Low-resilience high-early-strength admixture for sprayed concrete and preparation method of low-resilience high-early-strength admixture

Abstract

The invention discloses a low-resilience high-early-strength admixture for sprayed concrete and a preparation method of the low-resilience high-early-strength admixture. The low-resilience high-early-strength admixture for the sprayed concrete comprises a component A and a component B, the component A is prepared from a polymer monomer, a cross-linking agent, a polymerization inhibitor and water according to the mass ratio of (4 to 8): (0.5 to 1): (0.25 to 0.75): 2; the component B is prepared from an initiator, a polycarboxylic acid water reducing agent and a seed crystal early strength agent according to the mass ratio of (0.1 to 0.5) to (0.01 to 0.05) to (2.7 to 10.6). In-situ polymerization of a polymer three-dimensional network is introduced into the sprayed concrete and is stably combined with a cement hydration product, so that the viscosity of the sprayed concrete is greatly improved, meanwhile, homogeneous nanocrystal seeds with high specific surface area are introduced, cement hydration is accelerated to form a hardened three-dimensional network structure, and rapid deep mutual embedding of the two grid structures is realized, so that the viscosity of the sprayed concrete is improved. And the low rebound rate and higher early strength of the sprayed concrete are realized.

Description

Technical Field

[0001] The invention relates to the technical field of building material admixtures, and in particular to a low-rebound and high-early-strength admixture for shotcrete, and a preparation method and application thereof. Background Art

[0002] Shotcrete is a construction technology that uses compressed air to spray concrete or mortar onto a surface. It is widely used in many fields such as tunnel engineering, slope stabilization, building restoration, and water conservancy projects. As a special concrete construction method, shotcrete has the advantages of fast construction speed, strong adaptability, good adhesion, and high strength, which makes it perform well in scenes where traditional casting technology is difficult to apply, such as complex terrain, narrow spaces, and special-shaped structures. However, although shotcrete technology is quite mature, it still faces problems such as high rebound rate and insufficient early strength development in actual applications, which not only causes material waste and increases construction costs, but may also lead to insufficient stability of the support structure, affecting construction progress and project safety. Summary of the invention

[0003] In view of this, the present invention aims to provide a low-rebound and high-early-strength admixture for shotcrete, which forms a high-viscosity and high-toughness three-dimensional network structure in the early stage of cement hydration by means of in-situ polymerization of monomers and coordinated early strength of seed crystals. The seed crystals accelerate cement hydration to form a three-dimensional network structure of cementitious materials. After cement hydration, an intertwined and reinforced structure of the two networks is formed, which greatly accelerates the coagulation and hardening of cement, and effectively solves the problems of high rebound rate and slow early strength development of existing shotcrete.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0005] A low-rebound and high-early-strength admixture for shotcrete comprises a component A and a component B; the component A comprises a polymer monomer, a crosslinking agent, a polymerization inhibitor and water in a mass ratio of (4-8):(0.5-1):(0.25-0.75):2; the component B comprises an initiator, a polycarboxylic acid water reducer and a seed early-strength agent in a mass ratio of (0.1-0.5):(0.01-0.05):(2.7-10.6).

[0006] Optionally, the mass of the A component is 8.1-13.75% of the mass of the cementitious material of the shotcrete; the mass of the B component is 3.8-14.3% of the mass of the cementitious material of the shotcrete.

[0007] Optionally, the polymer monomer is one or both of sodium acrylate and 2-acrylamide-2-methylpropane sulfonic acid.

[0008] Optionally, when the polymer monomer consists of sodium acrylate and 2-acrylamide-2-methylpropane sulfonic acid, the mass ratio of the sodium acrylate to the 2-acrylamide-2-methylpropane sulfonic acid is (7-10):(1-3).

[0009] Optionally, the polymerization inhibitor is a 0.1 wt % 4-hydroxypiperidinyloxynitrogen free radical solution or a 0.1 wt % 4-methoxyphenol solution.

[0010] Optionally, the initiator consists of sodium persulfate and sodium bisulfite in a mass ratio of (1-2):1.

[0011] Optionally, the seed early strength agent is prepared by the following method:

[0012] A CSH nanoparticle suspension with a D50 of 155-356 nm and a solid content of 20.1-24.8% and an AFt nanoparticle suspension with a D50 of 153-312 nm and a solid content of 20.6-24.7% are mixed in a mass ratio of 1:(0.5-1) to obtain a seed early strength agent.

[0013] Optionally, the CSH nanoparticle suspension is prepared by the following method:

[0014] At room temperature, 32-48 parts of a 4 mol / L water-soluble silicon salt solution and 32-48 parts of a 4 mol / L water-soluble calcium salt solution are simultaneously added dropwise to 100 parts of a 10-15 wt% polycarboxylate water-reducing agent solution and stirred continuously. After the addition is completed, the pH of the solution is adjusted to 11.7, and stirring is continued for 24 hours to obtain a CSH nanoparticle suspension having a D50 of 155-356 nm and a solid content of 20.1-24.8%.

[0015] Optionally, the AFt nanoparticle suspension is prepared by the following method:

[0016] At room temperature, 5 parts of citric acid, 22-30 parts of polycarboxylic acid water reducer and 108-144 parts of 1 mol / L calcium hydroxide suspension are mixed, and 18-24 parts of 1 mol / L aluminum sulfate solution are added dropwise thereto with continuous stirring. After the addition is completed, stirring is continued for 24 hours to obtain an AFt nanoparticle suspension with a D50 of 153-312 nm and a solid content of 20.6-24.7%.

[0017] The second object of the present invention is to provide a method for preparing the above-mentioned low rebound and high early strength admixture for shotcrete, which comprises the following steps:

[0018] The polymer monomer, the cross-linking agent, the polymerization inhibitor and the water are uniformly stirred to obtain component A;

[0019] The initiator, the polycarboxylate water-reducing agent and the seed early strength agent are uniformly stirred to obtain component B.

[0020] The third object of the present invention is to provide an application of the above-mentioned low-rebound and high-early-strength admixture for shotcrete in shotcrete, which comprises the following steps: adding the component A and the component B to the shotcrete slurry at 8.1-13.75% and 3.8-14.3% of the mass of the shotcrete cementitious material respectively, and stirring evenly.

[0021] Mechanism of the present invention:

[0022] The present invention introduces uniformly distributed polymer monomers and crosslinking agents into the shotcrete, and under the action of an initiator, a crosslinked polymer network is quickly formed in the shotcrete to improve the overall viscosity of the shotcrete. The crosslinked polymer can enter the interlayer of CSH gel, calcium hydroxide, and calcium sulfonate generated during the cement hydration process to produce chemical bonding, and is firmly combined with hardened cement. However, the introduction of the polymer network can only improve its ductility and viscosity in the early stage of concrete spraying, and can only provide a certain mechanical strength, while the seed nanoparticles in the present invention have a high specific surface area, can provide a large number of homogeneous nucleation sites during the cement hydration process, accelerate the dissolution of calcium ions and aluminum ions, significantly shorten the cement hydration induction period, and have the same material composition as the cement hydration product, so that the cement hydration process is greatly accelerated, and the hardened cement paste is more compact. The polymer three-dimensional network and the three-dimensional network of the cementitious material are evenly distributed, and are connected to form a deep interlocking network at the same time, so that the cement paste can obtain a higher viscosity and harden in a short time under the action of the accelerator, which greatly reduces the rebound rate of the shotcrete and improves the early strength of the shotcrete.

[0023] Compared with the prior art, the low-rebound and high-early-strength admixture for shotcrete of the present invention has the following advantages:

[0024] 1. The present invention can realize the in-situ polymerization of the three-dimensional polymer network introduced into the shotcrete, which is firmly combined with the cement hydration product, so that the viscosity of the shotcrete is greatly improved. At the same time, homogeneous nano-crystal seeds with high specific surface area are introduced to accelerate the cement hydration to form a hardened three-dimensional network structure. The rapid and deep interpenetration of the two grid structures achieves the low rebound rate and high early strength of the shotcrete, and reduces the rebound rate of the shotcrete to below 7%. The setting time and compressive strength meet the national standard for accelerated setting agents for shotcrete (GB / T 35159-2017).

[0025] 2. The present invention can improve the rebound rate of shotcrete on the basis of improving the early strength of shotcrete, and provides a new method for comprehensively improving the rebound rate and early strength development of shotcrete. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions and technical effects of the present invention, several embodiments are provided below. Obviously, what is described below is only an embodiment and does not limit the protection scope of the present invention.

[0027] The drugs and materials used in the specific embodiments of the present invention are all purchased from the market, and the solid content of the polycarboxylate water-reducing agent is 40%.

[0028] Unless otherwise specified, parts in the specific embodiments of the present invention represent parts by mass.

[0029] The room temperature in the specific embodiment of the present invention refers to 20±2°C

[0030] The raw material mass ratio and preparation process parameters of the seed early strength agent in component B of the low rebound and high early strength admixture for shotcrete in various embodiments of the present invention are shown in Table 1 and Table 2.

[0031] Among them, the specific preparation method of the CSH (calcium silicate hydrate) nanoparticle suspension constituting the seed early strength agent (taking CSH-1 as an example) is as follows:

[0032] At room temperature, prepare a 4 mol / L sodium silicate solution, a 4 mol / L calcium nitrate solution, a 2 mol / L NaOH solution, and a 2 mol / L HNO3 solution;

[0033] Dissolve 15 parts of polycarboxylate water reducer in 85 parts of deionized water to obtain a 15 wt% polycarboxylate water reducer solution;

[0034] Take 32 parts of sodium silicate solution and 32 parts of calcium nitrate solution, and add the sodium silicate solution and the calcium nitrate solution drop by drop into the above-mentioned polycarboxylate water reducer (PCE) solution by a peristaltic pump, and stir continuously to complete the addition of the two solutions within 30 minutes. After the addition is completed, the pH of the suspension is adjusted to 11.7 using 2 mol / L NaOH solution and HNO3 solution, and stirring is continued for 24 hours to obtain a CSH nanoparticle suspension with a D50 of 155 and a solid content of 23.2%.

[0035] The specific preparation method of the AFt (ettringite) nanoparticle suspension constituting the seed early strength agent (taking AFt-1 as an example) is as follows:

[0036] At room temperature, prepare 1 mol / L calcium hydroxide suspension and 1 mol / L aluminum sulfate solution;

[0037] Take 28 parts of polycarboxylate water reducer and 5 parts of citric acid and dissolve them in 120 parts of calcium hydroxide suspension, take 20 parts of aluminum sulfate solution, add the aluminum sulfate solution dropwise to the mixed suspension by a peristaltic pump, and stir continuously to complete the addition of the aluminum sulfate solution within 15 minutes. After the addition is completed, continue stirring for 24 hours to obtain an AFt nanoparticle suspension with a D50 of 153 and a solid content of 22.6%, wherein the molar ratio of the calcium hydroxide suspension to the aluminum sulfate solution is 6:1.

[0038] Table 1 Preparation ratio and parameters of C-SH nanoparticle suspension

[0039]

[0040] Table 2 Preparation ratio and parameters of AFt nanoparticle suspension

[0041] sample Calcium hydroxide solution / part Aluminum sulfate solution / part Polycarboxylate water reducer / part Particle size D50 / nm Solid content / % AFt-1 120 20 28 153 22.6 AFt-2 108 18 22 312 20.4 AFt-3 144 24 30 219 24.7

[0042] The specific raw material mass ratios of component A and component B in the low-resilience and high-early-strength admixture for shotcrete of various embodiments of the present invention are shown in Tables 3 and 4.

[0043] The specific preparation steps of the low-rebound and high-early-strength admixture for shotcrete in each embodiment of the present invention are as follows: uniformly mixing the polymer monomer, the cross-linking agent, the polymerization inhibitor and water to obtain component A; uniformly mixing the seed early strength agent, the polycarboxylic acid water-reducing agent and the initiator to obtain component B.

[0044] Table 3A Component Raw Material Ratio

[0045]

[0046] Table 4B Component Raw Material Ratio

[0047]

[0048] With reference to the pure paste and mortar ratio in the test method of GB / T 8077-2012 "Concrete Admixture Homogeneity Test Method" and GB / T 50081-2017 "Shotcrete Accelerator", the pure paste setting time and mortar compressive strength of the low rebound and high early strength admixture for shotcrete of each embodiment of the present invention were tested, and compared with the case where no accelerator was added and no low rebound and high early strength admixture for shotcrete of the present invention was added (Comparative Examples 1 to 2). The admixture dosage (percentage of cement mass) and the test results are shown in Table 5.

[0049] Among them, the cement used in the embodiment is Huaxin Cement P.042.5, the amount of accelerated setting agent added is 7% of the cement mass, and the model is FSA-AF alkali-free accelerated setting agent produced by Shanxi Feike New Materials Technology Co., Ltd.

[0050] Table 5 Additive dosage, setting time and compressive strength in neat paste and mortar

[0051]

[0052] Referring to JGJ / T 372-2016 "Technical Specification for Application of Shotcrete", the shotcrete with low rebound and high early strength admixtures of Examples 1 to 12 was prepared, and the spraying process was wet spraying. The rebound rate of the shotcrete was tested and compared with that of the shotcrete with only the accelerator (Comparative Example 1). The test mix ratio used 450 parts of cement, 871 parts of sand, 869 parts of stone, 31.5 parts of commercially available accelerator, the corresponding amount of the admixture of the present invention and water, and the water-cement ratio was controlled to 0.4. The proportions of the admixtures of the embodiments of the present invention and the rebound rate test results are shown in Table 6.

[0053] It can be seen from Table 5 and Table 6 that the low rebound and high early strength admixture for shotcrete used in Examples 1 to 12 of the present invention is applied to shotcrete, and has higher compressive strength and lower rebound rate, the initial setting time of the net slurry is ≤3min, and the final setting time is ≤10min; the 1d strength of the mortar reaches 7.5MPa, and the 28d strength does not decrease; the rebound rate of the shotcrete is less than 7%.

[0054] Table 6 Dosage and rebound rate of admixtures of the present invention

[0055]

[0056] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-rebound and high-early-strength admixture for shotcrete, characterized in that: The invention comprises component A and component B; the component A comprises a polymer monomer, a crosslinking agent, an inhibitor and water in a mass ratio of (4-8):(0.5-1):(0.25-0.75):2; the component B comprises an initiator, a polycarboxylic acid water reducer and a seed early strength agent in a mass ratio of (0.1-0.5):(0.01-0.05):(2.7-10.6).

2. The low-resilience and high-early-strength admixture for shotcrete according to claim 1, characterized in that: The mass of the A component is 8.1-13.75% of the mass of the cementitious material of the shotcrete; the mass of the B component is 3.8-14.3% of the mass of the cementitious material of the shotcrete.

3. The low-resilience and high-early-strength admixture for shotcrete according to claim 1, characterized in that: The polymer monomer is one or two of sodium acrylate and 2-acrylamide-2-methylpropane sulfonic acid.

4. The low-resilience and high-early-strength admixture for shotcrete according to claim 3, characterized in that: When the polymer monomer consists of sodium acrylate and 2-acrylamide-2-methylpropane sulfonic acid, the mass ratio of the sodium acrylate to the 2-acrylamide-2-methylpropane sulfonic acid is (7-10):(1-3).

5. The low-resilience and high-early-strength admixture for shotcrete according to claim 1, characterized in that: The polymerization inhibitor is a 0.1 wt % 4-hydroxypiperidinyloxynitrogen free radical solution or a 0.1 wt % 4-methoxyphenol solution.

6. The low-resilience and high-early-strength admixture for shotcrete according to claim 1, characterized in that: The initiator consists of sodium persulfate and sodium bisulfite in a mass ratio of (1-2):

1.

7. The low-resilience and high-early-strength admixture for shotcrete according to claim 1, characterized in that: The seed early strength agent is prepared by the following method: A CSH nanoparticle suspension with a D50 of 155-356 nm and a solid content of 20.1-24.8% and an AFt nanoparticle suspension with a D50 of 153-312 nm and a solid content of 20.6-24.7% are mixed in a mass ratio of 1:(0.5-1) to obtain a seed early strength agent.

8. The low-resilience and high-early-strength admixture for shotcrete according to claim 7, characterized in that: The CSH nanoparticle suspension is prepared by the following method: At room temperature, 32-48 parts of a 4 mol / L water-soluble silicon salt solution and 32-48 parts of a 4 mol / L water-soluble calcium salt solution are simultaneously added dropwise to 100 parts of a 10-15 wt% polycarboxylate water-reducing agent solution and stirred continuously. After the addition is completed, the pH of the solution is adjusted to 11.7, and stirring is continued for 24 hours to obtain a CSH nanoparticle suspension having a D50 of 155-356 nm and a solid content of 20.1-24.8%.

9. The low-resilience and high-early-strength admixture for shotcrete according to claim 7, characterized in that: The AFt nanoparticle suspension is prepared by the following method: At room temperature, 5 parts of citric acid, 22-30 parts of polycarboxylic acid water reducer and 108-144 parts of 1 mol / L calcium hydroxide suspension are mixed, and 18-24 parts of 1 mol / L aluminum sulfate solution are added dropwise thereto with continuous stirring. After the addition is completed, stirring is continued for 24 hours to obtain an AFt nanoparticle suspension with a D50 of 153-312 nm and a solid content of 20.6-24.7%.

10. A method for preparing the low-resilience and high-early-strength admixture for shotcrete according to any one of claims 1 to 9, characterized in that: The following steps are involved: The polymer monomer, the cross-linking agent, the polymerization inhibitor and the water are uniformly stirred to obtain component A; The initiator, the polycarboxylate water-reducing agent and the seed early strength agent are uniformly stirred to obtain component B.

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