An inorganic shielding agent for eliminating the influence of residual flocculants on the workability of concrete and a method for applying the same

Abstract

The application discloses an inorganic shielding agent for eliminating the influence of residual flocculants in machine-made sand on the workability of concrete and an application method thereof. The inorganic shielding agent is composed of hydrogen peroxide and ferrous salt. In the mixing process of concrete or mortar, the shielding agent is added into mixing water, polycarboxylic acid water reducing agent and other raw materials, and hydroxyl radicals generated by Fenton reagent are used to rapidly degrade residual polyacrylamide (PAM) in machine-made sand by using the mixing and time provided by the mixing process, so that the competitive adsorption and tackifying effect of the residual PAM on the polycarboxylic acid water reducing agent are eliminated, and the workability of the concrete is restored. The application has the advantages of high efficiency, rapidness, low cost and simple operation, and the reaction product is harmless to the environment, and is suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a chemical shielding agent for eliminating the influence of residual flocculants in manufactured sand on the workability of concrete, and a method for applying the shielding agent. Background Technology

[0002] With the increasing depletion of natural sand resources, manufactured sand has become the main fine aggregate in the construction industry. Manufactured sand is made from rocks, pebbles, or mine tailings through mechanical crushing and screening, producing particles with a diameter of less than 4.75 mm. In the sand washing stage of its production process, polyacrylamide (PAM) flocculants are widely used to promote the settling of solid particles and the recycling of wastewater. However, PAM inevitably remains on the surface and inside the manufactured sand, severely negatively impacting the performance of subsequent concrete.

[0003] Polycarboxylate superplasticizer (PCE) is an indispensable admixture in modern high-performance concrete. It disperses cement particles through steric hindrance, significantly reducing mixing water consumption and improving fluidity. However, residual PAM in manufactured sand severely interferes with the normal function of PCE. Studies have shown that PAM and PCE compete for adsorption on the surface of cement particles. Polar groups such as the amide groups (-CONH2) on the PAM molecular chain occupy adsorption sites of PCE, hindering its dispersing effect. Simultaneously, PAM's strong hydrophilicity binds a large amount of free water, increasing the viscosity of the paste. The combined effect of these two factors leads to a significant reduction in the initial fluidity of concrete or mortar and accelerated fluidity loss over time, severely impacting the workability and construction quality of fresh concrete.

[0004] Existing technologies attempt to solve this problem by: (1) chemically modifying PAM and introducing ester groups to reduce the density of amide groups, but the cost is high; (2) heat-treating PAM-containing manufactured sand (e.g., 240°C for more than 6 hours) to thermally decompose PAM, but the energy consumption is high and the efficiency is low; (3) adding an inhibitor such as sulfonated β-cyclodextrin, which preferentially binds to PAM to protect PCE, but the inhibitor is expensive; (4) simply increasing the amount of water-reducing agent, which can partially restore fluidity, but greatly increases the cost and has limited effect on cases with high PAM residue.

[0005] Furthermore, Fenton's reagent (a combination of hydrogen peroxide and ferrous ions) has been studied for its use in degrading PAM in wastewater. Research indicates that the hydroxyl radicals (·OH) generated by the Fenton reaction can attack the PAM molecular chains, leading to chain breakage and a decrease in viscosity. However, these studies are limited to wastewater treatment, which requires processing times exceeding 30 minutes and necessitates heating to 40-80°C and adjusting the pH to 3-4 under acidic conditions. This differs significantly from concrete mixing processes (room temperature, 10-15 minutes, alkaline environment) and cannot be directly applied to concrete production.

[0006] Therefore, how to economically, efficiently, and conveniently eliminate the negative impact of residual PAM in manufactured sand on the workability of concrete is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] (a) Technical problems to be solved The present invention aims to provide an inorganic shielding agent and its application method that can quickly and efficiently eliminate the influence of residual polyacrylamide in manufactured sand on the workability of concrete, in order to solve the problems of high cost, long time consumption, low efficiency or difficulty in industrial application of existing technologies.

[0008] (II) Technical Solution Option 1: An inorganic shielding agent to eliminate the influence of residual flocculant in manufactured sand on the workability of concrete. An inorganic shielding agent for eliminating the influence of residual flocculants in manufactured sand on the workability of concrete, wherein the inorganic shielding agent is composed of an oxidant and a catalyst, wherein the oxidant is hydrogen peroxide and the catalyst is a ferrous salt.

[0009] In this invention, the ferrous salt is at least one of ferrous sulfate, ferrous chloride, or ferrous nitrate.

[0010] In this invention, when applied to concrete or mortar, the amount of hydrogen peroxide added is 0.35-1.05 liters per cubic meter of mixture, and the amount of ferrous salt added is 0.15-0.45 kg per cubic meter of mixture.

[0011] In this invention, the amount of ferrous salt and hydrogen peroxide added is controlled by a mass-volume ratio of FeSO4·7H2O (kg):H2O2 (L) = 0.4-0.5:1.

[0012] In this invention, the molar ratio of hydrogen peroxide to ferrous salt is controlled within the range of 4:1 to 6:1.

[0013] Option 2: An application method for an inorganic shielding agent An application method of an inorganic shielding agent according to the present invention includes the following steps: (1) Determine the amount of hydrogen peroxide and ferrous salt to be added based on the residual amount of polyacrylamide in the manufactured sand; (2) During the mixing stage of concrete or mortar, the hydrogen peroxide and ferrous salt are added to the mixing equipment along with the mixing water, polycarboxylate superplasticizer and other raw materials; (3) Stir at room temperature for 10-15 minutes to allow the hydroxyl radicals generated by Fenton reagent to fully react with the polyacrylamide remaining in the manufactured sand and degrade it into small molecules; (4) Continue stirring until homogeneous to obtain workable concrete or mortar.

[0014] In this invention, the method for determining the residual amount of polyacrylamide in step (1) is as follows: relative to the mass of manufactured sand, for every 0.01 wt% of residual polyacrylamide eliminated, approximately 0.175 liters / cubic meter of hydrogen peroxide is added to the mixture.

[0015] In this invention, the polyacrylamide is at least one of anionic, cationic, or nonionic polyacrylamide.

[0016] In this invention, the ferrous salt and hydrogen peroxide are added separately, with the ferrous salt added first and then the hydrogen peroxide added.

[0017] Option 2: Application of inorganic shielding agents in the preparation of concrete or mortar An application of an inorganic shielding agent provided by the present invention in the preparation of concrete or mortar.

[0018] (III) Beneficial Effects Compared with the prior art, the present invention has the following significant advantages: (1) High efficiency: Fenton reagent has strong oxidizing power and can effectively degrade PAM within 10-15 minutes of conventional mortar mixing, with a degradation rate of over 70%, quickly eliminating its negative impact on fluidity.

[0019] (2) Strong applicability: This invention is applicable to PAM residues of different ion types (anionic, cationic, nonionic) and different molecular weights, and the amount of shielding agent can be adjusted by linear proportion according to the actual residue amount.

[0020] (3) Low cost: Hydrogen peroxide and ferrous sulfate are both common industrial chemicals and are inexpensive. The increased cost of applying this method is far lower than that of adding additional water-reducing agents or using special resistance agents.

[0021] (4) Easy to operate: No need to modify the existing concrete production line or pre-treat the manufactured sand. The shielding agent is simply added as a "liquid admixture" along with the mixing water during the feeding stage of the mixing plant, which is easy to integrate into the existing production process.

[0022] (5) Environmental friendliness: The final degradation products of the Fenton reaction are mainly CO2 and H2O, as well as harmless inorganic iron salts. It does not introduce new harmful substances and is environmentally friendly. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is a graph showing the PAM degradation rate of the shielding agent of the present invention at different catalyst concentrations.

[0025] Figure 2 This is a graph showing the PAM degradation rate of the shielding agent of the present invention under different amounts of hydrogen peroxide. Detailed Implementation

[0026] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0027] Existing Fenton degradation PAM technologies are all applied in wastewater treatment, with reaction conditions of 30-60 minutes, 40-80℃, and pH 3-4. These conditions differ significantly from concrete mixing processes (room temperature, 10-15 minutes, alkaline environment), making it impossible to apply existing Fenton degradation PAM technologies to concrete production.

[0028] Through in-depth research into the kinetic characteristics of the Fenton reaction, the inventors discovered that the generation rate of hydroxyl radicals is related to Fe... 2+ The molar ratio of Fe / H2O2 is closely related. 2+ When the molar ratio of PAM to H2O2 is controlled within the range of 4:1 to 6:1, the generation rate of hydroxyl radicals reaches the optimal value, which can effectively degrade PAM molecules within 10-15 minutes. Based on this, it can be applied to concrete production, thus realizing "in-situ synchronous treatment". It does not require extending the mixing time of concrete production and does not change the existing concrete production process. It can effectively overcome the core problem that the existing Fenton degradation PAM technology requires too long a treatment time (time window mismatch) and cannot be applied to concrete production.

[0029] Furthermore, existing Fenton degradation technologies typically require adjusting the solution pH to an acidic range of 3-4 to ensure Fe... 2+ The stability and efficiency of ·OH formation. However, the cement paste in concrete systems is strongly alkaline (pH 12-13), which contradicts the traditional conditions for the Fenton reaction.

[0030] Based on in-depth research into the kinetic characteristics of the Fenton reaction, the inventors discovered through extensive creative work that the Fenton reaction can still proceed effectively in the alkaline environment of cement paste, and possesses unique advantages: the Fe produced by the reaction... 3+ It rapidly hydrolyzes in an alkaline environment to form ferric hydroxide precipitate, which effectively avoids Fe 3+ The potential risk of complexation reaction with PCE. Simultaneously, the Ca on the surface of cement particles... 2+ It has an adsorption effect on PAM molecules, which can anchor free PAM molecules on the surface of cement particles, allowing them to come into more complete contact with the ·OH generated by the shielding agent, thereby improving the degradation efficiency.

[0031] Therefore, the alkaline environment of cement paste is used to promote Fe 3+Hydrolysis and precipitation are used to avoid the negative impact of byproducts on PCE; Ca is utilized. 2+ The adsorption effect of PAM improves the contact efficiency between PAM and ·OH. This eliminates the need for additional pH adjustment, simplifies the process, and ensures that byproducts are "detoxified," guaranteeing the performance of the final concrete.

[0032] Based on the above mechanism, this invention provides an inorganic shielding agent to eliminate the influence of residual flocculant in manufactured sand on the workability of concrete. This agent requires an oxidant (H2O2) and a catalyst (Fe). 2+ The two are combined to form a whole.

[0033] Among them, Fe 2+ Catalyzing the decomposition of H₂O₂ to generate ·OH, which is used to degrade PAM. Fe 2+ Oxidized to Fe 3+ Subsequently, it can undergo a Fenton-like reaction with H2O2 under alkaline conditions, and some Fe... 3+ Reduced to Fe 2+ This forms a micro-cycle, continuously generating ·OH and prolonging the effective reaction time; Fe 2+ After being fully dissolved in the mixing water, PAM molecules can penetrate into the micropores and cracks on the surface of the manufactured sand, making "zero-distance" contact with the residual PAM molecules and achieving efficient in-situ degradation.

[0034] Furthermore, Fe in this inorganic shielding agent 2+ The molar ratio of Fe to H2O2 needs to be controlled within the range of 4:1 to 6:1, when Fe 2+ When the ratio is too low (molar ratio < 4:1), the ·OH formation rate is insufficient, and PAM degradation is incomplete; when Fe 2+ When the ratio is too high (molar ratio > 6:1), excess Fe 2+ It will consume H2O2 through Fenton-like reactions, which will reduce the efficiency of ·OH formation.

[0035] Furthermore, Fe 2+ Oxidized to Fe 3+ If the residual amount is too high, it may undergo a complexation reaction with PCE, affecting the water-reducing agent's effectiveness. This solution controls the Fe content... 2+ The initial addition amount ensures that the Fe generated by oxidation is... 3+ Complete hydrolysis and precipitation in the alkaline environment of cement paste does not have a negative impact on PCE.

[0036] In the inorganic shielding agent of this invention, by controlling Fe 2+ The molar ratio with H2O2, and the control of Fe 2+ The initial addition amount effectively restores the fluidity of mortar / concrete, bringing it to a level comparable to that of using pure sand.

[0037] The following details the formulation of the inorganic shielding agent for eliminating the influence of residual flocculant in manufactured sand on the workability of concrete, as provided in this invention, and the synergistic effect of its components.

[0038] The inorganic shielding agent provided in this invention is specifically composed of two components: hydrogen peroxide (H2O2) and ferrous salt.

[0039] Hydrogen peroxide (H2O2) acts as an oxidant, capable of reacting with Fe... 2+ Catalytic decomposition generates hydroxyl radicals (·OH), which are used to degrade PAM.

[0040] Furthermore, the hydrogen peroxide (H2O2) used in this scheme is preferably an industrial-grade hydrogen peroxide solution with a mass fraction of 27.5-35%. This concentration range ensures sufficient oxidizing power while also taking into account the safety of transportation and storage. If the concentration is too low, the amount added needs to be increased, leading to an increase in the amount of mixing water; if the concentration is too high, the operational safety is reduced.

[0041] Furthermore, the preferred dosage of hydrogen peroxide (H2O2) in this scheme is 0.35-1.05 liters per cubic meter of mixture. More preferably, approximately 0.175 liters per cubic meter of mixture are added relative to the mass of manufactured sand, for every 0.01 wt% of PAM residue eliminated.

[0042] Regarding the amount of hydrogen peroxide (H2O2) added in this scheme, if it is lower than the aforementioned lower limit, it will result in insufficient OH generation, incomplete PAM degradation, and limited recovery of fluidity; if it is higher than the aforementioned upper limit, it may introduce too much water, affecting the water-cement ratio and increasing costs.

[0043] The ferrous salt in this inorganic shielding agent acts as a catalyst to catalyze the decomposition of H2O2 to generate ·OH; it also participates in the redox cycle to maintain the continuity of the reaction.

[0044] Furthermore, the ferrous salt in this scheme is selected from at least one of ferrous sulfate (FeSO4·7H2O), ferrous chloride (FeCl2·4H2O), or ferrous nitrate (Fe(NO3)2·6H2O). Ferrous sulfate is preferred because it is widely available, inexpensive, and the sulfate ions have no adverse effect on the performance of concrete.

[0045] Furthermore, the preferred dosage of ferrous salt in this scheme is 0.15-0.45 kg per cubic meter of mixture. Simultaneously, the amount of ferrous salt added needs to be coordinated with the amount of hydrogen peroxide (H2O2) added according to a mass-volume ratio, with the mass-volume ratio controlled at: FeSO4·7H2O (kg): H2O2 (L) = 0.4-0.5:1; and the molar ratio of hydrogen peroxide (H2O2) to ferrous salt controlled at: 4:1 to 6:1.

[0046] Regarding the amount of ferrous salt added in this scheme, if it is below the lower limit mentioned above, it will result in insufficient ·OH generation rate and low degradation efficiency; if it is above the upper limit mentioned above, it will result in excessive Fe. 2+ It will consume H2O2, and Fe 3+ Residues may affect PCE performance.

[0047] The shielding agent of this invention exhibits a synergistic effect between its two components in a mixing water medium, where Fe... 2+ Both Fe and H₂O₂ are uniformly dispersed in molecular or ionic form. When they meet, Fe... 2+ As an electron donor, it transfers electrons to H2O2, causing it to undergo homolytic cleavage and generate ·OH and OH-. - This reaction can occur at room temperature without requiring additional energy input.

[0048] At the same time, Fe 2+ While catalyzing the formation of ·OH from H2O2, it is itself oxidized to Fe. 3+ In an alkaline cement paste environment, Fe 3+ It can undergo a Fenton-like reaction with H2O2: Fe 3+ + H2O2 → Fe 2+ + HO2· + H + ; This reaction causes some Fe... 3+ Reduced to Fe 2+ This allows for catalyst regeneration, forming a trace redox cycle. Although the efficiency of this cycle is limited, it extends the formation time of ·OH, ensuring the continuous generation of sufficient active species during the 10-15 minute stirring time.

[0049] Furthermore, after PAM is degraded, it generates small-molecule carboxylic acids, CO2, and H2O. These small-molecule products have no negative impact on the performance of concrete.

[0050] Meanwhile, the Fe produced by the reaction 3+ Rapid hydrolysis in the strongly alkaline environment (pH 12-13) of cement paste: Fe 3+ + 3OH - → Fe(OH)3↓; The generated ferric hydroxide precipitate is embedded in the cement hydration products and will not undergo a complexation reaction with PCE, nor will it have a negative impact on the final strength of the concrete, so that the application of the shielding agent will not introduce new side effects.

[0051] Ca on the surface of cement particles 2+It exhibits a strong adsorption effect on PAM molecules, anchoring free PAM molecules to the surface of cement particles, allowing for more thorough contact with ·OH groups diffused with water, thereby improving degradation efficiency. Simultaneously, after adsorption, the molecular chain conformation of PAM molecules changes, exposing the previously encapsulated amide groups, making them more susceptible to attack by ·OH groups.

[0052] Regarding the inorganic shielding agent provided in this invention for eliminating the influence of residual flocculant in manufactured sand on the workability of concrete, the following further describes the application method of the shielding agent of this invention.

[0053] The method for applying the inorganic shielding agent provided in this invention mainly includes the following steps: Step (1): Residual amount assessment and measurement.

[0054] This step assesses or determines the residual PAM content in the manufactured sand based on its source and production process. The residual PAM content is usually known during the production process or can be rapidly determined using the starch-cadmium iodide method, generally within the range of 0.02%-0.06 wt%.

[0055] Specifically, this step can be achieved by establishing a linear proportional relationship: for every 0.01 wt% of PAM residue eliminated, approximately 0.175 liters / cubic meter of hydrogen peroxide is added to the mixture, and ferrous salt is added in the corresponding proportion. This allows for precise control of the amount of shielding agent used, avoiding waste or insufficiency.

[0056] Step (2): Simultaneous feeding.

[0057] In this step, during the mixing stage of concrete or mortar, the measured hydrogen peroxide and ferrous salt from step (1) are added to the mixing equipment along with mixing water, polycarboxylate superplasticizer, and other raw materials (cement, manufactured sand, admixtures, etc.).

[0058] This step employs synchronous feeding, adding all components within the same time window to fully utilize the mixing conditions provided by the stirring process, ensuring that the inorganic shielding agent and the PAM-containing manufactured sand come into full contact and react in a water-containing environment.

[0059] As an alternative, this step can also involve adding hydrogen peroxide and ferrous salt separately, with the ferrous salt added first, followed by the hydrogen peroxide. This sequence allows Fe... 2+ It can be evenly dispersed in the mixing water first, and then the added H2O2 can immediately come into contact with it and react, avoiding excessively high local concentrations.

[0060] Step (3): In-situ reaction.

[0061] This step involves starting the stirring process and stirring at room temperature for 10-15 minutes. During this process, the hydroxyl radicals generated by hydrogen peroxide and ferrous salts undergo an oxidative chain-scission reaction with the residual PAM molecules in the manufactured sand, degrading the high molecular weight PAM into smaller molecules, eliminating its thickening and competitive adsorption capabilities, thereby allowing PCE to be properly adsorbed on the surface of cement particles to play a dispersing role, and restoring the fluidity of the mortar.

[0062] This step involves a room-temperature reaction, requiring no heating, utilizing the natural temperature (10-40℃) of the concrete mixing process; the degradation reaction occurs simultaneously with the regular mixing of concrete, without adding extra time.

[0063] Meanwhile, Fe in this step 2+ The H2O2 molar ratio is controlled between 4:1 and 6:1 to ensure that the ·OH generation rate matches the stirring time.

[0064] Step (4): Post-processing.

[0065] Continue mixing until homogeneous to obtain workable restored concrete or mortar. Subsequent construction processes are no different from those for ordinary concrete.

[0066] After the degradation reaction is complete, no separation or post-treatment is required, and all products remain in the concrete.

[0067] Based on the above formula and process, the shielding agent of the present invention has excellent application effect in the application process.

[0068] This invention verifies the degradation rate by determining the residual concentration of PAM in the system after the reaction using the starch-cadmium iodide method. The core evaluation index of the technical effect is the flowability of the mortar (tested according to relevant national standards). After successful application, the flowability of PAM-containing manufactured sand mortar at the discharge point and the flowability after 1 hour should be basically consistent with the reference mortar using pure sand.

[0069] See details Figure 1 The figure shows the PAM degradation rate curves of the shielding agent of the present invention at different catalyst concentrations.

[0070] As shown in the figure, the PAM degradation rate reached its optimal level (89%) when the FeSO4·7H2O concentration was 0.6 g / L. This indicates that at this concentration, Fe... 2+ The molar ratio with H2O2 is precisely matched to the formation rate of ·OH and the diffusion rate of PAM, achieving the most efficient degradation.

[0071] See details Figure 2 The figure shows the PAM degradation rate curves of the shielding agent of the present invention under different amounts of hydrogen peroxide.

[0072] When the amount of H2O2 was 1.2 ml / L and the amount of FeSO4·7H2O was 0.6 g / L, the PAM degradation rate reached over 70%. This result indicates that, under the optimized ratio, the present invention can achieve effective PAM degradation within a normal stirring time.

[0073] Example The effects of the present invention will be described in detail below through examples, but the scope of the present invention is not limited to the following examples.

[0074] <Materials> Cement: P·II 52.5 grade Portland cement, conforming to GB 175-2023 standard.

[0075] Manufactured sand: fineness modulus 2.8, mud content ≤1.0%, residual PAM content is simulated by adding PAM solution.

[0076] Polycarboxylate superplasticizer (PCE): Produced by Jiangsu Subote New Material Co., Ltd., with a solid content of 20% and a water reduction rate of ≥25%.

[0077] Hydrogen peroxide: Industrial grade, 27.5% by mass.

[0078] Ferrous sulfate: Industrial grade, FeSO4·7H2O content ≥98%.

[0079] Ferrous chloride: Industrial grade, FeCl2·4H2O content ≥98%.

[0080] Ferrous nitrate: Industrial grade, Fe(NO3)2·6H2O content ≥98% <Performance Testing Methods> Mortar flowability: The flowability of cement mortar was tested according to GB / T 2419-2005 "Determination of Flowability of Cement Mortar". The initial flowability and the flowability after 1 hour were tested respectively.

[0081] PAM degradation rate: The residual concentration of PAM in the solution was determined using the starch-cadmium iodide method, and the degradation rate was calculated. Specific method: The supernatant of the reacted mortar was taken, bromine water was added to oxidize PAM, then potassium iodide and starch were added for color development. The absorbance was measured at a wavelength of 590 nm, and the residual PAM concentration was calculated by comparing it with a standard curve.

[0082] <Examples 1-10> Mortar samples were prepared according to the formula shown in Table 1 and the process parameters shown in Table 2, and their fluidity and PAM degradation rate were tested.

[0083] Table 1. Formulation of Examples (per cubic meter of mixture)

[0084] In Example 10, FeSO4·7H2O and FeCl2·4H2O were mixed at a mass ratio of 1:1.

[0085] Table 2 Mixing process parameters

[0086] Table 3 Performance test results of the embodiments

[0087] <Comparative Examples 1-10> Table 4 Comparative formulations and process parameters

[0088] Table 5 Comparative Performance Test Results

[0089] <Analysis of Comparative Examples 1-3> Comparative Example 1 (without shielding agent) had an initial flowability of only 125 mm, demonstrating the serious negative impact of PAM residue on mortar flowability.

[0090] Comparative Example 2 (with only H2O2 added) showed a degradation rate of only 12% and a flowability that only recovered to 142 mm.

[0091] Comparative Example 3 (FeSO4 only) showed a degradation rate of only 5% and a flowability that only recovered to 138 mm.

[0092] Example 2 (two-component synergistic): The degradation rate reached 85%, and the flowability was restored to 218 mm.

[0093] The results of comparative examples 1-3 fully demonstrate the synergistic effect of the two components of the shielding agent of this invention, H2O2 and Fe. 2+ Synergistic action is necessary to generate sufficient ·OH and achieve effective degradation of PAM.

[0094] <Analysis of Comparative Examples 4-5> Comparative Example 4 (Fe) 2+ The proportion is too low (molar ratio 1:11.7), the degradation rate is only 35%, and the flowability is 158 mm.

[0095] Comparative Example 5 (Fe) 2+ The proportion is too high (molar ratio 1:2.1), the degradation rate is only 28%, and the flowability is 148 mm.

[0096] Example 2 (molar ratio 1:4.1) showed a degradation rate of 85% and a flowability of 218 mm.

[0097] Example 4 (molar ratio 1:6.2): ​​degradation rate 68%, flowability 198 mm.

[0098] By comparing the results of Comparative Examples 4-5 with those of Examples 2 and 4, it is demonstrated that Fe 2+ The molar ratio of Fe to H2O2 must be controlled within the range of 4:1-6:1. If the ratio is too low, the ·OH formation rate will be insufficient; if the ratio is too high, Fe will... 2+ Consume H2O2 and Fe 3+ Residual components negatively impact PCE performance. The preferred ratio range of 4:1 to 6:1 in this invention is the optimal range obtained through system optimization and has significant technical benefits.

[0099] <Analysis of Comparative Examples 6-7> In Comparative Example 6 (with increased PCE dosage), the flowability only recovered to 182 mm, but the PCE dosage doubled, resulting in a significant increase in cost.

[0100] Comparative Example 7 (sulfonated β-cyclodextrin with added resistance agent) only recovered to 165 mm flow rate, and the resistance agent was expensive.

[0101] Example 2 (of the present invention) shows that the fluidity is restored to 218 mm, and the cost is only 5-10% of the value of the water-reducing agent saved.

[0102] By comparing Comparative Examples 6-7 with Example 2, it is demonstrated that the present invention has a significant cost advantage over traditional solutions while achieving better workability recovery.

[0103] <Analysis of Comparative Examples 8-9> Although Comparative Example 8 (stirring for 30 minutes) achieved a degradation rate of 92% and a flowability of 210 mm, the stirring time was doubled, which affected production efficiency.

[0104] Although Comparative Example 9 (heat pretreatment for 6 hours) can achieve a degradation rate of 95% and a flowability of 215 mm, it has high energy consumption, long time, and requires special equipment.

[0105] Example 2 (stirring at room temperature for 10-15 minutes) achieved a degradation rate of 85% and a flowability of 218 mm.

[0106] The comparison results between Comparative Examples 8-9 and Example 2 demonstrate that the process of the present invention can achieve efficient degradation within the conventional stirring time without extending the process time or increasing energy consumption.

[0107] Specificity verification of oxidant selection Comparative Example 10 (using potassium permanganate as a substitute) had a degradation rate of only 32% and a flowability of only 152 mm.

[0108] Example 2 (Fenton's reagent): Degradation rate 85%, flowability 218 mm.

[0109] The comparison between Comparative Example 10 and Example 2 demonstrates that not all oxidants can effectively degrade PAM in concrete systems. The ·OH generated by Fenton's reagent has an extremely high oxidation potential, enabling it to rapidly attack the PAM molecular chains; while potassium permanganate has weak oxidizing power, and its reduction product, MnO2, may negatively impact concrete performance.

[0110] <Verification of Reaction Kinetic Matching> By comparing Examples 1-3 with Comparative Example 8, Comparative Example 8 required 30 minutes of stirring (simulating wastewater treatment conditions) to achieve a 92% degradation rate; the present invention, by optimizing the molar ratio, achieves an 85% degradation rate within 10-15 minutes.

[0111] This demonstrates that the present invention modulates Fe... 2+ The / H2O2 molar ratio successfully matches the kinetic characteristics of the Fenton reaction with the time window of the concrete mixing process.

[0112] <Verification of Alkaline Environment Adaptability> Example 2 achieved an 85% degradation rate and a flowability of 218 mm under conditions without pH adjustment (cement paste pH 12-13). Traditional Fenton degradation technology, however, requires acidic conditions at pH 3-4.

[0113] This comparison demonstrates that the present invention successfully utilizes the alkaline environment of cement paste, which not only fails to inhibit the Fenton reaction but also promotes the Fe reaction. 3+ Hydrolysis and precipitation avoid the negative impact of byproducts.

[0114] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An inorganic shielding agent for eliminating the influence of residual flocculant in manufactured sand on the workability of concrete, characterized in that, The inorganic shielding agent is composed of an oxidant and a catalyst. The oxidant is hydrogen peroxide, and the catalyst is a ferrous salt. The molar ratio of hydrogen peroxide to ferrous salt is controlled within the range of 4:1 to 6:

1.

2. The inorganic shielding agent according to claim 1, characterized in that, The ferrous salt is at least one of ferrous sulfate, ferrous chloride, or ferrous nitrate.

3. The inorganic shielding agent according to claim 1, characterized in that, The amount of hydrogen peroxide added is 0.35-1.05 liters per cubic meter of the mixture, and the amount of ferrous salt added is 0.15-0.45 kilograms per cubic meter of the mixture.

4. The inorganic shielding agent according to claim 3, characterized in that, The amount of ferrous salt and hydrogen peroxide added is controlled by a mass-volume ratio of FeSO4·7H2O (kg):H2O2 (L) = 0.4-0.5:

1.

5. A method for applying the inorganic shielding agent according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Determine the amount of hydrogen peroxide and ferrous salt to be added based on the residual amount of polyacrylamide in the manufactured sand; (2) During the mixing stage of concrete or mortar, the hydrogen peroxide and ferrous salt are added to the mixing equipment along with the mixing water, polycarboxylate superplasticizer and other raw materials; (3) Stir at room temperature for 10-15 minutes to allow the hydroxyl radicals generated by Fenton reagent to fully react with the polyacrylamide remaining in the manufactured sand and degrade it into small molecules; (4) Continue stirring until homogeneous to obtain workable concrete or mortar.

6. The method for applying the inorganic shielding agent according to claim 5, characterized in that, The method for determining the residual amount of polyacrylamide in step (1) is as follows: relative to the mass of manufactured sand, for every 0.01 wt% of residual polyacrylamide eliminated, approximately 0.175 liters / cubic meter of hydrogen peroxide is added to the mixture.

7. The method for applying the inorganic shielding agent according to claim 5, characterized in that, The polyacrylamide is at least one of anionic, cationic, or nonionic polyacrylamide.

8. The method of applying the inorganic shielding agent according to claim 5, characterized in that, The ferrous salt and hydrogen peroxide are added separately, with the ferrous salt added first and then the hydrogen peroxide added.

9. The use of any one of the inorganic shielding agents according to claims 1-3 in the preparation of concrete or mortar.

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