UHPC having non-shrinkage to micro-expansion deformation

Abstract

The present invention relates to the technical field of building materials. Particularly, disclosed is a UHPC having non-shrinkage to micro-expansion deformation. The UHPC pertains to a solution of shrinkage reduction across the full-scale of cement-active admixture-inert admixture-aggregate-fibers. The solution solves the problem of large autogenous shrinkage of traditional UHPC, and can achieve non-shrinkage or even micro-expansion of UHPC. After 28 days of standard curing, the UHPC has a compressive strength greater than 130 MPa, an ultimate flexural-tensile strength greater than 20 MPa, and an ultimate tensile strength greater than 8 MPa, realizing the balance between high mechanical properties and high volume stability. In addition, the proportion of cement usage in the UHPC is low, and a large amount of industrial waste residues and recycled construction waste products are used, rendering the UHPC more environmentally friendly; moreover, the use of ultrafine powder such as silica fume, ultrafine mineral powder, and rice husk ash, which are common in conventional UHPC, is avoided, further resulting in reduced energy consumption and costs, facilitating production and use, greatly improving construction efficiency, and indicating extremely high large-scale application value.

Description

UHPC with no shrinkage to micro-expansion deformation Technical Field

[0001] This invention belongs to the field of building materials technology, specifically, it relates to UHPC with no shrinkage to slight expansion deformation. Background Technology

[0002] Because the reaction of cementitious materials such as cement and active admixtures leads to volume reduction, and the decrease in relative humidity inside the matrix as the reaction proceeds also produces a self-drying effect, self-shrinkage is the main reason for the poor volume stability of cement-based materials.

[0003] For ordinary concrete and high-strength concrete, the autogenous shrinkage is generally 100με~200με and 200με~500με, respectively. Low shrinkage or even micro-expansion of ordinary concrete can be achieved by using internal curing materials such as zeolite powder, ceramsite sand, and recycled aggregates, or by using various expansive agents. For example, Chinese patents CN 112876157A and CN 111620662A reduce shrinkage by using modified recycled aggregates and zeolite powder, respectively, while Chinese patents CN 111978045A and CN 110698145A achieve micro-expansion of ordinary concrete by using expansive agents. However, with the increase in strength grade, for high-strength / ultra-high-strength concrete or high-strength / ultra-high-strength grouting materials, due to the reduction in water-cement ratio and the incorporation of ultrafine powders, the effect of using the above-mentioned single method to reduce autogenous shrinkage becomes less significant. It is usually necessary to combine the addition of internal curing materials and expansion agents, as shown in Chinese patents CN 113429181A, CN 113087483A, and CN 112110689A; or, based on one of these measures, further reduce the cement content (as shown in Chinese patents CN 111892342A and CN 115057659A), incorporate salt gypsum (as shown in Chinese patents CN 114213093A and CN 112358250A), or introduce activated steel slag sand (as shown in Chinese patent CN 110759678A) or copper tailings (as shown in Chinese patent CN 110759678A). This reduces the shrinkage of high-strength / ultra-high-strength concrete or high-strength / ultra-high-strength grouting materials (e.g., Chinese patents CN 114230278A, CN 110759678A, CN 113501695A, etc.). However, since a certain amount of highly active powder particles with high specific surface energy are still used, ultra-high-strength concrete and ultra-high-strength grouting materials can only achieve no shrinkage without reducing mechanical properties.

[0004] However, ultra-high performance concrete (UHPC) possesses extremely low water-cement ratios, high ultrafine powder content, steel fiber reinforcement, and ultra-high strength and toughness. The large amount of highly reactive materials and the rapid decrease in internal relative humidity result in significant autogenous shrinkage, typically reaching 600 με to 1000 με. Although the use of internal curing materials, expansion agents, reduced cement content, and their combined application as mentioned above can reduce UHPC autogenous shrinkage to some extent, its inherently lower water-cement ratio and higher content of ultrafine and highly reactive powders mean that, even with ultra-high strength concrete and ultra-high strength grouting materials only achieving zero shrinkage, UHPC still exhibits a certain degree of autogenous shrinkage. Therefore, current research on UHPC primarily focuses on minimizing shrinkage.

[0005] Furthermore, unlike ordinary concrete, high-strength / ultra-high-strength concrete, and high-strength / ultra-high-strength grouting materials, the ultra-high strength of UHPC originates from its dense microstructure. While adding more expansive agents and internal curing agents can significantly reduce shrinkage, the resulting expansion cracks and internal defects can negatively impact strength and fiber toughening effects. Therefore, the shrinkage reduction effect of expansive agents and internal curing agents on UHPC is limited. Materials such as salt gypsum, activated steel slag sand, and copper tailings are also unsuitable for use in UHPC due to their high chloride ion and heavy metal pollution risks, which can negatively impact internal steel fiber corrosion and environmental safety. Although some studies mention that activated steel slag sand contains f-CaO and f-MgO, which can act as expansive agents to prepare a shrinkage-free, sprayable ultra-high-performance concrete, these studies do not mention relevant shrinkage data. Moreover, the microsilica powder and slag powder used in these studies are still nano-silica fume and ultrafine mineral powders, possessing extremely high reactivity and specific surface area; therefore, the risk of shrinkage remains significant.

[0006] Comparative analysis of UHPC shrinkage reduction technology research reveals that current measures are mostly focused on one or a few limited aspects, such as internal curing agents (organic and inorganic porous / water-absorbing materials), expansion agents (electroponite, calcium oxide, magnesium oxide, etc.), and appropriately reducing cement usage. However, these measures cannot completely overcome the problem of its large autogenous shrinkage. Therefore, current research on UHPC still cannot achieve the effect of no shrinkage or even micro-expansion, and continuous improvement research is still needed. Summary of the Invention

[0007] Currently, research on UHPC shrinkage reduction technology is limited to a single or a few specific aspects. Little attention is paid to another key factor influencing self-shrinkage—the use of large amounts of highly reactive, high-surface-energy admixtures. The use of silica fume and ultrafine mineral powder inevitably leads to significant self-shrinkage. Although some studies have removed silica fume to avoid this problem, the high-reactivity, high-surface-energy calcined clay used as a substitute still results in substantial self-shrinkage. Therefore, addressing the current inability to completely overcome the significant self-shrinkage and achieve shrinkage-free or even micro-expansion UHPC, the inventors of this invention, based on long-term research on UHPC shrinkage reduction technology, have proposed a design scheme for full-scale shrinkage reduction from cement to reactive admixtures to inert admixtures to aggregates to fibers, developing a novel UHPC with shrinkage-free to micro-expansion deformation. This shrinkage-free to micro-expansion deformation UHPC can significantly reduce self-shrinkage, achieving shrinkage-free to micro-expansion effects while maintaining the mechanical properties of UHPC.

[0008] The present invention specifically adopts the following technical solution:

[0009] A UHPC with no shrinkage to slight expansion deformation, comprising the following components in parts by weight, mixed uniformly:

[0010] Cement: 300-600 parts;

[0011] Active admixture: 100-300 parts;

[0012] Inert admixtures: 120–380 parts;

[0013] Shrinkage-reducing admixtures: 60–250 parts;

[0014] Activity activator: 20-120 parts;

[0015] Sand: 900-1200 parts;

[0016] Coarse aggregate: 0-500 parts;

[0017] Fiber: 100-250 parts;

[0018] Compensator: 5-25 parts;

[0019] Water-reducing agent: 7-25 parts;

[0020] Water: 70-220 parts.

[0021] The active admixture is a mixture of fly ash and ground blast furnace slag powder, with the mass ratio of ground blast furnace slag powder to the active admixture being 0-50%. That is, the active admixture is either pure fly ash or a mixture of no more than half (including half) of ground blast furnace slag powder and fly ash. The average particle size of both fly ash and ground blast furnace slag powder is 5μm-20μm.

[0022] Furthermore, in this active admixture, powder particles with an average particle size of 5 μm to 10 μm account for 50% to 80% of the mass of the active admixture. That is, the active admixture is a mixture of 50 wt% to 80 wt% small-particle-size powder and the remaining 20 wt% to 50 wt% large-particle-size powder, wherein the average particle size of the small-particle-size powder is 5 μm to 10 μm, and the average particle size of the large-particle-size powder is 10 μm (excluding) to 20 μm.

[0023] The inert admixture is any one of limestone powder or quartz powder, or a mixture of the two in any proportion, and the average particle size of both limestone powder and quartz powder is 3μm to 20μm.

[0024] Furthermore, in this inert admixture, powder particles with an average particle size of 3 μm to 10 μm account for 50% to 100% of the mass of the inert admixture. That is, the inert admixture is either pure small-diameter powder or a mixture of no more than half (inclusive) large-diameter powder and small-diameter powder, wherein the average particle size of the small-diameter powder is 3 μm to 10 μm, and the average particle size of the large-diameter powder is 10 μm (exclusive) to 20 μm.

[0025] The shrinkage-reducing admixture is any one of zeolite powder, ceramic powder, and kaolin, or a mixture of at least two of them in any proportion, and the average particle size of zeolite powder, ceramic powder, and kaolin is 3μm to 20μm.

[0026] Furthermore, in this shrinkage-reducing admixture, powder particles with an average particle size of 3μm to 10μm account for 50% to 100% of the mass of the shrinkage-reducing admixture. That is, the shrinkage-reducing admixture is either pure small-diameter powder or a mixture of no more than half (inclusive) large-diameter powder and small-diameter powder, wherein the average particle size of the small-diameter powder is 3μm to 10μm, and the average particle size of the large-diameter powder is 10μm (exclusive) to 20μm.

[0027] The active activator is any one of anhydrite, hemihydrate gypsum, and dihydrate gypsum, or a mixture of at least two of them in any proportion, and the average particle size of anhydrite, hemihydrate gypsum, and dihydrate gypsum is 5μm to 30μm.

[0028] The sand is a mixture of porous sand and hard sand, and the mass of porous sand accounts for 10% to 20% of the total mass of the sand. That is, the sand is a mixture of 10 wt% to 20 wt% porous sand and the remaining 80 wt% to 90 wt% hard sand.

[0029] Furthermore, the porous sand is selected from any one of ceramic sand, coral sand, and recycled aggregate sand, or a mixture of at least two in any proportion; the hard sand is selected from any one of river sand and quartz sand, or a mixture of two in any proportion.

[0030] Generally, the maximum particle size of sand does not exceed 2.36 mm.

[0031] Generally, ordinary Portland cement and / or Portland cement with a strength grade of 42.5 or higher can be selected.

[0032] Generally, the coarse aggregate is selected from any one of basalt, limestone, and granite, or a mixture of at least two in any proportion, and the particle size of the coarse aggregate is 5 mm to 16 mm.

[0033] Generally, the fiber diameter is 0.15mm to 0.4mm and the length is 13mm to 25mm; and the shape is selected from any one of straight, hooked or wavy copper-plated steel fibers, or a mixture of at least two in any proportion.

[0034] Generally, the compensator is selected from any one of calcium oxide, magnesium oxide, calcium oxide-magnesium oxide composite, or a mixture of at least two in any proportion.

[0035] Generally, the water-reducing agent is a polycarboxylate superplasticizer, and the water reduction rate is not less than 30%.

[0036] The UHPC provided by this invention, which exhibits no shrinkage to minimal expansion deformation, is designed based on the concept of full-scale shrinkage reduction involving cement, active admixtures, inert admixtures, aggregates, and fibers. Specifically:

[0037] First, since the theoretical final hydration degree of cement in UHPC is only 30% to 60%, and the actual hydration degree is even lower, the present invention reduces the maximum proportion of cement in cementitious materials to less than 70% (currently, the cement content in conventional UHPC is usually more than 70% of the cementitious materials), thereby significantly reducing the amount of cement and reducing the self-shrinkage caused by cement hydration, the largest source of self-shrinkage.

[0038] Secondly, this invention uses only fly ash and ordinary mineral powder (i.e., finely ground slag powder) with relatively low activity and low surface energy as sources of active admixtures to reduce the self-shrinkage caused by active admixtures. In contrast, cementing materials such as silica fume, ultrafine mineral powder, and rice husk ash, which have extremely high activity and large surface energy, not only increase the volume shrinkage caused by chemical reactions, but also adsorb a large amount of free water, causing the internal relative humidity to drop rapidly, increasing the pore negative pressure, and further improving self-shrinkage.

[0039] Third, due to the low reactivity of reactive admixtures, a large amount of reactive admixtures do not participate in the reaction and only serve a filling function. However, the remaining unreacted reactive admixtures still affect autogenous shrinkage. Specifically, the more unreacted reactive admixtures remain, the higher the concentration of active components in the early reaction, increasing and accelerating the early autogenous shrinkage. Furthermore, if changes in the external environment later lead to increased humidity inside the UHPC, the remaining unreacted reactive admixtures will still react, increasing later autogenous shrinkage. Therefore, using a large amount of inactive inert admixtures and microporous shrinkage-reducing admixtures can reduce autogenous shrinkage caused by the reaction and reduce later shrinkage through internal curing. The low reactivity of reactive admixtures also makes it possible to use large amounts of inert admixtures and shrinkage-reducing admixtures. In addition, inert admixtures and shrinkage-reducing admixtures are mixtures with different gradations. By exerting a close packing effect, they can reduce the negative impact of removing materials such as silica fume and ultrafine mineral powder on mechanical properties. Furthermore, the filler dilution effect of inert admixtures and the internal curing effect of shrinkage-reducing admixtures will increase the reactivity of cementitious materials in UHPC and improve mechanical properties.

[0040] Fourth, due to the low reactivity of fly ash and ordinary mineral powder, activators are used to enhance their reactivity and promote the formation of ettringite, thus reducing self-shrinkage. The alkaline environment and increased concentrations of calcium and sulfate ions resulting from the dissolution of the activator can activate the reactivity of fly ash and ordinary mineral powder through alkali and sulfate. Furthermore, the alkaline environment can disrupt the surface structure of the slag powder (covalent bonds such as Si-O-Si, Al-O-Al, and Si-O-Al), further releasing internal Ca2+. 2+ Al 3+ SiO4 4- Plasma; while in high-calcium systems, the hydration products of alkaline cementitious materials are usually CASH, which has a higher elastic modulus than CSH, thus improving the mechanical properties of UHPC.

[0041] Fifth, the sand in this invention is limited to a mixture of porous sand and hard sand. Compared with general organic internal curing materials, porous sand has higher strength. When mixed with hard sand, it can not only ensure mechanical properties, but also reduce shrinkage through internal curing.

[0042] Sixth, fibers can play a bridging and restraining role, acting as a reinforcement while suppressing self-shrinkage.

[0043] Seventh, the UHPC with no shrinkage to micro-expansion deformation provided by this invention, based on the combined effects of the above six aspects, can significantly reduce the self-shrinkage of UHPC from the perspective of reducing and inhibiting shrinkage, achieving a near-no-shrinkage state; and on this basis, the expansion effect of the compensating agent can achieve the no-shrinkage and micro-expansion effect of UHPC. Meanwhile, due to the removal of nanoparticles such as silica fume, the density of the UHPC matrix in this invention is somewhat reduced, but the higher modulus of CASH, the higher degree of reactivity of the active admixtures, and the subsequent internal curing effect can ensure mechanical properties. Therefore, with an appropriate amount of compensating agent, its good expansion effect will not produce microcracks that would damage the interior of the matrix.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) Based on the all-round shrinkage reduction design concept of cement-active admixture-inert admixture-aggregate-fiber, this invention solves the problem of large self-shrinkage of traditional UHPC and can realize no shrinkage or even micro-expansion of UHPC.

[0046] (2) The UHPC of the present invention exhibits a standard curing strength of >130 MPa at 28 days, an ultimate flexural strength of >20 MPa at 28 days, and an ultimate tensile strength of >8 MPa at 28 days, achieving a balance between high mechanical properties and high volumetric stability. Compared with current UHPC, although the use of large amounts of highly active ultrafine powders (such as silica fume, ultrafine mineral powder, rice husk ash, etc.) is beneficial to mechanical properties, it also increases self-shrinkage. While the addition of expansion agents or internal curing materials reduces self-shrinkage, it is also detrimental to mechanical properties. The contradiction between the two is thus overcome.

[0047] (3) The UHPC of the present invention, which is free from shrinkage to slight expansion deformation, has a low cement content and uses a large amount of industrial waste residue and recycled construction waste products, which has excellent green and low carbon performance and meets the corresponding environmental protection requirements.

[0048] (4) The UHPC of the present invention, which is free from shrinkage to micro-expansion deformation, does not require the use of high-activity ultrafine powders (generally with a particle size <3μm) such as silica fume, ultrafine mineral powder, rice husk ash, etc., which are commonly used in UHPC. This not only reduces energy consumption and cost in the production, transportation and packaging of ultrafine powders, but also facilitates the production and use of UHPC, greatly improves construction efficiency, and has extremely high value for large-scale application. Attached Figure Description

[0049] Figure 1 is a self-shrinkage rate value-time curve of UHPC with no shrinkage to micro-expansion deformation according to Examples 1 to 5 of the present invention;

[0050] Figure 2 is a self-shrinkage rate value-time curve of UHPC from no shrinkage to micro-expansion deformation in Examples 6 to 10 of the present invention;

[0051] Figure 3 is a comparison of the self-shrinkage rate-time curves of the UHPC without shrinkage to micro-expansion deformation in Example 3 of the present invention and the UHPC in Comparative Example 1, and the UHPC without shrinkage to micro-expansion deformation in Example 6 and the UHPC in Comparative Example 2.

[0052] Figure 4 is a comparison of the self-shrinkage rate-time curves of the UHPC with no shrinkage to slight expansion deformation in Example 1 of the present invention and the comparative UHPCs in Comparative Examples 3 to 7.

[0053] Figure 5 is a comparison of the self-shrinkage rate-time curves of the UHPC with no shrinkage to slight expansion deformation in Example 1 of the present invention and the comparative UHPCs in Comparative Examples 8 to 12.

[0054] Figure 6 is a comparison of the self-shrinkage rate-time curves of the UHPC in Example 4 of the present invention (without shrinkage to slight expansion deformation) and the comparative UHPCs in Comparative Examples 13 to 16. Detailed Implementation

[0055] The embodiments of the present invention will now be described in detail. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the various embodiments of the invention and various modifications suitable for particular intended applications.

[0056] To verify the superior performance of the UHPC with no shrinkage to slight expansion deformation of the present invention, Examples 1 to 11 and Comparative Examples 1 to 16 are provided, which include two major UHPC systems: one with coarse aggregate and one with coarse aggregate.

[0057] The raw materials used to prepare UHPCs with no shrinkage to slight expansion deformation in Examples 1 to 11, and to prepare comparative UHPCs in Comparative Examples 1 to 16 are described below:

[0058] The cement used was Helin PO 42.5 cement; the fly ash consisted of two types with average particle sizes of 8 μm and 16 μm; the ground slag powder (referred to as mineral powder in Table 2 below) consisted of two types with average particle sizes of 8 μm and 16 μm; the inert admixture was a mixture of limestone powder and quartz powder in a 1:1 mass ratio, with the mixture consisting of two types with average particle sizes of 5 μm and 14 μm; the shrinkage-reducing admixture was a mixture of zeolite powder, ceramic powder, and kaolin in a 1:1:1 mass ratio, with the mixture consisting of two types with average particle sizes of 5 μm and 14 μm; the active activator was a mixture of anhydrite, hemihydrate gypsum, and dihydrate gypsum with an average particle size of 20 μm in a 1:1:1 mass ratio; the silica fume had an average particle size of 0.8 μm; and the ultrafine mineral powder had an average particle size of... The average particle size of the aggregate is 4.5 μm; the average particle size of the rice husk ash is 8 μm; the porous sand is any selection of coral sand, ceramic sand, or recycled aggregate sand with a maximum particle size not exceeding 2.36 mm (except for Example 11); the hard sand is river sand with a maximum particle size not exceeding 2.36 mm; the average particle size of the organic internal curing agent (superabsorbent polymer, SAP) is 130 μm, and the water absorption is 10 times the mass of SAP; the coarse aggregate is limestone coarse aggregate with a particle size of 5 mm to 16 mm; the fiber is copper-plated steel fiber with a hook end and a length of 0.2 mm; the compensating agent is calcium oxide-magnesium oxide composite compensating agent produced by Jiangsu Subote; the water reducing agent is polycarboxylate high-performance water reducing agent produced by Jiangsu Subote, with a water reduction rate of not less than 30%.

[0059] The components and their weight proportions in the UHPC provided in Examples 1 to 11 and Comparative Examples 1 to 16 are shown in Table 1 below.

[0060] Table 1. Components and their weight parts of Examples 1 to 11 and Comparative Examples 1 to 16

[0061] The material and particle size composition of the active admixture, the particle size composition of the inert admixture, the particle size composition of the shrinkage admixture, and the material composition of the sand in Examples 1 to 11 and Comparative Examples 1 to 16 are shown in Table 2 below.

[0062] Table 2. Material composition and weight ratio of active admixture, inert admixture, shrinkage-reducing admixture, and sand in Examples 1-11 and Comparative Examples 1-16.

[0063] Performance testing

[0064] The mixing time was calculated from the start of adding water and water-reducing agent until the ultra-high performance concrete mixture, exhibiting no shrinkage to slight expansion deformation, formed a homogeneous paste. The flowability of the ultra-high performance concrete after mixing was tested according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". After the flowability test, specimens were formed for compressive strength (100mm×100mm×100mm), flexural tensile strength (100mm×100mm×400mm), and axial tensile strength (dog-bone cross-section 50mm×100mm). These specimens were cured under standard conditions for 28 days, and their mechanical properties were tested according to T / CBMF 37-2018 "Basic Properties and Test Methods of Ultra-High Performance Concrete". Simultaneously, cylindrical specimens with a diameter of 100mm and a height of 400mm were formed, and the autogenous shrinkage of the ultra-high performance concrete, exhibiting no shrinkage to slight expansion deformation, was tested using the PVC pipe method, starting from the final setting time. A positive value for the autogenous contraction rate indicates contraction, while a negative value indicates expansion (unit: ×10). -6 (or με). The test results are shown in Figures 1 to 6 and Table 3 below.

[0065] Table 3. Test results of fresh-mixed and mechanical properties of UHPC in Examples 1-11 and Comparative Examples 1-16

[0066] Based on the test results in Figures 1 and 2 and Table 3, the UHPC described in this invention, which exhibits no shrinkage to slight expansion deformation, has a total stirring time of 5 to 8 minutes, a flowability of 540 mm to 780 mm, and 28-day compressive strength, ultimate flexural strength, and ultimate tensile strength of 132.5 MPa to 161.4 MPa, 20.8 MPa to 27.7 MPa, and 8.3 MPa to 13.5 MPa, respectively. Furthermore, it significantly improves upon the material properties of conventional UHPC, which exhibits large self-shrinkage, with a 60-day self-shrinkage of only -4.47 με to 46.05 με, resulting in UHPC exhibiting deformation properties of no shrinkage to slight expansion.

[0067] Specifically, Example 1 is a baseline group with relatively balanced components; the formulations of Examples 2 and 3 are respectively the maximum shrinkage group (minimum cement content + maximum admixture content + minimum sand / steel fiber content + minimum compensator content) and the low shrinkage group (minimum cement content + minimum active admixture content + maximum sand / steel fiber content + maximum compensator content) among the minimum cement content; the formulation of Example 4 is a low water-cement ratio group among the low shrinkage group of the minimum cement content; the formulations of Examples 5 and 6 are respectively the minimum shrinkage group among the maximum cement content (maximum cement content + minimum active admixture content + maximum sand / steel fiber content + maximum compensator content). The formulas for Examples 7 to 10 correspond to the maximum weight ratio of fly ash to mineral powder, the maximum particle size ratio of active admixtures, the maximum particle size ratio of inert admixtures and shrinkage-reducing admixtures, and the maximum amount of porous sand, respectively. The formula for Example 11 differs from Example 4 in that the porous sand is a mixture of ceramic sand, coral sand, and recycled aggregate sand. Therefore, the UHPC described in this invention, within the limits of each component, regardless of the adjustment of the component ratio, achieves a balance between no shrinkage to slight expansion deformation, good mechanical properties, and good workability.

[0068] Compared to the baseline example 3, Comparative Example 1 did not use a compensating agent but increased the amount of shrinkage-reducing admixture. Based on the test results in Figure 3 and Table 3, it can be seen that the fresh mix performance and mechanical properties of Comparative Example 1 did not show a significant decrease. However, due to the lack of the expansion effect of the compensating agent, even with the addition of inactive shrinkage-reducing admixture with internal curing properties, its autogenous shrinkage was still significant, reaching 143.42 με over 60 days, failing to achieve a zero-shrinkage effect.

[0069] Compared to the baseline example 6, Comparative Example 2 used an excessive amount of compensating agent, reducing the amount of cement. As shown in Figure 3 and Table 3, the compensating agent dosage in Comparative Example 2 was higher, with a self-shrinkage rate of -7.58 με, indicating a micro-expansion effect. However, the larger water requirement for the reaction reduced the workability of the mixture; and the expansion effect of the compensating agent reduced the fiber-matrix bonding performance, resulting in a significant decrease in ultimate flexural strength and ultimate tensile strength. Compared to Example 6, its 28-day ultimate flexural strength decreased by 46.9%, and its 28-day ultimate tensile strength decreased by 64.4%.

[0070] Compared to the baseline example 1, Comparative Example 3 used a small amount of active admixtures and correspondingly reduced the amount of coarse aggregate and increased the amount of inert and shrinkage-reducing admixtures to overcome the adverse effects of the small amount of active admixtures. Combining the test results in Figure 4 and Table 3, it can be seen that although Comparative Example 3 has a certain micro-expansion effect, due to the lack of active components and fewer hydration products, simply reducing the amount of coarse aggregate and increasing the amount of inert and shrinkage-reducing admixtures to improve the packing density cannot provide good mechanical properties. Its 28-day compressive strength decreased by 20.6% to only 115.1 MPa (which can no longer be called UHPC; typically, UHPC compressive strength is required to be >120 MPa), and its 28-day ultimate tensile strength decreased by 30.6% to only 7.7 MPa.

[0071] Compared to the baseline example 1, Comparative Example 4 used an excessive amount of active admixture and reduced inert and shrinkage-reducing admixtures to overcome the adverse effects of excessive active admixture. Based on the test results in Figure 4 and Table 3, it can be seen that although Comparative Example 4 exhibits good fresh mix performance and mechanical properties, the use of a large amount of active admixture leads to increased shrinkage caused by the chemical reaction, with a 60-day auto-shrinkage of 110.53 με, indicating a certain degree of auto-shrinkage.

[0072] Compared to Example 1 of the baseline group, Comparative Example 5 used a smaller amount of reactive activator and increased the amount of reactive admixture. Based on the test results in Figure 4 and Table 3, it can be seen that although Comparative Example 5 increased the amount of reactive admixture, the relatively low reactivity of the admixture itself, coupled with the lack of sufficient reactive activator, resulted in a decrease in the degree of reaction and density of the concrete, leading to a reduction in mechanical properties. Its 28-day compressive strength was <120 MPa, and its tensile strength was <8 MPa.

[0073] Compared to Example 1 of the baseline group, Comparative Example 6 used an excessive amount of activator and reduced the amount of cement. Based on the test results in Figure 4 and Table 3, it can be seen that Comparative Example 6 used a larger amount of activator, but due to the poor particle shape of the gypsum particles, it had a retarding effect, which was detrimental to the fresh mix performance, resulting in a total mixing time exceeding 16 minutes. Furthermore, excessive gypsum produced a large amount of ettringite, leading to poor concrete stability and unfavorable mechanical properties; its 28-day compressive strength was <120 MPa, and its flexural and tensile strengths decreased significantly.

[0074] Compared to the baseline example 1, comparative example 7 did not use porous sand. Based on the test results in Figure 4 and Table 3, it can be seen that although comparative example 7 exhibits good fresh mix performance and mechanical properties, the lack of internal curing effect from porous sand results in significant autogenous shrinkage, reaching 95.26 με over 60 days.

[0075] Compared to Example 1 in the baseline group, Comparative Example 8 used an excessive amount of porous sand. As shown in Figure 5 and Table 3, although Comparative Example 8 exhibited a slight expansion effect, the increased use of low-strength, low-modulus porous sand significantly reduced the fresh-mixed performance and mechanical properties. The total mixing time was close to 20 minutes, making it practically unusable under complex working conditions; furthermore, the 28-day compressive strength was <120 MPa, and the flexural and tensile strengths were significantly reduced.

[0076] Compared to the baseline example 1, the amount of fly ash in comparative example 9 was reduced, while the amount of ground granulated slag powder was increased. Based on the test results in Figure 5 and Table 3, it can be seen that comparative example 9 has higher mechanical properties. This is because the increased amount of more active ground granulated slag powder and the reduced amount of fly ash with a spherical ball effect result in poorer fresh-mixed performance and greater autogenous shrinkage.

[0077] Compared to the baseline example 1, Comparative Example 10 used active admixtures with particle sizes ranging from 5 μm to 10 μm. Based on the test results in Figure 5 and Table 3, it can be seen that in Comparative Example 10, due to the use of small-particle-size active admixtures, the reduced particle size leads to increased reactivity and a significant increase in the ability to adsorb free water, resulting in greater chemical shrinkage and self-drying shrinkage, and ultimately, a larger overall shrinkage.

[0078] Compared to Example 1 of the baseline group, Comparative Example 11 reduced the amount of active admixture by 5μm to 10μm, correspondingly increasing the amount of active admixture by 10μm to 20μm. Combined with the test results in Figure 5 and Table 3, it can be seen that while reducing the amount of small-particle-size active admixture in Comparative Example 11 is beneficial for reducing shrinkage, it leads to a decrease in the overall reaction degree and packing density, thus deteriorating the mechanical properties.

[0079] Compared to Example 1 of the baseline group, Comparative Example 12 reduced the amount of inert admixture with a particle size of 3μm to 10μm and increased the amount of inert admixture with a particle size of 10μm to 20μm. Combined with the test results in Figure 5 and Table 3, it can be seen that in Comparative Example 12, due to the reduced amount of small-particle-size inert admixture, its filling effect on small-scale pores is weakened, resulting in increased porosity and reduced matrix packing density, thus also deteriorating mechanical properties. Furthermore, for the same reasons, reducing the amount of 3μm to 10μm particles in the shrinkage admixture also reduces mechanical properties.

[0080] Compared to the baseline example 4, Comparative Examples 13-15 used some silica fume, ultrafine mineral powder, and rice husk ash in their active admixtures. Based on the test results in Figure 6 and Table 3, it can be seen that the use of highly active ultrafine powders in Comparative Examples 13-15 can shorten the stirring time and increase the flow height due to their filling and ball-bearing effects. However, the extremely small particle size significantly increases the amount of water adsorbed by the particles, causing a rapid decrease in internal relative humidity and thus increasing self-shrinkage. Simultaneously, the highly active ultrafine powders greatly promote hydration, which, while beneficial to mechanical properties, significantly increases self-shrinkage, resulting in a 60-day self-shrinkage greater than 140 με for Comparative Examples 13-15.

[0081] Compared to Example 4 (the baseline group), Comparative Example 16 used SAP (organic internal curing agent) instead of porous sand (inorganic internal curing agent). As shown in Figure 6 and Table 3, due to the self-swelling of SAP through water absorption and the internal curing effect of subsequent water release, its 60-day autogenous shrinkage was -45.2 με, exhibiting micro-swelling. However, the large particle size and high water absorption of SAP significantly increased stirring time, reduced fluidity, and deteriorated working performance; furthermore, SAP's competitive water absorption hindered the hydration reaction, its large particle size reduced particle packing density, and its extremely low strength resulted in a significant decrease in its mechanical properties. Compared to Example 4, its 28-day compressive strength, ultimate flexural strength, and ultimate tensile strength decreased by 31.3%, 23.7%, and 33.7%, respectively.

[0082] As can be seen, the UHPC of the present invention, which exhibits no shrinkage to slight expansion deformation, achieves full-scale shrinkage reduction by utilizing a combination of low cement content, low activity and active admixtures with a mix of coarse and fine particle sizes, inert admixtures with a mix of coarse and fine particle sizes, shrinkage-reducing admixtures with a mix of coarse and fine particle sizes for internal curing, fine aggregates for internal curing, compensators for expansion effects, coarse aggregates and fibers for inhibiting shrinkage. This results in the realization of ultra-high performance concrete and coarse aggregate ultra-high performance concrete with no shrinkage to slight expansion deformation while ensuring fresh mix performance and ultra-high mechanical properties. These components interact with each other in their combination, rather than existing independently.

[0083] It should be noted that, in the above embodiments of the present invention, although only one option is shown for the convenience of experimentation, such as the active admixture being a mixture of fly ash and ground blast furnace slag powder in a mass ratio of 1:1, this is not intended to limit the selection of all active admixtures. This is because, according to previous analysis, for active admixtures, when ground blast furnace slag powder is mixed with fly ash at a dosage not exceeding 50 wt%, the effect is equivalent to that of pure fly ash at different dosages. The same applies to the other components.

[0084] The embodiments described above are for illustrative purposes only and do not constitute a specific limitation on the present invention. Any modifications made without departing from the basic concept of the present invention, as well as any obvious modifications derived therefrom, are within the scope of protection of the present invention.

Claims

1. A UHPC with no shrinkage to slight expansion deformation, characterized in that, It consists of the following components, which are mixed evenly in parts by weight: Cement: 300-600 parts; Active admixture: 100-300 parts; Inert admixtures: 120–380 parts; Shrinkage-reducing admixtures: 60–250 parts; Activity activator: 20-120 parts; Sand: 900-1200 parts; Coarse aggregate: 0-500 parts; Fiber: 100-250 parts; Compensator: 5-25 parts; Water-reducing agent: 7-25 parts; Water: 70–220 parts; The active admixture is a mixture of 50% to 100% fly ash and 0% to 50% ground slag powder, and the powder particles with an average particle size of 5μm to 10μm account for 50% to 80% of the mass of the active admixture. In the inert admixture, powder particles with an average particle size of 3μm to 10μm account for 50% to 100% of the mass of the inert admixture; The sand is a mixture of 10wt% to 20wt% porous sand and 80wt% to 90wt% hard sand.

2. The UHPC with no shrinkage to micro-expansion deformation according to claim 1, characterized in that, The average particle size of both the fly ash and the ground slag powder is 5μm to 20μm.

3. The UHPC with no shrinkage to micro-expansion deformation according to claim 1, characterized in that, The inert admixture is selected from limestone powder and / or quartz powder, and the average particle size of limestone powder and quartz powder is 3μm to 20μm.

4. The UHPC with no shrinkage to micro-expansion deformation according to claim 1, characterized in that, The shrinkage-reducing admixture is selected from at least one of zeolite powder, ceramic powder, and kaolin, and the average particle size of zeolite powder, ceramic powder, and kaolin is 3μm to 20μm.

5. The UHPC with no shrinkage to micro-expansion deformation according to claim 4, characterized in that, In the shrinkage-reducing admixture, powder particles with an average particle size of 3μm to 10μm account for 50% to 100% of the mass of the shrinkage-reducing admixture; 6. The UHPC with no shrinkage to micro-expansion deformation according to claim 1, characterized in that, The active activator is selected from at least one of anhydrite, hemihydrate gypsum, and dihydrate gypsum, and the average particle size of anhydrite, hemihydrate gypsum, and dihydrate gypsum is 5μm to 30μm.

7. The UHPC with no shrinkage to micro-expansion deformation according to claim 1, characterized in that, The maximum particle size of the sand does not exceed 2.36 mm.

8. The UHPC with no shrinkage to micro-expansion deformation according to claim 7, characterized in that, The porous sand is selected from at least one of ceramic sand, coral sand, and recycled aggregate sand, and the hard sand is river sand and / or quartz sand.

9. The UHPC with no shrinkage to micro-expansion deformation according to any one of claims 1 to 8, characterized in that, The coarse aggregate is selected from at least one of basalt, limestone, and granite, and the particle size of the coarse aggregate is 5mm to 16mm. The fiber has a diameter of 0.15 mm to 0.4 mm and a length of 13 mm to 25 mm; and the fiber is selected from any one of copper-plated steel fibers with a straight, hooked, or wavy shape, or a mixture of at least two in any proportion. The compensator is selected from at least one of calcium oxide, magnesium oxide, and calcium oxide-magnesium oxide composite. The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent, and the water reduction rate is not less than 30%. The cement is ordinary Portland cement and / or Portland cement with a strength grade of 42.5 or higher.

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