A rubber-modified strain-hardening alkali-activated composite material and its preparation method

Abstract

The present invention discloses a rubber-modified strain-hardening alkali-activated composite material and a preparation method thereof, and belongs to the field of concrete technology. The present invention replaces 25-100% of natural fine aggregate by equal volume with rubber powder. By strictly controlling the replacement rate of rubber powder to natural fine aggregate, a rubber-modified strain-hardening alkali-activated composite material is prepared. At a 25% rubber powder volume replacement rate, R-SHAAM exhibits optimal axial tensile properties, with tensile strength increased by 8.1% and ultimate tensile strain increased by 4.1%. Moreover, when rubber completely replaces natural aggregate, R-SHAAM still maintains good compressive and tensile properties, meeting the requirements of structural applications.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete, and in particular relates to a rubber-modified strain-hardening alkali-activated composite material and a preparation method thereof. Background Art

[0002] Engineered cementitious composites (ECCs) exhibit strain hardening with multiple cracking behaviors, and their tensile stress-strain properties are similar to those of steel. This can delay structural aging and extend the service life of buildings. They are also known as strain-hardening cementitious composites (SHCCs). However, the preparation of SHCCs consumes significant amounts of energy and produces large amounts of CO2, significantly impacting the environment. To address this issue, researchers have developed a strain-hardening alkali-activated composite (SHAAM). Compared to SHCCs, the preparation of SHAAMs can reduce CO2 emissions by over 50%. SHAAMs not only possess excellent mechanical properties but also offer significant environmental and economic benefits. For example, Peng et al. studied a fly ash-slag alkali-activated composite material that achieved a maximum tensile strain exceeding 6%, a tensile strength of 6.6 MPa, and a crack width of 58 μm. They also compared the economic and environmental benefits of ECC-M45 and POM / PE-SHAAM, demonstrating that POM / PE-SHAAM reduced carbon emissions, energy consumption, and material costs by 375%, 122%, and 200%, respectively. This indicates that SHAAM has the potential to replace traditional SHCC materials.

[0003] With the continued growth in global automobile use, the amount of scrap tires closely related to automobiles is also increasing rapidly. If not handled promptly, they will cause serious environmental pollution. For the past two decades, the main method of disposal in various countries has been to use scrap tires as fuel, but the combustion process also causes environmental pollution. In addition, the aggregate used in concrete production is still mainly natural sand and gravel. However, the supply of natural sand and gravel is very limited and expensive. The mining, production, and transportation of natural sand and gravel require a lot of energy and have a significant impact on the environment. Moreover, with the growing global demand for natural sand and gravel and its widespread use, this natural raw material will gradually become depleted.

[0004] Therefore, in recent years, researchers have begun exploring the use of rubber granules / powder obtained from crushed and recycled waste tires as an aggregate component in concrete to improve the utilization rate of waste tires. Most studies have shown that the addition of rubber aggregate has a positive impact on the ductility, toughness, and high-temperature resistance of concrete. Abd-Elaty et al. found that replacing 20% of natural aggregate with rubber aggregate at a 1% PP fiber volume content increased concrete toughness by 27.5%, reduced thermal conductivity by 29.4%, and reduced thermal diffusivity by 40.7%. Furthermore, the addition of rubber aggregate can lead to a decrease in concrete properties such as fluidity, elastic modulus, and compressive strength. Mendis et al. found that the use of well-graded rubber aggregate in concrete improves workability at lower rubber contents (5% to 25%), and the hydrophobic properties of rubber can also improve concrete's water resistance. The low stiffness and strength of rubber aggregate are the primary causes of reduced concrete strength, but this is also affected by factors such as rubber aggregate content, size, and shape. Aiello et al. found that replacing natural coarse aggregate with 50% and 75% rubber coarse aggregate reduced compressive strength by 54% and 62%, respectively. Similarly, replacing natural fine aggregate with 50% and 75% rubber fine aggregate reduced compressive strength by 28% and 37%, respectively. When the rubber aggregate replacement ratio is low, the rubber is evenly distributed in the concrete, reducing voids within the concrete, allowing for uniform load energy absorption and reducing the width of the rubber-matrix interface transition zone. Consequently, Silva et al. found that replacing natural aggregate with rubber aggregate (at a 10% replacement ratio) increased the compressive strength of concrete by 8.5% at 7 days and by 2.2% at 28 days. Furthermore, Li et al. found that rubber particles treated with NaOH solution could improve the compressive strength of rubberized concrete. Their results showed that adding rubber particles to concrete treated with 10%, 20%, and 30% NaOH solutions for 24 hours increased the compressive strength by 11.6%, 13.9%, and 4%, respectively. More interestingly, Adesina et al. used rubber fine aggregate to completely replace natural fine aggregate to prepare SHCC, and the compressive strength was only 30.9 MPa. However, since its compressive strength was higher than 25 MPa, it could still be used in structures after evaluation.

[0005] Currently, researchers have attempted to use rubber fine aggregate to prepare strain-hardening alkali-activated composites. Lu'o'ng et al. replaced 5% of natural fine aggregate with rubber fine aggregate and found that the tensile strain increased by 36%, the number of cracks increased by 55%, and the crack width decreased by 10% to 74.1 μm, indicating that the addition of rubber had a significant positive impact on the crack control ability of SHAAM. Zhong et al. studied the compressive properties of SHAAM with low rubber substitution rates and found that the addition of rubber reduced the compressive strength. When the substitution rate was 40%, the compressive strength decreased by 43%. Although there have been some studies on rubber-modified strain-hardening alkali-activated composites, these studies focused on the effects of low rubber substitution rates on the performance of SHAAM. Application research on the use of rubber to replace natural fine aggregate in large quantities has not yet been conducted. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a rubber-modified strain-hardening alkali-activated composite material and a preparation method thereof.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A rubber-modified strain-hardening alkali-activated composite material is prepared by replacing 25-100% of natural fine aggregate by equal volume with rubber powder on the basis of the original formula of the alkali-activated composite material, preferably 100% replacement; the natural fine aggregate is quartz powder.

[0009] Furthermore, the rubber-modified strain-hardening alkali-activated composite material includes the following components: fly ash, blast furnace slag, quartz powder, rubber powder, water, alkali activator, retarder and PE fiber.

[0010] Furthermore, the rubber-modified strain-hardening alkali-activated composite material includes the following components in parts by mass: 850 parts of fly ash, 364 parts of blast furnace slag, 0-182.1 parts of quartz powder, 25.6-102.6 parts of rubber powder, 99.5 parts of water, 486 parts of alkali activator, 12.1 parts of retarder and 19.4 parts of PE fiber.

[0011] Furthermore, the fly ash is Class F fly ash, D 50 15.44μm;

[0012] The blast furnace slag is S105 grade ground blast furnace slag, D 50 53.80μm;

[0013] The quartz powder has a particle size of 50-300 μm and a density of 2.65 g / cm 3 , elastic modulus is 76GPa;

[0014] The rubber powder has a particle size of 100-150 μm and a density of 1.13 g / cm 3 , elastic modulus is 7GPa;

[0015] The retarder is barium chloride;

[0016] The PE fiber has a length of 18 mm, a diameter of 24 μm, an elastic modulus of 116 GPa, a strength of 3000 MPa, and a density of 0.97 g / cm 3 , elongation 3%.

[0017] Furthermore, the alkaline activator is a mixture of a 10 mol / L NaOH solution and a NaSiO2 solution having a modulus (SiO2:Na2O ratio) of 2.25 in a mass ratio of 1:2. The purity of the NaOH solid exceeds 96%, and the mass fractions of Na2O, SiO2, and H2O in the NaSiO2 solution are 13.75%, 29.99%, and 56.26%, respectively.

[0018] The present invention also provides a method for preparing a rubber-modified strain-hardening alkali-activated composite material, comprising the following steps:

[0019] Fly ash, blast furnace slag, quartz powder, rubber powder and retarder were stirred at a speed of 75 r / min for 2 minutes;

[0020] Add the alkaline activator to the above system and continue stirring at a speed of 75 r / min for 1 minute;

[0021] Continue to add water to the above system and stir at a speed of 75 r / min for 2 minutes;

[0022] Finally, PE fiber was added, and stirring was continued at 75 r / min for 2 minutes during the addition of PE fiber, and finally stirring was continued at 75 r / min for 2 minutes to complete the stirring to obtain a mixed slurry;

[0023] The mixed slurry is filled into a mold, vibrated, and coated, and then demoulded after standing at room temperature for 2 days, and then soaked in water in a sealed environment for curing for 28 days.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] This study produces a rubber-modified, strain-hardening, alkali-activated composite material (R-SHAAM) by strictly controlling the replacement ratio of rubber powder to natural fine aggregate. At a 25% volume replacement ratio of rubber powder, R-SHAAM exhibits optimal axial tensile properties, with an 8.1% increase in tensile strength and a 4.1% increase in ultimate tensile strain. Furthermore, when rubber completely replaces natural aggregate, R-SHAAM maintains good compressive and tensile properties, meeting the requirements of structural applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0027] Figure 1 This is the SEM image of the raw material of the present invention;

[0028] Figure 2 is the particle size distribution diagram of the raw materials of the present invention;

[0029] Figure 3 This is a flow chart of the preparation process of the present invention;

[0030] Figure 4 A fluidity testing device;

[0031] Figure 5 is the size of the cylindrical sample;

[0032] Figure 6 It is a uniaxial compressive strength test device;

[0033] Figure 7 is the size of the dog bone specimen device;

[0034] Figure 8 It is the experimental device for direct tensile test;

[0035] Figure 9 is the liquidity of R-SHAAM under different RP substitution rates;

[0036] Figure 10 The EDS results of the interface transition zone between fine aggregate quartz powder and rubber powder and the matrix in the R-SHAAM scanning electron microscope image;

[0037] Figure 11 SEM image of the R-SHAAM microstructure;

[0038] Figure 12 The compression failure morphologies of R-SHAAM with different RP substitution rates;

[0039] Figure 13is the compressive stress-strain curve of R-SHAAM with different RP substitution rates;

[0040] Figure 14 is the effect of RP substitution rate on the characteristic parameters of direct compression test;

[0041] Figure 15 is the R-SHAAM destruction process with different RP substitution rates;

[0042] Figure 16 The tensile failure morphologies of R-SHAAM with different RP substitution rates;

[0043] Figure 17 are the average crack width and crack density of R-SHAAM with different RP substitution ratios under tensile loading;

[0044] Figure 18 is the tensile stress-strain curve of R-SHAAM under different RP substitution rates;

[0045] Figure 19 is the supersaturated cracking of R-SHAAM with different RP substitution rates;

[0046] Figure 20 are the axial tensile strength, ultimate tensile strain, cracking strength, and cracking strain of R-SHAAM at different RP substitution rates;

[0047] Figure 21 Performance evaluation of R-SHAAM with different RP substitution rates. DETAILED DESCRIPTION

[0048] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0049] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0050] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0051] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0052] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0053] The present invention explores the effect of using rubber powder to replace natural aggregate to prepare rubber-modified strain-hardening alkali-activated composites (R-SHAAM). Through axial tensile tests and axial compression tests, the effects of different rubber volume replacement rates on R-SHAAM, including working performance, axial compression behavior and axial tensile behavior, were systematically explored. The results showed that R-SHAAM at all rubber replacement rates exhibited supersaturation cracking, providing higher safety for its engineering applications. In addition, the addition of rubber increased the crack density and reduced the crack width. At a rubber volume replacement rate of 25%, R-SHAAM exhibited the best axial tensile performance, with tensile strength increased by 8.1% and ultimate tensile strain increased by 4.1%. It is worth noting that when rubber completely replaces natural aggregate, R-SHAAM still maintains good compressive and tensile properties, meeting the requirements of structural applications. A compressive stress-strain model and a tensile stress-strain model for R-SHAAM were established, which are in good agreement with the experimental data, accurately describing the mechanical properties of R-SHAAM at different rubber replacement rates, and providing a reliable basis for its engineering application and numerical simulation.

[0054] The "parts" described in the present invention, unless otherwise specified, refer to parts by mass.

[0055] The raw materials required for the present invention include F-class fly ash (FA), S105-grade ground blast furnace slag (GGBS), quartz powder (QP), rubber powder (RP), water, an alkali activator, a retarder (BaCl2), and PE fiber, all of which were purchased on the market. The fly ash and slag were purchased from Henan Hougang Co., Ltd., the quartz powder was purchased from Shuangshui Synthetic Ceramic Glass Raw Material Processing Plant in Xinhui District, Jiangmen City, the rubber powder was purchased from Dujiangyan Huayi Rubber Co., Ltd., the barium chloride and sodium hydroxide were purchased from Xilong Science Co., Ltd., and the sodium silicate solution was purchased from Jiashan Yourui Refractory Material Co., Ltd.

[0056] The microstructure of the raw materials is as follows Figure 1 As shown. The alkaline activator is a mixture of 10 mol / L NaOH solution and a NaSiO2 solution with a modulus (SiO2:Na2O ratio) of 2.25 in a mass ratio of 1:2. The purity of the NaOH solid exceeds 96%, and the mass fractions of Na2O, SiO2 and H2O in the NaSiO2 solution are 13.75%, 29.99% and 56.26%, respectively. The D50 of GGBS and FA are 53.80μm and 15.44μm, respectively. The chemical composition is shown in Table 1, and the physical properties are shown in Table 2. The QP particle size is 50-300μm and the density is 2.65g / cm 3 , elastic modulus 76GPa. RP particle size is about 100-150μm, density is 1.13g / cm 3 , elastic modulus 7GPa. The particle size distribution of each powder is as follows Figure 2 The chemical composition and physical properties of fly ash and blast furnace slag are shown in Tables 1 and 2, and the physical characteristics and mechanical properties of PE fiber are shown in Table 3.

[0057] Table 1 Chemical composition of fly ash and blast furnace slag

[0058]

[0059] Table 2 Physical properties of fly ash and blast furnace slag

[0060] fly ash blast furnace slag Loss on ignition (%) 4.6 0.84 <![CDATA[Density (g / cm 3 )]]> 2.3 3.1 <![CDATA[Specific surface area (m 2 / kg)]]> 1835 429 Moisture content (%) 0.5 0.45

[0061] Table 3 Physical and mechanical properties of polyethylene fibers

[0062]

[0063] The technical solution of the present invention is further illustrated by the following examples.

[0064] Example 1

[0065] This experiment set up 5 groups of mixes with different rubber powder volume replacement rates as shown in Table 4.

[0066] Table 4

[0067]

[0068] Note: The mix ratio is named RX, where X represents the volume replacement rate of rubber powder to quartz powder, including 0, 25%, 50%, 75%, and 100%.

[0069] The specimens were prepared using a 20-liter planetary mortar mixer. The specific operations were as follows: (1) Fly ash, blast furnace slag, quartz powder, rubber powder, and retarder barium chloride were stirred at a speed of 75 r / min for 2 minutes to ensure that the materials were evenly mixed; (2) Alkali activator was added and stirred at a speed of 75 r / min for 1 minute, and then water was added and stirred at a speed of 75 r / min for 2 minutes to ensure that the slurry was evenly mixed; (3) PE fiber was gradually added, and the mixture was stirred at a speed of 75 r / min for 2 minutes, and finally stirred at a speed of 75 r / min for 2 minutes to ensure that the fibers were evenly dispersed. After stirring, the mixed slurry was tested for fluidity, and then the mold was immediately filled and vibrated on a vibrating table to eliminate bubbles in the specimen to ensure that the specimen was dense and uniform. Finally, the specimen was coated, left to stand in an indoor environment for 2 days, and then demolded. Then, the experiment was carried out after immersion in water for 28 days in a sealed environment (see Figure 3 The obtained product was named rubber modified strain hardening alkali activated composite (R-SHAAM).

[0070] The alkaline activator is prepared by mixing a 10 mol / L NaOH solution and a NaSiO2 solution with a modulus (SiO2:Na2O ratio) of 2.25 in a mass ratio of 1:2. The mixture is stirred evenly (the liquid does not become turbid when left standing), coated, and stored at room temperature before use. The purity of the NaOH solid exceeds 96%, and the mass fractions of Na2O, SiO2, and H2O in the NaSiO2 solution are 13.75%, 29.99%, and 56.26%, respectively.

[0071] 1. Testing

[0072] 1. Liquidity test

[0073] In this example, the fluidity of all slurries was measured according to the standard ASTM-C1437, 2013, and the jumping table test was used for evaluation. Figure 4 As shown, the upper opening diameter is 70mm. The lower opening diameter is 100mm, the depth is 50mm, and the wall thickness of the test mold is greater than 5mm. After the vibration is completed, the diameters of the slurry bottom surface in two mutually perpendicular directions are measured with a caliper, and the average value of the two diameters is reported.

[0074] 2. Uniaxial compression test

[0075] The axial compression test was carried out in accordance with ASTM-C469,2020. Cylinders, such as Figure 5 The test uses an electro-hydraulic servo press, and the test device is as follows: Figure 6 To avoid bias during loading due to uneven specimen surfaces, a layer of high-strength plaster was evenly applied to the top and bottom of the specimen before loading to level the surface. The specimen was slowly loaded to failure at a rate of 0.2 mm / min in displacement-controlled mode. During loading, two 20 mm strain gauges were placed in the axial direction of the specimen, and two LVDTs were placed in axially symmetrical positions to monitor deformation.

[0076] 3. Uniaxial tensile test

[0077] The dog-bone specimen used in this uniaxial tensile test has a size of 330 mm × 60 mm × 13 mm. Figure 7 The test was carried out using a microcomputer-controlled electronic universal testing machine. To avoid eccentric tension during loading, universal joints were installed at both ends of the fixture. The test device is as follows: Figure 8 As shown. The loading method adopts displacement control mode loading, and the loading rate is set to 0.5mm / min. Two displacement meters with a range of 25mm are used to measure the axial deformation in the middle 80mm area of the specimen at a frequency of 1Hz. The load data is provided by a microcomputer-controlled electronic universal testing machine, and the deformation data is collected by a TDS-540 high-performance static data acquisition instrument to obtain the tensile stress-strain curve of the specimen and determine its axial tensile properties. At the same time, white paint is applied to the surface of the specimen to observe the morphology and distribution of the cracks. During the test, a camera is used to record the crack development at a frequency of 0.2Hz. Five photos of each group of specimens under different strain conditions are selected for binarization processing to obtain the number of cracks, crack density and crack width of the specimen.

[0078] 2. Results

[0079] 1. Liquidity

[0080] The fiber dispersion has an important influence on the strain hardening properties of R-SHAAM and the bridging properties of fibers in R-SHAAM, and the fiber dispersion is closely related to the fluidity of R-SHAAM fresh pulp. Figure 9 is the fluidity of freshly mixed R-SHAAM at different RP replacement rates. Figure 9 It can be seen that the fluidity of the R-0 group specimens is 147mm, which increases with the increase of RP substitution rate until the fluidity reaches a maximum of 155mm when the addition amount is 75%, an increase of 5.4%. The reason for this phenomenon may be that NaOH solution can accelerate the oxidation and decomposition of RP, and Na +The formation of carboxyl groups increases the wettability of RP and improves the fluidity of R-SHAAM fresh paste.

[0081] However, when the RP replacement rate increased to 100%, the fluidity decreased from 155 mm to 148 mm, close to the value at 0% addition. This phenomenon can be attributed to the irregular shape of the RP, which easily leads to particle accumulation and increased friction between the particles. It may also be because at a certain RP addition rate, the adhesion between the R-SHAAM paste and the RP is insufficient to cover all the RP, resulting in cavities between the paste and the RP, where water is trapped.

[0082] Therefore, the fluidity of R-SHAAM can be improved by controlling the appropriate RP substitution rate. Good fluidity can not only improve the processability of R-SHAAM, but also improve the dispersion of fibers in R-SHAAM, thereby improving the strain hardening characteristics of R-SHAAM.

[0083] 2. Internal structure of R-SHAAM

[0084] Figure 10 The EDS results of the interface transition zone between fine aggregate quartz powder and rubber powder and the matrix in the R-SHAAM scanning electron microscope image are as follows: Figure 10 As shown in the figure, the width of the interfacial transition zone (ITZ) between the QP and RP substrates is compared. The RP substrate has a more pronounced gap, indicating a larger ITZ width. Energy dispersive spectroscopy (EDS) results also show a larger ITZ between the RP and substrate, confirming the poor adhesion between the RP and substrate interfaces. This suggests that the uneven surface of the RP has a significant negative impact on the adhesion between the substrate and the substrate.

[0085] Figure 11 The micromorphologies of R-0 and R-100 during axial tensile failure are shown. Both R-0 and R-100 exhibit typical fiber pullout failure, indicating a stable relative sliding process between the fiber and matrix. Furthermore, the presence of numerous pores within R-100 confirms that replacing QP with RP increases defects within the matrix.

[0086] 3. Uniaxial compression performance

[0087] 1) Uniaxial compression failure mode

[0088] Figure 12The failure modes of R-SHAAM axial compression specimens under different RP volume replacement rates are shown, which are different from the failure modes of ordinary SHCC and SHAAM under axial compression. As can be seen from the figure, the failure of R-SHAAM presents a multi-crack form similar to axial tensile failure, without excessive failure fragments, and has good ductility. In addition, unlike the phenomenon of ordinary SHCC and SHAAM with few cracks and many fragments when failing, the number of cracks in the R-SHAAM specimens increases with the increase of RP volume replacement rate, showing more obvious ductile failure. This is mainly attributed to the following two points: (1) The irregular shape and low elastic modulus of RP itself make the deformation and bridging ability stronger than QP, which can support R-SHAAM to produce more cracks and deformation when under axial compression; (2) PE fiber has a good bridging effect on R-SHAAM when cracks begin to form, ensuring the stable development of cracks.

[0089] 2) Figure 13 The axial compressive stress-strain curves of R-SHAAM with different RP volume substitution ratios are shown. The axial compression curve of R-SHAAM is divided into four stages: elastic stage, strain hardening stage, strain softening stage, and residual softening stage. In the elastic stage, R-SHAAM undergoes elastic deformation under axial compression without generating any microcracks, and unloading does not affect the axial compressive strength of R-SHAAM. As the compressive displacement increases, microcracks begin to appear in R-SHAAM, but the bridging effect of PE fibers and RP suppresses crack development, causing R-SHAAM to enter the strain hardening stage. In this stage, the deformation is minimal, and the strain hardening rate is similar to the elastic modulus. As the axial compressive displacement increases, primary cracks develop in R-SHAAM. The axial compressive strength reaches a peak and then begins to decline, leading to specimen failure and the softening stage. Finally, when the axial compressive strength reaches approximately 20 MPa, R-SHAAM enters the residual softening stage, which is mainly maintained by the bridging effect of PE fibers and RP. In addition, it can be seen from the figure that the softening stage of R-SHAAM is not obvious, which may be due to the large W / B (0.325) of this mix ratio, resulting in a steeper trend in the softening stage of R-SHAAM.

[0090] 3) Compressive strength, peak strain and elastic modulus

[0091] like Figure 14The axial compressive strength, peak strain and elastic modulus of R-SHAAM under different RP volume substitution rates are shown. It can be seen that as the RP substitution rate increases, the axial compressive strength and elastic modulus of R-SHAAM gradually decrease, mainly because the strength and elastic modulus of RP are lower than those of QP and the incorporation of RP increases the closed pores (i.e., voids) in R-SHAAM. However, the bridging effect of RP also increases the peak strain of R-SHAAM. Figure 14 It can be seen that when the replacement rate of RP transitions from 50% to 75%, the compressive strength only decreases by 2%, and the change rate is very small. This may be because too much RP fills part of the voids in R-SHAAM, weakening the negative impact of RP on the compressive strength.

[0092] When the RP substitution rate is 100%, the compressive strength is the lowest, which is 60.1 MPa. Compared with the 0% RP substitution rate, the compressive strength of SHAAM is reduced by 29.2%. This is mainly due to the following reasons: (1) After RP replaces QP, R-SHAAM produces a relatively high porosity, resulting in a relatively low microstructure density; (2) The hydrophobicity and high friction coefficient of RP lead to a relatively weak bonding force between RP and the substrate. Figure 10 This shows that the ITZ width between RP and the substrate is larger and the bonding strength is weaker. Nevertheless, since the compressive strength of R-SHAAM with 100% RP replacement is higher than 25MPa, it can be used in various building structures after evaluation.

[0093] 4. Uniaxial tensile properties

[0094] 1) Uniaxial tensile failure mode

[0095] Figure 15 and Figure 16 The crack initiation, crack development and final failure morphology of R-SHAAM under different RP volume replacement ratios under uniaxial tension are respectively shown. In this experiment, digital image binarization technology was used to process the 60mm test section of the specimen, and the maximum inter-class variance was used to determine the appropriate threshold. The crack distribution images under different tensile strains were obtained as follows: Figure 15 As shown. Figure 15 Typical microcrack development characteristics can be observed in R-SHAAM at different RP volume replacement ratios. Furthermore, at similar strains (approximately 4%), increasing the RP replacement ratio leads to more crack development. This is due to the increased internal defects in the matrix caused by the addition of RP and the poor interfacial adhesion between the RP and the matrix, which reduces the fracture toughness of the matrix and makes cracks more likely to develop.

[0096] Researchers based on Figure 15The average crack width and crack density of R-SHAAM under different RP volume replacement rates were quantitatively analyzed, e.g. Figure 17 As shown. Figure 17 As can be seen from the figure, the average crack width of R-SHAAM under ultimate tension is less than 150 μm, and the crack density is greater than 0.5. It can also be seen that with increasing RP volume replacement, the average crack width of R-SHAAM decreases, with a maximum decrease of 50.7%, while the crack density increases, with a maximum increase of 73.5%. After replacing QP with RP, the irregular shape and low elastic modulus of RP allow RP to interlock and stretch within the matrix, forming particle bridges that transfer load and inhibit crack opening. This provides a bridging effect for crack suppression, improving the material's crack control capabilities and enhancing its durability.

[0097] 2) Uniaxial tensile stress-strain curve

[0098] like Figure 18 The tensile stress-strain curves of R-SHAAM under different RP volume replacement rates. It can be seen that the five groups of specimens all exhibited typical strain hardening behavior under axial tensile load. The strain hardening stage is divided into two sections, and the slope of the second section is greater than that of the first section, resulting in a two-stage crack evolution phenomenon, which is also called supersaturated cracking. SHAAM with supersaturated cracking is more suitable for application in engineering, and can provide better safety for buildings. It has a higher safety factor than ordinary SHCC and SHAAM. Because at lower tensile strain levels (normal working conditions), the crack width is small, which can reduce the impact of the external environment on the interior of the matrix, which is beneficial to ensure good durability of the structure; at higher tensile strain levels (extreme working conditions, such as earthquakes), the crack width is large, the structure has better elastic properties, and can well alleviate impact loads.

[0099] At the same time, it can be seen from the figure that as the RP substitution rate continues to increase, when cracks appear in the specimen, the tensile stress fluctuation becomes smaller and smaller, even approaching a smooth curve. This shows that with the increase of the RP substitution rate, the crack width of R-SHAAM continues to decrease, which also reflects that RP has excellent control over the tensile stress fluctuation and crack width of R-SHAAM.

[0100] 3) Oversaturation cracking

[0101] Due to the presence of RP, the initial defects of R-SHAAM increase, resulting in an uneven matrix between the two parallel cracks in R-SHAAM. When the saturated cracking state is reached, local cracks begin to form as the tensile strain continues to increase. These cracks connect the two parallel cracks. At this time, the actual number of cracks is greater than the theoretical number of cracks, resulting in oversaturated cracking. The most obvious characteristic of the oversaturated cracking phenomenon is that the strain hardening stage is divided into two stages. In the first stage, the tensile strain continues to increase, multiple parallel cracks appear, the number of cracks increases linearly, the crack development speed is fast, and the crack width increases slowly. At this time, the increase in tensile strain mainly depends on the increase in the number of cracks. In the second stage, the number of cracks reaches saturation, the tensile strain continues to increase, the number of cracks remains basically unchanged, and the crack width increases. At this time, the increase in tensile strain mainly depends on the increase in crack width. Figure 19 The red marks in the middle are some cross cracks due to oversaturation cracking. Judging from the number of red marks, R-SHAAM under the five RP substitution rates has obvious oversaturation cracking.

[0102] 4) Ultimate tensile strength, ultimate tensile strain, initial crack strength and initial crack strain

[0103] Figure 20 The axial tensile strength, ultimate tensile strain, cracking strength and cracking strain of R-SHAAM at different RP substitution rates are shown. Figure 20 It can be seen that when the RP volume replacement rate is 25%, the axial tensile strength, ultimate tensile strain, cracking strength and cracking strain are all the highest, increasing by 8.1%, 4.1%, 9.4% and 147.8% respectively. Since the bridging strength of the fiber plays a decisive role in the tensile strength of R-SHAAM, the change in tensile strength is not obvious. It can be seen that the effect of the RP replacement rate on the bridging strength of the fiber is not significant. When the RP replacement rate is 25%, the tensile strength is slightly improved. This is mainly because the addition of an appropriate amount of rubber causes the plastic viscosity of R-SHAAM to be too high. Increasing the plastic viscosity can promote the dispersion of the fibers, making the PE fibers more evenly distributed in R-SHAAM and improving the fiber bridging effect. At the same time, when the RP volume replacement rate is 25%, the ultimate tensile strain reaches 7.97%, which is close to the minimum requirement for steel elongation (9%) of ASTM A615.

[0104] In addition, Figure 20 It can be seen that when the RP volume substitution rate is greater than 25%, the axial tensile strength, ultimate tensile strain, cracking strength and cracking strain of R-SHAAM begin to decrease. This is mainly because the strength of RP is lower than that of QP, and the increase in RP substitution rate will increase the internal defects of R-SHAAM, thereby weakening the mechanical properties of R-SHAAM.

[0105] Compared with R-SHAAM with 0% RP substitution, the tensile strength of R-SHAAM with 100% RP substitution decreased by 8.3% and the ultimate tensile strain decreased by 10.5%. This shows that the complete replacement of QP by RP has a relatively small impact on the performance of SHGC. R-SHAAM with complete RP replacement of QP still maintains good ductility and toughness, meeting the requirements of most engineering applications.

[0106] like Figure 21 The comprehensive performance of RM-SHAAC is demonstrated, including eight metrics: tensile strength, ultimate tensile strain, compressive strength, peak compressive strain, compressive elastic modulus, flowability, crack width, and crack density. As shown in the figure, the tensile properties of the five groups of specimens (R-0, R-25, R-50, R-75, and R-100) are relatively similar. However, from the perspective of crack control, the crack density and crack width of R-100 show a significant increase compared to R-0, indicating that R-100 exhibits superior crack control. In most engineering applications, tensile strength is not the primary consideration for SHAAC; good crack control and ductility are crucial. Although the mechanical properties of R-100 are somewhat reduced, it still meets the requirements of engineering applications. Its excellent crack control also enables the recycling of waste tires, reducing reliance on natural aggregates. This demonstrates the feasibility of preparing RM-SHAAC using only RP as a SHAAC aggregate. This RM-SHAAC meets the requirements of most engineering applications while achieving higher economic and environmental benefits.

[0107] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A rubber-modified strain-hardening alkali-activated composite material, characterized in that: Based on the original formula of the alkali-activated composite material, 75-100% of the natural fine aggregate is replaced by rubber powder in equal volume; the natural fine aggregate is quartz powder; The rubber-modified strain-hardening alkali-activated composite material comprises the following components in parts by mass: 850 parts of fly ash, 364 parts of blast furnace slag, 60.7 parts of quartz powder, 77 parts of rubber powder, 99.5 parts of water, 486 parts of alkali activator, 12.1 parts of retarder and 19.4 parts of PE fiber; The alkaline activator is a mixture of 10 mol / L NaOH solution and 2.25 modulus NaSiO2 solution in a mass ratio of 1:2; The fly ash is F-grade fly ash, D 50 15.44μm; The blast furnace slag is S105 grade ground blast furnace slag, D 50 53.80μm; The quartz powder has a particle size of 50-300 μm and a density of 2.65 g / cm 3 , elastic modulus is 76GPa; The rubber powder has a particle size of 100-150 μm and a density of 1.13 g / cm 3 , elastic modulus is 7GPa; The retarder is barium chloride; The PE fiber has a length of 18 mm, a diameter of 24 μm, an elastic modulus of 116 GPa, a strength of 3000 MPa, and a density of 0.97 g / cm 3 , elongation 3%; The method for preparing the rubber-modified strain-hardening alkali-activated composite material comprises the following steps: Fly ash, blast furnace slag, quartz powder, rubber powder and retarder were stirred at a speed of 75 r / min for 2 minutes; Add the alkaline activator to the above system and continue stirring at a speed of 75 r / min for 1 minute; Continue to add water to the above system and stir at a speed of 75 r / min for 2 minutes; Finally, PE fiber was added, and stirring was continued at 75 r / min for 2 minutes during the addition of PE fiber, and finally stirring was continued at 75 r / min for 2 minutes to complete the stirring to obtain a mixed slurry; The mixed slurry is filled into a mold, vibrated, and coated, and then demoulded after standing at room temperature for 2 days, and then soaked in water in a sealed environment for curing for 28 days.

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