Alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strengthening component, preparation method, and application

Abstract

The present invention provides an alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strength component, which includes an A component and a B component, wherein the mass ratio of the A and B components is 1:(1-2); the A component includes the following raw materials in mass parts: 4-5 parts of aluminum sulfate 18hydrate and 4-5 parts of water; the B component includes the following raw materials in mass parts: 1-2 parts of nanomaterials and 12-13 parts of water; the nanomaterial is a mixture of nano-ettringite and any one of nano-silicon dioxide, nano-aluminum dioxide, nano-titanium dioxide, and nano-hydrated calcium silicate; the content of nano-ettringite in the nanomaterial is not less than 70%. The nano-ettringite in the rapid-setting and early-strength component used in the present application has good dispersibility and does not require an additional dispersant; does not contain fluorine ions, thereby reducing harm to the human body; does not contain chloride ions, thereby effectively avoiding the corrosion harm of chloride ions to steel bars; does not contain sodium and potassium ions, truly achieving alkali-free rapid setting and avoiding strength shrinkage and durability problems in the later stage.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete admixtures, and in particular to an alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strengthening component, a preparation method and application thereof. Background Art

[0002] In civil engineering construction, especially in projects like tunnel excavation and slope support, the demand for shotcrete is increasing, and the performance requirements are also becoming increasingly stringent. Currently, accelerators, essential for shotcrete use, are trending towards liquid, alkali-free formulations. Alkali-free accelerators on the market primarily contain aluminum sulfate. The added aluminum and sulfate react with calcium ions and hydroxides in the liquid phase of the cement paste to form ettringite. This ettringite bonds rapidly, causing the paste to lose fluidity and achieve rapid setting.

[0003] GB / T35159-2017, "Accelerators for Shotcrete," specifies the following indicators for liquid accelerators: Initial setting time for the mortar containing the accelerator is 5 minutes, and final setting time is 12 minutes; the compressive strength of the mortar containing the accelerator must reach at least 7 MPa after one day. In actual projects, the requirements for early strength are increasing. For example, QCR807-2020, the China Railway Corporation Technical Standard, "Liquid Alkali-Free Accelerators for Tunnel Shotcrete," requires a compressive strength of 10 MPa after one day and 1 MPa after six hours.

[0004] Using aluminum sulfate as a single component as an accelerator has limited rapid setting effects and cannot meet the national standard requirements for setting time. Moreover, the early strength, especially the strength after 6 or 8 hours, is still far from meeting the actual engineering needs. In addition, there are stability issues such as easy coagulation at high concentrations of aluminum sulfate and poor adaptability to different cements. To meet the needs, commercial alkali-free accelerators are supplemented with various different components to meet the performance requirements of the accelerator. Some types of accelerators add fluorine-containing compounds to promote the stability and rapid setting effect of aluminum sulfate accelerators, such as the addition of sodium fluoride in CN113698124A. However, this does not help much in the early strength of shotcrete, and fluorine-containing compounds are toxic, raising concerns about their safety in use. Furthermore, patent CN113480221A adds multiple organic-inorganic composite components, such as organic amides, to an alkali-free liquid accelerator to enhance its effectiveness. Patent CN113603384A also designs and manufactures an ultra-early-strengthening, fluorine-free, alkali-free liquid accelerator containing multiple organic early-strengthening components. These organic early-strengthening agents are expensive, and their interaction mechanism with the accelerating components remains unclear. Some accelerators incorporate inorganic nanoparticles to enhance the early strength of cement-based materials, such as nanosilica or nanoaluminum hydroxide in CN113880485A. However, nanomaterials are prone to agglomeration, making dispersion difficult to ensure, and nanodispersants significantly increase costs. Therefore, there is an urgent need to develop new, green, and environmentally friendly alkali-free liquid accelerators that exhibit superior early-strengthening properties, have a clear mechanism of action, and are low-cost. Summary of the Invention

[0005] The single-component alkali-free quick-setting agent in the prior art has a poor early strength effect, but adding an organic component early strength agent will increase production costs. The present invention provides an alkali-free, fluorine-free, and chlorine-free quick-setting early strength component, a preparation method, and an application. The nano-ettringite suspension in the added B component has an excellent dispersion effect without using a dispersant. During the application process, the added nano-ettringite has the same crystal form and structure as the ettringite generated during the quick-setting process of the aluminum sulfate quick-setting agent. After use, it can be used as a crystal nucleus to provide a nucleation site for the nucleation and growth of ettringite during the quick-setting process of cement, accelerate the formation of ettringite in the liquid phase, and promote the overlapping generation of a coarser ettringite network structure, so that the quick-setting process of cement-based materials is accelerated, the initial and final setting times are shortened, and its early strength is significantly improved. Furthermore, the added nanomaterials including nano-ettringite also provide nucleation sites for the generation of cement hydration products, promote the hydration of early silicate cement, especially tricalcium silicate, and accelerate the development of early strength. Moreover, these inorganic nanomaterials with smaller particle sizes have a micro-filling effect, which is very helpful in improving the microscopic pore structure and enhancing the physical and mechanical properties.

[0006] An alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strength component, comprising a component A and a component B, wherein the mass ratio of the components A to B is 1:(1-2);

[0007] The above-mentioned component A comprises the following raw materials in parts by weight: 4-5 parts of aluminum sulfate 18hydrate and 4-5 parts of water;

[0008] The above-mentioned component B includes the following raw materials in parts by weight: 1-2 parts of nanomaterials and 12-13 parts of water;

[0009] Wherein, the nano material is a mixture of nano ettringite and any one of nano silicon dioxide, nano aluminum dioxide, nano titanium dioxide, and nano calcium silicate hydrate;

[0010] The content of nano-ettringite in the above nano-material is not less than 70%.

[0011] The component A of the rapid-setting early-strength component includes 4 parts of aluminum sulfate 18-hydrate and 4 parts of water; and the component B includes 1 part of nano-ettringite and 13 parts of water.

[0012] The nano-ettringite is obtained by the following method: adding aluminum sulfate 18hydrate and calcium hydroxide in a mass ratio of 3:2 into deionized water with a water-to-solid ratio of 50-100, adding a stirring paddle in a three-necked flask and maintaining a rotation speed of 100-300 r / min to mix the reaction system evenly, reacting in a water bath environment at 20-30°C for 24 hours to 48 hours; then centrifuging at 1500-3000 r / min to remove the supernatant to obtain a milky white suspension, and washing twice with deionized water. The obtained milky white suspension is the nano-ettringite.

[0013] The nano-calcium silicate hydrate is obtained by the following method: adding nano-silicon dioxide and calcium oxide in a mass ratio of 315:294 into deionized water, reacting in a sealed bottle with the bottle mouth sealed and not exposed to the atmosphere, with a water-to-solid ratio of 10-20, thoroughly mixing and then standing, reacting in a 20°C water bath for 7-14 days, shaking the sealed bottle every 24 hours during the reaction to ensure uniform mixing of the reaction system; after completion of the reaction, centrifuging at 1500-3000 rpm to remove the supernatant to obtain a milky white suspension, and washing twice with deionized water. The obtained milky white suspension is the nano-calcium silicate hydrate.

[0014] A method for preparing an alkali-free, fluorine-free, and chlorine-free rapid-setting early-strength component comprises the following steps: (1) dissolving aluminum sulfate 18hydrate in water and mixing uniformly to obtain component A; and (2) stirring and dispersing nanomaterials in water to obtain component B.

[0015] The invention discloses an alkali-free, fluorine-free and chlorine-free rapid-setting and early-strength component. The rapid-setting and early-strength component is applied in the construction process of cement-based materials. The cement-based material is first mixed with water and other admixtures, and then component B is added and mixed evenly with the cement-based material. Finally, component A is added and mixed evenly with the cement-based material.

[0016] The amount of component A in the rapid setting and early strength component is 7%-9% of the mass of the gelling material in the cement-based material, and the amount of component B is 9%-14% of the mass of the gelling material in the cement-based material.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) Among the rapid-setting and early-strength components used in this application, nano-calcium vanadium has a great dispersibility advantage in suspension compared with other types of nanomaterials such as nano-silicon dioxide, nano-alumina, nano-titanium dioxide, etc., and there is no need to add additional dispersants to make the nanomaterial work.

[0019] (2) The rapid-setting and early-strengthening component used in this application does not contain fluorine ions, greatly reducing its harmfulness to the human body; does not contain chloride ions, effectively preventing the corrosion damage of chloride ions to steel bars; and does not contain sodium and potassium ions, truly achieving alkali-free rapid setting and avoiding later strength shrinkage and durability issues. The composition is simple, the mechanism is clear, and it does not produce additional changes to the aluminum sulfate rapid setting process, nor does it cause new chemical reactions, and the effect is significant.

[0020] (3) The rapid setting component of the present application does not contain an organic early strength agent, the cost is relatively low and controllable, and a significant early strength effect can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the state of natural dispersion of different nanoparticles in component B;

[0022] Figure 2 Comparison of the dispersion states of component B in Example 1 and Comparative Example 5

[0023] Figure 3 Transmission electron microscopy images of different nanoparticles in component B;

[0024] Figure 4 is the setting time of the pure slurry after adding the rapid setting and early strength components obtained in various embodiments and comparative examples;

[0025] Figure 5 It is the 8-hour strength of the mortar after adding the rapid-setting early-strength components obtained in various examples and comparative examples. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In this application, unless otherwise specified, all percentages are weight percentages.

[0027] The nano-ettringite and nano-calcium silicate hydrate in the following examples were prepared by the following methods:

[0028] 33.3g of aluminum sulfate 18hydrate and 22.2g of calcium hydroxide (both analytical grade reagents) were added to 5L of deionized water and reacted in a 5L three-necked flask. A stirring paddle was added to maintain a rotation speed of 200r / min to mix the reaction system evenly, and the reaction was carried out in a 20°C water bath environment for 48 hours. After the reaction is completed, the solution becomes a milky white suspension, and after standing for a period of time, the supernatant is separated. After the suspension is mixed evenly, it is centrifuged at a speed of 1500-3000r / min, and the supernatant is removed to obtain a thicker milky white suspension. The suspension is washed twice with deionized water, and then the suspension is ultrasonicated for 2min at a power of 375W using a cell wall disruptor to obtain a nano-ettringite suspension (different centrifugal speeds can produce suspensions with a nano-ettringite content of 10-15%).

[0029] Add 31.5g of nano-silicon dioxide (gas phase, particle size ~15nm) and 29.4g of calcium oxide (analytical grade) to 600ml of deionized water, react in a sealed bottle, keep the bottle mouth closed and not in contact with the atmosphere, mix thoroughly and let it stand, react in a 20°C water bath for 7 days, and shake the sealed bottle every 24 hours during the reaction to mix the reaction system evenly. After the suspension is mixed evenly, centrifuge at 1500-3000r / min, remove the supernatant to obtain a thicker milky white suspension, wash twice with deionized water, and then ultrasonicate the suspension at 300W power for 2 minutes using a cell wall disruptor to obtain a nano-calcium silicate hydrate suspension (different centrifugal speeds can produce suspensions with a nano-calcium silicate hydrate content of 10-15%).

[0030] Example 1:

[0031] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0032] Component B is 140 g of nano-ettringite suspension, including 14 g of nano-ettringite.

[0033] Example 2:

[0034] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0035] 120 g of nano-ettringite suspension (nano-ettringite content: 12 g) and 20 g of nano-hydrated calcium silicate suspension (nano-hydrated calcium silicate content: 2 g) were weighed and mixed evenly to obtain component B. The nano-ettringite content in the nanomaterial was 86%.

[0036] Example 3:

[0037] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0038] 120 g of nano-ettringite suspension (nano-ettringite content: 12 g), 2 g of nano-silicon dioxide (gas phase, particle size: 30 nm), and 18 g of water were weighed and mixed uniformly to obtain component B. The nano-ettringite content in the nanomaterial was 86%.

[0039] Example 4:

[0040] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0041] 120 g of nano-ettringite suspension (nano-ettringite content: 12 g), 2 g of nano-aluminum oxide (particle size: 30 nm), and 18 g of water were weighed and stirred and mixed uniformly to obtain component B. The nano-ettringite content in the nanomaterial was 86%.

[0042] Example 5:

[0043] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0044] Weigh 130g of nano-ettringite suspension (nano-ettringite content 13g), 1g of nano-titanium dioxide (particle size 30nm), and 9g of water and stir and mix them evenly to obtain component B. The nano-ettringite content in the nanomaterial is 93%. Comparative Example 1:

[0045] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0046] Weigh 140 g of nano calcium silicate hydrate as component B, of which the calcium silicate hydrate is about 14 g.

[0047] Comparative Example 2:

[0048] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0049] Weigh 14 g of nano-titanium dioxide and 126 g of water and stir and mix them evenly to obtain component B.

[0050] Comparative Example 3:

[0051] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0052] 70 g of nano-ettringite suspension (nano-ettringite content 7 g) and 7 g of nano-silicon dioxide were weighed, mixed with 63 g of water and stirred uniformly to obtain component B. The nano-ettringite content in the nanomaterial was 50%.

[0053] Comparative Example 4:

[0054] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0055] Weigh 140 g of water as component B.

[0056] Comparative Example 5:

[0057] Comparative Example 5: Nano-ettringite is obtained by the following method: a nano-ettringite suspension is vacuum dried and then ground to powder, which is then passed through a 200-mesh sieve to obtain high-purity nano-ettringite.

[0058] Weigh 36 g of aluminum sulfate 18hydrate (analytical grade) and dissolve it in 36 g of deionized water under stirring at room temperature to obtain component A.

[0059] Component B is prepared by mixing 14 g of nano-ettrone powder with 126 g of water and stirring them evenly.

[0060] Test Example 1: Pure Slurry Setting Time Test

[0061] Weigh 400g PI42.5 Portland cement and 80g water into a mixing pot and stir at low speed for 30s. After stopping stirring, add 40g component B and stir at high speed for 10s. Then add 32g component A and stir at low speed for 5s and then at high speed for 15s. Take a sample and measure the setting time of the slurry. The results are shown in the attached. Figure 4 .

[0062] Compared with Comparative Example 4, in which component B was water, Example 1, in which nano-ettringite was additionally added as component B, exhibited significantly shorter initial and final setting times. This is because the well-dispersed ettringite material in component B acts as a crystal nucleus, accelerating the lap jointing of the ettringite network during the rapid setting process and generating larger ettringite, resulting in more lap joint sites and rapid slurry coagulation.

[0063] Compared to Example 1, Examples 2-5 incorporate additional nanomaterials other than nano-ettringite, serving as materials of different sizes than the nano-ettringite to fill micropores. The increased water requirement due to the high specific surface area also accelerates the slurry's setting time. However, as shown in Comparative Example 3, where the nano-ettringite content is less than 70% of the nanomaterial, a nano-ettringite content of 70% or more is required to significantly shorten the setting time. This is because the low nano-ettringite content results in insufficient dispersion of the entire system.

[0064] Compared with Example 1, although other nanomaterials were added to Comparative Examples 1 and 2, Figure 1 The dispersibility shown is poor, and the effect of shortening the setting time of the slurry is significantly weakened. Comparison of Comparative Example 3 with Examples 1 and 3 shows that the content of nano-ettringite in component B needs to reach or exceed 70% to significantly improve the setting time.

[0065] Comparison of Comparative Example 5 with Example 1 shows that nano-ettringite has good dispersibility only in the suspension state. In Comparative Example 5, the powder obtained after drying the ettringite suspension will agglomerate. Figure 2 As shown, even if mixed with water, it is difficult to disperse and has little effect on the setting time of the mortar.

[0066] Test Example 2: Mortar Strength Test

[0067] Weigh 900g PI42.5 Portland cement and 230g water into a mixing pot and stir at low speed for 30s. Stir at low speed for another 30s and add 1350g standard sand at the same time. Stir at high speed for another 30s. After stopping stirring, scrape off the raw materials attached to the mixing pot and blades with a scraper. Stir at high speed for another 20s. After stopping stirring, add 140g component B. After stirring at high speed for 10s, add 72g component A. Stir at low speed for 5s and then at high speed for 15s. Quickly put the mortar into the mold and maintain it in an environment of 20℃±3℃ and relative humidity ≥90% with the mold. Measure the mortar strength after the age. The results are shown in the attached Figure 5 .

[0068] Compared to Comparative Example 4, where Component B was water, the mortar specimens of Example 1, in which nano-ettringite was added as Component B, showed a significant increase in strength after 8 hours. This is because the ettringite in the suspension acts as a crystal nucleus, providing nucleation sites for the nucleation and growth of ettringite during the rapid setting process, accelerating its formation and generating larger ettringite. This allows the ettringite network to overlap more quickly, resulting in more overlapping sites and promoting slurry hardening.

[0069] Compared with Example 1, Example 2 adds a nano-calcium silicate hydrate suspension, which can be used as a material of a different size from the nano-calcium vanadium to fill the micropores. It also serves as a nucleation site for calcium silicate hydrate, the main hydration product of cement, to promote hydration, thereby increasing the early strength of the mortar. The performance improvements of Examples 3, 4, and 5 compared to Example 1 are also based on the same reason. However, as shown in the results of Comparative Example 3, where the nano-calcium vanadium accounts for less than 70% of the nanomaterial, the nano-calcium vanadium content needs to reach or exceed 70% to achieve a more significant improvement in early strength. This is because the low content of nano-calcium vanadium leads to insufficient dispersion of the entire system.

[0070] Compared with Example 1, although other nanomaterials were added to Comparative Examples 1 and 2, Figure 1 The dispersibility shown is poor, the setting and hardening effect on the slurry is significantly weakened, and the mortar strength is also lower than that of Example 1. Comparison of Comparative Example 3 with Examples 1 and 3 shows that the content of nano-ettringite in component B needs to reach or exceed 70% to achieve a more significant improvement in early strength.

[0071] Comparison of Comparative Example 5 with Example 1 shows that nano-ettringite has good dispersibility only in the suspension state. In Comparative Example 5, the powder obtained after drying the ettringite suspension will agglomerate. Figure 2 As shown, even if mixed with water, it is difficult to disperse and the early strength of the mortar is not significantly improved.

[0072] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strengthening component, characterized by: The rapid setting early strength component includes component A and component B, and the mass ratio of component A to component B is 1:(1-2); The A component includes the following raw materials in parts by weight: 4-5 parts of aluminum sulfate 18hydrate and 4-5 parts of water; The B component includes the following raw materials in parts by weight: 1-2 parts of nanomaterials and 12-13 parts of water; Wherein, the nano material is nano ettringite or a mixture of nano ettringite and other components, and the other components are selected from any one of nano silicon dioxide, nano aluminum dioxide, nano titanium dioxide, and nano calcium silicate hydrate; The content of nano-ettringite in the nano-material is not less than 70%; The nano-ettringite is obtained by the following method: adding aluminum sulfate 18hydrate and calcium hydroxide in a mass ratio of 3:2 into deionized water, with a water-to-solid ratio of 50-100; adding a stirring paddle in a three-necked flask and maintaining a rotation speed of 100-300 r / min to uniformly mix the reaction system; reacting in a water bath environment at 20-30° C. for 24-48 hours; then centrifuging at 1500-3000 r / min to remove the supernatant to obtain a milky white suspension; and washing twice with deionized water. The obtained milky white suspension is the nano-ettringite.

2. The alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strength component according to claim 1, characterized in that: The component A of the rapid-setting early-strength component includes 4 parts of aluminum sulfate 18-hydrate and 4 parts of water; and the component B includes 1 part of nano-ettringite and 13 parts of water.

3. The alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strength component according to claim 1, characterized in that: The nanometer calcium silicate hydrate is obtained by the following method: adding nanometer silicon dioxide and calcium oxide in a mass ratio of 315:294 into deionized water, reacting in a sealed bottle with the bottle mouth sealed and not exposed to the atmosphere, with a water-to-solid ratio of 10-20, fully mixing and then standing, reacting in a 20°C water bath environment for 7-14 days, shaking the sealed bottle every 24 hours during the reaction process to uniformly mix the reaction system; after the reaction is completed, centrifuging at 1500-3000 r / min to remove the supernatant to obtain a milky white suspension, and washing twice with deionized water. The obtained milky white suspension is the nanometer calcium silicate hydrate.

4. The method for preparing an alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strength component according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) dissolving aluminum sulfate 18hydrate in water and mixing uniformly to obtain component A; (2) stirring and mixing the nanomaterial in water to obtain component B.

5. Use of an alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strengthening component according to any one of claims 1 to 3, characterized in that: The rapid-setting and early-strength component is used in the construction process of cement-based materials.

6. The use of an alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strengthening component according to claim 5, characterized in that: First mix the cement-based material with water and other admixtures, then add component B and mix it evenly with the cement-based material, and finally add component A and mix it evenly with the cement-based material.

7. The use of an alkali-free, fluorine-free, and chlorine-free rapid-setting and early-strengthening component according to claim 5, characterized in that: The amount of component A in the rapid-setting early-strength component is 7%-9% of the mass of the gelling material in the cement-based material, and the amount of component B is 9%-14% of the mass of the gelling material in the cement-based material.

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