A type of underwater anti-dispersion ultra-high performance concrete based on reversible mesh design, its preparation method and application

Abstract

An underwater anti-dispersion ultra-high performance concrete based on reversible network design, its preparation method, and its application. The ultra-high performance concrete comprises cementitious materials, water, polycarboxylate superplasticizer, and a synergistic anti-dispersion composite admixture; wherein the composite admixture consists of a main agent and auxiliary agents. The main agent and auxiliary agents are used to construct a three-dimensional reversible network structure with significant thixotropic properties in situ within the slurry, endowing the slurry with intelligent rheological properties of "shear thinning—static thickening": the yield stress reaches 50–320 Pa at rest to resist underwater erosion, and the plastic viscosity is maintained at 2–8 mPa·s during shearing to ensure pumpability. This invention effectively solves the problem of balancing rheological properties and anti-dispersion properties in ultra-high performance concrete systems, and is particularly suitable for the repair and reinforcement of underwater piers, pile foundations, and tunnel linings.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to an underwater anti-dispersion ultra-high performance concrete based on a reversible mesh design, its preparation method and application, which is suitable for use in the repair and reinforcement of concrete structures such as underwater piers, pile foundations and tunnel linings. Background Technology

[0002] Ultra-high performance concrete (UHPC) has broad application prospects in underwater structure repair and reinforcement due to its excellent mechanical properties and density. However, the underwater construction environment places stringent and contradictory rheological requirements on materials: on the one hand, the material must possess extremely strong anti-dispersion ability (high cohesion) to resist water erosion and prevent the loss of cementitious components and water pollution; on the other hand, in order to achieve vibration-free filling in complex and narrow spaces, the material must maintain excellent fluidity and self-compacting ability (low viscosity). How to break the rheological paradox of "high anti-dispersion inevitably leads to high viscosity" in UHPC systems with low water-cement ratios, and simultaneously solve the bonding problem at the interface between new and old concrete underwater, is a key bottleneck that urgently needs to be overcome in this field.

[0003] Existing technologies for improving the anti-dispersion properties of underwater concrete mainly include adding cellulose ether thickeners (such as HPMC), compounding thickening components, or utilizing aggregate interlocking. However, when these solutions are directly applied to ultra-high performance concrete systems that are extremely sensitive to rheological properties, the following significant drawbacks exist: (1) Rheological property conflict: Traditional thickeners follow a single thickening mechanism. While increasing the static yield stress of the paste to suppress dispersion, they inevitably increase the plastic viscosity significantly. This will cause ultra-high performance concrete to lose its characteristic high fluidity, resulting in a sharp increase in pumping resistance or even pipe blockage, making it difficult to meet the construction requirements of self-compacting concrete.

[0004] (2) Poor chemical compatibility: Ultra-high performance concrete relies heavily on polycarboxylate superplasticizers (PCE) to achieve dispersion at low water-cement ratios. However, most polymeric thickeners compete with PCE for adsorption on the surface of cement particles or interfere with the expansion of PCE through steric hindrance, resulting in reduced water reduction efficiency, significant slump loss over time, and even inducing abnormal flocculation.

[0005] (3) Insufficient interfacial bond strength: During underwater repair, water film is easily formed at the interface between new and old concrete, and cementitious materials are easily diluted and carried away, resulting in a loose and porous interfacial transition zone (ITZ). Existing technologies often fail to achieve chemical bonding or effective anchoring at the interface in an underwater environment, making the interface a weak link in structural reinforcement.

[0006] In summary, existing technologies struggle to achieve intelligent responses to both static erosion resistance and shear flowability at the microscopic scale of cementitious paste. Therefore, developing a novel ultra-high-performance concrete cementitious material system capable of constructing a shear-sensitive three-dimensional reversible network structure, thereby significantly improving underwater anti-dispersion and interfacial bonding performance while ensuring construction fluidity, is of significant engineering importance and application value. Summary of the Invention

[0007] The primary technical problem this invention aims to solve is to overcome the rheological contradiction between "high anti-dispersion" and "high fluidity" in existing ultra-high performance concrete during underwater construction. This invention provides an underwater anti-dispersion ultra-high performance concrete based on a reversible network design, its preparation method, and its application, creating a cementitious material system capable of intelligently responding to shear conditions. This system must maintain low viscosity during pumping while possessing extremely high yield stress in a static state to resist the erosion of the underwater environment. Another technical problem this invention aims to solve is addressing the challenges of low bond strength and numerous interfacial transition zone (ITZ) defects at the interface between new and old concrete underwater due to slurry loss and water film obstruction.

[0008] To address the aforementioned technical challenges, this invention proposes an underwater anti-dispersion ultra-high performance concrete based on a reversible network design, along with its preparation method and applications. It abandons the traditional approach of relying solely on thickeners to "simply increase overall viscosity," and innovatively adopts a "shear-sensitive synergistic network" design concept. Specifically, by combining anionic main agents with specific functional group adjuvants, a three-dimensional reversible network structure sensitive to shear rate is constructed at the microscale of the cementitious paste. This structure endows the material with significant thixotropy: under construction shear, the network rapidly deconstructs to significantly reduce plastic viscosity, ensuring the excellent flowability and pumpability of the ultra-high performance concrete; after shearing ceases (resting), the network rapidly reconstructs to significantly increase yield stress and cohesion, thereby achieving a synergistic unity of underwater anti-dispersion, high flowability, and interfacial chemical enhancement.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is: to provide an underwater anti-dispersion ultra-high performance concrete based on a reversible network design, comprising the following components based on the total mass of cementitious materials: (a) Cementitious material: 100 parts by weight; (b) Water: Water-to-binder ratio 0.16–0.20; (c) Polycarboxylate superplasticizer: 0.8–1.2 parts by weight; (d) Synergistic anti-dispersion composite admixture: 0.12–0.70 parts by weight, The composite admixture consists of the following two parts: (i) Main agent: anionic polyacrylamide, molecular weight 800–1500 million, dosage 0.10–0.50 parts by weight; (ii) Excipients: at least one selected from chitosan, guar gum or methylcellulose, in an amount of 0.02–0.20 parts by weight; The main and auxiliary agents are assembled in situ via electrostatic bonding, hydrogen bonding, or polymer chain entanglement to form a three-dimensional reversible network structure between the cementitious material particles. This structure endows the slurry with typical decoupled intelligent rheological behavior of "yield stress-plastic viscosity": In a static state, the three-dimensional network structure supports a large yield stress of 50–320 Pa, thereby generating sufficient structural viscosity to resist underwater erosion and inhibit particle dispersion; under construction shearing, such as stirring or pumping, the network structure undergoes reversible deconstruction, and the plastic viscosity is maintained at 2–8 mPa·s, thus ensuring that the ultra-high performance concrete slurry has good fluidity (spreadability ≥ 160 mm) and pumpability. In addition, this ultra-high performance concrete has excellent underwater anti-dispersion properties, with a suspension turbidity ≤ 30 NTU after 30 min of underwater pouring.

[0010] The cementitious material is composed of the following components: 60–75% silicate cement, 15–25% fly ash, and 8–12% silica fume, where the percentages are by mass and the total is 100%.

[0011] The ultra-high performance concrete also contains quartz sand with a particle size of 0.1–0.6 mm and a sand-binder ratio of 0.8–1.0.

[0012] The excipient is methylcellulose, and its 2% aqueous solution has a viscosity of 4000–6000 mPa·s.

[0013] The excipient is chitosan with a degree of deacetylation ≥ 85%, and the mass ratio of the main agent to the excipient is (4–10):1.

[0014] The method for preparing the ultra-high performance concrete includes the following steps: S1 Dissolve the main agent and the auxiliary agent separately in water at 20–40 ℃ to prepare a composite flocculant with a concentration of 0.5–2 wt%; S2 Dry mix the cementitious material with the optional fine aggregate for 30–60 s; Under stirring conditions of 300–450 rpm, the remaining water, polycarboxylate superplasticizer, and the composite flocculant obtained in S1 are added sequentially. Stirring is continued for 90–120 s to ensure that the main agent and auxiliary agent are uniformly dispersed in the shear field, resulting in a homogeneous slurry with shear thinning properties, known as network breaking and reversible recovery after standing, known as network recombination.

[0015] The slurry prepared by the method is used in the repair and reinforcement of defects in underwater piers, pile foundations, or tunnel linings.

[0016] In the ultra-high performance concrete, the main agent and the auxiliary agent synergistically construct an intelligent rheological structure with "shear thinning and static thickening" characteristics at the microscopic level. The specific mechanism of action is as follows: (1) Electrostatic in-situ assembly mechanism of polyelectrolytes (for chitosan system) This invention utilizes the polyelectrolyte complex (PEC) theory. The carboxyl group (-COO) on the anionic polyacrylamide chain of the main agent... - -) and the protonated amino group (-NH3) of the excipient chitosan. + In the cement paste environment, in-situ electrostatic attraction occurs, forming a high density of physical ionic bonds. Under static conditions, these bonds rapidly build a three-dimensional interconnected network with high yield stress, effectively resisting water erosion. Under applied shear, the ionic bonds reversibly dissociate, reducing flow resistance; after shearing stops, the network re-aggregates and reconstructs. Simultaneously, the amino and other active functional groups of chitosan possess excellent bioadhesion properties, contributing to enhanced chemical interactions between the material and the substrate interface.

[0017] (2) Hydrogen bond interpenetration network mechanism (for guar gum and methylcellulose systems) The abundant hydroxyl groups (-OH) in the excipient molecule - -) It acts as a physical crosslinking site, forming an interpenetrating network (IPN) structure with the main agent molecular chain and hydration products, mainly composed of hydrogen bonds and physical entanglements. This structure endows the system with significant thixotropy: in a static state (underwater environment), the number of hydrogen bond sites increases, the structural strength increases, and particle migration is inhibited; in a shear state (construction), the hydrogen bond network quickly unwinds, achieving shear thinning and maintaining low plastic viscosity, thereby ensuring the excellent fluidity and pumpability of the ultra-high performance concrete slurry.

[0018] Compared with the prior art, the present invention has the following significant advantages: 1. It solves the contradiction between underwater anti-dispersion and construction fluidity: Through the synergistic network of main and auxiliary agents, the yield stress of the system under static conditions is significantly increased to more than 300 Pa, effectively resisting erosion; while under construction shear, the plastic viscosity is maintained at a low level, at 2–8 mPa·s, and the spread is maintained at ≥ 160 mm, perfectly solving the problem that traditional ultra-high performance concrete is difficult to balance underwater anti-dispersion and self-leveling pumpability.

[0019] 2. Excellent underwater anti-dispersion and environmental protection: Thanks to the strong encapsulation effect of the three-dimensional network, almost no cementitious material is released when the slurry is poured in water. After 30 minutes of underwater pouring, the turbidity of the suspension is controlled below 30 NTU, which greatly reduces the pollution to the aquatic environment.

[0020] 3. Improved interfacial bonding performance: Certain additives (such as chitosan) contain active functional groups, which help improve the quality of the interfacial transition zone and enhance interfacial chemical interactions in underwater environments, thereby improving the bonding and durability of the interface between new and old concrete.

[0021] 4. Synergistic effect of high strength and anti-dispersion: This invention aims to achieve a balance between underwater anti-dispersion and high fluidity in ultra-high performance concrete systems, while maintaining the high strength advantage of ultra-high performance concrete, without significantly sacrificing mechanical properties for anti-dispersion performance.

[0022] 5. The key performance indicators of the ultra-high performance concrete of this invention are significantly better than the requirements of existing specifications: Anti-dispersion properties: The industry standard GB / T 37990-2019 "Technical Requirements for Underwater Non-dispersible Concrete Flocculants" usually requires a low content of suspended solids, corresponding to a turbidity in the range of 100-150 NTU. However, this invention reduces the turbidity to below 30 NTU through electrostatic mesh technology, achieving a "clear to the bottom" pouring effect and greatly reducing pollution to the water environment.

[0023] Mechanical properties: Existing underwater concrete standards require a water-to-land strength ratio of ≥ 70%, while this invention raises it to over 80%. Simultaneously, its compressive strength meets the national standard GB / T 31387-2025 "Ultra-High Performance Concrete," which requires a high strength grade of ≥ 100 MPa for ultra-high performance concrete, thus combining underwater non-dispersibility with the ultra-high mechanical properties of ultra-high performance concrete. Attached Figure Description

[0024] Figure 1 shows the state of the control group cementitious material without the composite admixture of the present invention when it is poured in water; as shown in the figure, the slurry disperses rapidly and the water becomes turbid.

[0025] Figure 2 shows the state of the cementitious material with the synergistic anti-dispersion composite admixture of the present invention when it is poured in water; as shown in the figure, the slurry maintains good cohesion, with no obvious dispersion, and the water is clear.

[0026] Figure 3 shows a scene of simulated underwater repair pouring using the ultra-high performance concrete of this invention; as shown in the figure, the slurry has good self-leveling properties and visibility underwater.

[0027] Figure 4 is a schematic diagram of the microstructure mechanism of the cementitious material described in this invention under static conditions; as shown in the figure, the main agent chain (blue curve) and the auxiliary agent chain (green curve) build a three-dimensional network between the cementitious material particles (circles) to form a structural support against dispersion.

[0028] Figure 5 is a schematic diagram of the network deconstruction mechanism of the cementitious material of the present invention under shearing action; as shown in the figure, under external shearing force, the physical cross-linking points are broken, the network structure is destroyed, which is conducive to the flow and pumping of the slurry.

[0029] Figure 6 is a schematic diagram of the network reconstruction mechanism of the cementitious material of the present invention after shearing is stopped; as shown in the figure, after the shearing force is removed, the network structure quickly and spontaneously recovers and rebuilds its anti-dispersion ability. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto. Example 1

[0031] This embodiment provides an example of underwater anti-dispersion ultra-high performance concrete based on a reversible mesh design, comprising the following components based on the total mass of cementitious materials: Raw materials and standard mix proportions In the two experimental examples and comparative examples of this invention, a uniform ultra-high performance concrete standard mix proportion was used. For ease of understanding and experimental reproduction, the following proportions are expressed in "parts by weight"; in the specific laboratory preparation process, 1 part by weight corresponds to 1 gram (g).

[0032] The reference components are as follows: Cementing materials: POII 52.5 Portland cement: 325 parts; Grade 1 fly ash: 100 parts; Silica fume: 75 parts, silica fume Content >95%; Fine aggregate: 380 parts of quartz sand, with a particle size range of 0.1 - 0.6 mm; Liquid components: Water: 90 parts; Polycarboxylate superplasticizer (40% solid content): 10 parts; Synergistic anti-dispersion compound admixture: 0.12–0.70 parts, The composite admixture consists of the following two parts: (i) Main agent: Anionic polyacrylamide (APAM), molecular weight 12 million, dosage 0.10–0.50 parts by weight; (ii) Excipients: at least one selected from chitosan or methylcellulose, in an amount of 0.02–0.20 parts by weight; Rheological tests were performed on the slurry prepared using the experimental formulation: 0.4 parts APAM + 0.05 parts chitosan / methylcellulose. The results are as follows: 1. Evolution of yield stress: The yield stress of the slurry increases significantly with the settling time, from about 10 Pa in the blank group of neat slurry to about 50–320 Pa.

[0033] 2. Plastic viscosity control: Despite the significant increase in yield stress, the plastic viscosity of the slurry varied only within a narrow range of 2–8 mPa·s, without significant thickening.

[0034] 3. Rheological model fitting: The shear stress-shear rate curves at all ages can be fitted using the modified Bingham model. Good fit (R²≥0.99) 4. Macroscopic State: Under static conditions, high yield stress and high structural viscosity effectively resist underwater erosion and inhibit particle dispersion; under shear conditions, low plastic viscosity ensures good fluidity. Measured data show that the spread of the ultra-high performance concrete is ≥ 160 mm, and the turbidity of the suspension after 30 minutes of underwater pouring is ≤ 30 NTU. These results confirm that the main agent and auxiliary agents successfully constructed a three-dimensional reversible network structure of "shear thinning—static thickening" between the cementitious material particles. Example 2

[0035] This embodiment describes the preparation method of underwater anti-dispersion ultra-high performance concrete based on reversible mesh design according to the present invention, including the following steps: S1 Dissolve the main agent and the auxiliary agent separately in water at 20–40 ℃ to prepare a composite flocculant with a concentration of 0.5–2 wt%; S2 Dry mix the cementitious material with the optional fine aggregate for 30–60 s; Under stirring conditions of 300–450 rpm, add the remaining water, polycarboxylate superplasticizer and the composite flocculant obtained in S1 in sequence, and continue stirring for 90–120 s until a uniform, clumping-free slurry is obtained.

[0036] To verify the effect of flocculants of different ion types at the same dosage on the performance of cementitious material compositions, a blank group, two comparative examples, and two experiments were conducted.

[0037] The performance of different ionic main agents was compared. Under the condition of fixed adjuvants or a single variable, the effects of anionic (the main agent of this invention) and nonionic polyacrylamide (PAM) on the performance of ultra-high performance concrete paste were compared. The results are shown in Table 1.

[0038] Table 1. Effect of flocculants of different ion types at the same dosage on the properties of cementitious material compositions.

[0039] As can be seen from the data in Table 1, the choice of ion type has a decisive influence on the material properties: 1. Anti-dispersion properties (turbidity): At the same dosage, the anionic main agent showed significantly better turbidity reduction effect than the nonionic one. For example, at a dosage of 0.2%, the anionic turbidity of Experiment 1 was 53 NTU, far lower than the 165 NTU of Comparative Example 1 (nonionic). This confirms that the electrostatic adsorption between anionic groups and the surface of cement particles is the key to constructing a highly efficient anti-dispersion network.

[0040] 2. Mechanical properties: The 28-day compressive strength of Experiment 1 (122 MPa) is higher than that of Comparative Example 1 (117 MPa) and close to that of the blank group (neat paste) (126 MPa). This indicates that the anionic main agent selected in this invention has a smaller negative impact on the matrix strength while ensuring anti-dispersion.

[0041] Therefore, anionic polymers are more suitable as the main agent in the underwater anti-dispersion system of ultra-high performance concrete.

[0042] To verify the synergistic effect of incorporating different proportions of main agent and excipient, experiments were conducted as shown in Table 2.

[0043] Validation of the synergistic effect of main and auxiliary agents: Based on the determination of the anionic main agent, the synergistic effect of the main agent and auxiliary agents (chitosan and methylcellulose) after co-blending was further verified.

[0044] Table 2 Synergistic effects of incorporating different proportions of main agent and excipient

[0045] The data in Table 2 confirm a significant synergistic effect between the active ingredient and the excipients. 1. Verification of reduced quantity and increased efficiency (for Experiment 1): Dosage comparison: The total dosage of admixture in Experiment 1 was 0.25% (0.2 + 0.05), which was lower than the single admixture dosage of 0.3% in Comparative Example 1.

[0046] Performance comparison: With the total dosage reduced, the 1-day early strength (65 MPa) and 28-day strength (119 MPa) of Experiment 1 were actually higher than those of Comparative Example 1 (48 MPa / 115 MPa); at the same time, the turbidity (54 NTU) was also better than that of Comparative Example 1 (64 NTU).

[0047] This strongly demonstrates that an electrostatic complex network is formed between chitosan and APAM. This microstructure is more effective than simply increasing the polymer concentration, and truly achieves high performance at low dosage.

[0048] 2. Validation of superior anti-dispersion performance (for Experiment 3): In Experiment 3, when 0.1% methylcellulose was added, the turbidity of the system was as low as 9 NTU, which was nearly 7 times lower than that of the main agent alone (64 NTU). This indicates that methylcellulose, as a rigid framework, greatly enhances its ability to encapsulate fine particles through a hydrogen-bonded interpenetrating network mechanism, enabling the material to achieve almost zero dispersion underwater.

[0049] 3. Engineering adaptability: Although the addition of methylcellulose slightly reduces the later strength (102 MPa), it still far exceeds the standard of ordinary underwater concrete and maintains excellent fluidity (170-190 mm), which fully meets the engineering requirements of underwater grouting and repair.

Claims

1. An underwater anti-dispersion ultra-high performance concrete based on a reversible mesh design, characterized in that, Based on the total mass of the cementitious material, it includes the following components: a. Cementitious material: 100 parts by weight; b. Water: Water-to-binder ratio 0.16–0.20; c. Polycarboxylate superplasticizer: 0.8–1.2 parts by weight; d. Synergistic anti-dispersion compound admixture: 0.12–0.70 parts by weight, The composite admixture consists of the following two parts: (i) Main agent: anionic polyacrylamide, molecular weight 800–1500 million, dosage 0.10–0.50 parts by weight; (ii) Excipients: at least one selected from chitosan, guar gum or methylcellulose, in an amount of 0.02–0.20 parts by weight; The main agent and the excipient are configured in the slurry to synergistically construct a shear-sensitive three-dimensional reversible network structure through electrostatic interaction, hydrogen bonding, or polymer chain entanglement. The network structure has the following dynamic rheological properties: (1) Construction and reconstruction: Under static conditions or after shearing stops, the main agent and the excipient spontaneously form or reconstruct the network structure through in-situ assembly, thereby increasing the yield stress and inhibiting particle dispersion; (2) Breaking and deconstruction: Under shearing action, the network structure can undergo physical deconstruction, reducing plastic viscosity and improving fluidity.

2. The ultra-high performance concrete according to claim 1, characterized in that, The cementitious material is composed of the following: Silicate cement 60–75%, fly ash 15–25%, Silica fume 8–12%, The percentages mentioned above are mass percentages and the sum is 100%.

3. The ultra-high performance concrete according to claim 1 or 2, characterized in that, It also contains quartz sand with a particle size of 0.1–0.6 mm and a sand-to-cement ratio of 0.8–1.

0.

4. The ultra-high performance concrete according to any one of claims 1–3, characterized in that, The excipient is methylcellulose, and its 2% aqueous solution has a viscosity of 4000–6000 mPa·s.

5. The ultra-high performance concrete according to any one of claims 1–3, characterized in that, The excipient is chitosan with a degree of deacetylation ≥ 85%, and the mass ratio of the main agent to the excipient is 4–10:

1.

6. A method for preparing ultra-high performance concrete according to any one of claims 1-5, characterized in that, Includes the following steps: S1 Dissolve the main agent and the auxiliary agent separately in water at 20–40 ℃ to prepare a composite flocculant with a concentration of 0.5–2 wt%; S2 Dry mix the cementitious material with the optional fine aggregate for 30–60 s; Under stirring conditions of 300–450 rpm, the remaining water, polycarboxylate superplasticizer, and the composite flocculant obtained in S1 are added sequentially, and stirring is continued for 90–120 s to ensure that the main agent and the auxiliary agent are uniformly dispersed in the shear field, and a uniform slurry with shear thinning and reversible recovery characteristics after standing is obtained.

7. The ultra-high performance concrete according to any one of claims 1–5, characterized in that, The performance indicators of the ultra-high performance concrete are as follows: (1) underwater anti-dispersion performance: turbidity of underwater casting suspension ≤ 30 NTU; (2) mechanical properties of ultra-high performance concrete: compressive strength ≥ 100 MPa after 28 days of standard curing; (3) underwater molding mechanical properties: 28-day compressive strength ratio of underwater casting specimen to air-cast specimen ≥ 80%; (4) interfacial bonding performance: underwater interfacial bonding strength with old concrete substrate ≥ 2.0 MPa.

8. The application of the ultra-high performance concrete according to any one of claims 1–5 and 7 or the slurry prepared by the method of claim 6 in the repair and reinforcement of defects in underwater piers, pile foundations or tunnel linings.

Images