfonate, 0.01-0.5 part of polycarboxylate ether water reducing agent and 100-150 parts of 60-80 wt% ethanol water solution.

Graphene Oxide (GO) is a novel carbon nanomaterial that is receiving attention for its excellent mechanical, electrical, and thermal properties. In the prior art, the addition of the graphene oxide can reduce the internal porosity of cement and improve the mechanical property and durability of mortar. The functional group of the graphene can provide active sites for crystal growth and improve cementMicrostructure during hydration. The higher the dispersion degree of the graphene oxide in the cement matrix, the stronger the interface bonding force given by the C-S-H chemical bond generated by the graphene oxide. However, when graphene oxide is in an alkaline cement solution, carboxyl on the surface of the graphene oxide is easily subjected to Ca generated by cement hydration²⁺Crosslinking, which destabilizes the graphene oxide, causing it to solidify; further, the nucleation effect and the crack bridging effect of the cement-based composite material cannot be fully exerted, and the performance of the cement-based composite material cannot be positively influenced. Therefore, a method for reinforcing cement by using graphene needs to be improved, and the dispersion of graphene oxide in a cement alkaline solution mainly comprises physical ultrasonic treatment, surfactant addition, chemical modification and the like. The repulsion force between graphene oxide layers is enhanced by utilizing a polycarboxylate ether water reducing agent (PCE) through a steric hindrance effect, so that graphene oxide and Ca are prevented from being oxidized²⁺The contact of (2) is a method of uniformly dispersing graphene oxide in a cement matrix, but the treatment effect of the method is not ideal.

According to the method, firstly, a polydopamine in-situ polymerization method is adopted to prepare the graphene oxide sheet, polydopamine is taken as a reactive monomer to be adsorbed on the graphene oxide sheet, and oxidative autopolymerization is carried out in an alkaline environment. The polydopamine contains a plurality of active groups such as amino, hydroxyl, indole and the like, and can react with an epoxy group of the graphene oxide sheet. More oxygen-containing functional groups such as carboxyl, hydroxyl and the like are grafted on the surface of graphene oxide, polydopamine molecules grafted on a graphene oxide sheet layer have good stretchability and space stability, the functional groups are easily combined with organic molecules in the modes of hydrogen bond, static electricity or pi-pi bond accumulation and the like, the polymerization of siloxane molecules is better promoted, the crosslinking of a silane system is improved, and the stability and reliability of a polymer can be remarkably improved by the polydopamine modified graphene oxide.

The invention then applies polydopamine modified graphene oxide to silane polymerization, isobutyl triethoxysilane and tetraethoxysilane are grafted and condensed on graphene oxide by adopting a sol-gel method, and isobutyl triethoxysilane molecules and polydopamine molecules on the surface of graphene oxide mainly pass through NH₂And of OH groupsAnd (2) condensation reaction connection, namely bridging the graphene oxide sheets and silane molecules to form an amorphous compact network structure in the solution, so that the connected cement paste is more stable, a compact polymer film is formed on the surface of a cement matrix, an effective protection effect on hydration products is achieved, and the surface weight loss rate of the cement sample treated by the modified silane emulsion is lowest. This is because the polydopamine modified graphene oxide can be combined with more siloxane molecular chains to form a more stable multi-layer hydrophobic space network structure on the surface of the cement hydration product. With the addition of the graphene oxide nanosheets, the workability of the cement paste is reduced, since the graphene oxide nanosheets have a large surface area and a large water requirement for surface wetting. In addition, the dispersion stability of the nanosheets in a cement environment is poor, so that serious agglomeration can be caused, free water is adsorbed, the fluidity is obviously reduced, and the performance of cement mortar is influenced. In a water-alcohol solution, condensation of tetraethoxysilane and proton functional groups such as hydroxyl, carboxyl and the like on the surface of graphene oxide can form a silicon dioxide coating layer on the surface of graphene oxide, the change of the surface charge of the silicon dioxide coating layer can be ignored, and the small change of the surface charge can be attributed to abundant hydroxyl on silicon dioxide. The grafting of the silicon dioxide covers a carboxyl functional group, and the coating of the silicon dioxide in the graphene oxide can effectively relieve the crosslinking of the graphene oxide. In addition, the silicon dioxide coating may act as a spacer on the graphene oxide, physically separating the graphene oxide and weakening van der waals forces. The strength of the prepared cement mortar is improved, and the enhanced compressive strength is probably due to the fact that the dispersibility of the graphene oxide is improved, and the negative effects of pores and stress concentration are reduced. The graphene oxide improves the adhesive force between the coating and the cement matrix through the pi-pi effect, and improves the density and the crack expansion resistance of the polymer.

On the other hand, ca (OH)₂The silicon hydroxyl group of the C-S-H gel structure and the hydroxyl group of the silane molecule are subjected to more direct reactions due to continuous consumption in the reaction with the silane molecule, and the integrity and the stability of a silicate network are also improved. The silane composite material not only can form a complete hydrophobic film on the surface and in the cement base, but also can permeate into the capillary of concreteAnd in pores and gel pores, the diffusion and transmission of water and corrosive media in the pore channels are inhibited. The surface tension generated on the concrete surface is far lower than that of water and capillaries, so that the pores of the concrete capillaries are not blocked, and the normal air permeability of the concrete is kept. The grafting of silane in the graphene oxide can improve the molecular configuration and the space stability of a polymer system, and endow a polymer coating with excellent physical and chemical properties. The graphene oxide sheet not only can resist the diffusion and transportation of water and corrosive media in the polymer coating, but also can be used as a reaction platform to promote molecular polymerization. For the surface protection of porous heterogeneous materials such as concrete and the like, the modification of the graphene oxide can fully play the hydrophobicity of the isobutyl triethoxysilane, effectively improve the capability of resisting erosion ions, and further improve the durability of the concrete material.

Sodium p-dimethylaminoazobenzenesulfonate (C)₁₄H₁₄N₃SO₃Na) whose aromatic ring structure is similar to that of graphene oxide. Above all, the dye has wide application in the dyeing industry due to low production cost and good solubility in water. According to the characteristics, the sodium dimethylaminoazobenzenesulfonate is subjected to post-treatment, due to the high hydrophobicity of pi electron carbon atoms in graphene oxide, a pi system of the graphene oxide and a benzene ring in molecules of the sodium dimethylaminoazobenzenesulfonate are subjected to pi-pi interaction, the graphene oxide has physical adsorption capacity on the sodium dimethylaminoazobenzenesulfonate, and the sodium dimethylaminoazobenzenesulfonate can be adsorbed on graphene oxide sheet layers in an alkaline environment, so that the distance between the graphene oxide sheet layers is increased, and the graphene oxide sheet layers are prevented from being agglomerated. The surface of the sodium p-dimethylaminoazobenzenesulfonate is negatively charged, and Ca in the cement solution is reduced²⁺The concentration and partial hydrophilic functional groups can be adsorbed on the surface of unhydrated cement particles, and hydration shells with negative charges are formed outside the particles, so that the electrostatic repulsion between the connecting agents is enhanced, the retained free water is released, and the fluidity of the cement mortar is improved. The modified graphene oxide can promote and improve the structure of cement hydration products. The improvement effect depends to some extent on the degree of dispersion of the graphene oxide. And dimethylaminoazobenzeneThe addition of the sodium sulfonate promotes the dispersion of the graphene oxide in the mortar, so that the graphene oxide has a greater regulation effect on the formation of hydration products, and the formation of the hydration products is more compact.

Due to the adoption of the technical scheme, compared with the prior art, the preparation method of the anti-oxidation and anti-decarbonization isolation binder has the advantages that: 1) After the polydopamine is modified, isobutyl triethoxysilane and ethyl orthosilicate are grafted and condensed on graphene oxide, a stable and compact hydrophobic film can be formed on the surface of a cement matrix, diffusion and transmission of corrosive media in a pore channel are inhibited, the fluidity of mortar and sand is improved, water is saved, and the durability of the prepared concrete is improved. 2) The well-dispersed graphene oxide can promote the ordered arrangement of cement hydrated crystals, so that mortar forms a relatively compact structure, and the strength of prepared concrete is greatly improved. 3) The dimethylamino azobenzene sodium sulfonate is adsorbed on the graphene oxide sheet layer, so that the fluidity of the cement mortar is improved. 4) The synthesis process simply controls the use amounts of isobutyl triethoxysilane and ethyl orthosilicate, controls the silane content on the graphene oxide sheet, has good efficiency and controllability, and has feasibility of large-scale preparation.

Detailed Description

Sources of the main raw materials in the examples:

portland cement clinker: grade: grade a, xinglong county, fushui cement limited.

Slag: lingshu county Dan Hang building materials, inc.

Poly-dopamine: xi' an kangfuo biotechnology limited, particle size: 300-400 nm.

Tris hydrochloride salt: jiangsu Haolilong chemical industry, ltd, CAS no: 1185-53-1.

Ethyl orthosilicate: guangzhou double peach fine chemical Co., ltd, molecular weight 208.33, CAS number: 78-10-4.

Isobutyl triethoxysilane: nanchang hongdun waterproof materials, inc., appearance: clear liquid, CAS No.: 17980-47-1.

Sodium p-dimethylaminoazobenzenesulfonate: shenyang senil chemical industry hasLimit company, molecular formula: c₁₄H₁₄N₃NaO₃S, CAS number: 547-58-0.

Example 1

The environment-friendly portland cement comprises the following components in parts by weight: 36 parts of portland cement clinker, 15 parts of limestone, 10 parts of bentonite, 7 parts of fly ash, 3 parts of slag, 7 parts of calcined clay, 2 parts of gypsum, 2 parts of titanium dioxide and 16 parts of reinforcing agent.

The preparation method of the environment-friendly portland cement comprises the following steps:

step 1, weighing raw materials according to a formula; mixing and grinding limestone, bentonite, slag, gypsum and titanium dioxide until the particle size is 30-40 mu m, preparing a fine powder mixed material, and calcining the fine powder mixed material at a high temperature of 1500 ℃ for 60min to prepare a fine powder clinker;

and 2, respectively grinding the portland cement clinker and the calcined clay until the particle size is 50-80 microns, mixing the portland cement clinker and the calcined clay to obtain powder, adding the fine powder clinker prepared in the step 1, fly ash and a reinforcing agent into the powder, and uniformly mixing to obtain the portland cement.

The preparation steps of the reinforcing agent are as follows, and the parts are all parts by weight:

s1, adding 16 parts of graphene oxide, 2 parts of polydopamine and 3 parts of tris (hydroxymethyl) aminomethane hydrochloride into 400 parts of 70wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 25wt% ammonia aqueous solution into the uniform solution, adjusting the pH value to 8.5, and performing ultrasonic dispersion treatment for 1 hour to prepare a suspension;

s2, mixing 25 parts of the suspension prepared in the step S1, 7 parts of ethyl orthosilicate, 10 parts of isobutyl triethoxysilane, 0.2 part of fatty alcohol-polyoxyethylene ether, 0.3 part of polysorbate 80, 0.5 part of polyethylene glycol and 200 parts of water; reacting for 2 hours under the conditions of stirring and heating, wherein the stirring speed is 300r/min, the heating temperature is 40 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing 60 parts of the modified graphene silane solution prepared in the step S2, 3 parts of sodium p-dimethylaminoazobenzene sulfonate, 0.1 part of polycarboxylate ether water reducer and 125 parts of 70wt% ethanol water solution, and stirring for reaction for 1 hour at a stirring speed of 200r/min to obtain a suspension; centrifuging the suspension in a centrifuge at 12000r/min for 40min, collecting precipitate attached to the centrifuge tube, and washing with water and anhydrous ethanol for 2 times; drying and grinding the collected precipitate to obtain the reinforcing agent.

Example 2

An environment-friendly portland cement is prepared by the same method as the preparation method of the environment-friendly portland cement in example 1, and the only difference is that: the preparation method of the reinforcing agent is different.

The preparation method of the reinforcing agent in the embodiment comprises the following steps of:

s1, adding 16 parts of graphene oxide, 2 parts of polydopamine and 3 parts of tris (hydroxymethyl) aminomethane hydrochloride into 400 parts of 70wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 25wt% ammonia aqueous solution into the uniform solution, adjusting the pH value to 8.5, and performing ultrasonic dispersion treatment for 1 hour to prepare a suspension;

s2, mixing 25 parts of the suspension prepared in the step S1, 10 parts of isobutyl triethoxysilane, 0.2 part of fatty alcohol-polyoxyethylene ether, 0.3 part of polysorbate 80, 0.5 part of polyethylene glycol and 200 parts of water; reacting for 2 hours under the conditions of stirring and heating, wherein the stirring speed is 300r/min, the heating temperature is 40 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing 60 parts of the modified graphene silane solution prepared in the step S2, 3 parts of sodium p-dimethylaminoazobenzene sulfonate, 0.1 part of polycarboxylate ether water reducer and 125 parts of 70wt% ethanol aqueous solution, and stirring for reaction for 1 hour at the stirring speed of 200r/min to obtain a suspension; centrifuging the suspension in a centrifuge at 12000r/min for 40min, collecting precipitate attached to the centrifuge tube, and washing with water and anhydrous ethanol for 2 times; drying and grinding the collected precipitate to obtain the reinforcing agent.

Example 3

An environment-friendly portland cement is prepared by the same method as the preparation method of the environment-friendly portland cement in example 1, and the only difference is that: the preparation method of the reinforcing agent is different.

The preparation method of the reinforcing agent in the embodiment comprises the following steps of:

s1, adding 16 parts of graphene oxide, 2 parts of polydopamine and 3 parts of tris (hydroxymethyl) aminomethane hydrochloride into 400 parts of 70wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 25wt% ammonia aqueous solution into the uniform solution, adjusting the pH value to 8.5, and performing ultrasonic dispersion treatment for 1 hour to prepare a suspension;

s2, mixing 25 parts of the suspension prepared in the step S1, 7 parts of ethyl orthosilicate, 0.2 part of fatty alcohol-polyoxyethylene ether, 0.3 part of polysorbate 80, 0.5 part of polyethylene glycol and 200 parts of water; reacting for 2 hours under the conditions of stirring and heating, wherein the stirring speed is 300r/min, the heating temperature is 40 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing 60 parts of the modified graphene silane solution prepared in the step S2, 3 parts of sodium p-dimethylaminoazobenzene sulfonate, 0.1 part of polycarboxylate ether water reducer and 125 parts of 70wt% ethanol aqueous solution, and stirring for reaction for 1 hour at the stirring speed of 200r/min to obtain a suspension; centrifuging the suspension in a centrifuge at 12000r/min for 40min, collecting precipitate attached to the centrifuge tube, and washing with water and anhydrous ethanol for 2 times; drying and grinding the collected precipitate to obtain the reinforcing agent.

Example 4

The preparation method of the environment-friendly portland cement is basically the same as that of the environment-friendly portland cement in example 1, and the only difference is that: the preparation method of the reinforcing agent is different.

The preparation method of the reinforcing agent in the embodiment comprises the following steps of:

s1, adding 16 parts of graphene oxide, 2 parts of polydopamine and 3 parts of tris (hydroxymethyl) aminomethane hydrochloride into 400 parts of 70wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 25wt% ammonia aqueous solution into the uniform solution, adjusting the pH value to 8.5, and performing ultrasonic dispersion treatment for 1 hour to prepare a suspension;

s2, mixing 25 parts of the suspension prepared in the step S1, 7 parts of ethyl orthosilicate, 10 parts of isobutyl triethoxysilane, 0.2 part of fatty alcohol-polyoxyethylene ether, 0.3 part of polysorbate 80, 0.5 part of polyethylene glycol and 200 parts of water; reacting for 2 hours under the conditions of stirring and heating, wherein the stirring speed is 300r/min, the heating temperature is 40 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing 60 parts of the modified graphene silane solution prepared in the step S2, 0.1 part of polycarboxylate ether water reducer and 125 parts of 70wt% ethanol water solution, and stirring for reaction for 1 hour at a stirring speed of 200r/min to obtain a suspension; centrifuging the suspension in a centrifuge at 12000r/min for 40min, collecting precipitate attached to the centrifuge tube, and washing with water and anhydrous ethanol for 2 times; drying and grinding the collected precipitate to obtain the reinforcing agent.

Comparative example 1

An environment-friendly portland cement is prepared by the same method as the preparation method of the environment-friendly portland cement in example 1, and the only difference is that: the preparation method of the reinforcing agent is different.

The preparation method of the reinforcing agent in the embodiment comprises the following steps of:

s1, adding 16 parts of graphene oxide, 2 parts of polydopamine and 3 parts of tris (hydroxymethyl) aminomethane hydrochloride into 400 parts of 70wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 25wt% ammonia aqueous solution into the uniform solution, adjusting the pH value to 8.5, and performing ultrasonic dispersion treatment for 1 hour to prepare a suspension;

s2, mixing 25 parts of the suspension prepared in the step S1, 0.2 part of fatty alcohol-polyoxyethylene ether, 0.3 part of polysorbate 80, 0.5 part of polyethylene glycol and 200 parts of water; reacting for 2 hours under the conditions of stirring and heating, wherein the stirring speed is 300r/min, the heating temperature is 40 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing 60 parts of the modified graphene silane solution prepared in the step S2, 3 parts of sodium p-dimethylaminoazobenzene sulfonate, 0.1 part of polycarboxylate ether water reducer and 125 parts of 70wt% ethanol aqueous solution, and stirring for reaction for 1 hour at the stirring speed of 200r/min to obtain a suspension; centrifuging the suspension in a centrifuge at 12000r/min for 40min, collecting precipitate attached to the centrifuge tube, and washing with water and anhydrous ethanol for 2 times; drying and grinding the collected precipitate to obtain the reinforcing agent.

Comparative example 2

An environment-friendly portland cement is prepared by the same method as the preparation method of the environment-friendly portland cement in example 1, and the only difference is that: no reinforcing agent was added.

Test example 1

Water usage test for standard consistency

In order to test the influence of each embodiment and comparative example on the water consumption of the standard consistency of the cement, the water consumption of the standard consistency of the environment-friendly portland cement and the cone sinking depth are tested according to GB/T1346-2011 inspection method for water consumption, setting time and stability of the standard consistency of the cement, and the influence of different preparation methods on the water consumption of the standard consistency of the environment-friendly portland cement is further analyzed. The test results are shown in Table 1.

Test example 2

Coagulation time test

The setting time of the portland cement is tested according to GB/T1346-2011 'method for testing water consumption, setting time and stability of standard consistency of cement', and the setting time of environment-friendly portland cement in examples and comparative examples is measured under the condition of the same water consumption. The test results are shown in Table 1.

Test example 3

Cement paste fluidity test

The fluidity of the cement paste was measured according to GB/T8077-2012 "method for testing the homogeneity of concrete admixtures", and the dispersion effect of the cement pastes of examples and comparative examples was determined as the maximum diameter of the free flow of the cement paste on a glass plate. The test results are shown in Table 1.

Table 1: water consumption for standard consistency, net setting time and pulp fluidity test result

The use of example 1 can be seen from Table 1The water amount is the least, the setting time of cement is the longest, and the net slurry fluidity is the greatest, probably because the graphene oxide has a large specific surface area and many oxygen-containing groups exist on the surface. The large number of oxygen-containing groups makes graphene oxide highly hydrophilic and bonds to hydrogen atoms in water, and as the content of graphene oxide increases, more water is consumed. The dispersion stability of the single-component graphene oxide in a cement environment is poor, so that serious agglomeration can be caused, free water is absorbed, and the fluidity is obviously reduced. The graphene oxide sheet is prepared by a poly-dopamine in-situ polymerization method, poly-dopamine serving as a reactive monomer is adsorbed on the graphene oxide sheet, and oxidative self-polymerization is carried out in an alkaline environment. Introducing various active groups such as amino, hydroxyl, indole and the like to promote the polymerization of siloxane molecules, grafting and condensing isobutyl triethoxysilane and tetraethoxysilane on graphene oxide, wherein the isobutyl triethoxysilane molecules and polydopamine molecules on the surface of the graphene oxide mainly pass through NH₂The graphene oxide thin sheet is connected with OH groups through condensation reaction, the graphene oxide thin sheet and silane molecules are bridged, an amorphous compact network structure is formed in a solution, and the connected cement paste is more stable and shows the highest hydrophobicity; in a water-alcohol solution, tetraethoxysilane and proton functional groups such as hydroxyl, carboxyl and the like on the surface of graphene oxide undergo hydrolytic condensation. The grafting of the silicon dioxide covers carboxyl functional groups, a layer of silicon dioxide is coated in the graphene oxide, so that the crosslinking of the graphene oxide can be effectively relieved, the water consumption is reduced, the fluidity is increased, the integrity and the stability of a silicate network are enhanced by adding the dimethylamino azobenzene sodium sulfonate, and the processing of cement mortar is facilitated. Due to the high hydrophobicity of pi electron carbon atoms in the graphene oxide, a pi system of the graphene oxide and a benzene ring in molecules of the sodium p-dimethylaminoazobenzene sulfonate have pi-pi interaction, the graphene oxide has physical adsorption capacity on the sodium p-dimethylaminoazobenzene sulfonate, and the sodium p-dimethylaminoazobenzene sulfonate can be adsorbed on a graphene oxide sheet layer in an alkaline environment, so that the distance between the graphene oxide sheet layers is increased, and the graphene oxide sheet layers are prevented from being agglomerated. Sodium p-dimethylaminoazobenzenesulfonate surfaceHas negative charge and can reduce Ca in cement solution²⁺The concentration enhances the electrostatic repulsion between the connecting agents and releases the retained free water, thereby improving the fluidity of the cement mortar.

Test example 4

Mortar Strength test

The cement mortar strength of examples and comparative examples was tested according to GB/T17671-1999 "Cement mortar Strength test method", and the flexural strength and compressive strength of the cement mortar were tested for 3 days and 28 days, and the test results are shown in Table 2.

Table 2: mortar strength test results

It can be seen from table 2 that the flexural strength and compressive strength of example 1 are the best, probably due to the poor dispersion stability of graphene oxide alone in the cement environment, which can cause serious agglomeration and affect the strength of cement mortar. The graphene oxide is prepared by a poly-dopamine in-situ polymerization method, more oxygen-containing functional groups such as carboxyl, hydroxyl and the like are grafted on the surface of the graphene oxide, the functional groups are combined with organic molecules in the modes of hydrogen bonds, static electricity or pi-pi bond accumulation and the like, isobutyl triethoxysilane and tetraethoxysilane molecular chains are combined on the graphene oxide, and a more stable multilayer hydrophobic space network structure is formed on the surface of a cement hydration product. And (3) performing hydrolytic condensation on the tetraethoxysilane and proton functional groups such as hydroxyl, carboxyl and the like on the surface of the graphene oxide. The silicon dioxide coating on the graphene oxide may act as a spacer, physically separating the graphene oxide and weakening van der waals forces. Isobutyltriethoxysilane improves the integrity and stability of the silicate network. The silane composite material can not only form a complete hydrophobic membrane on the surface and in the cement base, but also permeate into capillary pores and gel pores of concrete, and inhibit the diffusion and transmission of water and corrosive media in the pore channels. The surface tension generated on the surface of the waterproof concrete is far lower than that of water and capillaries, so that the pores of the concrete capillaries are not blocked, the normal ventilation of the concrete is kept, the negative effects of pores and stress concentration are reduced, and the density and the crack expansion resistance of the polymer are improved. The addition of the sodium p-dimethylaminoazobenzene sulfonate further improves the fluidity of the cement mortar. The graphene oxide with good dispersibility does not change the composition of a cement hydration product, but can promote the growth of cement hydration crystals, the ordered arrangement in the crystals can greatly improve the strength of cement mortar, so that the mortar forms a relatively compact structure, and the flexural strength and compressive strength of the cement mortar are improved due to the regulating effect of the graphene oxide on the hydration product.

Claims (9)

1. The environment-friendly portland cement is characterized by comprising the following components in parts by weight: 30 to 45 portions of portland cement clinker, 10 to 20 portions of limestone, 5 to 15 portions of bentonite, 5 to 10 portions of fly ash, 1 to 5 portions of slag, 5 to 10 portions of calcined clay, 1 to 5 portions of gypsum, 1 to 5 portions of titanium dioxide and 10 to 20 portions of reinforcing agent.

2. The environment-friendly portland cement according to claim 1, wherein: the high-temperature calcination temperature in the step 1 is 1300-1700 ℃, and the calcination time is 20-80 min.

3. The environment-friendly portland cement according to claim 1 or 2, wherein the reinforcing agent is prepared by the following steps in parts by weight:

s1, adding graphene oxide, polydopamine and tris (hydroxymethyl) aminomethane hydrochloride into a 60-80 wt% ethanol aqueous solution, performing ultrasonic dispersion treatment for 2 hours to obtain a uniform solution, adding 10-40 wt% ammonia solution into the uniform solution, adjusting the pH value to 8-9, and performing ultrasonic dispersion treatment for 0.3-2 hours to prepare a suspension;

s2, mixing the suspension prepared in the step S1, ethyl orthosilicate, isobutyl triethoxysilane, a nonionic surfactant, a dispersing agent and water; reacting for 1-3 h under the conditions of stirring and heating, wherein the stirring speed is 100-500 r/min, the heating temperature is 30-50 ℃, and standing to room temperature to obtain a modified graphene silane solution;

s3, mixing the modified graphene silane solution prepared in the step S2, sodium p-dimethylaminoazobenzene sulfonate, a polycarboxylate ether water reducing agent and 60-80 wt% of ethanol water solution, and stirring for reaction for 0.3-2 h at the stirring speed of 100-400 r/min to obtain a suspension; centrifuging the suspension for 20-60 min at the rotating speed of 10000-15000 r/min, collecting the centrifuged precipitate, and washing the precipitate for 1-3 times by using water and absolute ethyl alcohol respectively; drying and grinding the collected precipitate to obtain the reinforcing agent.

4. The environment-friendly portland cement of claim 3, wherein the step S1 comprises the following components in parts by weight: 10-20 parts of graphene oxide, 1-3 parts of polydopamine, 1-5 parts of tris (hydroxymethyl) aminomethane hydrochloride and 300-600 parts of 60-80 wt% ethanol aqueous solution.

5. The environment-friendly portland cement of claim 3, wherein the step S2 comprises the following components in parts by weight: 20-30 parts of the suspension prepared in the step S1, 5-10 parts of ethyl orthosilicate, 5-15 parts of isobutyl triethoxysilane, 0.1-2 parts of nonionic surfactant, 0.1-1 part of dispersing agent and 100-300 parts of water.

6. The environment-friendly portland cement according to claim 3, wherein the nonionic surfactant in step S2 comprises the following substances in percentage by mass: the mass ratio of the fatty alcohol-polyoxyethylene ether to the polysorbate 80 is 1: (1-2).

7. The environment-friendly portland cement of claim 3, wherein the dispersant in step S2 is at least one of polyethylene glycol, polyethylene wax, magnesium stearate, and glyceryl tristearate.

8. The environment-friendly portland cement as claimed in claim 3, wherein the components in step S3 are in parts by weight: 40-80 parts of modified graphene silane solution, 1-5 parts of sodium p-dimethylamino azobenzene sulfonate, 0.01-0.5 part of polycarboxylate ether water reducing agent and 100-150 parts of 60-80 wt% ethanol water solution.

9. The method for preparing the environment-friendly portland cement according to any one of claims 1 to 8, comprising the following steps:

step 1, weighing raw materials according to a formula; mixing and grinding limestone, bentonite, slag, gypsum and titanium dioxide until the particle size is 20-50 mu m, preparing a fine powder mixed material, and calcining the fine powder mixed material at high temperature to prepare a fine powder clinker;

and 2, respectively grinding the portland cement clinker and the calcined clay until the particle size is 50-100 mu m, mixing the portland cement clinker and the calcined clay to prepare powder, adding the fine powder clinker prepared in the step 1, fly ash and a reinforcing agent into the powder, and uniformly mixing to prepare the portland cement.