Low-temperature-resistant concrete slump retaining agent and preparation method thereof

Abstract

The application provides a low-temperature-resistant concrete slump retaining agent and a preparation method thereof. The low-temperature-resistant concrete slump retaining agent comprises a triblock polymer, and the triblock polymer comprises a polyunsaturated polyether chain segment, a polyunsaturated phosphate chain segment and a polyunsaturated ester chain segment. The polyunsaturated polyether chain segment is at one end of the triblock polymer. According to the application, the triblock polymer can still achieve rapid dissolution and self-assembly to form a stable micellar structure in a low-temperature environment, and can realize phased regulation of cement hydration without interfering with the early adsorption of a water reducing agent, so as to improve the fluidity retention performance of a concrete mixture under low-temperature working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete admixtures, in particular to a low-temperature-resistant concrete slump retaining agent and a preparation method thereof. BACKGROUND

[0002] A concrete slump retaining agent is an admixture used to slow down the decline of concrete slump over time, and is widely used in long-distance conveying, large-volume structures, complex pouring components, and high-performance concrete engineering. The slump retaining agent is usually used in conjunction with polycarboxylate superplasticizer to balance the early fluidity and the later workability. Existing slump retaining agents include inorganic retarding components, organic small molecule inhibitors, and functional polymers, and their action mechanisms usually involve delaying the dissolution of cement particles, the generation of hydration products, or the interface adsorption process, thereby maintaining the fluidity of concrete under static or slow construction conditions.

[0003] However, in a low-temperature environment (such as 5-10℃), the dissolution rate of cement particles in the concrete system decreases, the viscosity of the reaction system increases, and the movement of the admixture molecules is limited, significantly slowing down the overall reaction kinetics. This environmental change interferes with the synergistic mechanism of the slump retaining agent and the superplasticizer, which is specifically manifested as follows: the slump retaining agent is difficult to fully disperse and function in the early stage, and the adsorption of the superplasticizer is also delayed due to the decreased dissolution and migration rate, and the mutual interference and competition between the two on the limited interface of the cement are more prominent. Some slump retaining agents have increased adsorption, uneven distribution, or premature effect in a low-temperature environment, which may preferentially occupy the position on the surface of the cement particles, thereby inhibiting the adsorption of the superplasticizer, resulting in insufficient initial fluidity or decreased pumping performance in the early construction stage.

[0004] Therefore, under low-temperature working conditions, the existing slump retaining agent has the problems of slow dispersion, uncontrolled effect, and incoordination with the adsorption behavior of the superplasticizer, which easily causes poor early fluidity of the concrete mixture, insufficient slump retaining ability in the later stage, and the like, affecting the continuity and stability of the engineering construction. Therefore, it is necessary to provide a low-temperature-resistant concrete slump retaining agent more suitable for low-temperature working conditions. SUMMARY

[0005] The present application provides a low-temperature-resistant concrete slump retaining agent, which aims to solve the problems of slow dispersion, uncontrolled effect, and incoordination with the adsorption behavior of the superplasticizer of the existing slump retaining agent in a low-temperature environment, thereby improving the fluidity of the concrete mixture in the early stage and the slump retaining performance in the middle and later stages.

[0006] In a first aspect, the present application provides a low-temperature-resistant concrete slump retaining agent, which includes a triblock polymer, the triblock polymer including a polyunsaturated polyether chain segment, a polyunsaturated phosphate chain segment, and a polyunsaturated ester chain segment; the polyunsaturated polyether chain segment being at one end of the triblock polymer.

[0007] According to the present application, the triblock polymer can still achieve rapid dissolution, self-assembly to form a stable micellar structure in a low-temperature environment, and realize the phased regulation of cement hydration without interfering with the early adsorption of the water reducing agent, thereby improving the fluidity retention performance of the concrete mixture under low-temperature working conditions.

[0008] Specifically, the polyunsaturated polyether segment is a hydrophilic segment, has good low-temperature solubility and segment flexibility, can rapidly expand and stabilize the micellar shell structure in the initial mixing stage, and improves the dispersion efficiency of the triblock polymer; the polyunsaturated ester segment has hydrophobicity, induces the triblock polymer to self-assemble to form a micellar core structure in an aqueous phase, and further realizes the confined distribution of the intermediate or adjacent segment; the polyunsaturated phosphate segment can be located at the middle or close to both ends of the triblock polymer, in the micellar structure, it is close to the hydrophobic core or in the inner shell layer region, and is protected by the steric hindrance of the outer polyether segment, so that it is difficult to directly contact the surface of the cement particles in the early mixing stage, thereby reducing the adsorption interference between the water reducing agent; in the system structure relaxation or micellar dynamic rearrangement process, the phosphate segment is gradually exposed and anchors with calcium ions in the cement particles, delays the hydration reaction, and plays a slump retention function.

[0009] Through the structure and space cooperation of the above three types of segments, the triblock polymer provided by the present application has good dissolution and dispersion capacity, structural stability and slump retention control time in a low-temperature environment, and is suitable for construction scenes with high requirements for the fluidity maintenance performance of concrete mixtures under low-temperature working conditions.

[0010] In some embodiments, the polyunsaturated phosphate segment is arranged between the polyunsaturated polyether segment and the polyunsaturated ester segment.

[0011] In some of the above embodiments, since the block order of the triblock polymer is polyunsaturated polyether segment-b-polyunsaturated phosphate segment-b-polyunsaturated ester segment, when a micellar structure is formed in an aqueous phase, the polyester segment shrinks and aggregates as a hydrophobic core, the polyether segment constitutes an external hydrophilic shell layer, and the polyunsaturated phosphate segment naturally locates in the “core-shell interface” region of the micelle and is double-confined by the inner and outer segments. This arrangement can significantly enhance the “latency” and response time regulation ability of the phosphate structure, effectively delay the contact time of the phosphate with the cement particles, and thus avoid hindering the normal adsorption behavior of the water reducing agent in the initial mixing stage. Compared with the structure in which the phosphate segment is randomly distributed or arranged at the chain end, the arrangement in the present embodiment makes the phosphate group have a more definite physical confinement boundary in the micellar structure, which helps to realize a clearer adsorption starting window and a more stable slump retention time window.

[0012] In addition, the phosphonate segment arranged between the hydrophilic segment and the hydrophobic segment helps to improve the uniformity of the aggregate structure of the triblock polymer, form a micelle system with more concentrated particle size and more controllable shell thickness, and thus improve the dispersion stability and construction adaptability of the slump retaining agent. The structural configuration can still maintain good micelle stability under low temperature conditions, and gradually release the phosphonate anchor site during the dynamic relaxation process of the structure, to realize more controllable later slump retaining function.

[0013] It should be noted that the polyunsaturated polyether segment, the polyunsaturated phosphonate segment and the polyunsaturated ester segment all have well-known meanings, the polyunsaturated polyether segment refers to a monomer polymerized to contain an unsaturated carbon-carbon bond and a polyether segment, the polyunsaturated polyether segment refers to a monomer polymerized to contain an unsaturated carbon-carbon bond and a phosphonate structure, and the polyunsaturated ester segment refers to a monomer polymerized to contain an unsaturated carbon-carbon bond and an ester bond.

[0014] In some embodiments, the triblock polymer is prepared by the following steps:

[0015] S1: the unsaturated polyether monomer is polymerized with the RAFT reagent under the action of an initiator to obtain a polyunsaturated polyether containing a RAFT site;

[0016] S2: the polyunsaturated polyether containing a RAFT site in step S1 is polymerized with an unsaturated phosphonate monomer under the action of an initiator to obtain a polyunsaturated polyether-b-polyunsaturated phosphonate containing a RAFT site;

[0017] S3: the polyunsaturated polyether-b-polyunsaturated phosphonate containing a RAFT site in step S2 is polymerized with an unsaturated ester monomer under the action of an initiator to obtain the triblock polymer.

[0018] In the above some embodiments, the polyunsaturated polyether segment, the polyunsaturated phosphonate segment and the polyunsaturated ester segment are sequentially introduced by stepwise RAFT polymerization, which not only realizes accurate construction of the triblock polymer structure, but also helps to control the order of the segments in the molecule. This polymerization path ensures that the polyether segment is located at one end of the polymer, so as to be exposed to the aqueous phase first when forming micelles, and to give the molecule good low-temperature solubility and initial dispersion capacity; at the same time, the phosphonate segment as the middle block is effectively confined between the polyether and the polyester, which helps to control its adsorption effective window and avoid early interference with the adsorption behavior of the water reducing agent.

[0019] Compared with the structure uncertain slump retaining agent obtained by the traditional random copolymerization system, the present embodiment ensures the consistency and repeatability of the triblock structure through the controllable polymerization steps, which is suitable for the functional control strategy driven by structural design, so as to make the low-temperature coagulation slump retaining agent have good low-temperature slump retaining performance.

[0020] In some embodiments, the triblock polymer is prepared by the following steps:

[0021] S1: dispersing 10 parts of unsaturated polyether monomer, 0.05-0.2 parts of 4-cyano-4-(phenylthiocarbamothioyl) valeric acid, and 0.01-0.05 parts of azobisisobutyronitrile in 50-100 parts of N,N-dimethylformamide, and reacting at 60-80°C for 5-7 hours under a nitrogen atmosphere to obtain a first mixed solution;

[0022] S2: adding 1-3 parts of unsaturated phosphate ester monomer and 0.01-0.05 parts of azobisisobutyronitrile to the first mixed solution, and reacting at 60-80°C for 3-5 hours under a nitrogen atmosphere to obtain a second mixed solution;

[0023] S3: adding 5-7 parts of unsaturated ester monomer and 0.01-0.05 parts of azobisisobutyronitrile to the second mixed solution, and reacting at 60-80°C for 4-6 hours under a nitrogen atmosphere to obtain the triblock polymer.

[0024] In some embodiments described above, by using a continuous three-step RAFT polymerization path and precisely controlling the proportion of reactants, temperature, time, and initiator dosage in each step, a triblock polymer system with clear structure distribution and stable segment order can be obtained. Specifically, the polyunsaturated polyether segment, as the hydrophilic segment, is used in a dosage of 10 parts, which dominates the total monomers, ensuring that the triblock polymer has good water solubility and segment flexibility, and quickly unfolds at low temperatures to form a stable micellar shell structure; the polyunsaturated phosphate ester segment, as the anchoring functional segment, is introduced in a low proportion of 1-3 parts, which can effectively provide anchoring sites to achieve hydration inhibition function, while avoiding excessive distribution in the structure, which may cause early adsorption or competition with water reducing agents, thereby maintaining the controllability of the adsorption timing; the polyunsaturated ester segment, as the hydrophobic segment, is used in a proportion of 5-7 parts to construct a hydrophobic core structure, which not only supports micellar self-assembly, but also enhances the confinement effect on the phosphate ester segment through steric hindrance, further delaying its exposure timing, and achieving phased release of the slump retention function.

[0025] The synergistic design of the proportions of the three monomers enables the triblock polymer to have the triple attributes of hydrophilic dispersion, functional latency, and hydrophobic nucleation at the molecular scale, and through the structure self-assembly behavior, it realizes rapid dissolution at low temperatures, self-stable micelle formation, and dynamic regulation of the slump retention anchoring function, which helps to improve the flowability maintenance performance of concrete in cold construction environments.

[0026] In some embodiments, the unsaturated polyether monomer in step S1 includes polyethylene glycol monomethyl ether methacrylate with a number average molecular weight of 800-1200.

[0027] In some of the above embodiments, the polyethylene glycol monomethyl ether methacrylate is used as a hydrophilic monomer to construct the polyether segment in the triblock polymer, and the size of the molecular weight directly affects the solubility performance of the slump retaining agent in water, the micelle formation rate and the shell thickness. When the number average molecular weight is controlled in the range of 800-1200, the polyether segment can not only rapidly unfold in a low-temperature water environment to form a stable micellar shell, but also provide moderate segment flexibility and steric hindrance, thereby coating the intermediate functional segment, delaying its contact with the cement particles, and enhancing the time sequence control ability of the slump retaining agent.

[0028] In contrast, if the molecular weight of the polyether segment is too high, the segment is prone to entanglement or crystallization in a low-temperature environment, resulting in an increase in solution viscosity and a decrease in dispersion speed. If the molecular weight is too low, it is not enough to provide effective micellar shell thickness and steric hindrance protection. Therefore, controlling the number average molecular weight of the polyether segment in the range of 800-1200 is the preferred solution to achieve a balance between low-temperature rapid dissolution, dispersion uniformity and structural stability, and is particularly suitable for constructing a block type concrete slump retaining agent with limited domain protection and controlled release behavior.

[0029] In some embodiments, the unsaturated phosphate ester monomer in step S2 includes 2-hydroxyethyl methacrylate phosphate ester.

[0030] In some of the above embodiments, 2-hydroxyethyl methacrylate phosphate ester is a functional monomer that contains both an unsaturated polymerization group and a phosphate ester anchoring site in its structure. It contains a hydroxyethyl flexible side chain in its molecule, has good hydrophilicity and polymer compatibility, and is suitable for being introduced into a block polymer structure by controlled radical polymerization (such as RAFT polymerization). In a triblock polymer system, this monomer can be uniformly embedded in the main chain to form a well-defined functional segment, which has both anchoring and flexible properties. It can be confined to the core-shell interface region in the micellar structure and be shielded by the polyether segment, which helps to avoid early exposure to the surface of the cement particles, thereby reducing the risk of adsorption competition with the superplasticizer.

[0031] In contrast, although vinyl phosphate monomers also contain phosphate ester structures, they lack flexible linking groups, have low olefin polymerization activity, slow polymerization reaction rate and low conversion rate, which is not conducive to the construction of block polymers with controllable structure. In addition, during the formation of micelles, the rigid segments tend to aggregate in the interior, the release behavior lacks adjustment ability, the functional exposure is out of control, and the overall slump retention time and low-temperature adaptability are affected.

[0032] In summary, the use of 2-hydroxyethyl methacrylate phosphate as an unsaturated phosphate monomer can achieve controllable polymerization, clear positioning, and controlled release time, and is suitable for constructing a three-block polymer system that still has good dispersibility and dynamic slump retention regulation ability under low temperature conditions, further improving the adaptability and slump retention effect stability of the slump retention agent under low temperature construction environment.

[0033] In some embodiments, the unsaturated ester monomer in step S3 includes caprolactone acrylate.

[0034] In some embodiments described above, caprolactone acrylate is a functional monomer containing both a polymerizable acrylate group and a hydrophobic caprolactone repeating structure in its structure, which is usually prepared by ring-opening addition reaction of hydroxyalkyl acrylate and ε-caprolactone, and has certain flexibility, flexible chain conformation, and moderate polarity. The polyester segment formed after polymerization of such monomers has good hydrophobicity in water and can be used as a hydrophobic segment of a three-block polymer to drive the self-assembly of molecules to form a micellar core structure in an aqueous phase, thereby providing a physical basis for the confinement of the phosphate segment.

[0035] In contrast, traditional alkyl acrylate monomers such as hexyl methacrylate (HMA) also have hydrophobicity, but their side chains are linear aliphatic alkyl groups that lack embedded polar groups, have high rigidity, and have too strong hydrophobic driving force, making it difficult for the polymer to form aggregates with clear shell-core structure and controllable size. In the low temperature environment (5-10°C) involved in the present application, such rigid hydrophobic segments are more likely to cause the collapse of the micellar structure or the decrease in dispersibility, thereby affecting the low temperature adaptability and time stability of the entire slump retention agent.

[0036] Further, the polyester segment formed after polymerization of caprolactone acrylate contains multiple embedded ester bond structures. When the slump retention agent undergoes micellar structure relaxation and exposure of the hydrophobic core portion during concrete mixing, the polyester segment will be in a high alkaline environment (pH≥12) of the cement system. Under this condition, the ester bond will undergo partial hydrolysis reaction, and carboxylic acid structures will be cleaved, thereby introducing new anionic groups in the later stage, enhancing the electrostatic adsorption force between this segment and the surface of the cement particles. This property gives the polyester segment a "late-stage auxiliary anchoring" function, forming a dynamic transition process from physical confinement to chemical adsorption, which helps to further consolidate the synergistic adsorption and hydration inhibition effect of the phosphate anchoring segment.

[0037] Therefore, caprolactone acrylate not only has good hydrophobic core construction ability, but also has the potential to gradually transform into a functional anchoring group in a high alkaline environment after polymerization, which can synergistically enhance the structural stability, anchoring efficiency, and action time of the three-block slump retention agent under low temperature environment, and is the preferred unsaturated polyester monomer in the low temperature responsive slump retention agent system of the present application.

[0038] In some embodiments, water is further included, and the solid content of the low-temperature resistant concrete slump retaining agent is 1% to 20%.

[0039] In some embodiments described above, the triblock polymer can be pre-dispersed in deionized water to form a stable aqueous dispersion system, constituting a commercial liquid slump retaining agent product, which has good storage stability and use convenience. The slump retaining agent can be directly added to concrete for use, and is suitable for various use scenarios such as pre-mixing at a commercial mixing station and secondary deployment at a construction site. Within the concentration range, the triblock polymer can quickly expand in mixing water and form micellar structures, while not interfering with the initial adsorption behavior of the polycarboxylate superplasticizer, and releasing functional segments during dynamic rearrangement of the micelles to play a late slump retaining role.

[0040] Therefore, the triblock polymer is configured as an aqueous dispersion with a certain solid content, which not only facilitates storage and use, but also enhances its rapid response capability, structural stability and slump retaining effect consistency under low temperature conditions, meeting the actual construction requirements of concrete projects in winter or cold regions.

[0041] In a second aspect, the application provides a method for preparing a low-temperature resistant concrete slump retaining agent, comprising:

[0042] The triblock polymer in the low-temperature resistant concrete slump retaining agent according to any one of the embodiments of the first aspect is provided.

[0043] The triblock polymer is dispersed in water to obtain the low-temperature resistant concrete slump retaining agent.

[0044] According to the application, the method obtains a slump retaining agent in a stable aqueous dispersion system, which is convenient for transportation, storage and metering, and has good on-site adaptability. The method is suitable for large-scale preparation and does not depend on high-temperature, high-shear or emulsification equipment, so that the triblock polymer can be quickly dissolved and self-assembled at room temperature or low temperature, thereby maintaining the spatial arrangement characteristics and late release capability of the functional segments.

[0045] In addition, the aqueous dispersion system can maintain good micellar stability and dispersion uniformity under low temperature environment, quickly disperses without destroying the block structure in the initial stage of concrete mixing, which helps to exert the time sequence advantage of the block polymer in the application in the adsorption of the superplasticizer and the inhibition of hydration, thereby improving the fluidity retention capability of the concrete under low temperature conditions.

[0046] In a third aspect, the application provides a low-temperature resistant concrete comprising the low-temperature resistant concrete slump retaining agent according to any one of the embodiments of the first aspect or prepared by the method according to any one of the embodiments of the second aspect.

[0047] According to the application, the low-temperature-resistant concrete slump retaining agent can be directly mixed during the concrete mixing process, and is usually used in cooperation with a polycarboxylic acid water reducing agent to play a two-stage role of early dispersion and later slump retention. In the initial stage of concrete mixing, the triblock polymer realizes rapid dissolution and dispersion through the polyether segment, and at the same time, the polyester segment constructs a micelle core structure, limits the functional phosphate segment to the core-shell interface, and is protected by the steric hindrance of the polyether segment, thereby avoiding premature adsorption interference with the cement particles, so as to ensure the initial dispersion efficiency of the water reducing agent and the early fluidity of the concrete.

[0048] With the passage of time and the gradual relaxation of the system structure, the phosphate segment is gradually exposed in the dynamic rearrangement of the micelles, and reacts with Ca 2+ to inhibit the cement hydration process, thereby realizing the delayed start of the slump retention function. In the low-temperature working condition, the action process can still proceed smoothly, and the slump retaining agent system can effectively prolong the construction time window of the concrete and improve the slump retention performance, and is suitable for application scenarios such as winter construction, night pouring or long-distance transportation in a low-temperature environment in cold regions.

[0049] Therefore, the low-temperature-resistant concrete slump retaining agent provided by the application not only has good preparation stability and structural response capability, but also can realize the phased release and functional stable output of the slump retention effect under low-temperature conditions, thereby enhancing the adaptability and construction continuity of the concrete system.

[0050] Compared with the prior art, the application has at least the following beneficial effects:

[0051] 1. A triblock polymer structure with a polyunsaturated polyether segment, a polyunsaturated phosphate segment and a polyunsaturated polyester segment is provided, which can self-assemble to form a micelle system in water, and realize the spatial decoupling of dispersion and anchoring functions through the synergistic arrangement of hydrophilic-functional-hydrophobic segments.

[0052] 2. The triblock polymer still has good solubility and micelle stability under low-temperature conditions, which can avoid the problems of dispersion delay, structure collapse or release out of control of conventional slump retaining agents in a 5-10℃ environment, and is suitable for concrete slump retaining requirements in winter or cold regions.

[0053] 3. The polyether segment preferentially expands to form a micelle shell, the polyester segment constitutes a hydrophobic core, and the phosphate segment is limited to the core-shell interface region and is shielded by the steric hindrance of the polyether segment, which can effectively delay the exposure time of the slump retention function segment, avoid adsorption competition with the water reducing agent, and enhance the synergistic stability of the two.

[0054] 4. The polyester segment is introduced by polymerization of caprolactone acrylate. In addition to the function of constructing the hydrophobic core, it can also be partially hydrolyzed in the high alkaline environment of the cement system, introducing carboxylic acid structure, further enhancing the adsorption capacity of the later cement particles, and realizing the dynamic response enhancement of the slump retention function. DETAILED DESCRIPTION

[0055] Each embodiment or example in the present specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments.

[0056] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0057] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "plurality" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0058] In the description of the present specification, "parts" means "mass parts" unless otherwise specified.

[0059] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only for the purpose of explaining the present application, and cannot be understood as a limitation on the present application. In the embodiments, the specific techniques or conditions not noted are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not noted by the manufacturer are all conventional products that can be obtained by purchase.

[0060] 4-cyano-4-(phenylthiocarbamoylthio)pentanoic acid, CAS No. 201611-92-9;

[0061] Polyethylene glycol monomethyl ether methacrylate, CAS No. 26915-72-0;

[0062] 2-hydroxyethyl methacrylate phosphate ester (PM-2), CAS No. 52628-03-2;

[0063] Vinyl phosphate, CAS No. 1746-03-8;

[0064] Caprolactone acrylate, 2-oxepanone homopolymer 2-[(1-oxo-2-propenyl)oxy]ethyl ester, CAS No. 110489-05-9;

[0065] Hexyl methacrylate, CAS No. 142-09-6;

[0066] Polycarboxylate water reducer, model PCA®-300P.

[0067] Preparation Example 1

[0068] Preparation of the triblock polymer:

[0069] 10 parts of polyethylene glycol monomethyl ether methacrylate with an average molecular weight of about 1000, 0.1 part of 4-cyano-4-(phenylthiocarbamoylthio)valeric acid, and 0.03 part of azobisisobutyronitrile were dispersed in 80 parts of N,N-dimethylformamide, transferred into a reactor with a condensing reflux device, and reacted at 70°C in an oil bath for 6 h under a nitrogen atmosphere to obtain a first mixed solution;

[0070] After cooling to room temperature, 2 parts of 2-hydroxyethyl methacrylate phosphate and 0.02 parts of azobisisobutyronitrile were continuously added to the reactor, and the reaction was continuously carried out at 70°C in an oil bath for 4 h under a nitrogen atmosphere to obtain a second mixed solution;

[0071] After cooling to room temperature, 6 parts of caprolactone acrylate and 0.02 parts of azobisisobutyronitrile were continuously added to the reactor, and the reaction was continuously carried out at 70°C in an oil bath for 5 h under a nitrogen atmosphere. After the reaction was completed, the reaction solution was poured into excess cold ether for precipitation, and then filtered and dried to obtain the triblock polymer A.

[0072] Preparation Example 2

[0073] Preparation of the triblock polymer:

[0074] 10 parts of polyethylene glycol monomethyl ether methacrylate with an average molecular weight of about 1000, 0.1 part of 4-cyano-4-(phenylthiocarbamoylthio)valeric acid, and 0.03 part of azobisisobutyronitrile were dispersed in 80 parts of N,N-dimethylformamide, transferred into a reactor with a condensing reflux device, and reacted at 70°C in an oil bath for 6 h under a nitrogen atmosphere to obtain a first mixed solution;

[0075] After cooling to room temperature, 6 parts of caprolactone acrylate and 0.02 parts of azobisisobutyronitrile were continuously added to the reactor, and the reaction was continuously carried out at 70°C in an oil bath for 5 h under a nitrogen atmosphere to obtain a second mixed solution;

[0076] After cooling to room temperature, 2 parts of 2-hydroxyethyl methacrylate phosphate ester and 0.02 parts of azobisisobutyronitrile were continuously added to the reactor, and the reaction was continuously carried out under a nitrogen atmosphere at 70°C in an oil bath for 4 h. After the reaction was completed, the reaction solution was poured into an excess of cold diethyl ether to precipitate, and then filtered and dried to obtain the triblock polymer B.

[0077] Preparation Example 3

[0078] Preparation of the triblock polymer:

[0079] The same as Preparation Example 1, except that polyethylene glycol monomethyl ether methacrylate having a number average molecular weight of about 500 was used instead of polyethylene glycol monomethyl ether methacrylate having a number average molecular weight of about 1000, to obtain the triblock polymer C.

[0080] Preparation Example 4

[0081] Preparation of the triblock polymer:

[0082] The same as Preparation Example 1, except that polyethylene glycol monomethyl ether methacrylate having a number average molecular weight of about 1500 was used instead of polyethylene glycol monomethyl ether methacrylate having a number average molecular weight of about 1000, to obtain the triblock polymer D.

[0083] Preparation Example 5

[0084] Preparation of the triblock polymer:

[0085] The same as Preparation Example 1, except that vinyl phosphate ester was used instead of 2-hydroxyethyl methacrylate phosphate ester, to obtain the triblock polymer E.

[0086] Preparation Example 6

[0087] Preparation of the triblock polymer:

[0088] The same as Preparation Example 1, except that hexyl methacrylate was used instead of caprolactone acrylate, to obtain the triblock polymer F.

[0089] Comparative Preparation Example 1

[0090] Preparation of the triblock polymer:

[0091] 6 parts of caprolactone acrylate, 0.1 parts of 4-cyano-4-(phenylthiocarbamothioyl) valeric acid and 0.02 parts of azobisisobutyronitrile were dispersed in 80 parts of N,N-dimethylformamide, and transferred into a reactor with a condenser reflux device, and the reaction was carried out under a nitrogen atmosphere at 70°C in an oil bath for 5 h to obtain a first mixed solution;

[0092] After cooling to room temperature, 10 parts of polyethylene glycol monomethyl ether methacrylate with an average molecular weight of about 1000, 0.03 parts of azobisisobutyronitrile were continuously added to the reactor, and the reaction was continued under a nitrogen atmosphere at 70°C in an oil bath for 6h to obtain a second mixed solution;

[0093] After cooling to room temperature, 2 parts of 2-hydroxyethyl methacrylate phosphate and 0.02 parts of azobisisobutyronitrile were continuously added to the reactor, and the reaction was continued under a nitrogen atmosphere at 70°C in an oil bath for 4h. After the reaction was completed, the reaction solution was poured into excess cold ether to precipitate, and was filtered and dried to obtain a triblock polymer G.

[0094] Comparative Preparation Example 2

[0095] Preparation of a random copolymer:

[0096] 10 parts of polyethylene glycol monomethyl ether methacrylate with an average molecular weight of about 1000, 2 parts of 2-hydroxyethyl methacrylate phosphate, 6 parts of caprolactone acrylate, 0.1 parts of 4-cyano-4-(phenylthiocarbamothioyl) valeric acid, and 0.07 parts of azobisisobutyronitrile were dispersed in 80 parts of N,N-dimethylformamide, transferred into a reactor with a condensation reflux device, and reacted under a nitrogen atmosphere at 70°C in an oil bath for 12h. The reaction solution was poured into excess cold ether to precipitate, and was filtered and dried to obtain a random copolymer.

[0097] Example 1

[0098] Preparation of a low-temperature concrete retarding agent:

[0099] The triblock polymer A was added to deionized water to control the solid content to 10wt%, and was stirred and dissolved to obtain a low-temperature concrete retarding agent.

[0100] Example 2

[0101] Preparation of a low-temperature concrete retarding agent:

[0102] The triblock polymer B was added to deionized water to control the solid content to 10wt%, and was stirred and dissolved to obtain a low-temperature concrete retarding agent.

[0103] Example 3

[0104] Preparation of a low-temperature concrete retarding agent:

[0105] The triblock polymer C was added to deionized water to control the solid content to 10wt%, and was stirred and dissolved to obtain a low-temperature concrete retarding agent.

[0106] Example 4

[0107] Preparation of a low-temperature concrete retarding agent:

[0108] The triblock polymer D was added to deionized water to control the solid content to 10wt%, and stirred and dissolved to obtain a low-temperature concrete slump retaining agent.

[0109] Example 5

[0110] Preparation of a low-temperature concrete slump retaining agent:

[0111] The triblock polymer E was added to deionized water to control the solid content to 10wt%, and stirred and dissolved to obtain a low-temperature concrete slump retaining agent.

[0112] Example 6

[0113] Preparation of a low-temperature concrete slump retaining agent:

[0114] The triblock polymer F was added to deionized water to control the solid content to 10wt%, and stirred and dissolved to obtain a low-temperature concrete slump retaining agent.

[0115] Comparative Example 1

[0116] Preparation of a low-temperature concrete slump retaining agent:

[0117] The triblock polymer G was added to deionized water to control the solid content to 10wt%, and stirred and dissolved to obtain a low-temperature concrete slump retaining agent.

[0118] Comparative Example 2

[0119] Preparation of a low-temperature concrete slump retaining agent:

[0120] The random copolymer was added to deionized water to control the solid content to 10wt%, and stirred and dissolved to obtain a low-temperature concrete slump retaining agent.

[0121] Test section:

[0122] Concrete ratio to be tested: 360kg / m 3 P.O42.5 ordinary portland cement; 688kg / m 3 River sand; 1152kg / m 3 5~20mm continuous particle size gravel; 1162kg / m 3 Tap water; 0.15wt% of polycarboxylic acid water reducing agent corresponding to the mass of cement; 0.2wt% of low-temperature concrete slump retaining agent to be tested corresponding to the mass of cement.

[0123] After the concrete was mixed according to the above ratio at an ambient temperature of 8±2℃, the initial slump H0(mm) of the concrete mixture to be tested at 8±2℃ was tested according to the standard GB / T 50080-2016 Performance Test Methods for Ordinary Concrete Mixtures, and the 90min concrete slump H 90 (mm) and the 90min concrete slump loss ΔH(mm)=H0-H90 The results are shown in Table 1.

[0124] (The concrete mixture is covered with a heat-insulating cover during standing to prevent evaporation of water.)

[0125]

[0126] According to Table 1, each of the examples is better than Comparative Examples 1 and 2, indicating that the triblock polymer provided in the application has better concrete slump retention capability in a low-temperature environment; the possible reason is that in Comparative Example 1, the synthesis order of the triblock polymer is changed, the phosphate segment is exposed to the surface of the cement particles in advance, competes with the polycarboxylic acid water reducer for adsorption, resulting in a decrease in the initial slump of the concrete and an insufficient slump retention period; in Comparative Example 2, the slump retaining agent is a random copolymer, which lacks the ability of limited distribution and controlled release of functional segments, resulting in strong adsorption of the slump retaining agent with cement at the initial mixing stage, which seriously interferes with the dispersibility of the system, causing obvious loss of fluidity.

[0127] According to Examples 1 and 2, changing the position of the phosphate segment and the polyester segment will affect the slump retaining effect; in Example 1, the phosphate segment is located in the middle position, the limiting effect is better, and the anchoring release is more time-effective, and the slump loss ΔH is 32 mm, which is better than 38 mm of Example 2, indicating that the phosphate segment located between the hydrophilic segment and the hydrophobic segment is more conducive to the function distribution regulation and the delayed release of the slump retaining effect.

[0128] According to Examples 1, 3 and 4, the number average molecular weight of the polyether segment has a significant influence on the slump retaining performance. In Example 1, the number average molecular weight is about 1000, the slump retaining effect is best; when Mn is 500 (Example 3), the segment is too short, the micelle shell protection is insufficient, ΔH rises to 61 mm; when Mn is 1500 (Example 4), the segment may be too long due to the flexibility, causing entanglement or crystallization, affecting the dispersibility, and ΔH is 53 mm. It is indicated that the molecular weight of the polyether segment controlled between 800-1200 is more conducive to low-temperature dissolution, micelle stability and control of the action window of the slump retaining agent.

[0129] According to Examples 1 and 5, the structure of the phosphate monomer has a great influence on the slump retaining performance. In Example 1, 2-hydroxyethyl methacrylate phosphate is used, which has a flexible side chain and controllable polymerization position, which is conducive to block polymerization and limited structure construction; while in Example 5, vinyl phosphate is used, which has poor polymerization activity and strong structure rigidity, resulting in uneven distribution of the phosphate segment and uncontrolled release, ΔH rises to 67 mm, indicating that the use of a flexible and highly reactive phosphate monomer is more conducive to enhancing the controlled release ability and low-temperature slump retaining stability.

[0130] According to Examples 1 and 6, the structure type of the hydrophobic segment can significantly affect the micelle stability and dynamic release capacity. In Example 1, caprolactone acrylate is used as the hydrophobic monomer, the segment is flexible and has moderate structure polarity, which is conducive to the construction of a dynamically responsive micelle core and the formation of a new anchor point in an alkaline environment, and the anti-caking performance is better; while in Example 6, hexyl methacrylate is used as the polyester monomer, the segment is rigid and has poor response capacity, and ΔH rises to 65 mm, indicating that the use of flexible polyester segments with late response capacity can improve the late adsorption capacity and stabilize the low-temperature anti-caking effect.

[0131] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A cold weather resistant concrete slump retaining agent, characterized by, The tri-block polymer comprises a polyunsaturated polyether segment, a polyunsaturated phosphate segment and a polyunsaturated ester segment; The tri-block polymer is prepared by the following steps: S1: polymerization of an unsaturated polyether monomer and a RAFT agent under the action of an initiator to obtain a polyunsaturated polyether containing a RAFT site; the unsaturated polyether monomer is polyethylene glycol monomethyl ether methacrylate, and the number average molecular weight of the polyethylene glycol monomethyl ether methacrylate is 800-1200; S2: polymerization of the polyunsaturated polyether containing a RAFT site in step S1 and an unsaturated phosphate monomer under the action of an initiator to obtain a polyunsaturated polyether-b-polyunsaturated phosphate containing a RAFT site; the unsaturated phosphate monomer is 2-hydroxyethyl methacrylate phosphate; S3: polymerization of the polyunsaturated polyether-b-polyunsaturated phosphate containing a RAFT site in step S2 and an unsaturated ester monomer under the action of an initiator to obtain the tri-block polymer; the unsaturated ester monomer is caprolactone acrylate.

2. The cold resistant concrete slump retaining agent according to claim 1, characterized in that, The tri-block polymer is prepared by the following steps: S1: dispersing 10 parts of an unsaturated polyether monomer, 0.05-0.2 parts of 4-cyano-4-(phenylthiocarbamothioyl) valeric acid and 0.01-0.05 parts of azobisisobutyronitrile in 50-100 parts of N,N-dimethylformamide, and reacting at 60-80°C for 5-7h under a nitrogen atmosphere to obtain a first mixed solution; S2: adding 1-3 parts of an unsaturated phosphate monomer and 0.01-0.05 parts of azobisisobutyronitrile to the first mixed solution, and reacting at 60-80°C for 3-5h under a nitrogen atmosphere to obtain a second mixed solution; S3: adding 5-7 parts of an unsaturated ester monomer and 0.01-0.05 parts of azobisisobutyronitrile to the second mixed solution, and reacting at 60-80°C for 4-6h under a nitrogen atmosphere to obtain the tri-block polymer.

3. The cold-resistant concrete slump retaining agent according to claim 1 or 2, characterized in that, Water is further included, and the solid content of the low-temperature-resistant concrete slump retaining agent is 1%-20%.

4. A process for the preparation of a cold weather resistant concrete slump retaining agent, characterized by, It comprises: providing the tri-block polymer in the low-temperature-resistant concrete slump retaining agent according to any one of claims 1-3; dispersing the tri-block polymer in water to obtain a low-temperature-resistant concrete slump retaining agent.

5. A cold-resistant concrete, characterized by, It comprises the low-temperature-resistant concrete slump retaining agent according to any one of claims 1-3 or prepared by the method according to claim 4.

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