Geopolymer mucilage for cold recycling of asphalt pavement and preparation method of geopolymer mucilage

Abstract

The invention provides geopolymer mucilage for asphalt pavement cold regeneration and a preparation method thereof, belongs to the technical field of pavement material preparation, and solves the problems that the coagulation time of a current coal ash slag-based geopolymer is too short, and a retarder affects the strength of the geopolymer and is difficult to replace cement for asphalt pavement cold regeneration. According to the technical scheme, the adhesive cement is prepared from the following components in parts by mass: 100 parts of fly ash, 50 parts of mineral powder, 7 parts of sodium hydroxide, 39.1 parts of liquid sodium silicate, 25.5 parts of water, 6.6 parts of sodium tetraborate and 0.66 part of y-aminopropyltriethoxysilane. The preparation method comprises the following steps: preparing the alkali activator 24 hours in advance, then hydrolyzing sodium tetraborate and y-aminopropyltriethoxysilane in the alkali activator until the solution is clear, finally stirring the precursor at a low speed, adding the solution, and stirring at a high speed to obtain the mucilage. The setting time of the coal ash slag-based geopolymer is prolonged, and the coal ash slag-based geopolymer can replace cement to be used in an asphalt pavement cold regeneration technology and has the application prospects of energy conservation, emission reduction, carbon emission reduction and the like.

Description

Technical Field

[0001] The present application discloses a geopolymer mortar for cold regeneration of asphalt pavement and a preparation method thereof, belonging to the technical field of pavement material preparation. Background Art

[0002] In order to develop green building materials and reduce the carbon footprint in the field of civil engineering, geopolymers have been one of the materials that have been actively studied internationally in recent years. Under the action of alkali or alkali salts, minerals containing aluminosilicates dissolve, and the [SiO 4 ] - 、[AlO 4 ] - Ion clusters and Na + The ion reaction generates a hydration product with a three-dimensional amorphous structure. 4 ] - and [AlO 4 ] - Ion clusters polymerize in an alkaline environment and release free water to form sodium aluminosilicate hydrate. Solid wastes generated by industries such as fly ash, slag, silica fume, high-altitude land, and steel slag are exactly the raw materials of geopolymers. The use of geopolymers not only reduces carbon emissions, but also increases the utilization rate of solid wastes by reducing the consumption of raw materials, which doubles the concept of sustainable green development.

[0003] However, alkali-activated materials currently have problems such as high alkalinity, high shrinkage, and rapid coagulation. For fly ash-based and slag-based geopolymers, the calcium content has a significant impact on the formation process of geopolymers. The essence is that when the content of alkaline oxides (CaO and MgO) in the mineral is higher than that of acidic oxides (SiO 2 and Al 2 O 3 ) content, the calcium-rich phase rapidly hydrates and disintegrates, forming a large amount of gel in a short time, which leads to rapid coagulation and hardening of the slurry. With the increase of calcium content in the raw materials, the mechanical properties of the geopolymer tend to increase first and then decrease. When the product is mainly (C, N)-ASH gel, it is conducive to the development of strength. Fast coagulation time is the main feature of this calcium-based polymer. Although this type of geopolymer exhibits excellent mechanical properties, some studies have found that the initial coagulation time of the material is less than 0.5 hours, and even the final coagulation time does not exceed 1 hour. Of course, it can play a unique advantage in some emergency projects. However, the problem of rapid coagulation of geopolymers limits the application field of this material, expands its limitations, and may even lead to its commercial failure. For example, the cement added in the cold regeneration of asphalt pavement requires that the initial coagulation time cannot be less than 180 minutes and the final coagulation time cannot exceed 360 minutes. This requirement is a huge challenge for fast-coagulating geopolymers.

[0004] A large number of chemical reagents, such as phosphates, borates, alkali metal salts, zinc salts, and sugars, are applied to geopolymers as retarders, and they delay the setting time to varying degrees. However, almost all of these retarders have a negative effect on the mechanical strength of geopolymers. Therefore, it is urgent to find a retarder that can regulate the setting time within a wide range and does not reduce the performance of the original geopolymer materials. Silane coupling agents are applied to composite materials to optimize the compatibility between polymers and organic substances in the composite materials. Research shows that amino silane coupling agents can delay the hydration rate of Portland cement and improve the mechanical properties of mortar. However, the retarding effect of silane coupling agents on geopolymers, especially fly ash and slag-based geopolymers, is not clear, and the retarding mechanism is not yet clear. The influence of coupling agents on other properties of geopolymers has not been confirmed. In addition, geopolymers have a wide range of application fields, and it is necessary to expand and precisely adjust the setting time of geopolymers with high calcium content within the required range.

[0005] In view of this, the present application provides a geopolymer mortar for cold recycling of asphalt pavement and a preparation method thereof. The method uses fly ash slag-based geopolymer as the main cementitious material, and sodium tetraborate and aminopropyltriethoxysilane as retarders, controls the setting time of the mortar to about 180 minutes for initial setting and about 360 minutes for final setting, and does not affect other properties of the geopolymer. It can be used in the cold recycling of asphalt pavement, promoting the development of low-carbon building materials and the recycling of solid waste. Summary of the Invention

[0006] (1) Technical Problem

[0007] Aiming at the problems of the too short setting time of fly ash slag-based geopolymers and the influence of existing retarders on the strength of fly ash slag-based geopolymers, the present application provides a geopolymer mortar for cold recycling of asphalt pavement and a preparation method thereof, solving the problems of low mechanical strength of cold recycled mixtures for asphalt pavement, too short setting time of fly ash slag-based geopolymers, the influence of existing retarders on the properties of geopolymers, and the difficulty in replacing cement for cold recycling of asphalt pavement, which helps to promote the popularization and application of green fly ash slag-based geopolymer materials in cold recycling projects of asphalt pavement.

[0008] (2) Technical Solution

[0009] To solve the problem that the setting time of fly ash slag-based geopolymers is too short and it is difficult to be used in the cold recycling project of asphalt pavement, the present application adopts the following technical solution: A fly ash slag-based geopolymer mortar, including precursor materials: 100 parts of fly ash and 50 parts of slag powder; alkali activator raw materials: 7 parts of sodium hydroxide, 39.1 parts of liquid sodium silicate, 25.5 parts of water, and retarders: 6.6 parts of sodium tetraborate and 0.66 parts of aminopropyltriethoxysilane. The sodium tetraborate and the silane coupling agent synergistically retard the geopolymer mortar and do not reduce the mechanical properties of the material.

[0010] Preferably, the fly ash is primary fly ash.

[0011] Preferably, the mineral powder is S 95 grade slag powder.

[0012] Preferably, the sodium hydroxide is flaky 96%-98% analytically pure sodium hydroxide.

[0013] Preferably, the liquid sodium silicate is a liquid sodium silicate with a degree of 40 Baume and a modulus of 3.2, wherein the silicon dioxide content is 26.2%, the sodium oxide content is 8.3%, and the water content is 65.5%.

[0014] Preferably, the water is ordinary tap water.

[0015] Preferably, the sodium tetraborate is analytically pure anhydrous sodium tetraborate with the molecular formula B 4 O 7 Na 2 .

[0016] Preferably, the silane coupling agent is y-aminopropyltriethoxysilane (APTES); molecular formula: NH 2 (CH 2 ) 3 Si(OC 2 H 5 ) 3 .

[0017] As a preferred embodiment, the mass ratio of fly ash to mineral powder is 2:1, the modulus of the alkali activator is 1.2, the water-binder ratio is 0.3, and the alkali equivalent (solid Na 2 O to cementitious material mass ratio) is 6%, sodium tetraborate accounts for 3% of the mass of the polymer mortar, and APTES accounts for 1% of the mass of the polymer mortar. In this way, the compressive strength of the polymer mortar is the largest, and the setting time is within the range of 180 minutes for initial setting and 360 minutes for final setting.

[0018] Another object of the present application is to provide a laboratory preparation method of the fly ash slag-based geopolymer mortar, comprising the following steps:

[0019] 1) Sodium hydroxide, liquid sodium silicate and water are fully stirred and mixed to form an alkali activator solution, and then the alkali activator is placed in a wide-mouth bottle, sealed and cooled for 24 hours;

[0020] 2) adding a corresponding amount of sodium tetraborate to the alkaline activator prepared in step 1), manually stirring until uniformly mixed, then slowly dropping a corresponding amount of APTES and fully manually stirring until the solution is clear;

[0021] 3) stirring the corresponding mass of mineral powder and fly ash at low speed for 3 minutes, then adding the solution prepared in step 2) and stirring at low speed for 1 minute, and then stirring at high speed for 3 minutes to obtain a mixture;

[0022] 4) Pour the geopolymer mortar prepared in step 3) into a mold, shape it, vibrate it, and put it into a cement curing room for curing. After 24 hours, demould it and put the test piece into a curing box again for curing to a specified age, so as to obtain the fly ash slag-based geopolymer mortar.

[0023] Preferably, in step 3), the low stirring speed is 150-200 rpm, and the high stirring speed is 400-500 rpm. The stirring speed and stirring time mainly control whether the materials are mixed evenly.

[0024] Preferably, the curing in step 4) is performed by standing for 3 days, 7 days and 28 days in a constant temperature and humidity environment at 20°C±3°C and 60%.

[0025] (3) Beneficial effects

[0026] Compared with the prior art, this application has the following beneficial effects:

[0027] (1) The fly ash mineral powder-based geopolymer mortar of the present application uses APTES and sodium tetraborate in combination, so that the setting time can be controlled within the range of 180-360 minutes, which meets the requirements of cold regeneration of pavement to replace cement mortar. Figure 1 As shown in the figure, the boron oxide network affects the connection mode of the skeleton network by forming BO-Si bridges or BO-Al bonds. APTES hydrolyzes in an alkaline environment to produce hydroxyl groups, which react with the hydroxyl groups of the aluminum oxide network through condensation to form cross-linking reactions. In the sample with borax and APTES added at the same time, the boron oxide network introduced by borax is cross-linked with the Si-OH or Si-O-Si network of APTES, which enhances the structural stability of the system and further promotes the retarding effect.

[0028] (2) While ensuring the setting time, the method provided by the present application stabilizes the mechanical properties. Figure 2 As shown, the combined effect of borax and APTES significantly reduced the rate of skeleton network formation, and the retarding mechanism avoided the microstructural defects caused by rapid coagulation, resulting in higher structural uniformity and improved later performance of the geopolymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Fourier transform infrared spectra of implementation examples and comparative examples

[0030] 1-Comparative Example I 2-Comparative Example II 3-Comparative Example III 4-Implementation Example

[0031] Figure 2Comparison of microscopic morphology of implementation example and comparative example

[0032] 1-Comparative Example I 2-Comparative Example II 3-Comparative Example III 4-Implementation Example DETAILED DESCRIPTION

[0033] The present application is further described in detail below in conjunction with specific embodiments. In the following embodiments, the fly ash is first-class fly ash, the mineral powder is S 95 grade slag powder, the sodium hydroxide is flaky 96%-98% analytically pure sodium hydroxide, the liquid sodium silicate is 40 degrees Baume and 3.2 modulus liquid sodium silicate, the water is ordinary tap water, the sodium tetraborate is analytically pure anhydrous sodium tetraborate, and the silane coupling agent is y-aminopropyl triethoxysilane. The liquid sodium silicate has a silicon dioxide content of 26.2%, a sodium oxide content of 8.3%, and a water content of 65.5%.

[0034] 1. A method for preparing geopolymer mortar for cold regeneration of asphalt pavement.

[0035] Implementation Examples

[0036] A method for preparing geopolymer mortar for cold regeneration of asphalt pavement includes precursor materials: 100 parts of fly ash and 50 parts of slag powder; alkali activator raw materials: 7 parts of sodium hydroxide, 39.1 parts of liquid sodium silicate, and 25.5 parts of water; retarder: 6.6 parts of sodium tetraborate and 0.66 parts of aminopropyltriethoxysilane (APTES). The amount of sodium tetraborate added is 3% of the mass of the geopolymer mortar, and the amount of APTES added is 1% of the mass of the geopolymer mortar, and the geopolymer mortar is prepared in the following manner:

[0037] (1) Sodium hydroxide, liquid sodium silicate and water are fully stirred and mixed to obtain an alkali activator solution, which is then placed in a wide-mouth bottle and sealed and cooled for 24 hours;

[0038] (2) adding a corresponding amount of sodium tetraborate to the alkaline activator prepared in step 1), manually stirring until uniformly mixed, and then slowly dropping a corresponding amount of APTES and fully manually stirring until the solution is clear;

[0039] (3) stirring the corresponding mass of mineral powder and fly ash at a low speed of 150 rpm for 3 minutes, then adding the alkaline activator solution prepared in step 2) and stirring at a low speed of 150 rpm for 1 minute, and then stirring at a high speed of 400 rpm for 3 minutes to obtain geopolymer mortar;

[0040] (4) Pour the slurry prepared in step (3) into a mold for forming, and then place it in a constant temperature and humidity curing box at a temperature of 20°C ± 3°C and a relative humidity of 60%. Demould after 24 hours, and then place the specimen in a curing room for curing for 3 days, 7 days and 28 days.

[0041] Comparative Example I

[0042] The amount of sodium tetraborate added is 0% of the mass of the geopolymer mortar, the amount of APTES added is 0% of the mass of the geopolymer mortar, and the other steps are the same as the implementation example.

[0043] Comparative Example II

[0044] The amount of sodium tetraborate added is 3% of the mass of the geopolymer mortar, the amount of APTES added is 0% of the mass of the geopolymer mortar, and the other steps are the same as in the embodiment.

[0045] Comparative Example III

[0046] The addition amount of sodium tetraborate is 0% of the mass of the geopolymer mortar, the addition amount of APTES is 1% of the mass of the geopolymer mortar, and the other steps are the same as those in the embodiment.

[0047] 2. Geopolymer mortar performance test

[0048] 1. According to the "Test Method for Performance of Ordinary Concrete Mixtures" (GB / T 50080-2016), the setting time of the mortar of the implementation example and comparative examples I to III was tested using a DL-AWK automatic Vicat instrument. The results are shown in Table 1.

[0049] Table 1

[0050]

[0051] As can be seen from Table 1, 3% borax extended the initial setting time of Comparative Example I by 3.8 times and the final setting time by 4.8 times; 1% APTES extended the initial setting time of Comparative Example I by 1.1 times and the final setting time by 1.5 times. This shows that 3% borax has the most significant effect in extending the setting time, and the use of borax can extend the setting time several times. 1% APTES has little effect on the initial setting time, but can extend the final setting time. By adding 3% borax and 1% APTES additives at the same time, the setting time is effectively controlled within the target range of 180-360min, and the setting time of the embodiment is not the superposition of the time extension of the first two retarders, which shows that the two additives play a synergistic retarding role.

[0052] 2. According to the "Cement Mortar Strength Test Method (ISO) Method" (GB / T 17671-2021), the implementation example and comparative examples I to III were subjected to 28-day strength tests using a compression and flexural all-in-one machine. The results are shown in Table 2.

[0053] Table 2

[0054]

[0055] As can be seen from Table 2, when 3% borax is added, the compressive strength decreases by 14.5% and the flexural strength decreases by 17%; when 1% is added, the compressive strength increases by 5.2% and the flexural strength increases by 2.3%. For the example with the simultaneous addition of 3% borax and 1% APTES, the compressive strength only decreases by 0.7% and the flexural strength only decreases by 2.3%. The addition of APTES eliminates the adverse effects brought by borax, making the strength of the composite material with the simultaneous addition of two retarders equivalent to that of the original group.

[0056] 3. According to "Fluidity of Cement Mortar" (GB / T 2419 - 2005), the fluidity tests were carried out on the examples and Comparative Examples I - III, and the results are shown in Table 3.

[0057] Table 3

[0058]

[0059] As can be seen from Table 3, for the original control group without retarder, borax improves the fluidity of the mortar. This is because borax itself contains crystal water. After adding it to the geopolymer system, it can stabilize the hydroxyl groups in the geopolymer structure by providing extra moisture. The fluidity of the geopolymer mortar gradually decreases with the increase of the APTES dosage, indicating that APTES reduces the fluidity of the geopolymer mortar. This is because the amino group (-NH) and the siloxethyl group in APTES have strong hydrophilicity. The addition of borax and APTES reconciles the viscosity of the slurry. This synergistic effect significantly enhances the water retention capacity of the internal system of the material, reducing the contact rate between the alkali activator and fly ash / slag, thus delaying the setting of the geopolymer.

[0060] In summary, taking the extension of the setting time as the first goal and the macroscopic properties such as fluidity and strength as important indicators, the effects of borax and APTES as retarders on fly ash - slag - based geopolymers are comprehensively evaluated. It is found that the example with the simultaneous addition of 3% borax and 1% APTES has the most excellent retardation function, ensuring the basic macroscopic properties of the geopolymer slurry.

[0061] 4. Use a Fourier transform infrared spectrometer (BRUKER ALPHA II) to analyze the chemical bond and functional group changes of the examples and comparative examples, with the wave number range of 4000 - 400 cm -1 , and the KBr tablet method is adopted. The samples are selected from the middle part of the specimens after the 28 - day - age compressive test, immediately put into an isopropyl alcohol solution to terminate the hydration reaction, and then immediately tested after being placed in an environment of 40°C for 1 day. The results are as Figure 1 shown.

[0062] From Figure 1 it can be seen that for Comparative Example I, at 13465 cm -1The stretching vibration of OH is at 1628cm -1 The HOH bending vibration is a typical characteristic absorption peak of water. -1 The peak at 738cm is the Si-O-Si or Si-O-Al asymmetric stretching vibration, which is the characteristic peak of the geopolymer skeleton, indicating the existence of silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron. -1 This corresponds to the symmetrical vibration of Si-O or Al-O, which further supports the existence of the geopolymer skeleton structure; 561cm -1 The low wave number feature may be related to the bending vibration of TO (Si or Al), which indicates the change of the local structure of the geopolymer skeleton; 453 cm -1 The 971 cm-1 of Comparative Example II is a bending vibration of Ca, Si or Al metal oxide. -1 The peak intensity is low, indicating that the addition of borax slows down the formation rate of Si-O-Si and Si-O-Al bridge bonds, which directly leads to the delayed coagulation of the geopolymer system. -1 The absorption intensity of the sample is slightly higher than that of the comparative example I, which may be because the Si-OH groups formed after the hydrolysis of the siloxyethyl groups of APTES may further cross-link with the aluminum oxide network or metal oxide in the geopolymer, resulting in enhanced bending vibration in the local area. -1 and 1630cm -1 It shows that both borax and APTES have hydrophilic groups (such as B-OH, Si-OH, -NH), which can form a stable hydrogen bond network with water molecules and delay the volatilization of water. -1 The borax and APTES may interfere with the polymerization process of silicon-oxygen and aluminum-oxygen tetrahedrons. Borax affects the connection mode of the skeleton network by forming BO-Si bridges or BO-Al bonds, while APTES slows down the generation rate of the skeleton network by providing siloxyethyl or amino groups to compete with the silicon-aluminum skeleton. 559cm -1 and 461cm -1 The boron oxide network introduced by borax may be cross-linked with the Si-OH or Si-O-Si network of the silane coupling agent, thereby enhancing the structural stability of the system and further achieving the retarding effect.

[0063] 5. The microstructure of the samples of the implementation example and the comparative example was characterized by using a desktop field emission scanning electron microscope. The samples were gold-sprayed before analysis. The results are as follows: Figure 2 shown.

[0064] from Figure 2It can be seen that each sample has unreacted fly ash particles. It is worth noting that no traces of slag were found in the scanning area. This shows that the slag with a low dosage is more active and has reacted completely at an early stage. It is not difficult to find that regardless of whether a retarder is added, the geopolymer structure at this ratio is relatively dense, which can be verified from the strength test results. For Comparative Example I, some fine cracks distributed vertically and horizontally can be seen, which is caused by the shrinkage of the material. However, a wider crack appeared in Comparative Example II, which led to a decrease in mechanical properties from a macroscopic perspective. The retarding effect of borax causes the aluminosilicate polymerization reaction in some areas to be unable to proceed completely, forming weakly bonded areas or incompletely solidified gel products. On the other hand, the boron element in borax (such as B(OH) 4- ) may participate in the reaction of geopolymers, changing the chemical structure and volume properties of the gel products. The samples with coupling agents added have obvious differences in microscopic morphology. It can be seen that a large amount of hydration products adhere to the surface of the geopolymer, which reduces the occurrence of cracks and makes the surface look rougher. From the perspective of macroscopic performance, coupling agents enhance interfacial bonding and can improve durability to a certain extent, which improves the overall performance of geopolymers.

Claims

1. A geopolymer mortar for cold regeneration of asphalt pavement, characterized in that The precursor materials include: 100 parts of fly ash and 50 parts of slag powder; alkali activator raw materials: 7 parts of sodium hydroxide, 39.1 parts of liquid sodium silicate, and 25.5 parts of water; retarder: 6.6 parts of sodium tetraborate and 0.66 parts of y-aminopropyltriethoxysilane.

2. The geopolymer mortar according to claim 1, characterized in that: The fly ash is first-grade fly ash, the mineral powder is S95-grade slag powder, the sodium hydroxide is flaky 96%-98% analytically pure sodium hydroxide, and the liquid sodium silicate is 40 degrees Baume and 3.2 modulus liquid sodium silicate, wherein the silicon dioxide content is 26.2%, the sodium oxide content is 8.3%, and the water content is 65.5%.

3. The geopolymer mortar according to claim 1, characterized in that: The sodium tetraborate is analytically pure anhydrous sodium tetraborate, and the silane coupling agent is y-aminopropyltriethoxysilane.

4. The geopolymer mortar according to claim 1, characterized in that: The mass ratio of fly ash to mineral powder is 2:1, the modulus of the alkali activator is 1.2, the water-binder ratio is 0.3, and the alkali equivalent is 6%.

5. The geopolymer mortar according to claim 1, characterized in that: The sodium tetraborate accounts for 3% of the mass of the polymer mortar, and the y-aminopropyltriethoxysilane accounts for 1% of the mass of the polymer mortar.

6. The method for preparing the geopolymer mortar for cold regeneration of asphalt pavement according to any one of claims 1 to 5, characterized in that The specific steps of this method are as follows: 1) Sodium hydroxide, liquid sodium silicate and water are fully stirred and mixed, then placed in a wide-mouth bottle, sealed and cooled for 24 hours, a corresponding mass of sodium tetraborate is added to the alkaline activator prepared in step 1), manually stirred until the mixture is uniform, and then a corresponding mass of silane coupling agent is slowly dropped and fully manually stirred until the solution is clear, to obtain an alkaline activator; 2) stirring the corresponding mass of mineral powder and fly ash at a low speed of 150 rpm for 3 minutes, then adding the alkali activator prepared in step 1) and stirring at a low speed of 150 rpm for another 1 minute, and then stirring at a high speed of 400 rpm for 3 minutes to prepare a geopolymer mortar; 3) pouring the geopolymer mortar prepared in step 2) into a mold for molding, and conducting fluidity and setting time tests; casting prism specimens, placing them in a constant temperature and humidity curing box at 20°C ± 3°C and 60%, and demolding them after 24 hours; then placing the specimens in a curing box for curing for 3 days, 7 days and 28 days, conducting strength tests, and comprehensively evaluating the various properties of the geopolymer mortar.

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