CN114685734B - Polymer-based nano composite early strength agent and preparation method and application thereof - Google Patents

Polymer-based nano composite early strength agent and preparation method and application thereof Download PDF

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CN114685734B
CN114685734B CN202011604006.1A CN202011604006A CN114685734B CN 114685734 B CN114685734 B CN 114685734B CN 202011604006 A CN202011604006 A CN 202011604006A CN 114685734 B CN114685734 B CN 114685734B
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early strength
silicon dioxide
nano silicon
strength agent
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CN114685734A (en
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张茜
于诚
姜骞
袁森森
李贞�
秦涛
吕健
张天
许洋
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Sobute New Materials Co Ltd
Bote New Materials Taizhou Jiangyan Co Ltd
Nanjing Bote New Materials Co Ltd
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Sobute New Materials Co Ltd
Bote New Materials Taizhou Jiangyan Co Ltd
Nanjing Bote New Materials Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F292/00—Macromolecular compounds obtained by polymerising monomers on to inorganic materials
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B24/00—Use of organic materials as active ingredients for mortars, concrete or artificial stone, e.g. plasticisers
    • C04B24/40—Compounds containing silicon, titanium or zirconium or other organo-metallic compounds; Organo-clays; Organo-inorganic complexes
    • C04B24/405—Organo-inorganic complexes
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
    • C04B40/0028—Aspects relating to the mixing step of the mortar preparation
    • C04B40/0039—Premixtures of ingredients
    • C04B40/0046—Premixtures of ingredients characterised by their processing, e.g. sequence of mixing the ingredients when preparing the premixtures
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
    • C08F283/06—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polyethers, polyoxymethylenes or polyacetals
    • C08F283/065—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polyethers, polyoxymethylenes or polyacetals on to unsaturated polyethers, polyoxymethylenes or polyacetals
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
    • C04B2103/10—Accelerators; Activators
    • C04B2103/14—Hardening accelerators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Abstract

The invention provides a polymer-based nano composite early strength agent, a preparation method thereof and application thereof in cement-based materials. The composite early strength agent comprises a copolymer obtained by copolymerizing a cation unit A, a carboxylic acid/nano silicon dioxide unit B, a polyether unit C and a modified alcohol amine unit D. The composite early strength agent utilizes the structural characteristics of the composite early strength agent, improves the dispersibility of nano silicon dioxide through charge adsorption dispersion effect, remarkably improves the active release of the nano silicon dioxide, and fully exerts the activity of the nano silicon dioxide through grafting the nano silicon dioxide on a molecular chain of the composite early strength agent through Si-O chemical bonds; the TPEG long chain forms steric hindrance, so that the dispersing capability of the composite early strength agent on cement particles is further improved, and in addition, the hydration process is accelerated through complexation reaction, so that the early strength of the cement-based material can be obviously improved when the TPEG long chain is applied to the cement-based material.

Description

Polymer-based nano composite early strength agent and preparation method and application thereof
Technical Field
The invention belongs to the technical field of concrete additives, and particularly relates to a polymer-based nano composite early strength agent, a preparation method thereof and application of the early strength agent in cement-based materials.
Background
In recent years, cement-based materials represented by concrete are building materials which are used in large quantities in the construction of national infrastructure and the construction of national key engineering, and play an important role in the increase of national economy and the progress of society. Meanwhile, with the development of economic level and scientific technology, new construction industry modes, namely assembly type construction, are developed. The demand of prefabricated building on concrete prefabricated components increases sharply, but because of the reasons of actual production of admixture, low winter production temperature and the like, the early strength development of cement-based materials is slower, and at present, measures such as steam curing and the like are generally adopted to improve the early strength of the cement-based materials, however, the mode needs to consume a large amount of energy resources, so that the production cost is increased, and the environment is greatly influenced. Based on the development trend of green, efficient and environment-friendly, various inorganic salt early strength agents or alcohol amine organic early strength agents are added into cement-based materials under the natural curing process condition, but the single early strength agents have the problems of reduced later performance strength, sensitive doping amount and the like.
The nanometer material is a novel superfine solid material which is rapidly developed in the last 20 years, and the special small-size effect, the surface and interface effect, the quantum size effect and the like of the nanometer material provide new directions and ideas for the development of concrete additives. The nano silicon dioxide has the characteristics of excellent thixotropic property, thickening property, reinforcing property and the like, and is widely applied in the industrial field. Based on the excellent performance of nano silicon dioxide, scholars at home and abroad explore and research on cement-based materials containing nano silicon dioxide to different degrees. At present, the literature shows that nano silicon dioxide is introduced into a cement-based material, the generation of hydrated calcium silicate can be promoted based on the nano crystal nucleus effect, the micro aggregate effect and the volcanic ash activity of the nano silicon dioxide, more hydration products are generated, the three-dimensional structure of the hydration products is densified, and the early strength of the cement-based material is improved.
The nano effect of nano silicon dioxide depends on the dispersibility to a great extent, but the nano silicon dioxide is difficult to uniformly disperse in cement paste due to the characteristics of high surface energy and the like, and the agglomeration phenomenon is easy to form, so that the application effect of the nano silicon dioxide is greatly reduced under the current situations. Therefore, development of a suitable dispersant to solve the problem of dispersion stability of nanosilica is a precondition for nanosilica application.
Although there are many reports on modified nano silica, such as an additive for improving the flexural and tensile strength of cement-based materials and a preparation method thereof, wherein a hybrid additive (silica is a shell layer) with a core-shell structure and a preparation method thereof are disclosed, the additive can greatly improve the flexural and tensile strength of cement-based materials, but the process is complex and the conditions are severe, which causes a certain limit to the wide application of the additive; in another example, the concrete admixture for inhibiting the transmission of erosion media in a marine environment provides a concrete admixture prepared by compounding silicon dioxide and various siloxanes and a preparation method thereof, and the admixture can reduce the electric flux of concrete, improve the erosion resistance of the concrete to chloride salt, but has no obvious improvement effect on the early strength of the concrete; for example, an additive for improving the strength of cement-based materials, a preparation method thereof and application thereof are disclosed, wherein in order to grow hydrated calcium silicate nanogel on the surface of nano silicon dioxide by means of the seed crystal effect of nano silicon dioxide, the titration process is complex, and the stability of the solution by the titration process is not described. In summary, the modification of nano silica is reported at present, and basically, surfactant is used to chemically modify nano silica, so that it can be seen that the working performance and stability of the additive doped with nano silica are one of the difficulties in solving various patents.
Therefore, the method for improving the dispersibility of the nano silicon dioxide can fully exert the nano effect of the nano silicon dioxide to improve the early strength of the cement-based material, and has great significance for the development of the cement-based material.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a polymer-based nano composite early strength agent with a brand new structure, which utilizes the structural characteristics of the early strength agent, improves the dispersibility of nano silicon dioxide through charge adsorption dispersion effect, obviously improves the activity release of the nano silicon dioxide, and fully exerts the activity of the nano silicon dioxide by grafting the nano silicon dioxide on the molecular chain of the composite early strength agent through Si-O chemical bonds; the compound early strength agent further improves the dispersing capability of cement particles by forming steric hindrance through the TPEG long chain, and accelerates the hydration process through complexation reaction, thereby finally ensuring that the early strength of the cement-based material can be obviously increased when the compound early strength agent is applied to the cement-based material.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
a polymer-based nanocomposite early strength agent, which comprises a copolymer obtained by copolymerizing a cation unit A, a carboxylic acid/nano silicon dioxide unit B, a polyether unit C and a modified alcohol amine unit D; wherein the structural formulas of the cationic unit A, the carboxylic acid/nano silicon dioxide unit B, the polyether unit C and the modified alcohol amine unit D are respectively shown as follows:
cation unit a:
carboxylic acid/nanosilica unit B:
polyether unit C:
modified alcohol amine unit D:
in the above structural formula, R 1 And R is 2 Are all selected from any one of H or methyl; n is an integer of 45 to 95.
Further, in the structural formula of the copolymer, the ratio of the average repeating unit number a, B, C, D of the cationic unit A, the carboxylic acid/nano silicon dioxide unit B, the polyether unit C and the modified alcohol amine unit D is 1:3-7:1:1; wherein the weight average molecular weight of the copolymer is 20000 to 70000, and the polymer dispersion index is not more than 2.
Further, the carboxylic acid/nano silicon dioxide unit B is obtained by esterification reaction of acrylic acid or methacrylic acid and nano silicon dioxide; the modified alcohol amine unit D is obtained by amidation reaction of maleic anhydride and triethanolamine.
Another object of the present invention is to provide a method for preparing the polymer-based nanocomposite early strength agent according to any one of the above, comprising the steps of:
s1, preparing a nano silicon dioxide aqueous solution;
s2, blending the nano silicon dioxide aqueous solution with a cationic unit A, acrylic acid or methacrylic acid, a polyether unit C, a modified alcohol amine unit D, an oxidant and a mercaptan chain transfer agent in a water system, and carrying out free radical copolymer reaction at 30-60 ℃, wherein nano silicon dioxide is grafted on acrylic acid or methacrylic acid through esterification reaction to form a carboxylic acid/nano silicon dioxide unit B; the cationic unit A, the carboxylic acid/nano silicon dioxide unit B, the polyether unit C and the modified alcohol amine unit D are copolymerized to obtain a copolymer, so that the polymer-based nano composite early strength agent is obtained;
wherein the ratio of the amounts of the substances of the cation unit A, the acrylic acid or the methacrylic acid, the polyether unit C and the modified alcohol amine unit D is 1:3-7:1:1; the mass of the nano silicon dioxide in the nano silicon dioxide aqueous solution is 5-30% of the mass of the acrylic acid or methacrylic acid; the amount of the substances of the oxidant is 0.2-2% of the total substances of the cation unit A, the acrylic acid or the methacrylic acid, the polyether unit C and the modified alcohol amine unit D, and the amount of the substances of the mercaptan chain transfer agent is 1-6% of the total substances of the cation unit A, the acrylic acid or the methacrylic acid, the polyether unit C and the modified alcohol amine unit D.
Further, in the step S2, the polymerization concentration is 30% to 60%.
Further, the oxidizing agent is selected from any one of persulfates, water-soluble azo compounds and peroxides, and the thiol chain transfer agent is selected from any one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, mercaptoethylamine and dodecyl mercaptan.
Further, in the step S1, the solid mass fraction of the aqueous solution of nano-silica is 30%, wherein the purity of the nano-silica is not less than 98%, and the average particle diameter is 20nm to 150nm.
In the aspect of selecting the particle size of the nano silicon dioxide, the spontaneous agglomeration is difficult to inhibit due to the too high activity of the nano silicon dioxide, so that the grafting reaction is not facilitated; and the too large particle size has too low activity, which affects the working performance of the obtained polymer-based nano composite early strength agent as an additive. Wherein, the nano silicon dioxide refers to nano silicon dioxide in various state forms prepared by various known commercial methods.
The invention also aims to provide the application of the polymer-based nanocomposite early strength agent in cement-based materials, which is obtained by mixing and stirring the polymer-based nanocomposite early strength agent and cement-based material raw materials; wherein the folding and solidifying blending amount of the polymer-based nano composite early strength agent is 0.2% -0.3% of the dosage of the cementing material in the cement-based material.
The nano silicon dioxide is adsorbed in a large amount through the structural unit A with positive charges, so that the dispersibility of the nano silicon dioxide is improved, and the activity is further improved. Secondly, as the surface of the nano silicon dioxide contains a large amount of silicon hydroxyl groups, the silicon hydroxyl groups have higher activity in aqueous solution, and under alkaline environment, carboxyl groups can be condensed with part of nano silicon dioxide, and the nano silicon dioxide forms carboxylic acid/nano silicon dioxide units B through Si-O chemical bonds, namely grafting; in addition, due to the introduction of the nano silicon dioxide, on one hand, the molecular chain growth of the composite early strength agent can be influenced to a certain extent, and the relative molecular weight is increased, so that the steric hindrance effect of the composite early strength agent molecule on cement particles is improved when the composite early strength agent molecule is applied to cement-based materials, and the dispersing capability of the early strength agent on the cement particles is improved; on the other hand, the grafted structure of the nano silicon dioxide can also improve the dispersibility of nano silicon dioxide particles, so that the nano crystal nucleus effect, the micro aggregate effect and the volcanic ash activity of the nano silicon dioxide can be fully exerted in the cement-based material. Meanwhile, in the compound early strength agent molecule, N atoms on the modified alcohol amine unit D are utilized, and the unshared electron pair on the atoms can be combined with Ca 2+ Fe (Fe) 3+ The plasma forms a complex which is easy to dissolve in water, promotes the dissolution of tricalcium aluminate and tetracalcium aluminoferrite, accelerates the reaction of the tricalcium aluminate and the tetracalcium aluminoferrite with gypsum to generate ettringite, thereby promoting the remarkable increase of the early strength of cement-based materials; secondly, the TPEG long chain in the polyether unit C is mutually soluble with water but has low surface affinity, and the TPEG long chain and the water are mutually soluble and extend in a medium to form steric hindrance, so that a sufficiently thick adsorption layer is formed, nano silicon dioxide is difficult to agglomerate, and the stability and the dispersibility of the nano silicon dioxide are improved.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail. This invention may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application so that others skilled in the art will be able to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated.
The existing common early strength agent mainly comprises calcium salt, organic-inorganic composite and high-valence cation, and the like, and the action mechanism of the early strength agent is that the surface tension of cement clinker particles contacted with water is reduced, the solubility of the cement clinker particles in water is increased, and meanwhile, the concentration of cement hydrolysate in water is reduced through the added early strength agent, so that C is promoted 3 S、C 2 S、C 3 A、C 4 The dissolution rate of the cement components such as AF is improved, the generation of hydration products such as ettringite, C-S-H gel and the like is accelerated, and the setting and hardening of cement are accelerated. The ion content in the early strength agent is too high, which may cause structural damage of cement-based materials, so according to the current performance requirements of the early strength of the cement-based materials and the research current analysis of the nucleation of nano silicon dioxide in the cement-based materials, the invention provides a polymer-based nano composite early strength agent which is only a single organic-inorganic hybrid material and is not a common organic-inorganic composite early strength agent (namely, organic acid, alcohol amine substances and nitrate are compounded according to a certain proportion). The polymer-based nano composite early strength agent provided by the invention can fully exert the activity of nano silicon dioxide through a specific structural design, and solves the dispersion stability problem of the nano silicon dioxide.
The polymer-based nanocomposite early strength agent of the present invention and a method for preparing the same will be described in detail below.
The polymer-based nano composite early strength agent provided by the invention comprises a copolymer obtained by copolymerizing a cation unit A, a carboxylic acid/nano silicon dioxide unit B, a polyether unit C and a modified alcohol amine unit D.
The following Table 1 shows the structural formulas of cationic unit A (hereinafter referred to as "A unit"), carboxylic acid/nanosilica unit B (hereinafter referred to as "B unit"), polyether unit C (hereinafter referred to as "C unit") and modified alcohol amine unit D (hereinafter referred to as "D unit").
Table 1, structural units A and B, C, D
In the above structural formula, R 1 And R is 2 Are all selected from any one of H or methyl; the average number n of the ethoxy chain units in the C unit is an integer of 45 to 95.
The structural formula of the copolymer is formed by the above A, B, C, D units being bonded to each other, and the final effect is mainly represented by the respective structural properties of A, B, C, D units irrespective of the arrangement order, so that it is not necessary to limit the specific arrangement order of A, B, C, D units, and it may be a structural formula such as shown in the following formula:
in the structural formula of the copolymer, the average repeating unit number a, b, c, d of A, B, C, D units is generally limited to 1:3-7:1:1, and the specific average repeating unit number of A, B, C, D units is adjusted so that the weight average molecular weight of the copolymer is 20000-70000 and the Polymer Dispersion Index (PDI) is not more than 2.
Specifically, the B unit is obtained by esterification of acrylic acid or methacrylic acid with nano silica, and the D unit is obtained by amidation of maleic anhydride with triethanolamine.
The composite early strength agent provided by the invention is generally prepared by the following method, and the preparation method is simple.
First, an aqueous solution of nanosilica was prepared.
Generally, the solid mass fraction of the aqueous solution of nano-silica is controlled to be about 30%, wherein the purity of the nano-silica is not lower than 98%, and the average particle size is 20nm to 150nm. Too small particle size can cause spontaneous agglomeration to be difficult to inhibit due to too high activity, and is unfavorable for subsequent grafting reaction; and the too large particle size has too low activity, which affects the working performance of the obtained composite early strength agent as an additive.
Then, the nano silicon dioxide aqueous solution, an A unit, acrylic acid or methacrylic acid, a C unit, a D unit, an oxidant and a mercaptan chain transfer agent are blended in a water system, and a free radical copolymer reaction is carried out at 30-60 ℃ to obtain the composite early strength agent.
Specifically, the process of the radical copolymer reaction is as follows: part of nano silicon dioxide is grafted on acrylic acid or methacrylic acid through esterification reaction to form a B unit; the A unit, the B unit, the C unit and the D unit are copolymerized to obtain a copolymer.
In the reaction, the ratio of the amounts of substances of the A unit, the acrylic acid or the methacrylic acid, the C unit and the D unit is controlled to be 1:3-7:1:1; meanwhile, the mass of the nano silicon dioxide in the nano silicon dioxide aqueous solution is controlled to be 5-30% of the mass of acrylic acid or methacrylic acid (hereinafter referred to as F value); the amount of the substance of the oxidizing agent is 0.2 to 2% of the total substance of the A unit, the acrylic acid or the methacrylic acid, the C unit and the D unit, and the amount of the substance of the thiol chain transfer agent is 1 to 6% of the total substance of the A unit, the acrylic acid or the methacrylic acid, the C unit and the D unit.
Further, the oxidizing agent may be any one of persulfate, water-soluble azo compound, and peroxide, and the thiol chain transfer agent may be any one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, mercaptoethylamine, and dodecylmercaptan.
In the above reaction, the polymerization concentration of the polymerization system may be controlled to 30% to 60%.
In the reaction process, the APTAC/MAPTAC structure in the A unit has positive charges, so that nano silicon dioxide with surface electronegativity can be adsorbed, on one hand, the esterification reaction between the nano silicon dioxide and acrylic acid or methacrylic acid is promoted to generate the B unit by improving the dispersibility of the nano silicon dioxide, and on the other hand, part of nano silicon dioxide can be adsorbed by the self; this dual effect promotes good dispersion of the nanosilica.
The above-mentioned composite type early strength agent of the present invention will be described by way of specific examples, and the following table 2 shows the respective composite type early strength agents of examples 1 to 6 and their polymer structure parameters.
The weight average molecular weight of the composite early strength agent described in each example was determined using Shimadzu LC-20A high performance gel chromatograph (GPC) with a column using TSKgel PW XL CP series, column temperature 40 ℃, eluent 0.1mol/L NaNO 3 The flow rate of the aqueous solution was 1.0mL/min, the sample loading was 20. Mu.L of 1% sample in water, and a dextran standard (Sigma-Aldrich) was used for the standard curve preparation.
The particle size distribution of the composite early strength agent in each embodiment is measured by an ALV-CGS-3 integrated light scattering instrument, and an object to be measured is prepared into an aqueous solution with the concentration of 0.1 mg/mL.
In order to verify the effect of the composite early strength agent of the present invention when applied to cement-based materials, three comparative early strength agents of comparative examples 1 to 3 and their high molecular structure parameters are also provided in table 2 below.
Table 2 composite type early strength agent of examples 1 to 6, comparative early strength agent of comparative examples 1 to 3, and parameters of polymer structure
That is, in the structure of the first comparative early strength agent provided in comparative example 1, it is different from the composite early strength agent in the above-described example 2 of the present invention in that the first comparative early strength agent does not contain nano silica grafted on acrylic acid, that is, the polymerized group B of acrylic acid alone corresponds to no nano silica at the B unit; in the structure of the second comparative early strength agent provided in comparative example 2, it is different from the composite early strength agent in the above-described example 2 of the present invention in that the second comparative early strength agent does not contain an a unit; in the structure of the third comparative early strength agent provided in comparative example 3, it is different from the composite early strength agent in the above-described example 2 of the present invention in that the third comparative early strength agent does not contain a D unit.
Table 3 shows the particle diameter parameters of the composite early strength agents in examples 1 to 6.
Table 3 particle size parameters of the composite early strength Agents of examples 1 to 6
As can be seen from table 3, each composite early strength agent provided in the examples of the present invention is at a nano level, which also confirms that the nano silica in the composite early strength agent is well dispersed, but not agglomerated; meanwhile, the composite early strength agent is a nano material and can maintain good stability.
The composite early strength agents of examples 1 to 6 above were applied to cement-based materials by the following methods, and their performance was tested.
Mixing and stirring the composite early strength agent with other cement-based material raw materials; the folding and solidifying doping amount of the composite early strength agent is controlled to be 0.2 to 0.3 percent of the dosage of the cementing material.
The test gum sand was substantially blended with the cement P.O 42.5.42.5 cement and the test sand was ISO standard sand as shown in Table 4.
In order to verify the beneficial effect of the composite early strength agent in the early strength aspect, the proportion of the early strength agent which is not mixed is taken as a background group; meanwhile, the same method is adopted to apply the comparative early strength agents in the comparative examples 1 to 3 to cement-based materials.
Table 4 Experimental proportions of the composite early-strength Agents in examples 1 to 6 and the comparative early-strength Agents in comparative examples 1 to 3 applied to Cement-based materials and background groups
The cement mortar strength test method is according to GB/T17671-1999 (ISO method).
The performance test results are shown in tables 5 and 6.
Table 5 compressive strengths of cement-based materials obtained from the composite early strength agents of examples 1 to 6, the comparative early strength agents of comparative examples 1 to 3, and the background groups at different ages
As can be seen from table 5, when the composite early strength agent provided by examples 1 to 6 of the present invention is applied to cement-based materials, the significant increase of the early strength of the cement-based materials can be significantly promoted, and the 12h compressive strength and the 1d compressive strength of the prepared cement-based materials are significantly improved; in particular, the 12h compressive strength and the 1d compressive strength of the cement-based material obtained by the composite early strength agent in the embodiment 4 can reach 10.56MPa and 20.17MPa. In addition, it can be seen that under the same mixing amount, the early strength effect achieved by the composite early strength agent from different embodiments is also different, and the reason for this trend is presumed that when the content of the nano silicon dioxide is lower, other dispersing units in the early strength agent occupy more units, and the dispersibility of the nano silicon dioxide is better, but the active sites and defects on the surface of the nano silicon dioxide are reduced, so that better adsorption effect cannot be generated with the surface of cement particles, and the strength is further improved; when the content of the nano silicon dioxide is higher, silicon hydroxyl groups on the surface of the nano silicon dioxide are easy to aggregate to form a polymer, so that the adsorption capacity of the early strength agent is damaged to a certain extent, and the dispersion performance is poor; when the content of the nano silicon dioxide is optimal, the active hydroxyl on the surface of the nano silicon dioxide and the hydroxyl on the surface of the cement particles are dehydrated and condensed, so that a chemical adsorption effect is generated, and the strength of the cement-based material can be obviously improved.
Compared with the composite early strength agent provided in example 2, the comparative cement-based materials obtained correspondingly by the comparative early strength agents provided in comparative examples 1-3 have significantly lower working strength than the cement-based materials obtained by the composite early strength agent of the invention; the method shows that the nano silicon dioxide cannot be effectively dispersed by only adsorbing the nano silicon dioxide by the cationic unit A or grafting the nano silicon dioxide by the carboxyl/nano silicon dioxide group B, and the combined action of the cationic unit A and the carboxyl/nano silicon dioxide group B is needed; in addition, the modified alcohol amine unit D has certain working efficiency on the early strength of the cement-based material, and can promote the early strength increase of the cement-based material.
Meanwhile, the composite early strength agent in the above example 2 was applied to cement-based materials according to different addition amounts, and the relationship between the addition amount and compressive strength was tested, and the test results are shown in table 6.
TABLE 6 compressive Strength of different composite early-strength Agents at different ages
It is clear from table 6 that the working strength of the obtained cement-based material increases slowly as the amount of the composite early strength agent added increases; however, if the doping amount is continuously increased, the working strength of the corresponding cement-based material has obvious reduction trend, and it is proved that when the dosage of the composite early strength agent is excessive, the composite early strength agent is likely to enter a supersaturated state, and the nano silicon dioxide is likely to generate a secondary agglomeration phenomenon due to the adsorption bridge effect caused by the adsorption groups on the composite early strength agent; when the concentration of the composite early strength agent is further increased, the polymer chain parts in the composite early strength agent can be intertwined, so that the dispersion performance of cement is reduced, and finally, the working strength of the obtained cement-based material is lower.
The invention utilizes the structural characteristics of the composite early strength agent, improves the dispersibility of the nano silicon dioxide by the charge adsorption dispersion effect, and further releases the activity of the nano silicon dioxide; the nano silicon dioxide is grafted on the molecular chain of the composite early strength agent through the esterification reaction between the active hydroxyl and carboxyl on the nano silicon dioxide, so that the activity of the nano silicon dioxide is exerted while the relative molecular weight of the composite early strength agent is remarkably improved, and the hydration reaction degree of cement is improved, thereby ensuring that the structure of the cement-based material is compact, improving the early strength of the cement-based material, and finally achieving the purposes of saving the cost, improving the working performance of the cement-based material and improving the compressive strength.
While the invention has been shown and described with reference to certain embodiments, those skilled in the art will appreciate that: various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims (8)

1. The polymer-based nano composite early strength agent is characterized by comprising a copolymer obtained by copolymerizing a cation unit A, a carboxylic acid/nano silicon dioxide unit B, a polyether unit C and a modified alcohol amine unit D; wherein the structural formulas of the cationic unit A, the carboxylic acid/nano silicon dioxide unit B, the polyether unit C and the modified alcohol amine unit D are respectively shown as follows:
cation unit a:
carboxylic acid/nanosilica unit B:
polyether unit C:
modified alcohol amine unit D:
in the above structural formula, R 1 And R is 2 Are all selected from any one of H or methyl; n is an integer of 45 to 95.
2. The polymer-based nanocomposite early strength agent according to claim 1, wherein in the structural formula of the copolymer, the average repeating unit number a, B, C, D of the cationic unit a, the carboxylic acid/nanosilica unit B, the polyether unit C, the modified alcohol amine unit D is 1:3 to 7:1:1; wherein the weight average molecular weight of the copolymer is 20000 to 70000, and the polymer dispersion index is not more than 2.
3. The polymer-based nanocomposite early strength agent according to claim 1 or 2, wherein the carboxylic acid/nanosilica unit B is obtained by esterification of acrylic acid or methacrylic acid with nanosilica; the modified alcohol amine unit D is obtained by amidation reaction of maleic anhydride and triethanolamine.
4. A method for preparing the polymer-based nanocomposite early strength agent according to any one of claims 1 to 3, comprising the steps of:
s1, preparing a nano silicon dioxide aqueous solution;
s2, blending the nano silicon dioxide aqueous solution with a cationic unit A, acrylic acid or methacrylic acid, a polyether unit C, a modified alcohol amine unit D, an oxidant and a mercaptan chain transfer agent in a water system, and carrying out free radical copolymer reaction at 30-60 ℃, wherein nano silicon dioxide is grafted on acrylic acid or methacrylic acid through esterification reaction to form a carboxylic acid/nano silicon dioxide unit B; the cationic unit A, the carboxylic acid/nano silicon dioxide unit B, the polyether unit C and the modified alcohol amine unit D are copolymerized to obtain a copolymer, so that the polymer-based nano composite early strength agent is obtained;
wherein the ratio of the amounts of the substances of the cation unit A, the acrylic acid or the methacrylic acid, the polyether unit C and the modified alcohol amine unit D is 1:3-7:1:1; the mass of the nano silicon dioxide in the nano silicon dioxide aqueous solution is 5-30% of the mass of the acrylic acid or methacrylic acid; the amount of the substances of the oxidant is 0.2-2% of the total substances of the cation unit A, the acrylic acid or the methacrylic acid, the polyether unit C and the modified alcohol amine unit D, and the amount of the substances of the mercaptan chain transfer agent is 1-6% of the total substances of the cation unit A, the acrylic acid or the methacrylic acid, the polyether unit C and the modified alcohol amine unit D.
5. The method according to claim 4, wherein the polymerization concentration in the step S2 is 30% to 60%.
6. The method according to claim 4 or 5, wherein the oxidizing agent is selected from any one of persulfates, water-soluble azo compounds, and peroxides, and the thiol chain transfer agent is selected from any one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, mercaptoethylamine, and dodecylmercaptan.
7. The method according to claim 4 or 5, wherein in the step S1, the solid mass fraction of the aqueous nanosilica solution is 30%, wherein the nanosilica has a purity of not less than 98% and an average particle diameter of 20nm to 150nm.
8. The application of the polymer-based nano composite early strength agent in cement-based materials according to any one of claims 1 to 3, which is characterized in that the polymer-based nano composite early strength agent is mixed with cement-based material raw materials and stirred; wherein the folding and solidifying blending amount of the polymer-based nano composite early strength agent is 0.2% -0.3% of the dosage of the cementing material in the cement-based material.
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