Alkali-free liquid coagulant and use method thereof

Abstract

The invention relates to the technical field of concrete coagulation accelerating, in particular to an alkali-free liquid coagulation accelerator and a use method thereof. The composite additive in the coagulant effectively improves the mechanical properties and durability of the concrete through a'structure enhancement-stress buffering-pH regulation 'triple mechanism of the C-S-H inducer, the chitosan and the calcium trichloride, and is more suitable for construction of a large foundation structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete setting accelerator, more particularly, it relates to a kind of alkali-free liquid setting accelerator and its use method. BACKGROUND

[0002] Concrete accelerator, also known as setting accelerator, refers to the external agent that can promote the rapid setting and hardening of cement or concrete. Due to its characteristics, it is widely used in support, leakage plugging and repair engineering of mine shaft, tunnel, culvert and marine engineering, and according to the nature and state of the accelerator, it can be divided into four categories: alkaline powder, alkali-free powder, alkaline liquid and alkali-free liquid. The present application takes alkali-free liquid setting accelerator as an example.

[0003] The alkali-free liquid accelerator in the related art is mainly prepared by mixing industrial-grade aluminum sulfate as the main setting component and adding early strength agent, stabilizer, ph regulator and other additives. Due to the compounding of the components, it has the characteristics of safety and environmental protection, and can ensure stable and rapid construction.

[0004] It can be seen that the above-mentioned alkali-free liquid accelerator has become the mainstream technology of accelerator today, but in the construction of large-scale infrastructure and marine facilities, due to the problem of concentrated hydration heat, the internal temperature is high, and the cracking phenomenon is particularly obvious, which seriously affects the performance of large-scale concrete components. Based on this, a kind of alkali-free liquid setting accelerator and its use method are provided. SUMMARY

[0005] In order to protect the hydration process and mechanical properties of concrete and reduce the risk of cracks in large components due to temperature stress, the present application provides a kind of alkali-free liquid setting accelerator and its preparation method.

[0006] In the first aspect, the present application provides an alkali-free liquid setting accelerator, which comprises the following components by weight percentage: aluminum sulfate 8-12wt%, organic amine 2-4wt%, composite additive 1-5wt%;

[0007] The composite additive is compounded by C-S-H inducer, chitosan and calcium tricitrate, and the C-S-H inducer, chitosan and calcium tricitrate are packaged separately.

[0008] By adopting the above technical scheme, the composite additive compounded by C-S-H inducer, chitosan and calcium tricitrate effectively makes up for the shortcomings of single setting accelerator in stress concentration and alkalinity control through the triple mechanism of "structure enhancement-stress buffering-pH regulation", and optimizes the hydration process, and guarantees the microstructure and mechanical properties of large-scale concrete components.

[0009] The theoretical basis is as follows: after chitosan molecules are dissolved in water, a viscous solution is formed, and a flexible network skeleton is preliminarily constructed by means of hydrogen bonds and Van der Waals forces, and the carboxylate groups in calcium tricitrate can chelate Ca 2+ in the cement slurry, delay the initial hydration process, and buffer pH at the same time;

[0010] In addition, in the chelation process, the C-S-H gel formed under the action of the C-S-H inducer is templated by the chitosan network, forms a more compact nanosheet structure through heterogeneous nucleation, and is bridged with the chitosan chain through Ca 2+ , and forms an organic-inorganic hybrid network. The composite additive in the application realizes the triple mechanism of "structure enhancement-stress buffering-pH regulation" through the hybrid network.

[0011] Further, the composite additive is compounded by the C-S-H inducer, chitosan and calcium tricitrate in a weight ratio of (2-6):(1-6):(2-10).

[0012] Further, the C-S-H inducer is selected from any one of silica fume or nano-silicon dioxide.

[0013] Further, the content of SiO2 in the silica fume is ≥90%, and the specific surface area is ≥15000 m 2 / kg.

[0014] Further, the chitosan is selected from any one of hydroxyethyl chitosan, carboxymethyl chitosan or derivatives thereof.

[0015] Further, the chitosan is epoxy-modified carboxymethyl chitosan, which is prepared by the reaction of carboxymethyl chitosan and epichlorohydrin.

[0016] Further, the preparation steps of the epoxy-modified carboxymethyl chitosan are as follows:

[0017] A1, pretreatment of carboxymethyl chitosan: first dissolve the carboxymethyl chitosan in deionized water at a concentration of 2-5wt%, and adjust the pH to 5.0-6.0 by citric acid;

[0018] A2, citric acid activation: add 1-ethyl-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide to the solution obtained in A1 to form an active ester intermediate;

[0019] A3, grafting reaction: first, under a nitrogen atmosphere, constant temperature at 30-40℃ for 4-6 hours, then add epichlorohydrin, and continue to react at 40-50℃ for 6-8 hours to complete the preparation.

[0020] Further, the amounts of each material in A2 and A3 are as follows:

[0021] The amount of 1-ethyl-(3-dimethylaminopropyl)carbodiimide is 1.5-2.0% of the total weight of the solution obtained in A1;

[0022] The amount of N-hydroxysuccinimide is 1.0-1.5% of the total weight of the solution obtained in A1;

[0023] The amount of epichlorohydrin is 0.04-0.08% of the total weight of the solution obtained in A2.

[0024] By using the above technical solution, the epoxy-modified carboxymethyl chitosan prepared by reacting carboxymethyl chitosan and epichlorohydrin has significantly enhanced hydrolytic stability and alkali resistance due to the additional introduction of citric acid during the reaction, and is more suitable for concrete environments that are sensitive to pH and require metal chelation, such as large marine construction.

[0025] In a second aspect, the application provides a method for using the alkali-free liquid setting accelerator, specifically as follows:

[0026] B1, first dry mix C-S-H inducer with cement and mineral admixtures;

[0027] B2, then pre-dissolve chitosan and calcium tricitrate in water to form a homogeneous solution;

[0028] B3, finally mix the mixture obtained in B1, the homogeneous solution obtained in B2, aluminum sulfate and organic amine and add them to the stirring system, and stir for 5-10 minutes to complete the use.

[0029] By using the above technical solution, only the alkali-free liquid setting accelerator for large components in a specific use order and method can stably exert its effect. The reason is that the use in a non-specific order will affect the formation of organic-inorganic hybrid network, and the early addition of calcium tricitrate will cause aluminum sulfate to precipitate, thereby affecting its workability, and the same applies to the amount of each component.

[0030] In a third aspect, the application provides an epoxy-modified carboxymethyl chitosan, which has significantly enhanced hydrolytic stability and alkali resistance.

[0031] In a fourth aspect, the application provides a multifunctional composite additive, which is compounded from separately packaged C-S-H inducer, chitosan and calcium tricitrate, and the weight ratio of the C-S-H inducer, chitosan and calcium tricitrate is (2-6):(1-6):(2-10).

[0032] In summary, the application has the following beneficial effects:

[0033] 1. The setting accelerator provided by the present application effectively improves the mechanical properties and durability of concrete through the triple mechanism of "structure enhancement-stress buffering-pH regulation" of the C-S-H inducing agent, chitosan and calcium tricitrate in the composite additive, and is more suitable for the construction of large-scale infrastructure.

[0034] 2. The composite additive in the present application can form an organic-inorganic hybrid network by bridging the nanosheet structure and chitosan chains through heterogeneous nucleation through a specific use method, thereby significantly optimizing the hydration process and reducing the risk of cracks in large components due to temperature stress.

[0035] 3. The epoxy-modified carboxymethyl chitosan prepared in the present application has significantly enhanced hydrolytic stability and alkali resistance due to the introduction of citric acid, and has superior application prospects in concrete environments that are sensitive to pH and require metal chelation, such as large-scale marine construction.

[0036] 4. The multifunctional composite additive in the present application can be applied not only to the setting accelerator listed in the present application, but also to any product field that requires stability, pH regulation, structure enhancement, stress buffering and slow-release performance, including but not limited to heavy metal ion treatment agents, dressings and slow-release agents. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below in conjunction with various embodiments.

[0038] Preparation Example 1

[0039] An epoxy-modified carboxymethyl chitosan is prepared by the following steps:

[0040] A1, Carboxymethyl chitosan pretreatment: First, 10g of carboxymethyl chitosan is dissolved in 500ml of deionized water, and the pH is adjusted to 5.4 by citric acid;

[0041] A2, Citric acid activation: Add 9.2g of 1-ethyl-(3-dimethylaminopropyl) carbodiimide and 5.76g of N-hydroxysuccinimide to the solution obtained in A1 to form an active ester intermediate;

[0042] A3, Grafting reaction: First, under a nitrogen atmosphere, heat to 40℃ for 6 hours, then add 14.8ml of epichlorohydrin and heat to 50℃ for 8 hours to complete the preparation.

[0043] Preparation Examples 2-6

[0044] A composite additive is prepared by separately packaging C-S-H inducing agent, chitosan and calcium tricitrate, and the weights (g) of each component are shown in Table 1:

[0045] Table 1: Components and their weights (g) in Preparation Examples 2-6

[0046]

[0047] wherein the C-S-H inducer is silica fume with a SiO2content of > 90%, a specific surface area of > 15000 m 2 / kg, and the chitosan is the epoxy-modified carboxymethyl chitosan obtained in Preparation Example 1.

[0048] Preparation Examples 7-10

[0049] A composite admixture, which differs from Preparation Example 4 in that the specific selection of the C-S-H inducer or chitosan is different, and the selection of each component is shown in Table 2:

[0050] Table 2: Selection of components in Preparation Examples 7-10

[0051] Group Details of component selection Preparation Example 7 Silica fume is replaced by equal amount of nano-silica (particle size 100 nm) Preparation Example 8 Epoxy-modified carboxymethyl chitosan is replaced by equal amount of hydroxyethyl chitosan Preparation Example 9 Epoxy-modified carboxymethyl chitosan is replaced by equal amount of hydroxymethyl chitosan Preparation Example 10 C-S-H inducer is metakaolin (Al2O3·2SiO2) particle size 10 um

[0052] Performance detection test

[0053] The alkali-free liquid setting accelerator prepared in each example and comparative example was selected for detection, and was first cured into corresponding concrete members, and then each performance was tested, and the specific detection items and methods are as follows:

[0054] 1) Test sample - concrete member preparation

[0055] 1.1 Member specification: mass concrete foundation pile - 15m*8m*3m;

[0056] 1.2 Gel ratio: 400 kg / m 3 (cement 280 kg + fly ash 80 kg + mineral powder 40 kg;

[0057] wherein the cement is p.o 42.5R type, purchased from Liangping Hailuo Cement Co., Ltd., the fly ash is I grade, and the mineral powder is S95 grade;

[0058] 1.3 Curing method - the dosage of the alkali-free liquid setting accelerator is 5wt% of the weight of the cement:

[0059] B1, first dry mix the C-S-H inducer with the cement and mineral admixture according to the corresponding weight;

[0060] B2, then pre-dissolve the chitosan and calcium tricitrate in water and form a homogeneous solution;

[0061] B3, finally mix and add the mixture obtained in B1, the homogeneous solution obtained in B2, aluminum sulfate, and organic amine into the stirring system, and stir for 10 min, and then pour into the mold.

[0062] 2) Test Items - Concrete Element Performance

[0063] 2.1 Setting Time Test: Test the initial and final setting time of the concrete;

[0064] 2.2 pH Stability: Measure the pH of the hardened body leachate;

[0065] 2.3 Shrinkage Test: Measure the 28d drying shrinkage of the concrete element;

[0066] 2.4 Compressive Strength Test: Test the 28d compressive strength of the concrete element;

[0067] 2.5 Temperature Rise Peak: Embed thermocouples at the center of the element, at distances of (7.5, 4, 1.5) m from the surface, and then analyze the hydration exothermic peak of the concrete test piece using isothermal calorimetry.

[0068] Examples 1-5

[0069] An alkali-free liquid accelerator for large elements, the components thereof and their respective weights (g) are shown in Table 3, wherein the composite adjuvant is prepared according to Preparation Example 2, the organic amine is triethanolamine, and the solvent is water.

[0070] Table 3: Components and their weights (kg) in Examples 1-5

[0071]

[0072] Comparative Example 1

[0073] An alkali-free liquid accelerator, which differs from Example 2 in that the composite adjuvant used therein does not contain a C-S-H inducer, and is replaced by an equal amount of water.

[0074] Comparative Example 2

[0075] An alkali-free liquid accelerator, which differs from Example 2 in that the composite adjuvant used therein does not contain chitosan, and is replaced by an equal amount of water.

[0076] Comparative Example 3

[0077] An alkali-free liquid accelerator, which differs from Example 2 in that the composite adjuvant used therein does not contain calcium tricitrate, and is replaced by an equal amount of water.

[0078] Comparative Example 4

[0079] An alkali-free liquid accelerator, which differs from Example 2 in that the calcium tricitrate in the composite adjuvant used therein is replaced by an equal amount of sodium citrate.

[0080] The alkali-free liquid setting accelerator in the above Examples 1-5 and Comparative Examples 1-4 was extracted, and its setting time (min), pH stability, 28d dry shrinkage, 28d compressive strength, and temperature rise peak value were tested according to the above measurement steps, and the test results are recorded in Tables 4-1 and 4-2.

[0081] Table 4-1: Performance test results of Examples 1-5

[0082]

[0083] Table 4-2: Performance test results of Comparative Examples 1-4 and the blank group

[0084]

[0085]

[0086] As can be seen from the above table, the alkali-free liquid setting accelerator in Examples 1-5 effectively balances the hydration process and mechanical properties of the concrete, thereby reducing the risk of cracks in large components due to temperature stress, with an initial setting time of 45-46 min, a final setting time of 91-93 min, a pH stability of 11.2-11.5, a dry shrinkage of 0.025-0.030%, a compressive strength of 53 MPa, and a temperature rise peak value of 61-63°C.

[0087] Based on the data of the examples and comparative examples, it can be seen that the performance of each example has improved to varying degrees compared to the blank group and Comparative Examples 1-4. The possible reasons are as follows:

[0088] 1) After the chitosan molecule is dissolved in water, it forms a viscous solution and initially builds a flexible network skeleton with the help of hydrogen bonds and van der Waals forces. The carboxylate groups in tricalcium citrate can chelate the Ca 2+ in the cement paste, delaying the initial hydration process while buffering the pH;

[0089] 2) During the chelation process, the C-S-H gel formed under the action of the C-S-H inducer takes the chitosan network as a template, forms a more compact nanosheet structure through heterogeneous nucleation, and bridges the Ca 2+ with the chitosan chain to form an organic-inorganic hybrid network. The composite additive in this application realizes the triple mechanism of "structure enhancement-stress buffering-pH regulation" through this hybrid network.

[0090] Therefore, the mechanical properties of Comparative Example 1 lacking a CSH inducer, Comparative Example 2 lacking chitosan, and Comparative Example 3 lacking calcium tricitrate were not improved, and their hydration process could not be improved either. The peak temperature rise was still as high as 76-78°C, posing a high risk of cracking. Although the sodium citrate used in Comparative Example 4 can also achieve a similar triple mechanism, the rapid release of sodium citrate can easily hinder CSH formation, resulting in relatively slow strength development and coagulation.

[0091] In summary, it can be concluded that the composite adjuvant composed of CSH inducer, chitosan and calcium tricitrate effectively compensates for the shortcomings of single accelerator in stress concentration and alkalinity control through the triple mechanism of "structure enhancement-stress buffering-pH regulation", thereby optimizing the hydration process and ensuring the microstructure and mechanical properties of large concrete components.

[0092] Furthermore, it can be seen from Examples 1-5 that the alkali-free liquid coagulant for large components is preferably composed of the following components in weight percentage: 8-12 wt% of aluminum sulfate, 2-4 wt% of an organic amine, and 1-5 wt% of a composite additive; the composite additive is compounded from a CSH inducer, chitosan, and calcium tricitrate, and the CSH inducer, chitosan, and calcium tricitrate are packaged separately. Adjustment of the amount of any component within this range can take into account both the hydration process and the mechanical properties of the concrete.

[0093] Comparative Example 1

[0094] An alkali-free liquid coagulant is different from Example 1 in that the curing method of the concrete component is different. The amounts and selections of other raw materials are the same, as follows:

[0095] C1. First, dry mix cement and mineral admixtures according to the corresponding weight;

[0096] C2. Add the mixture obtained in C1, water, composite additives, aluminum sulfate, and organic amine into the stirring system, stir for 5-10 minutes, and then pour into the mold.

[0097] The concrete components obtained in the above comparative example 1 were sampled and their setting time (min), pH stability, 28d drying shrinkage, 28d compressive strength, and peak temperature rise were tested. The test results are recorded in Table 4-3.

[0098] Table 4-3: Performance test results of comparative example 1

[0099]

[0100]

[0101] From the above table, it can be seen that although the use amount and selection of each component of Comparative Example 1 are the same as those of Example 1, the function of the additive is lost due to the different curing method, and the hydration process and mechanical properties of the concrete cannot be considered, and the large component is still prone to cracks due to temperature stress;

[0102] The initial setting time is 56 min, and the final setting time is 110 min, which is 18.3-21.7% longer than that of Example 1, and only 3.6-4.5% higher than that of the blank group. The reason is analyzed as follows:

[0103] When directly mixed, the epoxy-modified CMCS is not pre-dissolved into glue, and its particles are easy to agglomerate and block the pores, thereby hindering the diffusion of hydration products, so that the setting time is abnormal.

[0104] The pH stability is 0.7 higher than that of Example 1, and basically no improvement compared with the blank group. The reason is analyzed as follows: calcium tricitrate directly contacts with aluminum sulfate to form a precipitate.

[0105] The dry shrinkage rate is 0.042%, which is 40% lower than that of Example 1, and basically no improvement compared with the blank group. The reason is analyzed as follows:

[0106] The epoxy-modified CMCS needs to be gradually cross-linked to form a network in an alkaline environment, and direct mixing will cause the slurry to quickly lose water and interrupt the cross-linking reaction.

[0107] The compressive strength is 51 MPa, which is 3.8% lower than that of Example 1, and only 5.8% higher than that of the blank group. The reason is analyzed as follows:

[0108] The CMCS network is not formed, which cannot inhibit the pore coarsening reaction, and the water is easy to evaporate to form connected capillary pores (pore size > 100 nm), and the filling effect of silica fume is also offset.

[0109] The temperature rise peak is 76°C, which is 20.6% higher than that of Example 1, and only 2.6% lower than that of the blank group. The reason is analyzed as follows:

[0110] In addition to the fact that the epoxy-modified CMCS interrupts the cross-linking reaction due to the rapid loss of water in the slurry, the chitosan molecular chain also cannot stretch due to lack of water, losing the stress energy dissipation effect, and then the temperature rise peak is too high.

[0111] In summary, it can be concluded that the composite additive in the present application mainly realizes the triple mechanism of "structure enhancement-stress buffering-pH regulation" through the formation of a hybrid network, so even if the same raw material composition is used, the hydration process cannot be improved if the hybrid network is not formed, and the temperature rise peak is still as high as 76-78°C, which still has a high risk of cracking.

[0112] Example 6

[0113] A liquid alkali-free accelerator for large components, except that the composite adjuvant is prepared from Preparation Example 3, and the other components are selected and the use process is the same as in Example 4.

[0114] Example 7

[0115] A liquid alkali-free accelerator for large components, except that the composite adjuvant is prepared from Preparation Example 4, and the other components are selected and the use process is the same as in Example 4.

[0116] Example 8

[0117] A liquid alkali-free accelerator for large components, except that the composite adjuvant is prepared from Preparation Example 5, and the other components are selected and the use process is the same as in Example 4.

[0118] Example 9

[0119] A liquid alkali-free accelerator for large components, except that the composite adjuvant is prepared from Preparation Example 6, and the other components are selected and the use process is the same as in Example 4.

[0120] Extract the alkali-free liquid accelerator in the above Examples 6-9, and test its setting time (min), pH stability, 28d dry shrinkage, 28d compressive strength, and temperature rise peak according to the above measurement steps. The test results are recorded in Table 5.

[0121] Table 5: Performance test results of Examples 6-9

[0122]

[0123] As can be seen from the above table, the alkali-free liquid accelerators in Examples 6-9 effectively balance the hydration process and mechanical properties of the concrete, thereby reducing the risk of cracks in large components due to temperature stress. The initial setting time is 45-47 min, the final setting time is 91-95 min, the pH stability is 11.0-11.5, the dry shrinkage is 0.022-0.028%, the compressive strength is 53 MPa, and the temperature rise peak is 60-61°C.

[0124] Combining the data of each example and the blank group, it can be seen that each performance has changed to varying degrees compared to Example 4. The reasons are analyzed as follows:

[0125] 1) C-S-H gel, as the core product of cement hydration, provides mechanical strength, but its microstructure is loose and prone to shrinkage, so the ratio of C-S-H inducer and chitosan mainly affects the mechanical properties;

[0126] 2) Citrate mainly chelates Ca 2+The hydration process is regulated, and at the same time, it neutralizes the alkaline environment as a pH buffer, but the proportion should not be too high, otherwise it will affect the strength development and setting.

[0127] In conclusion, it can be concluded that the composite additive is preferably compounded by C-S-H inducer, chitosan and calcium tricitrate in a weight ratio of (2-6):(1-6):(2-10), and the preferred example is Example 7, and the adjustment and fluctuation in this range can effectively reduce the temperature rise peak value inside the large component.

[0128] Example 10

[0129] A non-alkali liquid setting accelerator for large components, except that the composite additive is prepared from Preparation Example 7, and other components and use process are the same as Example 7.

[0130] Example 11

[0131] A non-alkali liquid setting accelerator for large components, except that the composite additive is prepared from Preparation Example 8, and other components and use process are the same as Example 7.

[0132] Example 12

[0133] A non-alkali liquid setting accelerator for large components, except that the composite additive is prepared from Preparation Example 9, and other components and use process are the same as Example 7.

[0134] Example 13

[0135] A non-alkali liquid setting accelerator for large components, except that the composite additive is prepared from Preparation Example 10, and other components and use process are the same as Example 7.

[0136] Extract the non-alkali liquid setting accelerator in the above Examples 10-13, and test its setting time (min), pH stability, 28d dry shrinkage, 28d compressive strength, and temperature rise peak value according to the above measurement steps, and record the test results in Table 6.

[0137] Table 6: Performance test results of Examples 10-13

[0138]

[0139]

[0140] As can be seen from the above table, the non-alkali liquid setting accelerator in Examples 10-13 effectively balances the hydration process and mechanical properties of the concrete, thereby reducing the risk of cracks in large components due to temperature stress, with an initial setting time of 45 min, a final setting time of 91-92 min, a pH stability of 11.2, a dry shrinkage rate of 0.024-0.030%, a compressive strength of 51-53 Mpa, and a temperature rise peak value of 60-63℃.

[0141] Combining the data of each embodiment and the blank group, it can be seen that the various properties thereof have changed to varying degrees compared with those of Example 7. The specific analysis is as follows:

[0142] 1) The performance of Example 10 (i.e., Preparation Example 7) did not change significantly compared to that of Example 7, indicating that silica fume can meet the saturation of its application effect as a structural modifier. Even if it is replaced with nano-silica, a theoretically more superior component, its performance is no longer improved.

[0143] 2) Compared with Example 7, the performance of Examples 11-12 (i.e., Preparation Examples 8-9) has decreased to varying degrees. It can be seen that the epoxy-modified carboxymethyl chitosan prepared only by the reaction of carboxymethyl chitosan and epichlorohydrin has significantly enhanced hydrolytic stability and alkali resistance due to the additional introduction of citric acid during the reaction process. The non-modified group obviously does not have the corresponding effect.

[0144] 3) Compared with Example 7, the mechanical properties of Example 13 (i.e., Preparation Example 10) decreased significantly. The reasons for this were as follows: when the CSH inducer was metakaolin (Al2O3·2SiO2), its highly active Al2O3 promoted the formation of ettringite (AFt), increasing early chemical shrinkage. In addition, the later microstructure refinement also led to an increase in capillary negative pressure, exacerbating autogenous shrinkage.

[0145] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An alkali-free liquid coagulant, characterized in that: The invention comprises the following components in weight percentage: 8-12 wt% of aluminum sulfate, 2-4 wt% of organic amine, and 1-5 wt% of composite auxiliary agent; The composite auxiliary agent is prepared by compounding a CSH inducer, chitosan and tricalcium citrate, and the CSH inducer, chitosan and tricalcium citrate are packaged separately.

2. The alkali-free liquid coagulant according to claim 1, characterized in that The composite auxiliary agent is prepared by compounding a CSH inducer, chitosan and calcium tricitrate in a weight ratio of (2-6): (1-6): (2-10).

3. The alkali-free liquid coagulant according to claim 1, characterized in that The CSH inducer is selected from either silica fume or nano-silicon dioxide.

4. The alkali-free liquid coagulant according to claim 3, characterized in that The content of SiO2 in the silica fume is ≥90%, and the specific surface area is ≥15000m 2 / kg.

5. The alkali-free liquid coagulant according to claim 1, characterized in that The chitosan is selected from hydroxyethyl chitosan, carboxymethyl chitosan or derivatives thereof.

6. The alkali-free liquid coagulant according to claim 5, characterized in that The chitosan is epoxy-modified carboxymethyl chitosan, which is prepared by reacting carboxymethyl chitosan with epichlorohydrin.

7. The alkali-free liquid coagulant according to claim 6, characterized in that The preparation steps of the epoxy-modified carboxymethyl chitosan are as follows: A1. Carboxymethyl chitosan pretreatment: carboxymethyl chitosan was first dissolved in deionized water at a concentration of 2-5 wt%, and the pH was adjusted to 5.0-6.0 with citric acid; A2, citric acid activation: 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide are added to the solution obtained in A1 to generate an active ester intermediate; A3. Grafting reaction: First, keep the temperature at 30-40°C under nitrogen atmosphere for 4-6 hours, then add epichlorohydrin and raise the temperature to 40-50°C and continue the reaction for 6-8 hours to complete the preparation.

8. The alkali-free liquid coagulant according to claim 7, characterized in that The amount of each material in A2 and A3 is as follows: The amount of 1-ethyl-(3-dimethylaminopropyl)carbodiimide used is 1.5-2.0% of the total weight of the solution obtained in A1; The amount of N-hydroxysuccinimide used is 1.0-1.5% of the total weight of the solution obtained in A1; The amount of epichlorohydrin used is 0.04-0.08% of the total weight of the solution obtained in A2.

9. The method for using the alkali-free liquid coagulant according to any one of claims 1 to 8, characterized in that: The details are as follows: B1. First, dry mix the CSH inducer with cement and mineral admixtures; B2. Pre-dissolve chitosan and calcium tricitrate in water to form a homogeneous solution; B3. Finally, add the mixture obtained in B1, the homogeneous solution obtained in B2, aluminum sulfate, and organic amine into the stirring system and stir for 5-10 minutes before use.

10. An epoxy-modified carboxymethyl chitosan obtained by the preparation method according to claim 7.

11. A multifunctional composite auxiliary agent, characterized in that: The invention is prepared by compounding separately packaged CSH inducer, chitosan and tricalcium citrate, wherein the weight ratio of the CSH inducer, chitosan and tricalcium citrate is (2-6): (1-6): (2-10).

Images