An underwater self-compacting low-carbon concrete and a preparation method thereof

Abstract

This invention discloses an underwater self-compacting low-carbon concrete and its preparation method. The concrete is composed of the following components by weight: 100 parts low-carbon cementitious material, 180-250 parts coarse aggregate, 150-200 parts fine aggregate, 30-80 parts modified mineralized aggregate, 0.5-3.0 parts flocculant, 0.3-1.2 parts polycarboxylate superplasticizer, 0.05-0.30 parts retarder, and 30-50 parts water. This invention, through the design of the low-carbon cementitious material system, the introduction of carbon dioxide mineralized aggregate, and the synergistic effect of the special flocculant, ensures the excellent fluidity, anti-dispersion properties, and mechanical properties of the underwater self-compacting concrete. At the same time, it reduces the carbon emissions per unit volume by 30%-50% compared to ordinary underwater concrete of the same strength grade with ordinary Portland cement as the sole cementing component, thus achieving low-carbonization of underwater concrete materials. The preparation method is simple and suitable for underwater concrete structure engineering such as underwater pile foundations, underwater abutments, and underwater piers.

Description

Technical Field

[0001] This invention relates to the field of concrete materials technology, specifically to an underwater self-compacting low-carbon concrete and its preparation method. Background Technology

[0002] Self-compacting concrete refers to concrete that can flow and compact under its own weight, completely filling the formwork even with dense reinforcing steel, while achieving good homogeneity and requiring no additional vibration. Underwater self-compacting concrete, based on self-compacting concrete, further requires it to have good anti-dispersion properties during underwater pouring, resisting the erosion of water without separation of cement paste and aggregate.

[0003] With the development of marine engineering, water conservancy engineering, and bridge engineering, the demand for underwater concrete structure construction is increasing. Traditional underwater concrete construction usually requires complex processes such as cofferdam drainage or tremie casting, resulting in long construction cycles and high costs. The emergence of underwater self-compacting concrete provides an effective solution to these problems.

[0004] An underwater self-compacting concrete, with announcement number CN111960740B, comprises 720-750 parts coarse aggregate, 450-500 parts fine aggregate, 500-540 parts cement, 200-240 parts water, 140-155 parts porous microspheres, 13-15 parts film-forming agent, and 35-55 parts thickener. An underwater pile foundation non-dispersible manufactured sand self-compacting concrete, with publication number CN111732390A, comprises cement, nano-sized spherical silica powder, micron-sized spherical silica powder, highly active siliceous calcium powder, and a high-polysaccharide composite flocculant, etc.

[0005] The existing technologies mentioned above still have the following shortcomings: 1. The cement usage is high, resulting in a large amount of carbon emissions from concrete, which does not meet the requirements of green and low-carbon development; 2. There is a lack of systematic consideration of carbon emissions throughout the entire life cycle of concrete, and carbon emissions are not reduced in a coordinated manner from both the cementitious material system and the aggregate system; 3. The thickening or anti-dispersion components of existing underwater self-compacting concrete are mostly single-function admixtures, which are difficult to simultaneously meet the multiple requirements of fluidity, anti-dispersion and low carbon emissions. Summary of the Invention

[0006] The purpose of this invention is to provide an underwater self-compacting low-carbon concrete and its preparation method, to solve the technical problems of high carbon emissions and difficulty in simultaneously achieving low carbon content and underwater construction performance in existing underwater self-compacting concrete. This invention significantly reduces carbon emissions while ensuring excellent underwater construction performance through the design of a low-carbon cementitious material system, the application of carbon dioxide mineralized aggregates, and the synergistic effect of a special flocculant enhancer.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] An underwater self-compacting low-carbon concrete is composed of the following components in parts by weight:

[0009] 100 parts low-carbon cementitious material; 180-250 parts coarse aggregate; 150-200 parts fine aggregate; 30-80 parts modified mineralized aggregate; 0.5-3.0 parts flocculant enhancer; 0.3-1.2 parts polycarboxylate superplasticizer; 0.05-0.30 parts retarder; 30-50 parts water.

[0010] Low-carbon cementitious materials contain the following components by weight percentage: 40%–65% silicate cement, 15%–30% granulated blast furnace slag powder, 10%–25% fly ash, and 5%–15% limestone powder.

[0011] Modified mineralized aggregates are recycled aggregates or porous aggregates that have undergone carbon dioxide mineralization treatment. Their carbon dioxide absorption is 3% to 12% of the aggregate mass, and their apparent porosity is reduced by 5% to 20% compared with that before mineralization treatment.

[0012] The aforementioned concrete uses low-carbon cementitious materials to replace a large amount of ordinary Portland cement. Granulated blast furnace slag powder and fly ash react with calcium hydroxide released from the cement during hydration, generating additional hydrated calcium silicate gel that fills the pores within the paste, making the hardened structure more compact and improving later-stage strength without increasing the amount of cementitious materials. Limestone powder, as micro-aggregate, fills the gaps between cementitious material particles, improving the paste particle packing density and increasing paste fluidity. During carbonation, modified mineralized aggregates react with calcium and magnesium components in the aggregates to form carbonate minerals. These reaction products deposit in the microcracks and open pores on the aggregate surface, sealing water penetration channels and reducing aggregate water absorption. Simultaneously, the roughened aggregate surface increases the mechanical bonding force and chemical bonding area with the cement paste, strengthening the weak points in the transition zone between the aggregate and the paste. Under the combined effect of the above factors, this concrete maintains the necessary spread and flow rate for self-compacting while resisting the erosion and dispersion caused by water flow during underwater pouring. It can be poured directly into water without segregation of cement paste and aggregate. The difference in strength between the hardened concrete and that cured in terrestrial environments is controlled within an acceptable range. Furthermore, the carbon emissions per unit volume of this concrete are significantly lower than those of conventional underwater concrete, mitigating the impact on the atmospheric environment while meeting the structural requirements of underwater structures.

[0013] The flocculant enhancer comprises the following components by mass percentage: 30%–60% polyacrylamide flocculant, 20%–40% cellulose ether, 5%–15% nano-silica, and 5%–20% redispersible latex powder, with the sum of the mass percentages of each component being 100%. Polyacrylamide flocculant has a long molecular chain structure. When the concrete is immersed in water, these long-chain molecules rapidly extend in the water, and the active groups on their chain segments simultaneously adsorb multiple cement particles or fine aggregate particles, bridging these dispersed solid particles into a spatial network of flocs. This effectively resists the scouring and dilution effects of water flow, making the slurry less prone to dissipation. Cellulose ether, after dissolving in water, increases the viscosity of the slurry liquid phase, reducing the settling velocity of cement particles in water. Simultaneously, its hydrophilic groups in its molecular structure combine with a large number of water molecules, binding free water within the slurry and reducing the outward migration of water under hydrostatic pressure. Nano-silica particles… With its extremely small size and huge specific surface area, the unsaturated silica bonds on its surface exhibit high reactivity in the hydration environment, rapidly reacting with the calcium hydroxide produced during cement hydration to form a dense calcium silicate gel. Simultaneously, its tiny particles fill the nanoscale voids between cement hydration products, reducing the porosity of the hardened paste. During cement hydration, the redispersible latex powder's polymer particles gradually fuse to form a continuous polymer film. This film coats the aggregate surface and the interior of the cement paste, bridging the gap between aggregates and the paste, as well as between various hydration products within the paste, forming an organic-inorganic interpenetrating network structure that enhances the interfacial bonding of the components. These four components work synergistically within their respective defined proportions: the flocculant provides the main underwater anti-dispersion framework, the cellulose ether regulates the paste viscosity to ensure its stability, the nano-silica compensates for the potentially low early strength caused by the large-scale replacement of cement by auxiliary cementitious materials, and the latex powder improves the interfacial adhesion and crack resistance of the underwater-formed specimens. Together, they ensure that the concrete possesses reliable underwater anti-dispersion performance and sufficient mechanical strength while meeting self-compacting fluidity requirements.

[0014] The preparation method of modified mineralized aggregate includes the following steps: placing recycled aggregate or porous aggregate in a closed carbonization container and carbonizing it for 24 to 72 hours under the conditions of carbon dioxide volume concentration of 20% to 99%, relative humidity of 40% to 90%, and temperature of 20 to 60°C, to obtain modified mineralized aggregate with carbon dioxide absorption of 3% to 12% of aggregate mass and apparent porosity reduced by 5% to 20% compared with that before mineralization treatment.

[0015] Under these carbon dioxide concentration conditions, the carbonization atmosphere provides sufficient carbon dioxide molecules for the water film inside the aggregate pores to absorb and dissolve, maintaining a high concentration of dissolved carbon dioxide and ensuring a sufficient supply of reactants for the carbonization reaction. With relative humidity between 40% and 90%, the water film inside the aggregate pores will not evaporate and dry out due to excessively low humidity, thus preventing a lack of necessary ion transport medium for the carbonization reaction, nor will excessively high humidity block the pore channels and hinder the inward diffusion of carbon dioxide gas. With the temperature controlled between 20 and 60 degrees Celsius, the carbonization reaction rate increases with increasing temperature, but this upper temperature limit avoids excessively high temperatures that could cause decomposition of carbonate minerals, ensuring the carbonization reaction is in a favorable state both kinetically and thermodynamically. A carbonization treatment time of 24 to 72 hours ensures the carbonization reaction proceeds fully, allowing the calcium and magnesium components deep within the aggregate pore walls to fully contact and react with carbon dioxide, resulting in a more uniform overall carbonization degree for the aggregate. Under the above conditions, the amount of carbon dioxide fixed in the aggregate reaches 3% to 12% of its own mass, while the apparent porosity of the aggregate decreases by 5% to 20%. These two indicators are related and jointly reflect the effect of carbonization treatment, ensuring both sufficient carbon sequestration and significant improvement in aggregate performance.

[0016] As a preferred embodiment of the present invention, the coarse aggregate is continuously graded crushed stone or gravel with a particle size of 5 to 25 mm, a crushing index of no more than 12%, and a needle-like or flaky particle content of no more than 8%; the fine aggregate is natural sand or manufactured sand with a fineness modulus of 2.3 to 3.0 and a mud content of no more than 3%.

[0017] The coarse aggregate adopts a continuous gradation of 5 to 25 mm, so that the aggregate particles are filled from large to small in a stepwise manner. The porosity between particles is low, and under the condition of a certain amount of paste, a relatively dense skeleton structure can be obtained, which improves the volume stability of concrete. The crushing index is controlled below 12% to ensure that the aggregate itself has sufficient crushing resistance and will not fail first under high stress, thus ensuring the full utilization of the load-bearing capacity of concrete. The content of needle-shaped and flaky particles is not greater than 8%, which avoids the problem of these particles hindering the flow of paste and increasing the frictional resistance between particles in the mixture, making the concrete easier to spread and compact under its own weight. Fine aggregate with a fineness modulus of 2.3 to 3.0 falls within the range of medium sand. Within this range, the sand particle size distribution is moderate. It is neither too fine, requiring excessive slurry to cover its large specific surface area, nor too coarse, leading to separation of the slurry and aggregate and increased porosity in the hardened body. The mud content is no more than 3%, which avoids the excessive adsorption of polycarboxylate superplasticizer and mixing water by clay substances, ensuring that the dispersion effect of the superplasticizer is fully utilized. At the same time, it also reduces the interference of clay impurities on the cement hydration process and the weakening of interfacial bond strength.

[0018] As a preferred embodiment of the present invention, the polycarboxylate superplasticizer is a high-performance polycarboxylate superplasticizer with a solid content of 20% to 40% and a water reduction rate of not less than 30%; the retarder is at least one of sodium gluconate, citric acid or tartaric acid.

[0019] The polyoxyethylene side chains in the polycarboxylate superplasticizer molecular structure create a steric hindrance effect on the surface of cement particles, effectively preventing particle agglomeration. This allows the cement particles to disperse sufficiently even with lower water content, releasing free water trapped within the cement flocculation structure. This reduces actual water consumption while maintaining fluidity, decreases the number of capillaries in the hardened body, and improves the density and strength of the concrete. A solid content controlled between 20% and 40% ensures a moderate concentration of the effective components of the superplasticizer, facilitating metering and uniform dispersion. A water reduction rate of no less than 30% ensures the fluidity required for self-compacting concrete is achieved even under low water-cement ratio conditions. The addition of a retarder delays the onset of cement hydration induction, allowing the cement paste to remain in a plastic state for a longer period. This is particularly important for underwater construction, as underwater pouring often requires a considerable amount of time for transportation, material placement, and pouring. Retarding prevents premature setting of the concrete during construction, which would result in loss of fluidity and pumpability, ensuring uniform pouring quality.

[0020] As a preferred embodiment of the present invention, the slump expansion of the underwater self-compacting low-carbon concrete is 550-750mm, the T500 flow time is 3-15 seconds, the suspended solids content during underwater pouring is not greater than 150mg / L, and the water-to-land strength ratio is not less than 75% after 28 days.

[0021] A slump spread exceeding 550 mm indicates that the concrete mixture can spread freely under its own weight without vibration, sufficient to fill all corners of the formwork and penetrate dense steel reinforcement gaps. A spread not exceeding 750 mm avoids the risk of aggregate settling and segregation due to excessively thin slurry. A T500 flow time between 3 and 15 seconds reflects that the concrete has a sufficient flow rate to ensure construction efficiency without causing material separation due to excessive flow, and also indirectly indicates that its viscosity is suitable for underwater construction. Suspended solids content controlled below 150 mg / L during underwater pouring indicates that the cement paste and fine particles are effectively bound in the flocculated structure and rarely diffuse into the surrounding water as the concrete falls through the water layer and into the underwater pouring surface. This indicator directly reflects the excellent anti-dispersion performance of the concrete underwater, ensuring the component uniformity of the concrete after underwater molding and reducing pollution to the construction water area. The 28-day water-to-land strength ratio reached over 75%, indicating that the compressive strength of the underwater-cast specimen and the normally formed specimen on land was similar after the same curing age. This means that the underwater casting environment did not have a significant adverse effect on the strength development of the concrete, and the concrete could achieve the designed load-bearing capacity after underwater hardening.

[0022] As a preferred embodiment of the present invention, the carbon emission factor of the low-carbon cementitious material is no greater than 560 kg. The carbon emissions per unit volume of underwater self-compacting low-carbon concrete are 30% to 50% lower than those of ordinary underwater concrete of the same strength grade that uses ordinary Portland cement as the only cementing component.

[0023] In this low-carbon cementitious material, the proportion of silicate cement is controlled below 65%, while auxiliary components such as granulated blast furnace slag powder, fly ash, and limestone powder account for more than 35% in total. These auxiliary components only require grinding energy during production and do not involve the high-temperature decomposition of carbonate raw materials. Their carbon emissions per unit mass are far lower than those of silicate cement clinker. Therefore, the overall carbon emission factor of the cementitious material is significantly reduced, falling below 560 kg CO2 equivalent per ton. In a unit volume of concrete, the amount of cementitious material and the water-cement ratio are kept within a reasonable range, ensuring that the total mass of cementitious material per cubic meter of concrete is not excessive. Combined with the low-emission characteristics of the low-carbon cementitious material, the total carbon emissions per cubic meter of concrete are reduced by 30% to 50% compared to concrete of the same strength grade using pure ordinary silicate cement as the cementitious material. This technological effect allows underwater concrete structure engineering to achieve carbon emission reduction from the material selection stage while meeting the requirements of load-bearing capacity and construction performance, eliminating the need for additional carbon offsetting measures after construction.

[0024] This invention also provides a method for preparing the above-mentioned underwater self-compacting low-carbon concrete, comprising the following steps:

[0025] Step 1: Preparation of low-carbon cementitious material: Mix silicate cement, granulated blast furnace slag powder, fly ash and limestone powder evenly according to the formula to obtain low-carbon cementitious material.

[0026] This step involves pre-mixing silicate cement with granulated blast furnace slag powder, fly ash, and limestone powder. This ensures that the auxiliary cementitious materials are evenly distributed in the cement, avoiding local enrichment or deficiency that may occur during on-site mixing. As a result, the hydration reaction rate and product composition of each portion of cementitious paste tend to be consistent, which is beneficial to the uniformity and stability of the hardened concrete performance.

[0027] Step 2: Preparation of modified mineralized aggregate: Place the recycled aggregate or porous aggregate in a sealed carbonization container and carbonize it for 24 to 72 hours under the conditions of carbon dioxide volume concentration of 20% to 99%, relative humidity of 40% to 90%, and temperature of 20 to 60°C to obtain modified mineralized aggregate with carbon dioxide absorption of 3% to 12% of the aggregate mass and apparent porosity reduced by 5% to 20% compared with that before mineralization treatment.

[0028] This step provides a controlled carbonization reaction environment for the aggregate within a sealed carbonization container. The combined control of carbon dioxide concentration, relative humidity, temperature, and time allows the carbonization reaction to proceed under favorable kinetic conditions. Carbon dioxide gas fully dissolves within the aggregate pores and reacts with calcium and magnesium ions to generate stable carbonate minerals. These reaction products grow and fill in situ within the aggregate pores, simultaneously improving the density and mechanical properties of the aggregate, while also achieving permanent solidification and sequestration of carbon dioxide.

[0029] Step 3: Aggregate pre-wetting treatment: After mixing coarse aggregate, fine aggregate and modified mineralized aggregate according to the proportion, add some water for pre-wetting treatment. The pre-wetting time is 10 to 30 minutes to make the aggregate reach a saturated surface-dry state.

[0030] This step allows the porous modified mineralized aggregate to absorb some moisture in advance, reaching a saturated surface-dry state. This prevents the aggregate from absorbing large amounts of free water and water-reducing agents from the slurry during subsequent concrete mixing, thus preventing the slurry's fluidity from decreasing during mixing and pouring. This ensures the stability and repeatability of the concrete mixture's performance. At the same time, the mixing of coarse and fine aggregates during the pre-wetting process allows aggregate particles of different sizes to initially form a relatively compact packing structure in a wet state, which is beneficial for the subsequent slurry to fully fill the voids in the aggregate.

[0031] Step 4: Slurry preparation: Add low-carbon cementitious material, flocculant enhancer, polycarboxylate superplasticizer, retarder and residual water into a mixer and stir for 60-120 seconds to obtain a uniform cementitious slurry.

[0032] This step employs a process route that first prepares a cementitious slurry, allowing the cementitious materials and admixtures to be fully dispersed and dissolved in water to form a uniform slurry medium. The components of the flocculant are pre-distributed evenly in the slurry, avoiding agglomeration and uneven local concentration that may occur when directly adding materials. This ensures that the flocculant can exert its maximum effectiveness in the subsequent concrete mixture. At the same time, the polycarboxylate superplasticizer and retarder are in full contact with the cement particles in the slurry stage, and their dispersion and retarding effects are fully utilized.

[0033] Step 5: Concrete mixing: Add the pre-wetted aggregate mixture to the cementitious paste and continue mixing for 120-240 seconds until all components are evenly mixed to obtain underwater self-compacting low-carbon concrete.

[0034] This step involves adding pre-wetted aggregate to the prepared cementitious paste and mixing it. The aggregate is immediately coated by the paste upon addition, reducing direct collisions and friction between aggregate particles and improving the uniformity of the concrete. Continued mixing ensures that the paste fully fills the voids between aggregate particles and forms a uniform paste coating on the aggregate surface, resulting in a final concrete mixture with excellent workability and uniform component distribution. The entire method is simple in its process steps, with reasonable transitions between steps, and is suitable for conventional production equipment in on-site mixing plants and precast component factories.

[0035] In step three of the above preparation process, the amount of pre-wetting water used is 30% to 60% of the total water volume; in step four, the stirring speed of the mixer is 20 to 45 revolutions per minute.

[0036] Pre-wetting water accounts for 30% to 60% of the total mixing water. This proportion is sufficient to allow the porous modified mineralized aggregates to fully absorb water and reach a saturated surface-dry state, while avoiding excessive pre-wetting water that would cause excessive free water to adhere to the aggregate surface, thus increasing the actual water-cement ratio in subsequent mixing and ensuring the accuracy of the mix proportions. The water adsorbed by the aggregates during pre-wetting is gradually released during concrete hardening, providing a continuous internal curing water source for the surrounding cement particles, promoting the hydration reaction of cement in the interface zone around the aggregates, and improving the microstructure of the interface transition zone. The mixing speed is controlled within a low range of 20 to 45 rpm. This ensures that the components in the cementitious paste achieve macroscopic homogeneity in a short time, while avoiding the introduction of excessive air bubbles and mechanical breakage of long molecular chains in flocculant reinforcing agents caused by high-speed mixing. Low-speed mixing also reduces equipment wear and energy consumption, making it particularly suitable for the continuous production of large-volume underwater concrete.

[0037] In step two above, the carbonization process is carried out under a pressure of 0.1 to 0.5 MPa; the carbon dioxide is derived from carbon dioxide captured and purified from industrial waste gas or carbon dioxide produced as a byproduct of industry.

[0038] Applying pressure higher than atmospheric pressure within a sealed carbonization container increases the amount of carbon dioxide dissolved in the water film within the aggregate pores, thus raising the concentration of dissolved carbon dioxide and accelerating its reaction rate with calcium and magnesium ions in the aggregate. This results in a higher degree of carbonization conversion within the same processing time. Simultaneously, the pressure forces carbon dioxide into the deeper pores of the aggregate, ensuring that the pore walls within the aggregate can fully contact the carbon dioxide and undergo a carbonization reaction, rather than being limited to the surface. This guarantees the uniformity of performance improvement throughout the aggregate. A pressure range of 0.1 to 0.5 MPa falls within the low- to medium-pressure range. This pressure condition does not place high demands on equipment sealing and strength; conventional industrial carbonization equipment suffices, eliminating the need for high-pressure specialized equipment and balancing treatment effectiveness with the feasibility of industrial implementation. Using carbon dioxide captured and purified from industrial waste gas or industrial by-product carbon dioxide as the carbonization gas source effectively utilizes and permanently seals carbon dioxide that would otherwise be emitted into the atmosphere within the aggregate, achieving the dual environmental benefits of waste resource utilization and carbon emission reduction.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. This invention utilizes a low-carbon cementitious material system, replacing a portion of silicate cement with granulated blast furnace slag powder, fly ash, and limestone powder, significantly reducing the carbon emission factor of the cementitious material (controllable to 560 kg). The following (referring to the process of achieving low carbon emissions from the source of materials)

[0041] 2. This invention uses recycled aggregates or porous aggregates modified by carbon dioxide mineralization, which not only realizes the resource utilization of industrial solid waste and the permanent sequestration of carbon dioxide, but also reduces the apparent porosity of the aggregates by 5% to 20% through mineralization reaction, thereby improving the interfacial properties and volume stability of the aggregates and enhancing the mechanical properties of concrete.

[0042] 3. This invention achieves a balance between high fluidity, high anti-dispersion properties, and good mechanical properties in concrete through the multi-component synergistic design of the flocculant (the sum of the mass percentages of polyacrylamide flocculant, cellulose ether, nano silica, and redispersible latex powder is 100%), thus meeting the stringent requirements of underwater self-compacting construction.

[0043] 4. This invention systematically reduces the carbon emissions of concrete from three levels: cementitious materials, aggregates, and admixtures. The carbon emissions per unit volume are reduced by 30% to 50% compared to ordinary underwater concrete of the same strength grade that uses ordinary Portland cement as the sole cementing component, demonstrating significant environmental benefits.

[0044] 5. The preparation method of this invention is simple and easy to operate, suitable for large-scale industrial production, and has good economic benefits and promotional value. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only examples of embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart of an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0048] See Figure 1 In the following embodiments, the slump expansion and T500 flow time were tested according to GB / T 50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; the suspended solids content during underwater pouring was tested according to DL / T 5117 "Test Procedure for Underwater Non-Dispersible Concrete"; the compressive strength was tested according to GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete"; and the water-land strength ratio was the ratio of the 28-day compressive strength of the underwater-formed standard specimen to the 28-day compressive strength of the land-formed standard specimen.

[0049] Example 1:

[0050] The underwater self-compacting low-carbon concrete of this embodiment is composed of the following components in parts by weight:

[0051] 100 parts of low-carbon cementitious materials (including 50 parts of silicate cement, 22 parts of granulated blast furnace slag powder, 18 parts of fly ash, and 10 parts of limestone powder).

[0052] 220 parts of coarse aggregate (5-25mm continuously graded crushed stone);

[0053] 180 parts of fine aggregate (natural river sand with a fineness modulus of 2.6);

[0054] 50 parts of modified mineralized aggregate (carbon dioxide mineralization treated recycled coarse aggregate);

[0055] 1.5 parts of flocculant enhancer (of which 45% polyacrylamide, 30% cellulose ether, 10% nano silica, and 15% redispersible latex powder, the sum of the mass percentages of each component is 100%).

[0056] 0.8 parts of polycarboxylate superplasticizer (30% solid content, 35% water reduction rate);

[0057] 0.15 parts of retarder (sodium gluconate);

[0058] 42 parts water.

[0059] The preparation method in this embodiment is as follows:

[0060] Step 1: Preparation of low-carbon cementitious material: According to the formula, mix silicate cement, granulated blast furnace slag powder, fly ash and limestone powder in a powder mixer for 15 minutes to obtain low-carbon cementitious material.

[0061] Step 2: Preparation of modified mineralized aggregate: The recycled coarse aggregate is placed in a sealed carbonization container, and a mixed gas with a carbon dioxide volume concentration of 60% is introduced. The relative humidity is controlled at 70% and the temperature at 40℃. The carbonization is carried out at a pressure of 0.2MPa for 48 hours to obtain modified mineralized aggregate with a carbon dioxide absorption of 7.5% of the aggregate mass and an apparent porosity that is 12% lower than that before the mineralization treatment.

[0062] Step 3: Aggregate pre-wetting treatment: After mixing coarse aggregate, fine aggregate and modified mineralized aggregate according to the proportion, add water equal to 45% of the total water volume for pre-wetting treatment. The pre-wetting time is 20 minutes to make the aggregate reach a saturated surface-dry state.

[0063] Step 4: Slurry preparation: Add low-carbon cementitious material, flocculant enhancer, polycarboxylate superplasticizer, retarder and residual water into a mixer and stir for 90 seconds at a stirring speed of 30 rpm to obtain a uniform cementitious slurry.

[0064] Step 5: Concrete mixing: Add the pre-wetted aggregate mixture to the cementitious paste and continue mixing for 180 seconds until all components are evenly mixed to obtain underwater self-compacting low-carbon concrete.

[0065] The performance test results of the underwater self-compacting low-carbon concrete prepared in this embodiment are as follows: slump spread is 680 mm, T500 flow time is 7 seconds, suspended solids content during underwater pouring is 85 mg / L, and the 28-day water-to-land strength ratio is 82%. The carbon emission factor of the low-carbon cementitious material in this embodiment is calculated to be 522 kg. (Among them, the carbon emission factor of silicate cement is 850kg) Calculated as 150 kg CO2 / t for granulated blast furnace slag powder and 100 kg CO2 / t for fly ash. Calculation, limestone powder per 100kg According to calculations, the carbon emissions per unit volume are reduced by 42% compared to ordinary underwater concrete of the same strength grade that uses ordinary Portland cement as the sole cementing component.

[0066] Example 2:

[0067] The underwater self-compacting low-carbon concrete of this embodiment is composed of the following components in parts by weight:

[0068] 100 parts of low-carbon cementitious materials (including 45 parts of silicate cement, 28 parts of granulated blast furnace slag powder, 20 parts of fly ash, and 7 parts of limestone powder).

[0069] 200 parts of coarse aggregate (5-20mm continuously graded crushed stone);

[0070] 165 parts of fine aggregate (manufactured sand with a fineness modulus of 2.8);

[0071] 65 parts of modified mineralized aggregate (carbon dioxide mineralized ceramsite);

[0072] 2.0 parts of flocculant enhancer (of which 50% is polyacrylamide, 25% is cellulose ether, 12% is nano silica, and 13% is redispersible latex powder, with the sum of the mass percentages of each component being 100%).

[0073] 1.0 part of polycarboxylate superplasticizer (25% solid content, 32% water reduction rate);

[0074] 0.20 parts of retarder (citric acid);

[0075] 38 portions of water.

[0076] The preparation method of this embodiment is basically the same as that of Example 1, except that: in step two, the carbonization conditions are 80% carbon dioxide volume concentration, 60% relative humidity, 50℃ temperature, 0.3MPa pressure, and 36 hours, resulting in modified mineralized aggregate with a carbon dioxide absorption of 9.0% of the aggregate mass and an apparent porosity reduced by 16% compared to before the mineralization treatment; in step three, the pre-wetting water amount is 50% of the total water amount; in step four, the stirring speed is 25 rpm and the stirring time is 100 seconds; in step five, the stirring time is 200 seconds.

[0077] The performance test results of the underwater self-compacting low-carbon concrete prepared in this embodiment are as follows: slump spread is 650 mm, T500 flow time is 9 seconds, suspended solids content during underwater pouring is 72 mg / L, and the 28-day water-to-land strength ratio is 85%. The carbon emission factor of the low-carbon cementitious material in this embodiment is calculated to be 485 kg. The carbon emissions per unit volume are reduced by 46% compared to ordinary underwater concrete of the same strength grade that uses ordinary Portland cement as the only cementing component.

[0078] Example 3:

[0079] The underwater self-compacting low-carbon concrete of this embodiment is composed of the following components in parts by weight:

[0080] 100 parts of low-carbon cementitious materials (including 60 parts of silicate cement, 18 parts of granulated blast furnace slag powder, 12 parts of fly ash, and 10 parts of limestone powder).

[0081] 235 parts of coarse aggregate (5-25mm continuously graded pebbles);

[0082] 190 parts of fine aggregate (natural sand with a fineness modulus of 2.5);

[0083] 40 parts of modified mineralized aggregate (carbon dioxide mineralization treated recycled fine aggregate);

[0084] 1.2 parts of flocculant enhancer (of which 40% is polyacrylamide, 35% is cellulose ether, 8% is nano silica, and 17% is redispersible latex powder, with the sum of the mass percentages of each component being 100%).

[0085] 0.6 parts of polycarboxylate superplasticizer (35% solid content, 38% water reduction rate);

[0086] 0.10 parts of retarder (tartaric acid);

[0087] 45 parts water.

[0088] The preparation method of this embodiment is basically the same as that of Example 1, except that: in step two, the carbonization conditions are 40% carbon dioxide volume concentration, 80% relative humidity, 30℃ temperature, 0.15MPa pressure, and 60 hours, resulting in modified mineralized aggregate with a carbon dioxide absorption of 5.5% of the aggregate mass and an apparent porosity that is 8% lower than that before mineralization treatment; in step three, the pre-wetting water amount is 40% of the total water amount; in step four, the stirring speed is 35 rpm and the stirring time is 75 seconds; in step five, the stirring time is 150 seconds.

[0089] The performance test results of the underwater self-compacting low-carbon concrete prepared in this embodiment are as follows: slump spread is 710 mm, T500 flow time is 5 seconds, suspended solids content during underwater pouring is 95 mg / L, and the 28-day water-to-land strength ratio is 79%. The carbon emission factor of the low-carbon cementitious material in this embodiment is calculated to be 552 kg. (When the proportion of silicate cement reaches 60%, the carbon emission factor is close to the upper limit.) The carbon emission per unit volume is reduced by 38% compared with ordinary underwater concrete of the same strength grade that uses ordinary silicate cement as the only cementing component.

[0090] Comparative Example 1:

[0091] To compare the contribution of the modified mineralized aggregate in this invention, Comparative Example 1 was set up. The composition of Comparative Example 1 is basically the same as that of Example 1, except that ordinary recycled aggregate without carbon dioxide mineralization treatment is used instead of modified mineralized aggregate. The remaining components and preparation methods are the same as those of Example 1.

[0092] The concrete prepared in Comparative Example 1 had a slump spread of 620 mm, a T500 flow time of 12 seconds, a suspended solids content of 135 mg / L during underwater pouring, and a 28-day water-to-land strength ratio of 68%. Compared with Example 1, Comparative Example 1 showed a significant decrease in fluidity, anti-dispersion properties, and mechanical properties, indicating that carbon dioxide mineralization treatment has a significant effect on improving concrete performance by reducing the apparent porosity of aggregates and improving interfacial properties.

[0093] Comparative Example 2:

[0094] To compare the contribution of the low-carbon cementitious material system in this invention, Comparative Example 2 was set up. The composition of Comparative Example 2 is basically the same as that of Example 1, except that ordinary silicate cement is used to completely replace the low-carbon cementitious material (i.e., the amount of cement used is the same as the amount of low-carbon cementitious material used in Example 1, and the carbon emission factor of cement is set at 850 kg). (Calculated), the remaining components and preparation methods are the same as in Example 1.

[0095] The concrete prepared in Comparative Example 2 had a slump spread of 660 mm, a T500 flow time of 8 seconds, a suspended solids content of 90 mg / L during underwater pouring, and a 28-day water-to-land strength ratio of 83%. The workability and mechanical properties of Comparative Example 2 were comparable to those of Example 1, but its carbon emissions per unit volume were only 8% lower than those of ordinary underwater concrete of the same strength grade with ordinary Portland cement as the sole cementing component (mainly due to the carbon sequestration contribution of modified mineralized aggregates), far lower than the 42% of Example 1. This indicates that the low-carbon cementitious material system of the present invention significantly reduces carbon emissions while ensuring performance.

[0096] The underwater self-compacting low-carbon concrete and its preparation method of this invention can be widely applied to various underwater concrete structure projects such as underwater pile foundations, underwater pile caps, underwater piers, submarine tunnel linings, and underwater repair and reinforcement. The preparation method of this invention is simple in process, convenient in operation, and uses widely available raw materials, making it suitable for large-scale industrial production and offering good economic and social benefits.

[0097] In summary, the working principle of this invention is as follows:

[0098] 1. Synergistic Effect of Low-Carbon Cementitious Material System: In this embodiment of the invention, a low-carbon cementitious material system is adopted, which is a compound of silicate cement, granulated blast furnace slag powder, fly ash, and limestone powder. Granulated blast furnace slag powder and fly ash serve as auxiliary cementitious materials. Through pozzolanic reaction, they consume the calcium hydroxide produced by cement hydration, generating additional hydrated calcium silicate gel. This not only improves the density and later strength of the concrete but also significantly reduces cement usage and lowers carbon emissions. Limestone powder acts as a micro-aggregate filler, improving particle size distribution and enhancing the fluidity and stability of the paste.

[0099] 2. Carbon Sequestration and Interface Strengthening Effects of Carbon Dioxide Mineralized Aggregates: The modified mineralized aggregates used in this embodiment of the invention are prepared by mineralizing recycled aggregates or porous aggregates in a carbon dioxide-rich atmosphere. Carbon dioxide reacts with calcium and magnesium ions in the aggregates to form stable carbonate minerals, achieving permanent carbon dioxide sequestration. Simultaneously, the carbonate crystals generated by the mineralization reaction fill the microcracks and pores on the aggregate surface, reducing the apparent porosity of the aggregates by 5%–20%, improving the interfacial properties of the aggregates, and increasing the bond strength between the aggregates and cement paste. The reduction in apparent porosity also reduces the absorption of mixing water by the aggregates, which helps maintain a stable actual water-cement ratio in the concrete mixture and ensures the reliability of its self-compacting properties. After being incorporated into concrete, the modified mineralized aggregates replace some natural aggregates, reducing the consumption of natural resources; furthermore, they continuously perform carbon sequestration in the concrete, further reducing the carbon footprint of the concrete.

[0100] 3. Multifunctional Synergistic Effect of Flocculant Enhancer: In this embodiment of the invention, the flocculant enhancer is composed of polyacrylamide flocculant, cellulose ether, nano-silica, and redispersible latex powder, with the sum of their mass percentages being 100%. The polyacrylamide flocculant, through the bridging effect of its long molecular chains, rapidly adsorbs cement particles and fine aggregates in the underwater environment, forming a three-dimensional network structure that effectively resists water erosion and dispersion. The cellulose ether increases the viscosity and water retention of the slurry, improving the cohesiveness of the concrete. The nano-silica has high pozzolanic activity and a micro-filling effect, promoting hydration reactions and increasing the density of the interfacial transition zone. The redispersible latex powder forms a polymer film during cement hydration, enhancing the interfacial adhesion between aggregates and the slurry, and improving the strength of underwater molded specimens.

[0101] 3. Overall Optimization of Mix Design: This invention, through the synergistic combination of low-carbon cementitious materials, modified mineralized aggregates, flocculants, polycarboxylate superplasticizers, and retarders, achieves a balance of high fluidity, high anti-dispersion properties, and low carbon content in concrete mixtures under appropriate water content and aggregate gradation. The polycarboxylate superplasticizer provides sufficient dispersion and water-reducing effects, ensuring that the concrete retains the fluidity required for self-compacting even at low water-cement ratios; the retarder regulates setting time to meet the requirements of underwater construction; and the pre-wetting treatment of aggregates prevents the porous structure of the modified mineralized aggregates from absorbing free water from the slurry, ensuring the stability of the slurry composition.

[0102] The above description illustrates the basic principles of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The above embodiments and descriptions in the specification are only for illustrating the principles of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and scope of the present invention without departing from the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. An underwater self-compacting low-carbon concrete, characterized in that... It consists of the following components in parts by weight: 100 parts low-carbon cementitious material; 180-250 parts coarse aggregate; 150-200 parts fine aggregate; 30-80 parts modified mineralized aggregate; 0.5-3.0 parts flocculant enhancer; 0.3-1.2 parts polycarboxylate superplasticizer; 0.05-0.30 parts retarder; 30-50 parts water; The low-carbon cementitious material comprises the following components by weight percentage: 40%–65% silicate cement, 15%–30% granulated blast furnace slag powder, 10%–25% fly ash, and 5%–15% limestone powder; The modified mineralized aggregate is a recycled aggregate or porous aggregate that has undergone carbon dioxide mineralization treatment, and its carbon dioxide absorption is 3% to 12% of the aggregate mass.

2. The underwater self-compacting low-carbon concrete according to claim 1, characterized in that: The flocculant enhancer comprises the following components by mass percentage: 30%–60% polyacrylamide flocculant, 20%–40% cellulose ether, 5%–15% nano silica, and 5%–20% redispersible latex powder, and the sum of the mass percentages of each component is 100%.

3. The underwater self-compacting low-carbon concrete according to claim 1, characterized in that: The modified mineralized aggregate has a carbon dioxide absorption capacity of 3% to 12% of the aggregate mass, and the apparent porosity of the modified mineralized aggregate is reduced by 5% to 20% compared with that before mineralization treatment.

4. The underwater self-compacting low-carbon concrete according to claim 1, characterized in that: The coarse aggregate is continuously graded crushed stone or gravel with a particle size of 5-25mm, a crushing index of no more than 12%, and a needle-like or flaky particle content of no more than 8%; the fine aggregate is natural sand or manufactured sand with a fineness modulus of 2.3-3.0 and a mud content of no more than 3%.

5. The underwater self-compacting low-carbon concrete according to claim 1, characterized in that: The polycarboxylate superplasticizer is a high-performance polycarboxylate superplasticizer with a solid content of 20% to 40% and a water reduction rate of not less than 30%; the retarder is at least one of sodium gluconate, citric acid or tartaric acid.

6. The underwater self-compacting low-carbon concrete according to claim 1, characterized in that: The slump extension of the underwater self-compacting low-carbon concrete is 550-750mm, the T500 flow time is 3-15 seconds, the suspended solids content during underwater pouring is not greater than 150mg / L, and the water-to-land strength ratio is not less than 75% after 28 days.

7. The underwater self-compacting low-carbon concrete according to claim 1, characterized in that: The carbon emission factor of the low-carbon cementitious material is no greater than 560 kg. The carbon emissions per unit volume of the underwater self-compacting low-carbon concrete are 30% to 50% lower than those of ordinary underwater concrete of the same strength grade that uses ordinary Portland cement as the only cementing component.

8. A method for preparing underwater self-compacting low-carbon concrete according to any one of claims 1-7, characterized in that: Includes the following steps: Step 1: Preparation of low-carbon cementitious material: Mix silicate cement, granulated blast furnace slag powder, fly ash and limestone powder evenly according to the formula to obtain low-carbon cementitious material; Step 2: Preparation of modified mineralized aggregate: Place the recycled aggregate or porous aggregate in a closed carbonization container and carbonize it for 24 to 72 hours under the conditions of carbon dioxide volume concentration of 20% to 99%, relative humidity of 40% to 90%, and temperature of 20 to 60°C to obtain modified mineralized aggregate with carbon dioxide absorption of 3% to 12% of the aggregate mass. Step 3: Aggregate pre-wetting treatment: After mixing coarse aggregate, fine aggregate and modified mineralized aggregate according to the proportion, add some water for pre-wetting treatment. The pre-wetting time is 10 to 30 minutes to make the aggregate reach a saturated surface dry state. Step 4, Slurry preparation: Add low-carbon cementitious material, flocculant enhancer, polycarboxylate superplasticizer, retarder and residual water into a mixer and stir for 60-120 seconds to obtain a uniform cementitious slurry; Step 5: Concrete mixing: Add the pre-wetted aggregate mixture to the cementitious slurry and continue stirring for 120-240 seconds until all components are evenly mixed to obtain underwater self-compacting low-carbon concrete.

9. The method for preparing underwater self-compacting low-carbon concrete according to claim 8, characterized in that, In step three, the amount of pre-wetting water used is 30% to 60% of the total water usage; in step four, the mixing speed of the mixer is 20 to 45 revolutions per minute.

10. A method for preparing underwater self-compacting low-carbon concrete according to claim 8, characterized in that: In step two, the carbonization process is carried out under a pressure of 0.1 to 0.5 MPa.

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