An activator for recycled fine powder of waste concrete, its preparation method and application

Abstract

The present invention discloses a waste concrete recycled fine powder activator, its preparation method and application, belonging to the technical field of cement-based material admixtures. The recycled fine powder activator includes a polyether side chain-modified polyethylenepolyamine organic activation molecule and nano-silica. For the waste concrete recycled fine powder activator of the present invention, the adsorption of specific functional groups in the organic activation molecule on the surface of the recycled fine powder can effectively improve the dissolution-crystallization process of the recycled fine powder in the cement-based material system, induce the formation of mineral phases beneficial to the microstructure, thereby enhancing the utilization efficiency and quality of the recycled fine powder. Compared with the single-component organic activation molecule, the organic molecule-nanoparticle hybrid activator of the present invention has better activation efficiency for the recycled fine powder and more obvious improvement in the performance of the recycled fine powder mortar / concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of admixtures for cement-based materials, and particularly relates to an activator for waste concrete recycled fine powder, a preparation method thereof, and an application thereof. Background Art

[0002] Waste concrete refers to the waste concrete blocks after the building is demolished. The high-quality concrete blocks and sand powder after crushing and screening can be used as recycled coarse / fine aggregates for concrete respectively. A large amount of fine powder can be used as the raw material of recycled binder. The concrete prepared from recycled aggregates and recycled binder can enter the next cycle. During the whole cycle process, zero discharge of waste is achieved. However, in the past, the recycling of waste concrete has focused on recycled aggregates, and about 30-40% of the waste concrete fine powder has not been effectively utilized due to its low quality. Therefore, making full use of waste concrete fine powder is not only the need for environmental protection and low emissions, but also can alleviate the problem of the increasingly scarce resources of mineral admixtures in China, which has important practical significance.

[0003] Different from ordinary cement and mineral admixtures, recycled fine powder has low activity and strong adsorption. After being incorporated as a cementitious material, it is easy to interact with other cementitious components during the hydration process, thus affecting the hydration hardening, mechanical properties, and durability of recycled fine powder mortar / concrete; in addition, the adsorption and chemical interaction between recycled fine powder and chemical admixtures (such as water reducers, thickeners, etc.) are the key to affecting the workability of recycled fine powder mortar / concrete. Therefore, developing an efficient solubilization and activation technology for recycled fine powder is a major scientific issue for improving the performance of recycled fine powder mortar / concrete.

[0004] Patent applications CN115569687A, CN115745531A, CN114507050A, CN112876145A, etc. respectively mention the preparation methods and applications of concrete blocks and sand powder after crushing and screening of waste concrete as recycled coarse / fine aggregates, while there are few reports on the utilization of micro powder generated from waste concrete as recycled binder; Patent applications CN109320162A and CN113788638A report the preparation of recycled micro powder and its application in concrete, but the recycled micro powder therein lacks efficient activation means, which affects the performance of concrete. The addition of functional chemical admixtures can effectively improve the performance of cement / concrete. Compared with pure organic admixtures, organic-inorganic hybrid admixtures with nano-silica as the organic molecular carrier (Construction and Building Materials, 2023, 362, 129739; Materials, 2022, 15, 7993) have a better improvement effect on the performance of mortar / concrete. Therefore, through molecular design, the development of an activator for recycled micro powder hybridized with nano-silica and organic molecules is expected to have a better activation effect on recycled micro powder of waste concrete, but there is no report on this aspect of research at present. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides an activator for recycled micro powder of waste concrete, its preparation method and application, which have better activation efficiency for recycled micro powder and more obvious improvement in the performance of recycled micro powder mortar / concrete.

[0006] The present invention is realized through the following technical solutions:

[0007] An activator for recycled micro powder of waste concrete, comprising a polyether side-chain modified polyethylenepolyamine organic activation molecule and nano-silica; the structural formula of the polyether side-chain modified polyethylenepolyamine organic activation molecule is shown as general formula I:

[0008]

[0009] In general formula I: m is a natural number from 1 to 5, and n is a natural number from 5 to 20.

[0010] Preferably, the nano-silica is prepared by the sol-gel method, using ammonia water as the solvent and tetraethoxysilane as the silicon source; wherein, the mass ratio of the polyether side-chain modified polyethylenepolyamine organic activation molecule, ammonia water and tetraethoxysilane is (5 - 15):1:2.

[0011] Preferably, the average particle size of the recycled micro powder activator is 100 - 200 nm.

[0012] The preparation method of the above-mentioned waste concrete recycled micro-powder activator comprises the following steps:

[0013] Step 1) Polyethylene polyamine is introduced into ethylene oxide under the action of a catalyst and reacted for 1 to 3 hours to obtain a polyether side chain-modified polyethylene polyamine organic activating molecule;

[0014] Step 2) The polyether side chain-modified polyethylene polyamine organic activating molecule and ammonia water are stirred and mixed at 30 to 40 °C, tetraethoxysilane is slowly added and continuously stirred at 30 to 40 °C for 5 to 10 hours; the obtained solid is filtered and washed with a small amount of absolute ethanol, and after vacuum drying, it is obtained.

[0015] Preferably, the temperature for introducing ethylene oxide in Step 1) is 120 to 140 °C.

[0016] Preferably, the catalyst in Step 1) is sodium hydride, sodium methoxide or sodium tert-butoxide.

[0017] Preferably, the structural formula of the polyethylene polyamine in Step 1) is as shown in General Formula II:

[0018]

[0019] In General Formula II: m is a natural number from 1 to 5;

[0020] The molar ratio of the polyethylene polyamine, the catalyst and the ethylene oxide is 1:[0.01(2 + m) to 0.1(2 + m)]:[5(2 + m) to 20(2 + m)].

[0021] Preferably, the concentration of the ammonia water in Step 2) is 28%.

[0022] The application of the above-mentioned waste concrete recycled micro-powder activator, or the waste concrete recycled micro-powder activator prepared by the above preparation method, in activating the waste concrete recycled micro-powder.

[0023] Preferably, the activator and the recycled micro-powder obtained by crushing, impurity removal and grinding of the waste concrete are fully mixed according to a mass ratio of (0.2 to 2):100.

[0024] The beneficial effects of the present invention are as follows:

[0025] The waste concrete recycled fine powder activator of the present invention, in terms of chemical structure, adopts an organic-inorganic hybrid method. First, a polyether side chain is introduced into the molecular structure of polyethylenepolyamine to obtain an organic activation molecule, and then nano-silica is used as the carrier of the organic activation molecule to obtain an activator of organic molecule-nano-particle hybridization. Among them, the adsorption of specific functional groups in the organic activation molecule on the surface of the recycled fine powder can effectively improve the dissolution-crystallization process of the recycled fine powder in the cement-based material system, induce the formation of mineral phases beneficial to the microstructure, and thus enhance the utilization efficiency and quality of the recycled fine powder. Compared with the single-component organic activation molecule, the organic molecule-nano-particle hybrid activator of the present invention has better activation efficiency for the recycled fine powder and more obvious improvement in the performance of the recycled fine powder mortar / concrete. Detailed implementation mode

[0026] The following further elaborates on the present invention with specific embodiments.

[0027] All the materials used in the following examples are commercially available chemicals. All the reagents (chemically pure) used in the synthesis of the waste concrete recycled fine powder activator are purchased from Anengji Technology Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd. The polycarboxylate water reducer, air-entraining agent, water-retaining agent, and retarder are all from Jiangsu Sobute New Materials Co., Ltd. The active recycled fine powder used is the recycled fine powder obtained by crushing, impurity removal, and grinding of the waste concrete (strength grade C50) from a construction site in Nanjing, which meets the technical indicators of Class II recycled fine powder in the industry standard JG / T 573-2020 "Recycled Fine Powder for Concrete and Mortar".

[0028] A waste concrete recycled fine powder activator includes a polyethylenepolyamine organic activation molecule modified with a polyether side chain and nano-silica.

[0029] The structure of the polyethylenepolyamine organic activation molecule modified with a polyether side chain conforms to General Formula I:

[0030]

[0031] In General Formula I: m is a natural number from 1 to 5, and n is a natural number from 5 to 20 (the same hereinafter).

[0032] The nano-silica is prepared by the sol-gel method, using ammonia water as the solvent and tetraethoxysilane as the silicon source; among them, the mass ratio of the polyethylenepolyamine organic activation molecule modified with a polyether side chain, ammonia water, and tetraethoxysilane is (5-15):1:2.

[0033] A preparation method of a waste concrete recycled fine powder activator specifically comprises the following steps:

[0034] (1) Polyethylene polyamine and a catalyst are placed in a high-pressure reactor. Ethylene oxide is introduced at 120 - 140 °C, and the reaction proceeds for 1 - 3 h to obtain an organically activated molecule with a polyether side-chain modified polyethylene polyamine.

[0035] The structure of the polyethylene polyamine conforms to the general formula II:

[0036]

[0037] The reaction formula for the above reaction is as shown in Reaction Formula III:

[0038]

[0039] Among them, the catalyst is sodium hydride, sodium methoxide or sodium tert-butoxide; the molar ratio of the polyethylene polyamine, the catalyst and ethylene oxide is 1:[0.01(2 + m) - 0.1(2 + m)]:[5(2 + m) - 20(2 + m)].

[0040] (2) The nano-silica is prepared by the sol-gel method well-known in the art. Using the above-mentioned organically activated molecule as a template reagent and tetraethoxysilane (TEOS) as a silicon source, it is prepared under alkaline conditions. Specifically: The organically activated molecule with a polyether side-chain modified polyethylene polyamine is stirred and mixed with 28% ammonia water at 30 - 40 °C, TEOS is slowly added and continuously stirred at 30 - 40 °C for 5 - 10 h; the obtained solid is filtered and washed with a small amount of absolute ethanol, and after vacuum drying, the waste concrete recycled fine powder activator is obtained.

[0041] Example 1

[0042] A preparation method of a waste concrete recycled fine powder activator, the specific steps are as follows:

[0043] (1) 10 mmol of diethylenetriamine and 0.3 mmol of sodium hydride are placed in a high-pressure reactor. 150 mmol of ethylene oxide is introduced at 120 °C, and the reaction proceeds for 1 h to obtain an organically activated molecule.

[0044] (2) 50 g of the organically activated molecule is stirred and mixed with 10 g of 28% ammonia water at 30 °C, 20 g of TEOS is slowly added and continuously stirred at 30 °C for 5 h. The obtained solid is filtered and washed with a small amount of absolute ethanol, and after vacuum drying, a recycled fine powder activator (in formula I, m = 1, n = 5) is obtained, with an average particle size of 120 nm.

[0045] Example 2

[0046] A preparation method of a waste concrete recycled fine powder activator, the specific steps are as follows:

[0047] (1) Place 10 mmol of tetraethylenepentamine and 2.5 mmol of sodium methoxide in a high-pressure reactor. Introduce 500 mmol of ethylene oxide at 130 °C and react for 2 h to obtain an organic activated molecule.

[0048] (2) Stir and mix 100 g of the organic activated molecule with 10 g of 28% ammonia water at 35 °C. Slowly add 20 g of TEOS and continuously stir at 35 °C for 7 h. Filter the obtained solid and wash it with a small amount of absolute ethanol. After vacuum drying, a regenerated micropowder activator (in formula I, m = 3, n = 10) with an average particle size of 160 nm is obtained.

[0049] Example 3

[0050] A method for preparing a regenerated micropowder activator for waste concrete, the specific steps are as follows:

[0051] (1) Place 10 mmol of hexaethyleneheptamine and 7 mmol of sodium tert-butoxide in a high-pressure reactor. Introduce 1400 mmol of ethylene oxide at 140 °C and react for 3 h to obtain an organic activated molecule.

[0052] (2) Stir and mix 150 g of the organic activated molecule with 10 g of 28% ammonia water at 40 °C. Slowly add 20 g of TEOS and continuously stir at 40 °C for 10 h. Filter the obtained solid and wash it with a small amount of absolute ethanol. After vacuum drying, a regenerated micropowder activator (in formula I, m = 5, n = 20) with an average particle size of 170 nm is obtained.

[0053] Comparative Example 1

[0054] Use the organic activated molecule in Example 3 directly as a regenerated micropowder activator (in formula I, m = 5, n = 0, without nano-silica).

[0055] Comparative Example 2

[0056] Commercially available nano-silica particles with an average particle size of 150 - 200 nm are directly used as a regenerated micropowder activator.

[0057] Test Example 1 Preparation and evaluation of ready-mixed (dry-mixed) mortar using active regenerated micropowder

[0058] The mortar mix ratio is: 89 g of Conch 52.5R.P.II cement, 30 g of fly ash, 51 g of active regenerated micropowder (containing 0.5% of the regenerated micropowder activator and having been activated), 820 g of river sand (fineness modulus Mx = 2.6), and 150 g of water.

[0059] The admixture formula is: 35 g of air-entraining agent, 105 g of water-retaining agent, 60 g of retarder, and 800 g of fly ash.

[0060] Mix the above powders evenly, and the dosage in the mortar is 1 g. First, mix and stir the dry mortar and the admixture for 30 s, and then slowly stir with water for 90 s. Referring to the relevant provisions of the national standard GB / T 25181-2019 "Ready-mixed Mortar", the index data of the ready-mixed mortar were tested.

[0061] The recycled micro-powder activators tested were the 5 recycled micro-powder activator samples prepared in Examples 1-3 and Comparative Examples 1 and 2. The experimental results are shown in Table 1.

[0062] Table 1 Performance comparison of different recycled micro-powder activators in ready-mixed (dry-mixed) mortar

[0063]

[0064]

[0065] As can be seen from Table 1, compared with the blank sample (original mortar) without the recycled micro-powder activator (the recycled micro-powder is not activated), for the 3 samples with the recycled micro-powder activators prepared in Examples 1-3, their bulk density and consistency data remain stable, the water retention rate data increases slightly, and the 28-day compressive strength increases significantly, with increases of 37.5%, 47.9% and 63.5% respectively compared with the blank sample. This shows that the recycled micro-powder activator of the present invention has a good activation efficiency for the recycled micro-powder and significantly improves the performance of the recycled micro-powder mortar. Compared with Comparative Example 1 (a single organic active molecule without hybridization with nano-silica) and Comparative Example 2 (single nano-silica), the recycled micro-powder activators prepared in Examples 1-3 can further improve the compressive strength of the mortar, indicating that the present invention has a higher activation efficiency for the recycled micro-powder compared with conventional single-component organic activators, and also more significantly improves the performance of the recycled micro-powder mortar.

[0066] Test Example 2 Preparation and evaluation of concrete using activated recycled micro-powder

[0067] The concrete mix ratio is as follows: 3.3 kg of Conch 52.5R.P.II cement, 0.4 kg of fly ash, 1.6 kg of activated recycled micro-powder (containing 0.8% of the recycled micro-powder activator and activated), 11.0 kg of river sand (fineness modulus Mx = 2.6), 11.55 kg of large stones (particle size 10 - 25 mm), 4.95 kg of small stones (particle size 5 - 10 mm), and 2.5 kg of water.

[0068] The admixture formula is as follows: polycarboxylate water reducer with a solid content of 20%, dosage of 52.5 g; water retention agent with a solid content of 3%, dosage of 7.5 g.

[0069] According to the relevant regulations of the national standards GB / T 8076-2008 "Concrete Admixtures" and GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the slump / expansion degree and compressive strength of concrete were respectively tested.

[0070] The recycled micro-powder activators tested were the 5 recycled micro-powder activator samples prepared in Examples 1-3 and Comparative Examples 1-2. The experimental results are shown in Table 2.

[0071] Table 2 Performance comparison of different recycled micro-powder activators in concrete

[0072]

[0073]

[0074] As can be seen from Table 2, compared with the blank sample (original concrete) without the recycled micro-powder activator (recycled micro-powder not activated), for the 3 samples with the recycled micro-powder activators prepared in Examples 1-3, the slump / expansion degree data remained stable, while the 28-day compressive strength increased significantly, with increases of 21.0%, 36.9% and 40.9% respectively compared with the blank sample. This shows that the recycled micro-powder activator of the present invention has a very good activation efficiency for recycled micro-powder and significantly improves the performance of recycled micro-powder concrete. Compared with Comparative Example 1 (single organic active molecule, not hybridized with nano-silica) and Comparative Example 2 (single nano-silica), the recycled micro-powder activators prepared in Examples 1-3 can achieve a greater increase in the compressive strength of concrete, indicating that the present invention has a better activation efficiency for recycled micro-powder compared with conventional single-component organic activators, and the improvement in the performance of recycled micro-powder concrete is also more obvious.

[0075] In summary, the recycled micro-powder activator of the present invention has a very good activation efficiency for waste concrete recycled micro-powder and significantly improves the performance of recycled micro-powder mortar / concrete.

[0076] The embodiments described above are only a part of the embodiments of the present invention, not all of them. The detailed description of the embodiments of the present invention is not intended to limit the scope of the present invention claimed, but merely represents the selected embodiments of the present invention. The protection scope of the present invention shall be subject to the scope claimed in the claims. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A waste concrete recycled fine powder activator, characterized in that, It includes a polyether side-chain modified polyethylenepolyamine organic activating molecule and nano-silica; the structural formula of the polyether side-chain modified polyethylenepolyamine organic activating molecule is shown as general formula I: General formula I; In general formula I: m is a natural number from 1 to 5, and n is a natural number from 5 to 20; The nano-silica is prepared by the sol-gel method, using ammonia water as the solvent and tetraethoxysilane as the silicon source; wherein, the mass ratio of the polyether side-chain modified polyethylenepolyamine organic activating molecule, ammonia water and tetraethoxysilane is (5 - 15):1:2; The average particle size of the recycled fine powder activator is 100 - 200 nm.

2. The preparation method of an activator for recycled fine powder of waste concrete according to claim 1, characterized in that It includes the following steps: Step 1) Polyethylenepolyamine is introduced into ethylene oxide under the action of a catalyst and reacted for 1 - 3 h to obtain a polyether side-chain modified polyethylenepolyamine organic activating molecule; Step 2) The polyether side-chain modified polyethylenepolyamine organic activating molecule and ammonia water are stirred and mixed at 30 - 40 °C, tetraethoxysilane is slowly added and continuously stirred at 30 - 40 °C for 5 - 10 h; the obtained solid is filtered and washed with a small amount of absolute ethanol, and after vacuum drying, it is obtained.

3. The preparation method of an activator for recycled fine powder of waste concrete according to claim 2, characterized in that, In step 1), the temperature for introducing ethylene oxide is 120 - 140 °C.

4. The preparation method of an activator for recycled fine powder of waste concrete according to claim 2, characterized in that, In step 1), the catalyst is sodium hydride, sodium methoxide or sodium tert-butoxide.

5. The preparation method of an activator for recycled fine powder of waste concrete according to claim 2, characterized in that, In step 1), the structural formula of the polyethylenepolyamine is shown as general formula II: General formula II; In general formula II: m is a natural number from 1 to 5; The molar ratio of the polyethylenepolyamine, the catalyst and ethylene oxide is 1:[0.01(2 + m) - 0.1(2 + m)]:[5(2 + m) - 20(2 + m)].

6. The preparation method of an activator for waste concrete recycled fine powder according to claim 2, characterized in that, In step 2), the concentration of the ammonia water is 28%.

7. The application of the waste concrete recycled fine powder activator as described in claim 1, or the waste concrete recycled fine powder activator prepared by the preparation method as described in any one of claims 2 - 6 in the activation treatment of waste concrete recycled fine powder.

8. The application according to claim 7, characterized in that, The activator and the recycled fine powder obtained by crushing, impurity removal and grinding of waste concrete are fully mixed according to the mass ratio of (0.2 - 2):100, and that's it.

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