Low-shrinkage ultra-high performance concrete as well as preparation method and application thereof

Abstract

The invention discloses low-shrinkage ultra-high performance concrete as well as a preparation method and application thereof, and belongs to the technical field of building materials. The low-shrinkage ultra-high performance concrete is prepared from the following raw materials in parts by weight: 500 to 600 parts of cement, 1000 to 1500 parts of magnesium-titanium slag sand, 150 to 200 parts of fly ash, 150 to 200 parts of silica fume, 100 to 150 parts of rice hull ash, 150 to 180 parts of steel fiber, 20 to 30 parts of a water reducing agent and 150 to 180 parts of water. The invention further discloses a preparation method and application of the low-shrinkage ultra-high performance concrete. The low-shrinkage ultra-high performance concrete prepared by the invention can better solve the problem of poor long-term durability of the concrete caused by high shrinkage characteristic of the existing ultra-high performance concrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a low-shrinkage ultra-high performance concrete, its preparation method, and its application. Background Technology

[0002] Due to its excellent mechanical properties and long-term durability, ultra-high performance concrete (UHPC) has become a key material for major engineering structures, such as large-span structures and protective engineering projects. However, the realization of UHPC's ultra-high performance depends on extremely low water consumption and extremely high cementitious material content. Therefore, its widespread application has been limited by its inherent high shrinkage, which can be several times that of ordinary concrete. This high shrinkage characteristic easily leads to cracking, which is detrimental to long-term durability.

[0003] Meanwhile, the resource utilization of high-magnesium and high-titanium slag (MgTi slag), as a massive industrial solid waste, is urgently needed. Compared to high-titanium slag with high TiO2 content (35-55 wt%), MgTi slag has a TiO2 content of only 18 wt%, and its alkalinity is around 1.0, classifying it as alkaline slag. Furthermore, its MgO content is as high as 10.2 wt%, which easily causes volume stability problems in cement-based materials. Therefore, how to effectively stimulate its beneficial cementitious and micro-expansion properties while suppressing its destructive expansion remains an unresolved challenge in the field of solid waste utilization.

[0004] In response to the current challenges in the development of UHPC technology, there is still a technological gap in how to combine precise regulation of internal maintenance with safe activation of high-risk solid waste to achieve a high proportion of solid waste in UHPC and realize synergistic effects. Summary of the Invention

[0005] The problem this invention aims to solve is to provide a low-shrinkage ultra-high performance concrete, its preparation method, and its application, in order to address the problem of poor long-term durability of existing ultra-high performance concrete due to its high shrinkage characteristics.

[0006] The technical solution adopted to solve the technical problem is to provide a low-shrinkage ultra-high performance concrete, comprising the following raw materials in parts by weight: 500-600 parts cement, 1000-1500 parts magnesium-titanium slag sand, 150-200 parts fly ash, 150-200 parts silica fume, 100-150 parts rice husk ash, 150-180 parts steel fiber, 20-30 parts water-reducing agent, and 150-180 parts water.

[0007] The beneficial effects of the above-mentioned technical solution of the present invention are as follows: The low-shrinkage ultra-high performance concrete of the present invention compensates for shrinkage stress through the micro-expansion characteristics of magnesium titanium slag sand, and combines fly ash, rice husk ash and silica fume to reduce drying shrinkage and autogenous shrinkage. At the same time, the three-dimensional distribution of steel fibers effectively disperses crack propagation, and the water-reducing agent regulates the water-cement ratio to further inhibit plastic shrinkage caused by free water evaporation. The synergistic effect of multiple components significantly reduces the shrinkage rate of concrete, improves crack resistance, impermeability and carbonation resistance, extends structural durability, and realizes the high-value utilization of industrial solid waste.

[0008] Preferred low-shrinkage ultra-high performance concrete comprises the following raw materials in parts by weight: 540 parts cement, 1365 parts magnesium-titanium slag sand, 185 parts fly ash, 170 parts silica fume, 135 parts rice husk ash, 160 parts steel fiber, 25.75 parts water-reducing agent, and 165 parts water.

[0009] Preferably, the cement is silicate cement; the median particle size of fly ash is 12~13 μm; and the median particle size of silica fume is 0.1~0.2 μm.

[0010] More preferably, the cement is P·O 52.5 silicate cement; the fly ash is Class F Grade I fly ash with a median particle size of 12.78 μm; and the silica fume has a median particle size of 0.15 μm.

[0011] Preferably, the particle size of magnesium-titanium slag sand is 0.08~1.25 mm.

[0012] Preferably, rice husk ash is obtained by the following steps: (1) Remove impurities from rice husks and dry them to obtain pretreated rice husks; (2) After the pretreated rice husks are burned in two stages and then cooled, pretreated rice husk ash is obtained. (3) The pretreated rice husk ash is ball-milled to obtain rice husk ash.

[0013] More preferably, the two-stage calcination in step (2) includes the following steps: calcining the pretreated rice husks at 300~320℃ for 30~90 min, and then calcining them at 600~650℃ for 90~150 min; in step (3), the ball milling speed is 50~70 rpm and the time is 15~30 min; the median particle size of the rice husk ash is 5~6 μm.

[0014] More preferably, the ball milling speed is 60 rpm and the time is 20 min; the median particle size of rice husk ash is 5.6 μm.

[0015] Preferably, the steel fibers have a tensile strength ≥2850 MPa, a length of 10~15 mm, and a diameter of 0.18~0.3 mm; the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate >23%.

[0016] More preferably, the length of the steel fiber is 13 mm.

[0017] The present invention also provides a method for preparing the above-mentioned low-shrinkage ultra-high performance concrete, comprising the following steps: (1) Mix cement, magnesium titanium slag sand, fly ash, silica fume and rice husk ash and stir evenly to obtain mixture A; (2) Mix the water-reducing agent and water to obtain mixture B; (3) Divide mixture B into 2-3 equal parts by weight and add them to mixture A in sequence, stirring until homogeneous to obtain mixture C; (4) Divide the steel fibers into 3 to 4 equal parts by weight and add them to mixture C in sequence and stir evenly to obtain mixed mortar; (5) The mixed mortar is poured and cured in sequence to obtain the final product.

[0018] Preferably, in step (1), the stirring speed is 15~25 rpm and the time is 1~3 min; in step (3), the stirring speed is 15~25 rpm and the time is 2~4 min; in step (4), the stirring speed is 15~25 rpm and the time is 3~5 min.

[0019] More preferably, in step (1), the stirring speed is 20 rpm and the time is 2 min; in step (3), the stirring speed is 20 rpm and the time is 3 min; in step (4), the stirring speed is 20 rpm and the time is 3 min.

[0020] More preferably, the curing in step (5) includes the following steps: curing at room temperature for 45-50 hours, and then curing in still water at 18-22°C until the desired age, with the pH value of the water not lower than 7.

[0021] More preferably, the curing in step (5) includes the following steps: curing at room temperature for 48 hours, and then curing in still water at 20°C until the desired age, with the pH value of the water not lower than 7.

[0022] The present invention also provides the application of the above-mentioned low-shrinkage ultra-high performance concrete in the elastic shielding layer, the main structure of long-span bridges and high-rise buildings.

[0023] The present invention has the following beneficial effects: (1) The low-shrinkage ultra-high performance concrete of the present invention has the characteristics of low shrinkage. Through the micro-expansion compensation of magnesium titanium slag sand and the synergistic shrinkage reduction of multi-source solid waste, its early self-shrinkage is controlled at the 90 micro-strain level, so that the early self-shrinkage of UHPC is reduced to the level of ordinary concrete. The shrinkage reduction effect is significantly better than the existing multi-source solid waste composite technology. (2) The low-shrinkage ultra-high performance concrete of the present invention exhibits obvious strain hardening characteristics in tensile behavior and combines high strength and high toughness. (3) The low-shrinkage ultra-high performance concrete of the present invention can improve the utilization rate of solid waste while meeting the performance requirements of UHPC, realize the complete replacement of traditional quartz sand with magnesium titanium slag sand, and increase the amount of rice husk ash. This can reduce carbon emissions and solve the problem of industrial waste treatment, forming a technical closed loop of high performance and green development. Attached Figure Description

[0024] Figure 1 The stress-strain curve; Figure 2 This is a graph showing the relationship between shrinkage value and time. Figure 3 Microstructure diagrams of specimens prepared for Comparative Example 2 and Example 1; wherein, (a) is Comparative Example 2; (b) is Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0026] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but only to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] The features and performance of the present invention will be further described in detail below with reference to the embodiments. In this invention, the P·O52.5 silicate cement is sourced from Fushun Aose Company; the magnesium-titanium slag sand is sourced from Huaxi Lushe Company; the fly ash is sourced from Henan Borun Company; the silica fume is sourced from IMERYS Company; the steel fiber is sourced from Hengshui Maurer Metal Products Factory; and the water-reducing agent is Boyu high-efficiency polycarboxylate water-reducing agent, sourced from Sichuan Huaxi Lushe Huaxing Construction Technology Co., Ltd.

[0028] Example 1 A low-shrinkage ultra-high performance concrete comprises the following raw materials in parts by weight: 540 parts of P·O 52.5 silicate cement, 1365 parts of magnesium-titanium slag sand with a particle size of 1 mm, 185 parts of Class I fly ash of type F with a median particle size of 12.78 μm, 170 parts of silica fume with a median particle size of 0.15 μm, 135 parts of rice husk ash, 160 parts of steel fiber, 25.75 parts of polycarboxylate superplasticizer with a water reduction rate >23%, and 165 parts of water. Among them, the steel fibers have a tensile strength ≥2850 MPa, a length of 13 mm, and a diameter of 0.18~0.3 mm; The median particle size of rice husk ash is 5.6 μm, and it is prepared by the following steps: (1) Wash the rice husks with tap water to separate them from impurities, then remove the impurities by screening, and then dry the rice husks after removing impurities at room temperature to constant weight to obtain pretreated rice husks. (2) The pretreated rice husks were calcined at 310℃ for 60 min, then calcined at 630℃ for 120 min, and then cooled to room temperature with the furnace to obtain pretreated rice husk ash. (3) The pretreated rice husk ash was ball-milled at 60 rpm for 20 min to obtain rice husk ash.

[0029] The method for preparing low-shrinkage ultra-high performance concrete in this embodiment includes the following steps: (1) P·O 52.5 silicate cement, magnesium titanium slag sand with a particle size of 1 mm, Class I fly ash of F type with a median particle size of 12.78 μm, silica fume with a median particle size of 0.15 μm and rice husk ash with a median particle size of 5.6 μm are poured into a mixer with a speed of 20 rpm and mixed for 2 min to obtain mixture A; (2) Mix the polycarboxylate superplasticizer with a water reduction rate > 23% with water to obtain mixture B; (3) Divide mixture B into two equal parts by weight and add them to a mixer containing mixture A in sequence. Stir at 20 rpm for 3 min to obtain mixture C; (4) Keep the mixer speed at 20 rpm, divide the steel fiber into 3 equal parts by weight and add them to the mixture C in sequence within 2 min, and then stir for 1 min to obtain the mixed mortar; (5) Pour the mixed mortar into the mold that has been coated with machine oil, place it on a vibration table with a vibration frequency of 50 Hz and vibrate for 30 s, then smooth the surface and cover it with plastic film, and cure it at room temperature for 48 h. After demolding, transfer the specimen to non-flowing water at a temperature of 20℃ and cure it until the required age. The pH value of the water should not be lower than 7 to obtain low shrinkage ultra-high performance concrete.

[0030] Example 2 A low-shrinkage ultra-high performance concrete comprises the following raw materials in parts by weight: 500 parts of P·O 52.5 silicate cement, 1000 parts of magnesium-titanium slag sand with a particle size of 0.08 mm, 150 parts of Class I fly ash of type F with a median particle size of 12 μm, 150 parts of silica fume with a median particle size of 0.1 μm, 100 parts of rice husk ash, 150 parts of steel fiber, 20 parts of polycarboxylate superplasticizer with a water reduction rate >23%, and 150 parts of water. Among them, the steel fibers have a tensile strength ≥2850 MPa, a length of 13 mm, and a diameter of 0.18~0.3 mm; The median particle size of rice husk ash is 5 μm, and it is prepared by the following steps: (1) Wash the rice husks with tap water to separate them from impurities, then remove the impurities by screening, and then dry the rice husks after removing impurities at room temperature to constant weight to obtain pretreated rice husks. (2) The pretreated rice husks were calcined at 300℃ for 90 min, then calcined at 600℃ for 150 min, and then cooled to room temperature with the furnace to obtain pretreated rice husk ash. (3) The pretreated rice husk ash was ball-milled at 50 rpm for 15 min to obtain rice husk ash.

[0031] The method for preparing low-shrinkage ultra-high performance concrete in this embodiment includes the following steps: (1) P·O 52.5 silicate cement, magnesium titanium slag sand with a particle size of 0.08 mm, 150 parts of Class I fly ash with a median particle size of 12 μm, silica fume with a median particle size of 0.1 μm and rice husk ash with a median particle size of 5 μm are poured into a mixer with a speed of 15 rpm and mixed for 1 min to obtain mixture A; (2) Mix the polycarboxylate superplasticizer with a water reduction rate > 23% with water to obtain mixture B; (3) Divide mixture B into two equal parts by weight and add them to a mixer containing mixture A in sequence. Stir at 15 rpm for 2 min to obtain mixture C; (4) Keep the mixer speed at 15 rpm, divide the steel fiber into 3 equal parts by weight and add them to the mixture C in sequence within 3 min, and then stir for 1 min to obtain the mixed mortar; (5) Pour the mixed mortar into the mold that has been coated with machine oil, place it on a vibration table with a vibration frequency of 50 Hz and vibrate for 30 s, then smooth the surface and cover it with plastic film, and cure it at room temperature for 45 h. After demolding, transfer the specimen to non-flowing water at a temperature of 20℃ and cure it until the required age. The pH value of the water should not be lower than 7 to obtain low shrinkage ultra-high performance concrete.

[0032] Example 3 A low-shrinkage ultra-high performance concrete comprises the following raw materials in parts by weight: 600 parts of P·O 52.5 silicate cement, 1500 parts of magnesium-titanium slag sand with a particle size of 1.25 mm, 200 parts of Class I fly ash of type F with a median particle size of 13 μm, 200 parts of silica fume with a median particle size of 0.2 μm, 150 parts of rice husk ash, 180 parts of steel fiber, 30 parts of polycarboxylate superplasticizer with a water reduction rate >23%, and 180 parts of water. Among them, the steel fibers have a tensile strength ≥2850 MPa, a length of 13 mm, and a diameter of 0.18~0.3 mm; The median particle size of rice husk ash is 6 μm, and it is prepared by the following steps: (1) Wash the rice husks with tap water to separate them from impurities, then remove the impurities by screening, and then dry the rice husks after removing impurities at room temperature to constant weight to obtain pretreated rice husks. (2) The pretreated rice husks were calcined at 320°C for 30 min, then calcined at 650°C for 90 min, and then cooled to room temperature in the furnace to obtain pretreated rice husk ash. (3) The pretreated rice husk ash was ball-milled at 70 rpm for 30 min to obtain rice husk ash.

[0033] The method for preparing low-shrinkage ultra-high performance concrete in this embodiment includes the following steps: (1) P·O 52.5 silicate cement, magnesium titanium slag sand with a particle size of 1.25 mm, Class I fly ash of F type with a median particle size of 13 μm, silica fume with a median particle size of 0.2 μm and rice husk ash with a median particle size of 6 μm are poured into a mixer with a speed of 25 rpm and mixed for 3 min to obtain mixture A; (2) Mix the polycarboxylate superplasticizer with a water reduction rate > 23% with water to obtain mixture B; (3) Divide mixture B into two equal parts by weight and add them to a mixer containing mixture A in sequence. Stir at 25 rpm for 4 min to obtain mixture C; (4) Keep the mixer speed at 25 rpm, divide the steel fiber into 3 equal parts by weight and add them to the mixture C in sequence within 3 min, and then stir for 2 min to obtain the mixed mortar; (5) Pour the mixed mortar into the mold coated with machine oil, place it on a vibration table with a vibration frequency of 50 Hz and vibrate for 30 s. Then smooth the surface and cover it with plastic film. Cure it at room temperature for 50 h. After demolding, transfer the specimen to non-flowing water at a temperature of 20℃ and cure it until the required age. The pH value of the water should not be lower than 7 to obtain low shrinkage ultra-high performance concrete.

[0034] Comparative Example 1 An ultra-high performance concrete comprises the following raw materials in parts by weight: 675 parts of P·O 52.5 silicate cement, 1150 parts of quartz sand with a particle size of 40 mesh, 185 parts of Class I fly ash of type F with a median particle size of 12.78 μm, 170 parts of silica fume with a median particle size of 0.15 μm, 160 parts of steel fiber, 25.75 parts of polycarboxylate superplasticizer with a water reduction rate of >23%, and 165 parts of water; The steel fibers have a tensile strength ≥2850 MPa, a length of 13 mm, and a diameter of 0.18~0.3 mm.

[0035] The ultra-high performance concrete in this comparative example was prepared through the following steps: (1) P·O 52.5 silicate cement, quartz sand with a particle size range of 20~70 mesh, F-type Class I fly ash with a median particle size of 12.78 μm and silica fume with a median particle size of 0.15 μm are poured into a mixer with a speed of 20 rpm and mixed for 2 min to obtain mixture A; (2) Mix the polycarboxylate superplasticizer with a water reduction rate > 23% with water to obtain mixture B; (3) Divide mixture B into two equal parts by weight and add them to a mixer containing mixture A in sequence. Stir at 20 rpm for 3 min to obtain mixture C; (4) Keep the mixer speed at 20 rpm, divide the steel fiber into 3 equal parts by weight and add them to the mixture C in sequence within 2 min, and then stir for 1 min to obtain the mixed mortar; (5) Pour the mixed mortar into the mold coated with machine oil, place it on a vibration table with a vibration frequency of 50 Hz and vibrate for 30 s. Then smooth the surface and cover it with plastic film. Cure at room temperature for 48 h. After demolding, transfer the specimen to non-flowing water at a temperature of 20℃ and cure it until the required age. The pH value of the water should not be lower than 7 to obtain ultra-high performance concrete.

[0036] Comparative Example 2 An ultra-high performance concrete comprises the following raw materials in parts by weight: 675 parts of P·O 52.5 silicate cement, 1365 parts of magnesium-titanium slag sand with a particle size of 1 mm, 185 parts of Class I fly ash of type F with a median particle size of 12.78 μm, 170 parts of silica fume with a median particle size of 0.15 μm, 160 parts of steel fiber, 25.75 parts of polycarboxylate superplasticizer with a water reduction rate >23%, and 164.4 parts of water; The steel fibers have a tensile strength ≥2850 MPa, a length of 13 mm, and a diameter of 0.18~0.3 mm.

[0037] The ultra-high performance concrete in this comparative example was prepared through the following steps: (1) P·O 52.5 silicate cement, magnesium titanium slag sand with a particle size of 1 mm, Class I fly ash of F type with a median particle size of 12.78 μm and silica fume with a median particle size of 0.15 μm are poured into a mixer with a speed of 20 rpm and mixed for 2 min to obtain mixture A; (2) Mix the polycarboxylate superplasticizer with a water reduction rate > 23% with water to obtain mixture B; (3) Divide mixture B into two equal parts by weight and add them to a mixer containing mixture A in sequence. Stir at 20 rpm for 3 min to obtain mixture C; (4) Keep the mixer speed at 20 rpm, divide the steel fiber into 3 equal parts by weight and add them to the mixture C in sequence within 2 min, and then stir for 1 min to obtain the mixed mortar; (5) Pour the mixed mortar into the mold coated with machine oil, place it on a vibration table with a vibration frequency of 50 Hz and vibrate for 30 s. Then smooth the surface and cover it with plastic film. Cure at room temperature for 48 h. After demolding, transfer the specimen to non-flowing water at a temperature of 20℃ for curing. The pH value of the water should not be lower than 7 to obtain ultra-high performance concrete.

[0038] Experimental Example The chemical composition of the magnesium-titanium slag sand (Examples 1-3, Comparative Example 2) used in this invention is shown in Table 1 below.

[0039] Table 1 Chemical composition of magnesium-titanium slag and high-titanium slag 1. Compressive strength test The ultra-high performance concrete obtained in Example 1 and Comparative Example 1 were used to prepare standard specimens for compressive strength testing, and compressive strength tests were conducted at 7 days and 28 days of age. The tests were carried out in accordance with GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)". The test results are shown in Table 1.

[0040] Table 1 Compressive strength test results As shown in Table 1, the compressive strength of the low-shrinkage ultra-high performance concrete prepared in Example 1 of this invention is about 20 MPa higher than that of the ultra-high performance concrete prepared in Comparative Example 1, fully meeting the compressive strength requirements of UHPC. Furthermore, the use of magnesium-titanium ore slag sand in the preparation of UHPC in this invention has a more significant effect on improving its mechanical properties, because magnesium-titanium ore slag is a medium-alkaline slag and has a certain degree of self-cementing properties.

[0041] 2. Tensile property test Standard specimens of the ultra-high performance concrete prepared in Example 1 and Comparative Example 2 were used for direct tensile testing. The experiments were conducted according to the method described in "Recommendations for Design and Construction of HighPerformance Fiber Reforced Cement Composites with Multiple Fine Cracks". The results are as follows: Figure 1 As shown.

[0042] from Figure 1 As can be seen from the above, the low-shrinkage ultra-high performance concrete prepared in Example 1 of the present invention has significantly better ultimate tensile strength and ultimate tensile strain than the ultra-high performance concrete prepared in Comparative Example 2, and also has better tensile strain hardening behavior.

[0043] 3. Analysis of shrinkage effect To verify whether rice husk ash and magnesium-titanium slag sand can synergistically reduce shrinkage in this invention, the early autogenous shrinkage of UHPC was controlled below 100 microstrains. Cement-based materials were prepared according to Comparative Example 1, Comparative Example 2, and Example 1, and corrugated pipe tests were conducted. The experiments were carried out according to ASTM C1698-09, "Standard Test Method for Self-Stress of Cement Grout and Cement Mortar." The results are as follows. Figure 2 As shown.

[0044] Existing research shows that adding 10% rice husk ash alone can control the early autogenous shrinkage of UHPC to 250 microstrains, which is about 1.5 to 5 times that of ordinary concrete (50~150 μm / m). The optimal admixture of traditional high-titanium slag sand is 30~40% volume replacement rate (considering both shrinkage reduction and mechanical properties), with a shrinkage reduction range of 15~25% (from references 1~4). It can be seen that existing solid waste shrinkage reduction technologies are difficult to control the early autogenous shrinkage of UHPC to within 100 microstrains.

[0045] from Figure 2 As can be seen from the data, magnesium-titanium slag sand has a certain shrinkage reduction effect (Comparative Example 2), but the autogenous shrinkage value still exceeds 300 microstrain, which is about 2 to 6 times that of ordinary concrete (50~150 μm / m). The autogenous shrinkage of the low-shrinkage ultra-high performance concrete prepared in Example 1 is much smaller than that of the ultra-high performance concrete prepared in Comparative Examples 1 and 2. Its autogenous shrinkage after 3 days decreases to 90 microstrain, indicating that the synergistic anti-shrinkage effect of rice husk ash and magnesium-titanium slag sand is significant and significantly exceeds the UHPC solid waste shrinkage reduction method in existing studies (autogenous shrinkage value in the range of 200~300 microstrain after 3 days).

[0046] This effect stems from the synergistic effect of magnesium-titanium slag sand and rice husk ash, which promotes full hydration of cement near the slurry-aggregate interface. The microstructure was observed using a FEI Nova NanoSEM 450, and the results are as follows... Figure 3 As shown in the figure, it can be observed that the synergistic effect of magnesium titanium slag sand and rice husk ash can effectively refine the slurry-bone interface, thereby strengthening the original shrinkage-resistant weak area in UHPC. This is the core microscopic mechanism of the synergistic shrinkage reduction of the two.

[0047] Reference 1: Ye Guang, VTNGUYEN. Analysis of the mechanism of rice husk ash inhibiting autogenous shrinkage of ultra-high performance concrete [J]. Silicate Science, 2012, 40(02): 212-216. Document 2: X. Li, J. Li, Z. Lu, L. He, J. Chen, Preparation and properties of reactive powder concrete by using titanium slag aggregates, Constr. Build.Mater. 234 (2020) 117342. Document 3: S. Middlemas, ZZ Fang, P. Fan, Life cycle assessment comparison of emerging and traditional titanium dioxide manufacturing processes, J. Clean. Prod. 89 (2015) 137-147. Document 4: XY Li, J. Li, ZY Lu, Study on properties and paste-aggregate interaction mechanism of ultra-high performance concrete with hightitanium slag aggregate, J. Wuhan Univ. Technol. 44 (2022) 17-24. The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A low-shrinkage ultra-high performance concrete, characterized in that, The raw materials include the following parts by weight: 500-600 parts cement, 1000-1500 parts magnesium-titanium slag sand, 150-200 parts fly ash, 150-200 parts silica fume, 100-150 parts rice husk ash, 150-180 parts steel fiber, 20-30 parts water-reducing agent, and 150-180 parts water.

2. The low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that, The raw materials include the following parts by weight: 540 parts cement, 1365 parts magnesium-titanium slag sand, 185 parts fly ash, 170 parts silica fume, 135 parts rice husk ash, 160 parts steel fiber, 25.75 parts water-reducing agent, and 165 parts water.

3. The low-shrinkage ultra-high performance concrete as described in claim 1 or 2, characterized in that, The cement is silicate cement; the median particle size of the fly ash is 12~13 μm; and the median particle size of the silica fume is 0.1~0.2 μm.

4. The low-shrinkage ultra-high performance concrete as described in claim 1 or 2, characterized in that, The particle size of the magnesium-titanium slag sand is 0.08~1.25 mm.

5. The low-shrinkage ultra-high performance concrete as described in claim 1 or 2, characterized in that, The rice husk ash is obtained by the following steps: (1) Remove impurities from rice husks and dry them to obtain pretreated rice husks; (2) After the pretreated rice husks are burned in two stages and then cooled, pretreated rice husk ash is obtained. (3) The pretreated rice husk ash is ball-milled to obtain rice husk ash.

6. The low-shrinkage ultra-high performance concrete as described in claim 5, characterized in that, The two-stage burning process in step (2) includes the following steps: burning the pretreated rice husks at 300~320℃ for 30~90 min, and then burning them at 600~650℃ for 90~150 min; the ball milling speed in step (3) is 50~70 rpm and the time is 15~30 min; the median particle size of the rice husk ash is 5~6 μm.

7. The low-shrinkage ultra-high performance concrete as described in claim 1 or 2, characterized in that, The steel fiber has a tensile strength ≥2850 MPa, a length of 10~15 mm, and a diameter of 0.18~0.3 mm; the water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate >23%.

8. The method for preparing low-shrinkage ultra-high performance concrete according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Mix cement, magnesium titanium slag sand, fly ash, silica fume and rice husk ash and stir evenly to obtain mixture A; (2) Mix the water-reducing agent and water to obtain mixture B; (3) Divide mixture B into 2-3 equal parts by weight and add them to mixture A in sequence, stirring until homogeneous to obtain mixture C; (4) Divide the steel fibers into 3 to 4 equal parts by weight and add them to mixture C in sequence and stir evenly to obtain mixed mortar; (5) The mixed mortar is poured and cured in sequence to obtain the final product.

9. The method for preparing low-shrinkage ultra-high performance concrete as described in claim 8, characterized in that, In step (1), the stirring speed is 15-25 rpm and the time is 1-3 min; in step (3), the stirring speed is 15-25 rpm and the time is 2-4 min; in step (4), the stirring speed is 15-25 rpm and the time is 3-5 min.

10. The application of the low-shrinkage ultra-high performance concrete according to any one of claims 1 to 7 in the elastic shielding layer, the main structure of long-span bridges and high-rise buildings.

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