Reduction type polycarboxylate superplasticizer as well as preparation method and application thereof

Abstract

The invention belongs to the field of building materials, and particularly relates to a reduction type polycarboxylate superplasticizer as well as a preparation method and application thereof. The preparation method of the water reducing agent comprises the following steps: preparing an HDDA monomer, taking acrylic acid, the HDDA monomer, sodium methallyl sulfonate and water as a material A, uniformly mixing a reducing agent, a chain transfer agent and water as a material B, dropwise adding the material A and the material B into an initiator, adjusting the pH value to 6.5-7, and adding water to adjust the pH value to a specified concentration, thereby obtaining the shrinkage-reducing polycarboxylic acid water reducing agent. The application of the shrinkage-reducing type polycarboxylic acid water reducer is that the shrinkage-reducing type polycarboxylic acid water reducer is doped into an alkali-activated slag cementing material according to 0.45-0.5% of the mass of slag. The reduction type polycarboxylate superplasticizer is introduced to reduce the functional monomer HDDA, and the HDDA reduces the surface tension of a pore solution, inhibits the negative pressure of a capillary tube, optimizes the pore size distribution and reduces gt; the proportion of macropores of 50 nm improves the compactness of the microstructure, and the 28d dry shrinkage rate of the alkali-activated slag slurry can be obviously reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a shrinkage-reducing polycarboxylate water reducer, a preparation method thereof, and an application thereof. Background Art

[0002] Ordinary Portland cement (OPC) is widely used in the construction field due to its excellent mechanical properties and durability. However, its production process has high energy consumption and generates a large amount of carbon dioxide emissions. In addition, the production of OPC requires a large amount of limestone and is calcined at a high temperature of 1500 °C, which further exacerbates energy consumption and environmental pollution. Therefore, finding a low-carbon and energy-saving alternative material has become an important topic in the construction industry.

[0003] Alkali-activated materials (AAM) have received extensive attention due to their low energy consumption and carbon dioxide emissions during the production process and are considered promising alternatives to OPC. Alkali-activated slag (AAS) cementitious materials are one of the most potential alternatives, which have advantages such as low permeability, high strength, good thermal stability, and excellent chemical corrosion resistance. Compared with OPC concrete, AAS concrete can reduce carbon dioxide emissions by 25% - 50% and reduce the embodied energy by more than 40%.

[0004] However, the large-scale application of AAS still faces some challenges, and the most prominent problem is its volume instability, that is, large shrinkage. It is reported that the shrinkage of AAS is about 2 - 4 times higher than that of OPC. This significant shrinkage will cause non-uniform deformation of the material, form tensile stress, and then lead to the formation of harmful cracks. Shrinkage is the main reason for the volume instability of concrete structures and the formation of related cracks, which is mainly caused by water loss to the environment or self-drying. This shrinkage will cause early autogenous shrinkage, generate high internal stress and early cracking, and further damage the long-term durability performance of concrete such as corrosion resistance, freeze-thaw resistance, and alkali-silica reaction resistance.

[0005] To effectively reduce the shrinkage and crack problems of concrete, the industry has taken various measures. For example, water reducers can be used, especially polycarboxylate-based high-performance water reducers, which can reduce the plastic shrinkage and drying shrinkage of concrete by reducing the water-cement ratio. However, the water-reducing effect of conventional polycarboxylate water reducers in alkali-activated slag (AAS) materials is not ideal, and the problem of its volume instability cannot be well solved.

[0006] In summary, developing a new type of shrinkage-reducing polycarboxylate water reducer to solve the problems of shrinkage and crack formation in alkali-activated slag (AAS) materials has important theoretical and practical significance. Summary of the Invention

[0007] The object of the present invention is to overcome the deficiencies of the prior art and provide a shrinkage-reducing polycarboxylate water reducer, its preparation method and application. This shrinkage-reducing polycarboxylate water reducer can effectively reduce the dry shrinkage of AAS, improve its volume stability, and enhance the workability of AAS paste.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A preparation method of a shrinkage-reducing polycarboxylate water reducer, comprising the following steps:

[0010] Step 1, prepare HDDA monomer;

[0011] Step 2, mix methallyl polyoxyethylene ether and water in a reaction vessel, and stir well at 40 - 60 °C until the methallyl polyoxyethylene ether is completely dissolved; mix acrylic acid (AA), HDDA monomer, sodium methallyl sulfonate and water evenly to obtain Material A; the HDDA monomer accounts for 2.3% - 3.4% of the mass of methallyl polyoxyethylene ether; the dosage of acrylic acid (AA) accounts for 10.8% - 13.5% of the mass of methallyl polyoxyethylene ether respectively, that is, the molar ratio of acrylic acid to methallyl polyoxyethylene ether (acid-ether ratio) is (3.6 - 4.5):1; the dosage of sodium methallyl sulfonate accounts for 0.2% - 0.3% of the mass of methallyl polyoxyethylene ether;

[0012] Mix the reducing agent, chain transfer agent and water evenly to obtain Material B; the reducing agent and chain transfer agent respectively account for 0.15% - 0.3% and 0.4% - 1.0% of the total mass of the HDDA monomer;

[0013] Step 3, add the initiator to the reaction vessel, stir for 3 min - 5 min and then start to dropwise add Material A and Material B simultaneously. After the dropping is completed, obtain the solution to be adjusted. Keep the solution to be adjusted at 50 °C - 60 °C and stir for 30 min - 60 min; the dosage of the initiator is 0.7% - 1.3% of the total mass of the HDDA monomer

[0014] Step 4, after the solution to be adjusted cools down, use sodium hydroxide solution to adjust the pH of the solution to be adjusted to 6.5 - 7, add water to adjust the solid content to the specified concentration, and stir evenly to obtain the shrinkage-reducing polycarboxylate water reducer.

[0015] Further, Step 1, preparing the HDDA monomer includes the following steps:

[0016] (1) Mix acrylic acid (AA), 1,6 - hexanediol (HD), catalyst, molecular sieve in a container, and add benzene as a water-carrying agent; place the container in an oil bath at 125 °C - 140 °C and heat for 2 - 4 hours for an esterification reaction to obtain a mixed liquid; wherein, the mass ratio of acrylic acid to 1,6 - hexanediol (acid-alcohol ratio) is (3.8 - 4.4):1.

[0017] (2) Cool the mixed solution to room temperature, filter out the molecular sieve, and distill to recover p-xylene to obtain an HDDA monomer with an esterification rate ≥ 95%.

[0018] Furthermore, the catalyst is one or two of maleic anhydride and toluene sulfonic acid, and the catalyst accounts for 0.5% - 1.5% of the total mass of acrylic acid and 1,6 - hexanediol;

[0019] The p-xylene is p-dimethylbenzene, and the mass of the p-xylene is 3 - 4 times the total mass of acrylic acid, 1,6 - hexanediol, and the catalyst in Step 1;

[0020] The molecular sieve is zeolite molecular sieve, and the dosage of the molecular sieve is 3% - 5% of the total mass of acrylic acid (AA), 1,6 - hexanediol (HD), and the catalyst in Step 1;

[0021] Furthermore, in Step 3, when dropping A material and B material, control the dropping rate of A material at 12 - 21 drops per minute and complete it within 120 - 210 minutes; control the dropping rate of B material at 6 - 10 drops per minute and complete it within 150 - 240 minutes.

[0022] Furthermore, the reducing agent is one or several of vitamin C, sodium formaldehyde sulfoxylate, epoxy resin E51, ferrous sulfate, sodium bisulfite, sodium dithionite, and sodium thiosulfate.

[0023] Furthermore, the chain transfer agent is one or several of 2 - mercaptoethanol, mercaptoacetic acid, 3 - mercaptopropionic acid, 2 - mercaptobutyric acid, and sodium hypophosphite.

[0024] Furthermore, the initiator is one or several of 30% hydrogen peroxide solution, ammonium persulfate, potassium persulfate, and peracetic acid.

[0025] The present invention also provides a shrinkage - reducing polycarboxylate water - reducing agent, which is prepared by using the preparation method of the aforementioned shrinkage - reducing polycarboxylate water - reducing agent.

[0026] The present invention also provides an application of the shrinkage - reducing polycarboxylate water - reducing agent, adding the shrinkage - reducing polycarboxylate water - reducing agent to an alkali - activated slag cementitious material; the dosage of the solid solute in the shrinkage - reducing polycarboxylate water - reducing agent is 0.45% - 0.5% of the mass of the slag in the alkali - activated slag cementitious material, such as adding a shrinkage - reducing polycarboxylate water - reducing agent accounting for 0.48% of the mass of the slag.

[0027] The beneficial effects of the present invention are:

[0028] 1. The shrinkage-reducing polycarboxylate superplasticizer (SR-PCE) of the present invention is prepared by introducing a shrinkage-reducing functional monomer (HDDA cross-linked structure) through a polymerization reaction to obtain a polycarboxylate superplasticizer with excellent dispersibility and shrinkage reduction. The shrinkage-reducing functional monomer can reduce the surface tension of the pore solution, inhibit capillary negative pressure, and at the same time optimize the pore size distribution, reduce the proportion of macropores larger than 50 nm, and improve the compactness of the microstructure. The SR-PCE of the present invention can significantly reduce the 28-day dry shrinkage rate of alkali-activated slag (AAS) paste.

[0029] 2. The shrinkage-reducing polycarboxylate superplasticizer SR-PCE of the present invention regulates the side chain length and density by grafting HDDA monomers, significantly increasing the adsorption amount of SR-PCE on the surface of slag particles and significantly enhancing the steric hindrance effect, improving the initial fluidity of AAS and meeting the requirements of complex construction scenarios.

[0030] 3. The SR-PCE of the present invention can significantly improve the microscopic pore structure of AAS mortar. The dry shrinkage rate of AAS mortar is reduced by about 30%, indicating that SR-PCE has obvious advantages in reducing the proportion of macropores and optimizing the pore size distribution. The reduction of the dry shrinkage rate indirectly reflects the improvement of the compactness of the mortar microstructure, thereby improving the compressive strength and durability.

[0031] 4. The present invention adopts the molecular sieve cyclic dehydration technology, which can effectively remove the water generated in the reaction compared with the traditional HDDA preparation method, enabling the esterification reaction to proceed efficiently at a lower temperature (130 °C oil bath). This method can reduce energy consumption by 40% - 45% and ensure that the esterification rate of HDDA monomers reaches or exceeds 95%, providing sufficient and stable functional monomers for subsequent polymerization.

[0032] 5. This scheme selects benzene (i.e., p-xylene) as the water-carrying agent, which can not only promote the removal of water and ensure the reaction equilibrium, but also be recovered by condensation with a recovery rate of more than 95%. The high recovery rate of benzene not only reduces raw material consumption and production costs, but also meets the requirements of green and low-carbon production, significantly improving the economy and environmental protection of the process compared with traditional methods.

[0033] 6. The synthesis process of the present invention adopts low-temperature polymerization (40 - 60 °C) combined with molecular sieve cyclic dehydration technology, which can reduce the cement consumption per ton of SR-PCE by 150 - 200 kg and reduce CO2 emissions by 120 - 150 kg, meeting the carbon neutrality goal. Detailed Embodiments

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments.

[0035] Example 1

[0036] A preparation method of a shrinkage-reducing polycarboxylate water reducer, comprising the following steps:

[0037] Step 1: Prepare the HDDA (1,6-hexanediol diacrylate) monomer. The steps are as follows: Add 40 g of acrylic acid (AA), 10 g of 1,6-hexanediol, 0.5 g of toluenesulfonic acid (as a catalyst), 10.1 g of molecular sieve, and 202 g of p-xylene as a water-carrying agent into a container (such as a three-necked flask). Place the container in an oil bath at 130 °C and heat for 2 hours for an esterification reaction to obtain a mixed miscellaneous liquid. Subsequently, use the methods of cooling and vacuum distillation to remove impurities from the mixed miscellaneous liquid, cool and discharge to obtain a shrinkage-reducing monomer (HDDA monomer) with an esterification rate ≥ 95%, and at the same time recover p-xylene with a p-xylene recovery rate ≥ 95%;

[0038] In Step 2, the molecular weight of methallyl polyoxyethylene ether (HPEG) is 2160 - 2640, and HPEG-2400 is selected in the present invention; vitamin C is used as the reducing agent, 2-mercaptoethanol is used as the chain transfer agent, and 30% hydrogen peroxide is used as the initiator;

[0039] Mix 400 g of methallyl polyoxyethylene ether (HPEG) and water in a reaction container and stir well at 50 °C for 2.5 h;

[0040] Mix 12 g of the HDDA monomer, 48 g of acrylic acid (AA), 1 g of sodium methallylsulfonate (MAS), and a certain amount of deionized water (only used to dissolve the solute) to prepare Material A; the HDDA monomer accounts for 3% of the mass of methallyl polyoxyethylene ether;

[0041] Mix 0.03 g of vitamin C, 0.72 g of 2-mercaptoethanol, and an appropriate amount of deionized water (only used to dissolve the solute) to prepare Material B;

[0042] In Step 3, add 0.12 g of the initiator 30% hydrogen peroxide into the reaction container, stir for 3 - 5 min, and then start to simultaneously dropwise add Material A and Material B. Control the dropping rate of Material A at 12 - 21 drops / minute and complete it within 120 - 210 minutes; control the dropping rate of Material B at 6 - 10 drops / minute and complete it within 150 - 240 minutes. After the dropping of Material A and Material B is completed, a solution to be adjusted is obtained. Continue to keep it warm and stir at 50 °C for 30 - 60 min and then cool; the dosage of the initiator is 1% of the total mass of the HDDA monomer;

[0043] In Step 4, add a 30 wt% sodium hydroxide solution to the reaction container to adjust the pH of the solution to be adjusted to 7, calculate the mass of the existing substances, and add water to adjust the solid content to 40 wt% (the solid content refers to the mass ratio of the effective polycarboxylate water reducer in the solution), stir evenly to obtain a shrinkage-reducing polycarboxylate water reducer SR-PCE. In practice, the concentration of the shrinkage-reducing polycarboxylate water reducer SR-PCE is set as required. In the examples and comparative examples of the present invention, the solid content is uniformly adjusted to 40%.

[0044] Example 2

[0045] The difference between this Example 2 and Example 1 lies in that: maleic anhydride is used as the catalyst when preparing the HDDA monomer. Ferrous sulfate is used as the reducing agent, mercaptoacetic acid is used as the chain transfer agent, and ammonium persulfate is used as the initiator; in addition, the dosages of some substances are adjusted.

[0046] A preparation method of a shrinkage-reducing polycarboxylate water reducer comprises the following steps:

[0047] Step 1, preparing the HDDA monomer, and the steps are as follows: adding 40 g of acrylic acid (AA), 10 g of 1,6-hexanediol, 0.27 g of maleic anhydride (as the catalyst), 9.77 g of molecular sieve and 189.95 g of p-xylene as the water-carrying agent into a container (such as a three-necked flask), placing the container in an oil bath at 130 °C and heating for 2 hours for an esterification reaction to obtain a mixed miscellaneous liquid; then removing impurities from the mixed miscellaneous liquid by using a cooling and vacuum distillation method, cooling and discharging to obtain a shrinkage-reducing monomer (HDDA monomer) with an esterification rate ≥ 95%, and simultaneously recovering p-xylene with a p-xylene recovery rate ≥ 95%;

[0048] Step 2, mixing 400 g of methallyl polyoxyethylene ether and water in a reaction container, and fully stirring at 50 °C for 2.5 h;

[0049] Mixing 9.2 g of the HDDA monomer, 43.2 g of acrylic acid (AA), 0.8 g of sodium methallylsulfonate (MAS) and a certain amount of deionized water (for dissolving solutes) to prepare Material A; the HDDA monomer accounts for 2.3% of the mass of methallyl polyoxyethylene ether;

[0050] Mixing 0.0285 g of ferrous sulfate, 0.0368 g of mercaptoacetic acid and an appropriate amount of deionized water (for dissolving solutes) to prepare Material B;

[0051] Step 3, adding 0.0644 g of ammonium persulfate (initiator) into the reaction container, stirring for 3 - 5 min and then starting to simultaneously dropwise add Material A and Material B, controlling the dropping rate of Material A to be 12 - 21 drops per minute and completing within 120 - 210 minutes; controlling the dropping rate of Material B to be 6 - 10 drops per minute and completing within 150 - 240 minutes; after the dropping of Material A and Material B is completed, a solution to be adjusted is obtained, and continue to keep warm and stir at 50 °C for 30 - 60 min and then cool; the dosage of the initiator is 0.7% of the total mass of the HDDA monomer;

[0052] Step 4, adding a 30 wt% sodium hydroxide solution into the reaction container to adjust the pH of the solution to be adjusted to 7, calculating the mass of the existing substances, and adding water to adjust the solid content to 40 wt% (the solid content refers to the mass ratio of the effective polycarboxylate water reducer in the solution), and stirring evenly to obtain the shrinkage-reducing polycarboxylate water reducer SR-PCE.

[0053] Example 3

[0054] The difference between this Example 3 and Example 2 lies in that: the catalyst used in the preparation of the HDDA monomer is toluenesulfonic acid. In addition, the dosages of some substances are adjusted.

[0055] A preparation method of a shrinkage-reducing polycarboxylate water reducer includes the following steps:

[0056] Step 1, prepare the HDDA monomer. The steps are as follows: add 38 g of acrylic acid (AA), 10 g of 1,6-hexanediol, 0.576 g of toluenesulfonic acid (as a catalyst), 7.286 g of molecular sieve and 194.304 g of benzene as a water-carrying agent into a container (such as a three-necked flask), place the container in an oil bath at 130 °C and heat for 2 hours for an esterification reaction to obtain a mixed miscellaneous liquid; then use the methods of cooling and vacuum distillation to remove impurities from the mixed miscellaneous liquid, cool and discharge to obtain a shrinkage-reducing monomer (HDDA monomer) with an esterification rate ≥ 95%, and at the same time recover benzene, and the benzene recovery rate ≥ 95%;

[0057] Step 2, mix 400 g of methallyl polyoxyethylene ether and water in a reaction container, and stir well at 50 °C for 2.5 h;

[0058] Mix 13.6 g of the HDDA monomer, 54 g of acrylic acid (AA), 1.2 g of sodium methallylsulfonate (MAS) and a certain amount of deionized water (for dissolving solutes) to prepare Material A; the HDDA monomer accounts for 3.4% of the mass of methallyl polyoxyethylene ether;

[0059] Mix 0.0272 g of ferrous sulfate, 0.1088 g of mercaptoacetic acid and an appropriate amount of deionized water (for dissolving solutes) to prepare Material B;

[0060] Step 3, add 0.136 g of ammonium persulfate (initiator) into the reaction container, stir for 3 - 5 min and then start to dropwise add Material A and Material B simultaneously; after the dropping of Material A and Material B is completed, a solution to be adjusted is obtained, and continue to keep warm and stir at 50 °C for 30 - 60 min and then cool; the dosage of the initiator is 1% of the total mass of the HDDA monomer;

[0061] Step 4, add a 30 wt% sodium hydroxide solution into the reaction container to adjust the pH of the solution to be adjusted to 7, calculate the mass of the existing substances, and add water to adjust the solid content to 40 wt% (the solid content refers to the mass ratio of the effective polycarboxylate water reducer in the solution), stir evenly to obtain a shrinkage-reducing polycarboxylate water reducer SR-PCE.

[0062] Comparative Example 1

[0063] The difference between this Comparative Example 1 and Example 1 is only that the reaction temperature of the esterification reaction in Step 1 is 90 °C.

[0064] Comparative Example 2

[0065] The difference between this Comparative Example 2 and Example 1 is only that the dosage of HDDA monomer in Component A is 16 g.

[0066] Comparative Example 3

[0067] The difference between this Comparative Example 3 and Example 1 is that: the dosage of acrylic acid (AA) in Component A is 19.18 g, and the dosage of HDDA monomer is 11.508 g.

[0068] Comparative Example 4

[0069] The difference between this Comparative Example 4 and Example 1 is only that in Step 2, the temperature for stirring and mixing allyl methyl polyoxyethylene ether and water in the reaction vessel is 40°C.

[0070] Comparative Example 5

[0071] The difference between this Comparative Example 5 and Example 1 is that: the dosage of allyl methyl polyoxyethylene ether (HPEG) in Step 2 is 319.2 g; the dosage of HDDA in Component A is 10.853 g; the dosage of reducing agent in Component B is 0.0217 g, and the dosage of chain transfer agent is 0.0651 g; the dosage of initiator in Step 3 is 0.1085 g.

[0072] Comparative Example 6

[0073] The difference between this Comparative Example 6 and Example 1 is only that in Step 2, the dosage of acrylic acid (AA) is 30 g.

[0074] Comparative Example 7

[0075] The difference between this Comparative Example 7 and Example 1 is only that in Step 1, the dosage of 1,6 - hexanediol is 8 g.

[0076] Verification Example 8

[0077] This comparative example provides a preparation method of a common polycarboxylate water - reducing agent, which is basically the same as the steps of the example, and the difference is only that in Step (3), the HDDA shrinkage - reducing monomer is not added.

[0078] Specimens were made for the AAS pastes added with SR - PCE prepared in the above - mentioned Example 1 - Example 3 and Comparative Example 1 - Comparative Example 7 according to GB / T8077 - 2012 "Test Methods for Homogeneity of Concrete Admixtures" and JC / T603 - 2004 "Test Method for Dry Shrinkage of Mortar", and fluidity and drying shrinkage tests were carried out.

[0079] The preparation steps of the test piece are as follows: Take 6 ml of the prepared polycarboxylate water reducer and mix it with 500 g of slag, 1000 g of standard sand and a certain amount of water. The water consumption is adjusted according to the water-binder ratio of the slag, the moisture content of each raw material and the expected fluidity of the mixture. Specifically, refer to GB / T8077-2012 "Test Methods for Homogeneity of Concrete Admixtures" and JC / T603-2004 "Test Methods for Dry Shrinkage of Mortar". After stirring evenly, pour it into a mold with dimensions of 25 mm×25 mm×280 mm, and then place it in a curing box at a temperature of 23°C and a relative humidity of 95% for 24 hours, and then transfer it to a shrinkage chamber at a temperature of 23°C and a humidity of 54%. The test results are shown in the following table; among them, 7d and 28d respectively represent the time placed in the shrinkage chamber.

[0080] Table 1 Test results of examples and comparative examples.

[0081]

[0082] As can be seen from the above table, the designs of Examples 1-3 significantly reduced the 7-day and 28-day drying shrinkage rates of AAS mortar, while optimizing the pore structure of the mortar and improving the fluidity. The 28-day drying shrinkage rates of Examples 1-3 were significantly lower than those of all comparative examples, and the 7-day drying shrinkage rates also decreased significantly, with a large increase in fluidity. This indicates that reasonably optimized SR-PCE synthesis parameters can effectively improve the comprehensive performance of AAS mortar, especially showing significant advantages in controlling dry shrinkage and improving fluidity. Examples 1-3 successfully synthesized SR-PCE with excellent shrinkage-reducing performance by strictly controlling the acid-alcohol ratio (mass ratio of acrylic acid to 1,6-hexanediol), acid-ether ratio (mass ratio or molar ratio of acrylic acid to HPEG), and the esterification and polymerization reaction temperatures, resulting in a significant reduction in the proportion of key pore sizes (>50 nm) in AAS mortar and a more uniform pore distribution, thereby effectively reducing the capillary pressure and the risk of shrinkage cracking.

[0083] In contrast, due to the unreasonable setting of reaction parameters in the comparative examples, the synthesis amounts of SR-PCE or HDDA were insufficient, which in turn affected the shrinkage reduction effect and the properties of the mortar. For example, in Comparative Example 1, the esterification reaction temperature was reduced, resulting in a low esterification rate and insufficient amount of the effective shrinkage-reducing monomer (HDDA monomer); in Comparative Example 2, the amount of HDDA monomer was reduced, failing to provide sufficient shrinkage-reducing monomers and effectively reducing the shrinkage of the mortar; in Comparative Examples 3 and 4, due to the reduction of the acid-ether ratio and the polymerization reaction temperature respectively, the polymerization reaction was incomplete, and finally the content of SR-PCE was insufficient; in Comparative Example 5, due to the excessive acid-ether ratio, the polymerization efficiency decreased, and the amount of the effective polycarboxylate water reducer produced was insufficient; in Comparative Examples 6 and 7, due to the unreasonable adjustment of the acid-alcohol ratio, the esterification rate was low and the effective synthesis amount of HDDA was significantly reduced respectively. These parameter deviations directly led to the AAS mortar in the comparative examples showing a higher dry shrinkage rate, poorer fluidity and an unsatisfactory pore structure. By comparing Examples 1-3 and the blank control Comparative Example 8, it can be seen that under the condition of not adding shrinkage-reducing monomers, the 28-day drying shrinkage rate of the AAS mortar was significantly higher than that of Examples 1-3 and other comparative examples, and the 7-day drying shrinkage rate was also significantly higher. The proportion of the key pore size (>50 nm) in the AAS mortar was not improved, indicating that the addition of the shrinkage-reducing monomer HDDA could significantly improve the dry shrinkage rate of the AAS mortar.

[0084] Through comparison, it can be found that on the basis of optimizing the acid-alcohol ratio and the acid-ether ratio, the examples accurately controlled the esterification and polymerization reaction conditions, effectively balanced the generation efficiency of HDDA and SR-PCE, significantly improved the dispersibility and the action effect of the shrinkage reducer in the mortar, and finally achieved excellent dry shrinkage control and pore structure optimization. This not only shows the scientificity and rationality of the preparation method design of the present invention, but also highlights the application potential and superiority of SR-PCE in improving the properties of AAS mortar, providing important experimental basis and theoretical support for the further promotion and application of shrinkage-reducing polycarboxylate water reducers.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A preparation method of a reduced polycarboxylate water reducer, characterized in that, It includes the following steps: Step 1, prepare HDDA monomer; Step 2, mix methallyl polyoxyethylene ether and water in a reaction vessel, and stir well at 40 - 60 °C until the methallyl polyoxyethylene ether is completely dissolved; mix acrylic acid, HDDA monomer, sodium methallyl sulfonate and water evenly to obtain Material A; the HDDA monomer accounts for 2.3% - 3.4% of the mass of methallyl polyoxyethylene ether; the dosages of acrylic acid and sodium methallyl sulfonate respectively account for 10.8% - 13.5% and 0.2% - 0.3% of the mass of methallyl polyoxyethylene ether; Mix a reducing agent, a chain transfer agent and water evenly to obtain Material B; the reducing agent and the chain transfer agent respectively account for 0.15% - 0.3% and 0.4% - 1.0% of the total mass of the HDDA monomer; Step 3, add an initiator into the reaction vessel, stir for 3 - 5 min and then start to dropwise add Material A and Material B simultaneously. After the dropping is completed, obtain a solution to be adjusted. Keep the solution to be adjusted at 50 °C - 60 °C and stir for 30 min - 60 min; the dosage of the initiator is 0.7% - 1.3% of the total mass of the HDDA monomer Step 4, after the solution to be adjusted cools down, use sodium hydroxide solution to adjust the pH of the solution to be adjusted to 6.5 - 7, add water to adjust the solid content to a specified concentration, and stir evenly to obtain a shrinkage-reducing polycarboxylate water reducer.

2. The preparation method of the reduced polycarboxylate water reducer according to claim 1, characterized in that: Step 1, the preparation of HDDA monomer includes the following steps: (1) Mix acrylic acid, 1,6 - hexanediol, a catalyst, and molecular sieve in a container, and add p - xylene as a water - carrying agent; place the container in an oil bath at 125 °C - 140 °C and heat for 2 - 4 hours for an esterification reaction to obtain a mixed liquid; (2) Cool the mixed liquid to room temperature, filter out the molecular sieve, distill and recover p - xylene to obtain an HDDA monomer with an esterification rate ≥ 95%.

3. The preparation method of the reduced polycarboxylate water reducer according to claim 2, characterized in that: In Step 1, the mass ratio of acrylic acid to 1,6 - hexanediol is (3.8 - 4.4):

1.

4. The preparation method of the reduced polycarboxylate water reducer according to claim 2, characterized in that: The catalyst is one or both of maleic anhydride and toluene sulfonic acid, and the catalyst accounts for 0.5% - 1.5% of the total mass of acrylic acid and 1,6 - hexanediol; The p - xylene is p - dimethylbenzene, and the mass of the p - xylene is 3 - 4 times the total mass of acrylic acid, 1,6 - hexanediol, and the catalyst in Step 1; The molecular sieve is zeolite molecular sieve, and the dosage of the molecular sieve is 3% - 5% of the total mass of acrylic acid, 1,6 - hexanediol, and the catalyst in Step 1.

5. The preparation method of the reduced polycarboxylate water reducer according to claim 1, characterized in that: In Step 3, when dropping Material A and Material B, control the dropping rate of Material A at 12 - 21 drops per minute and complete it within 120 - 210 minutes; control the dropping rate of Material B at 6 - 10 drops per minute and complete it within 150 - 240 minutes.

6. The preparation method of the reduced polycarboxylate water reducer according to claim 1, characterized in that: The reducing agent is one or several of vitamin C, Rongalite, epoxy resin E51, ferrous sulfate, sodium bisulfite, sodium dithionite, and sodium thiosulfate.

7. The preparation method of the reduced polycarboxylate water reducer according to claim 1, characterized in that: The chain transfer agent is one or several of 2 - mercaptoethanol, mercaptoacetic acid, 3 - mercaptopropionic acid, 2 - mercaptobutyric acid, and sodium hypophosphite.

8. The preparation method of the reduced polycarboxylate water reducer according to claim 1, characterized in that: The initiator is one or several of 30% hydrogen peroxide solution, ammonium persulfate, potassium persulfate, and peracetic acid.

9. A reduced-type polycarboxylate water reducer, characterized in that: It is prepared by using the preparation method of the shrinkage - reducing polycarboxylate water reducer according to any one of claims 1 to 8.

10. Application of a reduced polycarboxylate water reducer, characterized in that: A shrinkage-reducing polycarboxylate superplasticizer is added to the alkali-activated slag cementitious material; the dosage of the solid solute in the shrinkage-reducing polycarboxylate superplasticizer is 0.45% - 0.5% of the mass of the slag in the alkali-activated slag cementitious material.

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