Underwater non-dispersible fine aggregate concrete and preparation method thereof

Abstract

The invention provides underwater non-dispersible fine aggregate concrete and a preparation method thereof, and belongs to the technical field of concrete. The underwater non-dispersible fine aggregate concrete is prepared from the following components in parts by weight: 200 to 220 parts of water, 400 to 488 parts of cement, 1020 to 1120 parts of coarse aggregate, 550 to 650 parts of fine aggregate, 3 to 8 parts of efficient water reducing agent, 0.50 to 2.00 parts of anti-dispersing agent, 0.10 to 0.20 part of retarder and 0.50 to 3.00 parts of plant nano cellulose fiber. By adjusting the particle size of the coarse aggregate, the mixing amount of the anti-dispersing agent, the high-efficiency water reducing agent and the plant nano cellulose fiber and other conditions, the anti-dispersing performance of a concrete mixture is remarkably improved, and the prepared underwater non-dispersible fine aggregate concrete has underwater anti-dispersing performance and flowability, can accurately reach a pouring position through a guide pipe, and can be used for preparing the underwater non-dispersible fine aggregate concrete. The method has the characteristic of improving early strength.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and particularly relates to an underwater non-dispersible fine aggregate concrete and its preparation method. Background Technology

[0002] Concrete, as the primary building material in water conservancy projects such as dams, sluice gates, and power stations, directly affects the quality and operational safety of underwater engineering structures. Using ordinary concrete in underwater construction presents serious drawbacks: firstly, water erosion exacerbates cement paste loss, leading to significant aggregate segregation; secondly, the turbulent environment in areas like the tailrace and spillway of power stations significantly affects the settling of concrete particles, resulting in uneven distribution of cementitious materials and aggregates, and loss of cohesive properties. Practice shows that these problems lead to defects such as segregation and voids in concrete structures, severely impacting their strength, impermeability, and durability.

[0003] In water conservancy and hydropower engineering construction, concrete is often poured using ducts or pumps. Underwater non-dispersible concrete achieves its anti-dispersion and anti-erosion capabilities by adding anti-dispersion agents. Flocculants significantly reduce the fluidity of concrete. In the underwater construction environment, the buoyancy of water makes the concrete even more difficult to flow and affects its self-leveling and self-compacting properties. In engineering practice, existing concrete mix proportions typically add only 2% (by mass of cementitious materials) of anti-dispersion agent to ensure the fluidity of concrete underwater. However, this does not achieve a satisfactory anti-dispersion effect in actual construction. Therefore, research on the formulation and preparation methods of underwater non-dispersible concrete needs to comprehensively consider both anti-dispersion and fluidity requirements. To effectively solve the problems of complex processes, long construction periods, and high costs in the underwater construction of ordinary concrete, this invention proposes an underwater non-dispersible fine aggregate concrete and its preparation method. Summary of the Invention

[0004] To solve the above-mentioned technical problems, this invention proposes an underwater non-dispersible fine aggregate concrete and its preparation method, which enables the concrete to be poured by pouring, open-bottom container, tremie pipe and pumping methods, and can directly contact the ambient water and has the effect of underwater non-dispersibility.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of the present invention:

[0007] An underwater non-dispersible fine aggregate concrete comprises, by weight: 200-220 parts water, 400-488 parts cement, 1020-1120 parts coarse aggregate, 550-650 parts fine aggregate, 3-8 parts high-efficiency water-reducing agent, 0.50-2.00 parts anti-dispersing agent, 0.10-0.20 parts retarder, and 0.50-3.00 parts plant nanocellulose fiber.

[0008] Furthermore, the coarse aggregate is basalt fine stone with a particle size of 5-10 mm, and is continuously graded.

[0009] Basalt fine stones with a particle size of 5-10mm can effectively fill voids to improve the density and impermeability of concrete; at the same time, they increase the contact area between aggregate and cement paste, strengthen the structure of the interface transition zone, and thus improve mechanical strength.

[0010] Furthermore, the fine aggregate is river sand with a fineness modulus of 2.7.

[0011] Furthermore, the high-efficiency water-reducing agent is a polycarboxylate water-reducing agent.

[0012] After adding an early-strength water-reducing agent to cement paste, the hydrophobic groups of the water-reducing agent are adsorbed on the surface of cement particles, which increases the electrostatic repulsion between cement particles and reduces the overall particle size of cement particles. The small cement particles will occupy the water adsorption positions on the original long chain of flocculant, and the distribution will also tend to be uniform. This weakens the adsorption and binding of water by the anti-dispersant (polyacrylate flocculant), increases the content of free water, and thus improves the fluidity of concrete mixture.

[0013] Furthermore, the antidispersant is hydroxypropyl methylcellulose ether flocculant.

[0014] Within the range of anti-dispersant addition, the viscosity of concrete mixtures can be significantly increased, and the surface potential of the particle system can be changed, significantly reducing the repulsive potential energy between particles and increasing the attractive potential energy between particles, thereby causing the more dispersed particles to aggregate together and form stable flocs. Hydroxypropyl methylcellulose ether flocculant, as a high molecular weight long-chain polymer, has active groups that specifically bind with cement particles to form a three-dimensional stable structure. Through the formation of crisscrossing bridges between cement particles by molecular chains, many particles are connected together to form a stable floc structure, enabling the underwater non-dispersible concrete of the present invention to directly contact the ambient water and effectively resist water erosion.

[0015] Furthermore, the retarder is citric acid powder.

[0016] Furthermore, the plant nanocellulose fiber is anionic nanocellulose fiber with a three-dimensional hydrogen bond network structure, a fiber diameter of 5-50 nm and a length of 100 nm to several micrometers, which can improve the cohesiveness and compressive strength of concrete.

[0017] Furthermore, the cement is ordinary Portland cement with a strength grade of 42.5.

[0018] The second technical solution of the present invention:

[0019] A method for preparing the underwater non-dispersible fine aggregate concrete includes the following steps:

[0020] Cement, coarse aggregate, fine aggregate and anti-dispersing agent are mixed, and then high-efficiency water-reducing agent, retarder, plant nanocellulose fiber and water are mixed and added, and then mixed to obtain the underwater non-dispersible fine stone concrete.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] (1) By adjusting the particle size of coarse aggregate, the dosage of anti-dispersant agent and early strength water-reducing agent, this invention significantly improves the anti-dispersibility of concrete mixture, reduces cement loss caused by water flow during pouring, and ensures that the concrete has good fluidity.

[0023] (2) The underwater non-dispersible fine stone concrete of the present invention has the characteristics of improving the anti-dispersion and fluidity of underwater non-dispersible concrete, accurately reaching the pouring position through the conduit and improving early strength. During use, it can be poured by pouring method, open container method, conduit method and pumping method, or directly contacted with the ambient water, and has the effect of underwater non-dispersion. Detailed Implementation

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0028] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0029] This invention provides an underwater non-dispersible fine aggregate concrete, comprising, by weight: 200-220 parts water, 400-488 parts cement, 1020-1120 parts coarse aggregate, 550-650 parts fine aggregate, 3-8 parts high-efficiency water-reducing agent, 0.50-2.00 parts anti-dispersing agent, 0.10-0.20 parts retarder, and 0.50-3.00 parts plant nanocellulose fiber.

[0030] In a preferred embodiment of the present invention, the coarse aggregate is basalt fine stone with a particle size of 5-10 mm, and is continuously graded.

[0031] In a preferred embodiment of the present invention, the fine aggregate is river sand with a fineness modulus of 2.7.

[0032] In a preferred embodiment of the present invention, the high-efficiency water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of 25%.

[0033] In a preferred embodiment of the present invention, the antidispersant is hydroxypropyl methylcellulose ether flocculant.

[0034] In a preferred embodiment of the present invention, the retarder is citric acid powder.

[0035] In a preferred embodiment of the present invention, the plant nanocellulose fiber has a three-dimensional hydrogen bond network structure, with a fiber diameter of 5-50 nm and a length of 100 nm to several micrometers, which can improve the cohesiveness and compressive strength of concrete. The plant nanocellulose fiber used in the embodiments of the present invention is anionic plant nanocellulose fiber produced by Jinan Shengquan Group Co., Ltd.

[0036] In a preferred embodiment of the present invention, the cement is ordinary Portland cement with a strength grade of 42.5.

[0037] This invention significantly improves the anti-dispersion performance of concrete mixtures by adjusting the particle size of coarse aggregates and the dosage of anti-dispersion agents and early-strength water-reducing agents, reducing cement loss caused by water flow during pouring, while ensuring good concrete fluidity. Specifically, the polyacrylate flocculant used dissolves in water to form a polymer network structure, which adsorbs onto the surface of cement particles and aggregates during mixing, forming a viscous gel layer that inhibits the segregation and diffusion of cement paste underwater. The coarse aggregate (5-10mm basalt fine stone) and fine aggregate (river sand with a fineness modulus of 2.7) form a densely graded skeleton, with the anti-dispersion agent filling the gaps in the skeleton, forming an aggregate-flocculator network structure that further prevents cement paste loss.

[0038] Ordinary Portland cement provides the cementitious base, while the anti-dispersant interacts with the cement hydration products through hydrogen bonds, enhancing the cohesiveness of the paste and enabling the concrete to maintain its overall structure when exposed to water underwater, thus preventing cement paste leakage and aggregate settlement.

[0039] Polycarboxylate superplasticizer disperses cement particles through steric hindrance. With a water content of 200-220 parts, it significantly reduces the water-cement ratio (usually ≤0.5), improves the fluidity of the paste, and allows concrete to be transported through pipes, pumps, etc. While maintaining fluidity, the superplasticizer avoids excessively high paste viscosity caused by excessive anti-dispersant, ensuring that the concrete can still flow underwater without disintegrating.

[0040] The combination of coarse aggregate with a particle size of 5-10mm and fine aggregate with a fineness modulus of 2.7 forms a low-porosity skeletal structure, reducing the amount of cement paste required and lowering underwater flow resistance. The preparation process, which involves "dry mixing the anti-dispersant agent with the aggregate and cement first, then adding the aqueous solution containing the water-reducing agent," ensures that the anti-dispersant agent uniformly coats the aggregate, avoiding excessive local flocculation and guaranteeing the homogeneity of the mixture. Citric acid, sodium tripolyphosphate, and sodium hexametaphosphate are compounded in a specific ratio to complex the Ca in the cement. 2+ Adsorbed on the surface of cement particles, it slows down the cement hydration rate and prevents the concrete from setting too early during the pouring process;

[0041] The early hydration rate of ordinary silicate cement, combined with the high compressive strength of basalt coarse aggregate, enables concrete to develop sufficient strength in a short time after pouring, meeting the requirements of rapid load-bearing in underwater engineering.

[0042] Furthermore, all raw materials in this invention are water-soluble and do not react adversely with ions in the ambient water, thus avoiding the impact of water quality on concrete performance and ensuring that the anti-dispersion effect can be maintained in different underwater environments such as fresh water and seawater.

[0043] This invention also proposes a method for preparing underwater non-dispersible fine aggregate concrete, comprising the following steps:

[0044] Cement, coarse aggregate, fine aggregate, and anti-dispersing agent are mixed together. Then, high-efficiency water-reducing agent, retarder, plant nanocellulose fiber, and water are mixed together and added to obtain underwater non-dispersible fine aggregate concrete.

[0045] In the preferred embodiment of the present invention, all raw materials used are commercially available.

[0046] In the embodiments of this invention, unless otherwise specified, "parts" refers to "number of parts by weight".

[0047] The technical solution of the present invention will be further illustrated by the following embodiments.

[0048] Example 1

[0049] A method for preparing underwater non-dispersible fine aggregate concrete includes the following steps:

[0050] (1) Weigh the following raw materials by mass: 488 parts cement, 1050 parts coarse aggregate, 600 parts fine aggregate, 4 parts high-efficiency water-reducing agent, 1.50 parts anti-dispersing agent, 0.1 parts retarder, 3 parts plant nanocellulose fiber, and 220 parts water. Among them, the coarse aggregate is basalt fine stone with a particle size of 5-10 mm and continuous gradation; the fine aggregate is river sand with a fineness modulus of 2.7; the high-efficiency water-reducing agent is polycarboxylate water-reducing agent with a water reduction rate of 25%; the anti-dispersing agent is polyacrylamide hydroxypropyl methylcellulose ether flocculant; the retarder is citric acid powder; and the cement is ordinary Portland cement with a strength grade of 42.5.

[0051] (2) Before mixing with a concrete mixer, the inside of the machine, the mixing steel plate and the iron shovel should be cleaned and kept moist.

[0052] (3) Mix cement, coarse aggregate, fine aggregate and anti-dispersant agent for 3 minutes to obtain mixture A;

[0053] (4) Mix water, water-reducing agent, plant nanocellulose fiber and retarder thoroughly to obtain mixture B;

[0054] (5) Add 1 / 2 of the mixture B to the obtained mixture A and stir for 1 min. Then add the remaining mixture B and stir for 2 min to obtain underwater non-dispersible fine stone concrete.

[0055] Example 2

[0056] A method for preparing underwater non-dispersible fine aggregate concrete includes the following steps:

[0057] (1) Weigh the following raw materials by mass: 488 parts cement, 1050 parts coarse aggregate, 600 parts fine aggregate, 6 parts high-efficiency water-reducing agent, 1.5 parts anti-dispersing agent, 0.1 parts retarder, 1 part plant nanocellulose fiber, and 220 parts water. Among them, the coarse aggregate is basalt fine stone with a particle size of 5-10 mm and continuous gradation; the fine aggregate is river sand with a fineness modulus of 2.7; the high-efficiency water-reducing agent is polycarboxylate water-reducing agent with a water reduction rate of 25%; the anti-dispersing agent is polyacrylamide hydroxypropyl methylcellulose ether flocculant; the retarder is citric acid powder; and the cement is ordinary Portland cement with a strength grade of 42.5.

[0058] (2) Before mixing with a concrete mixer, the inside of the machine, the mixing steel plate and the iron shovel should be cleaned and kept moist.

[0059] (3) Mix cement, coarse aggregate, fine aggregate and anti-dispersant agent for 3 minutes to obtain mixture A;

[0060] (4) Mix water, water-reducing agent, plant nanocellulose fiber and retarder thoroughly to obtain mixture B;

[0061] (5) Add 1 / 2 of the mixture B to the obtained mixture A and stir for 1 min. Then add the remaining mixture B and stir for 2 min to obtain underwater non-dispersible fine stone concrete.

[0062] Example 3

[0063] A method for preparing underwater non-dispersible fine aggregate concrete includes the following steps:

[0064] (1) Weigh the following raw materials by mass: 488 parts cement, 1050 parts coarse aggregate, 600 parts fine aggregate, 8 parts high-efficiency water-reducing agent, 1.5 parts anti-dispersing agent, 0.1 parts retarder, 1.5 parts plant nanocellulose fiber, and 220 parts water. Among them, the coarse aggregate is basalt fine stone with a particle size of 5-10 mm and continuous gradation; the fine aggregate is river sand with a fineness modulus of 2.7; the high-efficiency water-reducing agent is polycarboxylate water-reducing agent with a water reduction rate of 25%; the anti-dispersing agent is polyacrylamide hydroxypropyl methylcellulose ether flocculant; the retarder is citric acid powder; and the cement is ordinary Portland cement with a strength grade of 42.5.

[0065] (2) Before mixing with a concrete mixer, the inside of the machine, the mixing steel plate and the iron shovel should be cleaned and kept moist.

[0066] (3) Mix cement, coarse aggregate, fine aggregate and anti-dispersant agent for 3 minutes to obtain mixture A;

[0067] (4) Mix water, water-reducing agent, plant nanocellulose fiber and retarder thoroughly to obtain mixture B;

[0068] (5) Add 1 / 2 of the mixture B to the obtained mixture A and stir for 1 min. Then add the remaining mixture B and stir for 2 min to obtain underwater non-dispersible fine stone concrete.

[0069] Example 4

[0070] A method for preparing underwater non-dispersible fine aggregate concrete includes the following steps:

[0071] (1) Weigh the following raw materials by mass: 488 parts cement, 1050 parts coarse aggregate, 600 parts fine aggregate, 8 parts high-efficiency water-reducing agent, 1 part anti-dispersing agent, 0.1 parts retarder, 1 part plant nanocellulose fiber, and 220 parts water. Among them, the coarse aggregate is basalt fine stone with a particle size of 5-10 mm and continuous gradation; the fine aggregate is river sand with a fineness modulus of 2.7; the high-efficiency water-reducing agent is polycarboxylate water-reducing agent with a water reduction rate of 25%; the anti-dispersing agent is hydroxypropyl methylcellulose ether flocculant; the retarder is citric acid powder; and the cement is ordinary Portland cement with a strength grade of 42.5.

[0072] (2) Before mixing with a concrete mixer, the inside of the machine, the mixing steel plate and the iron shovel should be cleaned and kept moist.

[0073] (3) Mix cement, coarse aggregate, fine aggregate and anti-dispersant agent for 3 minutes to obtain mixture A;

[0074] (4) Mix water, water-reducing agent, plant nanocellulose fiber and retarder thoroughly to obtain mixture B;

[0075] (5) Add 1 / 2 of the mixture B to the obtained mixture A and stir for 1 min. Then add the remaining mixture B and stir for 2 min to obtain underwater non-dispersible fine stone concrete.

[0076] Comparative Example 1

[0077] Same as Example 1, except that the following raw materials are weighed by mass:

[0078] The ingredients are: 488 parts cement, 990 parts coarse aggregate, 660 parts fine aggregate, 3 parts high-efficiency water-reducing agent, 0.50 parts anti-dispersing agent, 0.1 parts retarder, 3 parts plant nanocellulose fiber, and 220 parts water.

[0079] Comparative Example 2

[0080] Same as Example 1, except that the following raw materials are weighed by mass:

[0081] The ingredients are: 488 parts cement, 900 parts coarse aggregate, 750 parts fine aggregate, 3 parts high-efficiency water-reducing agent, 0.50 parts anti-dispersing agent, 0.1 parts retarder, 3 parts plant nanocellulose fiber, and 220 parts water.

[0082] Comparative Example 3

[0083] Same as Example 1, except that polyacrylamide flocculant is used instead of hydroxypropyl methylcellulose ether flocculant in Example 1.

[0084] Comparative Example 4

[0085] Same as Example 4, except that the addition of plant nanocellulose fibers is omitted.

[0086] Comparative Example 5

[0087] Same as Example 1, except that the addition of high-efficiency water-reducing agent is omitted.

[0088] Comparative Example 6

[0089] Same as Example 1, except that the addition of the retarder is omitted.

[0090] Performance testing

[0091] Referring to DL / T5117-2000 "Test Procedure for Underwater Non-dispersible Concrete", the slump, spread, underwater HP value and compressive strength of the underwater non-dispersible fine aggregate concrete prepared in Examples 1-4 and Comparative Examples 1-6 were tested. The results are shown in Table 1.

[0092] Table 1. Test results of concrete performance in Examples 1-4 and Comparative Examples 1-6

[0093] Slump (mm) Diffusion (mm) HP value 7-day compressive strength (MPa) 28-day compressive strength (MPa) 7-day compressive strength (MPa) of underwater casting Compressive strength (MPa) after 28 days of underwater casting Example 1 205 355 11.34 22.5 30.9 18.9 22.9 Example 2 230 385 11.32 21.4 30.0 19.2 19.4 Example 3 240 465 11.85 21.9 23.7 16.2 20.0 Example 4 185 355 11.13 23.5 29.6 20.5 26.4 Comparative Example 1 80 250 11.89 26.2 30.7 10.7 15.9 Comparative Example 2 50 230 11.87 17.6 21.6 8.7 14.0 Comparative Example 3 150 300 12.11 22.9 26.0 11.7 12.7 Comparative Example 4 235 435 11.89 18.9 26.3 19.1 23.5 Comparative Example 5 collapse collapse 11.24 23.3 24.7 - - Comparative Example 6 230 430 11.65 21.6 28.4 17.2 19.8

[0094] As can be seen from the results in Table 1, the underwater non-dispersible fine aggregate concrete in the embodiments of the present invention possesses both good fluidity and compressive strength. Compared with the embodiments:

[0095] Comparative Example 1: Due to the increase in fine aggregate, the surface area of ​​the aggregate increases, the amount of cement paste required to coat the aggregate is relatively reduced, the total friction increases, resulting in poor fluidity.

[0096] Comparative Example 2: Due to the increase in fine aggregate, the surface area of ​​the aggregate increases, the amount of cement paste required to coat the aggregate is relatively reduced, the total friction increases, resulting in poor fluidity.

[0097] Comparative Example 3: Due to the use of polyacrylamide flocculant instead of antidispersant, its antidispersibility is not as good as that of hydroxypropyl methylcellulose ether flocculant, resulting in poor antidispersibility, poor fluidity, and low compressive strength in underwater casting.

[0098] Comparative Example 4: Due to the omission of plant-based nanocellulose fibers, the lack of nanofillers and fiber reinforcement resulted in poor compressive strength.

[0099] Comparative Example 5: Due to the omission of the addition of high-efficiency water-reducing agent, the cohesion of the concrete increased, resulting in a significant decrease in concrete fluidity, difficulty in self-compacting, and poor compressive strength.

[0100] Comparative Example 6: Due to the omission of the retarder, the setting time was too fast, which is not conducive to construction.

[0101] The reason is as follows:

[0102] Compared to Example 1 (1050 parts coarse aggregate and 600 parts fine aggregate), Comparative Example 1 reduced the coarse aggregate to 990 parts and increased the fine aggregate to 660 parts, while keeping other components such as cement (488 parts) and water (220 parts) unchanged. The coarse aggregate was 5-10mm continuously graded basalt fine stone, which served to form a dense skeleton and fill voids; the fine aggregate was river sand with a fineness modulus of 2.7. The fine aggregate and coarse aggregate worked together to achieve aggregate filling. After increasing the amount of fine aggregate in Comparative Example 1, the total specific surface area of ​​the aggregate increased significantly (the specific surface area of ​​fine aggregate was much higher than that of coarse aggregate), while the fixed amount of cement paste (488 parts cement + 220 parts water) could not fully coat the surface of the new fine aggregate. In concrete mixtures, aggregates rely on cement paste for lubrication to reduce friction. Excessive fine aggregate leads to the adsorption of a large amount of cement paste on its surface, increasing inter-aggregate friction and weakening lubrication. This manifests as a decrease in slump from 205mm to 80mm and a decrease in spread from 355mm to 250mm, resulting in significantly deteriorated fluidity. During underwater pouring, insufficiently coated fine aggregate easily separates from the cement paste: under the scouring of water, loose fine aggregate detaches from the paste, leading to paste loss and exposed aggregate. After hardening, numerous pores appear inside, causing the underwater 7-day compressive strength to decrease from 18.9MPa to 10.7MPa and the 28-day strength from 22.9MPa to 15.9MPa.

[0103] Compared to Example 1, Comparative Example 2 reduced coarse aggregate to 900 parts and increased fine aggregate to 750 parts, with the increase in fine aggregate being greater than that in Comparative Example 1. The further increase in the proportion of fine aggregate resulted in the total specific surface area of ​​the aggregates far exceeding the coating capacity of the cement paste. At this point, the cement paste was insufficient to cover the aggregate surface and fill the gaps between the aggregates. The mixture lacked free water, there was no effective lubrication between the aggregates, the slump dropped to 50 mm, the spread dropped to 230 mm, and the fluidity was almost lost. Severe gradation imbalance damaged the density of the aggregate skeleton: insufficient coarse aggregate weakened the supporting effect, while excessive fine aggregate prevented the cement paste from fully filling the gaps, leading to an increased void ratio (the porosity of fine aggregate was higher than that of continuously graded coarse aggregate), resulting in interconnected pores within the hardened concrete. Meanwhile, during underwater casting, the pores become channels for water infiltration, accelerating the loss of cement slurry. Ultimately, the underwater 7-day compressive strength was only 8.7 MPa (18.9 MPa in Example 1), and the underwater 28-day strength was only 14.0 MPa (22.9 MPa in Example 1), with strength loss far exceeding that of Comparative Example 1.

[0104] In Comparative Example 3, polyacrylamide flocculant was used to replace the hydroxypropyl methylcellulose ether flocculant in Example 1, while other components remained unchanged. Due to the poor dispersion of polyacrylamide, loose flocs formed, unable to construct a stable three-dimensional network, easily disintegrated upon contact with water flow underwater, leading to cement paste loss and a significant decrease in anti-dispersion properties. Simultaneously, the high internal porosity of the flocs resulted in uneven viscosity of the mixture, with localized pore defects. The slump decreased from 205 mm to 150 mm, and the spread decreased from 355 mm to 300 mm. The main reasons for the underwater strength degradation were: water erosion during pouring, uneven aggregate distribution in the concrete, and lack of effective bonding between aggregates. The underwater compressive strength was only 11.7 MPa at 7 days (18.9 MPa in Example 1) and only 12.7 MPa at 28 days (22.9 MPa in Example 1). The failure of anti-dispersion directly led to strength collapse.

[0105] Compared to Example 4, Comparative Example 4 omitted 3 parts of plant nanocellulose fibers, while other components remained unchanged. The plant nanocellulose fibers are anionic, 5-50 nm in diameter, and contain a three-dimensional hydrogen-bonded network structure. Their core function is to fill the micropores in cement paste, enhance its cohesiveness, and inhibit crack propagation through the bridging effect of the nanocellulose fibers, thereby improving compressive strength. Without these fibers, the cement paste lacks nanoscale filling: the micropores (diameter <100 nm) inside the concrete lack nanocellulose fiber filling, resulting in decreased density and a 7-day compressive strength of 18.9 MPa and a 28-day strength of 26.3 MPa. The decreased cohesiveness indirectly affects underwater performance: although the slump (235 mm) and spread (435 mm) slightly increase due to the lack of fiber constraint, the decreased cohesiveness makes the paste easily dispersed during underwater pouring. Without the bridging effect of nanocellulose fibers, cracks easily propagate, and the 28-day underwater compressive strength drops to 23.5 MPa (seemingly close, but in reality, internal defects increase, leading to poor strength stability).

[0106] Compared to Example 1, Comparative Example 5 omitted 4 parts of polycarboxylate superplasticizer, while other components remained unchanged. After this omission, the cement particles agglomerated severely. Without the superplasticizer, the cement particles formed large flocs due to van der Waals forces, trapping free water inside these flocs. This resulted in very little free water available for lubrication in the mixture, leading to hardening and a "collapsed" state in both slump and spread, completely failing to meet the requirements for pouring (using the tremie method and pump method). Due to the loss of fluidity, the concrete could not densely fill the formwork during underwater pouring, leaving numerous voids. Underwater strength could not be tested, and even after onshore hardening, the 7-day and 28-day compressive strengths were low due to poor density, only 23.3 MPa and 24.7 MPa (lower than the 22.5 MPa and 30.9 MPa of Example 1, and with poor data stability).

[0107] Compared with Example 1, Comparative Example 6 omitted 0.1 parts of citric acid powder (retarder), while other components remained unchanged. Omitting the citric acid powder resulted in excessively rapid cement hydration. Ordinary Portland cement (grade 42.5) exhibited rapid early-stage hydration heat release. Without a retarder, the mixture began to set before pouring. Although the slump (230 mm) and spread (430 mm) were initially normal, the concrete gradually lost its fluidity during pouring, failing to fully fill the formwork or conduit, leading to internal defects such as honeycomb and pitting. After hardening, these internal defects became stress concentration points, causing the 7-day compressive strength to decrease from 22.5 MPa to 21.6 MPa and the 28-day strength from 30.9 MPa to 28.4 MPa. The underwater 7-day strength decreased from 18.9 MPa to 17.2 MPa and the 28-day strength from 22.9 MPa to 19.8 MPa.

[0108] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An underwater non-dispersible fine aggregate concrete, characterized in that, By weight, it includes: 200-220 parts water, 400-488 parts cement, 1020-1120 parts coarse aggregate, 550-650 parts fine aggregate, 3-8 parts high-efficiency water-reducing agent, 0.50-2.00 parts anti-dispersing agent, 0.10-0.20 parts retarder, and 0.50-3.00 parts plant nanocellulose fiber.

2. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The coarse aggregate is basalt fine stone with a particle size of 5-10 mm.

3. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The fine aggregate is river sand with a fineness modulus of 2.

7.

4. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The high-efficiency water-reducing agent is a polycarboxylate water-reducing agent.

5. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The antidispersant is hydroxypropyl methylcellulose ether flocculant.

6. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The retarder is citric acid powder.

7. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The plant nanocellulose fibers have a diameter of 5-50 nm.

8. The underwater non-dispersible fine aggregate concrete according to claim 1, characterized in that, The cement is ordinary Portland cement.

9. A method for preparing underwater non-dispersible fine aggregate concrete as described in any one of claims 1-8, characterized in that, Includes the following steps: Cement, coarse aggregate, fine aggregate and anti-dispersing agent are mixed, and then high-efficiency water-reducing agent, retarder, plant nanocellulose fiber and water are mixed and added, and then mixed to obtain the underwater non-dispersible fine stone concrete.