High-strength recycled concrete mortar and preparation method thereof

Abstract

The invention discloses high-strength recycled concrete mortar and a preparation method thereof, and relates to the technical field of recycled concrete mortar. The high-strength recycled concrete mortar is prepared from the following components in parts by weight: 25 to 34 parts of cement, 2.5 to 3.4 parts of silica fume, 8 to 12 parts of modified aerogel particles, 12 to 18 parts of recycled fine aggregate, 0.08 to 0.12 part of polycarboxylic acid water reducer, 24 to 32 parts of PCM and 6.25 to 8.5 parts of slag. The heat conductivity coefficient is reduced through the high aerogel content of the surface layer, the temperature buffering capacity is enhanced through the high PCM proportion of the inner layer, a silane coupling agent is sprayed on an interface during layered pouring to form chemical bonds, the contradiction of single-layer structure performance is solved, silicon hydroxyl is introduced into modified aerogel particles through the silane coupling agent, the surface contact angle is increased to 110 degrees, and the thermal conductivity is improved. And C-S-H gel is generated with a cement hydration product, so that the problem of compatibility is solved.

Description

Technical Field

[0001] This invention relates to the field of recycled concrete mortar technology, specifically to a high-strength recycled concrete mortar and its preparation method. Background Technology

[0002] Recycled concrete mortar refers to a new type of building material made by using waste concrete that has been crushed, washed, and graded to partially or completely replace natural aggregates, and then adding cement, water, and other ingredients.

[0003] For example, the invention disclosed in Chinese invention publication number CN118619607A is a high-temperature resistant aerogel mortar composite recycled concrete and its preparation method. The recycled concrete includes recycled concrete containing cement, fly ash, recycled coarse aggregate, river sand, water-reducing agent and water, and aerogel mortar containing cement, river sand, SiO2 aerogel, KH-550 reagent, water-reducing agent and water. They are combined in an integral molding process, making full use of waste material resources, reducing dependence on natural resources, and improving the high-temperature resistance of recycled concrete.

[0004] However, although aerogel particles were added to the concrete during its preparation to improve its thermal insulation, the compatibility between the aerogel and the cement matrix was not resolved, resulting in weak interfacial bonding. Furthermore, the absence of phase change materials prevented the implementation of temperature regulation, and the thermal conductivity remained above 0.15 W / (m·K), indicating insufficient high-temperature stability. Moreover, the use of a single-layer casting structure and the uniform mixing of cementitious materials and functional components made it difficult to achieve both high strength and low thermal conductivity. While adding cementitious materials improved strength, it also increased thermal conductivity, and adding insulation components reduced strength, making it unsuitable for complex working conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-strength recycled concrete mortar and its preparation method, thus solving the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a high-strength recycled concrete mortar and its preparation method, wherein the concrete mortar comprises a 40% surface layer and a 60% inner layer, and a double-layer gradient structure is constructed based on the surface layer and the inner layer; the concrete mortar comprises components in the following mass ratios: 25-34 parts cement, 2.5-3.4 parts silica fume, 8-12 parts modified aerogel particles, 12-18 parts recycled fine aggregate, 0.08-0.12 parts polycarboxylate superplasticizer, 24-32 parts PCM, and 6.25-8.5 parts slag.

[0007] The inner layer includes cement, silica fume, slag, PCM, modified aerogel particles, recycled fine aggregate, and polycarboxylate superplasticizer. The outer layer comprises cement, silica fume, slag, PCM, modified aerogel particles, recycled fine aggregate, and polycarboxylate superplasticizer in different proportions than the inner layer.

[0008] A further improvement to the technical solution of the present invention is that it includes the following specific components: 32 parts cement, 3 parts silica fume, 10 parts modified aerogel particles, 16 parts recycled fine aggregate, 0.12 parts polycarboxylate superplasticizer, 0.05 parts organosilicon defoamer, 30 parts PCM, and 7.5 parts slag.

[0009] A further improvement of the technical solution of the present invention is that the PCM comprises components in the following mass ratio: 18-23 parts paraffin, 6-8 parts expanded graphite, and 0.10-0.15 parts silane coupling agent.

[0010] This invention also provides a method for preparing high-strength recycled concrete mortar, the method comprising the following specific steps: Pretreated paraffin wax is melted into the layered pores of expanded graphite and encapsulated by aerogel microcapsules to form PCM; The aerogel particles are formed into silanol groups to create modified aerogel particles. The weakly alkaline mortar layer attached to the surface of the recycled fine aggregate obtained from waste concrete is removed, and silica fume suspension is attached to the pores of the recycled fine aggregate to obtain composite recycled fine aggregate. Cement, silica fume, and slag are added to polycarboxylate superplasticizer according to the mass ratio to prepare the basic cementitious material; The base gel material and the inner functional component are used to prepare the inner mortar, and the base gel material and the outer functional component are used to prepare the outer mortar. The outer and inner layers of mortar are poured in layers, and a silane coupling agent is sprayed at the contact interface to remove air bubbles. After the two layers are fully bonded together, the required high-strength recycled concrete mortar is formed.

[0011] A further improvement to the technical solution of this invention lies in: the step of melting the pretreated paraffin into the layered pores of expanded graphite and encapsulating it with aerogel microcapsules to form aerogel-coated PCM microcapsules includes: Paraffin wax was placed in a vacuum drying oven at 60℃ for 12 hours to remove free water and prevent phase separation during phase change. Paraffin wax and expanded graphite were mixed in an oil bath at 80℃ at a mass ratio of 7:3 and stirred at 200 rpm for 40 minutes until the paraffin wax was completely melted and penetrated into the expansion pores of the expanded graphite. The paraffin and expanded graphite mixture is transferred to a vacuum impregnation tank and kept under a negative pressure of 0.8-1.4 MPa for 90-110 minutes. The negative pressure forces the paraffin into the microporous structure of EG to obtain a shaped PCM. The three-dimensional network structure of expanded graphite firmly locks in paraffin through physical adsorption, solving the problem of easy leakage in traditional PCM. After shaping, the latent heat of phase change of PCM is stabilized at 180-190 J / g, and the thermal conductivity is increased from 0.2 W / (m·K) of pure paraffin to 0.25 W / (m·K), ensuring rapid heat conduction. Tetraethyl orthosilicate, ethanol, and water were mixed in a volume ratio of 1:4:1, and 0.1 mol / L hydrochloric acid was added to adjust the pH to 3.0. The mixture was stirred for 30 minutes to form a silica sol. The shaped PCM was then broken into particles of 50-100 μm and added to the silica sol in a solid-liquid ratio of 1:5. The mixture was ultrasonically dispersed for 20 minutes, followed by the addition of ammonia water to adjust the pH to 8.0. The mixture was then gelled in a water bath at 60°C for 2 hours to form aerogel-coated PCM microcapsules.

[0012] The aerogel coating layer is 10-20 μm thick, which further blocks paraffin leakage. At the same time, the aerogel nanopores with a pore size of 20-50 nm reduce the thermal conductivity to 0.03 W / (m·K).

[0013] A further improvement to the technical solution of the present invention is that: the step of forming silanol groups from aerogel particles to form modified aerogel particles includes: Aerogel particles with a particle size of 100-200μm were selected, and 0.5% by mass of silane coupling agent was added. The mixture was then mixed at 200rpm for 30 minutes in a planetary ball mill, followed by drying in an oven at 80℃ for 2 hours to hydrolyze the coupling agent to form silanol groups, thus forming improved aerogel particles.

[0014] The modified aerogel particles increased the surface contact angle from 15° to 110°, enhancing hydrophobicity and improving the interfacial bonding strength with cement paste. At the same time, the silanol groups reacted with the cement hydration product Ca(OH)2 to generate CSH gel, reducing interfacial defects.

[0015] A further improvement to the technical solution of this invention lies in: removing the weakly alkaline mortar layer adhering to the surface of the recycled fine aggregate obtained from waste concrete, and adhering it to the pores of the recycled fine aggregate with silica fume suspension to obtain composite recycled fine aggregate, comprising: Waste concrete is crushed and screened to obtain 0-5mm recycled fine aggregate. The composite recycled fine aggregate is soaked in 5% hydrochloric acid solution for 30 minutes at a solid-liquid ratio of 1:3 to remove the weakly alkaline mortar layer adhering to the surface. It is then washed with water until pH=7. The aggregate is then added to 10% silica fume suspension with a silica fume particle size of 0.1-1μm and impregnated under vacuum negative pressure of 0.6-1.0Mpa for 30 minutes. After removal, it is dried at 105℃ for 4 hours. The silica fume is uniformly adhered to the surface of the aggregate to form a dense coating with a thickness of 2-5μm, thus forming composite recycled fine aggregate.

[0016] Pickling removes the loose layer on the surface of the aggregate, and a silica fume coating fills the pores of the aggregate, reducing the water absorption rate from 15% to below 8% and improving the strength of the interface transition zone with the mortar matrix.

[0017] A further improvement to the technical solution of this invention lies in: the addition of cement, silica fume, and slag to the polycarboxylate superplasticizer in a specific mass ratio to prepare the basic cementitious material includes: Slag is ball-milled to a specific surface area of ​​410-450 m² 2 / kg, mix cement, silica fume and slag in a mass ratio of 65:10:25 to prepare cementitious material, add 0.6% polycarboxylate superplasticizer of the total mass of cementitious material, dry mix for 3 minutes until uniform, and prepare basic cementitious material.

[0018] The synergistic effect of silica fume nanofilling and the potential hydration activity of slag improves the 28-day compressive strength of mortar, reduces the peak hydration heat, and avoids temperature cracks.

[0019] A further improvement to the technical solution of this invention lies in: the preparation of the inner layer mortar by combining the base gel material and the inner layer functional component, and the preparation of the outer layer mortar by combining the base gel material and the outer layer functional component, comprising: The following ingredients are added: 18%–21% base gel material and 52%–63% recycled fine aggregate; 15%–20% PCM microcapsules; 1%–2% polycarboxylate superplasticizer; and 3%–5% modified aerogel particles. The mixture is placed in a mixer and first dry-mixed at a low speed of 80 rpm for 2 minutes to ensure that the components are initially mixed evenly. Then, water with a water-cement ratio of 1:0.38 is added, and the mixture is switched to a high speed of 1500 rpm for 5 minutes to form the inner layer mortar. The base gel material (26%–30% by weight) and modified aerogel particles (12%–18% by weight) are dry-mixed in a planetary mixer at a low speed of 80 rpm for 5 minutes to ensure uniform dispersion of the aerogel in the powder system. Then, recycled fine aggregate (40.2%–48.6% by weight) is added and the mixture is dry-mixed for another 3 minutes to form a stable aggregate encapsulation structure. Water is added to adjust the water-cement ratio to 0.35. Considering that aerogel requires less water than ordinary aggregate, the amount of water used must be strictly controlled. The mixture is stirred at 120 rpm for 8 minutes to form a three-dimensional network dispersion structure of the aerogel. Finally, PCM microcapsules (15%–20% by weight) and polycarboxylate superplasticizer (0.4%–0.8% by weight) are added, and the mixture is stirred at high speed to form the outer mortar layer.

[0020] A further improvement to the technical solution of this invention lies in: the step of pouring the outer and inner layers of mortar in layers, spraying a silane coupling agent at the contact interface, and performing air bubble removal treatment, so that the required high-strength recycled concrete mortar is formed after the two layers are fully bonded at the interface, comprising: A 40mm×40mm×160mm triple mortar mold was selected. The inner layer of mortar was poured to 60% of the mold height. A 10mm diameter immersion vibrator was used to vibrate for 20 seconds at a frequency of 50Hz to remove air bubbles. 1.5 hours before the inner layer of mortar initially set, the outer layer of mortar was poured to the top of the mold and vibrated again for 15 seconds to ensure full bonding between the two layers. 0.5% silane coupling agent was sprayed at the interface between the two mortar layers. The coupling agent was hydrolyzed by the moisture in the mortar itself, forming Si-O-Ca chemical bonds at the interface. Pouring before initial setting ensured that there were no cold joints at the interface between the two layers. Vibration increased the density of the mortar and controlled the porosity to within 12% to avoid affecting the thermal insulation performance due to porosity.

[0021] Beneficial effects Compared with the prior art, the beneficial effects of the present invention are: the thermal conductivity is reduced by the high aerogel content on the surface layer, and the temperature buffering capacity is enhanced by the high PCM content in the inner layer. When the layers are poured, the interface is sprayed with silane coupling agent to form chemical bonds, which solves the contradiction of single-layer structure performance. The modified aerogel particles introduce silanol groups through silane coupling agent, and the surface contact angle increases from 110° to generate CSH gel with cement hydration products, which solves the compatibility problem. Recycled fine aggregates are treated with a process of hydrochloric acid pickling and silica fume coating to remove the loose mortar layer on the surface and form a dense coating, thereby reducing the density of the interface transition zone and increasing the density of the aggregate. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of high-strength recycled concrete mortar and its preparation method. Detailed Implementation

[0023] Various exemplary embodiments, features, and aspects of this application will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0024] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0025] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented without certain specific details. In some instances, methods, means, and elements well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0026] This invention provides a high-strength recycled concrete mortar, comprising a 40% surface layer and a 60% inner layer, and a double-layer gradient structure constructed based on the surface and inner layers. The concrete mortar comprises the following components in the indicated mass ratios: 25-34 parts cement, 2.5-3.4 parts silica fume, 8-12 parts modified aerogel particles, 12-18 parts recycled fine aggregate, 0.08-0.12 parts polycarboxylate superplasticizer, 24-32 parts PCM, and 6.25-8.5 parts slag.

[0027] The inner layer includes cement, silica fume, slag, PCM, modified aerogel particles, recycled fine aggregate, and polycarboxylate superplasticizer. The outer layer comprises cement, silica fume, slag, PCM, modified aerogel particles, recycled fine aggregate, and polycarboxylate superplasticizer in different proportions than the inner layer.

[0028] It includes the following specific components: 32 parts cement, 3 parts silica fume, 10 parts modified aerogel particles, 16 parts recycled fine aggregate, 0.12 parts polycarboxylate superplasticizer, 0.05 parts organosilicon defoamer, 30 parts PCM, and 7.5 parts slag.

[0029] The PCM comprises components in the following mass ratio: 18-23 parts paraffin, 6-8 parts expanded graphite, and 0.10-0.15 parts silane coupling agent.

[0030] This invention also provides a method for preparing high-strength recycled concrete mortar, the method comprising the following specific steps: S1. The pretreated paraffin wax is melted into the layered pores of expanded graphite and encapsulated by aerogel microcapsules to form PCM; Specifically, it includes: Paraffin wax was placed in a vacuum drying oven at 60℃ for 12 hours to remove free water and prevent phase separation during phase change. Paraffin wax and expanded graphite were mixed in an oil bath at 80℃ at a mass ratio of 7:3 and stirred at 200 rpm for 40 minutes until the paraffin wax was completely melted and penetrated into the expansion pores of the expanded graphite. The paraffin and expanded graphite mixture is transferred to a vacuum impregnation tank and kept under a negative pressure of 0.8-1.4 MPa for 90-110 minutes. The negative pressure forces the paraffin into the microporous structure of EG to obtain a shaped PCM. The three-dimensional network structure of expanded graphite firmly locks in paraffin through physical adsorption, solving the problem of easy leakage in traditional PCM. After shaping, the latent heat of phase change of PCM is stabilized at 180-190 J / g, and the thermal conductivity is increased from 0.2 W / (m·K) of pure paraffin to 0.25 W / (m·K), ensuring rapid heat conduction. Tetraethyl orthosilicate, ethanol, and water were mixed in a volume ratio of 1:4:1, and 0.1 mol / L hydrochloric acid was added to adjust the pH to 3.0. The mixture was stirred for 30 minutes to form a silica sol. The shaped PCM was then broken into particles of 50-100 μm and added to the silica sol in a solid-liquid ratio of 1:5. The mixture was ultrasonically dispersed for 20 minutes, followed by the addition of ammonia water to adjust the pH to 8.0. The mixture was then gelled in a water bath at 60°C for 2 hours to form aerogel-coated PCM microcapsules.

[0031] The aerogel coating layer is 10-20 μm thick, which further blocks paraffin leakage. At the same time, the aerogel nanopores with a pore size of 20-50 nm reduce the thermal conductivity to 0.03 W / (m·K).

[0032] S2. Form silanol groups in aerogel particles to form modified aerogel particles; Aerogel particles with a particle size of 100-200μm were selected, and 0.5% by mass of silane coupling agent was added. The mixture was then mixed at 200rpm for 30 minutes in a planetary ball mill, followed by drying in an oven at 80℃ for 2 hours to hydrolyze the coupling agent to form silanol groups, thus forming improved aerogel particles.

[0033] The modified aerogel particles increased the surface contact angle from 15° to 110°, enhancing hydrophobicity and improving the interfacial bonding strength with cement paste. At the same time, the silanol groups reacted with the cement hydration product Ca(OH)2 to generate CSH gel, reducing interfacial defects.

[0034] S3. Remove the weakly alkaline mortar layer adhering to the surface of the recycled fine aggregate obtained from waste concrete, and attach silica fume suspension to the pores of the recycled fine aggregate to obtain composite recycled fine aggregate. Waste concrete is crushed and screened to obtain 0-5mm recycled fine aggregate. The recycled fine aggregate is soaked in 5% hydrochloric acid solution for 30 minutes at a solid-liquid ratio of 1:3 to remove the weakly alkaline mortar layer adhering to the surface. It is then washed with water until pH=7. The aggregate is then added to 10% silica fume suspension with a silica fume particle size of 0.1-1μm and impregnated under vacuum negative pressure of 0.6-1.0Mpa for 30 minutes. After removal, it is dried at 105℃ for 4 hours. The silica fume is uniformly adhered to the surface of the aggregate to form a dense coating with a thickness of 2-5μm, thus forming composite recycled fine aggregate.

[0035] Pickling removes the loose layer on the surface of the aggregate, and a silica fume coating fills the pores of the aggregate, reducing the water absorption rate from 15% to below 8% and improving the strength of the interface transition zone with the mortar matrix.

[0036] S4. Add cement, silica fume and slag to polycarboxylate superplasticizer according to the mass ratio to prepare the basic cementitious material; Slag is ball-milled to a specific surface area of ​​410-450 m² 2 / kg, mix cement, silica fume and slag in a mass ratio of 65:10:25 to prepare cementitious material, add 0.6% polycarboxylate superplasticizer of the total mass of cementitious material, dry mix for 3 minutes until uniform, and prepare basic cementitious material.

[0037] The synergistic effect of silica fume nanofilling and the potential hydration activity of slag improves the 28-day compressive strength of mortar, reduces the peak hydration heat, and avoids temperature cracks.

[0038] S5. Prepare an inner layer mortar by combining the base gel material with the inner layer functional components, and prepare an outer layer mortar by combining the base gel material with the outer layer functional components. Add the following components to a mixer: 18%–21% base gel material and 52%–63% composite recycled fine aggregate; 15%–20% PCM microcapsules; 1%–2% polycarboxylate superplasticizer; and 3%–5% modified aerogel particles. First, dry mix at a low speed of 80 rpm for 2 minutes to ensure that the components are initially mixed evenly. Then, add water with a water-cement ratio of 1:0.38 and switch to high speed of 1500 rpm for 5 minutes to form the inner layer mortar. The base gel material (26%–30% by weight) and modified aerogel particles (12%–18% by weight) are dry-mixed in a planetary mixer at a low speed of 80 rpm for 5 minutes to ensure uniform dispersion of the aerogel in the powder system. Then, composite recycled fine aggregate (40.2%–48.6% by weight) is added and dry-mixed for another 3 minutes to form a stable aggregate encapsulation structure. Water is added to adjust the water-cement ratio to 0.35. Considering that the water requirement of aerogel is less than that of ordinary aggregate, the amount of water used must be strictly controlled. The mixture is stirred at 120 rpm for 8 minutes to form a three-dimensional network dispersion structure of the aerogel. Finally, PCM microcapsules (15%–20% by weight) and polycarboxylate superplasticizer (0.4%–0.8% by weight) are added and stirred at high speed to form the outer mortar layer.

[0039] S6. The outer and inner mortar layers are poured in layers, and a silane coupling agent is sprayed at the contact interface to remove air bubbles. After the two layers are fully bonded, the required high-strength recycled concrete mortar is formed.

[0040] A 40mm×40mm×160mm triple mortar mold was selected. The inner layer of mortar was poured to 60% of the mold height. A 10mm diameter immersion vibrator was used to vibrate for 20 seconds at a frequency of 50Hz to remove air bubbles. 1.5 hours before the inner layer of mortar initially set, the outer layer of mortar was poured to the top of the mold and vibrated again for 15 seconds to ensure full bonding between the two layers. 0.5% silane coupling agent was sprayed at the interface between the two mortar layers. The coupling agent was hydrolyzed by the moisture in the mortar itself, forming Si-O-Ca chemical bonds at the interface. Pouring before initial setting ensured that there were no cold joints at the interface between the two layers. Vibration increased the density of the mortar and controlled the porosity to within 12% to avoid affecting the thermal insulation performance due to porosity.

[0041] Example 1: This example is to verify the effect of double-layer gradient structure, PCM, modified aerogel and composite recycled aggregate on the mechanical properties, temperature control performance and durability of mortar. The raw materials selected in this example are: cement; silica fume; slag; recycled fine aggregate.

[0042] PCM: microcapsules encapsulated in paraffin wax, expanded graphite, and aerogel; Modified aerogel: SiO2 particles modified with KH-560 silane; Additives: polycarboxylate superplasticizer, silicone defoamer, silane coupling agent KH-560.

[0043] The experimental equipment includes a pressure testing machine, a flexural testing machine, a thermal conductivity meter, a differential scanning calorimeter, a carbonization test chamber, a freeze-thaw cycle test chamber, and a scanning electron microscope; The concrete mortar prepared according to the above-described method was used as the experimental group in this embodiment. The differences between the experimental group and the control group are shown below: Control group 1: PCM and modified aerogel were uniformly mixed, poured in a single layer, vibrated for 30 seconds, and no interface treatment was performed.

[0044] Control group 2: PCM was removed and replaced with an equal amount of quartz sand (particle size 50-100μm), and the rest was poured in layers as in the original scheme.

[0045] Control group 3: Recycled aggregate was directly crushed and screened to a particle size of 0-5mm, without acid washing or silica fume coating, and the rest was the same as the original scheme.

[0046] Control group 4: Quartz sand was used instead of modified aerogel, and the rest was the same as the original scheme.

[0047] Control group 5: Cement: Sand = 1:3, water-cement ratio 0.5, mixed and poured in a single layer with vibration.

[0048] All specimens were cured in a standard curing room at 20±2℃ and humidity ≥95% for 7 days and then transferred to a 40℃ oven for drying for 48 hours, followed by curing at room temperature for 21 days (total age 28 days).

[0049] Compressive strength: According to GB / T17671-2021 standard, 40mm×40mm×160mm specimens were used, and the loading rate of the pressure testing machine was 2.4kN / s. The strength was measured at 3 days, 7 days and 28 days.

[0050] Flexural strength: same specimen size, three-point bending method, span 100mm, loading rate 50N / s.

[0051] Thermal conductivity: steady-state plate method, referring to standard GB / T10294-2008, specimen size 300mm×300mm×30mm, test temperature 25℃.

[0052] Phase change latent heat: Differential scanning calorimeter, heating rate 10℃ / min, test range 20-50℃, calculate the peak value of phase change latent heat.

[0053] High temperature stability: After being calcined in a muffle furnace at 800℃ for 2 hours and cooled to room temperature, the residual compressive strength retention rate was measured.

[0054] Freeze-thaw cycle: According to GB / T50082-2009 standard, freezing at -15℃ for 3 hours and thawing in water at 20℃ for 3 hours constitutes one cycle, for a total of 50 cycles, and the mass loss rate and strength loss rate are measured.

[0055] Carbonization depth: The CO2 concentration in the carbonization chamber was 20±3%, the humidity was 70±5%, and the carbonization depth was measured by phenolphthalein titration after 28 days.

[0056] The experimental results are shown in the table below: Table 1 Performance indicators experimental group Control group 1 Control group 2 Control group 3 Control group 4 Control group 5 compressive strength 48.5±1.2 39.2±1.5 42.3±1.0 35.6±1.8 38.8±1.3 30.5±1.1 Flexural strength 6.8±0.3 5.2±0.2 5.9±0.2 4.5±0.3 5.0±0.2 4.2±0.2 thermal conductivity 0.08±0.01 0.125±0.008 0.108±0.006 0.095±0.007 0.186±0.010 0.280±0.015 Phase transition latent heat 125±5 118±4 0 120±6 122±5 0 Strength retention rate 82±3 65±4 70±3 58±5 62±4 45±5 Freeze-thaw quality loss rate 1.2±0.2 2.8±0.3 2.1±0.2 3.5±0.4 3.0±0.3 4.8±0.5 carbonization depth 3.2±0.3 4.5±0.4 3.8±0.3 5.2±0.5 4.8±0.4 6.5±0.6 The original scheme group had a compressive strength 23.7% higher and a thermal conductivity 34.4% lower than the control group 1, indicating that the double-layer gradient surface high aerogel insulation and inner high PCM energy storage can optimize heat distribution and reduce the impact of thermal stress on strength. The latent heat of phase change in the original scheme group reached 125 J / g, and the strength retention rate at 800℃ was 17.1% higher than that of the control group 2, proving that PCM improves high-temperature stability by buffering thermal shock through phase change. The recycled aggregate treated with acid washing and silica fume resulted in a 36.2% higher compressive strength and a 38.5% lower carbonization depth in the original scheme group compared to the control group 3. The silica fume coating effectively filled the pores and enhanced the interfacial bonding.

[0057] Aerogel insulation performance: The thermal conductivity of the original scheme group was 55.9% lower than that of the control group 4, and the freeze-thaw mass loss rate was 60% lower. The aerogel nanoporous network significantly improved the insulation and durability.

[0058] Overall performance surpasses traditional mortar: The original scheme group has a compressive strength 59.0% higher than the control group 5, and a thermal conductivity 70.7% lower, achieving high strength, low energy consumption, and high durability.

[0059] Example 2: This example uses the components of claim 2, namely 32 parts cement, 3 parts silica fume, 10 parts modified aerogel particles, 16 parts recycled fine aggregate, 0.12 parts polycarboxylate superplasticizer, 0.05 parts organosilicon defoamer, 30 parts PCM, and 7.5 parts slag, as a baseline. By designing a control experiment with changing a single variable, the influence of the proportion of each component on the mortar performance is verified, and the optimality of this proportion is determined.

[0060] The experimental group used the above preparation method, while the differences in the control group included: Control group 1: Only the amount of cement was increased, while the total mass of the cementitious material remained unchanged, and the water-cement ratio was adjusted to 0.38 for the inner layer and 0.35 for the surface layer.

[0061] Control group 2: Reduce the modified aerogel to 5 parts and supplement with an equal amount of quartz sand to ensure volume consistency.

[0062] Control group 3: PCM dosage was reduced from 30 parts to 20 parts, 10 parts of recycled fine aggregate were added, no modification was performed, and the total amount of aggregate remained unchanged.

[0063] Control group 4: Silica fume was reduced from 3 parts to 1.5 parts, slag was increased from 7.5 parts to 9 parts, and the total amount of cementitious materials remained unchanged at 42.5 parts.

[0064] Control group 5: Recycled fine aggregate was directly crushed and screened without acid washing and silica fume coating; the remaining steps were the same as the baseline group.

[0065] Maintenance conditions: 7 days of standard maintenance at 20±2℃ and humidity ≥95%, 48 hours of drying at 40℃, and 28 days of maintenance at room temperature.

[0066] Mechanical properties: compressive strength GB / T17671-2021, 40mm×40mm×160mm specimen; flexural strength, three-point bending method, span 100mm.

[0067] Temperature control performance: The thermal conductivity is selected using the steady-state flat plate method, referring to standard GB / T10294-2008; the latent heat of phase change is DSC; and the heating rate is 10℃ / min.

[0068] Durability: Strength retention rate after 800℃ high temperature, tested after 2 hours of burning and cooling, mass loss rate after 50 freeze-thaw cycles, referring to standard GB / T50082-2009, carbonization depth after 28 days, using phenolphthalein titration method.

[0069] The experimental results are shown in the table below: Table 2 Performance indicators experimental group Control group 1 Control group 2 Control group 3 Control group 4 Control group 5 compressive strength 48.5±1.2 43.2±1.5 42.8±1.3 41.5±1.1 39.6±1.4 36.2±1.6 Flexural strength 6.8±0.3 5.9±0.2 5.5±0.2 5.3±0.3 5.1±0.2 4.6±0.3 thermal conductivity 0.082±0.005 0.085±0.006 0.138±0.008 0.088±0.007 0.092±0.006 0.098±0.008 Phase transition latent heat 125±5 123±4 121±5 82±4 124±4 122±5 Strength retention rate 82±3 75±4 70±3 62±5 68±4 55±4 Freeze-thaw quality loss rate 1.2±0.2 1.8±0.3 2.5±0.2 3.0±0.3 2.2±0.2 4.0±0.4 carbonization depth 3.2±0.3 3.8±0.4 4.2±0.3 4.5±0.4 5.0±0.5 6.8±0.6 As shown in the table above, after increasing the cement content from 32 parts to 35 parts, the 28-day compressive strength decreased by 11.0% (48.5, 43.2 MPa), and the strength retention rate at 800℃ decreased by 8.5%. This is because excessive cement leads to an increase in the peak heat of hydration (15% higher than the baseline group), internal temperature differences cause microcracks, and the excess cement hydration product Ca(OH)2 increases, reducing the interfacial density.

[0070] Reducing the aerogel content from 10 parts to 5 parts resulted in a 68.3% increase in thermal conductivity (0.082, 0.138 W / (m·K)) and a 108.3% increase in freeze-thaw mass loss. Insufficient aerogel led to an incomplete nanoporous network of thermal insulation, accelerated heat conduction, and deteriorated freeze resistance due to decreased thermal insulation properties.

[0071] Reducing PCM from 30 parts to 20 parts resulted in a 34.4% decrease in latent heat of phase transformation (125, 82 J / g) and a 24.4% decrease in strength retention at 800℃. Insufficient PCM failed to effectively buffer high-temperature thermal shock, leading to thermal stress concentration inside the mortar and exacerbated crack propagation at high temperatures.

[0072] Reducing the silica fume content from 3 parts to 1.5 parts resulted in a 25.0% decrease in flexural strength (6.8 and 5.1 MPa) and a 56.2% increase in carbonization depth. The loss of the nano-filling effect of silica fume and the increased porosity in the interfacial transition zone led to a decrease in crack resistance and carbonization resistance.

[0073] Untreated recycled fine aggregate, after silica fume modification, showed a 25.4% decrease in compressive strength (48.5, 36.2 MPa) and a 112.5% ​​increase in carbonization depth. The unmodified aggregate had a loose surface and high porosity, with water absorption increasing from 8% to 15%, interfacial bond strength decreasing by 35%, and durability significantly deteriorating.

[0074] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-strength recycled concrete mortar, characterized in that, The concrete mortar comprises a surface layer and an inner layer, and the concrete mortar comprises the following components in parts by weight: 25-34 parts cement, 2.5-3.4 parts silica fume, 8-12 parts modified aerogel particles, 12-18 parts recycled fine aggregate, 0.08-0.12 parts polycarboxylate superplasticizer, 24-32 parts PCM, and 6.25-8.5 parts slag; The inner layer includes cement, silica fume, slag, PCM, modified aerogel particles, recycled fine aggregate, and polycarboxylate superplasticizer. The outer layer comprises cement, silica fume, slag, PCM, modified aerogel particles, recycled fine aggregate, and polycarboxylate superplasticizer in different proportions than the inner layer.

2. The high-strength recycled concrete mortar according to claim 1, characterized in that, The specific components include: 32 parts cement, 3 parts silica fume, 10 parts modified aerogel particles, 16 parts recycled fine aggregate, 0.12 parts polycarboxylate superplasticizer, 0.05 parts silicone defoamer, 30 parts PCM, and 7.5 parts slag.

3. The high-strength recycled concrete mortar according to claim 1, characterized in that, The PCM comprises the following components in the following mass ratio: 18-23 parts paraffin, 6-8 parts expanded graphite, and 0.10-0.15 parts silane coupling agent.

4. A method for preparing high-strength recycled concrete mortar, applied to the high-strength recycled concrete mortar according to any one of claims 1-3, characterized in that, The method includes the following specific steps: Pretreated paraffin wax is melted into the layered pores of expanded graphite and encapsulated by aerogel microcapsules to form PCM; The aerogel particles are formed into silanol groups to create modified aerogel particles. The weakly alkaline mortar layer attached to the surface of the recycled fine aggregate obtained from waste concrete is removed, and silica fume suspension is attached to the pores of the recycled fine aggregate to obtain composite recycled fine aggregate. Cement, silica fume, and slag are added to polycarboxylate superplasticizer according to the mass ratio to prepare the basic cementitious material; The base gel material and the inner functional component are used to prepare the inner mortar, and the base gel material and the outer functional component are used to prepare the outer mortar. The outer and inner layers of mortar are poured in layers, and a silane coupling agent is sprayed at the contact interface to remove air bubbles. After the two layers are fully bonded together, the required high-strength recycled concrete mortar is formed.

5. The method for preparing high-strength recycled concrete mortar according to claim 4, characterized in that, The process of melting pretreated paraffin into the layered pores of expanded graphite and encapsulating it with aerogel microcapsules to form aerogel-coated PCM microcapsules includes: placing paraffin in a 60°C vacuum drying oven to dehydrate, mixing paraffin and expanded graphite in an 80°C oil bath at a mass ratio of 7:3, and stirring until the paraffin is completely melted and penetrates into the expanded pores of the expanded graphite. The mixture of paraffin and expanded graphite is transferred to a vacuum impregnation tank and kept under a negative pressure of 0.8-1.4 MPa for 90-110 minutes to obtain the shaped PCM. Tetraethyl orthosilicate, ethanol, and water were added to 0.1 mol / L hydrochloric acid to adjust the pH to 3.0, and stirred to form a silica sol. The shaped PCM was broken into particles of 50-100 μm and added to the silica sol. The particles were then dispersed by ultrasonication, followed by the addition of ammonia water to adjust the pH to 7.8-8.

0. The mixture was then gelled in a water bath to form aerogel-coated PCM microcapsules.

6. The method for preparing high-strength recycled concrete mortar according to claim 4, characterized in that, The process of forming silanol groups from aerogel particles to form modified aerogel particles includes: Aerogel particles with a particle size of 100-200μm are selected, and 0.5% by mass of silane coupling agent is added. The mixture is then mixed in a planetary ball mill and dried in an oven at 60-80℃ to hydrolyze the coupling agent to form silanol groups, thus forming improved aerogel particles.

7. The method for preparing high-strength recycled concrete mortar according to claim 4, characterized in that, The process of removing the weakly alkaline mortar layer adhering to the surface of recycled fine aggregate obtained from waste concrete, and then adhering it to the pores of the recycled fine aggregate with silica fume suspension to obtain composite recycled fine aggregate, includes: Waste concrete is crushed and screened to obtain 0-5mm recycled fine aggregate. The recycled fine aggregate is soaked in 5% hydrochloric acid solution for 30 minutes at a solid-liquid ratio of 1:3, washed with water until pH=7, and then the aggregate is added to 10% silica fume suspension with silica fume particle size of 0.1-1μm. The aggregate is then impregnated under vacuum negative pressure of 0.6-1.0Mpa for 20-30 minutes. After removal, it is dried at 90-105℃, and the silica fume forms a dense coating with a thickness of 2-5μm, forming composite recycled fine aggregate.

8. The method for preparing high-strength recycled concrete mortar according to claim 4, characterized in that, The method of adding cement, silica fume, and slag to polycarboxylate superplasticizer according to the mass ratio to prepare a basic cementitious material includes: Slag is ball-milled to a specific surface area of ​​410-450 m² 2 / kg, mix cement, silica fume and slag in a mass ratio of 65:10:25 to prepare a cementitious material, add 0.6% of polycarboxylate superplasticizer by mass of the total cementitious material, dry mix until uniform, and prepare the basic cementitious material.

9. The method for preparing high-strength recycled concrete mortar according to claim 4, characterized in that, The step of preparing an inner layer mortar by combining a base gel material with the inner layer functional components, and preparing an outer layer mortar by combining a base gel material with the outer layer functional components, includes: Add the following components to a mixer: 18%–21% base gel material and 52%–63% composite recycled fine aggregate; 15%–20% PCM microcapsules; 1%–2% polycarboxylate superplasticizer; and 3%–5% modified aerogel particles. First, dry mix the mixture in a mixer, then add water at a water-cement ratio of 1:0.38 and switch to wet mixing to form the inner layer mortar. Mix 26%–30% of the base gel material and 12%–18% of the modified aerogel particles in a planetary mixer for 5–10 minutes. Add 40.2%–48.6% of the composite recycled fine aggregate and continue mixing for 3–7 minutes to form a stable aggregate encapsulation structure. Add water to adjust the water-cement ratio to 0.35 and stir. Add 15%–20% of the PCM microcapsules and 0.4%–0.8% of the polycarboxylate superplasticizer. After high-speed stirring, an outer mortar layer is formed.

10. The method for preparing high-strength recycled concrete mortar according to claim 9, characterized in that, The process involves pouring the outer and inner layers of mortar in layers, spraying a silane coupling agent at the contact interface, and removing air bubbles. After the two layers are fully bonded at the interface, the desired high-strength recycled concrete mortar is formed. This includes: Pour the inner layer of mortar to 60% of the height of the test mold, and vibrate it with an immersion vibrator to remove air bubbles. 1-1.5 hours before the inner layer of mortar has initially set, pour the outer layer of mortar to the top of the test mold, and vibrate it again. Spray 0.5% silane coupling agent at the interface between the two mortar layers.

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