Method for improving the reactivity of recycled GFRP powder geopolymer cementitious materials

Abstract

The invention discloses a method for improving the reactivity of recycled GFRP powder geopolymer gelling material, comprising the following steps: sieving GFRP waste powder through 400 meshes in a laboratory to retain pure GFRP powder; drying the GFRP powder in an oven, and putting the GFRP powder into a laboratory ball mill after cooling, wherein the grinding medium is steel balls; taking 1472kg / m 3 、Na2SiO3861.4kg / m 3 、NaOH139.5kg / m 3 、Water 176.6kg / m 3 GFRP geopolymer cementitious material test blocks were cast at different milling times (0min, 30min, 60min and 90min) and curing temperatures (25°C, 40°C, 60°C and 80°C). The present invention improves the mechanical properties of GFRP powder geopolymer, and recycling GFRP powder in the manner of preparing geopolymer can reduce resource consumption and energy consumption.

Description

Technical Field

[0001] The present invention belongs to the field of green and low-carbon materials, and specifically relates to improving the reactivity of a single recycled GFRP powder geopolymer cementitious material, and improving its mechanical properties through mechanical activation and temperature control. The impact of GFRP geopolymer on the environment is evaluated using the life cycle assessment (LCA) method, and is compared with the impact of cement on the climate. Background Art

[0002] With the increasing application of glass fiber composites (GFRP) in construction, wind energy and transportation, the management of GFRP waste has become an urgent concern in many countries. At present, the disposal methods of thermosetting resin-based GFRP waste are mainly incineration and landfill, which has caused great damage to the ecological environment. Because glass fibers contain silicon, aluminum, and calcium oxides, they can react with alkaline solutions to generate silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons, which can be used to prepare geopolymers. Previous studies by the research team have shown that with the highest compressive strength as the goal, the early strength development of a single GFRP geopolymer cementitious material is slow and its maximum compressive strength at 28 days is 7.13MPa. [1-3] .

[0003] The main methods to improve the reactivity of aluminosilicates are mechanical activation, thermal activation, physical separation and chemical activation. Mechanical activation is the most commonly used method, which is defined as the process of improving the reactivity of materials by grinding solid particles without changing the chemical composition or structure. Thermal activation refers to the process of increasing the reaction rate by increasing the temperature of the reaction system. Physical separation obtains purer solid materials through screening, gravity separation, centrifugal separation, etc. to improve reactivity and reduce the impact of impurities. Chemical activation is a method of improving the reactivity of a material system by adding admixtures. This patent aims to improve the activity of a single GFRP powder geopolymer, including the effects of particle size and temperature on its activity.

[0004] Life Cycle Assessment (LCA) is a powerful tool for environmental management and analysis. It can quantify resource consumption and environmental emissions from the perspective of the entire product life cycle, and objectively evaluate the impact of these consumption and emissions on natural resources and the ecological environment. The GWP value is a very important environmental assessment indicator that can help people evaluate and compare the hazards of different chemicals to global warming. For industries and policymakers involved in greenhouse gas emissions, reducing and lowering the GWP value is one of the important strategies to achieve environmental protection and climate change goals.

[0005] This patent uses recycled GFRP waste powder to prepare geopolymers, and improves the reactivity of GFRP geopolymers by changing the particle size and temperature. It not only improves the mechanical properties of GFRP powder geopolymers, but also uses the method of preparing geopolymers to recycle GFRP powder to reduce resource consumption and energy consumption. It has significant economic, environmental and social benefits, and promotes the development of engineering structures towards "high efficiency, durability and ecology". Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the reactivity of recycled GFRP powder geopolymer cementitious materials in view of the deficiencies in the prior art, consider the mechanical activation time and temperature control, explore its influence on the mechanical properties (compressive strength, flexural strength) of the geopolymer reaction, test the compressive and flexural strengths according to the "Test Method for Strength of Cement Mortar" (GB / T 17671-2021), and explore the evolution mechanism of GFRP powder in combination with phase and microscopic analysis. The method has high accuracy and strong applicability.

[0007] The technical solution adopted by the present invention is: a method for improving the reactivity of recycled GFRP powder geopolymer gelling material, comprising the following steps:

[0008] Step 1: The GFRP waste powder is sieved through 400 meshes in the laboratory by a physical separation method to remove impurities and retain pure GFRP powder.

[0009] The chemical composition of the GFRP powder is: SiO2 is 33.71%, Al2O3 is 10.62%, CaO is 20.57%, MgO is 3.45%, Fe2O3 is 0.63%, SO3 is 0.98%, K2O is 0.32%, Na2O is 0.21%, TiO2 is 0.51%, and TOL is 28.12%.

[0010] Step 2: Dry the GFRP powder in an oven, and after cooling, put it into a laboratory ball mill with steel balls as the grinding medium. Mill the powder at 200 rpm for 30 min, 60 min, and 90 min respectively.

[0011] Step 3: Take GFRP powder 1472kg / m 3 、Na2SiO3861.4 kg / m 3 、NaOH139.5 kg / m 3 、Water 176.6kg / m 3 GFRP geopolymer cementitious material test blocks were cast at different ball milling times (0min, 30min, 60min and 90min) and curing temperatures (25℃, 40℃, 60℃ and 80℃).

[0012] Step 4: Place the GFRP geopolymer cementitious material test block in a 40℃ curing box for curing and demoulding. Then, place the samples in a standard curing room at 25℃ and high-temperature steam curing boxes at 40℃, 60℃, and 80℃, respectively, and cure them at a relative humidity of 100% to the corresponding age for testing. The 28d sample is cured in a variable temperature, that is, high-temperature curing for 7d and standard curing for 28d.

[0013] Step 5: Based on the LCA method, the environmental impact of the entire life cycle of GFRP geopolymer is evaluated by calculating the amount of CO2 gas generated during the entire life cycle of GFRP geopolymer and its climate change potential (GWP) and comparing it with the GWP of ordinary Portland cement.

[0014] Furthermore, in step 2, the GFRP powder is placed in an oven for drying at a temperature of 90±5°C.

[0015] Furthermore, in the step 2, the ratio of GFRP powder to steel ball is 1:10.

[0016] Furthermore, the composition of the recovered GFRP powder geopolymer in step 3 is as shown in Table 1:

[0017] Table 1

[0018]

[0019] Further, GFRP powder 1472kg / m 3 、Na2SiO3861.4 kg / m 3 、NaOH139.5 kg / m 3 、Water 176.6kg / m 3 The casting of GFRP geopolymer cementitious material test blocks at a ball milling time of 30 minutes and a curing temperature of 60°C has the most significant improvement on the compressive strength of GFRP geopolymer cementitious material.

[0020] Beneficial effects of the present invention:

[0021] 1. Performance optimization

[0022] The present invention obtains the optimal conditions for improving the activity of alkali-activated single GFRP geopolymer cementitious materials. When ball milling for 30 minutes and the curing temperature is 60°C, the improvement of the compressive strength of the GFRP geopolymer cementitious materials is most significant and has the highest economic benefit. It is 3.7 times the compressive strength when not ball milled and not high-temperature cured. High-temperature curing has a more significant effect on its compressive strength. However, too high a temperature and too long a curing time will cause more microcracks inside the specimen, which is not conducive to its strength development.

[0023] 2. Energy saving and environmental protection

[0024] There is no need to separate the fibers and resins when recycling GFRP powder. Under the action of alkali, a gel is generated, which can partially replace cement-based cementitious materials and effectively solve the problem of the difficulty in recycling GFRP. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The working performance diagram of recycled GFRP powder geopolymer at different ball milling times;

[0026] Figure 2 The compressive strength diagram of recycled GFRP powder geopolymer at different ball milling times and different curing temperatures;

[0027] Figure 3 The flexural strength diagram of recycled GFRP powder geopolymer at different ball milling times and different curing temperatures;

[0028] Figure 4 Microscopic images of recycled GFRP powder geopolymer at different ball milling times and different curing temperatures. DETAILED DESCRIPTION

[0029] The specific implementation modes of the present invention are described in detail below with reference to the accompanying drawings.

[0030] Example 1: Take GFRP powder (1472kg / m 3 ), alkali activator (water glass 861.4kg / m 3 , sodium hydroxide 139.5kg / m 3 ), water (176.6kg / m 3 ).

[0031] like Figure 1 The working performance test shows that as the ball milling time increases, the fluidity begins to decrease. Ball milling for 30 minutes, 60 minutes, and 90 minutes reduces the fluidity by 4%, 6%, and 9%, respectively, but the effect of ball milling time on fluidity is limited. The ball milling time has little effect on the initial setting time of the slurry. When not ball milled, its initial setting time is 105 minutes and the final setting time is 217 minutes; when the ball milling time is 30 minutes, its initial setting time is 96 minutes and the final setting time is 195 minutes. Further increasing the setting time, the setting rate slows down and the setting time is close.

[0032] like Figure 2The compressive strength test shows that under the same 60℃ variable temperature curing condition, the compressive strength of the specimen before ball milling is 20.24MPa after 28 days of curing, and the specimen after ball milling for 30 minutes reaches 26.45MPa after curing, and the compressive strength increases by 30.7%. Obviously, the mechanical properties before and after ball milling are greatly affected. However, the ball milling time has limited effect on the strength improvement. The compressive strength of ball milling for 90 minutes is only 1.7% higher than that of ball milling for 30 minutes. Under the same ball milling condition of 30 minutes, the 28d compressive strength under standard curing conditions is 8.24MPa, and the compressive strength at 60℃ curing is 3.2 times that of standard curing. However, excessive temperature and excessive curing time will cause more microcracks inside the specimen, resulting in reduced compressive strength.

[0033] like Figure 3 The flexural strength test shows that the flexural strength matches the compressive strength well: the samples ball-milled for 30 minutes, 60 minutes and 90 minutes show the best bending performance when cured for 28 days. The flexural strength of the sample ball-milled for 90 minutes decreases, and it is obvious that the reactivity of the material increases after ball milling. Under standard curing, the flexural strength is measured at 28 days. With the increase of curing temperature, under the conditions of curing for 28 days at 40℃ and 80℃, the compressive strength of GFRP powder geopolymer cementitious material is 58% and 36% of the compressive strength under 60℃ curing conditions, respectively.

[0034] like Figure 4 As shown in the microscopic picture, many long glass fiber rods can be observed in the microstructure of the cementitious material before ball milling, and the long glass fiber rods cannot be activated. As the ball milling time increases, the number of long fiber rods in the cementitious material decreases. Obviously, ball milling can change the length of the glass fiber rods, resulting in a smaller particle size, increasing their specific surface area and reaction activity, making it easier for Si and Al ions to leach out. The unreacted glass fiber rods and glass fiber particles can be clearly seen in the specimens cured at 20°C. As the curing temperature increases, the geopolymerization reaction rate also increases, and the geopolymer base is gradually formed, which is generally considered to be NASH gel and CASH / CSH gel. However, too high a temperature (80°C) and too long a curing time will cause more microcracks and pores inside the specimen, which is not conducive to its strength development.

[0035] Table 2 is a comparison of the global warming potential of GFRP geopolymer cementitious materials and silicate cement, with "1t·GFRP geopolymer cementitious materials, strength of 26.45MPa" as the functional unit, compared with silicate cement with a strength grade of 32.5MPa. The strength ratio is 1.22, and the production of 1t of silicate cement produces 0.935t·CO2·eq, and the production of 1t·GFRP geopolymer at a high temperature of 60℃ and grinding for 30min produces 0.724t·CO2·eq. The GWP / mass / strength ratio of GFRP geopolymer cementitious materials is reduced by 12.1% compared with cement materials.

[0036] Table 2

[0037]

[0038] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and deformations of these embodiments within the scope of the principles and technical ideas of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for improving the reactivity of recycled GFRP powder geopolymer gelling material, characterized in that: The following steps are involved: Step 1: sieving the GFRP waste powder through 400 mesh in the laboratory by physical separation to remove impurities and retain pure GFRP powder; The chemical composition of the GFRP powder is: SiO2 is 33.71%, Al2O3 is 10.62%, CaO is 20.57%, MgO is 3.45%, Fe2O3 is 0.63%, SO3 is 0.98%, K2O is 0.32%, Na2O is 0.21%, TiO2 is 0.51%, and TOL is 28.12%; Step 2: Dry the GFRP powder in an oven, cool it, and put it into a laboratory ball mill with steel balls as the grinding medium; mill it at 200 rpm for 30 min, 60 min, and 90 min respectively; Step 3: Take GFRP powder 1472kg / m 3 、Na2SiO3861.4 kg / m 3 、NaOH139.5 kg / m 3 、Water 176.6kg / m 3 , casting GFRP geopolymer cementitious material test blocks at 0min, 30min, 60min and 90min ball milling time and 25℃, 40℃, 60℃ and 80℃ curing temperature; Step 4: Place the GFRP geopolymer cementitious material test block in a 40°C curing box for curing and demoulding; then place the samples in a standard curing room at 25°C and high-temperature steam curing boxes at 40°C, 60°C, and 80°C, respectively, and cure them at a relative humidity of 100% until the corresponding age is tested, wherein the 28-day sample is cured in a variable temperature, i.e., high-temperature curing for 7 days and standard curing for 28 days; Step 5: Based on the LCA method, the environmental impact of the GFRP geopolymer over its entire life cycle is evaluated by calculating the amount of CO2 gas and climate change potential generated by the GFRP geopolymer over its entire life cycle and comparing it with the GWP of ordinary Portland cement; Take GFRP powder 1472kg / m 3 、Na2SiO3861.4 kg / m 3 、NaOH139.5 kg / m 3 、Water 176.6kg / m 3 The compressive strength of GFRP geopolymer cementitious material was improved by casting the GFRP geopolymer cementitious material block at a ball milling time of 30 minutes and a curing temperature of 60°C, which was 3.7 times the compressive strength of the GFRP geopolymer cementitious material without ball milling and high-temperature curing.

2. A method for improving the reactivity of recycled GFRP powder geopolymer gelling material according to claim 1, characterized in that: In the step 2, the GFRP powder is placed in an oven for drying at a temperature of 90±5°C.

3. A method for improving the reactivity of recycled GFRP powder geopolymer gelling material according to claim 1, characterized in that: In the step 2, the ratio of GFRP powder to steel ball is 1:

10.

4. A method for improving the reactivity of recycled GFRP powder geopolymer gelling material according to claim 1, characterized in that: The composition of the recovered GFRP powder geopolymer in step 3 is shown in Table 1: Table 1

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