70GPa-grade high-modulus coarse aggregate UHPC and preparation method thereof

Abstract

The invention discloses 70GPa-grade high-modulus coarse aggregate UHPC (Ultra High Performance Concrete) and a preparation method thereof. The coarse aggregate UHPC material comprises cement, coarse aggregate, calcium carbonate whiskers, aluminum oxide nanofibers and ultra-high molecular weight polyethylene fibers. The coarse aggregate UHPC product with high elastic modulus is prepared by mixing the calcium carbonate whiskers, the alumina nanofibers, the cement, the coarse aggregate and other materials and then adding the ultra-high molecular weight polyethylene fibers and the steel fibers step by step, so that the coarse aggregate UHPC product has the characteristics of high compressive strength, tensile strength and breaking strength and low cost; and meanwhile, the elastic modulus of the product can be effectively improved and reaches 70 GPa level, and the production cost can be effectively reduced under the condition that the material quality is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of concrete materials, and in particular to 70GPa grade high modulus coarse aggregate UHPC and a preparation method thereof. Background Art

[0002] The development trend of ultra-high, ultra-long and multi-layer bridges has put forward higher and newer requirements for the lightweight of steel-concrete composite structures. Ultra-high-performance concrete (UHPC) is an ultra-high-strength cement-based material with high strength, high toughness and high durability, and has excellent mechanical properties. The relatively low elastic modulus / compressive strength ratio and poor volume stability (large shrinkage) are the main problems faced by UHPC in practical engineering applications. Among them, the compressive strength of UHPC is generally more than twice that of traditional high-performance concrete (above C50), but its elastic modulus is less than 1 / 3 of that of traditional high-performance concrete, which makes the lightweight UHPC structure designed based on strength significantly larger than that of ordinary concrete structure; and the poor volume stability makes UHPC materials have extremely high requirements for curing conditions and are prone to shrinkage and cracking. Therefore, further improving the performance of UHPC materials (such as elastic modulus), narrowing the performance differences between steel and concrete materials (such as shrinkage and creep), and based on this, optimizing the cross-section of components and innovating the structural system are the main ways to achieve lightweight steel-concrete composite structures.

[0003] To this end, relevant researchers have adopted the method of adding coarse aggregate, increasing the amount of steel fiber, and increasing the amount of active powder to increase the elastic modulus of ultra-high performance concrete. However, the addition of excessive coarse aggregate will introduce a large number of interface transition zones with weak mechanical properties, and at the same time affect the uniform distribution of fibers in UHPC, resulting in a decrease in the material's flexural toughness. In addition, simply increasing the amount of coarse aggregate still cannot increase the elastic modulus of coarse aggregate UHPC to more than 70GPa. Increasing the amount of steel fiber can easily cause agglomeration, affect the working performance of the mixture, and increase the preparation cost. Increasing the amount of active powder will increase the heat of hydration, increase the risk of shrinkage cracking, and also increase the preparation cost.

[0004] If the elastic modulus of the material is to reach 70GPa while ensuring high flexural toughness, expensive artificial aggregates such as silicon carbide and sintered bauxite corundum need to be used, which will greatly increase the material cost of coarse aggregate UHPC and limit its further large-scale promotion and application.

[0005] In view of the above problems, the present invention, based on the concept of green and low-carbon construction, proposes to add multi-scale mixed fibers such as ultra-high molecular weight polyethylene fibers, calcium carbonate whiskers and alumina nanofibers to prepare a more economical and practical high-toughness and high-elastic modulus 70GPa ultra-high performance concrete. Summary of the invention

[0006] One of the purposes of the present invention is to provide a coarse aggregate UHPC material with an elastic modulus of 70 GPa, which can effectively improve the elastic modulus of the product to 70 GPa.

[0007] The second object of the present invention is to provide a method for preparing a coarse aggregate UHPC material with an elastic modulus of 70 GPa, which ensures that conventional material components can prepare a high elastic modulus product while having the characteristics of high compressive strength, tensile strength, flexural strength and low cost, thereby completing the task of large-scale preparation.

[0008] The third object of the present invention is to provide a coarse aggregate UHPC material with an elastic modulus of 70 GPa for use in the fields of road surface and bridge deck materials.

[0009] The first aspect of the present invention discloses a 70 GPa grade high modulus coarse aggregate UHPC, comprising the following components: Cement 600~800kg / m 3 Admixture 200~400kg / m 3 Calcium carbonate whisker 25~75kg / m 3 Alumina nanofiber 3.93~7.85kg / m 3 Particle size 0.075-0.2mm river sand 0-100kg / m 3 Particle size 0.2-0.4mm river sand 100-200kg / m 3 Particle size 0.4-0.6mm river sand 100-200kg / m 3 Particle size 0.6-1.18mm river sand 100-250kg / m 3 Particle size 1.18-2.36mm river sand 100-150kg / m 3 Particle size 2.36-4.75mm river sand 0-150kg / m 3 Coarse aggregate 300~550kg / m 3 Water 120~160kg / m 3 Water reducing agent 24~28kg / m 3 Ultra-high molecular weight polyethylene fiber 5.5~10.5kg / m 3 Steel fiber 78.5~157kg / m 3

[0010] Preferably, the admixture is composed of silica fume and fly ash, and the silica fume, fly ash and cement ternary cementitious system is matched into a close-packed system according to the continuous level of 0-0.075 mm. According to the difference in material particle size, q takes an appropriate value in the range of 0.2-0.25.

[0011] Furthermore, the silica content in silica ash is ≥95%, the water requirement ratio is ≤125, and the activity index is ≥105%; the silica content in fly ash is ≥60%, the water requirement ratio is <100, and the particle size distribution is 1~10µm.

[0012] Preferably, the calcium carbonate whisker has a length of 20-30 μm, a diameter of 0.5-2 μm, a tensile strength of ≥3 GPa, and an elastic modulus of ≥410 GPa.

[0013] Preferably, the alumina nanofibers have a length of 200-300 nm, a diameter of 4-8 nm, a purity of ≥99%, and a specific surface area of ​​250-300 m 2 / g.

[0014] Preferably, the coarse aggregate is metamorphic sandstone crushed stone with good grading, compactness, hardness and rough surface, and is fed according to continuous particle size of Ф5-Ф8, with a crushing value of 7.0-9.0%.

[0015] Preferably, the water reducer is a polycarboxylic acid-based water reducer with a solid content of 35% and a water reduction rate greater than 40%.

[0016] Preferably, the ultra-high molecular weight polyethylene fiber has a diameter of 20-50 μm, a length of 30 mm, a tensile strength of ≥3000 MPa, an elastic modulus of ≥100 GPa, and an ultimate elongation of 2.5%-4.0%.

[0017] Preferably, the steel fiber is at least one of a straight copper-plated steel fiber and an end hook type copper-plated steel fiber. The straight copper-plated steel fiber or the end hook type copper-plated steel fiber can be used alone, or a mixture of the two in any proportion, with a length of 13-20 mm, an aspect ratio of 65, and a base material tensile strength of ≥3000 MPa. The end hook type steel fiber can be a new type of fine multi-segment folded end hook steel fiber.

[0018] The second aspect of the present invention discloses a method for preparing the 70 GPa grade high modulus coarse aggregate UHPC, comprising the following steps: Weigh each component in proportion; Pour the cement, mineral admixture, calcium carbonate whisker, alumina nanofiber, river sand and coarse aggregate into a mixer and stir to obtain a mortar mixture; Mix water and water reducing agent evenly, slowly add into the mortar mixture and stir; Ultra-high molecular weight polyethylene fiber and steel fiber are added to the mixture respectively, and after stirring, a coarse aggregate UHPC with an elastic modulus of 70 GPa is obtained.

[0019] Furthermore, the ultra-high molecular weight polyethylene fibers and steel fibers are sprinkled into the mixture in small amounts for multiple times.

[0020] The third aspect of the present invention discloses the application of coarse aggregate UHPC with an elastic modulus of 70 GPa in the field of road surface and bridge surface materials.

[0021] From a macroscopic mechanical perspective, the addition of coarse aggregate changes the mechanical behavior of concrete, changing it from a single microscopic matrix behavior to a "matrix-coarse aggregate-interface" composite material behavior; from a microscopic perspective, coarse aggregate effectively enhances the rigidity of UHPC by changing the stress distribution and crack propagation path of the matrix. The addition of coarse aggregate can improve the internal microstructure of UHPC, making it exhibit the following characteristics:

[0022] 1) Reduce the volume shrinkage of the matrix: The addition of coarse aggregate reduces the volume ratio of the pure cement matrix, thereby reducing the internal stress caused by matrix shrinkage, which helps to reduce the generation and expansion of cracks.

[0023] 2) Optimization of stress transfer mechanism: During loading, the coarse aggregate acts as a "rigid skeleton" and can bear the main stress under the action of external force, so that the cement matrix mainly bears the stress transfer and bonding functions. This synergistic mechanism improves the overall elastic modulus.

[0024] The new multi-segment end hook steel fiber forms an effective reinforcement network in the matrix through its unique geometric shape and distribution characteristics, and uses the "mechanical bite" and "friction slip" mechanisms to transfer tensile stress at the interface, which can significantly improve the deformation resistance of the composite material. The hook-shaped structure at the end improves the anchoring force of the fiber in the matrix, and the multi-segment design ensures the synergistic effect of the fiber in different loading directions. From a microscopic point of view, the steel fiber and the matrix work together to improve the microstructure. Its existence affects the distribution of hydration reaction products in the matrix, especially the "gripping" effect of the generated CSH gel on the fiber, which further enhances the interfacial adhesion.

[0025] The mechanism of action of multi-scale hybrid fibers is closely related to the multi-scale distribution characteristics of fibers, interface effects, and optimization of microstructures. Hybrid fibers are usually composed of fibers of different lengths and diameters, including short fibers (such as steel fibers, ultra-high molecular weight polyethylene) and nano / micron-scale fibers (such as calcium carbonate whiskers, alumina nanofibers). These fibers complement each other through scale differences in the matrix:

[0026] 1) Strengthening effect of short fibers: Short fibers form a physical "bridging" effect inside the matrix, which improves the matrix's crack resistance and stress transfer ability, thereby increasing the elastic modulus of the material.

[0027] 2) Filling effect of nano / micro fibers: Nanofibers and ultrafine fibers can fill micro cracks and pores in the matrix, effectively improving the density of the matrix and reducing the impact of defects.

[0028] 3) Synergistic effect: The multi-scale fibers work together to optimize the stress distribution characteristics and deformation behavior of UHPC at both the micro and macro levels. Enhanced stress transfer efficiency: The multi-scale fibers form a network structure through staggered distribution, which can effectively disperse the external load and evenly distribute the stress in the matrix.

[0029] Nano-active powders (such as nano-calcium carbonate whiskers, alumina nanofibers, etc.) have extremely small particle sizes and high specific surface areas, and can play a significant filling role in UHPC:

[0030] 1) Pore filling: The size of nanopowder is much smaller than that of ordinary cement particles and micron-sized mineral admixtures. It can fill the unfilled micropores in the matrix, thereby significantly improving the density of the matrix.

[0031] 2) Optimization of particle packing: The addition of nanoparticles improves the particle gradation inside the concrete, making the matrix denser and thus increasing the elastic modulus.

[0032] 3) Interface densification: Nanopowders can effectively fill the interface transition zone (ITZ) between coarse aggregate and matrix, reduce its porosity, and improve the interface bonding strength.

[0033] 70GPa is a difficult gap for UHPC to cross, especially when it is necessary to ensure the compressive, flexural and tensile properties of the material at the same time. The elastic modulus of the coarse aggregate UHPC described in the present invention is at the 70GPa level that cannot be achieved with conventional proportions. The efficient use of common and inexpensive materials in this field ensures that the material has excellent compressive strength, flexural strength and tensile strength while having an extremely high elastic modulus. The UHPC material obtained by the proportion and method described in the present invention has a compressive strength of 210~230MPa, a flexural strength of 30~38MPa, a tensile strength of 12~15MPa, and an expansion of 400~500mm. The present invention can achieve the effect of the same elastic modulus as adding silicon carbide, and in the field of concrete materials where the use of various materials is extremely large, it can effectively reduce production costs while ensuring material quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1: is the cross-sectional distribution diagram of the coarse aggregate UHPC phase in the present invention, wherein (A) is the cross-sectional view of the coarse aggregate UHPC, (B) is the coarse aggregate, and (C) is the steel fiber.

[0035] Figure 2 It is the distribution uniformity of the coarse aggregate and steel fiber of the coarse aggregate UHPC in the present invention, wherein (A) is the content of coarse aggregate in different layers, (B) is the spacing between coarse aggregates, (C) is the content of steel fibers in different layers, and (D) is the spacing between steel fibers.

[0036] Figure 3 : is the spatial distribution diagram of the coarse aggregate UHPC phase in the present invention, wherein (A) is the core sample, (B) is the fiber, and (C) is the pore.

[0037] Figure 4 : This is the probability distribution diagram of the coarse aggregate UHPC fiber and voids with thickness in the present invention, wherein (A) is a schematic diagram of a core sample slice, (B) is the fiber volume content at different thicknesses, and (C) is the porosity at different thicknesses.

[0038] Figure 5 It is the characterization of the fiber orientation of the coarse aggregate UHPC in the present invention, wherein (A) is the spherical coordinate system and (B) is the fiber orientation distribution.

[0039] Figure 6 It is a schematic diagram of a fine multi-segment folded-end hook steel fiber, where (A) is a structural schematic diagram and (B) is a schematic diagram of mechanical bite force enhancement.

[0040] Figure 7 These are the test results of shrinkage performance of 70GPa grade coarse aggregate UHPC.

[0041] Figure 8 It is the test result of creep coefficient of 70GPa grade coarse aggregate UHPC. DETAILED DESCRIPTION

[0042] The following embodiments and comparative examples are used to further describe the technical scheme of the present invention, so that those skilled in the art can understand and utilize the present invention well, but they are not intended to limit the scope of protection of the present invention.

[0043] The names and abbreviations of the experimental methods, production processes, instruments and equipment involved in the embodiments and comparative examples of the present invention are conventional names in the field and are very clear and unambiguous in the relevant application fields. Technicians in the field can understand the conventional process steps and apply the corresponding equipment based on the names and implement them according to conventional conditions or conditions recommended by the manufacturer.

[0044] The various raw materials or reagents used in the examples and comparative examples of the present invention are not particularly limited in their sources, and are all conventional products that can be purchased commercially.

[0045] The compressive strength test, flexural strength test, tensile strength test, elastic modulus test, shrinkage and creep test involved in the embodiments of the present invention are carried out with reference to existing standards. Among them, the compressive performance test is carried out with reference to GB / T 31387-2015 "Reactive Powder Concrete", and the concrete cube compressive strength test specimen is a cube specimen with a side length of 100 mm. During the test, the load is uniformly applied at a speed of 1.2 MPa / s, and the experiment is repeated 3 times in parallel.

[0046] The flexural test was carried out in accordance with GB / T 31387-2015 "Reactive Powder Concrete". The specimen for the concrete flexural strength test was a prism specimen with a side length of 100×100×400mm. During the test, the load was uniformly applied at a speed of 0.1MPa / s, and the experiment was repeated three times in parallel.

[0047] The tensile test was carried out in accordance with GB / T 31387-2015 "Reactive Powder Concrete". The concrete tensile strength test specimen was a dog-bone shaped specimen. The loading was carried out in displacement control mode with a loading rate of 0.25 mm / min and six parallel experiments.

[0048] The elastic modulus test was carried out in accordance with GB / T 31387-2015 "Reactive Powder Concrete". The concrete elastic modulus test specimen was a prism specimen with a side length of 100mm×100mm×300mm. The loading speed was 1.2 MPa / s, and the experiment was repeated three times in parallel.

[0049] The shrinkage and creep tests are carried out in accordance with the standard JTG 3420-2020 "Test Procedures for Cement and Cement Concrete for Highway Engineering". Example 1

[0050] According to the components shown in Table 1, the raw materials are configured, cement, mineral admixtures, calcium carbonate whiskers, alumina nanofibers, selected river sand and coarse aggregate are poured into the mixer and stirred for 2 minutes. Then, the water and the water reducer are evenly mixed, slowly added to the mortar mixture, and stirred for 3 minutes. Finally, the ultra-high molecular weight polyethylene fibers and steel fibers are uniformly, in small amounts, and multiple times sprinkled into the mixture, and stirred for about 5 minutes until the steel fibers are evenly dispersed to obtain the UHPC material containing coarse aggregate. The prepared UHPC material is used to make test specimens. After the test specimens are formed, they are placed in an environment of (20±2)℃ for curing for 24 hours and then demolded. Then, they are cured with 90℃ steam for 48 hours. After the test specimens are cooled, they are tested;

[0051] Note: The steel fibers in this example are straight type and end hook type mixed in a mass ratio of 1:1.

[0052] The phase cross-section distribution of the prepared specimen is as follows: Figure 1 As shown, its phase space distribution is as follows Figure 3 As described above, an X-ray tomography scanner was used to obtain a grayscale image of the sample cross section, and the ImageJ software was used to analyze the uniformity of the coarse aggregate and steel fiber distribution. Figure 2 As shown, the overall distribution is relatively uniform.

[0053] The probability distribution of fibers and voids with thickness is analyzed, and the results are as follows: Figure 4 As shown, the average fiber volume content is 2.5%, the average void volume content is 1.0%, and the fiber orientation is characterized as follows Figure 5 The end hook steel fiber mixed in the above steel fiber is a new type of fine multi-segment folded end hook steel fiber, such as Figure 6 As shown in the figure, the multi-segment folded structure at both ends can increase the mechanical bite force between the fiber and the concrete matrix by more than 2 times, further improving the crack resistance of UHPC.

[0054] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 215.3 MPa, a tensile strength of 15.5 MPa, a flexural strength of 35.4 MPa and an elastic modulus of 66.3 GPa. Example 2

[0055] According to the components shown in Table 2, the raw materials are configured, cement, mineral admixtures, calcium carbonate whiskers, alumina nanofibers, selected river sand and coarse aggregate are poured into the mixer and stirred for 2 minutes. Then, the water and the water reducer are mixed evenly, slowly added to the mortar mixture, and stirred for 3 minutes. Finally, the ultra-high molecular weight polyethylene fibers and steel fibers are sprinkled into the mixture evenly, in small amounts, and multiple times, and stirred for about 5 minutes until the steel fibers are evenly dispersed to obtain UHPC materials containing coarse aggregate. After the specimen is formed, it is placed in an environment of (20±2)℃ for curing for 24 hours and then demolded. Then, it is cured with 90℃ steam for 48 hours. After the specimen is cooled, it is tested;

[0056] Note: The steel fibers in this example are straight type and end hook type mixed in a mass ratio of 1:1.

[0057] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 220.7 MPa, a tensile strength of 16.3 MPa, a flexural strength of 34.7 MPa and an elastic modulus of 69.5 GPa. Example 3

[0058] According to the components shown in Table 3, the raw materials are configured, cement, mineral admixtures, calcium carbonate whiskers, alumina nanofibers, selected river sand and coarse aggregate are poured into the mixer and stirred for 2 minutes. Then, the water and the water reducer are evenly mixed, slowly added to the mortar mixture, and stirred for 3 minutes. Finally, the ultra-high molecular weight polyethylene fibers and steel fibers are uniformly, in small amounts, and multiple times sprinkled into the mixture, and stirred for about 5 minutes until the steel fibers are evenly dispersed to obtain UHPC materials containing coarse aggregates. After the specimen is formed, it is placed in an environment of (20±2)℃ for curing for 24 hours and then demolded. Then, it is cured with 90℃ steam for 48 hours. After the specimen is cooled, it is tested;

[0059] Note: The steel fibers in this example are straight type and end hook type mixed in a mass ratio of 1:1.

[0060] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 224.9 MPa, a tensile strength of 14.7 MPa, a flexural strength of 32.5 MPa and an elastic modulus of 72.6 GPa. Example 4

[0061] According to the components shown in Table 4, the raw materials are configured, cement, mineral admixtures, calcium carbonate whiskers, alumina nanofibers, selected river sand and coarse aggregate are poured into the mixer and stirred for 2 minutes. Then, the water and the water reducer are mixed evenly, slowly added to the mortar mixture, and stirred for 3 minutes. Finally, the ultra-high molecular weight polyethylene fibers and steel fibers are sprinkled into the mixture evenly, in small amounts, and multiple times, and stirred for about 5 minutes until the steel fibers are evenly dispersed to obtain an ultra-high performance concrete material containing coarse aggregate. After the specimen is formed, it is placed in an environment of (20±2)℃ for curing for 24 hours and then demolded. Then, it is cured with 90℃ steam for 48 hours. After the specimen is cooled, it is tested;

[0062] Note: The steel fibers in this example are straight type and end hook type mixed in a mass ratio of 1:1.

[0063] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 227.4 MPa, a tensile strength of 14.1 MPa, a flexural strength of 31.3 MPa and an elastic modulus of 74.8 GPa. Example 5 (Comparative Example 1)

[0064] This embodiment (i.e., comparative example 1) contains three mixing ratios, which are recorded as comparative examples 1-1, 1-2, and 1-3 respectively: 1) UHPC material was prepared according to the method described in Example 1 and the proportions shown in Table 5;

[0065] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 211.3 MPa, a tensile strength of 13.7 MPa, a flexural strength of 33.5 MPa and an elastic modulus of 65.5 GPa.

[0066] 2) UHPC material was prepared according to the method described in Example 1 and the proportions shown in Table 6;

[0067] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 198.8 MPa, a tensile strength of 13.5 MPa, a flexural strength of 33.9 MPa and an elastic modulus of 66.3 GPa.

[0068] 3) UHPC material was prepared according to the method described in Example 1 and the proportions shown in Table 7;

[0069] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 209.4 MPa, a tensile strength of 13.7 MPa, a flexural strength of 34.2 MPa and an elastic modulus of 67.5 GPa.

[0070] The three experiments in Comparative Example 1 show that the elastic modulus of the test pieces prepared using conventional ratios cannot reach 70 GPa level even if calcium carbonate whiskers / aluminum oxide nanofibers / ultra-high molecular weight polyethylene fibers are added respectively, and the three parameters of compressive strength, flexural strength and tensile strength are also significantly lower than those of Example 1. Example 6 (Comparative Example 2)

[0071] UHPC materials were prepared according to the method described in Example 2 and the proportions shown in Table 8;

[0072] The compressive strength, flexural strength, tensile strength and elastic modulus of the specimens were tested with reference to existing standards. After testing, the coarse aggregate UHPC prepared in this example had a compressive strength of 214.3 MPa, a tensile strength of 15.4 MPa, a flexural strength of 35.1 MPa and an elastic modulus of 68.9 GPa.

[0073] It can be seen from the test results conducted in this embodiment that adding calcium carbonate whiskers, alumina nanofibers and ultra-high molecular weight polyethylene fibers simultaneously in a conventional ratio can effectively improve the elastic modulus, compressive strength, flexural strength and tensile strength parameters of the prepared test specimens, but the elastic modulus of the material randomly superimposed with calcium carbonate whiskers, alumina nanofibers and ultra-high molecular weight polyethylene fibers cannot reach the 70 GPa level.

[0074] In addition, the test pieces with the three micro-materials added at the same time did not show significant changes in the three parameters of compressive strength, flexural strength, and tensile strength. It can be seen that although calcium carbonate whiskers, alumina nanofibers, and ultra-high molecular weight polyethylene fibers have improved the performance of the material, the room for improvement is limited. Even if they are used in combination, there is a "ceiling" in their effect, and the three most important and common parameters of UHPC materials cannot be efficiently improved. Example 7 Analysis of shrinkage performance and creep coefficient

[0075] 1) Shrinkage performance With reference to the T0575-2020 section of the standard JTG 3420-2020 and in accordance with the proportions of Example 1, the shrinkage performance test was performed.

[0076] Apply lubricating oil inside the test mold, lay two layers of plastic film or place a piece of polytetrafluoroethylene (PTEF) sheet, and evenly apply a layer of lubricating oil on the surface where the film or polytetrafluoroethylene sheet contacts the test mold. Fix the reflective targets at both ends of the test mold.

[0077] After that, the concrete mixture is poured into the test mold, vibrated and smoothed, and then immediately moved into the constant temperature and humidity chamber with the mold. While the specimen is being molded, the initial setting time of the concrete is measured. The environment of the initial setting test of concrete is the same as that of the early-age shrinkage test. When the concrete is initially set, the initial readings on the left and right sides of the specimen are measured, and thereafter, the deformation readings on both sides of the specimen are measured at least every 1 hour or at the set time interval.

[0078] The results are shown in Table 9 and Figure 7 As shown in the figure, the shrinkage rate increases exponentially with time, and remains basically unchanged after 240 days. The final shrinkage rate is also lower than the shrinkage rate of conventional standard curing.

[0079] 2) Creep coefficient The creep analysis of the sample obtained according to Example 1 was performed with reference to part T0578-2020 of the standard JTG 3420-2020.

[0080] (1) Set up the probe and instrument, place the creep specimen on the lower pressure plate of the creep instrument, make the axes of the specimen, loading device, dynamometer and creep instrument coincide, and record the initial reading.

[0081] (2) Take the creep stress as 40% of the measured compressive strength of the prism, and first pressurize to 20% of the creep stress for alignment. After the alignment is completed, continue to load until the creep stress is reached, read the deformation values ​​on both sides, and take the average value of the deformation on both sides at this time as the initial deformation value under the creep load. The loading and measurement time from the completion of the alignment to the measurement of the initial deformation value shall not exceed 1 minute. Then tighten the nut on the upper end of the load-bearing screw, loosen the jack to unload, and observe the changes in the deformation values ​​on both sides.

[0082] (3) Measure the deformation value of the specimen at 1d, 3d, 7d, 14d, 28d, 45d, 90d, 120d, 150d, 180d, 270d and 360d after loading.

[0083] The results are shown in Table 10 and Figure 8 As shown in the figure, the creep of the test group developed rapidly within 45 days of load holding, and then gradually slowed down;

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. 70GPa high modulus coarse aggregate UHPC, including the following components: Cement 600~800kg / m 3 Admixture 200~400kg / m 3 Calcium carbonate whisker 25~75kg / m 3 Alumina nanofiber 3.93~7.85kg / m 3 Particle size 0.075-0.2mm river sand 0-100kg / m 3 Particle size 0.2-0.4mm river sand 100-200kg / m 3 Particle size 0.4-0.6mm river sand 100-200kg / m 3 Particle size 0.6-1.18mm river sand 100-250kg / m 3 Particle size 1.18-2.36mm river sand 100-150kg / m 3 Particle size 2.36-4.75mm river sand 0-150kg / m 3 Coarse aggregate 300~550kg / m 3 Water 120~160kg / m 3 Water reducing agent 24~28kg / m 3 Ultra-high molecular weight polyethylene fiber 5.5~10.5kg / m 3 Steel fiber 78.5~157kg / m 3 .

2. The coarse aggregate UHPC according to claim 1, wherein the admixture consists of silica fume and fly ash, and the silica fume, fly ash and the cement ternary cementitious system are formulated into a tightly packed system in a continuous grade of 0-0.075 mm.

3. The coarse aggregate UHPC according to claim 2, wherein the silica content in the silica ash is ≥95%, the water requirement ratio is ≤125%, and the activity index is ≥105%; the silica content in the fly ash is ≥60%, the water requirement ratio is <100%, and the particle size distribution is 1~10µm.

4. The coarse aggregate UHPC according to claim 1, wherein the calcium carbonate whisker has a length of 20-30 μm, a diameter of 0.5-2 μm, a tensile strength of ≥3 GPa, and an elastic modulus of ≥410 GPa.

5. The coarse aggregate UHPC according to claim 1, wherein the alumina nanofiber has a length of 200-300 nm, a diameter of 4-8 nm, a purity of ≥99%, and a specific surface area of ​​250-300 m 2 / g.

6. The coarse aggregate UHPC according to claim 1, wherein the coarse aggregate is metamorphic sandstone crushed stone, which is fed according to a continuous particle size of Φ5-Φ8 and a crushing value of 7.0-9.0%.

7. The coarse aggregate UHPC according to claim 1, wherein the water reducer is a polycarboxylic acid-based water reducer with a solid content of 35% and a water reduction rate greater than 40%.

8. The coarse aggregate UHPC according to claim 1, wherein the ultra-high molecular weight polyethylene fiber has a diameter of 20-50 μm, a length of 30 mm, a tensile strength of ≥3000 MPa, an elastic modulus of ≥100 GPa, and an ultimate elongation of 2.5%-4.0%.

9. The coarse aggregate UHPC according to claim 1, wherein the steel fiber is at least one of a straight type and a hook-end copper-plated steel fiber, with a length of 13-20 mm, an aspect ratio of 65, and a base material tensile strength of ≥3000 MPa.

10. The method for preparing the 70 GPa grade high modulus coarse aggregate UHPC according to claim 1, comprising the following steps: Weigh each component in proportion; Pour the cement, admixture, calcium carbonate whisker, alumina nanofiber, river sand and coarse aggregate into a mixer and stir to obtain a mortar mixture; Mix water and water reducing agent evenly, add into mortar mixture and stir; Ultra-high molecular weight polyethylene fiber and steel fiber are added to the mixture respectively, and after stirring, a coarse aggregate UHPC with an elastic modulus of 70 GPa is obtained.

11. The method for preparing coarse aggregate UHPC according to claim 10, wherein the ultra-high molecular weight polyethylene fibers and steel fibers are successively sprinkled into the mixture in small amounts and multiple times.

12. Application of the coarse aggregate UHPC according to claim 1 in the field of road surface and bridge surface materials.

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