A high-performance lightweight building material, its preparation method and application

Abstract

This invention relates to the field of building materials technology, specifically to a high-performance lightweight building material, its preparation method, and its application. The preparation method of the high-performance lightweight building material includes the following steps: heating deionized water, adding chitosan powder and stirring, then adding nano-hydroxyapatite for ultrasonic dispersion, and finally adding calcium chloride solution and stirring to obtain a nano-hydroxyapatite-chitosan solution; sorting, crushing, surface cleaning, and weak slurry stripping of waste concrete, then adding it to the nano-hydroxyapatite-chitosan solution for vibration impregnation treatment to obtain recycled coarse aggregate; finally, mixing the recycled coarse aggregate with expanded perlite to obtain multi-graded aggregate; stirring the multi-graded aggregate, adding cement and fly ash for dry mixing, and finally adding a water-soluble water-reducing agent and stirring to obtain the lightweight building material. The lightweight building material prepared by this invention can achieve a strength grade of C40 or higher.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a high-performance lightweight building material, its preparation method, and its application. Background Technology

[0002] Waste concrete is a major component of construction waste, which mainly includes cement hydration products such as calcium silicate gel, calcium hydroxide, ettringite, unhydrated cement particles and pore structures, natural crushed stone or pebbles, natural sand, metal objects such as steel bars and wires, external pollutants such as soil, wood, and plastics, and cement paste adhering to the surface.

[0003] With the rise of recycled aggregates from waste concrete, research institutions and universities are conducting related research projects to explore their application in concrete. For example, the China Academy of Building Research, Tsinghua University, and Peking University are all carrying out related research and experiments. Meanwhile, some local governments have also introduced policies to encourage the use of recycled aggregates, promoting their application in concrete. For instance, the construction of parks used a large amount of construction waste aggregates, which were used to pave park roads, plazas, and parking lots, as well as to create subgrades for flower beds and tree pits. During the Shanghai World Expo, the construction of the Expo Park also used a large amount of construction waste aggregates, which were used to create foundation subgrades for temporary buildings, road paving, and landscaping. In recent years, the construction of the Guangzhou Metro has also used construction waste aggregates, which were used to construct the walls and floors of subway stations, as well as tunnel linings.

[0004] However, recycled aggregates from construction waste are mostly used in road graded crushed stone layers, water-stabilized materials, recycled bricks, blocks, etc. The workability, mechanical properties, and durability of recycled aggregate concrete are inferior to those of ordinary concrete. It is only used in low-grade non-structural parts, with strength grades mainly below C30. There is not much systematic research on its durability, and the construction industry still has concerns about the application effect of recycled aggregate concrete. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-performance lightweight building material, its preparation method, and its application. This invention involves adding treated waste concrete into a nano-hydroxyapatite-chitosan solution for treatment and mixing it with expanded perlite to obtain multi-graded aggregate, which is then used to prepare a lightweight building material. This lightweight building material can achieve a strength grade of C40 or higher.

[0006] Therefore, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides, in optional embodiments, a method for preparing a high-performance lightweight building material, comprising the following steps:

[0008] S1: After heating deionized water, add chitosan powder and stir to obtain a transparent colloid. Then add nano hydroxyapatite and disperse it ultrasonically. Finally, add calcium chloride solution dropwise and stir to obtain nano hydroxyapatite-chitosan solution.

[0009] S2: After sorting, crushing, surface cleaning and weak slurry stripping of waste concrete, it is added to nano hydroxyapatite-chitosan solution for vibration impregnation treatment to obtain recycled coarse aggregate. Finally, the recycled coarse aggregate is mixed with expanded perlite to obtain multi-grade aggregate.

[0010] S3: After mixing the multi-graded aggregate, add cement and fly ash for dry mixing, and finally add water-reducing agent soluble in water for mixing to obtain lightweight building materials.

[0011] In this invention, nano-hydroxyapatite (n-HAP) can undergo ion exchange with calcium hydroxide (CH), a cement hydration product, to generate carbon hydroxyapatite (C-HAP) crystals. Through lattice matching, these crystals form strong chemical bonds with the aggregate surface. The amino (-NH2) and hydroxyl (-OH) groups on the chitosan molecular chain can be adsorbed onto the aggregate surface via hydrogen bonds, forming an organic-inorganic interpenetrating network with the n-HAP particles, filling the pores. Furthermore, after mixing recycled coarse aggregate with expanded perlite particles, the adhesive encapsulation effect of chitosan can be utilized to form a "hard core-soft shell" composite aggregate unit.

[0012] In this invention, calcium chloride promotes calcium ion bridging between chitosan molecular chains, forming an elastic gel layer and alleviating interfacial stress concentration between recycled aggregate and cementitious materials. Chitosan undergoes partial deprotonation in an alkaline environment, allowing it to form chemical graft chains with the CSH gel generated during cement hydration, thereby enhancing interfacial bonding strength.

[0013] Preferably, in step S1, the mass fraction of chitosan in the nano-hydroxyapatite-chitosan solution is 1-2%, the mass fraction of nano-hydroxyapatite is 3-5%, and the mass fraction of calcium chloride is 0.5-1%; and / or, the concentration of the calcium chloride solution is 4-6%. The temperature of the heated deionized water is 35-45℃; and / or, after adding the chitosan powder, the stirring time is 20-40 min, and the rotation speed is 450-550 r / min. The ultrasonic dispersion time is 15-25 min, and the frequency is 35-45 kHz; and / or, after adding the calcium chloride solution, the stirring time is 8-12 min.

[0014] Preferably, in step S2, the temperature of the vibration impregnation treatment is 50-70℃, and the time is 30-60 min; and / or, the frequency of the vibration impregnation treatment is 15-25 Hz. The volume ratio of the recycled coarse aggregate to the expanded perlite is 6-7:3-4; and / or, the particle size of the recycled coarse aggregate is 10-30 mm, and the particle size of the expanded perlite is 2-5 mm.

[0015] Preferably, in step S3, the stirring time for the multi-graded aggregate is 20-40 seconds; and / or, the dry mixing time is 1-2 minutes; and / or, the stirring time for adding the water-soluble water-reducing agent is 2-3 minutes.

[0016] Preferably, the mass ratio of the multi-graded aggregate, cement, fly ash, water-reducing agent, and water is 1400-1500:350-400:80-100:6-8:160-180; and / or, the water-reducing agent is a polycarboxylate water-reducing agent.

[0017] Secondly, in an optional embodiment, the present invention provides a high-performance lightweight building material obtained by the above-described preparation method.

[0018] Thirdly, in an optional embodiment, the present invention provides an application of the aforementioned high-performance lightweight building material in prefabricated building wall panels.

[0019] Compared with the prior art, the present invention has one of the following beneficial effects:

[0020] 1. This invention involves adding treated waste concrete into a nano-hydroxyapatite-chitosan solution for treatment, and then mixing it with expanded perlite to obtain multi-graded aggregates, which are then used to prepare lightweight building materials. The strength grade of these lightweight building materials can reach C40 or higher. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the process for preparing building materials according to Embodiment 1 of the present invention;

[0023] Figure 2 Here is a photograph of the recycled aggregate prepared in Example 1 of this invention;

[0024] Figure 3 This is a physical image of the building materials prepared in Embodiment 1 of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] In the following examples and comparative examples, the water-reducing agent was a polycarboxylate water-reducing agent, purchased from Shandong Huangteng Building Materials Co., Ltd., model HT polycarboxylate high-performance water-reducing agent, and the cement was PO 42.5 cement.

[0027] The technical solution of the present invention will be described below with reference to embodiments.

[0028] Example 1

[0029] See Figure 1 This embodiment provides a method for preparing building materials, including the following steps:

[0030] S1: After removing metal (steel bars, wires), wood, and plastic debris from the waste concrete, the aggregate is fed into a jaw crusher and crushed to a particle size ≤80mm. The crushed aggregate is then poured into a drum washing machine and rotated at 20r / min while being washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is then removed using mechanical grinding to obtain recycled aggregate. See [link to relevant documentation]. Figure 2 .

[0031] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0032] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 60℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0033] S4: After mixing 1450kg of multi-graded aggregate for 30 seconds, add 380kg of cement and 90kg of fly ash and dry mix for 1 minute. Finally, slowly add 7kg of water-reducing agent dissolved in 170kg of water and mix for 3 minutes to obtain the building material. (See attached image) Figure 3 .

[0034] Example 2

[0035] This embodiment provides a method for preparing building materials, including the following steps:

[0036] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0037] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0038] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 50°C, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45 minutes. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5 minutes to obtain multi-grade aggregate.

[0039] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0040] Example 3

[0041] This embodiment provides a method for preparing building materials, including the following steps:

[0042] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0043] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0044] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 70℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0045] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0046] Example 4

[0047] This embodiment provides a method for preparing building materials, including the following steps:

[0048] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0049] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0050] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 60℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0051] S4: After mixing 1400kg of multi-grade aggregate for 30s, add 400kg of cement and 80kg of fly ash and dry mix for 1min. Finally, dissolve 8kg of water-reducing agent in 160kg of water and slowly add it, stirring for 3min to obtain the building material.

[0052] Example 5

[0053] This embodiment provides a method for preparing building materials, including the following steps:

[0054] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0055] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0056] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 60℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0057] S4: After mixing 1500kg of multi-grade aggregate for 30s, add 350kg of cement and 100kg of fly ash and dry mix for 1min. Finally, dissolve 6kg of water-reducing agent in 180kg of water and slowly add it, stirring for 3min to obtain the building material.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing a building material, including the following steps:

[0060] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0061] S2: Add recycled aggregate (average particle size of 10-30mm) and expanded perlite (average particle size of 2-5mm) to a mixer (speed of 300r / min) at a volume ratio of 6:4 and mix for 5 minutes to obtain multi-graded aggregate.

[0062] S3: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing a building material, including the following steps:

[0065] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0066] S2: After heating deionized water to 40°C, slowly add chitosan powder and stir at 500 r / min for 30 min to obtain a chitosan solution (the mass fraction of chitosan in the solution is 1.5%).

[0067] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the chitosan solution obtained in step S2, turn on the constant temperature water bath to 60℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0068] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0069] Comparative Example 3

[0070] This comparative example provides a method for preparing a building material, including the following steps:

[0071] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0072] S2: Add nano-hydroxyapatite powder to deionized water and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20 minutes to obtain nano-hydroxyapatite solution (the mass fraction of nano-hydroxyapatite in the solution is 4%).

[0073] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano hydroxyapatite solution obtained in step S2, turn on the constant temperature water bath to 60℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0074] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0075] Comparative Example 4

[0076] This comparative example provides a method for preparing a building material, including the following steps:

[0077] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0078] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to ultrasonically disperse for 20min to obtain a nano hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5% and the mass fraction of nano hydroxyapatite is 4%).

[0079] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 60℃, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0080] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0081] Comparative Example 5

[0082] This comparative example provides a method for preparing a building material, including the following steps:

[0083] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0084] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0085] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 45°C, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until the surface is dry to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0086] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0087] Comparative Example 6

[0088] This comparative example provides a method for preparing a building material, including the following steps:

[0089] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0090] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0091] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano-hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 75°C, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45min. Then drain the solution and dry it until the surface is dry to obtain recycled coarse aggregate (average particle size of 10-30mm). Finally, add the recycled coarse aggregate and expanded perlite (average particle size of 2-5mm) to the mixer (speed of 300r / min) at a volume ratio of 6:4 and stir for 5min to obtain multi-grade aggregate.

[0092] S4: After mixing 1450kg of multi-graded aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0093] Comparative Example 7

[0094] This comparative example provides a method for preparing a building material, including the following steps:

[0095] S1: After removing metal (steel bars, wires), wood and plastic and other debris from the waste concrete, it is fed into a jaw crusher to be crushed to a particle size ≤80mm. Then, the crushed aggregate is poured into a drum washing machine and rotated at a speed of 20r / min. At the same time, it is washed with a high-pressure water gun for 3-5 minutes to remove surface dirt and laitance. The cement paste on the surface of the aggregate is peeled off by mechanical grinding to obtain recycled aggregate.

[0096] S2: After heating deionized water to 40℃, slowly add chitosan powder and stir at 500r / min for 30min to form a transparent colloid. Add nano-hydroxyapatite powder to the transparent colloid and turn on the ultrasonic disperser (frequency 40kHz) to disperse for 20min to form a suspension. Finally, add 5% calcium chloride solution and stir for 10min to obtain nano-hydroxyapatite-chitosan solution (the mass fraction of chitosan in the solution is 1.5%, the mass fraction of nano-hydroxyapatite is 4%, and the mass fraction of calcium chloride is 1%).

[0097] S3: Add the recycled aggregate obtained in step S1 to the impregnation tank, pour in the nano hydroxyapatite-chitosan solution obtained in step S2, turn on the constant temperature water bath to 60°C, and at the same time start the low frequency vibrator (frequency of 20Hz) for impregnation treatment for 45 minutes. Then drain the solution and dry it until there is no water on the surface to obtain recycled coarse aggregate (average particle size of 10-30mm).

[0098] S4: After mixing 1450kg of recycled coarse aggregate for 30s, add 380kg of cement and 90kg of fly ash and dry mix for 1min. Finally, dissolve 7kg of water-reducing agent in 170kg of water and slowly add it, stirring for 3min to obtain the building material.

[0099] Experimental Example

[0100] The apparent density (accurate to 10 kg / m³) of the building materials prepared in Examples 1-5 and Comparative Examples 1-7 was determined according to the method in GB / T 50080-2016. 3 The apparent densities of the building materials prepared in Examples 1-5 and Comparative Examples 1-6 were tested and found to be 1680 kg / m³. 3 1690kg / m 3 1670kg / m 3 1710kg / m 3 1650kg / m 3 1950kg / m 3 1820kg / m 3 1880kg / m 3 1750kg / m 3 1730kg / m 3 and 1700kg / m 3 All are ≤1950kg / m 3 It belongs to lightweight building materials. The apparent density of the building material prepared in Comparative Example 7 is 2200 kg / m³. 3 Since it is not a lightweight building material, the building material prepared in Comparative Example 7 will not be tested for compressive strength, flexural strength and strength grade in subsequent experiments.

[0101] The building materials prepared in Examples 1-5 and Comparative Examples 1-6 were tested for compressive strength, flexural strength, and strength grade. The specific methods are as follows:

[0102] Compressive strength, flexural strength, and strength grade were all tested according to the methods in GB / T 50081-2019. The results are shown in Table 1.

[0103] Table 1. Compressive strength, flexural strength, and strength grade of building materials in Examples 1-5 and Comparative Examples 1-6

[0104]

[0105]

[0106] Table 1 shows that the building materials prepared in Examples 1-5 all have a compressive strength greater than 45 MPa. Compared to Comparative Example 1 (i.e., traditional recycled building materials), their strength grade has increased from C25 to C45, showing a significant improvement. Compared to Comparative Examples 2-3, it can be seen that the organic-inorganic interconversion network formed by nano-hydroxyapatite and chitosan is key to improving the strength of the building materials. Compared to Comparative Example 4, the addition of calcium chloride solution during the preparation of the nano-hydroxyapatite-chitosan solution promotes calcium ion bridging between chitosan molecular chains, forming an elastic gel layer, alleviating the interfacial stress concentration between recycled aggregate and cementitious material, and improving the strength of the building materials. Compared to Comparative Examples 5-6, it can be seen that controlling the temperature during vibration impregnation treatment can further improve the strength of the building materials.

[0107] Although the principles of the present invention have been described in detail above with reference to preferred embodiments, those skilled in the art should understand that the above embodiments are merely illustrative explanations of the implementation of the present invention and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute a limitation on the scope of the present invention. Any obvious changes, such as equivalent transformations or simple substitutions, based on the technical solutions of the present invention without departing from the spirit and scope of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance lightweight building material, characterized in that, Includes the following steps: S1: After heating deionized water, add chitosan powder and stir to obtain a transparent colloid. Then add nano hydroxyapatite and disperse it ultrasonically. Finally, add calcium chloride solution dropwise and stir to obtain nano hydroxyapatite-chitosan solution. S2: After sorting, crushing, surface cleaning and weak slurry stripping of waste concrete, it is added to nano hydroxyapatite-chitosan solution for vibration impregnation treatment to obtain recycled coarse aggregate. Finally, the recycled coarse aggregate is mixed with expanded perlite to obtain multi-grade aggregate. S3: After mixing the multi-graded aggregate, add cement and fly ash for dry mixing, and finally add water-reducing agent soluble in water for mixing to obtain lightweight building materials.

2. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, In step S1, the mass fraction of chitosan in the nano-hydroxyapatite-chitosan solution is 1-2%, the mass fraction of nano-hydroxyapatite is 3-5%, and the mass fraction of calcium chloride is 0.5-1%; and / or, The concentration of the calcium chloride solution is 4-6%.

3. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, In step S1, the temperature of the heated deionized water is 35-45℃; and / or, After adding chitosan powder, the stirring time is 20-40 minutes and the stirring speed is 450-550 r / min.

4. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, In step S1, the ultrasonic dispersion time is 15-25 min, and the frequency is 35-45 kHz; and / or, After adding the calcium chloride solution, the stirring time is 8-12 minutes.

5. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, In step S2, the vibration impregnation treatment is performed at a temperature of 50-70°C for 30-60 minutes; and / or, The frequency of the vibration impregnation treatment is 15-25Hz.

6. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, In step S2, the volume ratio of the recycled coarse aggregate to expanded perlite is 6-7:3-4; and / or, The recycled coarse aggregate has a particle size of 10-30 mm, and the expanded perlite has a particle size of 2-5 mm.

7. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, In step S3, the mixing time for the multi-graded aggregate is 20-40 seconds; and / or, The dry mixing time is 1-2 minutes; and / or, Add the water-soluble water-reducing agent and stir for 2-3 minutes.

8. The method for preparing high-performance lightweight building materials according to claim 1, characterized in that, The mass ratio of the multi-graded aggregate, cement, fly ash, water-reducing agent, and water is 1400-1500:350-400:80-100:6-8:160-180; and / or, The water-reducing agent is a polycarboxylate water-reducing agent.

9. A high-performance lightweight building material, characterized in that, It is obtained by the preparation method described in any one of claims 1-8.

10. The application of the high-performance lightweight building material of claim 9 in prefabricated building wall panels.

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