Localized special mortar as well as preparation method and application thereof

Abstract

The invention provides localized special mortar as well as a preparation method and application thereof, and relates to the technical field of building materials. According to the method, the target fineness modulus is dynamically corrected by introducing the edge coefficient based on the crushing value of the machine-made sand, so that quantitative response to the edge difference of different batches of machine-made sand is realized; a cement-fly ash-activated recycled concrete micro powder ternary cementing material system is adopted, so that the early strength and the long-term performance are synergistically improved; and redispersible latex powder and hydroxypropyl methyl cellulose are compounded to form a water-retaining, tackifying and film-forming-enhanced composite admixture system, so that multiple targets of stable mortar workability, excellent mechanical properties and solid waste resource utilization are achieved, and the mortar has a wide engineering application prospect.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a localized special mortar, its preparation method, and its application. Background Technology

[0002] As a fundamental material used in large quantities in construction projects, the performance stability of building mortar directly affects the quality of the project. With the depletion and limited mining of natural river sand resources, manufactured sand has become the main source of mortar aggregate. However, differences in the production process and parent rock characteristics of manufactured sand lead to significant differences in particle morphology and angular features between different batches. Even manufactured sand with the same fineness modulus can have significantly different degrees of sharpness in its edges. The sharper the edges of manufactured sand, the larger its specific surface area and the higher the frictional resistance between particles, resulting in increased water demand and deteriorated workability of the mortar. Traditional compounding schemes based on a fixed fineness modulus cannot solve this batch-to-batch difference in edge sharpness, causing large fluctuations in mortar consistency and unstable workability.

[0003] Therefore, how to solve the batch fluctuation problem of manufactured sand edges while improving mortar and its early strength, long-term performance, bonding performance and solid waste utilization is of great significance for the application of localized special mortar. Summary of the Invention

[0004] In view of this, the present invention provides a localized special mortar, its preparation method, and its application. The present invention achieves a quantitative response to the differences in the edge angles of different batches of manufactured sand by introducing a dynamic correction of the target fineness modulus based on the angularity coefficient of the crushing value of manufactured sand; it employs a cement-fly ash-activated recycled concrete micro-powder ternary cementitious material system to synergistically improve early strength and long-term performance; and it combines redispersible latex powder (VAE) and hydroxypropyl methylcellulose (HPMC) to form a composite admixture system that enhances water retention, thickening, and film formation, achieving multiple objectives such as stable mortar workability, excellent mechanical properties, and resource utilization of solid waste, thus possessing broad engineering application prospects.

[0005] The first aspect of this invention is to provide a localized special mortar, which includes compound aggregates, ternary cementitious materials, composite admixtures and water; The compound aggregate is composed of manufactured sand and ultrafine sand in a specific mass ratio. The fineness modulus of the manufactured sand is 2.7~3.5, and the fineness modulus of the ultrafine sand is ≤1.0. The mass ratio of the manufactured sand to the ultrafine sand is determined by the following method: The crushing value of this batch of manufactured sand was determined, and the angularity coefficient K was calculated using the following formula: K = 1.0 + (Measured crushing value - Baseline crushing value) / Baseline crushing value × α The crushing value baseline is 20%, the correction coefficient α is 0.5~0.8, and the value of K is 1.0~1.4. The target fineness modulus is dynamically corrected based on the angle coefficient K, and the correction formula is as follows: FM target (correction) = FM baseline × [1 + β × (K - 1.0)] The FM benchmark is 2.3, and the corrected strength factor β is 0.10~0.15. Based on the revised FM target value, the mass percentage of ultrafine sand (x) is calculated using mass interpolation: x = (FM manufactured sand - FM target correction) / (FM manufactured sand - FM extra-fine sand) The mass ratio of manufactured sand to ultrafine sand is determined based on the calculated x value; Each batch of manufactured sand must be re-measured for crushing value upon arrival, K value dynamically updated, FM target value corrected and compounding ratio recalculated. The ternary cementitious material is composed of cement, fly ash, and activated recycled concrete powder (RCP), and the amount of activated RCP is 10% to 20% of the total mass of the cementitious material. The composite admixture is composed of redispersible latex powder (VAE) and hydroxypropyl methylcellulose (HPMC), wherein the amount of VAE redispersible latex powder is 1.5% to 3.0% of the total mass of the cementitious material, and the amount of HPMC is 0.05% to 0.15% of the total mass of the cementitious material.

[0006] Preferably, in the ternary cementitious material, cement accounts for 60% to 65% of the total mass of the cementitious material, fly ash accounts for 15% to 25%, and activated RCP accounts for 15% to 20%.

[0007] Preferably, the proportions of the ternary cementitious material are: 65% cement, 20% fly ash, and 15% activated RCP.

[0008] Preferably, the activated RCP is ultrafine powder with a particle size of less than 0.075 mm collected from waste concrete from building demolition after crushing and screening, which is then calcined and activated at 900±50℃ for 30 min and ground to a specific surface area ≥450 m². 2 / kg; the loss on ignition of the activated RCP is ≤8%, and the chloride ion content is ≤0.06%.

[0009] Preferably, the fly ash is Class I, Type F fly ash, with a loss on ignition ≤5% and a water requirement ratio ≤95%; the cement is P·O 42.5 ordinary Portland cement; the HPMC has a viscosity ≥40000 mPa·s; and the VAE redispersible latex powder has a glass transition temperature Tg ≤0℃.

[0010] Preferably, the amount of VAE redispersible latex powder is 2.0% to 2.5% of the total mass of the cementitious material, and the amount of HPMC is 0.08% to 0.12% of the total mass of the cementitious material.

[0011] Preferably, the stone powder content of the manufactured sand is 4% to 6%, and the crushing value meets the requirements of JGJ52 standard.

[0012] A second aspect of the present invention is to provide a method for preparing the aforementioned localized special mortar, comprising the following steps: S1. Determine the crushing value of this batch of manufactured sand, calculate the angularity coefficient K, and dynamically correct the target fineness modulus FM based on the K value. Then, use mass interpolation to calculate the blending ratio of manufactured sand and ultrafine sand according to the corrected FM target value. S2. Mix the manufactured sand and the ultrafine sand according to the compounding ratio determined in step one to obtain the compounded aggregate; S3. Weigh the ternary cementitious material according to the ratio of cement, fly ash and activated RCP. Add HPMC and VAE redispersible latex powder to the cementitious material for premixing. Then add the compound aggregate and dry mix to obtain a dry powder mixture. S4. Add water to the dry powder mixture in two steps and stir to obtain wet-mixed mortar.

[0013] The correction method of this invention solves the problem that although different batches of manufactured sand have the same fineness modulus, the difference in the angle of the edges and corners significantly affects the workability of the mortar. By introducing an angle coefficient K to dynamically correct the FM target value, the x value of each batch is recalculated, forming a control method of "measuring crushing value → calculating K → correcting FM → calculating x → batching".

[0014] In step S3, HPMC and VAE redispersible latex powder and cementitious materials are fully premixed in the dry powder stage; after the compound aggregate is added, the dry mixing time is not less than 3 minutes. In step S4, 70% of the calculated water volume is added in the first step, and the mixture is stirred at a high speed of not less than 150 rpm for 4 minutes; it is then allowed to stand and mature for 5-8 minutes; in the second step, the remaining water volume is added, and the mixture is stirred at a low speed for 1 minute before being discharged. The consistency is measured and the water volume is adjusted slightly to the target value.

[0015] In step S2, manufactured sand and ultrafine sand are mixed in a dry mixing device at a speed of not less than 300 rpm for not less than 5 minutes. After mixing, samples are taken for sieve analysis and verification. The measured fineness modulus should be within the range of FM correction ±0.1. Otherwise, the ratio is adjusted and the verification is repeated until it is qualified.

[0016] A third aspect of the present invention is to provide the application of the above-mentioned localized special mortar in plastering mortar or masonry mortar in building engineering.

[0017] This invention uses manufactured sand and ultrafine sand to form a binary composite aggregate. It dynamically corrects the target fineness modulus determined by traditional interpolation by introducing an edge coefficient K based on the crushing value. This allows for adjustment of edge differences between different batches of manufactured sand, overcoming the workability instability problem caused by batch fluctuations in fixed-ratio schemes. The crushing value is chosen as the basis for calculating the K value because it has a significant positive correlation with the sharpness of edges and corners, and is a routine incoming inspection indicator specified in JGJ52, requiring no additional equipment. The crushing value benchmark is 20% (corresponding to a medium edge level), the correction coefficient α is 0.5~0.8 (determined by calibration tests), and the K value range is limited to 1.0~1.4—no correction is made when it is below the benchmark, and when it is above the upper limit, it should be improved by adjusting the amount of cementitious materials and admixtures. The FM benchmark is set at 2.3 instead of the upper limit of the range because the introduction of fine sand has increased the specific surface area of ​​the aggregate, and a water demand margin is reserved under the benchmark condition; the correction strength coefficient β is 0.10~0.15 to ensure that the correction range is moderate, and the mass ratio of fine sand x is finally calculated from the target FM value.

[0018] In terms of cementitious materials, recycled concrete micropowder activated by high-temperature calcination serves as the third component, forming a ternary system with cement and fly ash. Residual unhydrated cement particles in the activated RCP undergo continuous secondary hydration in an alkaline environment to compensate for early strength. Its micro-aggregate effect, combined with the pozzolanic effect of fly ash, synergistically enhances 28-day strength and density, while simultaneously achieving high-value utilization of construction solid waste. Regarding admixtures, VAE redispersible latex powder is compounded with HPMC to form a composite system: after hardening, the latex powder forms a continuous polymer film network at pores and interfaces, bridging microcracks at the edges of the manufactured sand, fundamentally improving interfacial bonding performance and endowing the mortar with elastic deformation capabilities, overcoming the limited bonding improvement effect of a single HPMC system.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention effectively solves the problem of unstable mortar consistency caused by batch-to-batch fluctuations in traditional fixed-ratio compounding schemes, thereby improving the stability and controllability of mortar.

[0020] This invention employs a ternary cementitious material consisting of cement, fly ash, and activated recycled concrete micropowder. The continuous secondary hydration of residual unhydrated cement particles in the activated recycled concrete micropowder under alkaline conditions compensates for insufficient early strength. At the same time, the micro-aggregate effect of the recycled micropowder and the pozzolanic effect of fly ash work synergistically to effectively improve long-term strength and density, thereby enhancing early strength while achieving high-value utilization of construction solid waste.

[0021] The present invention provides a continuous polymer film network formed by redispersible latex powder during the mortar hardening process, which bridges the microcracks at the edges of the manufactured sand, fundamentally improving the interfacial bonding performance between the mortar and the substrate and giving the mortar elastic deformation capability. This overcomes the problem that the single hydroxypropyl methylcellulose system has limited effect on improving the bonding strength, and significantly improves the bonding performance and durability of the mortar.

[0022] This invention achieves multiple goals, including stable mortar workability, excellent mechanical properties, and resource utilization of solid waste, through optimized aggregate compounding ratio, ternary cementitious agents, and synergistic effects of composite admixtures, and has broad prospects for engineering applications. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] The following examples and comparative examples all use the following raw materials: Manufactured sand: taken from the same batch in the same quarry, with a fineness modulus (FM) of 3.2, a crushing value of 23%, and a stone powder content of 5.1%; Extra-fine sand: FM 0.9, mud content 0.8%, residue on 0.315 mm sieve 3.2%; Cement: P·O 42.5 ordinary Portland cement; Fly ash: Grade I, Class F, loss on ignition 3.8%, water requirement ratio 92%, residue on 45 μm sieve 11.5%; VAE redispersible latex powder: ethylene-vinyl acetate copolymer, glass transition temperature Tg of -5℃, ash content of 12.3%; HPMC: Hydroxypropyl methylcellulose, viscosity (2% aqueous solution, 20℃) 42000 mPa·s, degree of methoxy substitution 28.5%, degree of hydroxypropyl substitution 8.6%.

[0025] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as mean ± standard deviation.

[0026] Example 1: A method for preparing a localized special mortar, comprising the following steps: S1. Calculation of angularity coefficient and dynamic correction of target fineness modulus: The crushing value of this batch of manufactured sand was determined to be 23%. The angularity coefficient K was calculated using the following formula: K = 1.0 + (23 - 20) / 20 × 0.5 = 1.075 The strength coefficient β is corrected to 0.12, and the target fineness modulus is corrected using the following formula: FM target (revised) = 2.3 × [1 + 0.12 × (1.075 - 1.0)] = 2.3 × 1.009 = 2.321 Calculate the mass percentage of ultrafine sand (x) using mass interpolation: x=(3.2-2.321) / (3.2-0.9)=0.879 / 2.3≈0.382 That is, the mass ratio of ultrafine sand to manufactured sand is approximately 38:62; S2. Preparation of compound aggregates: Weigh the fine sand and manufactured sand at a mass ratio of 38:62, place them in a dry mixing device and mix at 320 rpm for 5 min. Take a 100 g sample for sieve analysis and verification. The measured FM=2.32. S3, Powder Mixing: Weigh the cementitious materials according to the ratio (cement:fly ash:activated RCP = 65:20:15, by mass); add HPMC and VAE redispersible latex powder to the cementitious materials and premix at low speed for 2 minutes to ensure uniform dispersion; add the compound aggregate and dry mix for 3 minutes to obtain the dry powder mixture. The dosage of each raw material per cubic meter of mortar is as follows:

[0027] Note: The dosage of VAE latex powder and HPMC is calculated based on the total mass of cementitious materials (269 kg); The method for preparing activated RCP is as follows: Waste concrete from building demolition is crushed and sieved to collect ultrafine powder with a particle size <0.075 mm. This powder is then calcined and activated at 900±50℃ for 30 min, followed by grinding. The activated RCP has a specific surface area of ​​468 m². 2 / kg, loss on ignition 6.2%, chloride ion content 0.042%; S4. Add water and stir in two steps: Add approximately 70% of the calculated water volume to the dry powder mixture and stir at a high speed of ≥150 rpm for 4 minutes; let it stand and mature for 5~8 minutes to allow HPMC to fully hydrate and VAE to begin to disperse; add the remaining water volume, stir again at low speed for 1 minute, and then discharge the material. The consistency is measured to be 92 mm, and no adjustment of the water volume is required.

[0028] Example 2 The difference from Example 1 is that the amount of each raw material used per cubic meter of mortar is as follows:

[0029] Note: The dosage of VAE latex powder and HPMC is calculated based on the total mass of cementitious materials.

[0030] Example 3 The difference from Example 1 is that the ternary cementitious material ratio is cement:fly ash:activated RCP = 65:15:20 (mass ratio), wherein the activated RCP content is increased to 20% of the total mass of the cementitious material. Specifically: 175 kg of cement, 41 kg of fly ash, 54 kg of activated RCP, total cementitious material 270 kg, 5.40 kg (2.0%) of VAE latex powder, 0.27 kg (0.10%) of HPMC, 1200 kg of compound aggregate, 252 kg of water, and a water-cement ratio of 0.93.

[0031] Example 4 The difference from Example 1 is that the content of VAE redispersible latex powder is increased to 2.5% of the total mass of the cementitious material, and the content of HPMC is increased to 0.12%.

[0032] Example 5 The difference from Example 1 is that the crushing value of this batch of manufactured sand is 26% (higher angularity), and the angularity coefficient K is recalculated according to the formula: K = 1.0 + (26 - 20) / 20 × 0.5 = 1.15 Target FM Correction: FM target (revised) = 2.3 × [1 + 0.12 × (1.15 - 1.0)] = 2.3 × 1.018 = 2.341 Percentage of extra-fine sand: x=(3.2-2.341) / (3.2-0.9)=0.859 / 2.3≈0.373 That is, the mass ratio of ultrafine sand to manufactured sand is 37:63.

[0033] Comparative Example 1 The difference from Example 1 is that the cementitious material uses a dual-blending system (cement:fly ash = 80:20, by mass), without the addition of activated RCP; the admixture uses only HPMC (0.10%), without the addition of VAE redispersible latex powder. The specific proportions are: 216 kg cement, 54 kg fly ash, 270 kg total cementitious material, 0.27 kg HPMC, 1200 kg compound aggregate, 258 kg water, and a water-cement ratio of 0.96.

[0034] Comparative Example 2 The difference from Example 1 is that: no angularity coefficient K is introduced; instead, the traditional fineness modulus interpolation method is used to directly calculate the blending ratio with a fixed target FM=2.3. x = (3.2 - 2.3) / (3.2 - 0.9) = 0.391, meaning the ratio of extra-fine sand to manufactured sand is 39:61 (fixed and not updated with each batch). Five batches of slurry were continuously prepared using different bags of manufactured sand from the same batch (with differences in edge angles within the normal production fluctuation range). The consistency of each batch was recorded to assess stability.

[0035] Comparative Example 3 The difference from Example 1 is that only HPMC (0.10%) is used as an admixture, and no VAE redispersible latex powder is added.

[0036] Test Example 1 The performance of the samples from Examples 1-5 and Comparative Examples 1-3 was tested, and the results are shown in Tables 1 and 2. The consistency stability data are shown in Table 3.

[0037] Table 1. Effects of different cementitious systems and admixture formulations on the basic properties of mortar (plastering mortar)

[0038] Note: Comparative Example 1 had insufficient overall performance and was not subjected to freeze-thaw resistance testing.

[0039] Table 2. Effects of different cementitious systems and admixture formulations on the basic properties of mortar (masonry mortar)

[0040] The 7-day compressive strength of Examples 1-4 was significantly higher than that of the dual-admixture system in Comparative Example 1 (P<0.05), with an increase of 10.6%-18.8%, demonstrating that the secondary hydration activity of the residual unhydrated cement particles in activated RCP has a significant reinforcing effect on early strength. The 28-day compressive strength of Example 3 was better than that of Example 1, indicating that increasing the RCP dosage within a reasonable range can synergistically enhance the micro-aggregate effect and pozzolanic effect.

[0041] Examples 1-4, containing VAE redispersible latex powder, showed significantly higher 28-day tensile bond strengths than Comparative Example 3 (P<0.05); their water retention was also significantly higher than that of Comparative Examples 1 and 3 (P<0.05). Example 4 achieved a 28-day tensile bond strength of 0.53±0.02 MPa and increased its freeze-thaw cycle resistance to ≥30 cycles, indicating that the VAE polymer film network plays a crucial role in improving interfacial adhesion and durability. Comparative Example 1 showed the lowest performance in all aspects, with significant differences from Example 1 (P<0.05).

[0042] Table 3. Comparison of the working stability of the dynamic correction method for the angle coefficient K and the traditional fixed ratio method.

[0043] After introducing K-value correction in Examples 1 and 5, the consistency range of the five consecutive batches was only 6 mm and 7 mm, respectively, with no batches exceeding the standard. In contrast, Comparative Example 2, using a traditional fixed proportion of ingredients, had a consistency range of 21 mm, with 2 / 5 batches exceeding the ±10 mm control range, showing a significant difference (P<0.05). As the batch angularity level increased (K increased from 1.075 to 1.15), dynamically reducing the proportion of ultrafine sand effectively offset the increased water demand caused by the increased angularity, maintaining consistency stability.

[0044] Comparative Example 4 The difference from Example 1 is that RCP is not subjected to calcination activation treatment; instead, the ultrafine powder with a particle size <0.075 mm obtained from crushing and screening construction waste concrete is directly ground to a specific surface area of ​​460 m². 2 After / kg, the activated RCP was replaced with the same dosage and incorporated into the ternary cementitious system.

[0045] Comparative Example 5 The difference from Example 1 is that the RCP calcination temperature was reduced from 900±50℃ to 700±50℃, while the calcination time remained unchanged at 30 min.

[0046] Table 4. Effects of RCP activation treatment on mortar properties

[0047] The 7-day and 28-day compressive strengths of the Example were significantly higher than those of Comparative Example 4 (P<0.05), indicating that calcination activation plays an irreplaceable role in stimulating the secondary hydration activity of RCP and improving its insufficient early strength. In the unactivated RCP, the inert calcium carbonate coating layer blocked the contact between residual cement particles and the alkaline pore solution, resulting in near-loss of secondary hydration activity; simultaneously, the loss on ignition was as high as 14.8%, introducing a large amount of inert organic residue, significantly increasing the 28-day drying shrinkage rate (significantly different from Example 1, P<0.05).

[0048] Comparative Example 5 had an incomplete decomposition of calcium carbonate, resulting in a loss on ignition of 11.3%, which did not meet the requirement of ≤8% of the present invention. Furthermore, its 7-day compressive strength and 28-day compressive strength were significantly lower than those of Example 1 (P<0.05), demonstrating that a calcination temperature parameter of 900±50℃ is necessary for fully activating RCP activity.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A localized, specialized mortar, characterized in that, Includes compound aggregates, ternary cementitious materials, composite admixtures, and water; The compound aggregate is composed of manufactured sand and ultrafine sand in a specific mass ratio. The fineness modulus of the manufactured sand is 2.7~3.5, and the fineness modulus of the ultrafine sand is ≤1.

0. The mass ratio of the manufactured sand to the ultrafine sand is determined by the following method: The crushing value of this batch of manufactured sand was determined, and the angularity coefficient K was calculated using the following formula: K = 1.0 + (Measured crushing value - Baseline crushing value) / Baseline crushing value × α The crushing value baseline is 20%, the correction coefficient α is 0.5~0.8, and K is 1.0~1.

4. The target fineness modulus is dynamically corrected based on the angle coefficient K, and the correction formula is as follows: FM target = FM baseline × [1 + β × (K - 1.0)] The FM benchmark is 2.3, and the corrected strength factor β is 0.10~0.

15. Based on the revised FM target value, the mass percentage of ultrafine sand (x) is calculated using mass interpolation: x = (FM manufactured sand - FM target correction) / (FM manufactured sand - FM extra-fine sand) Each batch of manufactured sand must be re-measured for crushing value upon arrival, K value dynamically updated, FM target value corrected and compounding ratio recalculated. The ternary cementitious material is composed of cement, fly ash, and activated recycled concrete powder (RCP), and the amount of activated RCP is 10% to 20% of the total mass of the cementitious material. The composite admixture is composed of redispersible latex powder (VAE) and hydroxypropyl methylcellulose (HPMC), wherein the amount of VAE redispersible latex powder is 1.5% to 3.0% of the total mass of the cementitious material, and the amount of HPMC is 0.05% to 0.15% of the total mass of the cementitious material.

2. The localized special mortar according to claim 1, characterized in that, In the ternary cementitious material, cement accounts for 60% to 65% of the total mass of the cementitious material, fly ash accounts for 15% to 25%, and activated RCP accounts for 15% to 20%.

3. The localized special mortar according to claim 1, characterized in that, The proportions of the ternary cementitious material are: 65% cement, 20% fly ash, and 15% activated RCP.

4. The localized special mortar according to claim 1, characterized in that, The activated RCP is made from ultrafine powder with a particle size of less than 0.075 mm collected from waste concrete from building demolition after crushing and screening. This powder is then activated by calcination at 900±50℃ for 30 min and ground to a specific surface area ≥450 m². 2 / kg; the loss on ignition of the activated RCP is ≤8%, and the chloride ion content is ≤0.06%.

5. The localized special mortar according to claim 1, characterized in that, The fly ash is Class I, Type F fly ash; the cement is P·O 42.5 ordinary Portland cement; the viscosity of HPMC is ≥40000 mPa·s; and the glass transition temperature Tg of the VAE redispersible latex powder is ≤0℃.

6. The localized special mortar according to claim 1, characterized in that, The amount of VAE redispersible latex powder is 2.0% to 2.5% of the total mass of the cementitious material, and the amount of HPMC is 0.08% to 0.12% of the total mass of the cementitious material.

7. The localized special mortar according to claim 1, characterized in that, The stone powder content of the manufactured sand is 4% to 6%.

8. The method for preparing the localized special mortar according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Determine the crushing value of this batch of manufactured sand, calculate the angularity coefficient K, and dynamically correct the target fineness modulus FM based on the K value. Then, use mass interpolation to calculate the blending ratio of manufactured sand and ultrafine sand according to the corrected FM target value. S2. Mix the manufactured sand and the ultrafine sand according to the compounding ratio determined in step one to obtain the compounded aggregate; S3. Weigh the ternary cementitious material according to the ratio of cement, fly ash and activated RCP. Add HPMC and VAE redispersible latex powder to the cementitious material for premixing. Then add the compound aggregate and dry mix to obtain a dry powder mixture. S4. Add water to the dry powder mixture in two steps and stir to obtain wet-mixed mortar.

9. The preparation method according to claim 8, characterized in that, First, add 70% of the calculated water volume and stir at a high speed of no less than 150 rpm for 4 minutes; let it stand and mature for 5-8 minutes; second, add the remaining water volume, stir again at low speed for 1 minute, then discharge the material, measure the consistency, and adjust the water volume slightly to the target value.

10. The application of the localized special mortar according to any one of claims 1 to 7 in plastering mortar or masonry mortar for building construction.

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