A core-shell type cement admixture, and a preparation method and application thereof

Abstract

The application provides a core-shell cement additive and a preparation method and application thereof, the additive is formed by a Pickering emulsion method and takes modified calcium silicate hydrate treated by a silane coupling agent as a shell layer and an alcohol amine fatty acid ester as a slow-release hydrophobic component; a core-shell functional hybrid material with an alcohol amine fatty acid ester core and an early-strength inorganic material (modified calcium silicate hydrate) shell layer is prepared by the Pickering emulsion method, the compatibility between the alcohol amine fatty acid ester and a hydration product is improved, the release rhythm of the alcohol amine fatty acid ester in a cement paste is controlled, the beneficial effects of the calcium silicate hydrate seed and the alcohol amine fatty acid ester type controlled-release material are synergized, the early strength of a cement-based material can be improved, the microstructure impermeability of the cement-based material is enhanced, and a certain strength synergistic effect is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a core-shell type cement admixture and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the in-depth study of the microstructure of cement-based materials, precise optimization of the performance of cement-based materials from the micro level has become a new direction for the development of functional admixtures. Therefore, the development of various nano and micro slow-release pore plug materials has attracted increasing attention. Among them, micro slow-release materials modify the hydration products by releasing hydrophobic components through the reaction with calcium hydroxide and other alkaline products during hydration. However, due to the lack of compatibility between the organic slow-release components and the hydration products as inorganic substances, the dispersion of such materials is poor when they are directly added to the cement paste, and their adhesion to the mineral phase surface affects the dissolution of the mineral phase, thereby affecting the early strength development. How to improve the compatibility between the components and the hydration products and make the component release and hydration reaction pace more matched is the primary problem faced by such materials in design and construction. Using inorganic materials as a buffer between the hydrophobic components and the hydration products to construct hybrid materials is a feasible solution. In recent years, several patents based on this idea have been disclosed.

[0003] Patent CN112194396A reports a slow-release hydrophobic agent for cement-based materials, hydrophobic cement, and a preparation method thereof. The slow-release hydrophobic agent for cement-based materials is modified floating beads with a sealing agent on the surface and a hydrophobic modifier stored inside. The modified floating beads disclosed in the invention are prepared by introducing a modifier after acid corrosion of fly ash floating beads, which has the beneficial effect of achieving hydrophobic effect while reducing the impact on cement hydration. However, the acid corrosion process requires the use of highly toxic hydrofluoric acid, which causes serious environmental pollution.

[0004] Patent CN106495602B reports a method for preparing a surface hydrophobic cement stone material using hydrophobic silica gel material. Ordinary Portland cement is used as the raw material, nano materials are used as the modified material, and hydrophobic silica gel material is used as the base for cement hydration and hardening. The hardened cement material is cured in water to obtain a surface hydrophobic cement stone material. The invention uses hydrophobic materials to modify the surface of the cement in a contact mode, and the nano materials do not form a micro-hybrid with the hydrophobic silica gel material.

[0005] Patent CN202110095755.4 A kind of nanomaterial adsorbs steel fiber and its preparation method and application, utilize silane coupling agent to tightly adsorb nanomaterial on the surface of steel fiber, the functional group (carboxyl, hydroxyl) attached to nanomaterial and the chemical bond between hydrated calcium silicate in cement matrix is generated, can promote the chemical bonding force of steel fiber-matrix interface, greatly increase interface performance.The patent only carries out high hydrophobic treatment to steel fiber, and does not need to finely adjust the hydrophobicity of the modified nanomaterial as much as the technical solution provided by the present application to obtain a semi-hydrophobic material capable of forming a Pickering emulsion.

[0006] Patent CN202111271428.6 A kind of early strength type polycarboxylic acid water reducer of calcium silicate crystal nucleus, and its preparation method, by first grafting silane group to polycarboxylic acid water reducer main chain, then using the condensation of silane group hydrolysis and the surface hydroxyl of hydrated calcium silicate produces chemical adsorption.But the patent grafts hydrophilic dispersant on hydrated calcium silicate, its purpose is to improve the dispersibility of hydrated calcium silicate in aqueous solution, rather than finely adjusting the hydrophilicity and hydrophobicity of the modified nanomaterial. SUMMARY

[0007] In order to solve the problem of lack of compatibility between organic release component and hydration product as inorganic substance in the prior art, which leads to poor dispersion of organic release component added in cement paste and affects the dissolution of mineral phase, and further affects the development of early strength, etc. The present application provides a core-shell type cement additive and its preparation method and application. The additive is a modified hydrated calcium silicate treated by silane coupling agent as shell layer, and an alcohol amine fatty acid ester as release hydrophobic component, formed by Pickering emulsion method. The additive is an organic-inorganic hybrid material with core-shell structure, and in the preparation process of the additive, microwave is used to assist in improving reaction efficiency and saving reaction time.

[0008] A core-shell type cement additive, prepared by Pickering emulsion method, comprising, by weight: modified hydrated calcium silicate 2.5-5 parts, alcohol amine fatty acid ester 14-28 parts, and water 67-83 parts. The additive has a core-shell structure with alcohol amine fatty acid ester as core and modified hydrated calcium silicate as shell. The modified hydrated calcium silicate is prepared by in-situ co-precipitation of calcium salt and silicate under the regulation of dispersant. The contact angle of the modified hydrated calcium silicate is 40°-70° after modification with 10%-25% of alkyl silane coupling agent in water-ethanol mixed solution.

[0009] The alcohol amine fatty acid ester conforms to at least one of the following general formulas (2)-(4):

[0010]

[0011] wherein, R1a R 1b R 1c is a hydrogen atom or a methyl group, R 2a R 2b R 2c is an alkyl group having 7-17 carbon atoms. The alcohol amine fatty acid ester can be prepared by the esterification process known to those skilled in the art using the corresponding alcohol amine and saturated fatty acid.

[0012] The mass ratio of the alcohol amine fatty acid ester to the calcium silicate hydrate is (2.5-5) : (14-28).

[0013] The dispersant is a homopolymer or copolymer of an anion or non-ionic monomer having a dispersing effect, having a weight average molecular weight of 5000-20000 and a molecular weight dispersity index of ≤2.0. The mass concentration of the dispersant is 1.0-2.5%.

[0014] The dispersant is selected from at least one of polyacrylic acid, polymethacrylic acid and polyvinylpyrrolidone.

[0015] The calcium salt is a soluble inorganic calcium salt, and the mass concentration is 25-40%. The silicate is sodium silicate or potassium silicate, and the mass concentration is 8-15%. The molar ratio of calcium ions to silicon ions in the calcium salt and the silicate is 0.8-1.2:1. The total amount of the calcium salt and the silicate is 1.5-4 times the amount of the dispersant.

[0016] The alkyl silane coupling agent has the following general structure (1) : wherein X is a methoxy group, an ethoxy group or an acetoxy group, and R9 is an alkyl group having 4-8 carbon atoms. The amount of the alkyl silane coupling agent is 10-25% of the mass of the calcium silicate hydrate. The alkyl silane coupling agent functions to modify the surface of the calcium silicate hydrate with a proper amount of alkyl groups, so that the calcium silicate hydrate has both oil and water affinity.

[0017] A preparation method of a core-shell cement admixture, comprising the following steps: mixing modified calcium silicate hydrate and alcohol amine fatty acid ester in water to obtain a Pickering emulsion; then cooling, and forming core-shell structure particles after the alcohol amine fatty acid ester solidifies; and then centrifugally separating the particles and washing the particles with water, preferably adding 2-5 times the mass of the particles, uniformly dispersing into a slurry, and then obtaining the core-shell cement admixture. Specifically, under the condition of 50-75 DEG C, the modified calcium silicate hydrate and the alcohol amine fatty acid ester are mixed in water, and microwave treatment is carried out under the condition of 900-1800 rpm rapid stirring for 10-30 min, to obtain the Pickering emulsion; then cooling to below 30 DEG C, and forming the core-shell structure particles after the alcohol amine fatty acid ester solidifies; and then centrifugally separating the particles and washing the particles with water 2-3 times, preferably adding 5-10 times the mass of the particles each time, adding 2-5 times the mass of the particles, uniformly dispersing into a slurry, and then obtaining the core-shell cement admixture.

[0018] The modified calcium silicate hydrate is obtained by the following steps: adding a dispersant into a reactor of a refluxing and microwave-assisted reaction device, stirring under the condition of 15-35 DEG C, nitrogen protection and 300-600 rpm, and simultaneously starting to uniformly add a calcium salt and a silicate, for 30 min-1 h; then adding an ethanol solution of an alkyl silane coupling agent into the system, heating to 45-75 DEG C, and then microwave-assisted refluxing for 20-45 min; centrifugally separating the obtained semi-hydrophobic calcium silicate hydrate and washing 2-4 times with 10-20 times the theoretical mass of water to remove by-products, to obtain the modified calcium silicate hydrate.

[0019] The total mass of the ethanol solution of the alkyl silane coupling agent is 35%-65% of the total mass of the foregoing dispersant aqueous solution, calcium salt solution and silicate solution.

[0020] In the preparation of the modified calcium silicate hydrate and the core-shell cement admixture, the power density of the microwave treatment reaction is 1-10 W / g of total amount of reactants (including solvents), and lower than this value, the auxiliary reaction effect is not obvious, and higher than this value, the economy is poor.

[0021] The application of the core-shell cement admixture is applied to the concrete construction process, and the content of the core-shell cement admixture is 0.8%-2.0% of the mass of the cementitious material in the concrete.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] 1. A core-shell functional hybrid material with alcohol amine fatty acid ester core and early strength inorganic material (modified calcium silicate hydrate) shell prepared by Pickering emulsion method, wherein the alcohol amine fatty acid ester plays a role of hydrolyzing to release a hydrophobic component. Since the alcohol amine fatty acid ester is not compatible with the hydration product, direct addition into the cement paste will cause significant retarding and strength reduction. The present application improves the compatibility between the alcohol amine fatty acid ester and the hydration product by the shell coating method. The alcohol amine fatty acid ester is wrapped by the calcium silicate hydrate shell, avoiding direct contact between the alcohol amine fatty acid ester and the cement mineral phase and the hydration product in the early hydration stage, thereby avoiding the retarding effect caused thereby. Meanwhile, the shell coating slows down the contact between the alcohol amine fatty acid ester and the hydroxide in the pore solution, thereby controlling the reaction rate and improving the connection between the release of the hydrophobic pore blocking component of the alcohol amine fatty acid ester and the hydration rhythm of the cement. Meanwhile, the calcium silicate hydrate has a certain crystal seed effect, which can accelerate the early hydration. The present application realizes the synergy of the beneficial effects of the organic material and the inorganic material, can improve the early strength of the cement-based material and the microstructure impermeability of the cement-based material, and has a certain strength efficiency.

[0024] 2. The Pickering emulsion is a stable dispersion system formed by arranging the particles with oil-water amphiphilic property on the oil / water droplet and water / oil dispersion phase interface through mechanical action after specific surface treatment. The Pickering emulsion formed by the modified inorganic nanoparticles and the organic release component, and then the inorganic / organic core-shell material generated by solidification / polymerization, is a convenient means for synthesizing the core-shell material. Compared with the traditional method of forming the core-shell structure by polymerization / assembly of small molecules, the method has the advantages of simple operation and easy scale-up. The synthesis steps of the present application are assisted by microwave, short time-consuming, high efficiency, and conducive to large-scale production. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be described clearly and completely below by combining with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0026] The parameters and structures of the dispersants and alcohol amine fatty acid esters used in each embodiment are shown in Table 1 below. In the following description, the alcohol amine fatty acid esters are represented by the abbreviations AAE-1 to 8 in the table for convenience. The concentrations in the embodiments are all mass concentrations. The hydrophobicity of the modified calcium silicate hydrate in the embodiments is represented by the contact angle, which is directly measured by a contact angle measuring instrument (Dataphysics OCA25) after pressing the sample on a glass slide.

[0027] Table 1

[0028]

[0029]

[0030] Example 1

[0031] In a reactor with reflux and microwave-assisted reaction device, under the conditions of 25 degrees, nitrogen protection, 300 rpm stirring, 53.0 parts of 30% calcium nitrate solution and 118.4 parts of 10% sodium silicate solution were simultaneously and uniformly added into 500 parts of water solution containing 1.5% sodium polyacrylate, and the addition lasted for 30 min. Then, 300 parts of ethanol solution containing 1.7 parts of octyltrimethoxysilane was added into the system, and the temperature was raised to 60 degrees. After that, the system was subjected to microwave-assisted reflux reaction for 25 min. Then, the obtained semi-hydrophobic hydrated calcium silicate was centrifugally separated and washed with water for 3 times at 15 times the theoretical mass of the product to remove byproducts, thereby obtaining modified hydrated calcium silicate intermediate C-1. The contact angle of the obtained modified hydrated calcium silicate was 55.2°.

[0032] At 60 degrees, 5 parts of modified hydrated calcium silicate was mixed with 60 parts of alcohol amine ester AAE-1 in 650 parts of water, and the mixture was subjected to microwave treatment for 20 min under rapid stirring at 1500 rpm to obtain a Pickering emulsion. The emulsion was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles. Then, the particles were centrifugally separated and washed with water for 2 times at 8 times the mass of the particles each time to remove excess dispersant and byproducts. After that, 3 times the mass of water was added, and the mixture was uniformly dispersed into a slurry to obtain core-shell cement additive CA-1.

[0033] Example 2

[0034] In a reactor with reflux and microwave-assisted reaction device, under the conditions of 35 degrees, nitrogen protection, 360 rpm stirring, 58.9 parts of 40% calcium chloride solution and 205.4 parts of 12% sodium silicate solution were simultaneously and uniformly added into 500 parts of water solution containing 2.0% sodium polymethacrylate, and the addition lasted for 45 min. Then, 490 parts of ethanol solution containing 6.0 parts of butyltriacetoxysilane was added into the system, and the temperature was raised to 50 degrees. After that, the system was subjected to microwave-assisted reflux reaction for 45 min. Then, the obtained semi-hydrophobic hydrated calcium silicate was centrifugally separated and washed with water for 3 times at 20 times the theoretical mass of the product to remove byproducts, thereby obtaining modified hydrated calcium silicate intermediate C-2. The contact angle of the obtained modified hydrated calcium silicate was 67.0°.

[0035] In a reactor with reflux and microwave-assisted reaction device, 6 parts by mass of modified calcium silicate hydrate and 48 parts by mass of alcohol amine ester AAE-2 were mixed in 650 parts by mass of water at 60 degrees, and treated by microwave for 10 minutes under rapid stirring at 1800 rpm to obtain a Pickering emulsion, which was cooled to below 30 degrees. The alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water 2 times at 10 times the mass of the particles each time to remove excess dispersant and byproducts. After that, 3 times the mass of water was added to uniformly disperse the particles into a slurry to obtain core-shell cement additive CA-2.

[0036] Example 3

[0037] In a reactor with reflux and microwave-assisted reaction device, 6 parts by mass of modified calcium silicate hydrate and 48 parts by mass of alcohol amine ester AAE-2 were mixed in 650 parts by mass of water at 60 degrees, and treated by microwave for 10 minutes under rapid stirring at 1800 rpm to obtain a Pickering emulsion, which was cooled to below 30 degrees. The alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water 2 times at 10 times the mass of the particles each time to remove excess dispersant and byproducts. After that, 3 times the mass of water was added to uniformly disperse the particles into a slurry to obtain core-shell cement additive CA-2.

[0038] In a reactor with reflux and microwave-assisted reaction device, 6 parts by mass of modified calcium silicate hydrate and 48 parts by mass of alcohol amine ester AAE-2 were mixed in 650 parts by mass of water at 60 degrees, and treated by microwave for 10 minutes under rapid stirring at 1800 rpm to obtain a Pickering emulsion, which was cooled to below 30 degrees. The alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water 2 times at 10 times the mass of the particles each time to remove excess dispersant and byproducts. After that, 3 times the mass of water was added to uniformly disperse the particles into a slurry to obtain core-shell cement additive CA-2.

[0039] Example 4

[0040] In a reactor with reflux and microwave-assisted reaction device, 6 parts by mass of modified calcium silicate hydrate and 48 parts by mass of alcohol amine ester AAE-2 were mixed in 650 parts by mass of water at 60 degrees, and treated by microwave for 10 minutes under rapid stirring at 1800 rpm to obtain a Pickering emulsion, which was cooled to below 30 degrees. The alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water 2 times at 10 times the mass of the particles each time to remove excess dispersant and byproducts. After that, 3 times the mass of water was added to uniformly disperse the particles into a slurry to obtain core-shell cement additive CA-2.

[0041] In a reactor with reflux and microwave-assisted reaction device, 5 parts by mass of modified calcium silicate hydrate and 50 parts by mass of alcohol amine ester AAE-4 were mixed in 550 parts by mass of water at 65 degrees, and microwave treatment was performed for 15 minutes under rapid stirring at 1500 rpm to obtain a Pickering emulsion. The emulsion was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water at 8 times the mass of the particles for 3 times. After removing the excess dispersant and by-products, 4 times the mass of water was added, and the mixture was uniformly dispersed into a slurry to obtain core-shell cement additive CA-4.

[0042] Example 5

[0043] In a reactor with reflux and microwave-assisted reaction device, 5 parts by mass of modified calcium silicate hydrate and 50 parts by mass of alcohol amine ester AAE-4 were mixed in 550 parts by mass of water at 65 degrees, and microwave treatment was performed for 15 minutes under rapid stirring at 1500 rpm to obtain a Pickering emulsion. The emulsion was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water at 8 times the mass of the particles for 3 times. After removing the excess dispersant and by-products, 4 times the mass of water was added, and the mixture was uniformly dispersed into a slurry to obtain core-shell cement additive CA-4.

[0044] In a reactor with reflux and microwave-assisted reaction device, 5 parts by mass of modified calcium silicate hydrate and 50 parts by mass of alcohol amine ester AAE-4 were mixed in 550 parts by mass of water at 65 degrees, and microwave treatment was performed for 15 minutes under rapid stirring at 1500 rpm to obtain a Pickering emulsion. The emulsion was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles. The particles were then centrifugally separated and washed with water at 8 times the mass of the particles for 3 times. After removing the excess dispersant and by-products, 4 times the mass of water was added, and the mixture was uniformly dispersed into a slurry to obtain core-shell cement additive CA-4.

[0045] Example 6

[0046] In a reactor with reflux and microwave-assisted reaction device, under the conditions of 25 degrees, nitrogen protection, 300 rpm stirring, 66.3 parts of 35% calcium nitrate solution and 115.1 parts of 12% sodium silicate solution were synchronously and uniformly added into 500 parts of water solution containing 1.5% polyvinylpyrrolidone, the two were added for 35 min, then 350 parts of ethanol solution containing 3.30 parts of butyl triethoxysilane was added into the system, the temperature was raised to 45 degrees, then microwave-assisted reflux reaction was carried out for 30 min, then the obtained semi-hydrophobic hydrated calcium silicate was centrifuged and washed with 15 times of the theoretical mass of water to remove by-products for 3 times, and modified hydrated calcium silicate intermediate C-6 was obtained. The contact angle of the obtained modified hydrated calcium silicate is 58.3°.

[0047] At 65 degrees, 5 parts of modified hydrated calcium silicate was mixed with 50 parts of alcohol amine ester AAE-6 in 550 parts of water, and microwave treatment was carried out under rapid stirring at 1500 rpm for 15 min to obtain a Pickering emulsion, which was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles, then the particles were centrifuged and washed with 8 times the mass of water for 3 times, after removing the excess dispersant and by-products, 4 times the mass of water was added, and the slurry was uniformly dispersed to obtain core-shell cement admixture CA-6.

[0048] Example 7

[0049] In a reactor with reflux and microwave-assisted reaction device, under the conditions of 15 degrees, nitrogen protection, 540 rpm stirring, 74.2 parts of 30% calcium nitrate solution and 126.6 parts of 15% potassium silicate solution were synchronously and uniformly added into 500 parts of water solution containing 1.0% acrylic acid-maleic anhydride copolymer, the two were added for 50 min, then 380 parts of ethanol solution containing 1.80 parts of octyl trimethoxysilane was added into the system, the temperature was raised to 75 degrees, then microwave-assisted reflux reaction was carried out for 25 min, then the obtained semi-hydrophobic hydrated calcium silicate was centrifuged and washed with 15 times of the theoretical mass of water to remove by-products for 3 times, and modified hydrated calcium silicate intermediate C-7 was obtained. The contact angle of the obtained modified hydrated calcium silicate is 46.6°.

[0050] At 75 degrees, 6 parts of modified hydrated calcium silicate was mixed with 24 parts of alcohol amine ester AAE-7 in 400 parts of water, and microwave treatment was carried out under rapid stirring at 1200 rpm for 25 min to obtain a Pickering emulsion, which was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles, then the particles were centrifuged and washed with 8 times the mass of water for 3 times, after removing the excess dispersant and by-products, 2 times the mass of water was added, and the slurry was uniformly dispersed to obtain core-shell cement admixture CA-7.

[0051] Example 8

[0052] In a reactor with reflux and microwave-assisted reaction device, under the conditions of 25 degrees, nitrogen protection, 600 rpm stirring, 94.3 parts by mass of 30% calcium nitrate solution and 331.9 parts by mass of 8% potassium silicate solution were simultaneously and uniformly added into 500 parts by mass of an aqueous solution containing 1.0% acrylic acid-maleic anhydride copolymer, both of which were added for 55 min, then 500 parts by mass of an ethanol solution containing 2.40 parts by mass of octyl trimethoxysilane was added into the system, the temperature was raised to 75 degrees, then microwave-assisted reflux reaction was carried out for 25 min, then the obtained semi-hydrophobic hydrated calcium silicate was centrifuged and washed with water 3 times at 15 times the theoretical mass of the product to remove by-products, thus obtaining modified hydrated calcium silicate intermediate C-8. The contact angle of the obtained modified hydrated calcium silicate was 49.0°.

[0053] At 65 degrees, 6 parts by mass of modified hydrated calcium silicate was mixed with 24 parts by mass of alcohol amine ester AAE-8 in 450 parts by mass of water, and microwave treatment was carried out for 25 min under rapid stirring at 1200 rpm to obtain a Pickering emulsion, which was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified to form core-shell structure particles, then the particles were centrifuged and washed with water 3 times at 8 times the mass of the particles each time to remove excess dispersant and by-products, then 2 times the mass of water was added, and the particles were uniformly dispersed into a slurry to obtain core-shell cement additive CA-8.

[0054] Comparative Example 1

[0055] In a reactor with reflux and microwave-assisted reaction device, under the conditions of 25 degrees, nitrogen protection, 300 rpm stirring, 53.0 parts by mass of 30% calcium nitrate solution and 118.4 parts by mass of 10% sodium silicate solution were simultaneously and uniformly added into 500 parts by mass of an aqueous solution containing 1.5% sodium polyacrylate, both of which were added for 30 min, then the obtained hydrated calcium silicate was centrifuged and washed with water 3 times at 15 times the theoretical mass of the product to remove by-products, thus obtaining hydrated calcium silicate intermediate, which had a contact angle <10°.

[0056] At 60 degrees, 5 parts by mass of hydrated calcium silicate was mixed with 60 parts by mass of alcohol amine ester AAE-1 in 650 parts by mass of water, and microwave treatment was carried out for 20 min under rapid stirring at 1500 rpm, and the mixture was cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified, then the particles were centrifuged and washed with water 2 times at 8 times the mass of the particles each time to remove excess dispersant and by-products, then 3 times the mass of water was added, and the particles were uniformly dispersed into a slurry to obtain comparative CAR-1.

[0057] Comparative Example 2

[0058] This comparative example is a comparative example of processing alcohol amine ester AAE-1 without using modified hydrated calcium silicate.

[0059] At 60 degrees, 60 parts by mass of alcohol amine ester AAE-1 was mixed in 650 parts by mass of water, treated by microwave for 20 min under rapid stirring at 1500 rpm, cooled to below 30 degrees, and the alcohol amine fatty acid ester was solidified. After centrifugal separation of the particles and washing twice with 8 times the mass of water each time, 3 times the mass of water was added after removal of the excess dispersant and byproducts, and after stirring, the comparative CAR-2 was obtained.

[0060] Test Example 1: Compressive Strength Test

[0061] The test material specifications and test procedures were based on GB 8076-2008 and GB 50082-2009. In the test, unless otherwise specified, the dosage of each admixture sample was 1.6% of the total mass of the glue material. The cement used in the test was a reference cement of P I 42.5. The initial slump of all samples was adjusted to 18.0±1.0 cm using a water reducing agent. The water reducing agent used was PCA-VIII high performance water reducing agent from Jiangsu Subo New Materials Co., Ltd. During the durability test, the test blocks were all standard cured for 28 days. The mix proportion (kg / m 3 ) of the concrete used in the application example is as shown in Table 2 below:

[0062] Table 2

[0063] cement mineral powder fly ash water sand pebbles boulders 360 65 75 190 710 420 640

[0064] The compressive strength test results are shown in Table 3 below:

[0065] Table 3

[0066]

[0067] From the results in Table 3 above, it can be seen that the 12h strength of each example is significantly improved, which can reach 30-55% compared with the control. The strength of the comparative example is significantly decreased. The 1d strength of each example is also improved by more than 10%. In terms of 3d strength, each example is close to the control without admixture, which indicates that the cement admixture prepared according to the method of the example retains the early strength characteristics of hydrated calcium silicate, and the strength improvement interval is also consistent with that of the hydrated calcium silicate early strength agent (12h-1d). The 28d strength is slightly improved by 4-8%, which may be due to the synergistic effect caused by the slow hydrolysis of the alcohol amine ester to release alcohol amine. Compared with the examples, the strength development of the comparative example is significantly slower, and is also not as good as the control without admixture, which may be because the hydrated calcium silicate in the comparative example is not modified, and the hydrophilic and hydrophobic properties are difficult to match with the alcohol amine ester to form a Pickering emulsion, so that the alcohol amine ester is directly exposed to the cement paste, which affects the early strength development due to hydrolysis and coverage of the mineral phase and hydration products.

[0068] Test Example 2: Test of Resistance to Freeze-thaw and Chloride Ion Permeation

[0069] The test was performed according to GB8076-2008 "Concrete Admixture" related provisions, and the test results are shown in Table 4 below:

[0070] Table 4

[0071]

[0072] As can be seen from Table 4 above, the maximum impermeability pressure of the modified concrete samples incorporating each example is significantly improved, with an amplitude of more than 45%, and at the same time, the chloride ion diffusion coefficient is significantly reduced, and the diffusion coefficient of the best effect is even lower than 50% of the control without mixing. Compared with the examples, the impermeability pressure and the reduction amplitude of the chloride ion diffusion coefficient of Comparative Example 1 prepared using unmodified hydrated calcium silicate are both significantly less than those of the modified concrete samples of each example. This is because the alcohol amine ester in Comparative Example 1 fails to form a good core-shell complex with the hydrated calcium silicate, and the compatibility between the hydration products is poor, which in turn leads to poor spatial dispersion.

[0073] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A core-shell type cement admixture, characterized in that, The additive is prepared by the Pickering emulsion method from the following components in parts by weight: 2.5-5 parts of modified hydrated calcium silicate, 14-28 parts of alkanolamine fatty acid ester and 67-83 parts of water; the additive has a core-shell structure with alkanolamine fatty acid ester as the core and modified hydrated calcium silicate as the shell. The modified hydrated calcium silicate has a contact angle of 40°-70°; The modified hydrated calcium silicate was obtained by modifying hydrated calcium silicate with an alkylsilane coupling agent in a water-ethanol mixed solution; The general structural formula of the alkylsilane coupling agent is shown in formula (1) below: Wherein X is methoxy, ethoxy, or acetoxy, and R9 is an alkyl group with 4-8 carbon atoms; the amount of the alkylsilane coupling agent is 10-25% of the mass of hydrated calcium silicate; The hydrated calcium silicate was prepared by in-situ co-precipitation of calcium salt and silicate under the control of a dispersant. The alkanolamine fatty acid ester is at least one of the following general formulas (2)-(4): Among them, R 1a R 1b R 1c R is a hydrogen atom or a methyl group. 2a R 2b R 2c It is an alkyl group with 7-17 carbon atoms.

2. The core-shell cement admixture according to claim 1, characterized in that: The dispersant is a homopolymer or copolymer of anionic or nonionic monomers with 2-8 carbon atoms and a dispersing effect, with a weight-average molecular weight of 5000-20000 and a molecular weight dispersibility index ≤2.0; the mass concentration of the dispersant is 1.0-2.5%.

3. The core-shell cement admixture according to claim 2, characterized in that: The dispersant is selected from at least one of polyacrylic acid, polymethacrylic acid, and polyvinylpyrrolidone.

4. The core-shell cement admixture according to claim 1, characterized in that: The calcium salt is a soluble inorganic calcium salt with a mass concentration of 25-40%; the silicate is sodium silicate or potassium silicate with a mass concentration of 8%-15%; the molar ratio of calcium ions to silicon ions in the calcium salt and silicate is (0.8-1.2):1; the total amount of the calcium salt and silicate is 1.5-4 times the mass of the dispersant.

5. A method for preparing a core-shell cement admixture according to any one of claims 1-4, characterized in that, Includes the following steps: Modified hydrated calcium silicate and alcoholic fatty acid ester are mixed in water to obtain Pickering emulsion; after cooling, the alcoholic fatty acid ester solidifies to form core-shell structured particles. The particles are then separated by centrifugation and washed with water. Finally, 2 to 5 times the mass of the particles are added with water and the mixture is evenly dispersed into a slurry to obtain the core-shell cement admixture.

6. The method for preparing a core-shell cement admixture according to claim 5, characterized in that, The modified calcium silicate hydrate is obtained through the following steps: a dispersant is added to a reactor equipped with a reflux and microwave-assisted reaction device, and the mixture is stirred at 15–35°C, under nitrogen protection, and at 300–600 rpm, while calcium salt and silicate are added at a uniform rate for 30 min–1 h; then an ethanol solution of alkylsilane coupling agent is added to the system, the temperature is raised to 45–75°C, and then the mixture is refluxed with microwave assistance for 20–45 min; the semi-hydrophobic calcium silicate hydrate obtained by centrifugation is washed 2–4 times with 10–20 times the theoretical mass of the product to remove byproducts, thus obtaining the modified calcium silicate hydrate.

7. The application of a core-shell cement admixture according to any one of claims 1-4, characterized in that: The core-shell cement admixture is applied in the concrete construction process, and the dosage of the core-shell cement admixture is 0.8% to 2.0% of the mass of cementitious materials in the concrete.

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