Full-period low-shrinkage ultra-high performance concrete and preparation method thereof

Abstract

The invention belongs to the technical field of concrete, and particularly relates to full-period low-shrinkage ultra-high-performance concrete and a preparation method thereof. The full-period low-shrinkage ultra-high-performance concrete is prepared from 900-1110 parts of quartz sand, 600-700 parts of cement, 100-200 parts of silica fume, 200-250 parts of fly ash microspheres, 80-120 parts of steel fibers, 20-40 parts of a montmorillonite modified shrinkage reducing type water reducing agent, 5-10 parts of polyvinyl alcohol fibers, 30-50 parts of a composite expanding agent and 300-400 parts of water. According to the time-sharing shrinkage-inhibiting composite expanding agent disclosed by the invention, the full-time volume stability of concrete is improved, the volume shrinkage of set cement is greatly reduced, and the problem that the shrinkage of ultra-low water-binder ratio concrete is large is fundamentally solved.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and in particular to a low-shrinkage, ultra-high-performance concrete with high performance throughout the entire time period and its preparation method. Background Technology

[0002] Ultra-High Performance Concrete (UHPC) is a new type of cement-based composite material with ultra-high strength, high toughness, and high durability. Compared with ordinary concrete, UHPC has superior mechanical properties, durability, and resistance to penetration and blasting. For example, under the same penetration conditions, the penetration depth and pitting damage of UHPC are much smaller than those of ordinary concrete.

[0003] However, ultra-high performance concrete still has some unresolved drawbacks: its performance is influenced by complex factors related to raw materials, and the preparation process involves a wide variety of materials in large quantities, which has a complex impact on its preparation process and performance. In particular, the large amount of cementitious materials and the low water-cement ratio lead to incomplete hydration of the cementitious materials, resulting in significant early shrinkage due to the ultra-low water-cement ratio and high cement content. This situation negatively affects the volume stability and durability of ultra-high performance concrete.

[0004] Therefore, how to improve the mechanical properties of ultra-high performance concrete while reducing its shrinkage throughout the entire life cycle is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a low-shrinkage, ultra-high-performance concrete with all-time low shrinkage and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-shrinkage ultra-high performance concrete that operates throughout all time periods, wherein the ultra-high performance concrete is composed of the following components: 900-1110 parts of quartz sand, 600-700 parts of cement, 100-200 parts of silica fume, 200-250 parts of fly ash microspheres, 80-120 parts of steel fiber, 20-40 parts of montmorillonite-modified shrinkage-reducing water-reducing agent, 5-10 parts of polyvinyl alcohol fiber, 30-50 parts of composite expansion agent, and 300-400 parts of water.

[0007] Furthermore, the polyvinyl alcohol fiber has a length of 6-12 mm, a tensile strength ≥1200 MPa, and an alkali resistance ≥95%.

[0008] Furthermore, the specific surface area of ​​the fly ash microspheres is ≥1500 m². 2 / kg, bulk density is 300-500kg / m³ 3The particle size is 1-30μm; fly ash microspheres can improve fluidity, and the use of silica fume can increase the density of UHPC and improve its impermeability.

[0009] Furthermore, the quartz sand has a particle size of less than 3 mm, and the silica fume with a particle size of less than 1 μm accounts for no less than 30%.

[0010] Furthermore, the steel fibers have a diameter of 0.3-0.7 mm and a length of 5-15 mm. The steel fibers and polyvinyl alcohol fibers, acting as reinforcing and toughening materials, are randomly interwoven within the cementitious material, playing a role in crack prevention and stress transfer. The montmorillonite-modified shrinkage-inhibiting water-reducing agent not only has good water-reducing and reinforcing effects, regulating setting time and improving slurry fluidity retention, but also reduces the surface tension of the slurry liquid phase, thereby reducing cracking. The synergistic composite toughening system of steel fibers and polyvinyl alcohol fibers can reduce the formation of early microcracks in UHPC, especially cracks during the plastic phase, indirectly reducing the risk of later cracking; while the steel fibers can provide sufficient tensile strength for UHPC, further reducing the risk of cracking.

[0011] Further, the composite expansion agent is composed of the following components by weight: 2-8 parts of azo compound, 20-30 parts of magnesium oxide, 10-30 parts of calcium oxide, 30-50 parts of calcium aluminate-calcium sulfoaluminate cement clinker, 5-10 parts of pre-absorbed spherical sodium polyacrylate, and 5-10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres. Furthermore, the magnesium oxide is obtained by low-temperature calcination at 600-800℃. MgO expanding agent has a delayed micro-expansion effect, mainly acting on expansion in the middle and late stages. The direct driving force for the expansion of MgO expanding agent comes from the swelling force and crystallization pressure of Mg(OH)2 crystals. In the early stage of hydration, Mg(OH)2 crystals are very small, and the expansion of the slurry is mainly due to the swelling force of water absorption. As Mg(OH)2 crystals grow, the crystallization growth pressure of the crystals becomes the main driving force for expansion.

[0012] Furthermore, the montmorillonite-modified shrinkage-reducing agent is prepared by the following method: (1) Methoxy polyethylene glycol, diethylene glycol monomethyl ether, hydroxymethyl acrylamide and methacrylic acid in a molar ratio of 1:0.15:0.1:3 were added to the reactor in sequence and stirred at 40-45℃ to obtain mixture A. During the reaction, the water in the reactor was continuously removed by vacuuming. (2) Hydroquinone (0.05 wt% of total material weight) and concentrated sulfuric acid (0.6 wt% of total material weight) were added to mixture A in sequence, and the temperature was raised to 120°C and reacted for 6 hours to obtain esterified product B. (3) Cool the reactants to 60°C and dilute them with water; (4) Dissolve 0.15wt% of ammonium persulfate in water to prepare a drop feed C with a concentration of 8wt%, and add it evenly to the reactor in 3 hours. After the addition is completed, keep it warm for 3 hours. After cooling, add 35wt% sodium hydroxide solution to adjust the pH to 6.0-6.8 to obtain the shrinkage-reducing water-reducing agent. (5) Prepare the shrinkage-reducing water-reducing agent prepared in step (4) into an aqueous solution with a mass concentration of 20-40wt%, add montmorillonite powder to it, sonicate for 2-6 hours, and seal and store at 20-35℃ for 24-48 hours to obtain montmorillonite-modified shrinkage-reducing agent.

[0013] Further, in step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to the montmorillonite powder is 5:1; in step (5), the solid-liquid ratio of the shrinkage-reducing water-reducing agent aqueous solution to the montmorillonite powder is 5:1.

[0014] Under ultrasonic conditions, the shrinkage-reducing water-reducing agent flows into the interlayer structure of montmorillonite and deposits there, forming a montmorillonite-loaded shrinkage-reducing water-reducing agent. This invention uses methoxy polyethylene glycol, diethylene glycol monomethyl ether, hydroxymethyl acrylamide, and methacrylic acid for free radical polymerization to prepare a shrinkage-reducing water-reducing agent containing amide and carboxylic acid groups in its structure. The shrinkage-reducing water-reducing agent has a low surface energy, which can reduce the air pressure in the hollow structure of concrete and reduce the capillary tension of cement pores, thereby reducing the risk of shrinkage cracking in concrete. Combined with the bridging effect of steel fibers and polyvinyl alcohol fibers on the internal structure of concrete, the synergistic effect formed by them makes the concrete not only have low internal shrinkage stress but also have a significant crack resistance effect. Therefore, the final concrete prepared has excellent crack resistance.

[0015] This invention uses montmorillonite to load a shrinkage-reducing water-reducing agent. During the drying process of concrete, the internal pressure gradually decreases, and the shrinkage-reducing water-reducing agent slowly detaches from the montmorillonite under pressure. The amide and carboxylic acid groups contained in the shrinkage-reducing water-reducing agent can react with calcium hydroxide in the cement paste, thereby accelerating the hydration rate of C3S. This leads to a significant increase in the number of needle-like ettringite in the early cement blocks, thus reducing the early shrinkage of concrete and even enhancing its early strength.

[0016] Furthermore, the kaolin in the composite expanding agent has a particle size of 50-100 μm; the average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.3 cm-0.7 cm.

[0017] Furthermore, the spherical sodium polyacrylate in the composite expanding agent is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 3-5 mm; Furthermore, the proportion of calcium aluminate-calcium sulfoaluminate cement raw materials in the composite expansive agent is: bauxite 50-60%, limestone 30-45%, gypsum 5-18%; the mineral composition range of the clinker is: CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; bauxite: Al2O3 > 72%, SiO2 < 11%; limestone: CaO > 55%, SiO2 < 12%; gypsum: SO3 > 46%. After calcium oxide is mixed with cement and water, it undergoes a hydration reaction to generate calcium hydroxide, which produces the expansion force of the concrete. The expansion source is Ca(OH)2, and the solid phase volume almost doubles after the reaction. This invention uses calcium aluminate-calcium sulfoaluminate cement clinker as an expansive agent. When this expansive agent is added to cement to form expansive concrete or mortar and water, the calcium aluminate (CA) in the system first reacts with CaSO4 in the gypsum to form hydrated calcium sulfoaluminate. This reaction process proceeds synchronously with the cement hydration process. During the hydration of the calcium aluminate expansive agent, ettringite and hydrated aluminum hydroxide gel are simultaneously formed, resulting in a reasonable match between the expansive and cementitious phases, maintaining appropriate expansion while ensuring the strength of the cement paste. The early-formed ettringite has a significant expansion effect, which compensates for the chemical shrinkage and drying shrinkage of the cement paste. Both the calcium sulfoaluminate and calcium oxide expansive agents produce substantial expansion within 7 days. The ettringite also fills and blocks pores, improving the density and impermeability of the concrete, greatly reducing the volume shrinkage of the cement paste, and fundamentally improving the pore structure and stress state of the concrete.

[0018] Spherical sodium polyacrylate and polyacrylamide resins possess characteristics such as high water absorption, high water retention, and effective persistence. They can absorb tens or even hundreds of times their own weight in water. Their hydrophilic groups form hydrogen bonds in water or solutions, resulting in charged groups. These charged groups simultaneously increase the ion concentration inside the resin, increasing the osmotic pressure and providing the driving force for water absorption. Furthermore, spherical sodium polyacrylate and polyacrylamide resins absorb water not only through internal capillary adsorption but also through the physical adsorption of the polymer network, resulting in strong water retention capacity. Water adsorbed by the internal cross-linked network will not be released due to external mechanical action (such as stirring). When the spherical resin of this invention is mixed with cement, as the cement hydrates and hardens, the water retained inside the resin is gradually released, forming near-spherical, regular macropores in the cement paste, thus preparing porous, highly absorbent resin aggregate concrete. Due to the water-releasing curing characteristics of the spherical resin of this invention, a high-strength arched shell structure with a high degree of hydration and dense structure is formed around the spherical regular pores, making this pore structure fundamentally different from the pore structure in conventional foamed concrete. In the mid-to-late stages of the system, the core-shell structure of polyacrylamide resin / kaolin composite balls continues to play a role in water release, improving the shrinkage compensation efficiency of the composite expansion agent.

[0019] Furthermore, the kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 30-40 wt%. This core-shell structured polyacrylamide resin / kaolin composite sphere is a porous sphere comprising a polyacrylamide resin matrix as the core and a porous kaolin transport layer as the shell. Polyacrylamide resin has a large water storage capacity, and kaolin minerals have a large specific surface area and are stable. Therefore, this core-shell structured polyacrylamide resin / kaolin composite sphere has excellent water absorption and swelling effect. This core-shell structured polyacrylamide resin / kaolin composite sphere can be combined with sodium polyacrylate to solve the problems of slow water absorption rate, low efficiency, and small capacity of existing resins.

[0020] Furthermore, the preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin is activated by suspending it in a saturated sodium chloride aqueous solution for 2-3 hours, then dried and ground to 50-100 μm to obtain activated kaolin; (2) Immerse spherical polyacrylamide resin with a particle size of 1-2 mm in deionized water for 1-2 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of mass ratio range of 1:(10-15) for 5-10 minutes. (4) The product coated in step (3) is dried at 110℃-140℃ for 1-4 hours. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.

[0021] In step (3) of this invention, the mass ratio of the swollen spherical polyacrylamide resin to the activated kaolin is 1:(10-15) during the coating process, and the coating time is controlled at 5-10 minutes to ensure the coating effect. If the mixing time is too long, the resin will release too much water, which will affect the coating effect.

[0022] In step (2) of this invention, immersing the spherical polyacrylamide resin in deionized water for 1-2 hours can control the swelling volume of the spherical polyacrylamide resin and better control the resin-clay ratio in the subsequent coating stage. This invention controls the spherical polyacrylamide resin to absorb water to 2-3 times its original volume, ensuring the performance of the spherical polyacrylamide resin. Because if the water absorption and swelling volume of the spherical polyacrylamide resin is too high or too low, it will reduce the water absorption performance of the polyacrylamide resin / kaolin composite spheres or lead to a large breakage rate.

[0023] In step (4) of this invention, the core-shell structured polyacrylamide resin / kaolin composite ball is dried at 110℃-140℃ for 1-4 hours. Under the above temperature and drying time, the activated clay particles can fully interact with the surface of the swollen resin, ensuring that the prepared composite ball forms a porous structure on the surface after drying, while ensuring a high yield and low breakage rate.

[0024] The average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.3cm-0.7cm. The particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres of this invention can be adjusted to meet the requirements of different water absorption conditions. Furthermore, the controllable size of the core-shell structured polyacrylamide resin / kaolin composite spheres can meet various dimensional requirements during material use.

[0025] The activated kaolin and polyacrylamide resin of the present invention construct a porous structure on their surface to form a porous transport layer, which increases the specific surface area of ​​the composite sphere; at the same time, the transport layer can quickly liquefy water vapor to form liquid water and transport it to the internal polyacrylamide resin, thereby changing the original water absorption mechanism of high polyacrylamide resin and significantly improving the material's performance. Furthermore, the azo compound is one or a combination of several of the following: azodicarbonamide, azobisisobutyronitrile, isopropyl azodicarbonate, diethyl azodicarbonate, diazoaminobenzene, and barium azodicarbonate. When the azo organic foaming agent is added to concrete, due to the presence of unshared electron pairs on the amino nitrogen atom, the NN and N=N bonds break under certain temperature and alkaline conditions of cement hydration, releasing nitrogen gas. This can generate fine, uniform bubbles, establishing a moderate expansion during the plastic stage of the slurry to compensate for the volume shrinkage caused by plastic settlement and autogenous shrinkage before the cement slurry solidifies after hydration.

[0026] Another objective of this invention is to provide a method for preparing the above-mentioned all-time low-shrinkage ultra-high performance concrete, the method comprising the following steps: (1) 900-1110 parts of quartz sand, 600-700 parts of cement, 100-200 parts of silica fume, 200-250 parts of fly ash microspheres, 80-120 parts of steel fiber, and 5-10 parts of polyvinyl alcohol fiber are poured into a mixer, the mixing speed is set to 60-80 r / min, and the mixture is stirred for 5-10 min to obtain premix A; Add 20-40 parts of montmorillonite-modified shrinkage-reducing water-reducing agent, 30-50 parts of composite expansion agent, and 300-400 parts of water to the premix A prepared in step (1), and continue stirring for 5-10 minutes to obtain the all-time low-shrinkage ultra-high performance concrete.

[0027] Compared with the prior art, the present invention has the following technical effects and advantages: (1) In this invention, cement is used as the main cementitious material, and silica fume and fly ash microspheres are used as mineral admixtures to form a composite cementitious system together with cement. These three mineral admixtures all contain a large number of hydraulic minerals and have high activity. In the hydration reaction, they participate in secondary hydration, which can effectively reduce the alkali content and optimize the microstructure of ultra-high performance concrete, making a great contribution to the mechanical properties and durability of the entire system.

[0028] (2) This invention uses a composite expansive agent. When this expansive agent is added to cement to make expansive concrete or mortar and water, the CA in the system first reacts with CaSO4 in gypsum to generate hydrated calcium sulfoaluminate. This reaction process proceeds synchronously with the cement as the hydration process continues. The ettringite formed during the hydration of this expansive agent is generated simultaneously with the hydrated aluminum hydroxide gel, so that the expansive phase and the cementitious phase are reasonably matched, that is, maintaining appropriate expansion and ensuring the strength of the cement stone. The early-formed ettringite has a large expansion effect. The expansion during this period can compensate for the chemical shrinkage and drying shrinkage of the cement stone. Both the calcium aluminate-calcium sulfoaluminate expansive agent and the calcium oxide expansive agent produce a large amount of expansion within 7 days. The ettringite also has the function of filling and blocking pores, improving the compactness and impermeability of concrete, greatly reducing the volume shrinkage of cement stone, fundamentally improving the pore structure and stress state of concrete, and reducing the early shrinkage of cement. Low-temperature calcined magnesium oxide and core-shell structured polyacrylamide resin / kaolin composite spheres were used for mid-to-late stage expansion, which reduced the volume shrinkage of cement stone. The core-shell structured polyacrylamide resin / kaolin composite spheres improved the shrinkage compensation efficiency of the composite expansion agent, further reducing the shrinkage of concrete.

[0029] (3) The present invention uses montmorillonite-modified shrinkage-reducing water-reducing agent and composite expansion agent to achieve low shrinkage throughout the time period. Detailed Implementation

[0030] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0031] Example 1 A method for preparing all-time low-shrinkage ultra-high performance concrete, the method comprising the following steps: (1) 900 parts of quartz sand, 600 parts of cement, 100 parts of silica fume, 200 parts of fly ash microspheres, 80 parts of steel fiber, and 5 parts of polyvinyl alcohol fiber are poured into a mixer, the mixing speed is set to 60 r / min, and the mixture is mixed for 5 min to obtain premix A; (2) Add 20 parts of montmorillonite-modified shrinkage-reducing agent, 30 parts of composite expansion agent, and 300 parts of water to the premix A prepared in step (1), and continue stirring for 5 minutes to obtain the all-time low-shrinkage ultra-high performance concrete.

[0032] The polyvinyl alcohol fiber has a length of 6 mm, a tensile strength ≥1200 MPa, and an alkali resistance ≥95%.

[0033] The specific surface area of ​​the fly ash microspheres is ≥1500 m². 2 / kg, bulk density is 300-500kg / m³ 3 The particle size is 1-30μm; the quartz sand has a particle size of less than 3mm, and the silica fume with a particle size of less than 1μm accounts for not less than 30%.

[0034] The steel fiber has a diameter of 0.3 mm and a length of 5 mm.

[0035] Montmorillonite-modified shrinkage-reducing agents are prepared by the following method: (1) Methoxy polyethylene glycol, diethylene glycol monomethyl ether, hydroxymethyl acrylamide and methacrylic acid in a molar ratio of 1:0.15:0.1:3 were added to the reactor in sequence and stirred at 40°C to obtain mixture A. During the reaction, the water in the reactor was continuously removed by vacuuming. (2) Hydroquinone (0.05 wt% of total material weight) and concentrated sulfuric acid (0.6 wt% of total material weight) were added to mixture A in sequence, and the temperature was raised to 120°C and reacted for 6 hours to obtain esterified product B. (3) Cool the reactants to 60°C and dilute them with water; (4) Dissolve 0.15wt% of ammonium persulfate in water to prepare a drop feed C with a concentration of 8wt%, and add it evenly to the reactor in 3 hours. After the addition is completed, keep it warm for 3 hours. After cooling, add 35wt% sodium hydroxide solution to adjust the pH to 6.0-6.8 to obtain the shrinkage-reducing water-reducing agent. (5) Prepare the shrinkage-reducing water-reducing agent prepared in step (4) into an aqueous solution with a mass concentration of 20wt%, add montmorillonite powder to it, sonicate for 2 hours, and seal and store at 20°C for 24 hours to obtain montmorillonite-modified shrinkage-reducing agent.

[0036] In step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1; in step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1.

[0037] The composite expansion agent is composed of the following components by weight: 2 parts azo compound, 20 parts magnesium oxide, 10 parts calcium oxide, 30 parts calcium aluminate-calcium sulfoaluminate cement clinker, 5 parts pre-absorbed spherical sodium polyacrylate, and 5 parts core-shell structured polyacrylamide resin / kaolin composite spheres. The magnesium oxide was obtained by low-temperature calcination at 600℃.

[0038] The kaolin has a particle size of 50 μm; the core-shell structured polyacrylamide resin / kaolin composite spheres have an average particle size of 0.3 cm.

[0039] The spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 3 mm. The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement is: bauxite 50-60%, limestone 30-45%, and gypsum 5-18%.

[0040] The mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; The bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; gypsum has the following composition: SO3 > 46%. The kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 30 wt%. The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin was activated by suspending it in a saturated sodium chloride aqueous solution for 2 hours, then dried and ground to 50 μm to obtain activated kaolin; (2) Immerse 1mm spherical polyacrylamide resin in deionized water for 1 hour to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:10, and the time is controlled at 5 minutes. (4) The product coated in step (3) is dried at 110°C for 1 hour. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.

[0041] The azo compound is azodicarbonamide.

[0042] The preparation method of the composite expanding agent includes the following steps: (1) 10 parts calcium oxide and 30 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of ​​300 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of ​​500 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 2 parts of azo compound, 5 parts of pre-absorbed water spherical sodium polyacrylate and 5 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.

[0043] Example 2 A method for preparing all-time low-shrinkage ultra-high performance concrete, characterized in that: the preparation method includes the following steps: (1) 1000 parts of quartz sand, 650 parts of cement, 150 parts of silica fume, 230 parts of fly ash microspheres, 100 parts of steel fiber, and 8 parts of polyvinyl alcohol fiber are poured into a mixer, the mixing speed is set to 70 r / min, and the mixture is stirred for 8 min to obtain premix A; (2) Add 40 parts of montmorillonite-modified shrinkage-inhibiting water-reducing agent, 40 parts of composite expansion agent, and 350 parts of water to the premix A prepared in step (1), and continue stirring for 8 minutes to obtain the all-time low-shrinkage ultra-high performance concrete.

[0044] The polyvinyl alcohol fiber has a length of 8 mm, a tensile strength ≥1200 MPa, and an alkali resistance ≥95%.

[0045] The specific surface area of ​​the fly ash microspheres is ≥1500 m². 2 / kg, bulk density is 300-500kg / m³ 3 The particle size is 1-30μm; fly ash microspheres can improve fluidity, and the use of silica fume can increase the density of UHPC and improve its impermeability.

[0046] The quartz sand has a particle size of less than 3 mm, and the silica fume with a particle size of less than 1 μm accounts for no less than 30%.

[0047] The steel fiber has a diameter of 0.5 mm and a length of 10 mm.

[0048] The montmorillonite-modified shrinkage-reducing agent is prepared by the following method: (1) Methoxy polyethylene glycol, diethylene glycol monomethyl ether, hydroxymethyl acrylamide and methacrylic acid in a molar ratio of 1:0.15:0.1:3 were added to the reactor in sequence and stirred at 42°C to obtain mixture A. During the reaction, the water in the reactor was continuously removed by vacuuming. (2) Hydroquinone (0.05 wt% of total material weight) and concentrated sulfuric acid (0.6 wt% of total material weight) were added to mixture A in sequence, and the temperature was raised to 120°C and reacted for 6 hours to obtain esterified product B. (3) Cool the reactants to 60°C and dilute them with water; (4) Dissolve 0.15wt% of ammonium persulfate in water to prepare a drop feed C with a concentration of 8wt%, and add it evenly to the reactor in 3 hours. After the addition is completed, keep it warm for 3 hours. After cooling, add 35wt% sodium hydroxide solution to adjust the pH to 6.0-6.8 to obtain the shrinkage-reducing water-reducing agent. (5) Prepare the shrinkage-reducing water-reducing agent prepared in step (4) into an aqueous solution with a mass concentration of 30wt%, add montmorillonite powder to it, sonicate for 4h, and seal and store at 28℃ for 30h to obtain montmorillonite negative-modified shrinkage-reducing water-reducing agent.

[0049] In step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1; in step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1.

[0050] The composite expansion agent is composed of the following components by weight: 6 parts azo compound, 25 parts magnesium oxide, 20 parts calcium oxide, 40 parts calcium aluminate-calcium sulfoaluminate cement clinker, 8 parts pre-absorbed spherical sodium polyacrylate, and 8 parts core-shell structured polyacrylamide resin / kaolin composite spheres. The magnesium oxide was obtained by low-temperature calcination at 700℃.

[0051] The azo compound is an azodicarbonamide; The kaolin has a particle size of 75 μm; the core-shell structured polyacrylamide resin / kaolin composite spheres have an average particle size of 0.5 cm.

[0052] The spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 4 mm. The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement is: bauxite 50-60%, limestone 30-45%, and gypsum 5-18%.

[0053] The mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; The bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; gypsum has the following composition: SO3 > 46%. The kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 35 wt%. The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin was activated by suspending it in a saturated sodium chloride aqueous solution for 2.5 hours, then dried and ground to 75 μm to obtain activated kaolin; (2) Immerse 1.5 mm spherical polyacrylamide resin in deionized water for 1.5 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:12, and the time is controlled at 8 minutes. (4) The product coated in step (3) is dried at 120°C for 2 hours. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.

[0054] The azo compound is azodicarbonamide.

[0055] The preparation method of the composite expanding agent includes the following steps: (1) 20 parts calcium oxide and 40 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of ​​450 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of ​​750 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 4 parts of azo compound, 8 parts of pre-absorbed water spherical sodium polyacrylate and 8 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.

[0056] Example 3 A method for preparing all-time low-shrinkage ultra-high performance concrete, the method comprising the following steps: (1) 1110 parts of quartz sand, 700 parts of cement, 200 parts of silica fume, 250 parts of fly ash microspheres, 120 parts of steel fiber, and 10 parts of polyvinyl alcohol fiber are poured into a mixer, the mixing speed is set to 80 r / min, and the mixture is mixed for 10 min to obtain premix A; (2) Add 40 parts of montmorillonite-modified shrinkage-reducing agent, 50 parts of composite expansion agent, and 400 parts of water to the premix A prepared in step (1), and continue stirring for 5-10 minutes to obtain the all-time low-shrinkage ultra-high performance concrete.

[0057] The polyvinyl alcohol fiber has a length of 12 mm, a tensile strength ≥1200 MPa, and an alkali resistance ≥95%.

[0058] The specific surface area of ​​the fly ash microspheres is ≥1500 m². 2 / kg, bulk density is 300-500kg / m³ 3 The particle size is 1-30 μm; The quartz sand has a particle size of less than 3 mm, and the silica fume with a particle size of less than 1 μm accounts for no less than 30%.

[0059] The steel fiber has a diameter of 0.7 mm and a length of 15 mm.

[0060] The montmorillonite-modified shrinkage-reducing agent is prepared by the following method: (1) Methoxy polyethylene glycol, diethylene glycol monomethyl ether, hydroxymethyl acrylamide and methacrylic acid in a molar ratio of 1:0.15:0.1:3 were added to the reactor in sequence and stirred at 40-45℃ to obtain mixture A. During the reaction, the water in the reactor was continuously removed by vacuuming. (2) Hydroquinone (0.05 wt%) and concentrated sulfuric acid (0.6 t%) were added to mixture A in sequence, and the temperature was raised to 120°C and reacted for 6 hours to obtain esterified product B. (3) Cool the reactants to 60°C and dilute them with water; (4) Dissolve 0.15wt% of ammonium persulfate in water to prepare a drop feed C with a concentration of 8wt%, and add it evenly to the reactor in 3 hours. After the addition is completed, keep it warm for 3 hours. After cooling, add 35wt% sodium hydroxide solution to adjust the pH to 6.0-6.8 to obtain the shrinkage-reducing water-reducing agent. (5) Prepare the shrinkage-reducing water-reducing agent prepared in step (4) into an aqueous solution with a mass concentration of 20-40wt%, add montmorillonite powder to it, sonicate for 2-6 hours, and seal and store at 20-35℃ for 24-48 hours to obtain montmorillonite-modified shrinkage-reducing agent.

[0061] In step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1; in step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1.

[0062] The composite expansion agent is composed of the following components by weight: 8 parts of azo compound, 30 parts of magnesium oxide, 30 parts of calcium oxide, 50 parts of calcium aluminate-calcium sulfoaluminate cement clinker, 10 parts of pre-absorbed spherical sodium polyacrylate, and 10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres. The kaolin has a particle size of 100 μm; the average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.7 cm.

[0063] The spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 5 mm. The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement is: bauxite 50-60%, limestone 30-45%, and gypsum 5-18%.

[0064] The mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; The bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; gypsum has the following composition: SO3 > 46%. The magnesium oxide was obtained by low-temperature calcination at 800℃; The kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 40 wt%. The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin was activated by suspending it in a saturated sodium chloride aqueous solution for 3 hours, then dried and ground to 100 μm to obtain activated kaolin; (2) Immerse spherical polyacrylamide resin with a particle size of 2 mm in deionized water for 2 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:15, and the time is controlled at 10 minutes. (4) The product coated in step (3) is dried at 140°C for 4 hours. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.

[0065] The azo compound is azodicarbonamide.

[0066] The preparation method of the composite expanding agent includes the following steps: (1) 30 parts calcium oxide and 50 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of ​​600 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of ​​800 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 8 parts of azo compound, 10 parts of pre-absorbed water spherical sodium polyacrylate and 10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.

[0067] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the same weight proportions of shrinkage-reducing water-reducing agent were used, but montmorillonite was not used to modify the shrinkage-reducing water-reducing agent. Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the core-shell structured polyacrylamide resin / kaolin composite spheres were not used in the composite expansion agent; instead, spherical polyacrylamide resin of the same weight ratio was used to replace the core-shell structured polyacrylamide resin / kaolin composite spheres. Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the core-shell structured polyacrylamide resin / kaolin composite balls were not used in the composite expansion agent, and activated kaolin was used in place of the core-shell structured polyacrylamide resin / kaolin composite balls in the same weight proportion. Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the same weight proportion of unactivated kaolin is used instead of activated kaolin in the composite expanding agent; Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the average particle size of the core-shell structured polyacrylamide resin / kaolin composite balls used in the composite expanding agent is 1 cm.

[0068] The 3-day, 7-day, and 28-day compressive strengths of the concrete obtained in Examples 1-3 and Comparative Examples 1-5 were tested according to GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". Simultaneously, the 28-day total shrinkage rate of the concrete obtained was tested according to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The test results are shown in Table 1. Table 1 Experimental Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 3d compressive strength / MPa 99.2 99.4 99.5 98.3 96.1 95.0 94.4 96.8 7d compressive strength / MPa 111.3 111.6 111.7 110.1 109.1 99.8 98.4 100.4 28-day compressive strength / MPa 171.4 171.6 171.9 168.6 165.6 164.8 160.9 168.9 <![CDATA[7d self-shrinkage rate / 10 -6 > 198 191 193 202 203 204 206 208 <![CDATA[Total shrinkage rate at 28d / 10 -6 > 212 208 215 228 236 238 239 240 Slump / mm 266 265 267 263 262 261 262 264 Expansion / mm 676 678 676 664 664 663 662 660 As can be seen from the results in Table 1, the concrete obtained in Examples 1-3 of this invention has a good shrinkage inhibition effect; especially Example 2, whose 7-day shrinkage rate is only 191 × 10⁻⁶. -6 The 28-day shrinkage rate is only 208×10 -6 Furthermore, the compressive strength remains at a high level, and there is no significant decrease in strength when the shrinkage rate is reduced.

[0069] In Comparative Example 1, the same weight proportions of shrinkage-reducing water-reducing agent were used, but montmorillonite was not used to modify the shrinkage-reducing water-reducing agent. The compressive strength, autogenous shrinkage rate, and other indicators of the resulting concrete were slightly worse than those in Examples 1-3.

[0070] The core-shell structured polyacrylamide resin / kaolin composite spheres used in Comparative Example 4 had a larger average particle size, and their compressive strength, self-shrinkage rate, and other indicators were slightly worse than those in Examples 1-3.

[0071] The test results of Comparative Examples 1-3, which did not use core-shell structured polyacrylamide resin / kaolin composite balls, were all worse than those of Examples 1-3.

[0072] This demonstrates that the use of montmorillonite as a modified shrinkage-reducing water-reducing agent and core-shell structured polyacrylamide resin / kaolin composite spheres plays a crucial role in achieving low shrinkage of concrete throughout the entire time period.

[0073] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A low-shrinkage, ultra-high-performance concrete for all time periods, characterized in that: The ultra-high performance concrete is composed of the following components: 900-1110 parts of quartz sand, 600-700 parts of cement, 100-200 parts of silica fume, 200-250 parts of fly ash microspheres, 80-120 parts of steel fiber, 20-40 parts of montmorillonite-modified shrinkage-reducing water-reducing agent, 5-10 parts of polyvinyl alcohol fiber, 30-50 parts of composite expansion agent, and 300-400 parts of water.

2. The all-time low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that: The polyvinyl alcohol fiber has a length of 6-12 mm, a tensile strength ≥1200 MPa, and an alkali resistance ≥95%.

3. The all-time low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that: The specific surface area of ​​the fly ash microspheres is ≥1500 m². 2 / kg, bulk density is 300-500kg / m³ 3 The particle size is 1-30μm.

4. The all-time low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that: The quartz sand has a particle size of less than 3 mm, and the silica fume with a particle size of less than 1 μm accounts for no less than 30%.

5. The all-time low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that: The steel fibers have a diameter of 0.3-0.7 mm and a length of 5-15 mm.

6. The all-time low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that: The composite expansion agent is composed of the following components by weight: 2-8 parts of azo compound, 20-30 parts of magnesium oxide, 10-30 parts of calcium oxide, 30-50 parts of calcium aluminate-calcium sulfoaluminate cement clinker, 5-10 parts of pre-absorbed spherical sodium polyacrylate, and 5-10 parts of core-shell structured polyacrylamide resin / kaolin composite balls.

7. The all-time low-shrinkage ultra-high performance concrete as described in claim 6, characterized in that: The magnesium oxide was obtained by low-temperature calcination at 600-800℃.

8. The all-time low-shrinkage ultra-high performance concrete as described in claim 1, characterized in that: The montmorillonite-modified shrinkage-reducing water-reducing agent is prepared by the following method: (1) Methoxy polyethylene glycol, diethylene glycol monomethyl ether, hydroxymethyl acrylamide and methacrylic acid in a molar ratio of 1:0.15:0.1:3 were added to the reactor in sequence and stirred at 40-45℃ to obtain mixture A. During the reaction, the water in the reactor was continuously removed by vacuuming. (2) Hydroquinone (0.05 wt% of total material weight) and concentrated sulfuric acid (0.6 wt% of total material weight) were added to mixture A in sequence, and the temperature was raised to 120°C and reacted for 6 hours to obtain esterified product B. (3) Cool the reactants to 60°C and dilute them with water; (4) Dissolve 0.15wt% of ammonium persulfate in water to prepare a drop feed C with a concentration of 8wt%, and add it evenly to the reactor in 3 hours. After the addition is completed, keep it warm for 3 hours. After cooling, add 35wt% sodium hydroxide solution to adjust the pH to 6.0-6.8 to obtain the shrinkage-reducing water-reducing agent. (5) Prepare the shrinkage-reducing water-reducing agent prepared in step (4) into an aqueous solution with a mass concentration of 20-40wt%, add montmorillonite powder to it, sonicate for 2-6 hours, and seal and store at 20-35℃ for 24-48 hours to obtain montmorillonite-modified shrinkage-reducing agent.

9. The all-time low-shrinkage ultra-high performance concrete as described in claim 8, characterized in that: In step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:1; in step (5), the solid-liquid ratio of the shrinkage-reducing agent aqueous solution to montmorillonite powder is 5:

1.

10. A method for preparing all-time low-shrinkage ultra-high performance concrete as described in any one of claims 1-9, characterized in that: The preparation method includes the following steps: (1) 900-1110 parts of quartz sand, 600-700 parts of cement, 100-200 parts of silica fume, 200-250 parts of fly ash microspheres, 80-120 parts of steel fiber, and 5-10 parts of polyvinyl alcohol fiber are poured into a mixer, the mixing speed is set to 60-80 r / min, and the mixture is stirred for 5-10 min to obtain premix A; (2) Add 20-40 parts of montmorillonite-modified shrinkage-reducing water-reducing agent, 30-50 parts of composite expansion agent, and 300-400 parts of water to the premix A prepared in step (1), and continue stirring for 5-10 minutes to obtain the all-time low-shrinkage ultra-high performance concrete.