Water-retention and air-entraining admixture as well as preparation method and application thereof

Abstract

The invention discloses a water-retaining and air-entraining admixture and a preparation method and application thereof, and the water-retaining and air-entraining admixture comprises the following raw materials by mass: 18-22% of hydroxypropyl methyl cellulose; 12-15% of modified starch ether; 6-8% of an air entraining agent; 4-6% of a water reducing agent; 3-5% of a retarder; 2-3% of a reinforcing component; and the balance of fly ash microspheres. The admixture disclosed by the invention can simultaneously meet the key requirements of good water-retaining property, no bleeding, proper air entraining amount, good mortar flowability, enhancement effect and the like. Particularly, the contradiction between water retention and fluidity, the contradiction between air entraining and strength and the compatibility problem of solid waste materials and additives in the prior art need to be solved. Through innovative component design and preparation process, the synergistic effect of all functional components is realized, so that the technical progress and engineering application of the low-carbon dry-mixed mortar are promoted.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a water-retaining and air-entraining admixture and its preparation method. Background Technology

[0002] In the field of modern construction engineering, with the growing acceptance of sustainable development concepts, building materials are undergoing a transformation from traditional high-energy-consuming models to green and low-carbon ones. As one of the most widely used basic materials in construction engineering, mortar performance optimization has become a focus of industry attention, and the addition of admixtures has become an important means of improving its performance. Among these, composite materials with both water retention and air-entraining functions are gradually becoming a research hotspot. These materials can not only delay water evaporation and enhance slurry stability, but also improve freeze-thaw resistance and pumpability by introducing microbubbles. However, existing products generally suffer from insufficient synergy among functional components, and physicochemical conflicts between different components often lead to performance degradation. Especially in solid waste-based mortar systems, how to balance reinforcement effects and environmental friendliness remains a technical bottleneck that urgently needs to be overcome.

[0003] Currently available commercially available water-retaining and air-entraining admixtures mostly rely on single polymers or simple compound systems. The compatibility issues of various functional components are particularly prominent. For example, while cellulose derivatives can effectively lock in free water, their high viscosity makes stirring difficult, and they pose compatibility risks with modified starch ethers, easily leading to stratification and water separation during long-term storage. Chemical air-entraining components are prone to decomposition and inactivation in alkaline environments. Improper compounding with water-reducing agents may trigger intermolecular association, thus reducing water-reducing efficiency. The selection of retarding components requires even greater caution; excessive addition, while extending the working time, may result in a loose structure in the hardened mortar, severely restricting the later mechanical properties of the mortar. More critically, traditional admixtures often use silica fume or slag powder as carrier materials, which not only consumes large amounts of resources but also hinders the dispersion of active ingredients due to their surface inertness, restricting the efficient recycling of industrial solid waste. Summary of the Invention

[0004] The main objective of this invention is to provide a water-retaining and air-entraining admixture, its preparation method, and its application, aiming to solve the contradictions between water retention and flowability, air entrainment and strength in existing admixtures, as well as the compatibility issues between solid waste materials and admixtures.

[0005] To achieve the above objectives, the present invention provides a water-retaining and air-entraining admixture, wherein the raw materials comprise, by mass percentage:

[0006] Hydroxypropyl methylcellulose: 18–22%;

[0007] Modified starch ether: 12-15%;

[0008] Air-entraining agent: 6-8%;

[0009] Water-reducing agent: 4-6%;

[0010] Retarder: 3-5%;

[0011] Reinforcing component: 2-3%;

[0012] Carrier material: Balance;

[0013] The carrier material is fly ash microspheres.

[0014] Furthermore, the air-entraining agent is composed of sodium dodecyl sulfate and silicone polyether, with a mass ratio of sodium dodecyl sulfate to silicone polyether of 7:3.

[0015] Furthermore, the water-reducing agent is a polycarboxylate water-reducing agent;

[0016] Furthermore, the retarder is sodium gluconate.

[0017] Furthermore, the reinforcing component is nano-SiO2 or metakaolin.

[0018] The present invention also provides a method for preparing the above-mentioned water-retaining and air-entraining admixture, comprising the following steps:

[0019] S1: The reinforcing component and hydroxypropyl methylcellulose are put into a three-dimensional mixer and mixed under nitrogen protection to obtain the activated reinforcing component / hydroxypropyl methylcellulose complex.

[0020] S2: Add the modified starch ether into the mixing tank, add water-reducing agent and retarder under nitrogen protection and mix at low speed to obtain the initial mixture. Then spray the air-entraining agent into the initial mixture for shearing treatment. Finally, add the activated reinforcing component / hydroxypropyl methylcellulose complex in three batches and mix to obtain the final mixture.

[0021] S3: Crush the final mixture, then add fly ash microspheres, mix evenly, and finally adjust the pH to 8.5-9.0 with sodium bicarbonate solution.

[0022] Furthermore, in step S1, the rotation speed of the three-dimensional mixer for the mixing process is 200 rpm, and the time is 15 min.

[0023] Further, in step S2, the low-speed mixing treatment is performed at a speed of 120 rpm for 15 min; the shearing treatment is performed at a speed of 800 rpm for 5 min; after each addition of the reinforcing component / hydroxypropyl methylcellulose complex, the mixture is allowed to stand for 3 min, and then mixed at a speed of 150 rpm for 5 min.

[0024] Furthermore, in step S3, the pulverization process is carried out using an air jet mill, with a pulverization pressure of 0.8 MPa, a temperature of <45℃, and pulverization to a particle size of ≤50 μm.

[0025] The present invention also provides an application of the above-mentioned water-retaining and air-entraining admixture in the preparation of solid waste-based dry powder mortar.

[0026] The design principle of the additive formulation of this invention is as follows:

[0027] I. Synergistic Water Retention and Viscosity Optimization of Hydroxypropyl Methylcellulose and Modified Starch Ethers

[0028] The water-retention mechanism of hydroxypropyl methylcellulose (HPMC) involves the formation of hydrogen bonds between the hydroxyl and ether bonds on the HPMC molecular chain and water molecules, constructing a three-dimensional network structure. The degree of substitution of its methoxy and hydroxypropoxy groups controls the dissolution rate, forming a capillary network in the mortar and locking in free water through surface tension. Synergistically with modified starch ethers, the water retention rate is further enhanced.

[0029] By utilizing the thixotropic effect of modified starch ethers, the carboxymethyl (DS = 0.05-0.08) and hydroxypropyl (DS = 0.15-0.20) groups introduced through etherification modification charge and extend the starch molecular chains. Upon standing, these chains form a network through hydrogen bonding, which breaks under shearing. The synergistic effect with HPMC increases the thixotropic index of the mortar.

[0030] Hydroxypropyl methylcellulose (HPMC) and modified starch ether form a composite water-retaining network that combines rigidity and flexibility. The three-dimensional rigid framework of HPMC (methoxy DS = 1.8-2.0) provides a stable capillary water-locking structure, while the flexible branches of the modified starch ether (carboxymethyl DS = 0.05-0.08) endow the system with excellent thixotropy. The synergistic effect of both improves the water retention rate and optimizes the static / dynamic viscosity ratio, resolving the contradiction between water retention and workability.

[0031] II. Sodium dodecyl sulfate and silicone polyether composite air entrainment

[0032] Sodium dodecyl sulfate (SDS) reduces surface tension; the polysiloxane chains of silicone polyether self-assemble at the gas-liquid interface to form a composite film; SDS and silicone polyether are combined in a 7:3 ratio to construct a "foaming-stabilizing" system. SDS rapidly reduces surface tension to generate microbubbles (Φ50-100μm), and the polysiloxane chains of silicone polyether then self-assemble at the bubble interface to form a composite film with an elastic modulus >50MPa. This synergy extends the bubble half-life and stabilizes the gas content at 17.5±0.5%.

[0033] III. Synergistic Effects of Other Raw Materials

[0034] The -SO3H groups of APEG-type polycarboxylate superplasticizer can react with the Al groups on the surface of fly ash microspheres.3+ Coordination bonds are formed, and steric hindrance reduces the Zeta potential. Synergistic effects with HPMC can reduce adsorption losses of the water-reducing agent. Furthermore, the -SO3H groups of the polycarboxylate water-reducing agent and the -COO- groups of the retarder sodium gluconate form a dynamic equilibrium system. The water-reducing agent preferentially adsorbs onto the surface of solid waste particles, while the retarder selectively chelates Al in the liquid phase. 3+ The synergy of these two methods can effectively reduce the fluidity loss rate.

[0035] Under the guidance of the HPMC network, the reinforcing component nano-SiO2 can be selectively enriched at the bubble-slurry interface. Its dual effects are: nano-SiO2 can effectively fill 100-200 nm interfacial pores, increasing bubble wall thickness; and it achieves an ultra-high specific surface area (200 nm). 2 / g) promotes CSH gel nucleation in the interfacial region, resulting in an increase in the strength of the air-entrained mortar after 28 days instead of a decrease.

[0036] Fly ash microspheres, acting as a carrier, possess a porous structure that can adsorb liquid components to form microcapsules. This design improves the stability of active components such as air-entraining agents by three times in the dry powder state, while also enabling rapid release upon contact with water.

[0037] The beneficial effects of this invention are reflected in:

[0038] The admixture of this invention should simultaneously meet key requirements such as good water retention, no bleeding, appropriate air entrainment, good mortar fluidity, and reinforcing effect. In particular, it is necessary to resolve the contradictions between water retention and fluidity, air entrainment and strength in existing technologies, as well as the compatibility issues between solid waste materials and admixtures. Through innovative component design and preparation processes, the synergistic effect of each functional component is achieved, thereby promoting the technological advancement and engineering application of low-carbon dry powder mortar.

[0039] The water-retaining and air-entraining admixture provided by this invention exhibits superior comprehensive performance in low-carbon dry powder mortar. Through the synergistic effect among its components, it effectively solves the technical challenge of traditional admixtures in simultaneously achieving good water retention, air-entraining stability, and mechanical properties. This admixture employs a unique formulation design and preparation process, significantly improving both the workability and durability of the mortar, providing reliable technical support for the widespread application of solid waste-based low-carbon mortar.

[0040] In terms of water retention and workability, this invention utilizes the synergistic effect of hydroxypropyl methylcellulose and modified starch ether to construct a stable three-dimensional water-retaining network structure. This system effectively locks in moisture, significantly improving the problem of excessive water absorption in solid waste-based materials and ensuring full hydration of the cementitious materials. Simultaneously, the precise formulation of the composite air-entraining agent creates uniformly distributed microbubbles within the mortar, not only improving the workability of the slurry but also avoiding the defects of large bubbles and poor stability caused by traditional air-entraining agents. The rational combination of polycarboxylate superplasticizer and retarder further optimizes the mortar's fluidity and workability, meeting the needs of different construction environments.

[0041] In terms of mechanical properties and durability, the introduction of nano-reinforcing materials brings significant strengthening effects to the system. Nano-silica or metakaolin can effectively fill the micropores in the slurry, improve the structure of the interfacial transition zone, and participate in the secondary hydration reaction, thereby improving the density and later strength of the mortar. Particularly noteworthy is that the admixture of this invention, while introducing an appropriate amount of air bubbles, still maintains excellent mechanical properties, completely changing the traditional perception that air-entraining agents inevitably lead to a decrease in strength. The selection of fly ash microspheres as the carrier material not only realizes the resource utilization of industrial solid waste but also further optimizes the particle size distribution through its micro-aggregate effect.

[0042] In terms of environmental benefits and application prospects, this invention fully embodies the development concept of green building materials. By incorporating a high proportion of industrial solid waste, the environmental burden of building materials is significantly reduced. The synergistic effect of the components in the admixture enables the mortar to achieve low-carbon production while ensuring high performance. This product is suitable for various low-carbon dry powder mortar systems, including masonry, plastering, and flooring applications, and has broad market prospects and promotional value. Detailed Implementation

[0043] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0044] Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art. Wherein:

[0045] Hydroxypropyl methylcellulose, model HPMC F06, viscosity ≥4000 mPa·s, purchased from Shandong Heda Group Co., Ltd.; modified starch ether, model BLS-200, purchased from Jiangsu Boli New Material Technology Co., Ltd.; sodium dodecyl sulfate, model ACS-II, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; silicone polyether, model WAN-820, purchased from Nanjing Weier Chemical Co., Ltd.; polycarboxylate superplasticizer, model PCA-I, purchased from Jiangsu Subote New Material Co., Ltd.; sodium gluconate, model Gluconic Acid Sodium Salt 99%, purchased from Shandong Lemon Biochemical Co., Ltd.; nano SiO2, model AEROXIDE Alu C, specific surface area ≥200 m² / g. 2 / g, purchased from Jiangsu Tianxing New Material Technology Co., Ltd.; metakaolin, model KM-80, whiteness ≥90%, active alumina content ≥35%, specific surface area ≥15m². 2 / g, purchased from Shanxi Jinyu Kelin Technology Co., Ltd.; fly ash microspheres, model FAC-200, bulk density ≤0.3g / cm³ 3 The average particle size is ≤50μm, and it was purchased from Shandong Yankuang Group Lantian Clean Energy Co., Ltd.

[0046] Three-dimensional mixer, model CH-500, Changzhou Yibu Drying Equipment Co., Ltd.; Stainless steel reactor, model RJF-1000L, Wuxi Chemical Equipment Co., Ltd.; Four-blade paddle agitator, model ZJ-400, Jiangyin Changjing Chemical Machinery Co., Ltd.; Double cone vacuum mixer, model SZH-2000, Changzhou Lima Drying Equipment Co., Ltd.; High-speed shear machine, model SJ-1500, Shanghai Weiyu Machinery Manufacturing Co., Ltd.; Mixing vessel, model HJ-5000L, Zhangjiagang Jinling Machinery Manufacturing Co., Ltd.; Pressure spray system, model YPG-500, nozzle orifice diameter 0.5-1.2mm, Changzhou Yibu Drying Equipment Co., Ltd.; Airflow pulverizer, model QYF-400, Jiangsu Miyou Powder New Technology Co., Ltd.; Rotary homogenizing silo, model RH-3000, Jiangyin Jingliang Machinery Co., Ltd.

[0047] Example 1

[0048] Preparation of water-retaining and air-entraining admixtures

[0049] (1) Pretreatment of nanomaterials:

[0050] 5 kg of hydroxypropyl methylcellulose and 2.5 kg of nano-SiO2 were added to a three-dimensional mixer and mixed at 200 rpm for 15 minutes under nitrogen protection (flow rate 2 L / min) to obtain a nano-SiO2 / hydroxypropyl methylcellulose composite. The temperature was monitored in real time during mixing (controlled to ≤35℃) to ensure that the nanoparticles were uniformly dispersed in the hydroxypropyl methylcellulose matrix to form the composite. After mixing, samples were taken for testing, requiring particle agglomerate size ≤100 nm and moisture content ≤0.5%.

[0051] (2) Preparation of composite air-entraining agent:

[0052] 4.9 kg of sodium dodecyl sulfate and 2.1 kg of silicone polyether were added to a stainless steel reactor. A four-bladed paddle stirrer was started and stirred at 400 rpm for 20 minutes. During the stirring process, a constant temperature water bath system was turned on to maintain the temperature at 50°C until a homogeneous and transparent solution was formed, thus obtaining the composite air-entraining agent.

[0053] (3) Preparation of initial mixture:

[0054] 13 kg of modified starch ether, 5 kg of polycarboxylate superplasticizer, and 4 kg of sodium gluconate were sequentially added to a 500 L mixing vessel and mixed at low speed. The mixing parameters were set as follows: rotation speed 120 rpm, vacuum degree -0.08 MPa, and mixing time 15 minutes to obtain the initial mixture. Samples were taken every 3 minutes during the mixing process to check the uniformity, requiring the content deviation of each component to be ≤2%.

[0055] (4) Liquid-phase spray activation:

[0056] 7 kg of composite air-entraining agent was evenly sprayed into the primary mixture through a pressure spraying system (nozzle diameter 0.3 mm, spraying pressure 0.4 MPa). The spraying time was controlled at 10 minutes and the material temperature was ≤40℃. During the spraying process, a high-speed shearing machine was turned on simultaneously. After the spraying was completed, the material was sheared at 800 rpm for 5 minutes to ensure complete adsorption of the liquid and obtain the intermediate mixture.

[0057] (5) Introduction of nanocomposites:

[0058] The intermediate mixture was fed into a high-speed shear press, and then the nano-SiO2 / hydroxypropyl methylcellulose composite was added in three batches: the first batch of 30% was added, allowed to stand for 3 minutes, and then mixed at 150 rpm for 5 minutes; the second batch of 40% was added, and the mixture was allowed to stand and mix under the same conditions; finally, the remaining 30% was added, and the mixture was allowed to stand and mix under the same conditions. The dispersion was checked after each addition, and the nanoparticles were required to be uniformly distributed to obtain the final mixture.

[0059] (6) Micronization treatment:

[0060] The final mixture was pulverized using a fluidized bed jet mill to obtain pulverized material. The pulverization parameters were set as follows: compressed air pressure 0.8 MPa, classifier speed 4500 rpm, feed rate 25 kg / min, and discharge temperature 44℃. The particle size requirements for the pulverized material were: D10 = 8-10 μm, D50 = 20-25 μm, and D90 ≤ 45 μm.

[0061] (7) Performance tuning:

[0062] The pulverized material and 48.5 kg of fly ash microspheres were added to a rotary homogenizing silo and mixed at 5 rpm for 30 minutes. The pH was then adjusted to 8.8 with a 5% sodium bicarbonate solution. Finally, the mixture was aged for 24 hours under nitrogen protection, with the ambient temperature controlled at 20 ± 2℃ and the relative humidity ≤ 40%.

[0063] Example 2

[0064] Preparation of water-retaining and air-entraining admixtures

[0065] The preparation method of this embodiment is the same as that of Example 1, except that the raw material amounts are adjusted as follows: 18 kg of hydroxypropyl methylcellulose; 15 kg of modified starch ether; 8 kg of composite air-entraining agent; 6 kg of polycarboxylate superplasticizer; 3 kg of sodium gluconate; 3 kg of nano-SiO2; and 47 kg of fly ash microspheres.

[0066] Example 3

[0067] Preparation of water-retaining and air-entraining admixtures

[0068] The preparation method of this embodiment is the same as that of Example 1, except that the raw material amounts are adjusted as follows: 22 kg of hydroxypropyl methylcellulose; 12 kg of modified starch ether; 6 kg of composite air-entraining agent; 4 kg of polycarboxylate superplasticizer; 5 kg of sodium gluconate; 2 kg of nano-SiO2; and 49 kg of fly ash microspheres.

[0069] Comparative Example 1

[0070] Comparison of the preparation of water-retaining and air-entraining admixtures

[0071] The preparation method of this comparative example is the same as that of Example 1, except that the composite air-entraining agent is replaced with a single air-entraining agent containing only 7 kg of sodium dodecyl sulfate.

[0072] Comparative Example 2

[0073] Comparison of the preparation of water-retaining and air-entraining admixtures

[0074] The preparation method of this comparative example is the same as that of Example 1, except that the addition of nano-SiO2 is omitted and the amount of fly ash microspheres is increased to 51 kg.

[0075] Comparative Example 3

[0076] Comparison of the preparation of water-retaining and air-entraining admixtures

[0077] The preparation method of this comparative example is the same as that of Example 1, except that the composite air-entraining agent is not added through a pressure spray system, but is directly poured into the dry mix.

[0078] Comparative Example 4

[0079] Comparison of the preparation of water-retaining and air-entraining admixtures

[0080] The preparation method of this comparative example is the same as that of Example 1, except that the addition of hydroxypropyl methylcellulose is omitted.

[0081] Comparative Example 5

[0082] Comparison of the preparation of water-retaining and air-entraining admixtures

[0083] The preparation method of this comparative example is the same as that of Example 1, except that the addition of modified starch ether is omitted.

[0084] Comparative Example 6

[0085] Comparison of the preparation of water-retaining and air-entraining admixtures

[0086] The preparation method of this comparative example is the same as that of Example 1, except that the carrier material is replaced by slag powder instead of fly ash microspheres.

[0087] Comparative Example 7

[0088] Comparison of the preparation of water-retaining and air-entraining admixtures

[0089] The preparation method of this comparative example is the same as that of Example 1, except that the retarder is replaced by white sugar instead of sodium gluconate.

[0090] Comparative Example 8

[0091] Comparison of the preparation of water-retaining and air-entraining admixtures

[0092] The preparation method of this comparative example is the same as that of Example 1, except that the reinforcing component is replaced by silica fume instead of nano-SiO2.

[0093] Comparative Example 9

[0094] Comparison of the preparation of water-retaining and air-entraining admixtures

[0095] The preparation method of this comparative example is the same as that of Example 1, except that the nano-SiO2 / hydroxypropyl methylcellulose composite is added to the high-speed shear machine in one go (without adding it in three parts and allowing it to stand).

[0096] Performance testing

[0097] The water-retaining and air-entraining admixtures prepared in the above embodiments and comparative examples were subjected to performance tests according to the following methods:

[0098] Solid waste-based dry mortar mix proportion: Using typical solid waste-based dry mortar as the carrier, the benchmark mix proportion (mass percentage) is: cement (P·O 42.5, specific surface area 350m²) 2 40% ( / kg), 30% fly ash (Grade II, water requirement 102%, 45μm sieve residue 18%), and 30% slag powder (Grade S95, specific surface area 420m²). 2 / kg, fluidity ratio 98%) 30%, aggregate (natural sand, fineness modulus 2.5, mud content 2.8%, MB value 1.2) filled to 100% volume; admixture (example / comparative product) dosage is 2% of the total mass of dry powder mortar.

[0099] Water retention rate test: An electronic balance (accuracy 0.01g), a stainless steel circular mold (diameter 50mm±0.5mm, height 100mm±0.5mm, wall thickness ≥2mm), plastic wrap (thickness ≤0.05mm, airtight), and a standard curing room (temperature 20±2℃, relative humidity ≥90%) are required. During operation, first weigh 5kg of dry materials (cement, fly ash, slag, sand) according to the proportion, pour it into a forced mixer, mix at low speed for 30 seconds until uniform, then add the admixture (2% of the total dry material mass), mix at low speed for 1 minute, and then mix at high speed for 2 minutes until uniform. Pour the mixed mortar into the circular mold at once, smooth the surface with a trowel, ensuring the mortar is flush with the mold opening to avoid overflow. Immediately cover the surface of the circular mold tightly with plastic wrap (no wrinkles, no air leakage), let it stand for 10 minutes, and then mark the initial height line on the edge of the circular mold (10mm from the bottom of the mold). 0mm); Place the round mold horizontally on the cement mortar test block curing rack in the standard curing room (with 3mm thick filter paper at the bottom, the filter paper should be pre-soaked in water until saturated but not dripping), and let it stand for 24h±2h; After 24h, take out the round mold and weigh the total mass (m1) of the round mold + the remaining mortar using an electronic balance. Then transfer the remaining mortar in the round mold to a weighing bottle that has been constant in weight and weigh its mass (m2); Calculate the water retention rate: Water retention rate (%) = m2 / (m1-round mold mass)×100% (Note: m1-round mold mass is the initial total mass of mortar).

[0100] Gas content test: A gas content analyzer (model: HC-7L, volume 1L, accuracy ±0.1%), a vibration table (frequency 50Hz, amplitude 0.5mm) and an electronic balance (accuracy 0.01g) are required. During operation, take approximately 5L (accurate to 5000g) of representative mortar mixture and pour it into the container of the air content analyzer. Smooth the surface with a scraper to ensure the mortar is flush with the top of the container. Install the sealing cap of the analyzer and check that the sealing ring is intact to ensure there is no air leakage. Turn on the vibration table, fix the container on the vibration table, and stop vibrating immediately after 15s. Wipe away any mortar residue around the sealing cap, install an air pump on the pressure gauge, and slowly inflate until the pressure gauge pointer stabilizes (approximately 30s). Record the initial pressure value (P0). Open the operating valve to drain the bleed water from the mortar. After the pressure gauge pointer stabilizes, read the final pressure value (P) (Note: The venting process should be slow to avoid mortar splashing). Air content (%) = (P-P0) / 0.1×0.2+0.1 (look up the value directly in the table after calibration).

[0101] Construction performance testing includes consistency and segregation tests. Consistency testing requires a mortar consistency meter (conical top diameter 100mm ± 0.5mm, bottom diameter 70mm ± 0.5mm, height 60mm ± 0.5mm, mass 300g ± 2g), a tamping rod (diameter 10mm, length 350mm, hemispherical end), and an electronic stopwatch (accuracy 0.1s). During operation, place the conical cylinder on the consistency meter base and secure it firmly. Use the tamping rod to fill the conical cylinder in two batches (each time to 1 / 2 height). After each filling, use the tamping rod to evenly tamp the mortar 25 times in a spiral direction from the outside to the inside (tamping depth to the bottom of the cylinder). After tamping, use a scraper to smooth the surface and remove excess mortar. Press the release button on the consistency meter to allow the conical cylinder to fall freely. Record the depth (mm) of the mortar cone's sinking within 30 seconds; this is the mortar consistency value (take the average of two tests, error ≤ 1mm). The segregation test requires a segregation cylinder (upper diameter 150mm ± 1mm, lower diameter 100mm ± 1mm, height 300mm ± 2mm, wall thickness ≥ 2mm) and an electronic balance (accuracy 0.01g). During operation, the mixed mortar is poured into the segregation cylinder all at once and tamped 25 times with a tamping rod until the surface is smooth. After standing for 30min ± 2min, the top 2 / 3 of the mortar (approximately 200g) is carefully scraped off with a scraper and its mass (m³) is measured. The remaining 1 / 3 of the mortar (approximately 100g) is mixed evenly with the newly taken 200g of untested mortar, and poured back into the segregation cylinder. The consistency (h2) is measured according to the consistency test method described above. The initial consistency is h1 (i.e., the settling depth in the first test step). Segregation (mm) = |h1 - h2| (Note: If the segregation > 20mm, it indicates that the mortar is prone to bleeding and segregation).

[0102] Mechanical property testing (compressive strength): A planetary cement mortar mixer (model: JJ-5), 40mm×40mm×160mm molds (accuracy ±0.1mm), a pressure testing machine (model: NYL-300, accuracy ±1%), and a standard curing chamber (temperature 20±1℃, relative humidity ≥95%, curing conditions: specimen surface covered with a thin film, demolded after 7 days) are required. During operation, weigh 4kg of dry material according to the proportion (corresponding to 6 specimens per group, each specimen with approximately 667g of dry material), add the admixture (2% of the total dry material mass), and mix at low speed for 30s with the planetary mixer, then at high speed for 120s until uniform. The mixed mortar is then poured into the mold in two layers (approximately 80g per layer). The first layer is filled to half the height of the mold and tamped 15 times with a tamping rod. The second layer is filled completely and tamped 25 times with a tamping rod. Finally, the surface is smoothed with a scraper; after the specimen is formed, it is covered with a film and cured in a standard curing chamber for 24h±2h before demolding, and then cured for 7d and 28d; during testing, the specimen is placed at the center of the lower platen of the compression testing machine and loaded uniformly at a loading rate of 0.6MPa / s until the specimen fails, and the failure load (F) is recorded; compressive strength (MPa) = specimen cross-sectional area F (scaffold cross-sectional area = 40mm × 40mm = 1600mm²) 2 The average value of 6 specimens was taken, with an error ≤ 2MPa.

[0103] Durability testing includes freeze-thaw cycle testing and drying shrinkage testing. Freeze-thaw cycle testing requires a rapid freeze-thaw tester (model: FZ-100, volume: 50L, temperature control accuracy: ±2℃), an electronic balance (accuracy: 0.01g), and a dynamic modulus meter (model: DT-100, frequency range: 10kHz-1MHz). During pre-curing, the molded specimens (40mm×40mm×160mm) were cured in a standard curing chamber for 3 days ± 2 days. After reaching the required curing age, they were removed and the surface was wrapped with a damp cloth to prevent moisture evaporation. During freeze-thaw cycles, the specimens were placed in the specimen box of the freeze-thaw testing machine (the box was filled with deionized water, with the liquid level 2mm above the top surface of the specimen). The freeze-thaw machine was turned on, and the cycle was performed as "freezing for 4 hours (-18℃±2℃) → thawing for 4 hours (room temperature 20℃±2℃)" for a total of 25 cycles. During the mass loss test, after the freeze-thaw cycle, the specimens were removed, the surface moisture was wiped dry with a dry cloth, and their mass (m4) was measured. The mass before freeze-thaw was m5 (the value after pre-curing). The mass loss rate (%) = (m5-m4) / m5×100%. During the relative dynamic modulus test, the resonant frequency (f0) of the specimen was measured using a dynamic modulus meter before freeze-thaw, and the initial dynamic modulus (E0=10) was calculated. 5 ×(L / b) 4 ×1 / (f0×ρ) 2Where L is the specimen length, b is the specimen cross-sectional area, and ρ is the mortar density; after freeze-thaw, the resonant frequency (f1) is tested, and the relative dynamic modulus of elasticity (%) is calculated as E1 / E0 × 100% (E1 is the dynamic modulus of elasticity after freeze-thaw). The drying shrinkage rate test requires a vertical mortar shrinkage meter (model: SS-100, accuracy 0.01mm, measuring range 0-10mm), a standard curing chamber (temperature 20±1℃, relative humidity 60±5%), and an electronic balance (accuracy 0.01g). For initial length measurement, remove the specimen from the curing chamber after 7 days of curing, smooth the surface with sandpaper (to remove laitance), and immediately place it on the measuring frame of the shrinkage meter. After securing it firmly, read the initial length (L0) (Note: The ambient humidity must be ≥90% during measurement to avoid rapid water loss from the specimen). For drying curing, move the specimen to a standard drying environment (temperature 20±2℃, relative humidity 60±5%), avoiding direct sunlight, and dry for 28 days±2 days. For final length measurement, after drying, remove the specimen and read the final length (L0) using the same method. t ); Drying shrinkage rate (×10) -6 )=L0(L0-L t )×10 6 (Take the average value of 3 specimens).

[0104] The performance test results are shown in Table 1 below:

[0105] Table 1: Performance test results of each embodiment and comparative example

[0106]

[0107] As can be seen from Table 1, Examples 1-3 show significant improvement over Comparative Examples 1-9 in resolving the contradictions between water retention and flowability, air entrainment and strength, and the compatibility issues between solid waste materials and additives in existing admixtures.

[0108] Regarding the contradiction between water retention and flowability, Examples 1-3 effectively locked in free water (water retention rate 91.8%-93.1%) by leveraging the synergistic effect of the high viscosity of hydroxypropyl methylcellulose (HPMC) and the steric hindrance of the nano-SiO2 / metakaolin composite, while also maintaining the flowability of the mortar (consistency 83-87 mm, segregation 11-14 mm) by filling the slurry pores with nanoparticles and enhancing interfacial bonding, thus avoiding the problem of bleeding and segregation caused by high water retention. In contrast, Comparative Example 4, which did not contain HPMC, had a water retention rate of only 65.2%, but due to the lack of flocculation structure to inhibit bleeding, its short-term flowability (consistency 82 mm) was acceptable, but it was prone to segregation in the long term. Comparative Example 2 (without nano-SiO2, excessive fly ash microspheres) had a segregation of 25 mm (severe bleeding) and a consistency of only 80 mm (poor flowability) because the fly ash microspheres had a low density and were prone to floating. Neither of these examples solved the problem of balancing water retention and flowability.

[0109] Regarding the conflict between air entrainment and strength, Examples 1-3 employed a composite system of sodium dodecyl sulfate (anionic air entrainer) and silicone polyether (foam stabilizer) to form uniform microbubbles with a diameter ≤200μm (air content 17.9%-18.5%). The bubble film was stable and not easily broken, which both reduced the mortar density and improved pumpability by using bubbles, and buffered shrinkage stress by using bubbles. Combined with nanoparticles filling the pores, the 28-day compressive strength reached 34.5-35.8MPa. In contrast, Comparative Example 1 (single air entrainer) had poor bubble film stability (air content only 15.8%), and the bubbles were prone to merging and breaking to form pores, resulting in a strength of only 28.7MPa. Comparative Example 3 (dry-mixed air entrainer) had uneven dispersion of the air entrainer (air content 14.5%), and the local bubbles were too large, resulting in a weak structure. The 28-day strength was only 26.1MPa. None of these examples achieved a synergistic improvement in air entrainment and strength.

[0110] Regarding the compatibility of solid waste materials and admixtures, Examples 1-3 used highly active fly ash microspheres (smooth surface, low water demand ratio) as carrier materials. These microspheres were polarly matched with admixture components such as HPMC and modified starch ether, allowing the admixtures to be uniformly adsorbed onto the surface of the fly ash microspheres and released slowly, ensuring synergistic effects of functional components (such as water retention by HPMC and foam stabilization by air-entraining agents). However, Comparative Example 6 (non-fly ash carrier) suffered from poor adsorption of admixtures due to the inertness of the carrier surface (such as the high water demand ratio of slag powder), leading to easy agglomeration and failure of functional components, resulting in a significant decrease in performance. Comparative Example 5 (without modified starch ether) suffered from poor compatibility (weak interfacial bonding) between ordinary starch ether and cement, fly ash, and other adhesives, resulting in a loose internal structure of the mortar and a 28-day strength of only 29.4 MPa. None of these examples solved the interfacial compatibility problem between solid waste materials and admixtures.

[0111] In summary, Examples 1-3 systematically solved the three major contradictions in the prior art—water retention and flowability of admixtures, air entrainment and strength, and solid waste materials and admixtures—through component optimization and process synergy, exhibiting superior comprehensive performance (high water retention, good flowability, high strength, and excellent durability).

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-retaining and air-entraining admixture, characterized in that, By weight percentage, its raw materials include: Hydroxypropyl methylcellulose: 18–22%; Modified starch ether: 12-15%; Air-entraining agent: 6-8%; Water-reducing agent: 4-6%; Retarder: 3-5%; Reinforcing component: 2-3%; Carrier material: Balance; The carrier material is fly ash microspheres.

2. The water-retaining and air-entraining admixture as described in claim 1, characterized in that, The air-entraining agent is composed of sodium dodecyl sulfate and silicone polyether, with a mass ratio of sodium dodecyl sulfate to silicone polyether of 7:

3.

3. The water-retaining and air-entraining admixture as described in claim 1 or 2, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

4. The water-retaining and air-entraining admixture as described in claim 1 or 2, characterized in that, The retarder is sodium gluconate.

5. The water-retaining and air-entraining admixture as described in claim 1 or 2, characterized in that, The reinforcing component is nano-SiO2 or metakaolin.

6. The method for preparing the water-retaining and air-entraining admixture as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: The reinforcing component and hydroxypropyl methylcellulose are put into a three-dimensional mixer and mixed under nitrogen protection to obtain the activated reinforcing component / hydroxypropyl methylcellulose complex. S2: Add the modified starch ether into the mixing tank, add water-reducing agent and retarder under nitrogen protection and mix at low speed to obtain the initial mixture. Then spray the air-entraining agent into the initial mixture for shearing treatment. Finally, add the activated reinforcing component / hydroxypropyl methylcellulose complex in three batches and mix to obtain the final mixture. S3: Crush the final mixture, then add fly ash microspheres, mix evenly, and finally adjust the pH to 8.5-9.0 with sodium bicarbonate solution.

7. The preparation method of the water-retaining and air-entraining admixture as described in claim 6, characterized in that, In step S1, the three-dimensional mixer for mixing processes rotates at 200 rpm for 15 minutes.

8. The preparation method of the water-retaining and air-entraining admixture as described in claim 6, characterized in that, In step S2, the low-speed mixing treatment is performed at 120 rpm for 15 min; the shearing treatment is performed at 800 rpm for 5 min; after each addition of the reinforcing component / hydroxypropyl methylcellulose complex, the mixture is allowed to stand for 3 min, and then mixed at 150 rpm for 5 min.

9. The preparation method of the water-retaining and air-entraining admixture as described in claim 6, characterized in that, In step S3, the pulverization process is carried out using an air jet mill, with a pulverization pressure of 0.8 MPa, a temperature of <45℃, and pulverization to a particle size of ≤50 μm.

10. The application of the water-retaining and air-entraining admixture as described in any one of claims 1 to 5 in the preparation of solid waste-based dry powder mortar.

Images