Dry powder cement admixture, its preparation method and application

Abstract

The present invention relates to a dry powder cement admixture, its preparation method and application. By mass percentage, it includes: sodium thiocyanate 4% - 8%, sodium thiosulfate 8% - 16%, organic alkanolamine 0.4 - 1.2%, polymer resin 16 - 32%, carrier 54 - 68%; the polymer resin contains sulfonic acid groups, acrylic acid groups, amide groups and graphene oxide. The technical problem to be solved by the present invention is how to provide a dry powder cement admixture that has good performance when used in combination with the concrete system of downstream suppliers; after significantly reducing the addition ratio of the cementitious material during concrete preparation, the strength of the concrete can still reach a good level, saving costs, and thus being more suitable for practical use.

Description

Technical Field

[0001] The present invention belongs to the technical field of cement material manufacturing, and particularly relates to a dry powder cement admixture, a preparation method thereof, and an application thereof. Background Art

[0002] In the cement production process, there is a cement grinding process. Through cement grinding, the cement can reach a certain fineness and a relatively high specific surface area, thereby improving its performance. However, the cements produced by various cement plants and the concrete formulation systems used are different, resulting in great differences in the admixtures used during cement grinding. Therefore, the targeted research and development of suitable cement admixture products is of great significance for improving the performance of cement and saving the cost of concrete.

[0003] A certain cement plant downstream has been using a cement admixture to grind cement for many years and then preparing it into concrete for use. However, the current cement admixture formulation has the following problems: First, when preparing concrete, in order to achieve the mechanical properties that meet the standards, a relatively high proportion of cementitious materials needs to be added, resulting in a high cost of concrete materials; second, the water retention of concrete materials is poor, and the drying shrinkage rate is relatively large, and the concrete has a risk of drying and cracking. Adding a water retention agent to the concrete will cause a decrease in the mechanical properties of the cement. Summary of the Invention

[0004] The main purpose of the present invention is to provide a dry powder cement admixture, a preparation method thereof, and an application thereof. The technical problem to be solved is how to provide a dry powder cement admixture that has good performance when used in combination with the concrete system of downstream suppliers; after significantly reducing the addition ratio of cementitious materials during concrete preparation, the strength of the concrete can still reach a good level, and the cost is saved, making it more suitable for practical use.

[0005] The object of the present invention and the solution to its technical problems are achieved by the following technical solutions. A dry powder cement admixture according to the present invention, calculated by mass percentage, includes: sodium thiocyanate 4% - 8%, sodium thiosulfate 8% - 16%, organic alkanolamine 0.4 - 1.2%, polymer resin 16 - 32%, carrier 54 - 68%; the polymer resin contains sulfonic acid groups, acrylic acid groups, amide groups, and graphene oxide.

[0006] The object of the present invention and the solution to its technical problems can also be further realized by the following technical measures.

[0007] Preferably, in the aforementioned cement admixture, the polymer resin is a first gel structure with a particle size of 100 - 200 microns; a second gel structure is dispersed inside the first gel structure; the second gel structure includes inorganic salts, graphene oxide, and polyacrylamide.

[0008] Preferably, for the aforementioned cement admixture, based on the mass percentage, taking the mass of the polymer resin as 100%, the mass percentage of the second gel structure is 1-2%.

[0009] Preferably, for the aforementioned cement admixture, based on the mass percentage, taking the mass of the second gel structure as 100%, the second gel structure comprises 96.5-98.4% inorganic salts, 0.02-1% graphene oxide, and 1.5-3.4% polyacrylamide.

[0010] Preferably, for the aforementioned cement admixture, the first gel structure further comprises a homopolymer and / or copolymer of acrylic monomers, amide monomers, and sulfonic acid monomers with a mass percentage of 98-99%; the feeding mass ratio of the acrylic monomers, amide monomers, and sulfonic acid monomers is 1:5-10:4-9.

[0011] Preferably, for the aforementioned cement admixture, the slag is the slag produced by a power plant.

[0012] The object of the present invention and the technical problems to be solved are also achieved by the following technical solutions. A preparation method of a powdery cement admixture according to the present invention includes the following steps:

[0013] 1) Mix sodium thiocyanate and sodium thiosulfate to obtain a first mixture;

[0014] 2) Add a heat carrier and a polymer resin to the first mixture under stirring conditions to dissolve the sodium thiocyanate and sodium thiosulfate, obtaining a second mixture;

[0015] 3) Dropwise add an organic alkanolamine to the second mixture under stirring conditions to uniformly disperse the organic alkanolamine, sodium thiocyanate, sodium thiosulfate, and polymer resin in the carrier, obtaining a powdery cement admixture; based on the mass percentage, the powdery cement admixture comprises: 4%-8% sodium thiocyanate, 8%-16% sodium thiosulfate, 0.4-1.2% organic alkanolamine, 16%-32% polymer resin, and 54%-68% carrier; the polymer resin contains sulfonic acid groups, acrylic acid groups, amide groups, and graphene oxide.

[0016] The object of the present invention and the technical problems to be solved can also be further achieved by the following technical measures.

[0017] Preferably, for the aforementioned preparation method, the heat carrier in step 2) is the slag produced by a power plant, and its temperature is 80-100°C.

[0018] Preferably, for the aforementioned preparation method, the preparation method of the polymer resin in step 2) includes the following steps:

[0019] Under stirring conditions, an aluminum salt solution, a calcium salt solution, a polyacrylamide solution and a graphene oxide dispersion are added to a silicate solution, the solution temperature is controlled, and the reaction is carried out under stirring conditions for heat preservation; after the reaction is completed, suction filtration is carried out to obtain a second gel; by mass percentage, the second gel includes 90-93% of water, 0.10-0.35% of polyacrylamide, 0.01-0.1% of graphene oxide and 6.7-9.85% of inorganic salts;

[0020] An acrylic monomer and a sulfonic acid monomer are formulated into a solution with a degree of neutralization, an amide monomer, an initiator, a crosslinking agent and the second gel are added to the solution, stirred evenly, and heated for reaction to form a high molecular gel;

[0021] The high molecular gel is dried and ground to obtain a high molecular resin.

[0022] The object of the present invention and the technical problems solved by it are also achieved by the following technical solutions. An application of a dry powder cement admixture in the fields of cement and concrete according to the present invention is proposed.

[0023] By means of the above technical solutions, a dry powder cement admixture and its preparation method and application proposed by the present invention have at least the following advantages:

[0024] The dry powdered cement admixture proposed in the present invention, as well as its preparation method and application, has better performance by reasonably selecting the types of raw materials and designing an optimal dosage combination. The dry powdered cement admixture of the present invention is added to the cement material for grinding. On the one hand, it contains amine groups, which adsorb on the surface of cement particles to assist grinding. At the same time, the first gel structure of the polymer resin contains sulfonic acid groups, acrylic acid groups and amide groups, and the above groups all have certain polarities, and the gel also contains graphene oxide with excellent conductivity. Therefore, the technical solution of the present invention can disperse and neutralize the static electricity that may be generated during the cement grinding process by introducing the polymer resin with the above structure into the cement admixture, thereby effectively avoiding the agglomeration phenomenon caused by the electrostatic adsorption of cement. It has a good grinding aid effect and can greatly improve the grinding effect of cement. When the ground cement is used for concrete mixing, The amount of cementitious material added to the concrete can be reduced during preparation, while its mechanical properties can still be maintained without reduction, and the cost is more economical; on the other hand, the shrinkage reduction performance of the concrete during drying is also significantly improved. The concrete prepared with the ground cement has good water retention, so that the concrete maintains a high water content before hardening, avoiding cracking caused by too fast drying; as the concrete hardens, the water content in the concrete decreases, and the ion concentration in the concrete solution gradually increases. As the ions enter the gel, the gel loses water. At this time, the inorganic salt particles dispersed in the gel can act as crystal nuclei to promote the formation of hydration products by substances such as calcium ions in the water release pores of the gel. The hydration products can fill the holes caused by water loss in situ, which better avoids the reduction of the mechanical strength of the concrete.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0026] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of a dry powder cement admixture and its preparation method and application according to the present invention, its specific implementation method, structure, characteristics and effects in combination with the preferred embodiment. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0027] The present invention provides a dry powder cement admixture, which comprises, by weight percentage, 4% to 8% of sodium thiocyanate, 8% to 16% of sodium thiosulfate, 0.4% to 1.2% of organic alcohol amine, 16% to 32% of polymer resin, and 54% to 68% of a carrier; the polymer resin contains sulfonic acid groups, acrylic acid groups, amide groups and graphene oxide.

[0028] In the above technical solution, sodium thiocyanate is added to the cement admixture as an early strength agent. It can not only improve the 3-day early strength and 28-day late strength of the cement, improve the mechanical properties of the cement, but also increase and strengthen the cement cohesion and have a grinding aid effect, and can extend the life of the cement; sodium thiosulfate is added to the cement admixture as a concrete early strength agent, which can promote the early strength of mortar and concrete, and has a certain plasticizing effect on the cement and will not corrode steel bars; organic alkanolamine is added to the cement admixture as a cement grinding aid, and the alkanolamine group contained therein can adsorb on the surface of cement particles to play a role in cement grinding aid; the above several raw materials can all be commercial products purchased from the market, and the present invention does not make specific limitations on them.

[0029] In the above technical solution, the polymer resin is a multifunctional resin prepared by the applicant itself. Its structure contains sulfonic acid groups, acrylic acid groups, amide groups and graphene oxide. The specific preparation method is as follows: Dissolve silicate, calcium salt and aluminum salt into an aqueous solution and adjust their temperatures to be the same. The solution temperature is preferably 25-40°C; under stirring conditions, add aluminum salt solution, calcium salt solution, polyacrylamide solution and graphene oxide dispersion to the silicate solution, and stir to make it evenly dispersed; control the solution temperature and keep it at 30-40°C for reaction for 1.5-2.5 h under stirring conditions; the polyacrylamide used is linear polyacrylamide that has not undergone crosslinking. After the reaction, vacuum filter the suspension, and then wash it many times with a mixed solvent of ethanol and water to obtain a second gel; by mass percentage, the second gel includes 90-93% water, 0.10-0.35% polyacrylamide, 0.01-0.18% graphene oxide, and the rest are inorganic salts; among them, the silicate forms a silicon-oxygen tetrahedron skeleton, and polyacrylamide mainly acts as a dispersant and stabilizer, while aluminum salt, calcium salt and graphene oxide are evenly dispersed in the gel network formed by the silicon-oxygen tetrahedron skeleton and polyacrylamide, and water is evenly distributed in the gel network; in order to avoid the agglomeration and caking of the second gel itself, avoid damaging its activity and reducing its specific surface area, the present invention preferably prepares the second gel as needed and does not dry it; then, the acrylic acid monomers and sulfonic acid monomers are respectively formulated with sodium hydroxide into solutions with a certain degree of neutralization, and the amide monomer solution, initiator, crosslinking agent and the second gel prepared above are added to the neutralization solution, stirred evenly, heated and reacted to form a polymer gel; finally, the polymer gel is dried and ground to obtain the polymer resin.

[0030] The polymer resin prepared by the above method is obtained by drying a polymer gel, and its structure still remains the network porous structure of the gel, which is called the first gel structure in the present invention and has a relatively high specific surface area; inside the first gel structure, a second gel structure with a mass percentage content of 1-2% (calculated based on the mass of the polymer resin being 100%) is also uniformly dispersed. The second gel structure is also a network porous structure of the gel; moreover, the second gel structure includes inorganic salts, graphene oxide, and polyacrylamide.Among them, adding a certain amount of graphene oxide to the cement admixture is beneficial to dissipate and neutralize the static electricity that may be generated during the cement grinding process, effectively avoiding the risk of re-aggregation during cement grinding, helping to increase the specific surface area after cement grinding, and thus improving the grinding efficiency and mechanical strength of the cement; in the present invention, the mass percentage content of graphene oxide in the second gel structure is preferably 0.02 to 1%; in order to better play its role in dissipating and neutralizing the grinding static electricity, the present invention preferably grinds the polymer resin into particles with a particle size of 100 to 200 microns, so as to increase its contact area with the surface of the cement powder; at the same time, the polymerization monomers of the polymer resin include acrylic monomers, amide monomers and sulfonic acid monomers, and they carry out polymerization reactions under the action of initiators and cross-linking agents, including homopolymerization and / or copolymerization. The polymer contains sulfonic acid groups, acrylic acid groups and amide groups. These groups themselves have a certain polarity, which can, to a certain extent, dissipate and neutralize the static electricity that may be generated during the cement grinding process, effectively avoiding the risk of re-aggregation during cement grinding, helping to increase the specific surface area after cement grinding, and thus improving the grinding efficiency and mechanical strength of the cement; moreover, in addition to the above groups, the polymerization monomers may also contain alkyl groups and side long-chain segments, and the steric hindrance of the large chain segments can also contribute to the dispersibility of the cement, being beneficial to the improvement of the grinding effect and mechanical properties of the cement, so that it can still maintain good mechanical properties after significantly reducing the addition ratio of the gelling material, being able to save costs and improve efficiency; further, the above polymer resin of the present invention contains a variety of polymerization monomers. Among them, the acrylic monomers belong to water-releasing monomers, and acrylic acid and / or methacrylic acid can be selected; the sulfonic acid monomers belong to water-retaining monomers, and 2-acrylamido-2-methylpropanesulfonic acid, propene sulfonic acid and / or styrene sulfonic acid can be selected; the amide monomers belong to non-ionic monomers, and acrylamide and / or methacrylamide can be selected; the above several different types of polymerization monomers are polymerized in a certain proportion, so that the obtained polymer resin not only has a high liquid absorption ratio, but also can ensure that the absorbed water can be stably stored, enabling the water to be released in time during the subsequent drying process of the concrete, that is, it can achieve a better balance of water absorption, water storage and water release, thereby reducing its autogenous shrinkage during the drying process of the concrete; if too much of the above acrylic monomers are added, it may cause premature water release of the concrete, affecting the mortar strength, while if too little is added, the shrinkage reduction effect of the concrete will be reduced; if the addition amount of the above sulfonic acid monomers and amide monomers is too much or too little, it may cause the liquid absorption ratio of the concrete to be too low, making it difficult to produce a good shrinkage reduction effect; the present invention preferably selects the ratio of acrylic monomers, amide monomers and sulfonic acid monomers to be 1:5 to 10:4 to 9.; The second gel of the present invention contains silicon, calcium, and aluminum elements. Among them, the source of silicon element is sodium metasilicate nonahydrate and / or potassium silicate, and its main function is to provide sufficient silicon source to participate in the formation of the silicon-oxygen tetrahedron framework; the source of calcium element is calcium nitrate tetrahydrate and / or calcium nitrate, and its main function is to provide sufficient calcium source to ensure that the calcium-silicon ratio in the formed second gel is not too low to ensure its activity; the source of aluminum element is aluminum sulfate and / or aluminum nitrate, and its main function is to provide sufficient aluminum source to make the formed second gel have high activity and good effect in promoting the generation of hydration products. Under the preferred combination of types and contents of polymerization monomers, when the concrete dries, as the water in the concrete gradually decreases during hardening, the ion concentration in the concrete solution gradually increases. As the ions gradually enter the gel interior, it will cause the gel to lose water. In this way, the inorganic salt particles dispersed in the gel can act as crystal nuclei, which can promote the formation of hydration products such as calcium ions in the water release pores of the gel, and this hydration product can in-situ fill the pores generated by water loss, preferably avoiding the problem that the mechanical strength of the concrete decreases due to the generation of pores by the water release of the polymer resin, preferably balancing the problems of concrete drying cracking and mechanical strength loss, making the concrete prepared with the cement admixture of the present invention have both good concrete shrinkage reduction performance and high mechanical strength, and can also greatly reduce the addition ratio of the cementitious materials in the concrete, greatly reducing the material cost and improving the economic benefits.

[0031] All kinds of functional raw materials in the above technical solution are uniformly dispersed in the carrier. For the convenience of material selection and to digest the solid waste from the power plant, the present invention preferably uses the slag from the power plant as the carrier.

[0032] The organic alkanolamine in the above technical solution is preferably a combination of multiple alkanolamine raw materials. In some specific embodiments, the organic alkanolamine is a mixture of triethanolamine, triisopropanolamine, and diethanol monoisopropanolamine. By mass, the ratio is 1:0.5 - 2:0.3 - 0.9.

[0033] The present invention also provides a preparation method of a powdery cement admixture, which includes the following steps: First, weigh and mix sodium thiocyanate and sodium thiosulfate to obtain a first mixture; then, under stirring conditions, add a heat carrier and a polymer resin to the first mixture, and use the heat of the heat carrier itself to dissolve sodium thiocyanate and sodium thiosulfate to obtain a second mixture. The heat carrier can directly use the slag from the power plant without special heating and heat preservation processes. Preferably, the temperature of the heat carrier is 80 - 100 °C, which is beneficial to the dissolution and dispersion of sodium thiocyanate and sodium thiosulfate. Finally, under stirring conditions, add organic alkanolamine dropwise to the second mixture to make the organic alkanolamine, sodium thiocyanate, sodium thiosulfate, and polymer resin uniformly dispersed in the heat carrier, obtaining the aforementioned powdery cement admixture.

[0034] The present invention also provides an application of the dry powder cement admixture in the fields of cement and concrete. After the dry powder cement admixture of the present invention is mixed into cement in an amount of 0.4 - 0.6% by mass percentage for cement grinding, when using this kind of cement to prepare concrete, it has better adaptability with the concrete system of downstream suppliers. When preparing concrete with it, the strength of the concrete can still reach a good level after significantly reducing the addition ratio of the cementitious materials.

[0035] The present invention will be further described below in conjunction with specific embodiments, but it should not be construed as a limitation to the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the above content of the present invention still fall within the protection scope of the present invention.

[0036] Unless otherwise specified, the materials, reagents, etc. involved below are all commercially available products well-known to those skilled in the art; unless otherwise specified, the methods are all well-known methods in the art. Unless otherwise defined, the technical terms or scientific terms used should have the ordinary meaning understood by those of ordinary skill in the art to which the present invention pertains.

[0037] Preparation Example 1

[0038] This preparation example prepares a polymer resin, and its preparation steps are as follows:

[0039] Sodium silicate nonahydrate is prepared into an aqueous solution with a concentration of 50 g / L, calcium nitrate tetrahydrate is prepared into an aqueous solution with a concentration of 90 g / L, aluminum nitrate is prepared into an aqueous solution with a concentration of 30 g / L, and linear polyacrylamide is prepared into an aqueous solution with a concentration of 10 g / L. The temperatures of the above four solutions are all adjusted to 35°C; then, under stirring conditions, 250 mL of calcium nitrate tetrahydrate solution, 100 mL of aluminum nitrate solution, 100 mL of polyacrylamide solution, and 4 mL of graphene oxide aqueous dispersion with a mass concentration of 2% are added to 500 mL of sodium silicate nonahydrate solution. The mixed solution is placed in a water bath at 35°C and kept stirring for 2 h; then, the reaction solution is subjected to vacuum filtration, and then washed three times with a mixed solvent of ethanol and water with a mass ratio of 1:1, and filtered for 5 min to obtain a second gel; its mass is 736.7 g, and the water content is 93%.

[0040] 1.94 g of sodium hydroxide was dissolved in 100 mL of water, and the temperature was lowered to 2° C. after dissolution, and 5 g of acrylic acid monomer was added to the cold sodium hydroxide solution to prepare an aqueous solution with a neutralization degree of 70%. 8.69 g of sodium hydroxide was dissolved in 200 mL of water, and the temperature was lowered to 2° C. after dissolution, and 45 g of 2-acrylamide-2-methylpropanesulfonic acid monomer was added to the cold sodium hydroxide solution to prepare an aqueous solution with a neutralization degree of 100%. The two neutralization solutions were mixed, and 20 g of the second gel prepared in this preparation example, 50 g of acrylamide, 0.9 g of N,N'-methylenebisacrylamide, and 1 g of potassium persulfate or ammonium persulfate initiator were added to the mixed solution. The mixed solution was ultrasonically treated for 5 minutes and then stirred evenly. The mixture was transferred into a reactor and heated to 60°C. After stirring and reacting for 2 hours, the gel was cut into pieces and placed in a 70°C oven for drying for 48 hours to obtain a block sample. Finally, the block material was placed in a ball mill, ground, and sieved with 100 mesh and 200 mesh successively. The samples under the 100 mesh sieve and on the 200 mesh sieve were collected to obtain polymer resin 1#.

[0041] Preparation Examples 2 to 5

[0042] The process steps are the same as those in Preparation Example 1, and the differences are shown in Table 1. The obtained products are polymer resin 2#, polymer resin 3#, polymer resin 4#, and polymer resin 5#, respectively.

[0043] Table 1

[0044]

[0045]

[0046] Preparation Example 6

[0047] This preparation example prepares a dry powder cement admixture, and its preparation steps are as follows: weigh 7.6g of sodium thiocyanate and 8g of sodium thiosulfate, mix the two and stir them evenly; under stirring conditions, add 16g of polymer resin 1# and 68g of hot slag from the power plant to the above mixture, stir thoroughly, so that the sodium thiocyanate and sodium thiosulfate are dissolved and mixed evenly under the temperature conditions of the heat carrier; finally, add organic alcohol amine dropwise to the mixture under stirring conditions, stir evenly, and obtain dry powder cement admixture 1#; wherein the organic alcohol amine composition is a mixture of triethanolamine, triisopropanolamine and diethanol monoisopropanolamine; in terms of mass parts, the mass ratio is 1:0.5:0.3, as shown in the following Table 2.

[0048] Preparation Examples 7 to 13

[0049] The process steps are the same as those in Preparation Example 6, and the differences are shown in Table 2 in detail. The obtained products are dry powder cement admixtures 2#, 3#, 4#, 5#, 6#, 7#, and 8# respectively.

[0050] Table 2

[0051]

[0052] Examples 1 - 8

[0053] Add it to the cement clinker with a reference grade of PI 42.5 in a certain downstream cement plant at a ratio of 0.4% by mass percentage for grinding. The ratio is 100 kg of cement clinker, 4 kg of gypsum, and 0.4 kg of the dry powder cement admixture of the present invention, and the grinding time is 15 minutes.

[0054] Comparative Example 1

[0055] Same as Examples 1 - 8, the difference is that the cement admixtures used are the cement admixtures supplied by the original supplier of a certain downstream cement plant.

[0056] Comparative Example 2

[0057] Same as Comparative Example 1, the difference is that the grinding time is 40 minutes.

[0058] Comparative Example 3

[0059] The cement of a certain downstream cement plant without adding any cement admixture.

[0060] Test the specific surface area of the cement in Examples 1 - 8 and Comparative Examples 1 - 2 according to GB / T8074 - 2008 "Determination Method for Specific Surface Area of Cement - Blaine Method", and the results are shown in Table 3.

[0061] Table 3

[0062] <![CDATA[Specific surface area of cement m 2 / g]]> Example 1 392 Example 2 395 Example 3 385 Example 4 388 Example 5 390 Example 6 386 Example 7 393 Example 8 391 Comparative Example 1 308 Comparative Example 2 375 Comparative Example 3 271

[0063] It can be seen from the test data in Table 3 that the specific surface area of the cement in Examples 1 - 8 ≥ 385 m 2 / g, while the specific surface area of Comparative Example 1 is 308 m 2 / g, and the specific surface area of Comparative Example 3 is 271 m 2 / g. This shows that the grinding effect of the cement after adding the dry powder cement admixture of the present invention is good, and the specific surface area of the ground cement is relatively high; the grinding time of Comparative Example 2 is longer, which is 2.67 times that of the grinding time in the examples. Although its specific surface area is higher than that of Comparative Example 1, it is only basically equivalent to that of the examples, indicating that the cement has high grinding efficiency, low energy consumption, and cost savings after adding the dry powder cement admixture of the present invention.

[0064] Examples 9 - 16

[0065] The cement after grinding in the above Examples 1 - 8 was added to the cement mortar. The aggregate was ISO standard sand, the cement-sand ratio was 1:2, the water-cement ratio was 0.35, and the fluidity was controlled at 230 ± 2 mm by adding an appropriate amount of water-reducing agent in each group of mortar. After stirring evenly, concrete test blocks were prepared.

[0066] Comparative Examples 4 - 6

[0067] The cement after grinding in the above Comparative Examples 1 - 3 was added to the cement mortar. The aggregate was ISO standard sand, the cement-sand ratio was 1:2, the water-cement ratio was 0.35, and the fluidity was controlled at 230 ± 2 mm by adding an appropriate amount of water-reducing agent in each group of mortar. After stirring evenly, concrete test blocks were prepared.

[0068] Comparative Example 7

[0069] Same as Comparative Example 4, except that the cement-sand ratio was 4:5.

[0070] The compressive strength and drying shrinkage of the concrete in the above Examples 9 - 16 and Comparative Examples 4 - 7 were tested, and the test results are shown in Table 4. The test methods are as follows:

[0071] 1. The cement strength was tested in accordance with GB / T 17671-1999 "Test Method for Cement Mortar Strength (ISO Method)".

[0072] 2. T0574-2020 Test Method for Shrinkage of Cement Concrete (Contact Method).

[0073] Table 4

[0074] 28d compressive strength MPa 28d autogenous shrinkage μm / m Example 9 60.2 45 Example 10 61.3 48 Example 11 59.4 47 Example 12 58.7 50 Example 13 57.5 49 Example 14 59.8 48 Example 15 60.5 46 Example 16 60.9 44 Comparative Example 4 48 79 Comparative Example 5 52 78 Comparative Example 6 43 86 Comparative Example 7 56 92

[0075] It can be seen from the test data in Table 4 that the 28-day compressive strength of Examples 9 - 16 ≥ 58 MPa, while the 28-day compressive strength of Comparative Example 4 was 48 MPa, the 28-day compressive strength of Comparative Example 5 was 52 MPa, and the 28-day compressive strength of Comparative Example 6 was 43 MPa. This shows that the mechanical properties of the concrete prepared with the cement admixed with the dry powder cement admixture of the present invention have been greatly improved; in Comparative Example 7, the proportion of the cementitious material in the concrete was increased by more than ten percent, and although its 28-day compressive strength increased to some extent, it still did not reach the level of Examples 9 - 16. This shows that the cement grinding with the dry powder cement admixture of the present invention can better improve the mechanical properties of the concrete, reduce the addition proportion of the cementitious material, and reduce the cost.

[0076] As can be seen from the test data in Table 4, the 28-day autogenous shrinkage of Examples 9 to 16 is ≤50 μm / m, while the 28-day autogenous shrinkage of Comparative Example 4 is 79 μm / m, that of Comparative Example 5 is 78 μm / m, that of Comparative Example 6 is 86 μm / m, and that of Comparative Example 7 is 92 μm / m. This shows that the autogenous shrinkage of the concrete prepared with the cement admixed with the dry powder cement admixture of the present invention is small, and it has good comprehensive performance.

[0077] The technical features in the claims and / or the specification of the present invention can be combined, and the combination method is not limited to the combination obtained through the citation relationship in the claims. The technical solutions obtained by combining the technical features in the claims and / or the specification also fall within the protection scope of the present invention.

[0078] The above are only the preferred embodiments of the present invention, and do not impose any formal restrictions on the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. A dry powder cement admixture, characterized in that, By mass percentage, it includes: sodium thiocyanate 4% - 8%, sodium thiosulfate 8% - 16%, organic alkanolamine 0.4 - 1.2%, high molecular resin 16 - 32%, carrier 54 - 68%; the high molecular resin is a first gel structure with a particle size of 100 - 200 microns; a second gel structure is dispersed inside the first gel structure; the second gel structure includes inorganic salts, graphene oxide and polyacrylamide; based on the mass of the high molecular resin being 100%, the mass percentage of the second gel structure is 1 - 2%; the first gel structure also includes a homopolymer and / or copolymer of acrylic acid monomers, amide monomers and sulfonic acid monomers with a mass percentage of 98 - 99%; the carrier is the slag from the power plant.

2. The cement admixture according to claim 1, wherein Based on the mass of the second gel structure being 100%, the second gel structure includes 96.5 - 98.4% inorganic salts, 0.02 - 1% graphene oxide and 1.5 - 3.4% polyacrylamide.

3. The cement admixture according to claim 1, wherein The feeding mass ratio of the acrylic acid monomers, amide monomers and sulfonic acid monomers is 1:5 - 10:4 - 9.

4. A preparation method of a dry powder cement admixture, characterized in that, It includes the following steps: 1) Mix sodium thiocyanate and sodium thiosulfate to obtain a first mixture; 2) Add a heat carrier and a high molecular resin to the first mixture under stirring conditions to dissolve the sodium thiocyanate and sodium thiosulfate, obtaining a second mixture; the heat carrier is the slag from the power plant, and its temperature is 80 - 100°C; the preparation method of the high molecular resin includes the following steps: Add an aluminum salt solution, a calcium salt solution, a polyacrylamide solution and a graphene oxide dispersion liquid to a silicate solution under stirring conditions, control the solution temperature, and carry out a heat preservation reaction under stirring conditions; after the reaction ends, carry out suction filtration to obtain a second gel; by mass percentage, the second gel includes 90 - 93% water, 0.10 - 0.35% polyacrylamide, 0.01 - 0.1% graphene oxide and 6.7 - 9.85% inorganic salts; Prepare a solution with a neutralization degree from acrylic acid monomers and sulfonic acid monomers, add amide monomers, initiators, crosslinking agents and the second gel to the solution, stir evenly, and carry out a heating reaction to form a high molecular gel; Dry and grind the high molecular gel to obtain a high molecular resin; 3) Dropwise add an organic alkanolamine to the second mixture under stirring conditions to uniformly disperse the organic alkanolamine, sodium thiocyanate, sodium thiosulfate and high molecular resin in the carrier, obtaining a dry powder cement admixture; By mass percentage, the dry powder cement admixture includes: sodium thiocyanate 4% - 8%, sodium thiosulfate 8% - 16%, organic alkanolamine 0.4 - 1.2%, high molecular resin 16 - 32%, carrier 54 - 68%.

5. Use of the dry powder cement admixture according to any one of claims 1 to 3 in the fields of cement and concrete.

6. Use of the dry powder cement admixture prepared by the preparation method of the dry powder cement admixture according to claim 4 in the fields of cement and concrete.

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