Stone-like PC brick prepared based on recycled concrete and preparation method of stone-like PC brick

Abstract

The invention relates to the technical field of construction waste recycling, in particular to a stone-like PC brick prepared based on recycled concrete and a preparation method of the stone-like PC brick. The bottom layer is prepared from the following raw materials: recycled coarse aggregate, ordinary Portland cement, natural sand, composite modified recycled aggregate, fly ash, a polycarboxylate superplasticizer and water; the surface layer is prepared from the following raw materials: white Portland cement, colored sand, ferric oxide inorganic pigment, composite modified recycled aggregate, silica fume, acrylic emulsion and water; according to the technical scheme, an ultrasonic-microwave synergistic activation modification process is adopted, microwave can generate thermal stress by utilizing the electromagnetic performance difference between aggregate and attached mortar, more than 45% of old mortar is stripped, and meanwhile, ultrasonic waves form a micro-flow field in aggregate pores through a cavitation effect, so that the penetration depth of modification liquid is increased.

Description

Technical Field

[0001] This invention relates to the field of construction waste recycling technology, specifically to a stone-like PC brick based on recycled concrete and its preparation method. Background Technology

[0002] With the acceleration of urbanization, the amount of construction waste generated is constantly increasing. Although the recycling rate has improved, more than half of the recycled aggregate is only used in low-value-added areas such as road base layers, and high-value utilization technologies are still insufficient. As an important alternative to natural stone, imitation stone PC bricks are widely used in municipal engineering due to their strong decorative properties and good durability. However, traditional products usually rely on the mining of natural aggregates, which exacerbates ecological damage and is costly; or they directly use unmodified recycled aggregates, resulting in significant shortcomings in product performance.

[0003] There are some problems with existing recycled aggregate imitation stone PC bricks: First, the surface of recycled aggregate has a lot of old mortar attached and high porosity. Direct use will result in the brick's compressive strength being generally lower than 40MPa and the water absorption rate exceeding 8%, which makes it difficult to meet the requirements of municipal engineering for the mechanical properties of materials; Second, the aggregate treatment is simple, relying only on chemical soaking or single physical treatment, resulting in poor interfacial bonding, which makes the brick easy to crack and has insufficient wear resistance.

[0004] Based on this, the present invention provides a stone-like PC brick made from recycled concrete to solve the existing problems. Summary of the Invention

[0005] The purpose of this invention is to provide a stone-like PC brick based on recycled concrete and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A stone-like PC brick made from recycled concrete, wherein the stone-like PC brick is composed of a surface layer and a bottom layer; The bottom layer, by weight, comprises the following raw materials: 560-590 parts recycled coarse aggregate, 160-175 parts ordinary silicate cement, 280-320 parts natural sand, 60-90 parts composite modified recycled aggregate, 35-45 parts fly ash, 2.5-3.5 parts polycarboxylate superplasticizer, and 95-105 parts water. The surface layer, by weight, comprises the following raw materials: 95-105 parts white silicate cement, 165-175 parts colored sand, 8-12 parts iron oxide inorganic pigment, 35-55 parts composite modified recycled aggregate, 13-18 parts silica fume, 10-13 parts acrylic emulsion, and 38-45 parts water.

[0007] As a further technical solution, the preparation method of the composite modified recycled aggregate includes the following steps: a. After crushing the construction waste, it is sieved through a double-layer screen of 1-3mm and 4.75-9.5mm to obtain recycled aggregate of the corresponding particle size. After washing, it is dried at 80-100℃ until the moisture content is ≤1%. b. Impregnate the recycled aggregate in an ultrasonic-microwave synergistic activation and modification solution containing a silane coupling agent, with the mass ratio of the impregnation solution to the aggregate being 1:(0.9-1.1); The silane coupling agent is KH-550, accounting for 0.6-0.9% of the total weight of the modified solution; c. During the impregnation process, apply ultrasonic treatment at a frequency of 40kHz for 20-28 minutes to allow the modified liquid to penetrate into the pores of the aggregate. d. Remove the aggregate, drain off excess liquid, and dry at 130-140℃ for 3-5 hours to obtain composite modified recycled aggregate.

[0008] As a further technical solution, the ultrasonic-microwave synergistic activation and modification liquid is made of 100 parts water, 12-14 parts sodium silicate, 7-9 parts nano silica sol, 3-4.5 parts ammonium acrylate, 2.2-2.8 parts sodium hexametaphosphate, and 1-3 parts nano calcium carbonate by weight.

[0009] As a further technical solution, the preparation method of the ultrasonic-microwave synergistic activation modified liquid is as follows: water is heated to 48-52℃, sodium silicate and sodium hexametaphosphate are added sequentially, and the mixture is stirred at 300-500r / min until completely dissolved. Microwave activation is performed for 1-1.5 minutes. After stopping the microwave, the mixture is stirred at 800-1000r / min at high speed, and nano-silica sol, ammonium acrylate, nano-calcium carbonate and silane coupling agent KH-550 are slowly added. At the same time, ultrasonic treatment at a frequency of 25kHz is applied for 5-9 minutes to obtain a uniform and stable modified liquid.

[0010] As a further technical solution, the microwave activation parameters are a microwave power of 500W and a frequency of 2450MHz.

[0011] As a further technical solution, the solid content of the acrylic emulsion in the surface layer is ≥45%.

[0012] A method for preparing stone-like PC bricks based on recycled concrete includes the following steps: S1 Raw material preparation: Weigh each raw material according to the proportion; S2 surface layer slurry preparation: Dry mix the white cement, colored sand, pigment, and silica fume used for the surface layer at a speed of 200-300 r / min for 5-8 minutes, add acrylic emulsion and water, and stir at a speed of 400-600 r / min for 10-15 minutes, controlling the slurry flowability to be 180-200 mm. S3 bottom layer mixture preparation: Put the recycled coarse aggregate, natural sand, cement, fly ash and composite modified recycled aggregate used for the bottom layer into the mixer and dry mix at 150-250 r / min for 10-12 minutes. Dissolve the water-reducing agent in water and add it. Mix at 300-400 r / min for 15-20 minutes and control the slump of the mixture to be 0-5 mm. S4 composite fabric and vacuum extrusion molding: Preheat the mold to 30-40℃, first evenly spread a 3-5mm thick surface layer of slurry, then lay the bottom layer of mixture; send the mold into the vacuum extruder and extrude for 2-3 minutes to form the product; S5 curing: The molded brick blank is steam cured for 4-5.5 hours with the initial mold; after demolding, the curing is carried out alternately with circulating steam and natural curing to complete the curing and obtain the finished product.

[0013] As a further technical solution, the extrusion in S4 is carried out under vacuum conditions of -0.085 to -0.095 MPa and pressure of 16-18 MPa.

[0014] As a further technical solution, the initial steam curing in S5 is carried out in an environment of 58-62℃ and 92%-95% humidity.

[0015] As a further technical solution, the S5 uses alternating circulating steam and natural curing: first, curing in a steam environment of 40-45℃ and 85%-90% humidity for 2-3 days, then curing in a natural environment of 20-25℃ and ≥60% humidity for 3-4 days, alternating 2-3 times.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The technical solution of this invention employs an ultrasonic-microwave synergistic activation modification process. Microwave energy utilizes the difference in electromagnetic properties between aggregates and adhering mortar to generate thermal stress, peeling off more than 45% of the old mortar. Simultaneously, ultrasonic waves create a microfluidic field within the aggregate pores through cavitation, enhancing the penetration depth of the modification liquid. Nano-silica sol and nano-calcium carbonate in the modification liquid fill the 50-100nm-level pores within the aggregate, while sodium silicate and ammonium acrylate form a gel network to seal interconnected pores. Silane coupling agents construct chemical bridges on the aggregate surface, significantly improving its interfacial bonding with cementitious materials. This modification method reduces the water absorption rate of recycled aggregates from 10.5% to below 3%, and the crushing index from 28% to below 18%, overcoming the inherent defects of traditional recycled aggregates such as high porosity, low strength, and poor bonding. When incorporated into the surface and bottom layers respectively, it provides a stable framework for the bottom layer and complements the gradation of the colored sand in the surface layer, laying the foundation for subsequent performance improvements.

[0017] 2. The surface layer is a blend of white silicate cement and acrylic emulsion with a solid content ≥45%. The film-forming properties of the acrylic emulsion can form a continuous protective film on the aggregate surface, improving the surface layer's water resistance and stain resistance. Combined with the micro-aggregate effect of silica fume, it fills the gaps in cement hydration, increasing the surface layer's density. The bottom layer uses fly ash and polycarboxylate superplasticizer in synergy. The active components of fly ash react with cement hydration products to form a gel, while the superplasticizer disperses cement particles. This reduces water consumption while improving the workability of the mixture, avoiding the problems of dry hardness, difficulty in molding, and easy segregation associated with traditional mix proportions. The optimized preparation process of this invention further amplifies the advantages of the components: vacuum extrusion molding eliminates more than 90% of the air bubbles inside the brick blank under a negative pressure of -0.085 to -0.095 MPa, increasing density; circulating steam-natural curing promotes hydration with 40-45℃ steam and balances shrinkage naturally at 20-25℃, reducing micro-cracks caused by temperature stress. Compared to single steam curing, the brick's drying shrinkage rate is reduced.

[0018] 3. This invention, through the application of composite modified recycled aggregate, enables the amount of construction waste in PC bricks to reach more than 40%. If calculated based on an annual production capacity of 10 million bricks, it can dispose of more than 30,000 tons of construction waste annually, and significantly improve the resource recycling rate. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a stone-like PC brick based on recycled concrete. The stone-like PC brick is composed of a surface layer and a bottom layer. The invention also provides its preparation method, which mainly achieves the recycling of construction waste through specific raw material ratios (especially the introduction of composite modified recycled aggregate) and process parameters, while ensuring the mechanical properties and appearance quality of the stone-like PC brick. Specifically, the bottom layer, by weight, includes the following raw materials: 560-590 parts recycled coarse aggregate, 160-175 parts ordinary Portland cement, 280-320 parts natural sand, 60-90 parts composite modified recycled aggregate, 35-45 parts fly ash, 2.5-3.5 parts polycarboxylate superplasticizer, and 95-105 parts water. The surface layer, by weight, includes the following raw materials: 95-105 parts white silicate cement, 165-175 parts colored sand, 8-12 parts iron oxide inorganic pigments, 35-55 parts composite modified recycled aggregate, 13-18 parts silica fume, 10-13 parts acrylic emulsion, and 38-45 parts water.

[0021] In this invention, the raw materials used are sourced as follows: recycled coarse aggregate is obtained from crushing and screening construction waste, with a particle size controlled at 4.75-9.5mm; ordinary silicate cement is grade 42.5R, using commercially available conventional products; natural sand has a fineness modulus of 2.3-3.0 and is natural river sand for construction; fly ash is grade II; polycarboxylate superplasticizer is a commercially available high-performance superplasticizer; white silicate cement is commercially available white cement; colored sand is 20-40 mesh, and can be selected from sesame black, golden sesame, or medium-grained sand. National Black; iron oxide inorganic pigments are commercially available inorganic pigments for concrete; silica fume is commercially available microsilica powder with SiO2 content ≥90%; acrylic emulsion has a solid content ≥45% and is a commercially available concrete emulsion; silane coupling agent is KH-550, commercially available industrial grade; sodium silicate modulus 3.2-3.4, commercially available; nano silica sol has a SiO2 content of 30% and is commercially available; ammonium acrylate, sodium hexametaphosphate, and nano calcium carbonate (particle size 50-100nm) are all commercially available industrial grade raw materials.

[0022] The following are specific examples: Example 1: Preparation of composite modified recycled aggregate: a. After crushing the construction waste, it is screened through a double-layer screen of 1-3mm and 4.75-9.5mm to obtain recycled aggregates of two particle sizes; the aggregates are washed with clean water and dried in an 85℃ oven until the moisture content is ≤1%.

[0023] b. Preparation of ultrasonic-microwave synergistic activation modified solution: Take 100 parts of water, heat to 50℃, add 13 parts of sodium silicate (modulus 3.3) and 2.5 parts of sodium hexametaphosphate in sequence, stir at 400 r / min until completely dissolved; turn on the microwave (power 500W, frequency 2450MHz) for activation for 1.2 minutes; after stopping the microwave, stir at 900 r / min, slowly add 8 parts of nano silica sol (SiO2 content 30%), 3.8 parts of ammonium acrylate, 2 parts of nano calcium carbonate (particle size 50-100nm) and 0.75 parts of silane coupling agent KH-550 (accounting for 0.75% of the total weight of the modified solution), and simultaneously apply ultrasonic treatment at a frequency of 25kHz for 7 minutes to obtain a uniform and stable modified solution.

[0024] c. Impregnate the two types of recycled aggregates of different particle sizes from step a in the modification solution, with the mass ratio of the impregnation solution to the aggregate being 1:1.0. During the impregnation process, apply ultrasonic treatment at a frequency of 40kHz for 24 minutes to ensure that the modification solution penetrates into the pores of the aggregate.

[0025] d. Remove the soaked aggregate, drain off excess liquid droplets, and dry in a 135℃ oven for 4 hours to obtain composite modified recycled aggregates with two particle sizes (1-3mm and 4.75-9.5mm).

[0026] Raw material preparation: Base materials (by weight): 575 parts recycled coarse aggregate (4.75-9.5mm), 168 parts ordinary Portland cement (42.5R), 300 parts natural sand (fineness modulus 2.6), 75 parts composite modified recycled aggregate (4.75-9.5mm), 40 parts fly ash (Grade II), 3.0 parts polycarboxylate superplasticizer, and 100 parts water.

[0027] Surface layer materials (by weight): 100 parts white silicate cement, 170 parts colored sand (20-40 mesh sesame black), 10 parts iron oxide inorganic pigment, 45 parts composite modified recycled aggregate (1-3mm), 15 parts silica fume, 11.5 parts acrylic emulsion, and 42 parts water.

[0028] Preparation of surface layer slurry: The white silicate cement, colored sand, iron oxide inorganic pigments, and silica fume from the surface layer raw materials were added to a mixer and dry-mixed at 250 r / min for 6 minutes. Then, acrylic emulsion and water were added, and the speed was adjusted to 500 r / min and stirred for 12 minutes. The fluidity of the slurry was measured to be 190 mm.

[0029] Bottom layer mixture: The preparation process involves adding recycled coarse aggregate, natural sand, ordinary silicate cement, fly ash, and composite modified recycled aggregate from the bottom raw materials into a mixer and dry mixing at 200 r / min for 11 minutes. Polycarboxylate superplasticizer is dissolved in water, poured into the mixer, and the speed is adjusted to 350 r / min and mixed for 18 minutes. The slump of the mixture is measured to be 3 mm.

[0030] Composite fabrics and vacuum extrusion molding: Preheat the mold to 35°C. First, evenly spread a 4mm thick layer of surface slurry at the bottom of the mold, and then lay the bottom layer of mixture on top of the surface layer. Send the mold into the vacuum extruder and extrude it for 2.5 minutes under vacuum of -0.09MPa and pressure of 17MPa to complete the molding.

[0031] Maintenance: After molding, the brick blanks are sent to the curing room with the mold and undergo preliminary steam curing for 5 hours in an environment of 60℃ and 93% humidity. After demolding, the brick blanks undergo alternating cycles of circulating steam and natural curing: first, they are cured in a steam environment of 42℃ and 88% humidity for 2.5 days, and then cured in a natural environment of 23℃ and 65% humidity for 3.5 days. This process is repeated twice to complete the curing process and obtain the finished stone-like PC brick.

[0032] Example 2: Preparation of composite modified recycled aggregate: a. After crushing the construction waste, it is screened through a double-layer screen of 1-3mm and 4.75-9.5mm to obtain recycled aggregates of two particle sizes; the aggregates are washed with clean water and dried in an 80℃ oven until the moisture content is ≤1%.

[0033] b. Preparation of ultrasonic-microwave synergistic activation modified solution: Take 100 parts of water, heat to 48℃, add 12 parts of sodium silicate (modulus 3.2) and 2.2 parts of sodium hexametaphosphate in sequence, stir at 300 r / min until completely dissolved; turn on the microwave (power 500W, frequency 2450MHz) for 1 minute; after stopping the microwave, stir at 800 r / min, slowly add 7 parts of nano silica sol (SiO2 content 30%), 3 parts of ammonium acrylate, 1 part of nano calcium carbonate (particle size 50-100nm) and 0.6 parts of silane coupling agent KH-550 (accounting for 0.6% of the total weight of the modified solution), and simultaneously apply ultrasonic treatment at a frequency of 25kHz for 5 minutes to obtain a uniform and stable modified solution.

[0034] c. Impregnate the two types of recycled aggregates of different particle sizes from step a in the modification solution, with the mass ratio of the impregnation solution to the aggregate being 1:0.9. During the impregnation process, apply ultrasonic treatment at a frequency of 40kHz for 20 minutes to ensure that the modification solution fully penetrates into the pores of the aggregate.

[0035] d. Remove the soaked aggregate, drain off excess liquid droplets, and dry in a 130℃ oven for 3 hours to obtain composite modified recycled aggregates with two particle sizes (1-3mm and 4.75-9.5mm).

[0036] Raw material preparation: Base materials (by weight): 590 parts recycled coarse aggregate (4.75-9.5mm), 175 parts ordinary Portland cement (42.5R), 320 parts natural sand (fineness modulus 2.3), 90 parts composite modified recycled aggregate (4.75-9.5mm), 45 parts fly ash (Grade II), 3.5 parts polycarboxylate superplasticizer, and 105 parts water.

[0037] Surface layer raw materials (by weight): 105 parts white silicate cement, 175 parts colored sand (20-40 mesh golden sesame), 12 parts iron oxide inorganic pigment, 55 parts composite modified recycled aggregate (1-3mm), 18 parts silica fume, 13 parts acrylic emulsion, and 45 parts water.

[0038] Preparation of surface layer slurry: The white silicate cement, colored sand, iron oxide inorganic pigments, and silica fume from the surface layer raw materials were added to a mixer and dry-mixed at 200 r / min for 5 minutes. Then, acrylic emulsion and water were added, and the speed was adjusted to 400 r / min and stirred for 10 minutes. The fluidity of the slurry was measured to be 180 mm, which meets the requirements.

[0039] Preparation of the bottom mixture: Add the recycled coarse aggregate, natural sand, ordinary silicate cement, fly ash, and composite modified recycled aggregate from the bottom raw materials into the mixer and dry mix at 150 r / min for 10 minutes; dissolve the polycarboxylate superplasticizer in water, pour it into the mixer, adjust the speed to 300 r / min and mix for 15 minutes, and measure the slump of the mixture to be 0 mm.

[0040] Composite fabrics and vacuum extrusion molding: Preheat the mold to 30°C. First, evenly spread a 3mm thick layer of surface slurry at the bottom of the mold, and then lay the bottom layer of mixture on top of the surface layer. Send the mold into the vacuum extruder and extrude it for 2 minutes under vacuum of -0.085MPa and pressure of 16MPa to complete the molding.

[0041] Maintenance: After molding, the brick blanks are sent to the curing room with the mold and undergo preliminary steam curing for 4 hours in an environment of 58℃ and 92% humidity. After demolding, the brick blanks undergo alternating cycles of circulating steam and natural curing: first, they are cured in a steam environment of 40℃ and 85% humidity for 2 days, and then cured in a natural environment of 20℃ and 60% humidity for 3 days. This process is repeated twice to complete the curing process and obtain the finished stone-like PC brick.

[0042] Example 3: Preparation of composite modified recycled aggregate: a. After crushing the construction waste, it is screened through a double-layer screen of 1-3mm and 4.75-9.5mm to obtain recycled aggregates of two particle sizes; the aggregates are washed with clean water and dried in a 100℃ oven until the moisture content is ≤1%.

[0043] b. Preparation of ultrasonic-microwave synergistic activation modified solution: Take 100 parts of water, heat to 52℃, add 14 parts of sodium silicate (modulus 3.4) and 2.8 parts of sodium hexametaphosphate in sequence, stir at 300 r / min until completely dissolved; turn on microwave (power 500W, frequency 2450MHz) for activation for 1.5 minutes; after stopping microwave, stir at 900 r / min, slowly add 9 parts of nano silica sol (SiO2 content 30%), 4.5 parts of ammonium acrylate, 3 parts of nano calcium carbonate (particle size 50-100nm) and 0.9 parts of silane coupling agent KH-550 (accounting for 0.9% of the total weight of modified solution), and simultaneously apply ultrasonic treatment at a frequency of 25kHz for 9 minutes to obtain a uniform and stable modified solution.

[0044] c. Impregnate the two types of recycled aggregates of different particle sizes from step a in the modification solution, with the mass ratio of the impregnation solution to the aggregate being 1:1.1. During the impregnation process, apply ultrasonic treatment at a frequency of 40kHz for 28 minutes to ensure that the modification solution fully penetrates into the pores of the aggregate.

[0045] d. Remove the soaked aggregate, drain off excess liquid droplets, and dry in a 140℃ oven for 5 hours to obtain composite modified recycled aggregates with two particle sizes (1-3mm and 4.75-9.5mm).

[0046] Raw material preparation: Base materials (by weight): 560 parts recycled coarse aggregate (4.75-9.5mm), 160 parts ordinary Portland cement (42.5R), 280 parts natural sand (fineness modulus 3.0), 60 parts composite modified recycled aggregate (4.75-9.5mm), 35 parts fly ash (Grade II), 2.5 parts polycarboxylate superplasticizer, and 95 parts water.

[0047] Surface layer raw materials (by weight): 95 parts white silicate cement, 165 parts colored sand (20-40 mesh China Black), 8 parts iron oxide inorganic pigment, 35 parts composite modified recycled aggregate (1-3mm), 13 parts silica fume, 10 parts acrylic emulsion, and 38 parts water.

[0048] Preparation of surface layer slurry: The white silicate cement, colored sand, iron oxide inorganic pigments, and silica fume from the surface layer raw materials were added to a mixer and dry-mixed at 300 r / min for 8 minutes. Then, acrylic emulsion and water were added, and the speed was adjusted to 600 r / min and stirred for 15 minutes. The fluidity of the slurry was measured to be 200 mm, which meets the requirements.

[0049] Preparation of the bottom mixture: The recycled coarse aggregate, natural sand, ordinary silicate cement, fly ash, and composite modified recycled aggregate from the bottom raw materials were put into the mixer and dry-mixed at 250 r / min for 12 minutes. The polycarboxylate superplasticizer was dissolved in water, poured into the mixer, and the speed was adjusted to 400 r / min and mixed for 20 minutes. The slump of the mixture was measured to be 5 mm, which meets the requirements.

[0050] Composite fabrics and vacuum extrusion molding: Preheat the mold to 40°C. First, evenly spread a 5mm thick layer of surface slurry at the bottom of the mold, and then lay the bottom layer of mixture on top of the surface layer. Send the mold into the vacuum extruder and extrude it for 3 minutes under vacuum of -0.095MPa and pressure of 18MPa to complete the molding.

[0051] Maintenance: After molding, the brick blanks are sent to the curing room with the mold and undergo preliminary steam curing for 5.5 hours in an environment of 62℃ and 95% humidity. After demolding, the brick blanks undergo alternating cycles of steam and natural curing: first, they are cured in a steam environment of 45℃ and 90% humidity for 3 days, and then cured in a natural environment of 25℃ and 70% humidity for 4 days. This process is repeated 3 times to complete the curing process and obtain the finished stone-like PC brick.

[0052] Comparative Example 1: The difference from Example 1 is that neither the bottom layer nor the top layer raw materials contain composite modified recycled aggregate. The bottom layer uses an equal amount of recycled coarse aggregate (4.75-9.5mm) to replace the composite modified recycled aggregate, and the top layer uses an equal amount of colored sand to replace the composite modified recycled aggregate. The other raw material ratios, composite modified recycled aggregate preparation steps (this step is omitted), and preparation processes are the same as in Example 1.

[0053] Comparative Example 2: The difference from Example 1 is that in the preparation steps of the composite modified recycled aggregate, only ultrasonic treatment at a frequency of 40kHz (24 minutes) is used, and microwave activation is not performed (there is no microwave step in the preparation of the modified liquid, and no microwave synergy in the impregnation of the aggregate); other raw material ratios and preparation processes are the same as in Example 1.

[0054] Comparative Example 3: The difference from Example 1 is that no nano-silica sol and nano-calcium carbonate are added during the preparation of the ultrasonic-microwave synergistic activation modification liquid; the other raw material ratios, composite modified recycled aggregate preparation steps and preparation processes are the same as in Example 1.

[0055] Comparative Example 4: The difference from Example 1 is that the composite fabric is formed by ordinary extrusion molding without vacuuming, the extrusion pressure is still 17MPa, and the extrusion time is 2.5 minutes; the other raw material ratios, composite modified recycled aggregate preparation steps and preparation processes are the same as in Example 1.

[0056] Tests and experiments: Experiment 1: Compressive strength and flexural strength tests; Referring to GB / T25993-2020, three finished bricks were randomly selected from each example and comparative example, and cut into 100mm×100mm×100mm specimens (surface side up). After curing for 28 days under standard curing conditions (20±2℃, relative humidity ≥95%), the compressive strength (loading speed 2.4kN / s) and flexural strength (three-point bending method, span 80mm, loading speed 50N / s) were tested using a pressure testing machine. The average value of the three test results was taken, and the results are as follows: Table 1

[0057] As can be seen from Table 1, the compressive strength of Examples 1-3 is ≥55MPa and the flexural strength is ≥6.2MPa, which is better than that of the comparative examples. This shows that the raw material ratio and process of the present invention can effectively improve the mechanical properties of the imitation stone PC brick.

[0058] Experiment 2: Water absorption and abrasion resistance test; Water absorption test: Refer to GB / T25993-2020, select a 100mm×100mm×50mm specimen, dry it to constant weight (m1), soak it in clean water at 20±2℃ for 24 hours, take it out, wipe off the surface moisture and weigh it (m2). Water absorption rate = (m2-m1) / m1×100%, and take the average value of 3 times.

[0059] Abrasion resistance test: Following GB / T12988-2021, a Taber abrasion tester was used with a 500g load, a CS-10 grinding wheel, and a rotation speed of 1000 rpm. The length of the abrasion crater (mm) was measured, and the average of three measurements was taken (the shorter the abrasion crater length, the better the abrasion resistance). The results are as follows: Table 2

[0060] As can be seen from Table 2, Examples 1-3 have a water absorption rate of ≤4.2% and a pit length of ≤2.7mm, exhibiting excellent impermeability and wear resistance.

[0061] Experiment 3: Color difference and appearance quality test; Color difference test: Refer to GB / T7921-2008, use a colorimeter to test the color difference ΔE of the finished brick surface (compare with the standard sample, the standard sample is the surface color of Example 1). ΔE≤2 is excellent, 2<ΔE≤3 is first-class, and ΔE>3 is unqualified; take 5 test points and take the average value.

[0062] Appearance quality test: Refer to GB / T25993-2020, check the surface of the bricks for cracks, missing corners, chipped edges, and color spots, and record the number of qualified bricks (randomly select 10 bricks, and the number of qualified bricks ≥ 9 is considered excellent). The results are as follows: Table 3

[0063] As can be seen from Table 3, the color difference ΔE of Examples 1-3 is ≤1.5, and the number of qualified appearances is 10, which meets the superior product standard. This shows that the solution of the present invention can guarantee the appearance consistency and quality of the imitation stone PC bricks.

[0064] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A stone-like PC brick prepared based on recycled concrete, characterized in that, The imitation stone PC brick is composed of a surface layer and a bottom layer; The bottom layer, by weight, comprises the following raw materials: 560-590 parts recycled coarse aggregate, 160-175 parts ordinary silicate cement, 280-320 parts natural sand, 60-90 parts composite modified recycled aggregate, 35-45 parts fly ash, 2.5-3.5 parts polycarboxylate superplasticizer, and 95-105 parts water. The surface layer, by weight, comprises the following raw materials: 95-105 parts white silicate cement, 165-175 parts colored sand, 8-12 parts iron oxide inorganic pigment, 35-55 parts composite modified recycled aggregate, 13-18 parts silica fume, 10-13 parts acrylic emulsion, and 38-45 parts water.

2. The stone-like PC brick according to claim 1, characterized in that, The preparation method of the composite modified recycled aggregate includes the following steps: a. After crushing the construction waste, it is sieved through a double-layer screen of 1-3mm and 4.75-9.5mm to obtain recycled aggregate of the corresponding particle size. After washing, it is dried at 80-100℃ until the moisture content is ≤1%. b. Impregnate the recycled aggregate in an ultrasonic-microwave synergistic activation and modification solution containing a silane coupling agent, with the mass ratio of the impregnation solution to the aggregate being 1:(0.9-1.1); The silane coupling agent is KH-550, accounting for 0.6-0.9% of the total weight of the modified solution; c. During the impregnation process, apply ultrasonic treatment at a frequency of 40kHz for 20-28 minutes to allow the modified liquid to penetrate into the pores of the aggregate. d. Remove the aggregate, drain off excess liquid, and dry at 130-140℃ for 3-5 hours to obtain composite modified recycled aggregate.

3. The imitation stone PC brick according to claim 2, characterized in that, The ultrasonic-microwave synergistic activation and modification liquid is composed of 100 parts water, 12-14 parts sodium silicate, 7-9 parts nano silica sol, 3-4.5 parts ammonium acrylate, 2.2-2.8 parts sodium hexametaphosphate, and 1-3 parts nano calcium carbonate by weight.

4. The imitation stone PC brick according to claim 3, characterized in that, The preparation method of the ultrasonic-microwave synergistic activation modified liquid is as follows: water is heated to 48-52℃, sodium silicate and sodium hexametaphosphate are added in sequence, and the mixture is stirred at 300-500 r / min until completely dissolved. Microwave activation is performed for 1-1.5 minutes. After stopping the microwave, the mixture is stirred at 800-1000 r / min at high speed, and nano silica sol, ammonium acrylate, nano calcium carbonate and silane coupling agent KH-550 are slowly added. At the same time, ultrasonic treatment at a frequency of 25 kHz is applied for 5-9 minutes to obtain a uniform and stable modified liquid.

5. The imitation stone PC brick according to claim 4, characterized in that, The microwave activation parameters are 500W microwave power and 2450MHz frequency.

6. The stone-like PC brick according to claim 1, characterized in that, The solid content of the acrylic emulsion in the surface layer is ≥45%.

7. The method for preparing stone-like PC bricks based on recycled concrete according to claim 1, characterized in that, Includes the following steps: S1 Raw material preparation: Weigh each raw material according to the proportions; S2 surface layer slurry preparation: Dry mix the white cement, colored sand, pigment, and silica fume used for the surface layer at a speed of 200-300 r / min for 5-8 minutes, add acrylic emulsion and water, and stir at a speed of 400-600 r / min for 10-15 minutes, controlling the slurry flowability to be 180-200 mm. S3 bottom layer mixture preparation: Put the recycled coarse aggregate, natural sand, cement, fly ash and composite modified recycled aggregate used for the bottom layer into the mixer and dry mix at 150-250 r / min for 10-12 minutes. Dissolve the water-reducing agent in water and add it. Mix at 300-400 r / min for 15-20 minutes and control the slump of the mixture to be 0-5 mm. S4 composite fabric and vacuum extrusion molding: Preheat the mold to 30-40℃, first evenly spread a 3-5mm thick surface layer of slurry, then lay the bottom layer of mixture; send the mold into the vacuum extruder and extrude for 2-3 minutes to form the product; S5 curing: The molded brick blank is steam cured for 4-5.5 hours with the initial mold; after demolding, the curing is carried out alternately with circulating steam and natural curing to complete the curing and obtain the finished product.

8. The preparation method according to claim 7, characterized in that, The extrusion in S4 is carried out under vacuum conditions of -0.085 to -0.095 MPa and pressure of 16-18 MPa.

9. The preparation method according to claim 7, characterized in that, The initial steam curing in S5 is carried out in an environment of 58-62℃ and 92%-95% humidity.

10. The preparation method according to claim 7, characterized in that, S5 medium-circulating steam-natural curing alternation: first cure in a steam environment of 40-45℃ and 85%-90% humidity for 2-3 days, then cure in a natural environment of 20-25℃ and ≥60% humidity for 3-4 days, alternating 2-3 times.

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