Method for improving impact resistance by doping shear thickening fluid into mortar concrete

Abstract

The invention relates to the technical field of mortar concrete, in particular to a method for improving impact resistance by doping shear thickening fluid into mortar concrete, which comprises the following steps: dry-mixing cement and aggregate, adding water, stirring to prepare fresh mortar slurry, adding shear thickening fluid capsules into the fresh mortar slurry, and uniformly mixing and stirring; wherein the shear thickening liquid capsules are capsules filled with shear thickening liquid. By doping the shear thickening fluid capsule, an STF-based honeycomb network structure is generated in the mortar, the energy dissipation effect of the mortar is improved, meanwhile, nano SiO2 in the STF component can fill air gaps in the mortar, generation of hydration products (hydrated calcium silicate gel and ettringite crystals) is improved, compactness of a mortar matrix is promoted, and the strength of the mortar is improved. The compression resistance, the impact resistance and the like of the modified mortar material are obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of mortar concrete, and in particular to a method for improving the impact resistance of mortar concrete by adding a shear thickening fluid. Background Art

[0002] As the concrete matrix and the outermost layer of engineering structures, mortar is most susceptible to unexpected impact loads of varying degrees, leading to cracking and failure. Mortar performance directly impacts the quality of concrete. Therefore, improving mortar's impact resistance is of great practical engineering significance.

[0003] Previous research has primarily focused on improving the impact resistance of mortar by controlling the water-cement ratio, improving the mortar mix ratio, using modifiers (such as air-entraining agents, expansion agents, and polymer modifiers), and adding aggregates (such as fiber materials, rubber particles, and nanomaterials). The first three methods enhance the overall strength of the mortar to improve its impact resistance, while adding aggregates enhances the mortar's impact resistance by incorporating materials with excellent toughness and impact resistance. Therefore, adding aggregates is a more economical and simple method for improving mortar's impact resistance, and it is also the method most studied by researchers.

[0004] For example, Javad et al. added different volume fractions of polypropylene fibers to mortar to study its impact resistance. The results showed that polypropylene fibers improved the mortar's impact resistance, and there was a strong linear relationship between polypropylene fiber content and the mortar's impact resistance. Issam et al. added carbon fibers to mortar to prepare bulletproof concrete. The results showed that carbon fibers helped to increase the concrete's integrity upon failure, thereby improving its impact resistance. Similarly, glass fibers significantly improved the mortar's static tensile properties and high-strain-rate impact resistance. Furthermore, Chen et al. conducted low-velocity impact tests at different temperatures on mortars containing rubber particles. The tests showed that the rubber-modified mortar had a higher energy dissipation capacity and exhibited superior impact resistance at low temperatures to other modified materials. Furthermore, nano-SiO2 fills the pores between the aggregates in the mortar, thereby increasing the mortar's toughness and improving its impact resistance. Currently, the addition of aggregates is trending towards higher performance, and the search for more effective new admixtures to produce highly impact-resistant mortars has become a hot topic in mortar protective performance research.

[0005] In recent years, shear-thickening fluids (STFs) have attracted considerable attention in the field of vibration damping and protection. STFs are highly concentrated suspensions composed of a dispersed phase and a dispersion medium, and are non-Newtonian fluids. Their characteristic is that when subjected to sudden impact, their viscosity increases exponentially. Researchers have exploited the shear-thickening properties of STFs and applied them to various protective scenarios. For example, conventional Kevlar fabrics were impregnated with STFs to create flexible body armor. Research results showed that the puncture resistance of the STF-Kevlar composite material was significantly improved. Unsanhame et al. also found that shear thickening plays a decisive role in impact energy absorption. Lin et al. incorporated STFs into dampers for vibration damping of cable stays. The results showed that the maximum equivalent damping ratio of the STF damper was nearly three times that of a conventional damper, more effectively mitigating cable vibration. STFs play a significant role in vibration damping. Selim et al. studied the vibration attenuation performance of STF-filled aluminum panel sandwich structures and found that the shear-thickening properties of STFs significantly improved the vibration characteristics. Meanwhile, some researchers have developed an STF sandwich beam by adding STF as a core time-varying layer to a beam structure. The study found that the STF sandwich significantly affects the dynamic performance of the beam, reducing the stiffness of the bridge under load and exhibiting adaptive properties. STF has also found applications in areas such as explosion-proof batteries and industrial surface polishing.

[0006] Previous studies have shown that STF has rich potential applications in impact-resistant materials and structures, but the application of STF in building materials has not been reported. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for improving the impact resistance of mortar concrete by adding a shear thickening fluid.

[0008] The object of the present invention is achieved through the following technical solutions:

[0009] A method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar comprises the following steps: dry-mixing cement and aggregate, adding water and stirring to prepare a fresh mortar slurry, and then adding a shear thickening fluid capsule to the fresh mortar slurry and mixing and stirring uniformly; wherein the shear thickening fluid capsule is a capsule filled with a shear thickening fluid.

[0010] Furthermore, the capsule is a hydrophilic capsule, and its ingredients are gelatin and water.

[0011] Furthermore, the amount of the shear thickening fluid is 0.1% to 5% of the mass of the cement.

[0012] Furthermore, the dispersed phase of the shear thickening fluid includes one or more of silicon dioxide, cerium dioxide, carbon nanotubes, graphene, silicon carbide, starch, collagen, gelatin, polyvinyl chloride, calcium carbonate, polymethyl methacrylate, polystyrene ethyl acrylate, polystyrene acrylonitrile, carbon nanofibers, MOF-801, kaolin and titanium dioxide, and the dispersion medium includes one or more of polyethylene glycol, ethylene glycol, water, dioctyl phthalate, glycerol-water, decalin, ionic liquid and polyacrylic acid, and the mass ratio of the dispersed phase to the dispersion medium is 1:1 to 9:1.

[0013] Furthermore, the dispersed phase of the shear thickening fluid is silicon dioxide with a particle size range of 200nm to 800nm, the dispersion medium is polyethylene glycol with a molecular weight of 200 to 600g / mol, and the mass ratio of silicon dioxide to polyethylene glycol is 1:1 to 9:1, preferably 2:1 to 3:1.

[0014] Furthermore, the preparation method of the shear thickening fluid includes: mechanical stirring, ultrasonication, ball milling, and magnetic stirring. Preferably, the ball milling method is used, wherein a planetary ball mill is used for mixing and ball milling at a speed of 300-500 r / min and a ball milling time of 8-24 h.

[0015] Furthermore, the types of cement include one or more of Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite Portland cement.

[0016] Furthermore, the aggregate includes coarse aggregate and / or fine aggregate, and the aggregate is Chinese ISO standard sand that complies with GB / T 17671.

[0017] Furthermore, the fresh mortar slurry is also mixed with one or more of epoxy resin, water reducing agent, silica fume, quartz sand and fly ash.

[0018] The present invention also provides an application of the mortar concrete prepared by the above method as a concrete material for large-scale infrastructure and civil buildings. Examples include:

[0019] 1. Urban underground pipeline concrete and subsequent anti-seepage and wear-resistant repair; 2. The demand for anti-impact and wear-resistant concrete in the flow section of dam concrete, as well as concrete for the subsequent repair and maintenance of anti-seepage and anti-impact aspects of dam foundation concrete; 3. Concrete for offshore engineering platforms, concrete and mortar for marine filling; 4. Anti-impact and wear-resistant concrete for pile foundations of cross-sea bridges, as well as repair concrete or mortar for subsequent concrete repair and maintenance.

[0020] The principle of the present invention is:

[0021] CSH gel is the most important phase contributing to mortar strength, enhancing the mortar's mechanical properties by filling pores and forming a dense microstructure. Ca(OH)2 crystals exhibit a lamellar structure, which is prone to slippage between crystal layers, leading to the formation of pores and the expansion of cracks. This creates stress concentration areas within the material, hindering further improvement in mortar strength. However, Ca(OH)2 has a high elastic modulus, which enhances the mortar's elastic properties to a certain extent. AFt crystals exhibit a needle-rod structure, which can fill the mortar's internal pores and resist the expansion of small cracks, playing a positive role in the mortar's early strength development.

[0022] Combined with the results of hydration products, micromorphology and elemental analysis, it can be seen that compared with OM, the shear thickening fluid capsule modified mortar produced more CSH gel and AFt crystals during the hydration process, reduced the Ca(OH)2 content, and decreased the Ca / Si ratio, thereby improving the density and mechanical properties of the mortar.

[0023] The improved impact resistance of STFJ using the capsule incorporation method is primarily due to the following mechanisms: 1. The shear thickening fluid capsules form a honeycomb network structure within the mortar matrix, providing "adaptive" protection. Under low-speed impact forces, the shear thickening fluid's network structure effectively disperses the impact force, mitigating stress concentration and preventing rapid propagation of the impact force within the mortar matrix. Under stronger impact forces, however, the nanoparticles in the shear thickening fluid rub against each other, dissipating much of the impact energy and thus resisting external impact damage. 2. During the hydration process, the shear thickening fluid capsules release nano-SiO2 particles. These particles physically fill the tiny pores in the mortar, improving its density and uniformity. These nano-SiO2 particles dissipate impact energy through friction between the particles, filling the mortar and promoting hydration reactions, thereby enhancing impact resistance and mechanical strength. 3. Through the volcanic ash reaction, nano-SiO2 and Ca(OH)2 undergo a secondary hydration reaction, generating more CSH gel, which enhances the mechanical properties of the mortar, inhibits the accumulation of Ca(OH)2 crystals, and reduces the formation of cracks. It also promotes the formation of AFt crystals, forming a support structure in the pores, further improving the early strength and density of the mortar.

[0024] The beneficial effects of the present invention are:

[0025] This invention innovatively introduces STF capsules into mortar, developing a new mortar material based on the shear thickening fluid capsule modification mechanism. Compared with traditional mortar materials, the new mortar material modified with shear thickening fluid capsules in this invention has the following characteristics:

[0026] 1. Significantly improved compressive performance. The introduction of shear thickening fluid capsules increases energy dissipation pathways, enabling more efficient absorption and dispersion of energy when subjected to external loads. This delays the concrete's failure process, resulting in a certain degree of increased compressive strength at all ages. At 3 days, the compressive strength increase ranges from 7% to 32.1%, and at 14 days, the compressive strength increases by 48.1% to 61.6%.

[0027] 2. Early flexural strength is improved, with the increase ranging from 9.5% to 18.4%.

[0028] 3. Significantly improved impact resistance. Mortar specimens modified with shear thickening fluid capsules exhibited higher impact integrity; they were able to maintain a certain load-bearing capacity after impact and exerted a certain resistance to the impact force. They also possessed stronger impact energy absorption capacity, extending the time it takes for the mortar to absorb impact energy, delaying the point at which energy absorption reaches its limit, and increasing the total impact energy absorbed. Consequently, they exhibited superior impact resistance.

[0029] 4. Significantly improved high-speed impact strength. Mortar modified with shear thickening fluid exhibited significantly lower fragmentation than OM after SHPB impact loading, exhibiting less crack propagation and better mortar integrity, demonstrating enhanced impact resistance. Mortar modified with shear thickening fluid capsules exhibited a slower stress drop, and the bearing capacity of the specimens decreased gradually after impact. Mortars were able to withstand higher stresses despite greater deformation, delaying the onset of failure and demonstrating greater impact toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart for preparing the shear thickening fluid used in the present invention;

[0031] Figure 2 Schematic diagram of the preparation process of mortar specimens;

[0032] Figure 3 Photos of the universal testing machine: (a) compression test; (b) flexural test;

[0033] Figure 4 Compressive failure morphology of mortar: (a) OM; (b) STFJ group; (c) STFT group;

[0034] Figure 5 Compressive strength of mortar prepared by capsule incorporation method: (a) compressive strength at different ages; (b) compressive strength growth rate;

[0035] Figure 6 Compressive strength of surface coating mortar: (a) compressive strength at different ages; (b) compressive strength growth rate;

[0036] Figure 7 It is a drop weight impact test device;

[0037] Figure 8 The damage form of mortar under the impact of drop hammer;

[0038] Figure 9 The relationship between the impact force and time of the mortar during the drop hammer impact process;

[0039] Figure 10 The relationship between the impact force and displacement of the mortar during the drop hammer impact process;

[0040] Figure 11 Low-velocity impact performance of STFJ mortar: (a) absorbed impact energy-time curve; (b) energy density;

[0041] Figure 12 Schematic diagram of the SHPB test device;

[0042] Figure 13 is the failure form of mortar after HPB test;

[0043] Figure 14 The impact resistance of the mortar;

[0044] Figure 15 is the impact energy absorption property of the mortar;

[0045] Figure 16 It is the hydration product of the STFJ group specimen;

[0046] Figure 17 SEM images of OM: (a) and (b) mortar matrix morphology; (c) AFt crystals; (d) and (e) Ca(OH)2 crystals; (f) CSH gel;

[0047] Figure 18 SEM images of STFJ: (a) mortar matrix; (b) release effect of capsules; (c) CSH gel; (d) AFt crystals and Ca(OH)2 crystals;

[0048] Figure 19 This is the EDS element distribution diagram of the mortar modified with shear thickening fluid capsules. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0050] Example 1 Preparation of shear thickening fluid

[0051] The shear thickening fluid is prepared by mixing nano-silica (purity greater than 99.5%) and polyethylene glycol in a mass ratio of 7:3. The present invention selected four silica particles of different sizes (300nm, 350nm, 400nm and 500nm) and polyethylene glycol (PEG) with a molecular weight of 200g / mol to prepare four shear thickening fluids. The preparation process is as follows: Figure 1 As shown, the details are as follows:

[0052] First, dry the silica in a vacuum drying oven at 100°C for 12 hours to evaporate the water. Then, weigh the corresponding amounts of silica and polyethylene glycol in a 7:3 mass ratio and mix them in a planetary ball mill. During ball milling, add 10 mm diameter steel balls equal in mass to the raw materials to aid in grinding. For example, in this experiment, each milling jar held 100 g of raw material, so 20 10 mm diameter steel balls were added. Set the ball mill speed to 400 rpm and mill for 10 hours.

[0053] Example 2 Preparation of mortar specimens using the capsule incorporation method

[0054] The shear thickening liquid was processed and filled into capsule form, added to the fresh mortar slurry and stirred (50s) until uniform. Three sizes of specimens were cast. The specimen size for the compression test and drop hammer test was a 70.7mm cube, and the specimen size for the flexural test was 40mm×40mm×160mm. The specimen size for the split-Hopkinson compression bar test was a cylinder with a diameter of 50mm and a height of 50mm. After casting, the specimen was demoulded after curing indoors for 24 hours and moved to a standard curing box with a humidity of 100% and a temperature of 25°C for curing. According to different test contents, the specimens were cured for 3d, 14d and 28d respectively. After curing, all SPHB specimens were polished smooth on both sides using a polishing machine.

[0055] To effectively encapsulate the shear thickening fluid, a hydrophilic (pharmaceutical) capsule shell material was selected. The capsule shell, primarily composed of gelatin and water, is transparent and does not soften or dissolve immediately upon contact with water. It takes time to dissolve and release its contents. Its excellent water solubility facilitates uniform distribution of the shear thickening fluid in the mortar. The capsule body measures 9.3 mm in length and 4.68 mm in diameter.

[0056] PC42.5 ordinary Portland cement was used as the cementitious material, and the cement performance parameters are shown in Table 1. Fine aggregate was selected from Chinese ISO standard sand that complies with GB / T 17671, with a particle size range of 0.08-2 mm.

[0057] Table 1 Basic properties of cement used in the test

[0058]

[0059]

[0060] The preparation method of fresh mortar slurry is as follows: cement and standard sand are mixed according to the mix ratio and dry-mixed for 30 seconds to ensure that the cement and sand particles are evenly mixed. Subsequently, test water is slowly added and stirred for 100 seconds.

[0061] Comparative Example 1 Preparation of ordinary mortar specimens

[0062] Cement and standard sand were mixed according to the mix ratio and dry-mixed for 30 seconds to ensure uniform mixing of the cement and sand particles. Subsequently, test water was slowly added and stirred for 150 seconds. Three sizes of test pieces were cast according to the method of Example 2 and then cured and polished.

[0063] Comparative Example 2 Preparation of mortar specimens using the surface coating method

[0064] In comparative example 1, the surface of the solidified mortar specimen is coated with shear thickening liquid and encapsulated with epoxy resin. The specific method is as follows: a predetermined amount of shear thickening liquid is evenly applied on the surface of the specimen to ensure uniform coverage and fill the pores on the surface of the mortar. Subsequently, the epoxy resin and the curing agent are fully mixed in a mass ratio of 4:1 and stirred to a uniform state, and then the prepared epoxy resin is evenly applied to the surface of the shear thickening liquid to form an encapsulation layer. During the operation, attention should be paid to the wrapping integrity of the specimen edge, and the coating thickness should be controlled at about 1 mm to ensure effective encapsulation of the shear thickening liquid. Finally, the surface height difference of all coatings was measured to be controlled within 100 μm, indicating that the prepared coating has good flatness and uniformity, which meets the test requirements.

[0065] Epoxy resin and curing agent are used as film-forming materials for encapsulation. The selected epoxy resin is a milky white emulsion with good adhesion and chemical resistance; the curing agent is a light yellow viscous colloid. The two are mixed in a mass ratio of 4:1 to form a uniform and dense cross-linked structure. The basic performance parameters of the epoxy resin and curing agent are shown in Table 2.

[0066] Table 2 Properties of epoxy resin and curing agent

[0067]

[0068] Example 3 mortar mix ratio

[0069] In view of the fact that the dosage of functional admixtures is usually controlled within the range of 0.5% to 2% of the mass of cement, in order to give full play to the modifying effect of shear thickening fluid in mortar, its dosage is designed to be 2% of the mass of cement. The mortar mix ratios of Example 2 and Comparative Example 1 are shown in Table 3. Among them, OM represents the benchmark mortar of Comparative Example 1, STFJ represents the mortar with shear thickening fluid capsules added in Example 2 of the present invention, and STFT represents the mortar with shear thickening fluid coating in Comparative Example 2. The number following the number is the type of shear thickening fluid, i.e., 1 is 300nm silica, 2 is 350nm silica, 3 is 400nm silica, and 4 is 500nm silica. The mortar specimen preparation process of Example 2, Comparative Example 1 and benchmark mortar refers to Figure 2 .

[0070] Table 3 Mortar mix ratio (kg / m 3 )

[0071]

[0072] Experimental Example 1 Basic Mechanical Properties Test

[0073] The basic mechanical properties test was carried out in accordance with GB / T 17671-2021 "Test Method for Cement Mortar Strength", and the HUT-106A electro-hydraulic servo universal testing machine was used for uniform loading. Among them, the compressive strength test adopted the stress control mode, and the loading rate was set to 0.5MPa / s. During the test, the specimen was placed between the pressure plates of the testing machine, and the force-bearing surface was ensured to be flat and evenly compressed. During the test, the testing machine continued to load until the specimen was damaged, the maximum damage load was recorded, and the compressive strength was calculated. The flexural strength test was a three-point bending test. The specimen was placed horizontally on two fulcrums, and the two fulcrums were 100mm away from the edge of the specimen. A vertical load was applied to the center of the specimen through the loading device until the specimen broke. The flexural test adopted the force control mode, and the loading rate was set to 50N / s. Three specimens were tested in each case, and the average value was taken as the test result. The schematic diagram of the test apparatus and test process is shown in the figure. Figure 3 shown.

[0074] (1) Destruction form

[0075] The failure mode of mortar specimens in the compression test is as follows: Figure 4 As shown in the figure, specimen OM exhibits obvious brittle failure characteristics during compression, with rapid crack expansion and a crisp cracking sound. Figure 4 (a) It can be seen that the specimen OM shows a typical X-shaped failure morphology when it fails in compression, with few cracks and rapid expansion, accompanied by the peeling of some aggregate blocks and finally brittle failure.

[0076] In contrast, the mortar specimens incorporating shear thickening fluid capsules exhibited better compressive failure morphology. Figure 4 (b) It can be seen that when the specimen STFJ was subjected to compression failure, the crack propagation was significantly slowed down, and no aggregate peeling was observed. The specimen as a whole maintained a high degree of integrity. This indicates that the introduction of shear thickening fluid capsules increased the energy consumption pathway, enabling it to absorb and disperse energy more effectively when subjected to external loads, delaying the failure process and improving the compressive performance. In addition, Figure 4 (c) It can be seen that compared with OM, when the specimen STFT is damaged under pressure, the number of surface cracks increases significantly, and it presents a more tortuous expansion path. At the same time, the degree of specimen fragmentation is high, and more powdery debris is produced, showing more serious crushing damage. In addition, the shear thickening liquid coating overflows due to the extrusion effect during the compression process and eventually fails. This phenomenon shows that the strength of the shear thickening liquid coating is low and cannot withstand higher pressure. It can be seen that the capsule incorporation method of the present invention can effectively improve the overall integrity of the mortar and enhance its crack resistance, while the surface coating method is limited. Under the same method, different types of shear thickening fluids have little effect on the mortar failure morphology.

[0077] (2) Compressive strength

[0078] Overall, compared with OM, mortars incorporating shear thickening fluid capsules showed some improvement in compressive strength at all ages, with the most significant enhancement at 14 days. The reinforcing effect of the shear thickening fluid was already beginning to manifest at 3 days. Compared with OM, the compressive strength of the STFJ mortars increased by 7% to 32.1%, with specimen STFJ1 achieving the largest increase, reaching 29.6 MPa. However, the compressive strength of the STFT mortars at 3 days was similar to that of OM, with no significant improvement observed, indicating limited early-stage reinforcing effects.

[0079] At 14 days, the compressive strength of the mortar modified with shear thickening fluid capsules increased significantly, demonstrating a more pronounced strengthening effect. The compressive strength of the STFJ group increased by 48.1% to 61.6%, with specimen STFJ2 showing the largest increase, reaching 46.1 MPa. The STFT group, on the other hand, showed limited strengthening, with increases ranging from 22.8% to 30.1%. These results demonstrate that the shear thickening fluid capsules are fully effective at 14 days of age, and that the capsule incorporation method is more effective in increasing the compressive strength of the mortar matrix.

[0080] In the test piece group with shear thickening fluid capsules ( Figure 5(a)), the effect of different types of shear thickening fluid on the compressive strength of mortar showed obvious time dependence. At the age of 3d, the compressive strength of STFJ1 was significantly higher than that of STFJ2, STFJ3 and STFJ4, and the compressive strengths of the three decreased by 15.3%, 12.5% ​​and 18.9%, respectively. With the increase of age, the difference in compressive strength between the specimens gradually narrowed, and the 14d and 28d compressive strengths of STFJ1 were similar to those of specimens STFJ2, STFJ3 and STFJ4. At the age of 28d, the compressive strength of STFJ1 was 52.6MPa. In comparison, the compressive strengths of STFJ2, STFJ3 and STFJ4 decreased by 3.4%, 2.4% and 0.4%, respectively, and the difference was small. At the same time, the compressive strength change trends of mortars modified by different types of shear thickening fluid capsules were consistent ( Figure 5 (b)), the growth rate is large and rapid in the early stage (3d~14d), while the growth slows down in the later stage (14d~28d).

[0081] In the group with shear thickening fluid applied on the surface ( Figure 6 (a)), at the age of 3d and 28d, the compressive strength difference between STFT1 and STFT4 is small. At the age of 14d, the compressive strength of STFT1 is significantly higher than that of specimens STFT2, STFT3 and STFT4. The maximum 14d compressive strength of STFT1 is 37.1MPa. In comparison, the compressive strengths of STFT2, STFT3 and STFT4 decreased by 5.6%, 23.8% and 26.7%, respectively, showing a more obvious enhancement effect. The 28d compressive strengths of the three decreased by 2.3%, 6.2% and 1.8%, respectively, with little difference. At the same time, the compressive strength change trend of the mortar coated with shear thickening fluid is consistent (such as Figure 6 (b) shows that the compressive strength increases slowly from 3d to 14d, while from 14d to 28d, the compressive strength of each specimen increases gradually, especially for STFT3 and STFT4, the growth rate is the most obvious.

[0082] contrast Figure 5 and Figure 6 Compressive strength data for the same shear thickening fluids show that, within the A-70 group, the compressive strengths of STFJ1 and STFT1 were comparable at 28 days. However, a comparison of compressive strength growth rates reveals that the capsule incorporation method experienced rapid growth in the early stages (3-14 days) but plateaued in the later stages (14-28 days). Mortar compressive strength for the surface coating method increased linearly with age. The compressive strengths of the B-70, C-70, and D-70 mortars were similar to those of the A-70 mortar.

[0083] (3) Flexural strength

[0084] Compared with OM, the flexural strength of the mortar with capsules added into shear thickening fluid increased by 9.5% to 18.4% at the age of 3 days, showing a certain improvement.

[0085] Experimental Example 2 Drop Hammer Impact Test

[0086] In order to obtain the low-speed impact behavior of mortar specimens, a drop hammer test was carried out. The drop hammer impact test device is as follows: Figure 7 As shown. The present invention uses a 23.95kg arc-shaped hammer head, with the drop hammer positioned 258mm above the specimen, resulting in an initial impact velocity of 2.25m / s and an impact energy of 60J. During impact, the hammer head is aligned with the center of the specimen, and fixed baffles are positioned around the specimen to prevent force displacement when the hammer head contacts the specimen. Three parallel specimens are set up in each group, and the average value is taken as the test result.

[0087] (1) Damage morphology of drop hammer impact

[0088] The damage morphologies of the benchmark mortar and shear thickening fluid capsule modified mortar specimens under drop hammer impact are as follows: Figure 8 As shown. Figure 8 It can be seen that after the impact, the central region of specimen OM developed an impact crushing pit, and cracks rapidly expanded outward from the crushing center, eventually causing the specimen to break into two pieces, exhibiting typical brittle failure. In comparison, under the same impact conditions, the mortar specimens modified with shear thickening fluid capsules did not form cracks or ruptures, but only experienced crushing in a localized area at the center of the specimen, demonstrating higher impact integrity. Specifically, when an external impact acts on the mortar, the mortar absorbs the impact energy. When the energy exceeds the maximum energy absorption range of the mortar matrix, the energy is dissipated through crack propagation, ultimately leading to mortar failure. The mortar modified with shear thickening fluid capsules, on the other hand, effectively consumes most of the impact energy through the shear thickening fluid, thereby preventing the expansion of matrix cracks. Therefore, the mortar modified with shear thickening fluid capsules can withstand more impact energy before rupture failure, demonstrating superior impact resistance.

[0089] (2) Mortar impact bearing capacity

[0090] Based on the dynamic sensor data of the drop hammer test device, the impact force, displacement and action time of the mortar specimen during the drop hammer impact process were recorded in detail. The impact force-time relationship curve of the mortar is shown in Figure 2. Figure 9 As shown. Figure 9 As can be seen, after the drop hammer begins to impact, the impact force rises rapidly, then fluctuates for a short period of time and gradually rises until it reaches a peak. After reaching the peak impact force, the impact force drops rapidly, and the entire impact process lasts approximately between 1.9 and 3.5 seconds.

[0091] from Figure 9 As can be seen from (a), the impact process of specimen OM lasted for 1.9s, and the maximum impact force was 18100N. In the impact force drop stage, the impact force of specimen OM dropped faster and the slope was larger, indicating that the material strength of OM decayed rapidly after the impact and lost its bearing capacity in a short time. Figure 9 Figure (b) shows that the impact process for the STFJ specimens lasted 2.3 to 3.5 seconds, with maximum impact forces of specimens STFJ1 to STFJ4 reaching 13,700 N, 13,800 N, 16,400 N, and 15,200 N, respectively. The slope of the impact force decrease for the STFJ specimens was smaller, with a more gradual, fluctuating downward trend. This indicates that the STFJ was able to maintain a certain load-bearing capacity after the impact and provided some resistance to the impact force.

[0092] (3) Deformation of mortar after impact

[0093] The impact force-displacement relationship curve of mortar is as follows: Figure 10 As shown. Mortar is a brittle material, which usually breaks down when the deformation is very small. Figure 10 As can be seen, during the initial impact phase, the displacement of all specimens increased with increasing impact force, reaching approximately 4 mm. As the impact force approached its peak, deformation increased further, but the magnitude of deformation remained relatively limited, with the specimens ultimately reaching failure displacements ranging from 5 to 8.5 mm. Notably, the baseline mortar exhibited the smallest displacement at final failure, while the shear-thickening fluid-modified mortars exhibited greater deformation than the baseline mortar.

[0094] Depend on Figure 10 The failure displacement of specimen OM was 5.29 mm. In comparison, the failure displacements of specimens STFJ1 to STFJ4 increased by 34.6%, 25.5%, 7.6%, and 54.3%, respectively. This further demonstrates that the shear thickening fluid capsule-modified mortar has a stronger impact energy absorption capacity, effectively delaying the onset of failure and demonstrating excellent impact resistance.

[0095] (4) Impact resistance

[0096] The impact energy absorbed by the mortar can be quantitatively characterized by calculating the integral of the impact force and displacement, and the energy density can be used to characterize the impact energy absorbed per unit volume of the mortar, which is calculated by the following formula:

[0097]

[0098] Where W represents the energy density of the mortar, Q represents the impact energy absorbed by the mortar specimen, and V represents the volume of the mortar specimen.

[0099] Depend on Figure 11(a) It can be seen that the addition of shear thickening fluid capsules can prolong the time for mortar to absorb impact energy, delay the turning point where energy absorption reaches the limit, and increase the total impact energy absorbed. Figure 11 (b) shows that the energy absorption capacity of the STFJ group is improved compared with OM. The impact energy absorbed by STFJ1 to STFJ4 is 56.7J, 57.9J, 59.3J and 54.3J, which are increased by 6.8%, 8.9%, 11.6% and 2.3% respectively. This shows that the shear thickening fluid capsule can improve the energy absorption capacity of the mortar. At the same time, the energy density of the STFJ group is also improved compared with OM, with STFJ3 showing the highest energy density of 167.8kJ / m 3 , followed by STFJ2, then STFJ1, and finally STFJ4. It can be seen that under the same impact conditions, the impact resistance of STFJ is better than that of OM, especially STFJ3, which shows excellent impact toughness and energy absorption capacity.

[0100] Shear thickening fluid is added to the mortar matrix as a functional cementitious material. Its unique rheological properties significantly enhance the impact energy absorption capacity of the mortar, thereby improving the mortar's resistance to falling hammer impact.

[0101] Experimental Example 3SHPB impact test

[0102] A 100 mm diameter SHPB device was used to further supplement the high-speed impact behavior of the shear thickening fluid capsule modified mortar. Figure 12 As shown, the apparatus consists of a nitrogen pressure system, an incident rod, a reflective rod, a transmission rod, and a data acquisition system. The test controlled the impact bullet's velocity by adjusting the nitrogen pressure. The present invention controlled the impact velocity to approximately 5 m / s. Five parallel specimens were set up for each group, and the average value was used as the test result.

[0103] (1) SHPB impact failure mode

[0104] In the SHPB test, the impact velocity was further increased, and the bullet impacted the mortar specimens at a velocity of 5 m / s. All specimens were broken after the impact. Figure 13 As shown. Figure 13As can be seen, all mortars modified with shear thickening fluid capsules exhibited less fragmentation than the baseline mortar. Specimen OM exhibited smaller fragments, a higher degree of fragmentation, and produced more mortar powder. Specimen STFJ, on the other hand, exhibited larger fragments and a lower degree of fragmentation. At this impact velocity, the degree of fragmentation is positively correlated with the extent of crack propagation. This indicates that mortars modified with shear thickening fluid exhibit significantly lower fragmentation than OM after SHPB impact loading, resulting in less crack propagation and better mortar integrity, demonstrating superior impact resistance. This phenomenon is consistent with the results of the drop weight impact test.

[0105] (2) Stress-strain curve

[0106] like Figure 14 As shown in the figure, in the initial stage of the curve, the stress of the mortar specimen gradually increases with increasing strain until it reaches a peak value, which is the ultimate compressive strength of the mortar. After the peak value, the curve decreases, indicating that the material has failed. It can be observed from the figure that the stress curves of all mortars modified with shear thickening fluid capsules are generally higher than those of the baseline mortar, indicating that the modified mortars exhibit higher impact strength during impact. In comparison, the impact resistance of the baseline mortar is weaker. The descending section of the stress-strain curve reflects the bearing capacity of the material after impact. The stress drop of specimen OM is relatively steep, indicating that OM quickly loses its bearing capacity after impact. In contrast, the stress drop of all mortars modified with shear thickening fluid capsules is relatively slow, reflecting that the bearing capacity of these specimens decreases slowly after impact. They can withstand higher stresses under larger deformations, delaying the occurrence of failure and demonstrating stronger impact toughness.

[0107] (3) Impact energy absorption capacity

[0108] During the SHPB impact process, the impact energy absorbed by the mortar can be obtained by integrating the stress-strain curve. Figure 15 The energy absorption of each mortar group during SHPB impact is shown. All mortars modified with shear thickening fluid capsules absorbed significantly more total impact energy than the baseline concrete. Specimen OM absorbed 29.4 J of impact energy, while the STFJ groups absorbed 14.9%, 29.3%, 52%, and 44.6% more impact energy, respectively. STFJ3 demonstrates the strongest energy absorption capacity.

[0109] Experimental Example 4 Microstructure Analysis

[0110] The effect of shear thickening fluid capsules in mortar was systematically investigated using multiple microscopic characterization methods. First, X-ray diffraction (XRD) was used to qualitatively analyze the hydration products of the mortar and explore the influence of the shear thickening fluid capsules on the formation of hydration products. Second, scanning electron microscopy (SEM) was used to observe the internal microstructure of the mortar matrix, the morphology and distribution of key hydration products, and the distribution of the shear thickening fluid. Energy dispersive spectroscopy (EDS) was also used to analyze the elemental composition and Ca / Si ratio of the mortar, further revealing the mechanism of action of the shear thickening fluid capsules in the mortar.

[0111] (1) XRD results

[0112] Figure 16 The main crystalline phases of the STFJ group are shown. In the STFJ specimens, the strongest diffraction peak signal is still SiO2, with the main peak occurring at approximately 27°, while several secondary peaks also appear at 43° and 50°–70°. Compared to OM, the SiO2 peak intensity is weaker in the STFJ. This is primarily due to the slow release of the shear thickening fluid by the capsules, which allows the nano-SiO2 to react rapidly after release, resulting in no excess nano-SiO2. Furthermore, due to the presence of the capsule shell, which contributes a significant portion of the mass and does not contain a crystalline phase, the SiO2 content in the STFJ is lower than that in the OM. In the 29°–36° range, the STFJ also exhibits a diffraction peak signal of CSH gel. Compared to OM, the CSH gel content in the STFJ is significantly higher, also attributed to the secondary hydration of the nano-SiO2. The nano-SiO2 particles released from the shear thickening fluid capsules better align with the formation of Ca(OH)2, allowing them to react with it promptly, generating more CSH gel and improving the strength of the mortar. At about 40° and 46°, the Ca(OH)2 diffraction peak intensity of STFJ is significantly lower than that of OM, which reflects the large consumption of Ca(OH)2 in the secondary hydration reaction. At 18° and 21°, the AFt peak intensity of STFJ is lower than that of OM. This is because Ca(OH)2 reacts with SiO2 in large quantities, and the concentration of dissolved calcium ions in the system is low, which inhibits the formation of AFt. In addition, at about 37°, a weaker CaCO3 diffraction peak signal appears in STFJ. This shows that most of the Ca(OH)2 in STFJ is consumed by the volcanic ash reaction of nano-SiO2, thereby weakening the carbonization reaction. Figure 16 It can be seen that STFJ3 has the highest contents of SiO2, CSH gel and AFt, which is consistent with the impact resistance results. STFJ3 has the most outstanding impact resistance.

[0113] The shear thickening fluid capsules slowly release nano-SiO2, delaying the cement hydration reaction. The presence of the shear thickening fluid capsules increases CSH gel and AFt, while reducing the Ca(OH)2 content, improving the compressive strength and impact resistance of the mortar.

[0114] (2) SEM results

[0115] from Figure 17 The microstructural features of OM can be clearly observed from the SEM images. Figure 17 (a) and (b) show that there are obvious cracks and holes in the OM matrix, and these defects are unevenly distributed. The holes in some areas are relatively loose, and there is no hydration product filling inside the holes, resulting in high porosity. These defects are caused by the cement hydration process. At the same time, Figure 17 In (c), needle-shaped AFt crystals are clearly seen, concentrated around the edges of the holes. Figure 17 A large number of lamellar Ca(OH)2 crystals can be observed in (d) and (e), especially around cracks and holes. Ca(OH)2 can easily cause further crack expansion under stress. In addition, Figure 17 In (f), six-sided cubic CSH crystals can be seen filling the tiny pores of the mortar matrix. Consequently, the OM has poor compactness, and the numerous pores easily lead to stress concentration during stress loading. Excessive Ca(OH)₂ easily triggers crack propagation within the mortar, resulting in low impact resistance.

[0116] The microstructural characteristics of STFJ are as follows: Figure 18 shown. Figure 18 (a) shows that at 1.5k magnification, significant cracks and pores are observed in the STFJ matrix. These defects are primarily caused by capsule shell degradation and cement hydration. Compared to OM, the pores in the STFJ are relatively few and disconnected, with a more dispersed distribution, indicating that the STFJ mortar matrix has achieved a certain degree of density. Furthermore, no excess Ca(OH)2 crystals are observed in the STFJ matrix, indicating that the slow release of nano-SiO2 particles by the shear thickening fluid capsules effectively consumes Ca(OH)2 crystals, enhancing the mortar's crack resistance. Figure 18 (b) shows that after the shear thickening fluid capsules gradually degraded in the slurry, the shells shrank and partially ruptured, thus presenting a layered and stacked collapsed structure. Figure 18 In (c), it can be observed that the released nano-SiO2 particles are in the form of irregular aggregates, adsorbed in the mortar matrix to fill the pores, and undergo secondary hydration reactions with the surrounding cement and hydration products to generate more CSH gel, thereby improving the strength of the mortar. STFJ dissipates energy through friction between nano-SiO2 particles, thereby improving the impact resistance of the mortar. Figure 18 In (d), Ca(OH)2 crystals are visible within the pores, and AFt crystals have formed at the pore edges. Under stress, cracks penetrate some of the Ca(OH)2 crystals. Due to their small size and high surface energy, nano-SiO2 particles are easily adsorbed on the surface of the Ca(OH)2 crystals, where they combine and react with calcium ions, forming a new CSH gel on the surface of the Ca(OH)2 crystals and in the interlayer gaps. This further refines the pores and reduces crack propagation pathways, thus providing the mortar with improved impact and crack resistance.

[0117] (3) EDS results

[0118] Figure 19 The results show that compared with OM, the Ca content in STFJ is reduced, while the Si content is significantly increased, reflecting a decrease in the Ca / Si ratio. This change further proves that the introduction of shear thickening fluid capsules consumes Ca(OH)2, further generating more CSH gel, making the matrix structure denser and enhancing the mechanical properties and impact resistance of the mortar.

[0119] The foregoing description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A method for improving the impact resistance of mortar concrete by adding a shear thickening fluid, characterized in that: The method comprises the following steps: dry-mixing cement and aggregate, adding water and stirring to prepare fresh mortar slurry, and then adding shear thickening liquid capsules into the fresh mortar slurry and stirring evenly; wherein the shear thickening liquid capsules are capsules filled with shear thickening liquid.

2. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to mortar concrete according to claim 1, characterized in that: The capsule is a hydrophilic capsule, and its ingredients are gelatin and water.

3. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar concrete according to claim 1, characterized in that: The dosage of the shear thickening fluid is 0.1% to 5% of the mass of the cement.

4. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar concrete according to claim 1, characterized in that: The dispersed phase of the shear thickening fluid includes one or more of silicon dioxide, cerium dioxide, carbon nanotubes, graphene, silicon carbide, starch, collagen, gelatin, polyvinyl chloride, calcium carbonate, polymethyl methacrylate, polystyrene ethyl acrylate, polystyrene acrylonitrile, carbon nanofibers, MOF-801, kaolin and titanium dioxide, and the dispersion medium includes one or more of polyethylene glycol, ethylene glycol, water, dioctyl phthalate, glycerol-water, decalin, ionic liquid and polyacrylic acid. The mass ratio of the dispersed phase to the dispersion medium is 1:1 to 9:

1.

5. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to mortar concrete according to claim 4, characterized in that: The dispersed phase of the shear thickening fluid is silicon dioxide with a particle size range of 200nm to 800nm, the dispersion medium is polyethylene glycol with a molecular weight of 200 to 600g / mol, and the mass ratio of the silicon dioxide to the polyethylene glycol is 1:1 to 9:

1.

6. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar concrete according to claim 1, characterized in that: The preparation method of the shear thickening liquid includes: mechanical stirring method, ultrasonic method, ball milling method and magnetic stirring method.

7. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar concrete according to claim 1, characterized in that: The types of cement include one or more of Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite Portland cement.

8. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar concrete according to claim 1, characterized in that: The aggregate includes coarse aggregate and / or fine aggregate, and the aggregate is Chinese ISO standard sand that complies with GB / T 17671.

9. The method for improving the impact resistance of mortar concrete by adding a shear thickening fluid to the mortar concrete according to claim 1, characterized in that: The fresh mortar slurry is further mixed with one or more of epoxy resin, water reducing agent, silica fume, quartz sand and fly ash.

10. Application of the mortar concrete prepared by the method according to any one of claims 1 to 9 as a concrete material for large-scale infrastructure and civil buildings.

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