A method for preparing modified recycled micro powder and its application

Abstract

This invention discloses a method for preparing modified recycled micro-powder and its application, relating to the field of building materials technology. The preparation method includes the following steps: crushing and grinding waste concrete to obtain recycled micro-powder; adding alkaline industrial wastewater to the recycled micro-powder, heating, pressurizing, stirring, and filtering to obtain filtrate I and filter residue I; adding acidic industrial wastewater to filtrate I and filter residue I respectively, stirring, and filtering to obtain filter residue II and filter residue III respectively; mixing filter residue II and filter residue III, washing with water, filtering, drying, and grinding to obtain modified recycled micro-powder. The preparation method of this invention can effectively activate the recycled micro-powder. When used as an auxiliary cementitious material to partially replace cement, it can improve the compressive strength and density of concrete, while fully utilizing both alkaline and acidic industrial wastewater, achieving the goals of waste utilization and energy conservation.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a method for preparing modified recycled micro powder and its application. Background Technology

[0002] With the rapid pace of urban construction, a large number of buildings are constructed or demolished every year, which inevitably impacts the environment. Therefore, corresponding environmental protection measures are needed to reduce carbon emissions and resource waste. Existing technological research indicates that recycled micropowder can be produced by crushing and grinding waste concrete. This recycled micropowder can be used as an auxiliary cementitious material to replace part of the cement clinker, realizing the utilization of waste concrete resources and helping to promote the transformation of my country's cement industry towards a more environmentally friendly and low-carbon direction. It also has a positive impact on the construction industry and related industrial chains. However, the application of recycled micropowder as an auxiliary cementitious material faces two main challenges: First, the sources of recycled micropowder are diverse, including unhydrated cementitious materials from original concrete and petrographic components of coarse and fine aggregates, leading to a dispersed composition. Second, the main components of recycled micropowder are hydrated calcium silicate, unhydrated cement particles, calcium hydroxide, and silica. While unhydrated cement particles and calcium hydroxide have the ability to act as hydration nuclei for cement and to further hydrate and form gel products, the activity of silica and hydrated calcium silicate is far lower than that of cement, resulting in a significantly lower activity of recycled micropowder compared to cement.

[0003] Existing research on the modification methods of regenerated micropowders mainly includes mechanical activation, chemical activation, and high-temperature activation. Mechanical activation reduces the particle fineness of regenerated micropowders through mechanical action, improves the particle morphology, and exposes the unhydrated portions. Chemical activation uses chemical substances to stimulate the activity of regenerated micropowders and improve their utilization rate. High-temperature activation uses high-temperature treatment to reorganize or destroy the mineral structure of regenerated micropowders, thereby improving their activity.

[0004] The treatment of chemical wastewater is a key project in China, as its discharge damages the environment and wastes resources; further environmental treatment leads to even greater resource waste. For example, alkaline industrial wastewater from the paper, leather, and dyeing industries is often neutralized by adding acidic substances. During neutralization, the high-energy alkaline substances react with the high-energy acidic substances to form low-energy salts, resulting in a loss of chemical energy. Therefore, further research is needed on how to utilize industrial wastewater to modify and regenerate micro-powders, while simultaneously addressing the issues of component dispersion and low activity in the regenerated micro-powders. Summary of the Invention

[0005] The purpose of this invention is to address the component dispersion and low activity of regenerated micropowders when applied to auxiliary cementitious materials. A method for preparing modified regenerated micropowders using industrial wastewater is designed. Through the treatment of alkaline and acidic industrial wastewater, modified regenerated micropowders with higher content of aluminum hydroxide gel, silica gel, and calcium sulfate are obtained, thus overcoming the shortcomings of existing technologies. Specifically, this is achieved through the following techniques.

[0006] A method for preparing modified recycled micro powder includes the following steps:

[0007] Waste concrete is crushed and ground to obtain recycled micro powder; alkaline industrial wastewater is added to the recycled micro powder, heated, pressurized, stirred, and filtered for the first time to obtain filtrate I and filter residue I;

[0008] Add acidic industrial wastewater to the filtrate I, stir, and filter a second time to obtain filter residue II;

[0009] Acidic industrial wastewater was added to filter residue I, stirred, and filtered for the third time to obtain filter residue III;

[0010] The filter residues II and III are mixed, washed with water, filtered for the fourth time, dried, and ground to obtain modified regenerated micro powder.

[0011] The modified recycled micro-powder described in this invention can be used as an auxiliary cementitious material in cement-based materials for the following reasons: After crushing and ball milling, the surface energy of waste concrete increases, which can promote the activation of the activity of the recycled micro-powder. After treatment with alkaline industrial wastewater, the sand powder after grinding siliceous aggregates into SiO3... 2- The SiO3 in the regenerated micro-powder dissolves into the solution in the form of hydrated calcium silicate (CSH), calcium hydroxide (CH), and hydrated sulfoaluminate (AFt), while the products remain in the filter residue. In the acidic industrial wastewater treatment stage, as the pH decreases, the SiO3 in the solution... 2- Gradually dissolves and exists in the mixed phase as a SiO2 gel, CSH reacts with H in the solution. + and SO4 2- The reaction produces a CaSO4 and SiO2 gel, Ca 2+ With SO4 2- The combination of AFt and H+ in the solution promotes the conversion of CH4 to CaSO4. + and SO4 2- The reaction produces CaSO4 and Al(OH)3 gels. The regenerated micro powder obtained after co-treatment of alkaline and acidic industrial wastewater contains a large amount of CaSO4, SiO2 gel, and Al(OH)3 gel. After spray drying and ball milling, modified regenerated micro powder with small particle size and high active ingredients is obtained.

[0012] This invention patent activates regenerated micro powder using alkaline and acidic industrial wastewater, transferring the chemical energy contained in the industrial wastewater to the regenerated micro powder. This effectively promotes the formation of a mixture with high levels of components such as aluminum hydroxide gel, silica gel, and calcium sulfate in the regenerated micro powder, while also solving the problems of component dispersion and low activity in the regenerated micro powder.

[0013] The chemical reactions involved are as follows:

[0014] SiO2 + 2OH - →SiO3 2- +H2O

[0015] SiO3 2- +2H + →SiO2(gel) + H2O

[0016] CaSiO3+2H + +SO4 2- →CaSO4↓+SiO2(gel)+H2O

[0017] Ca(OH)₂ + 2H⁺ + →Ca 2+ +2H₂O; Ca 2+ +SO4 2- →CaSO4↓

[0018] 3CaO·Al2O3·3CaSO4·32H2O+6H + +3SO4 2- →6CaSO4↓+6Al(OH)3(gel)+26H2O

[0019] The SiO2 gel contained in the modified recycled micro powder has high surface activity. When incorporated into the cementitious system, it will generate more CSH gel, which can act as seed crystals to promote cement hydration and effectively compensate for the early strength loss caused by the incorporation of mineral admixtures (such as mineral powder and fly ash). CaSO4 can participate in the hydration of tricalcium aluminate (C3A) and promote the early formation of ettringite. Al(OH)3 can accelerate the cement hydration reaction and densify the hydration products.

[0020] Preferably, the heating temperature is 160-200℃ and the pressurization pressure is 0.5-1MPa.

[0021] Preferably, after adding alkaline industrial wastewater to the regenerated micro powder, the stirring time is 2-5 hours.

[0022] Preferably, acidic industrial wastewater is added to filtrate I while stirring until the solution pH = 8.0 ± 0.5, at which point the addition of acidic industrial wastewater is stopped.

[0023] Preferably, acidic industrial wastewater is added to filter residue I while stirring until the solution pH = 9.0 ± 0.5, at which point the addition of acidic industrial wastewater is stopped.

[0024] Preferably, the particle size d50 of the regenerated micro powder does not exceed 100 μm; the particle size d50 of the modified regenerated micro powder does not exceed 20 μm.

[0025] Preferably, the alkaline industrial wastewater is wastewater from alkaline straw papermaking, in which OH... - The concentration is not less than 10 -3 mol / L.

[0026] Preferably, the mass ratio of regenerated micro powder to alkaline industrial wastewater is 1:(1000-1000000).

[0027] Preferably, the acidic industrial wastewater is sulfuric acid wastewater discharged from the steel rolling process, in which H... + The concentration is not less than 10 -3 mol / L, SO4 2- The concentration is not less than 10 -4 mol / L.

[0028] Preferably, the drying temperature is 60-200℃.

[0029] Preferably, the first filtration uses filter paper with a pore size of 1-10 μm; the second, third, and fourth filtrations all use semi-permeable membranes with a pore diameter of 0.01-0.1 μm.

[0030] A modified regenerated micro powder prepared using the above-described method.

[0031] The application of modified recycled micro powder prepared by the above-mentioned method as an auxiliary cementitious material in building materials.

[0032] Preferably, the building material is a cement-based building material, and the modified recycled powder can replace 5-40% of the cement in the cement-based building material.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] (1) In the preparation method of the present invention, the inert calcium, silicon and aluminum in the recycled micro powder are chemically treated to transform them into highly active CaSO4, SiO2 and Al(OH)3, etc., which can all participate in the hydration reaction of cement-based materials, thus greatly improving the activity of the recycled micro powder.

[0035] (2) The preparation method of the present invention makes full use of alkaline industrial wastewater and acidic industrial wastewater, and achieves the purpose of waste utilization and energy saving and efficiency improvement;

[0036] (3) Using the modified recycled micro powder of the present invention to replace part of the cement in the preparation of concrete can improve the compressive strength of concrete and improve the density of high concrete. Detailed Implementation

[0037] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0038] A method for preparing modified recycled micro powder includes the following steps:

[0039] S1. The waste concrete is crushed and ground to obtain recycled micro powder; the recycled micro powder and alkaline industrial wastewater are added to a pressurized reaction vessel, heated, pressurized, stirred and filtered to obtain filtrate I and filter residue I.

[0040] S2. Add acidic industrial wastewater to the filtrate I in step S1, stir, filter, and obtain filter residue II;

[0041] S3. Add acidic industrial wastewater to filter residue I in step S1, stir, filter, and obtain filter residue III.

[0042] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash with water, filter, dry, and grind to obtain modified regenerated micro powder.

[0043] Optionally, in step S1, the heating temperature is 160-200℃ and the pressurization pressure is 0.5-1MPa.

[0044] Optionally, after adding alkaline industrial wastewater to the regenerated micro powder, the stirring time is 2-5 hours.

[0045] Optionally, the mass ratio of regenerated micro powder to alkaline industrial wastewater is 1:(1000-1000000).

[0046] Optionally, in step S2, acidic industrial wastewater is added to filtrate I while stirring until the solution pH = 8.0 ± 0.5, at which point the addition of acidic industrial wastewater is stopped.

[0047] Optionally, in step S3, acidic industrial wastewater is added to filter residue I while stirring until the solution pH = 9.0 ± 0.5, at which point the addition of acidic industrial wastewater is stopped.

[0048] Optionally, the particle size d50 of the regenerated micro powder in step S1 does not exceed 100 μm; the particle size d50 of the modified regenerated micro powder in step S4 does not exceed 20 μm.

[0049] Optionally, the alkaline industrial wastewater is wastewater from alkaline straw papermaking, in which OH... - The concentration is not less than 10 -3 mol / L.

[0050] Optionally, the acidic industrial wastewater is sulfuric acid wastewater discharged from the steel rolling process. In the acidic industrial wastewater, H... + The concentration is not less than 10 -3 mol / L, SO4 2- The concentration is not less than 10 -4 mol / L.

[0051] Optionally, the drying method in step S4 is spray drying, and the spray drying temperature is 60-200℃.

[0052] Optionally, the filtration in step S1 uses filter paper with a pore size of 1-10 μm; the filtration in steps S2, S3 and S4 uses a semi-permeable membrane with a pore diameter of 0.01-0.1 μm.

[0053] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The following examples and comparative examples selected three types of waste concrete from different sources, which were crushed step by step by a crusher and then ball-milled into recycled micro powders, designated as CRMP-1, CRMP-2 and CRMP-3. Their main chemical composition and particle size d50 are shown in Table 1 below.

[0055] The alkaline industrial wastewater in the following examples and comparative examples comes from the alkaline straw papermaking wastewater of a paper mill. Besides alkali and soluble organic matter, it also contains 9.85 g / L of silica, 32.00 g / L of lignin, 38.75 g / L of ash, and other substances. The acidic industrial wastewater comes from the sulfuric acid wastewater discharged from the rolling mill process of a steel pipe plant. The suspended solids (SS) in the wastewater are 220 mg / L, ferrous ions are 2300 mg / L, and impurities are 1.5 mg / L. The concentrations of some ions in three types of acidic and three types of alkaline industrial wastewater are shown in Table 2 below. The acidic industrial wastewater is designated as AIWW-1, AIWW-2, and AIWW-3. The alkaline industrial wastewater is designated as BIWW-1, BIWW-2, and BIWW-3.

[0056] Table 1. Main chemical composition and particle size of regenerated micro powder

[0057] code name CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> Particle size d50 CRMP-1 24.3％ 16.5％ 57.2％ 90μm CRMP-2 35.6％ 23.7％ 39.3％ 70μm CRMP-3 40.2％ 32.6％ 25.6％ 50μm

[0058] Table 2. Content of some ions in acidic and alkaline industrial wastewater.

[0059] code name <![CDATA[H + ]]> <![CDATA[SO4 2- ]]> code name <![CDATA[OH - ]]> AIWW-1 0.1 mol / L 0.02 mol / L BIWW-1 0.1 mol / L AIWW-2 0.01 mol / L 0.005 mol / L BIWW-2 0.01 mol / L AIWW-3 0.001 mol / L 0.0004 mol / L BIWW-3 0.001 mol / L

[0060] Example 1

[0061] The method for preparing the modified recycled micro powder in this embodiment includes the following steps:

[0062] S1. Add 1 part of ball-milled regenerated micro powder (CRMP-2) and 1000 parts of alkaline industrial wastewater (BIWW-2) to a pressurized reaction vessel, heat to 175℃, pressurize to 0.5MPa, and stir thoroughly for 4 hours to obtain a mixed slurry. Filter the mixed slurry through ordinary filter paper (filter pore size of 2μm) to obtain filtrate I and filter residue I.

[0063] S2. Add acidic industrial wastewater (AIWW-2) dropwise to filtrate I in step S1. When the pH drops to 8.2, stop adding the solution and continue stirring for 0.5 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (filter pore size of 0.03 μm) to obtain filter residue II.

[0064] S3. Add acidic industrial wastewater (AIWW-2) dropwise to filter residue I in step S1. When the pH drops to 9.1, stop adding the solution and continue stirring for 0.75 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (filter pore size of 0.03 μm) to obtain filter residue III.

[0065] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash repeatedly with clean water, and filter using a semi-permeable membrane (0.03 μm pore size). Repeat the washing-filtration process 5 times. Spray dry the resulting filter residue, and then ball mill it to obtain modified regenerated micro powder (MCRMP-1). The spray drying temperature is 80℃, and the particle size d50 of the obtained modified regenerated micro powder is 12 μm.

[0066] Example 2

[0067] The method for preparing the modified recycled micro powder in this embodiment includes the following steps:

[0068] S1. Add 1 part of ball-milled regenerated micro powder (CRMP-2) and 30,000 parts of alkaline industrial wastewater (BIWW-2) to a pressurized reaction vessel, heat to 160℃, pressurize to 0.8MPa, and stir thoroughly for 3 hours to obtain a mixed slurry. Filter the mixed slurry through ordinary filter paper (filter pore size of 2μm) to obtain filtrate I and filter residue I.

[0069] S2. Add acidic industrial wastewater (AIWW-2) to filtrate I from step S1. When the pH drops to 8.0, stop adding the solution and continue stirring for 0.6 hours to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (0.05 μm pore size) to obtain filter residue II.

[0070] S3. Add acidic industrial wastewater (AIWW-2) to filter residue I in step S1. When the pH drops to 8.7, stop adding the solution and continue stirring for 0.8 hours to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (with a pore size of 0.05 μm) to obtain filter residue III.

[0071] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash repeatedly with clean water, and filter using a semi-permeable membrane (0.05 μm pore size). Repeat the washing-filtration process 5 times. Spray dry the resulting filter residue, and then ball mill it to obtain modified regenerated micro powder (MCRMP-2). The spray drying temperature is 60℃, and the particle size d50 of the obtained modified regenerated micro powder is 15 μm.

[0072] Example 3

[0073] The method for preparing the modified recycled micro powder in this embodiment includes the following steps:

[0074] S1. Add 1 part of ball-milled regenerated micro powder (CRMP-3) and 70,000 parts of alkaline industrial wastewater (BIWW-3) to a pressurized reaction vessel, heat to 200℃, pressurize to 0.9MPa, and stir thoroughly for 5 hours to obtain a mixed slurry. Filter the mixed slurry through ordinary filter paper (10μm pore size) to obtain filtrate I and filter residue I.

[0075] S2. Add acidic industrial wastewater (AIWW-3) dropwise to filtrate I in step S1. When the pH drops to 7.8, stop adding the solution and continue stirring for 0.6 hours to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (filter pore size of 0.08μm) to obtain filter residue II.

[0076] S3. Add acidic industrial wastewater (AIWW-3) dropwise to filter residue I in step S1. When the pH drops to 8.9, stop adding the solution and continue stirring for 0.8 hours to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (with a pore size of 0.08 μm) to obtain filter residue III.

[0077] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash repeatedly with clean water, and filter using a semi-permeable membrane (0.08 μm pore size). Repeat the washing-filtration process four times. Spray dry the resulting filter residue, and then ball mill it to obtain modified regenerated micro powder (MCRMP-3). The spray drying temperature is 110℃, and the particle size d50 of the obtained modified regenerated micro powder is 18 μm.

[0078] Example 4

[0079] The method for preparing the modified recycled micro powder in this embodiment includes the following steps:

[0080] S1. Add 1 part of ball-milled regenerated micro powder (CRMP-1) and 300,000 parts of alkaline industrial wastewater (BIWW-2) to a pressurized reaction vessel, heat to 175℃, pressurize to 0.6MPa, and stir thoroughly for 4 hours to obtain a mixed slurry. Filter the mixed slurry through ordinary filter paper (filter pore size of 6μm) to obtain filtrate I and filter residue I.

[0081] S2. Add acidic industrial wastewater (AIWW-2) dropwise to filtrate I in step S1. When the pH drops to 7.6, stop adding the solution and continue stirring for 0.7 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (1.0 μm pore size) to obtain filter residue II.

[0082] S3. Add acidic industrial wastewater (AIWW-3) dropwise to filter residue I in step S1. When the pH drops to 9.2, stop adding the solution and continue stirring for 0.7 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (with a pore size of 0.1 μm) to obtain filter residue III.

[0083] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash repeatedly with clean water, and filter using a semi-permeable membrane (0.1 μm pore size). Repeat the washing-filtration process three times. Spray dry the resulting filter residue, and then ball mill it to obtain modified regenerated micro powder (MCRMP-4). The spray drying temperature is 150℃, and the particle size d50 of the obtained modified regenerated micro powder is 16 μm.

[0084] Example 5

[0085] The method for preparing the modified recycled micro powder in this embodiment includes the following steps:

[0086] S1. Add 1 part of ball-milled regenerated micro powder (CRMP-2) and 1,000,000 parts of alkaline industrial wastewater (BIWW-1) to a pressurized reaction vessel, heat to 165℃, pressurize to 1MPa, and stir thoroughly for 5 hours to obtain a mixed slurry. Filter the mixed slurry through ordinary filter paper (filter pore size of 3μm) to obtain filtrate I and filter residue I.

[0087] S2. Add acidic industrial wastewater (AIWW-3) dropwise to filtrate I in step S1. When the pH drops to 8.1, stop adding the solution and continue stirring for 0.7 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (filter pore size of 0.08 μm) to obtain filter residue II.

[0088] S3. Add acidic industrial wastewater (AIWW-2) dropwise to filter residue I in step S1. When the pH drops to 9.2, stop adding the solution and continue stirring for 0.7 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (filter pore size of 0.08 μm) to obtain filter residue III.

[0089] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash repeatedly with clean water, and filter using a semi-permeable membrane (0.08 μm pore size). Repeat the washing-filtration process four times. Spray dry the resulting filter residue, and then ball mill it to obtain modified regenerated micro powder (MCRMP-5). The spray drying temperature is 175℃, and the particle size d50 of the obtained modified regenerated micro powder is 19 μm.

[0090] Example 6

[0091] The method for preparing the modified recycled micro powder in this embodiment includes the following steps:

[0092] S1. Add 1 part of ball-milled regenerated micro powder (CRMP-3) and 4000 parts of alkaline industrial wastewater (BIWW-2) to a pressurized reaction vessel, heat to 195℃, pressurize to 0.6MPa, and stir thoroughly for 4 hours to obtain a mixed slurry. Filter the mixed slurry through ordinary filter paper (filter pore size of 4μm) to obtain filtrate I and filter residue I.

[0093] S2. Add acidic industrial wastewater (AIWW-1) dropwise to filtrate I in step S1. When the pH drops to 7.6, stop adding the solution and continue stirring for 0.9 hours to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (0.04 μm pore size) to obtain filter residue II.

[0094] S3. Add acidic industrial wastewater (AIWW-3) dropwise to filter residue I in step S1. When the pH drops to 8.8, stop adding the solution and continue stirring for 0.7 h to obtain a mixed slurry. Filter the mixed slurry through a semi-permeable membrane (filter pore size of 0.04 μm) to obtain filter residue III.

[0095] S4. Mix filter residue II from step S2 and filter residue III from step S3, wash repeatedly with clean water, and filter using a semi-permeable membrane (0.04 μm pore size). Repeat the washing-filtration process four times. Spray dry the resulting filter residue, and then ball mill it to obtain modified regenerated micro powder (MCRMP-6). The spray drying temperature is 200℃, and the particle size d50 of the obtained modified regenerated micro powder is 16 μm.

[0096] Comparative Example 1

[0097] The preparation method of the regenerated micro powder in this comparative example is basically the same as that in Example 1, except that in step S1, the alkaline industrial wastewater is replaced with an equal amount of sodium hydroxide solution, wherein the sodium hydroxide solution contains OH... - The concentration of OH in the alkaline industrial wastewater of Example 1 is similar to that in Example 1. - The concentrations are the same. That is, the modified regenerated micro powder (FCRMP-2.1) obtained in this comparative example does not undergo alkaline industrial wastewater treatment.

[0098] Comparative Example 2

[0099] The preparation method of the regenerated micro powder in this comparative example is basically the same as that in Example 1, except that in steps S2 and S3, the acidic industrial wastewater is replaced with an equal amount of sulfuric acid solution, wherein the sulfuric acid solution contains H + SO4 2- The concentration of H in the acidic industrial wastewater of Example 1 is similar to that in Example 1. + SO4 2- The concentrations are the same. That is, the modified regenerated micro powder (FCRMP-2.2) obtained in this comparative example does not undergo acidic industrial wastewater treatment.

[0100] Comparative Example 3

[0101] The modified regenerated micro powder (FCRMP-2.3) obtained in this comparative example was prepared by ball milling the regenerated micro powder (CRMP-2) using a ball mill. The particle size d50 of the regenerated micro powder in this comparative example was 12 μm.

[0102] Test case

[0103] The six modified recycled micro powders in Examples 1-6 and the three recycled micro powders in Comparative Examples 1-3 were applied to concrete. The concrete raw materials and dosages are shown in Table 3 below.

[0104] The 3-day and 28-day compressive strength of concrete were tested according to GB / T 50107-2010 "Standard for Testing and Evaluation of Concrete Strength", and the chloride ion flux was tested according to GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The test results are shown in Table 4 below.

[0105] Table 3 Concrete Raw Materials and Usage

[0106]

[0107] Note: The unit for the usage of each raw material in Table 3 is kg / m³. 3 .

[0108] Table 4. Concrete performance test results

[0109]

[0110] Based on the concrete performance test results in Table 4, it can be seen that:

[0111] (1) By comparing the blank group with Examples 1-6, the modified recycled micro powder prepared with different raw material sources and process conditions significantly improved the 3-day and 28-day strength of concrete after replacing cement. The 3-day strength increased by up to 21.6% and the 28-day strength increased by up to 9.6%. At the same time, the 28-day electrical flux decreased. The results show that the modified recycled micro powder can improve the compressive strength and compactness of concrete after replacing cement.

[0112] (2) By comparing Example 1 and Comparative Examples 1 and 2, it can be seen that the activity of the regenerated micro powder obtained by using acidic / alkaline industrial wastewater without the present invention is significantly lower than that of the modified regenerated micro powder of the present invention.

[0113] (3) By comparing the blank group and Comparative Example 3, it can be seen that after the recycled micro powder without chemical treatment replaced 20% of the cement, the 3-day and 28-day strength of the concrete decreased significantly, and the 28-day electrical flux increased significantly.

[0114] Based on the above test results, when the modified recycled micro powder prepared by this invention is used to partially replace cement in concrete, the strength and density of the concrete are improved. However, when recycled micro powder that has not been treated with acidic / alkaline industrial wastewater or has not been chemically treated is used to partially replace cement in concrete, the strength and density of the concrete decrease to varying degrees.

[0115] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing modified recycled micro powder, characterized in that, Includes the following steps: Waste concrete is crushed and ground to obtain recycled micro powder; alkaline industrial wastewater is added to the recycled micro powder, heated, pressurized, stirred, and filtered to obtain filtrate I and filter residue I; Acidic industrial wastewater was added to filtrate I and filter residue I, respectively, stirred, and filtered to obtain filter residue II and filter residue III, respectively. The filter residues II and III are mixed, washed with water, filtered, dried, and ground to obtain modified regenerated micro powder.

2. The preparation method according to claim 1, characterized in that, The heating temperature is 160-200℃, and the pressurization pressure is 0.5-1MPa.

3. The preparation method according to claim 1, characterized in that, The particle size d50 of the regenerated micro powder does not exceed 100 μm; the particle size d50 of the modified regenerated micro powder does not exceed 20 μm.

4. The preparation method according to claim 1, characterized in that, The alkaline industrial wastewater is wastewater from alkaline straw papermaking, and the alkaline industrial wastewater contains OH... - The concentration is not less than 10 -3 mol / L.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the regenerated micro powder to the alkaline industrial wastewater is 1:(1000-1000000).

6. The preparation method according to claim 1, characterized in that, The acidic industrial wastewater is sulfuric acid wastewater discharged from the steel rolling process. In this acidic industrial wastewater, H... + The concentration is not less than 10 -3 mol / L, SO4 2- The concentration is not less than 10 - 4 mol / L.

7. The preparation method according to claim 1, characterized in that, The drying temperature is 60-200℃.

8. A modified regenerated micro powder prepared by the preparation method according to any one of claims 1-7.

9. The application of the modified recycled micro powder as an auxiliary cementitious material in building materials according to claim 8.

10. The application according to claim 9, characterized in that, The building material is a cement-based building material, and the modified recycled micro powder can replace 5-40% of the cement in the cement-based building material.

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