An ultra-low-dosage composite nano early strength agent and a preparation method thereof

Abstract

This invention provides an ultra-low dosage composite nano-early strength agent and its preparation method. The preparation method includes the following steps: S1. Mixing nano-silica sol with silane-modified polycarboxylic acid and stirring to obtain suspension A; S2. Adding a calcium source and a dispersant to suspension A, adjusting the pH to 9-12, and stirring thoroughly to obtain base material B; S3. Dropwise adding a silicon source to base material B obtained in S2, performing high-speed shear stirring while maintaining the pH value of the reaction system unchanged. After the dropwise addition is completed, continuing high-speed shear stirring for 1-2 hours yields the ultra-low dosage composite nano-early strength agent. This ultra-low dosage composite nano-early strength agent can achieve excellent early strength effect under ultra-low dosage conditions, and can also significantly improve the later strength of concrete.

Description

Technical Field

[0001] This invention relates to the field of building materials and concrete technology, and in particular to an ultra-low dosage composite nano early strength agent and its preparation method. Background Technology

[0002] With the efficient and green development of the construction industry, the prefabricated building industry, with its energy-saving and environmentally friendly advantages, has developed rapidly. As the main component of prefabricated buildings, precast concrete, primarily consisting of precast components, subway tunnel segments, and pipe piles, has also begun to develop rapidly. Precast concrete has high standards for both structure and appearance. Furthermore, to achieve perfect splicing of all precast concrete components, standardized steel molds are generally required during production. To improve production efficiency, accelerate mold turnover, minimize construction time, and maximize benefits, the requirements for the early strength development of concrete are becoming increasingly stringent.

[0003] There are generally two methods to improve early strength: one is to use chemical admixtures to accelerate the hydration of silicate cement; the other is to steam-cur precast concrete components to improve early strength. However, steam curing not only consumes a lot of energy, but also damages the later strength and durability of concrete. Early strength agents, as admixtures that can accelerate the development of early strength in concrete, are in increasing demand in engineering applications.

[0004] Nano-CSH early-strength agents have gradually become a research hotspot in the field of early-strength agents due to their large specific surface area and excellent early-strength effect. For example, Chinese patent CN 113979661 A discloses a method for preparing a nano-calcium silicate suspension with high stability and good early-strength effect. Hydroxyl and amino groups are introduced into the molecular structure of the dispersant. The hydroxyl hydrogen or amino hydrogen can form hydrogen bonds with silicon atoms, preparing a highly stable nano-CSH early-strength agent with excellent early-strength performance. The dosage is 2%-4% of the cementitious material. Chinese patent CN 107235650A discloses a water-based nanocomposite early-strength admixture and its preparation method. The preparation process is simple, the product has good stability, and it can effectively improve the early strength of concrete. The 12h and 24h compressive strength of the mortar is increased by more than 30% and 16% respectively compared with ordinary commercially available early-strength polycarboxylate superplasticizers, while not affecting the later strength. Zhang Chaoyang et al. (Influence of nano-CSH on cement hydration, pore structure of hardened paste and concrete strength [J], 2019, 47(5), 585-593) reported a method for synthesizing nano-CSH gel and prepared a CSH gel suspension with a solid content of 10% with obvious promoting effect, but it had a significant negative impact on the concrete strength after 1 day.

[0005] The aforementioned patents and papers generally employ a co-precipitation method to prepare nano-CSH suspensions, which largely solves the suspension stability problem and exhibits a significant early strength promoting effect. However, in practical applications, the dosage of nano-CSH is relatively high, often reaching 2%-4% of the cementitious material; simultaneously, the promoting effect of nano-CSH suspensions on the strength of concrete after 1 day is significantly weakened, and even at 28 days, problems such as strength reduction may occur.

[0006] Chinese patent CN112830710A, "A Coupling Agent Modified Nano-Hydrated Calcium Silicate Nuclei Early Strength Agent and Its Preparation Method," discloses a method using a coupling agent to chemically bond the inorganic compound hydrated calcium silicate with an organic dispersant. One end of the coupling agent reacts with the hydrated calcium silicate, while the other end reacts with the dispersant, thereby improving the dispersion of CSH nuclei and inhibiting their growth. At lower dosages, this method can provide more effective specific surface area and achieve better early strength. However, the dosage is still relatively high, and the early strength effect still needs further improvement.

[0007] Therefore, it is of great significance to provide an ultra-low doping composite nano early strength agent with excellent early strength effect and its preparation method. Summary of the Invention

[0008] Given that existing composite nano-early strength agents still have relatively high dosages and the early strength effect still needs further improvement, this invention provides an ultra-low dosage composite nano-early strength agent and its preparation method. This ultra-low dosage composite nano-early strength agent can achieve excellent early strength effect under ultra-low dosage conditions, and can also significantly improve the later strength of concrete.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing an ultra-low doping composite nano-early strength agent includes the following steps:

[0011] S1. Mix nano-silica sol with silane-modified polycarboxylic acid and stir to obtain suspension A;

[0012] S2. Add the calcium source and dispersant to suspension A, adjust the pH to 9-12, stir thoroughly to obtain base material B;

[0013] S3. Add the silicon source dropwise to the substrate B described in S2, perform high-speed shearing and stirring, and maintain the pH value of the reaction system unchanged. After the dropwise addition is completed, continue high-speed shearing and stirring for 1-2 hours to obtain the ultra-low doping composite nano early strength agent.

[0014] Furthermore, the silane-modified polycarboxylic acid is prepared by the following method:

[0015] Step 1: Dissolve the polyether macromonomer, alkoxysilane, and deionized water in a water bath by heating and stirring. Set aside.

[0016] Step 2: Prepare solution A by mixing unsaturated carboxylic acid, reducing agent, chain transfer agent, and deionized water; prepare solution B by mixing initiator and deionized water for later use.

[0017] Step 3: Under continuous water bath heating, simultaneously add solution A and solution B obtained in step 2 to the mixed solution obtained in step 1. The total addition time is 2-2.5 hours. After the addition is completed, maintain water bath heating for 6-8 hours to continue the reaction. Cool to room temperature to obtain silane-modified polycarboxylic acid.

[0018] Furthermore, the mass ratio of the polyether macromonomer, alkoxysilane, and deionized water is (200-220):(8-10):(100-120);

[0019] The mass ratio of the unsaturated carboxylic acid, reducing agent, chain transfer agent, and deionized water is (18-26):(0.5-0.8):(0.8-1.2):(50-70).

[0020] The mass ratio of the initiator to deionized water is (2-2.6):(50-60);

[0021] The water bath heating temperature is 40-75℃.

[0022] Furthermore, the polyether macromonomer is an isopentenyl alcohol polyoxyethylene ether macromonomer with a number average molecular weight of 2400.

[0023] The unsaturated carboxylic acid is one or more of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid and their derivatives.

[0024] The initiator is one or more of ammonium persulfate, sodium persulfate, tert-butyl peroxyvalerate, and dicyclohexyl peroxydicarbonate.

[0025] The reducing agent is one or more of L-ascorbic acid, sodium bisulfite, ferrous sulfate, potassium bisulfite, and sodium hypophosphite;

[0026] The chain transfer agent is one or more of mercaptoacetic acid, mercaptopropionic acid, sodium methyl methacrylate, and mercaptoethanol.

[0027] The alkoxysilane is one or more of γ-methacryloxypropyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, and vinyldimethylethoxysilane.

[0028] Furthermore, the calcium source is one or more of calcium nitrate tetrahydrate, calcium formate, calcium gluconate, calcium acetate, calcium nitrite, and calcium dihydrogen phosphate.

[0029] The silicon source is one or more of sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, sodium fluorosilicate, and potassium silicate.

[0030] The dispersant is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and gum arabic.

[0031] Furthermore, the stirring temperature in S1 is 20-40℃, the stirring speed is 600r / min, and the stirring time is 3h.

[0032] Furthermore, the pH adjustment described in S2 is achieved by adjusting the pH value using a 30% NaOH solution and HNO3; the stirring temperature described in S2 is 15-20℃, the stirring speed is 600 r / min, and the stirring time is 0.5-1 h.

[0033] Furthermore, the droplet acceleration rate in S3 is 0.8-1.6 mL / min, the high-speed shear stirring temperature in S3 is 5-20℃, and the rotation speed is 2000-5000 r / min.

[0034] Furthermore, the weight ratio of the nano-silica sol, silane-modified polycarboxylic acid, calcium source, dispersant, and silicon source is (60-100):(180-220):(76-120):(20-40):(100-158); the concentration of the calcium source is 2-4 mol / L; the concentration of the silicon source is 1.7-3.2 mol / L; and the molar ratio of calcium to silicon in the calcium and silicon sources is (1.6-2.0):1.

[0035] Another objective of this invention is to provide an ultra-low dosage composite nano early strength agent.

[0036] An ultra-low doping composite nano-early strength agent is prepared according to any one of the preceding preparation methods.

[0037] Another objective of this invention is to provide an application of an ultra-low dosage composite nano early strength agent.

[0038] Application of the above-mentioned ultra-low dosage composite nano early strength agent in cement concrete.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] This invention provides a method for preparing an ultra-low dosage composite nano-early strength agent. First, silane-modified polycarboxylic acid (PCE) is reacted with nano-silica sol. The Si-OH functional groups on the side chains of the PCE undergo condensation polymerization with the Si-OH groups on the surface of the nano-silica sol, forming reliable chemical bonds to obtain a stable suspension A. Subsequently, a calcium source is thoroughly mixed with suspension A. By adjusting the pH to 9-12, the carboxylic acid groups on the PCE backbone are fully ionized, and the free calcium ions in the solution are fully complexed through electrostatic interaction. The calcium ions are controlled to be at a suitable supersaturation level, separating the nucleation and growth stages. Then, a silicon source is added dropwise to minimize the particle size of the generated nano-hydrated calcium silicate. Because the H atoms on the PCE backbone are closer to the surface, they can form hydrogen bonds with the numerous oxygen atom sites provided by the CSH gel, stabilizing the CSH while achieving a strong connection between the nano-silica sol and the CSH.

[0041] This invention provides an ultra-low dosage composite nano-early strength agent that stably disperses nano-silica sol and CSH gel through silane-modified polycarboxylic acid, achieving reliable bonding between the two. On one hand, nano-CSH provides numerous heterogeneous nucleation sites for cement hydration and forms a high ion concentration gradient on its surface, promoting the precipitation of hydration products and achieving excellent early strength. On the other hand, the nano-silica sol linked to the silane side chains undergoes a pozzolanic reaction with the alkaline solution released during cement hydration, increasing the amount of hydration products. Synergistically with nano-CSH, this further enhances the early strength of concrete. This achieves excellent early strength under ultra-low dosage conditions while significantly improving the later strength of concrete.

[0042] This invention provides a method for preparing an ultra-low dosage composite nano early strength agent, which is simple and easy to operate, can significantly reduce production costs, is suitable for large-scale promotion and industrial production, and shows significant environmental benefits and economic value, which is of positive significance for promoting the sustainable development of the construction industry. Attached Figure Description

[0043] The invention will be further illustrated with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the invention. For those skilled in the art, other drawings can be obtained based on the following drawings without any creative effort.

[0044] Figure 1 This is a schematic diagram of the microstructure of the ultra-low doping composite nano early strength agent of this application. Detailed Implementation

[0045] To better illustrate the objectives, technical solutions, and advantages of this invention, the following embodiments are provided. Obviously, the following embodiments are only a part of the embodiments of this invention, and not all of them; it should be understood that the embodiments of this invention are only used to illustrate the technical effects of this invention, and not to limit the scope of protection of this invention.

[0046] All raw materials used in the examples are commercially available; unless otherwise specified, the reagents, methods and equipment used in this invention are conventional reagents, methods and equipment in this technical field.

[0047] Example 1

[0048] A method for preparing an ultra-low doping composite nano-early strength agent includes the following steps:

[0049] Preparation of silane-modified polycarboxylic acid:

[0050] Step 1: Place 200 parts by weight of isopentenyl alcohol polyoxyethylene ether macromonomer with a molecular weight of 2400, 8 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, and 120 parts by weight of deionized water into a four-necked flask, heat in a water bath at 55°C, stir and dissolve, and set aside.

[0051] Step 2: Prepare solution A by mixing 20 parts by weight of acrylic acid, 0.5 parts by weight of ascorbic acid, 0.8 parts by weight of mercaptoacetic acid, and 50 parts by weight of deionized water; prepare solution B by mixing 2 parts by weight of H2O2 and 50 parts by weight, and set aside.

[0052] Step 3: Under continuous water bath heating at 55℃, simultaneously add solution A and solution B obtained in step 2 to the mixed solution obtained in step 1. The total addition time is 2 hours. After the addition is completed, maintain water bath heating for 7 hours. Cool to room temperature to obtain silane-modified polycarboxylic acid.

[0053] S1. Mix 75g of nano-silica sol with 180g of silane-modified polycarboxylic acid, stir at 25℃ and 600r / min for 3h to obtain suspension A;

[0054] S2. Add 106.2g of calcium nitrate tetrahydrate, 480g of deionized water and 10g of gum arabic to 113.6g of suspension A, adjust the pH to 12 with 30% NaOH solution and HNO3, stir thoroughly at 18℃ and 600r / min for 1h to obtain base material B;

[0055] S3. Add 83.2g of sodium silicate nonahydrate and 120g of deionized water dropwise at a rate of 0.8mL / min to the substrate B described in S2. Stir at 18℃ and 3000r / min at high speed while maintaining the pH value of the reaction system. After the addition is completed, continue high-speed shearing and stirring for 2h to obtain the ultra-low dosage composite nano early strength agent.

[0056] Example 2

[0057] A method for preparing an ultra-low doping composite nano-early strength agent includes the following steps:

[0058] Preparation of silane-modified polycarboxylic acid:

[0059] Step 1: Place 200 parts by weight of isopentenyl alcohol polyoxyethylene ether macromonomer with a molecular weight of 2400, 10 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, and 120 parts by weight of deionized water into a four-necked flask, heat in a water bath at 65°C, stir and dissolve, and set aside.

[0060] Step 2: Prepare solution A by mixing 22 parts by weight of acrylic acid, 0.6 parts by weight of ascorbic acid, 0.9 parts by weight of mercaptoacetic acid, and 70 parts by weight of deionized water; prepare solution B by mixing 2.2 parts by weight of H2O2 and 60 parts by weight, and set aside.

[0061] Step 3: Under continuous water bath heating at 65℃, simultaneously add solution A and solution B obtained in step 2 to the mixed solution obtained in step 1. The total addition time is 2.5h. After the addition is completed, maintain water bath heating for 8h. Cool to room temperature to obtain silane-modified polycarboxylic acid.

[0062] S1. Mix 80g of nano-silica sol with 200g of silane-modified polycarboxylic acid, stir at 25℃ and 600r / min for 3h to obtain suspension A;

[0063] S2. Add 129.8g of calcium nitrate tetrahydrate, 580g of deionized water and 15g of gum arabic to 135.2g of suspension A, adjust the pH to 11.7 with 30% NaOH solution and HNO3, and stir thoroughly at 20℃ and 600r / min for 0.5h to obtain base material B;

[0064] S3. Add 83.2g of sodium silicate nonahydrate and 120g of deionized water dropwise at a rate of 0.8mL / min to the substrate B mentioned in S2. Stir at 18℃ and 3500r / min at high speed while maintaining the pH value of the reaction system. After the addition is completed, continue high-speed shearing and stirring for 2h to obtain the ultra-low dosage composite nano early strength agent.

[0065] Example 3

[0066] A method for preparing an ultra-low doping composite nano-early strength agent includes the following steps:

[0067] Preparation of silane-modified polycarboxylic acid:

[0068] Step 1: Place 220 parts by weight of isopentenyl alcohol polyoxyethylene ether macromonomer with a molecular weight of 2400, 10 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, and 120 parts by weight of deionized water into a four-necked flask, heat in a water bath at 45°C, stir and dissolve, and set aside.

[0069] Step 2: Prepare solution A by mixing 20 parts by weight of acrylic acid, 0.5 parts by weight of ascorbic acid, 0.8 parts by weight of mercaptoacetic acid, and 70 parts by weight of deionized water; prepare solution B by mixing 2.1 parts by weight of H2O2 and 50 parts by weight, and set aside.

[0070] Step 3: Under continuous water bath heating at 45°C, simultaneously add solution A and solution B obtained in Step 2 to the mixed solution obtained in Step 1. The total addition time is 2.5 hours. After the addition is completed, maintain water bath heating for 8 hours. Cool to room temperature to obtain silane-modified polycarboxylic acid.

[0071] S1. Mix 90g of nano-silica sol with 220g of silane-modified polycarboxylic acid, stir at 25℃ and 600r / min for 3h to obtain suspension A;

[0072] S2. Add 106.2g of calcium nitrate tetrahydrate, 480g of deionized water and 10g of gum arabic to 113.6g of suspension A, adjust the pH to 11.7 with 30% NaOH solution and HNO3, stir thoroughly at 18℃ and 600r / min for 1h to obtain base material B;

[0073] S3. Add 83.2g of sodium silicate nonahydrate and 120g of deionized water dropwise to the substrate B mentioned in S2 at a rate of 1.0mL / min. Stir at 15℃ and 4000r / min at high speed while keeping the pH of the reaction system constant. After the addition is completed, continue high-speed shearing and stirring for 1.5h to obtain the ultra-low dosage composite nano early strength agent.

[0074] Comparative Example 1

[0075] A method for preparing a composite nano-early strength agent includes the following steps:

[0076] S1. Mix 75g of nano-silica sol with 180g of ordinary polycarboxylic acid, and stir at 25℃ and 600r / min for 3h to obtain suspension A;

[0077] S2. Add 106.2g of calcium nitrate tetrahydrate, 480g of deionized water and 10g of gum arabic to 113.6g of suspension A, adjust the pH to 12 with 30% NaOH solution and HNO3, stir thoroughly at 18℃ and 600r / min for 1h to obtain base material B;

[0078] S3. Add 83.2g of sodium silicate nonahydrate and 120g of deionized water dropwise at a rate of 0.8mL / min to the substrate B described in S2. Stir at 18℃ and 3000r / min at high speed while maintaining the pH value of the reaction system. After the addition is completed, continue high-speed shearing and stirring for 2h to obtain the composite nano early strength agent.

[0079] Compared to Example 1, this comparative example uses ordinary polycarboxylic acid instead of silane-modified polycarboxylic acid.

[0080] Comparative Example 2

[0081] A method for preparing a composite nano-early strength agent includes the following steps:

[0082] Preparation of silane-modified polycarboxylic acid:

[0083] Step 1: Place 200 parts by weight of isopentenyl alcohol polyoxyethylene ether macromonomer with a molecular weight of 2400, 8 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, and 120 parts by weight of deionized water into a four-necked flask, heat in a water bath at 55°C, stir and dissolve, and set aside.

[0084] Step 2: Prepare solution A by mixing 20 parts by weight of acrylic acid, 0.5 parts by weight of ascorbic acid, 0.8 parts by weight of mercaptoacetic acid, and 50 parts by weight of deionized water; prepare solution B by mixing 2 parts by weight of H2O2 and 50 parts by weight, and set aside.

[0085] Step 3: Under continuous water bath heating at 55℃, simultaneously add solution A and solution B obtained in step 2 to the mixed solution obtained in step 1. The total addition time is 2 hours. After the addition is completed, maintain water bath heating for 7 hours. Cool to room temperature to obtain silane-modified polycarboxylic acid.

[0086] S1. Mix 75g of nano-silica sol with 180g of silane-modified polycarboxylic acid, stir at 25℃ and 600r / min for 3h to obtain suspension A;

[0087] S2. Add 106.2g of calcium nitrate tetrahydrate and 480g of deionized water to 113.6g of suspension A, adjust the pH to 12 with 30% NaOH solution and HNO3, and stir thoroughly at 18℃ and 600r / min for 1h to obtain the base material B;

[0088] S3. Add 83.2g of sodium silicate nonahydrate and 120g of deionized water dropwise at a rate of 0.8mL / min to the substrate B described in S2. Stir at 18℃ and 3000r / min at high speed while maintaining the pH value of the reaction system. After the addition is completed, continue high-speed shearing and stirring for 2h to obtain the composite nano early strength agent.

[0089] Compared with Example 1, no additional dispersant was added in step S2 of this comparative example.

[0090] Comparative Example 3

[0091] The commercially available nano-CSH nucleation early strength agent is used, specifically BASF Masterset ACE100 early strength agent.

[0092] Comparative Example 4

[0093] A method for preparing a composite nano-early strength agent includes the following steps:

[0094] Preparation of silane-modified polycarboxylic acid:

[0095] Step 1: Place 200 parts by weight of isopentenyl alcohol polyoxyethylene ether macromonomer with a molecular weight of 2400, 8 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, and 120 parts by weight of deionized water into a four-necked flask, heat in a water bath at 55°C, stir and dissolve, and set aside.

[0096] Step 2: Prepare solution A by mixing 20 parts by weight of acrylic acid, 0.5 parts by weight of ascorbic acid, 0.8 parts by weight of mercaptoacetic acid, and 50 parts by weight of deionized water; prepare solution B by mixing 2 parts by weight of H2O2 and 50 parts by weight, and set aside.

[0097] Step 3: Under continuous water bath heating at 55℃, simultaneously add solution A and solution B obtained in step 2 to the mixed solution obtained in step 1. The total addition time is 2 hours. After the addition is completed, maintain water bath heating for 7 hours. Cool to room temperature to obtain silane-modified polycarboxylic acid.

[0098] S1. Mix 75g of nano-silica sol with 180g of silane-modified polycarboxylic acid, stir at 25℃ and 600r / min for 3h to obtain suspension A;

[0099] S2. Add 106.2g of calcium nitrate tetrahydrate, 480g of deionized water and 10g of gum arabic to 113.6g of suspension A, and stir thoroughly at 18℃ and 600r / min for 1h to obtain base material B;

[0100] S3. Add 83.2g of sodium silicate nonahydrate and 120g of deionized water dropwise at a rate of 0.8mL / min to the substrate B described in S2. Stir at 18℃ and 3000r / min at high speed while maintaining the pH value of the reaction system. After the addition is completed, continue high-speed shearing and stirring for 2h to obtain the composite nano early strength agent.

[0101] Compared to Example 1, this comparative example does not adjust the pH value.

[0102] Performance tests were conducted on the above embodiments and comparative examples. The experimental test methods are as follows:

[0103] The cement mortar strength of the above examples and comparative examples was tested according to the standard GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)" and the method guided by ASTM C109. The admixture dosage was the deductible dosage.

[0104] Comparative Example 4 was not tested because the prepared suspension was prone to precipitation due to the lack of pH adjustment, making it impossible to obtain a stable sample and significantly weakening the enhancement effect.

[0105] The results are shown below:

[0106] Table 1. Tests of cement mortar prepared in the examples and comparative examples.

[0107]

[0108] The control group consisted of blank experiments without any early-strength additives. All examples, comparative examples, and control groups used reference cement and were cured under standard curing conditions.

[0109] As shown in Table 1, the cement concrete using the ultra-low dosage composite nano-early strength agent prepared in Examples 1-3 of this invention exhibits significantly stronger 3-day and 28-day compressive strengths than the blank group and other comparative examples. This indicates that the composite nano-early strength agent prepared under the appropriate calcium-silicon ratio, dispersant, polycarboxylate superplasticizer, and synthesis process conditions described in this invention can significantly improve the compressive strength of cement concrete at various ages, including early and late stages, thus meeting the strength requirements of various engineering applications.

[0110] In Comparative Example 1, the use of ordinary polycarboxylate instead of silane-modified polycarboxylate resulted in insufficient later-stage strength of the concrete, with a 28-day compressive strength of only 56.98 MPa. Comparative Example 2, lacking a dispersant, exhibited poor stability and insufficient early-stage strength, with a 1-day compressive strength of only 21.18 MPa. Comparative Example 3, using a commercially available early-strength agent, demonstrated a strong overall early-strength effect, but its improvement in the later-stage strength of the concrete was far less significant than that of the other examples.

[0111] In summary, this invention involves first reacting silane-modified polycarboxylic acid with nano-silica sol, then thoroughly mixing a calcium source with suspension A, adjusting the pH to 9-12, and finally adding an ultra-low dosage composite nano-early strength agent prepared from a silicon source. The silane-modified polycarboxylic acid stabilizes and disperses the nano-silica sol and CSH gel, achieving a reliable bond between them. On one hand, nano-CSH provides numerous heterogeneous nucleation sites for cement hydration and forms a high ion concentration gradient on its surface, promoting the precipitation of hydration products and achieving excellent early strength. On the other hand, the nano-silica sol linked to the silane side chains undergoes a pozzolanic reaction with the alkaline solution released during cement hydration, increasing the amount of hydration products. This synergistic effect with nano-CSH further enhances the early strength of concrete. Thus, under ultra-low dosage conditions, it achieves excellent early strength while significantly improving the later strength of concrete. The preparation method of this ultra-low dosage composite nano early strength agent is simple and easy to operate, which can significantly reduce production costs and is suitable for large-scale promotion and industrial production. It shows significant environmental benefits and economic value, and has positive significance for promoting the sustainable development of the construction industry.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an ultra-low dosage composite nano-early strength agent, characterized in that, Includes the following steps: S1. Mix nano-silica sol with silane-modified polycarboxylic acid and stir to obtain suspension A; S2. Add the calcium source and dispersant to suspension A, adjust the pH to 9-12, stir thoroughly to obtain base material B; S3. Add the silicon source dropwise to the substrate B mentioned in S2, shear and stir at high speed, and keep the pH value of the reaction system constant. After the dropwise addition is completed, continue to shear and stir at high speed for 1-2 hours to obtain the ultra-low dosage composite nano early strength agent. The silane-modified polycarboxylic acid was prepared by the following method: Step 1: Dissolve the polyether macromonomer, alkoxysilane, and deionized water in a water bath by heating and stirring. Set aside. Step 2: Prepare solution A by mixing unsaturated carboxylic acid, reducing agent, chain transfer agent, and deionized water; prepare solution B by mixing initiator and deionized water for later use. Step 3: Under continuous water bath heating, simultaneously add solution A and solution B obtained in step 2 to the mixed solution obtained in step 1. The total addition time is 2-2.5 hours. After the addition is completed, maintain water bath heating for 6-8 hours to continue the reaction. Cool to room temperature to obtain silane-modified polycarboxylic acid. The polyether macromonomer is an isopentenyl alcohol polyoxyethylene ether macromonomer with a number average molecular weight of 2400. The alkoxysilane is One or more of methacryloyloxypropyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, and vinyldimethylethoxysilane.

2. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 1, characterized in that: The mass ratio of the polyether macromonomer, alkoxysilane and deionized water is (200-220):(8-10):(100-120); The mass ratio of the unsaturated carboxylic acid, reducing agent, chain transfer agent, and deionized water is (18-26):(0.5-0.8):(0.8-1.2):(50-70). The mass ratio of the initiator to deionized water is (2-2.6):(50-60); The water bath heating temperature is 40-75℃.

3. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 2, characterized in that: The unsaturated carboxylic acid is one or more of acrylic acid, methacrylic acid, fumaric acid and their derivatives. The initiator is one or more of ammonium persulfate, sodium persulfate, tert-butyl peroxyvalerate, and dicyclohexyl peroxydicarbonate. The reducing agent is one or more of L-ascorbic acid, sodium bisulfite, ferrous sulfate, potassium bisulfite, and sodium hypophosphite; The chain transfer agent is one or more of mercaptoacetic acid, mercaptopropionic acid, sodium methyl methacrylate, and mercaptoethanol.

4. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 1, characterized in that: The calcium source is one or more of calcium nitrate tetrahydrate, calcium formate, calcium gluconate, calcium acetate, calcium nitrite, and calcium dihydrogen phosphate. The silicon source is one or more of sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, sodium fluorosilicate, and potassium silicate. The dispersant is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and gum arabic.

5. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 1, characterized in that, The stirring temperature in S1 is 20-40℃, the stirring speed is 600r / min, and the stirring time is 3h.

6. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 1, characterized in that, S2 describes adjusting the pH value by using a 30% NaOH solution and HNO3; S2 describes a thorough stirring temperature of 15-20℃, a stirring speed of 600 r / min, and a stirring time of 0.5-1 h.

7. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 1, characterized in that, The droplet acceleration rate of S3 is 0.8-1.6 mL / min, and the high-speed shear stirring temperature of S3 is 5-20℃, and the rotation speed is 2000-5000 r / min.

8. The preparation method of the ultra-low doping composite nano-early strength agent according to claim 1, characterized in that, The weight ratio of the nano-silica sol, silane-modified polycarboxylic acid, calcium source, dispersant, and silicon source is (60-100):(180-220):(76-120):(20-40):(100-158); the concentration of the calcium source is 2-4 mol / L; the concentration of the silicon source is 1.7-3.2 mol / L; and the molar ratio of calcium to silicon in the calcium and silicon sources is (1.6-2.0):

1.

9. A low-dosage composite nano-early strength agent, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

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