Low-rebound high-early-strength admixture for shotcrete and preparation method thereof

Abstract

The application discloses a low-rebound high-early-strength additive for shotcrete and a preparation method thereof. The low-rebound high-early-strength additive for shotcrete comprises A component and B component; the A component is composed of polymer monomers, a crosslinking agent, a polymerization inhibitor and water with a mass ratio of (4-8):(0.5-1):(0.25-0.75):2; and the B component is composed of an initiator, a polycarboxylic acid water reducing agent and a seed early strength agent with a mass ratio of (0.1-0.5):(0.01-0.05):(2.7-10.6). The application introduces in-situ polymerization of a polymer three-dimensional network into shotcrete, stably combines with cement hydration products, greatly increases the viscosity of shotcrete, simultaneously introduces high specific surface area homogeneous nano seeds, accelerates cement hydration to form a hardened three-dimensional network structure, and realizes low rebound rate and higher early strength of shotcrete through rapid deep intermeshing of two kinds of network structures.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of admixtures for building materials, and particularly relates to a low-rebound high-early-strength admixture for shotcrete, a preparation method and application thereof. BACKGROUND

[0002] Shotcrete is a construction technology that sprays concrete or mortar onto the surface through compressed air, and is widely used in tunnel engineering, slope stabilization, building repair, water conservancy engineering and other fields. As a special concrete construction method, shotcrete has the advantages of fast construction speed, strong adaptability, good adhesion and high strength, making it perform well in complex terrain, narrow space and special-shaped structures where traditional pouring techniques are difficult to apply. However, despite the maturity of shotcrete technology, there are still problems such as high rebound rate and insufficient early strength development in actual application, not only causing material waste and increasing construction cost, but also possibly leading to insufficient stability of supporting structures, affecting construction progress and engineering safety. SUMMARY

[0003] Therefore, the present application aims to provide a low-rebound high-early-strength admixture for shotcrete, which forms a high-viscosity, high-toughness three-dimensional network structure in the early stage of cement hydration through in-situ polymerization of monomers and seed early strength, accelerates the formation of cement hydration to form a three-dimensional network structure of cementitious materials, and forms an interlocking reinforced structure of the two networks after cement hydration, greatly accelerating the setting and hardening of cement, effectively solving the problems of high rebound rate and slow early strength development of existing shotcrete.

[0004] To achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0005] A low-rebound high-early-strength admixture for shotcrete, comprising A component and B component; the A component is composed of polymer monomers, crosslinking agents, polymerization inhibitors and water in a mass ratio of (4-8):(0.5-1):(0.25-0.75):2; the B component is composed of initiators, polycarboxylic acid water reducing agent and 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 materials of the shotcrete; the mass of the B component is 3.8-14.3% of the mass of the cementitious materials 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 is composed of sodium acrylate and 2-acrylamide-2-methylpropane sulfonic acid, the mass ratio of the sodium acrylate and the 2-acrylamide-2-methylpropane sulfonic acid is (7-10):(1-3).

[0009] Optionally, the polymerization inhibitor is 0.1wt% 4-hydroxypiperidine oxyl radical solution or 0.1wt% 4-methoxyphenol solution.

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

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

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

[0013] Optionally, the C-S-H nanoparticle suspension is prepared by the following method:

[0014] At room temperature, 32-48 parts of 4mol / L water-soluble silicon salt solution and 32-48 parts of 4mol / L water-soluble calcium salt solution are simultaneously added dropwise into 100 parts of 10-15wt% polycarboxylic acid water reducer solution under constant stirring, and after the dropwise addition is completed, the solution pH is adjusted to 11.7, and the stirring is continued for 24h to obtain the C-S-H nanoparticle suspension with a D50 of 155-356nm 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 1mol / L calcium hydroxide suspension are mixed, and then 18-24 parts of 1mol / L aluminum sulfate solution is added dropwise thereinto under constant stirring, and after the dropwise addition is completed, the stirring is continued for 24h to obtain the AFt nanoparticle suspension with a D50 of 153-312nm and a solid content of 20.6-24.7%.

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

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

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

[0020] A third object of the present application is to provide an application of the low rebound high early strength admixture for shotcrete as described above in shotcrete, which comprises the following steps: adding the component A and the component B into the shotcrete paste at 8.1-13.75% and 3.8-14.3% of the shotcrete binder respectively, and stirring uniformly.

[0021] The mechanism of the present application is as follows:

[0022] The present application introduces uniformly distributed polymer monomers and crosslinking agents into shotcrete, and under the action of initiators, a crosslinked polymer network is quickly formed in the shotcrete, thereby improving the overall viscosity of the shotcrete. The crosslinked polymer can form chemical bonds in the interlayer of C-S-H gel, calcium hydroxide and ettringite generated in the cement hydration process, and is firmly combined with hardened cement. However, the introduction of the polymer network can only improve the ductility and viscosity of the shotcrete in the initial stage of shotcrete spraying, and can only provide certain mechanical strength. In the present application, the seed nanoparticles have a high specific surface area, can provide a large number of homogeneous nucleation sites in 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 products, so that the cement hydration process is greatly accelerated, and the hardened cement paste is more compact. The three-dimensional network of the polymer and the three-dimensional network of the cementitious material are uniformly distributed and simultaneously connected to form a deep interpenetrating network, so that the cement paste can obtain high viscosity and harden in a short time under the action of the accelerator, greatly reducing the rebound rate of the shotcrete and improving the early strength of the shotcrete.

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

[0024] 1. The present application can introduce a three-dimensional polymer network in situ in shotcrete, which is stably combined with the cement hydration products, thereby greatly improving the viscosity of the shotcrete. At the same time, high specific surface area homogeneous nano-seeds are introduced to accelerate the cement hydration to form a hardened three-dimensional network structure, and the two grid structures are quickly and deeply interpenetrated, realizing low rebound rate and high early strength of the shotcrete, so that the rebound rate of the shotcrete is reduced to below 7%, and the setting time and compressive strength meet the national standard for shotcrete accelerator (GB / T 35159-2017).

[0025] 2. The present application can improve the early strength of the shotcrete and improve the rebound rate of the shotcrete, thereby providing a new method for improving the rebound rate and early strength of the shotcrete. DETAILED DESCRIPTION

[0026] In order for those skilled in the art to better understand the technical solutions and technical effects of the present application, several embodiments will be provided below. It is obvious that the following description is only an embodiment and does not limit the protection scope of the present application.

[0027] The medicines and materials used in the specific embodiments of the present application are obtained from the market, and the polycarboxylic acid water reducing agent has a solid content of 40%.

[0028] In the specific embodiments of the present application, unless otherwise specified, the unit represents a mass part.

[0029] In the specific embodiments of the present application, room temperature refers to 20±2℃.

[0030] The raw material mass ratio and preparation process parameters of the seed early strength agent in the B component of the low-rebound high-early-strength admixture for sprayed concrete according to the embodiments of the present application are shown in Table 1 and Table 2.

[0031] The specific preparation method of the C-S-H (calcium silicate hydrate) nanoparticle suspension that constitutes the seed early strength agent (taking C-S-H-1 as an example) is as follows:

[0032] At room temperature, a sodium silicate solution with a concentration of 4 mol / L, a calcium nitrate solution with a concentration of 4 mol / L, a NaOH solution with a concentration of 2 mol / L, and a HNO3 solution with a concentration of 2 mol / L are prepared.

[0033] 15 parts of polycarboxylic acid water reducing agent are dissolved in 85 parts of deionized water to obtain a 15wt% polycarboxylic acid water reducing agent solution;

[0034] 32 parts of the sodium silicate solution and 32 parts of the calcium nitrate solution are added dropwise into the above-mentioned polycarboxylic acid water reducing agent (PCE) solution through a peristaltic pump, and the two solutions are continuously stirred to be added dropwise within 30 min. After the dropwise addition is completed, the pH of the suspension is adjusted to 11.7 using a 2 mol / L NaOH solution and a HNO3 solution, and the stirring is continued for 24 h to obtain a C-S-H 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 that constitutes the seed early strength agent (taking AFt-1 as an example) is as follows:

[0036] At room temperature, a 1 mol / L calcium hydroxide suspension and a 1 mol / L aluminum sulfate solution are prepared.

[0037] Take 28 parts of polycarboxylic acid water reducing agent, 5 parts of citric acid and dissolve in 120 parts of calcium hydroxide suspension liquid, take 20 parts of aluminum sulfate solution, drop the aluminum sulfate solution into the above mixed suspension liquid through the peristaltic pump drop by drop, and continuously stir, so that the aluminum sulfate solution is added dropwise within 15 min, after the dropwise addition is completed, continue to stir for 24 h, to obtain the AFt nanoparticle suspension liquid with D50 of 153 and solid content of 22.6%, wherein the molar ratio of the calcium hydroxide suspension liquid to the aluminum sulfate solution is 6:1.

[0038] Table 1C-S-H nanoparticle suspension liquid preparation ratio and parameters

[0039]

[0040] Table 2 AFt nanoparticle suspension liquid preparation ratio and parameters

[0041] Sample Ca(OH)2 solution / parts Al2(SO4)3 solution / parts Polycarboxylic acid water reducer / parts 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 ratio of the A component and the B component in the low-rebound high-early-strength admixture for sprayed concrete according to the embodiments of the present application is shown in Table 3 and Table 4.

[0043] The specific preparation steps of the low-rebound high-early-strength admixture for sprayed concrete according to the embodiments of the present application are as follows: uniformly stirring the polymer monomer, the crosslinking agent, the polymerization inhibitor and water to obtain the A component; uniformly stirring the seed early-strength agent, the polycarboxylic acid water reducing agent and the initiator to obtain the B component.

[0044] Table 3 Raw material ratio of A component

[0045]

[0046] Table 4 Raw material ratio of B component

[0047]

[0048] According to the neat paste and mortar ratio in GB / T 8077-2012 “Concrete Admixture Homogeneity Test Method” and GB / T 50081-2017 “Sprayed Concrete Accelerator” test method, the neat paste setting time and mortar compressive strength of the low-rebound high-early-strength admixture for sprayed concrete according to the embodiments of the present application are tested, and compared with the admixture without adding the accelerator and the low-rebound high-early-strength admixture for sprayed concrete (Comparative Examples 1-2) of the present application. The admixture dosage (percentage of cement mass) and test results are shown in Table 5.

[0049] The cement used in the embodiments is Huaxin Cement P.042.5, the accelerator addition amount is 7% of the mass of the cement, and the type is FSA-AF non-alkali accelerator of Shanxi Feike New Material Technology Co., Ltd.

[0050] Table 5 admixture dosage in net paste and mortar and setting time and compressive strength

[0051]

[0052] According to JGJ / T 372-2016 "Technical Specification for Shotcrete Application", the shotcrete with low rebound and high early strength admixture of examples 1-12 is used to prepare shotcrete, the shotcrete process is wet shotcrete, the rebound rate of shotcrete is tested, and it is compared with only adding accelerator (comparative example 1). The test mixture ratio is 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 application and water, and the water-cement ratio is controlled to be 0.4. The proportioning of the admixture of each example of the present application and the rebound rate test results are shown in Table 6.

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

[0054] Table 6 admixture dosage and rebound rate of the present application

[0055]

[0056] The above is only a preferred embodiment of the present application, and is not intended to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A low-rebound high-early-strength admixture for shotcrete, characterized by, Comprise A component and B component; the A component is composed of polymer monomer, crosslinking agent, polymerization inhibitor and water with mass ratio of (4-8):(0.5-1):(0.25-0.75):2; the B component is composed of initiator, polycarboxylic acid water reducer, seed early strength agent with mass ratio of (0.1-0.5):(0.01-0.05):(2.7-10.6); The polymer monomer is composed of sodium acrylate and 2-acrylamide-2-methylpropane sulfonic acid, and the mass ratio of the sodium acrylate and the 2-acrylamide-2-methylpropane sulfonic acid is (7-10):(1-3); The seed early strength agent is prepared by the following method: Mix C-S-H nanoparticle suspension with D50 of 155-356 nm and solid content of 20.1-24.8% and AFt nanoparticle suspension with D50 of 153-312 nm and solid content of 20.6-24.7% according to mass ratio of 1:(0.5-1), to obtain the seed early strength agent; The C-S-H nanoparticle suspension is prepared by the following method: At room temperature, drop 32-48 parts of 4 mol / L water-soluble silicon salt solution and 32-48 parts of 4 mol / L water-soluble calcium salt solution into 100 parts of 10-15 wt% polycarboxylic acid water reducer solution at the same time and continuously stir, adjust the solution pH to 11.7 after the dropping is completed, and continue to stir for 24 h to obtain C-S-H nanoparticle suspension with D50 of 155-356 nm and solid content of 20.1-24.8%; The AFt nanoparticle suspension is prepared by the following method: At room temperature, mix 5 parts of citric acid, 22-30 parts of polycarboxylic acid water reducer and 108-144 parts of 1 mol / L calcium hydroxide suspension, then drop 18-24 parts of 1 mol / L aluminum sulfate solution into it and continuously stir, continue to stir for 24 h after the dropping is completed to obtain AFt nanoparticle suspension with D50 of 153-312 nm and solid content of 20.6-24.7%.

2. The low-slump high-early-strength admixture for shotcrete according to claim 1, characterized by The mass of the A component is 8.1-13.75% of the mass of the cementitious material of the sprayed concrete; the mass of the B component is 3.8-14.3% of the mass of the cementitious material of the sprayed concrete.

3. The low-slump high-early-strength admixture for shotcrete according to claim 1, characterized by The polymerization inhibitor is 0.1 wt% 4-hydroxypiperidine oxy nitrogen radical solution or 0.1 wt% 4-methoxyphenol solution.

4. The low-slump high-early-strength admixture for shotcrete according to claim 1, characterized by The initiator is composed of sodium persulfate and sodium bisulfite with mass ratio of (1-2):

1.

5. A method of producing a low-slump high-early-strength admixture for sprayed concrete as claimed in any one of claims 1 to 4, characterized in that, Comprise the following steps: Stir the polymer monomer, the crosslinking agent, the polymerization inhibitor and the water uniformly to obtain the A component; Stir the initiator, the polycarboxylic acid water reducer and the seed early strength agent uniformly to obtain the B component.

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