Solid-waste-based green nano composite seed crystal early strength agent and preparation method thereof

Abstract

The invention discloses a solid-waste-based green nano-composite seed crystal early strength agent and a preparation method thereof, and relates to a green and environment-friendly seed crystal early strength agent. The solid-waste-based green nano composite seed crystal early strength agent is prepared from the following raw materials in parts by weight: 200 to 300 parts of deionized water, 100 to 150 parts of dispersing agent, 200 to 300 parts of Ca (NO3) 2 solution, 100 to 200 parts of Na2CO3 solution, 50 to 100 parts of steel slag powder and 50 to 140 parts of waste concrete recycled micro powder. The solid-waste-based green nano-composite seed crystal early strength agent disclosed by the invention takes the steel slag powder and the waste concrete recycled micro powder as raw materials, is low in cost, reduces the pollution of solid wastes to the environment, is green and environment-friendly, and is simple in process.

Description

Technical Field

[0001] The present invention relates to an early strength agent, in particular to a seed crystal early strength agent, and specifically to a solid waste-based green nano-composite seed crystal early strength agent and a preparation method thereof. Background Art

[0002] In cement-based materials, nano-CSH nucleation accelerators and nano-calcium carbonate accelerators enhance early strength through a dual mechanism: First, nanoparticles act as heterogeneous nucleation sites, reducing the nucleation barrier of CSH gels and accelerating the hydration reaction rate of cement clinker minerals. Second, the high-surface-area calcium carbonate particles adsorb onto the cement particle surface, promoting ion migration and precipitation crystallization, rapidly building a dense microstructure and significantly improving early strength. These accelerators are particularly suitable for low-temperature construction, prefabricated components, and other projects requiring rapid demolding, aligning with the development of green building materials. However, the preparation of traditional nano-CSH nucleation accelerators and nano-calcium carbonate accelerators typically relies on high-purity chemical raw materials (such as sodium silicate and calcium nitrate), which poses challenges such as high raw material costs and complex processes. Chemical synthesis requires the procurement of expensive calcium and silicon sources, making it uneconomical. Furthermore, the synthesis process easily generates saline wastewater or waste residue, posing a risk of secondary pollution.

[0003] Steel slag and waste concrete powder have significant resource potential. The chemical composition shows that the total CaO+SiO2 content of the two generally exceeds 60% (waste concrete powder contains a large amount of CSH gel and calcium hydroxide); mineral composition analysis shows that calcium silicate minerals such as C3S (specifically 3CaO·SiO2) and C2S (specifically 2CaO·SiO2) in steel slag account for 40-60%, while waste concrete powder retains the characteristics of cement hydration products (calcium hydroxide, CSH gel). This unique chemical and mineral composition provides a good material basis for the preparation of nano-calcium carbonate-nano-CSH crystal core composite seed-type early strength agent. The existing technology has reported the use of waste concrete recycled powder as a raw material for early strength agent, but there is no record of it being used as a raw material for early strength agent together with steel slag. Summary of the Invention

[0004] The first technical problem solved by the present invention is to provide a solid waste-based green nano-composite crystal seed early strength agent.

[0005] The second technical problem solved by the present invention is to provide a method for preparing a solid waste-based green nano-composite crystal seed early strength agent.

[0006] The technical solution of the present invention to solve the first technical problem is a solid waste-based green nano-composite crystal seed early strength agent, which includes the following raw materials in parts by weight: 200-300 parts of deionized water, 100-150 parts of dispersant, 200-300 parts of Ca(NO3)2 solution, 100-200 parts of Na2CO3 solution, 50-100 parts of steel slag powder and 50-140 parts of waste concrete recycled micropowder.

[0007] In the present invention, the solid waste-based green nano-composite crystal seed early strength agent can also be composed of the above-mentioned raw materials.

[0008] Preferably, the dispersant is composed of a polycarboxylate water reducer and a silane coupling agent KH 550, the solid content of the polycarboxylate water reducer is 25-30%, the solid content of the silane coupling agent is 25-30%, and the mass ratio of the polycarboxylate water reducer to the silane coupling agent is 5:6 to 6:5.

[0009] Preferably, the mass fraction of the Ca(NO3)2 solution is 30-50%.

[0010] Preferably, the mass fraction of the Na2CO3 solution is 20-30%.

[0011] Preferably, the solid waste powder contains 20-25% SiO2 and 40-60% CaO.

[0012] Preferably, the specific surface area of ​​the solid waste powder is 400-450 cm 2 / g.

[0013] The technical solution of the present invention to solve the second technical problem is a method for preparing the above-mentioned solid waste-based green nano-composite seed crystal early strength agent, comprising the following steps:

[0014] S1. Calcium source precipitation and silicon source dissolution:

[0015] reacting waste concrete recycled micro powder and / or steel slag powder with sodium carbonate solution under high-speed stirring;

[0016] S2, solid-liquid separation, to obtain the first reaction liquid:

[0017] The suspension after the reaction in step S1 is subjected to solid-liquid separation to obtain high-content calcium carbonate powder and the first reaction liquid respectively;

[0018] S3, the solution is concentrated to obtain a second reaction solution:

[0019] heating and concentrating the first reaction solution obtained in step S2 to obtain a second reaction solution;

[0020] S4, the second reaction solution and Ca(NO3)2 solution co-precipitation:

[0021] Water and a dispersant are sequentially added to a reaction kettle and stirred evenly to obtain a mixed solution, and Ca(NO3)2 solution and a second reaction liquid are simultaneously added dropwise to the mixed solution to obtain a solid waste-based green nano-composite crystal seed early strength agent.

[0022] Preferably, in step S1, the solid-liquid ratio of waste concrete recycled fine powder and steel slag powder to sodium carbonate solution is 0.8-1g / 10ml, the reaction temperature is 60-80°C, the reaction time is 6-10h, and high-speed stirring is carried out throughout the process and the rotation speed is controlled at 1000-1200rpm.

[0023] Preferably, in step S3, the reaction liquid is heated to maintain a boiling state, stirred at high speed throughout the process and the rotation speed is controlled to be 200-300 rpm, so that the mass fraction of sodium silicate in the concentrated solution is 30-40%.

[0024] Preferably, in step S4, the reaction temperature is controlled at 30-40° C., a high-speed stirring state is maintained and the rotation speed is controlled at 600-800 rpm, and the reaction time is 3-4 h.

[0025] In the preparation method of a solid waste-based green nano-composite crystal seed early strength agent of the present invention, steps S1-S4 are used in combination. Specifically, step S1 is used to react the calcium source in the solid waste to generate calcium carbonate precipitation, and the silicon source is dissolved to generate sodium silicate solution; the present invention strictly controls the reaction temperature, test piece and stirring rate in S2 to ensure that the calcium source is fully precipitated and the silicon source is fully dissolved; after solid-liquid separation in step S2, the obtained first reaction liquid is a mixed solution of sodium silicate, sodium hydroxide and sodium carbonate; step S3 heats and concentrates the first reaction liquid to obtain a second reaction liquid containing a high concentration of sodium silicate; step S4 gradually adds the second reaction liquid and the Ca(NO3)2 solution to an aqueous solution containing a dispersant at the same time to react, generates nano-CSH crystal nuclei and nano-calcium carbonate crystal nuclei, and obtains a solid waste-based green nano-composite crystal seed early strength agent.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The solid waste-based green nano-composite seed early strength agent provided by the present invention can utilize steel slag powder and waste concrete recycled micropowder to reduce the pollution of solid waste to the environment and promote the green development of the construction industry.

[0028] (2) The powder obtained by solid-liquid separation in step S2 of the present invention contains a large amount of calcium carbonate, which can be directly used as a mineral admixture for concrete. The first reaction liquid obtained in step S2 is directly concentrated and then used for co-precipitation synthesis of nano-CSH crystal nuclei and nano-calcium carbonate crystal nuclei, without generating wastewater and waste residue. The cement setting time can be effectively shortened, and the compressive strength of concrete can be significantly improved within one day, among which the improvement is most significant in 6 hours, up to 260% to 400%. By reusing the calcium source in mineral phases such as calcium hydroxide, calcium-containing admixtures, calcium silicate and calcium ferrite in the recycled micropowder and steel slag, the use of calcium nitrate, calcium chloride and calcium acetate as calcium sources can be indirectly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 The present invention provides a flow chart of the preparation method of a solid waste-based green nano-composite seed early strength agent. DETAILED DESCRIPTION

[0031] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0033] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0034] The formulation components of Examples 1-4 and Comparative Examples 1-5 are shown in Table 1.

[0035] Table 1 Formula components of Examples 1-4 and Comparative Examples 1-5

[0036]

[0037]

[0038] The preparation method of the above solid waste-based green nano-composite seed early strength agent is as follows: Figure 1As shown, the steps are:

[0039] S1. Calcium source precipitation and silicon source dissolution of recycled fine powder from waste concrete

[0040] The waste concrete recycled micro powder and steel slag powder with the required solid-liquid ratio are reacted with the sodium carbonate solution under high-speed stirring;

[0041] S2, solid-liquid separation, obtaining the first reaction liquid

[0042] The suspension after the reaction in step S1 is subjected to solid-liquid separation to obtain high-content calcium carbonate powder and the first reaction liquid respectively;

[0043] S3, the solution is concentrated to obtain the second reaction solution

[0044] heating and concentrating the first reaction solution obtained in step S2 to obtain a second reaction solution;

[0045] S4, co-precipitation of the second reaction solution:

[0046] Water and a dispersant are sequentially added into a reaction kettle and stirred evenly to obtain a mixed solution, and a Ca(NO3)2 solution and a second reaction liquid are simultaneously added dropwise into the mixed solution to obtain a solid waste-based green nano-composite crystal seed early strength agent.

[0047] In step S1, the specific surface area of ​​the waste concrete recycled fine powder is 400-450cm 2 / g

[0048] In step S1, the mass fraction of the sodium carbonate solution is 20-30%, the solid-liquid ratio is 0.8-1 g / 10 ml, the reaction temperature is 60-80° C., the reaction time is 6-10 h, and high-speed stirring is carried out throughout the process, and the rotation speed is controlled at 1000-1200 rpm.

[0049] In step S2, the powder obtained after solid-liquid separation is washed with water and dried at 105°C, and can be used as a mineral admixture for concrete.

[0050] In step S3, the heating and concentration conditions are as follows: the reaction solution is kept in a boiling state, stirred at high speed throughout the process and the rotation speed is controlled at 200 rpm, so that the mass fraction of sodium silicate in the concentrated solution is 30-40%.

[0051] Before the co-precipitation in step S4, the pH value of the second reaction solution is not less than 13.

[0052] In step S4, the mass fraction of the Ca(NO3)2 solution is 30-50%.

[0053] In step S4, the reaction parameters are controlled to be a temperature of 30-40° C., a high-speed stirring state is maintained, and the rotation speed is controlled at 600-800 rpm, and the reaction time is 3-4 hours.

[0054] The preparation process of the regenerated micropowder and steel slag described in the embodiments of the present invention is as follows:

[0055] (2) The preparation process of recycled micropowder mainly includes crushing and screening the waste concrete blocks to remove impurities and adjust the particle size, and then grinding the particles (specific surface area 400-450cm 2 / g) and activated to enhance its activity, and finally dried to remove moisture and stored to ensure its performance in subsequent applications;

[0056] (2) The preparation process of steel slag powder mainly includes pre-treatment of steel slag to remove impurities and adjust the particle size, and then grinding to refine the particles (specific surface area 400-450cm 2 / g), using a powder selection process to separate highly active mineral powders, and then chemically modifying them to enhance their properties. The steel slag powder selection process primarily includes pretreatment (such as slag-iron separation, crushing, and magnetic separation), grinding (using equipment such as ball mills, roller presses, or vertical mills), classification (using a powder selector to separate fine and coarse powders), iron removal (using multiple iron removal devices to remove metallic iron), and drying and transportation. Chemical modification methods involve using chemical activators (such as phosphoric acid and formic acid) to increase the hydration activity of the steel slag. Finally, the slag is stored in a finished product bin for subsequent use.

[0057] Mortar specimens prepared according to the mix ratios in Table 1 were prepared in accordance with the "Test Method for Cement Mortar Strength (ISO Method)". The one-day strength of the mortar without nanocrystalline cores was 7.9 MPa. The strength improvement rates of the examples and comparative examples were calculated based on this strength. The results are shown in Table 2.

[0058] Table 2

[0059]

[0060] The above examples and comparative results demonstrate that CSH nuclei prepared using steel slag alone as a silicon source significantly outperform recycled concrete powder in enhancing mortar strength, but are still inferior to the combination of steel slag and recycled powder. This is primarily due to the low content of reactive calcium silicate minerals and hydrated calcium silicate in recycled concrete powder, resulting in a limited source of extractable silicon. Combining steel slag with recycled powder not only enhances the strength-enhancing efficacy of CSH nuclei but also improves the resource utilization of the recycled powder. This synergistic effect is attributed to the fact that the introduction of recycled powder reduces the silicon concentration in the second reaction solution, thereby reducing the nuclei particle size and further improving their early activity and dispersibility.

[0061] The above-described embodiments represent only two examples of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A solid waste-based green nano-composite seed early strength agent, characterized in that: Calculated by weight, the components include: 200-300 parts of deionized water, 100-150 parts of dispersant, 200-300 parts of Ca(NO3)2 solution, 100-200 parts of Na2CO3 solution, 50-100 parts of steel slag powder and 50-140 parts of waste concrete recycled fine powder.

2. The solid waste-based green nano-composite seed early strength agent according to claim 1, characterized in that: The dispersant consists of a polycarboxylate water reducer and a silane coupling agent. The solid content of the polycarboxylate water reducer is 25-30%, the solid content of the silane coupling agent is 25-30%, and the mass ratio of the polycarboxylate water reducer to the silane coupling agent is 5:6 to 6:

5.

3. The solid waste-based green nano-composite seed early strength agent according to claim 1, characterized in that: The mass fraction of the Ca(NO3)2 solution is 30-50%.

4. The solid waste-based green nano-composite seed early strength agent according to claim 1, characterized in that: The mass fraction of the Na2CO3 solution is 20-30%.

5. The solid waste-based green nano-composite seed early strength agent according to claim 1, characterized in that: The specific surface area of ​​the steel slag powder or waste concrete recycled fine powder is 400-450cm 2 / g.

6. The method for preparing the solid waste-based green nano-composite seed early strength agent according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, reacting waste concrete recycled micro powder and steel slag powder with sodium carbonate solution under high-speed stirring; S2, separating the suspension after the reaction in step S1 into solid and liquid, and obtaining calcium carbonate powder and the first reaction liquid respectively; S3, heating and concentrating the first reaction solution obtained in step S2 so that the mass fraction of sodium silicate in the concentrated solution is 30-40%, thereby obtaining a second reaction solution; S4. Add water and dispersant into the reactor in sequence and stir evenly to obtain a mixed solution. Add Ca(NO3)2 solution and the second reaction liquid dropwise to the mixed solution at the same time to obtain a solid waste-based green nano-composite seed early strength agent by co-precipitation.

7. The method for preparing the solid waste-based green nano-composite seed early strength agent according to claim 6, characterized in that: In step S1, the solid-liquid ratio of waste concrete recycled fine powder and steel slag powder to sodium carbonate solution is 0.8-1g / 10ml, the reaction temperature is 60-80°C, the reaction time is 6-10h, and high-speed stirring is carried out throughout the process and the speed is controlled at 1000-1200rpm.

8. The method for preparing the solid waste-based green nano-composite seed early strength agent according to claim 6, characterized in that: In step S3, the heating state is controlled to keep the reaction liquid in a boiling state, and the stirring speed is controlled to 200-300 rpm.

9. The method for preparing the solid waste-based green nano-composite seed early strength agent according to claim 6, characterized in that: In step S4, the reaction temperature is controlled at 30-40° C., the stirring speed is controlled at 600-800 rpm, and the reaction time is 3-4 h.

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