C35 Underwater Granite Concrete and Its Preparation Method

Abstract

This invention discloses a C35 underwater granite concrete and its preparation method. The C35 underwater granite concrete comprises raw material components in the following mass ratio: cement: fly ash: manufactured sand: crushed stone: bamboo chips: nano-calcium carbonate: gypsum: potassium polyacrylate: retarder: mixing water, with a mass ratio of (354-360):(74.3-75.7):(746-774):(989-1027):(5.253-5.355):(10.70-10.90):(2.14-2.18):(0.0862-0.0878):(8.56-8.72):(171-173). The C35 underwater granite concrete provided by this invention fully utilizes granite as raw material to produce underwater granite concrete with good workability, long initial setting time, good casting quality, high compressive strength, and high flexural strength.

Description

Technical Field

[0001] This invention relates to the field of bridge pile foundation construction technology, and in particular, to a C35 underwater granite concrete and its preparation method. Background Technology

[0002] Drilled cast-in-place piles are a common type of pile foundation, formed by drilling holes in the ground and injecting concrete to create the pile body. They possess high bearing capacity and good lateral force resistance. Drilled cast-in-place piles with mud-wall construction are frequently used for bridge foundations in areas with high groundwater levels (such as those spanning lakes, rivers, lakes, and seas). When using existing concrete to pour concrete into drilled cast-in-place piles, factors such as low sand content and poor workability often cause concrete blockage in the tremie pipe, leading to interruptions in concrete pouring. If concrete is re-poured, laitance layers may remain within the drilled cast-in-place pile concrete, resulting in pile breakage.

[0003] In regions where alkaline limestone resources are scarce but acidic granite resources are abundant, granite (SiO2 > 66%) is an acidic igneous rock and a relatively easy-to-obtain common rock. While granite possesses advantages such as hardness, density, high strength, weather resistance, corrosion resistance, wear resistance, and low water absorption, its application in the construction field can ensure the strength and lifespan of buildings. However, due to the poor adhesion of acidic granite, manufactured sand and crushed stone are difficult to mix fully with cement and other substances, easily leading to cracks and spalling. This reduces the compressive, flexural, and tensile properties of concrete, affecting the strength, durability, and horizontal (vertical) bearing capacity of cast-in-place pile concrete. Furthermore, the high brittleness of acidic granite results in poor gradation and high maximum crushing value in the manufactured sand produced after processing. The crushed stone produced also suffers from poor gradation, excessive angularity and flaky texture, high crushing value, and poor heat resistance. Consequently, the workability of the mixed concrete is poor, and bleeding is prone to occur, leading to poor concrete encapsulation, sand and gravel separation, and ultimately, concrete blockage of tremie pipes or breakage of bored piles.

[0004] Taking the pouring of C35 underwater granite concrete into a 128m long, 2.2m diameter bored pile as an example, due to the numerous defects mentioned above in acidic granite manufactured sand and granite crushed stone, the underwater granite concrete in the bored pile is prone to segregation, reducing the strength, durability, and horizontal (vertical) bearing capacity of the pile. According to regulations, the underwater concrete pouring time for bored piles must not exceed the initial setting time of the first batch of concrete. For a 128m long, 2.2m diameter bored pile, the underwater concrete pouring time, from the bottom of the pile to the top, typically ranges from 9 to 14 hours, thus requiring an initial setting time of 15 to 17 hours. Currently, the initial setting time of ordinary underwater concrete is usually 3 to 5 hours, while the initial setting time of underwater concrete with retarders can reach 9 to 11 hours. The initial setting time of underwater concrete for bored piles with existing technology cannot meet the construction requirements of 15 to 17 hours for underwater concrete in bored piles with a depth of over 100 meters. Summary of the Invention

[0005] This invention provides a C35 underwater granite concrete and its preparation method, solving the technical problems of poor workability, short initial setting time, and low compressive and flexural strength of underwater concrete prepared using acidic granite as the concrete material.

[0006] According to one aspect of the present invention, a C35 underwater granite concrete is provided, comprising raw material components in the following mass ratio:

[0007] The mass ratio of cement, fly ash, manufactured sand, crushed stone, bamboo chips, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water is (354-360):(74.3-75.7):(746-774):(989-1027):(5.253-5.355):(10.70-10.90):(2.14-2.18):(0.0862-0.0878):(8.56-8.72):(171-173), wherein the manufactured sand and crushed stone are both made from crushed granite.

[0008] Furthermore, the fineness modulus of the manufactured sand is 2.3 to 3.0.

[0009] Furthermore, the crushed stone is a continuous-sized crushed stone with a particle size of 5-25 mm.

[0010] Furthermore, the bamboo shavings include bamboo shavings with a particle size of 0.15 to 4.75 mm, and bamboo shavings with a particle size of less than 0.15 mm.

[0011] Furthermore, the bamboo shavings undergo the following treatment process before use: soaking in a latex solution and drying.

[0012] Furthermore, the nano-calcium carbonate has a particle size of 10–30 nm and a density of 2.8–3.1 g / cm³. 3 .

[0013] Furthermore, the retarder includes a polycarboxylate superplasticizer.

[0014] Furthermore, the initial setting time of the granite concrete is 936–952 min.

[0015] According to another aspect of the present invention, a method for preparing C35 underwater granite concrete is also provided, comprising the following steps:

[0016] The manufactured sand and bamboo chips are mixed to obtain a mixed sand material;

[0017] Cement, fly ash, nano-calcium carbonate and gypsum are added to the mixed sand in sequence, and the mixture is stirred to obtain fine material;

[0018] Add crushed stone to the fine materials, stir and mix to make a mixture;

[0019] Potassium polyacrylate, retarder, and mixing water are added to the mixture in sequence, and the mixture is stirred to obtain concrete mix.

[0020] The concrete mix was poured to obtain C35 underwater granite concrete.

[0021] Furthermore, before adding the potassium polyacrylate, the method further includes: preparing the potassium polyacrylate into an aqueous solution.

[0022] The present invention has the following beneficial effects:

[0023] The C35 underwater granite concrete raw materials provided by this invention include cement, fly ash, manufactured sand, crushed stone, bamboo shavings, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water. By using manufactured granite sand and crushed granite as concrete materials, and adding a certain proportion of cement, fly ash, bamboo shavings, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water, and thoroughly mixing, underwater granite concrete with good workability, long initial setting time, good casting quality, high compressive strength, and high flexural strength is obtained. This solves the technical problems of poor workability, short initial setting time, poor casting quality, and low compressive and flexural strength of underwater concrete prepared using acidic granite as a concrete material. Simultaneously, it has the beneficial effects of fully utilizing acidic granite as a concrete material locally, solving the problem of alkaline limestone resource shortage, reducing engineering construction costs, and simplifying construction technology.

[0024] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a flowchart of the experimental preparation of C35 underwater granite concrete according to a preferred embodiment of the present invention. Detailed Implementation

[0027] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0028] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0029] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0030] Embodiments of this application provide a C35 underwater granite concrete, comprising raw material components in the following mass ratio:

[0031] The mass ratio of cement, fly ash, manufactured sand, crushed stone, bamboo chips, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water is (354-360):(74.3-75.7):(746-774):(989-1027):(5.253-5.355):(10.70-10.90):(2.14-2.18):(0.0862-0.0878):(8.56-8.72):(171-173), wherein the manufactured sand and crushed stone are both made from crushed granite.

[0032] According to the embodiments of this application, manufactured granite sand and crushed granite are used as concrete skeleton materials. The fineness modulus of the manufactured sand is 2.3 to 3.0, and the crushed stone is a continuous particle size crushed stone with a particle size of 5 to 25 mm. By adding a certain proportion of cement, fly ash, bamboo chips, nano-calcium carbonate, gypsum, polycarboxylate superplasticizer, potassium polyacrylate, and mixing water, and fully mixing, underwater granite concrete with good workability, long initial setting time, high compressive strength, high flexural strength, and good casting quality is prepared. This solves the technical problems of poor workability, short initial setting time, poor casting quality, and low compressive and flexural strength of underwater concrete prepared with acidic granite as the main concrete material.

[0033] According to the embodiments of this application, fly ash is incorporated, whose main mineral composition is aluminosilicate glass beads and sponges. The spherical glass beads are dense, smooth, fine-grained, and have a small internal specific surface area, resulting in low water adsorption and good fluidity. In the concrete mixture, they act as "ball bearings," reducing the water demand of the cement paste, improving the workability of fresh concrete, and filling the pores of the cement paste, thus improving the density of the hardened concrete. The activity of fly ash is also known as the pozzolanic effect. The active components of fly ash, such as SiO2 and Al2O3, react chemically with cement hydration products in mixing water or in free water formed after the addition of nano-calcium carbonate and potassium polyacrylate, generating hydrated calcium silicate and hydrated calcium aluminate, which fill the pores of the cement hydration products. This significantly reduces the porosity of the underwater concrete, leading to finer pores, altering the pore structure, and improving the bonding effect of the various components of the underwater concrete. The fine particles in fly ash are uniformly distributed in the matrix phase of cement paste, preventing the aggregation of cement particles and playing a dispersing and lubricating role. This breaks down the flocculated structure of the cement paste, which helps improve the uniformity of fresh and hardened underwater concrete and is beneficial to the hydration reaction of the mixture. At the same time, fly ash can also compensate for the lack of fine powder in underwater concrete, block the bleeding channels, and help reduce the bleeding rate. The increase of powder in the cement paste also increases the volume of the cement paste, improves the cohesion of underwater concrete, and inhibits the segregation and bleeding phenomenon of underwater concrete. Furthermore, due to the morphology and hydrophilic properties of fly ash particles, the spherical glassy particles can adsorb a layer of water film, meaning fly ash has good water retention properties. This is beneficial for reducing the water demand of underwater concrete and helps fill and refine the voids and capillaries in underwater concrete. Also, due to the bearing ball effect of fly ash, the fluidity of underwater concrete is improved, reducing fluidity loss over time. Moreover, fly ash can improve the interface structure of concrete, turning coarse particles into fine particles and coarse pores into fine pores, thereby increasing the density of concrete, improving its strength and impermeability, reducing the temperature rise of concrete, and delaying the time of the maximum temperature peak. This is extremely beneficial for the crack resistance and impermeability of concrete structures.

[0034] In the embodiments of this application, the bamboo shavings include bamboo shavings with a particle size of 0.15–4.75 mm and bamboo shavings with a particle size less than 0.15 mm. For example, bamboo shavings with a particle size of 4 mesh (sieve aperture size 4.75 mm) are added, and the bamboo shavings are composed of bamboo shavings with a particle size of 0.15–4.75 mm and bamboo shavings with a particle size less than 0.15 mm to form bamboo shavings with a particle size of 0–4.75 mm. Among them: 1) The particle size of bamboo chips with a particle size of 0.15~4.75mm is the same as that of sand particles (0.15~4.75mm grade). It can be used as part of the sand aggregate in underwater concrete. It can be mixed with manufactured sand to form mixed sand, thereby improving the poor particle size distribution of granite manufactured sand and making the particle size distribution of mixed sand reach the optimal range. It can fill the skeleton voids of manufactured sand, reduce the void ratio of manufactured sand, and overcome the disadvantage of the large single-stage maximum crushing value of granite manufactured sand causing a decrease in the compressive strength of underwater concrete. It can also give full play to the high tensile strength and high ultimate elongation of bamboo chips, overcome the brittleness of underwater granite concrete, improve the bending tensile performance of cast-in-place piles over 100 meters deep, and thus improve the horizontal bearing capacity and deformation capacity of cast-in-place piles over 100 meters deep, which are affected by the bending stiffness of the pile body section and the depth of the pile body into the soil. 2) Bamboo chips with a particle size of less than 0.15mm can be used as a fine powder component in underwater concrete. When mixed with cement, fly ash, nano-calcium carbonate, gypsum, and mixing water, they form a highly fluid cement slurry. This slurry coats the mixed sand and gravel, filling the gaps between the dense mixed sand and gravel skeleton, thus improving the compressive strength of the underwater concrete to meet engineering requirements, increasing the slump of the underwater concrete, blocking the bleeding channels of the underwater concrete, and reducing the amount of bleeding. The increase in fine powder in the cement slurry also increases the volume of the cement slurry. This improves the cohesiveness and water retention of underwater concrete, inhibits the segregation and bleeding of underwater concrete, and improves the durability of underwater concrete; 3) If bamboo chips with a particle size greater than 4.75mm are added, the larger bamboo chips in the underwater concrete will be coated on the surface of the manufactured sand and crushed stone particles, blocking the sliding of smaller particles and air bubbles in the underwater concrete, increasing the frictional resistance between the raw material particles of underwater concrete, reducing the fluidity of underwater concrete, causing blockage of the conduit, and leading to interruption of underwater concrete pouring.

[0035] Furthermore, the addition of bamboo chips to underwater concrete necessitates increasing the water content and water-cement ratio to maintain its workability, which can lead to a decrease in compressive strength. However, by incorporating water-reducing agents, nano-calcium carbonate, and potassium polyacrylate into underwater concrete, the water content and water-cement ratio can be reduced, thereby improving the early and later compressive strength of the underwater concrete in bored piles. This enhances the density, mechanical properties, and durability of the underwater concrete, ultimately increasing the vertical bearing capacity and deformation capacity of piles exceeding 100 meters in depth. Furthermore, the underwater granite concrete pouring method involves first drilling a bored pile, then pouring the concrete into the pile hole from the bottom through a guide pipe, and gradually filling the pile with underwater granite concrete. During the pouring of the 128m long underwater granite concrete, the large gravity of the falling underwater granite concrete generates significant pressure. This forces the underwater granite concrete to simultaneously push the wall slurry in the bored pile hole to overflow and be discharged towards the top of the pile, filling the hole, and simultaneously push the wall slurry in the bored pile hole to seep into the surrounding pile hole walls. This forms a thin mud layer between the underwater concrete and the soil layer of the pile hole wall, preventing groundwater from seeping into the underwater concrete and wetting and corroding the bamboo chips in the underwater concrete, thus providing corrosion protection for the bamboo chips and improving the density, mechanical properties, and durability of the underwater concrete.

[0036] In the embodiments of this application, the nano-calcium carbonate (CaCO3) has a particle size of 10–30 nm and a density of 2.8–3.1 g / cm³. 3With its high specific surface area and small particle size, the large surface energy and strong adsorption of nanoparticles make them prone to attracting each other and forming agglomerates and precipitates. Water-soluble polymers in underwater concrete can be directionally adsorbed on the surface of calcium carbonate, giving calcium carbonate charge characteristics and forming a stable physical and chemical adsorption layer on its surface, preventing calcium carbonate particles from agglomerating and improving the dispersibility of nano-calcium carbonate. Furthermore, due to the repulsion of like charges, nano-calcium carbonate is not easy to polymerize, thereby improving the dispersibility and stability of nano-calcium carbonate. Because nano-calcium carbonate particles, with a diameter of 20nm, are smaller than those of cement, fly ash, bamboo shavings, gypsum, and manufactured sand, their addition to underwater concrete acts as a ball bearing between the relatively large, plate-like and blocky cement particles, filling the voids between them. This reduces the amount of water in the cement mixture, allowing for more free water to be used. When mixed with the cement, fly ash, fine powder bamboo shavings, and gypsum, a highly fluid cement slurry is formed, which coats and fills the voids between the dense aggregate and sand, thus improving the compactness of the underwater concrete. This method improves the mechanical properties, reduces the permeability of underwater concrete, and enhances its durability. It also overcomes the drawback of increasing water content and water-cement ratio in underwater concrete to improve workability, which can lead to a decrease in compressive strength. Furthermore, it increases the total surface area of ​​the aggregate in underwater concrete, increasing its air content. The tiny air bubbles act as ball bearings, improving the slump of the underwater concrete. The increased air bubbles also enhance the cohesion of the underwater concrete, binding solid particles together. Reducing the settling of solid particles and water flow blocks the bleeding channels in underwater concrete, thus decreasing the amount of bleeding. The increased fine powder in the cement paste also increases the volume of the cement paste, improving the cohesiveness and water retention of the underwater concrete, inhibiting segregation and bleeding, and enhancing its durability. Adding nano-calcium carbonate to the underwater concrete, since calcium carbonate is essentially insoluble in water, increases the apparent density of the underwater concrete, thereby increasing the free-fall gravity of the underwater granite concrete and overcoming the problem of underwater granite bleeding in the middle and top areas of the cast-in-place pile. The low gravity of underwater granite concrete during free fall leads to a lack of density, which is a drawback of underwater granite concrete. This improvement increases the compressive strength of underwater granite concrete, thereby enhancing the vertical bearing capacity and deformation capacity of cast-in-place piles exceeding 100 meters in depth. It can also increase the lateral pressure of underwater concrete on the pile hole wall, making the pile hole wall more stable. Furthermore, it can coat acidic granite manufactured sand and granite gravel, forming a stable layer of calcium carbonate on the surface of the manufactured sand and gravel particles, transforming the acidic manufactured sand and gravel into alkaline manufactured sand and gravel, overcoming the poor adhesion of acidic granite manufactured sand and granite gravel.

[0037] According to embodiments of this application, gypsum (CaSO4·2H2O) is produced from natural gypsum ore through calcination and pulverization. Adding gypsum to underwater concrete can increase the Ca content in the underwater concrete. 2+ Ions, making Ca 2+ Ions and CO3 in underwater concrete 2- Ions combine to form water-insoluble CaCO3 precipitate, thereby increasing the apparent density of underwater concrete, increasing the free fall gravity of underwater granite concrete, improving the compressive strength of underwater granite concrete, and enhancing the vertical bearing capacity and deformation capacity of cast-in-place piles over 100 meters deep. It can also increase the lateral pressure of underwater concrete on the pile hole wall, making the pile hole wall more stable. Furthermore, it can coat acidic granite manufactured sand and gravel, forming a stable layer of calcium carbonate on the surface of the manufactured sand and gravel particles, transforming acidic manufactured sand and gravel into alkaline manufactured sand and gravel, overcoming the disadvantage of poor adhesion of acidic granite manufactured sand and gravel. Excessive alumina (Al2O3) content in cement clinker leads to an overabundance of tricalcium aluminate (C3A), while insufficient sulfur trioxide (SO3) or gypsum content of only about 3% or even less results in rapid dissolution of tricalcium aluminate (C3A) in water, quickly forming calcium aluminate hydrates. This causes the cement paste to solidify rapidly, resulting in the loss of plasticity in fresh concrete and severely impacting underwater concrete pouring. In underwater concrete, the addition of gypsum quickly reacts with tricalcium aluminate (C3A) and calcium hydroxide (CaO)... The reaction of HO)2) produces hydrated calcium sulfide (i.e., ettringite C3A3CaSO4Ca(HO)2), which is insoluble in water. This forms a coating layer on the surface of tricalcium aluminate (C3A) particles, preventing further hydration of tricalcium aluminate (C3A). This reduces the solubility of aluminate in the solution, so that the hydration products of calcium aluminate cannot be separated. This increases the concentration of the slower-reacting tricalcium silicate (C3S) colloidal solution, thereby delaying the cement setting time and thus prolonging the initial and final setting times of underwater granite concrete.

[0038] According to an embodiment of this application, when cement particles come into contact with water, the calcium silicate on the surface of the cement particles partially dissolves and releases calcium ions, hydroxide ions, and silicate ions. In underwater concrete, polycarboxylate superplasticizers are incorporated. The molecular structure of polycarboxylate superplasticizers contains functional groups such as hydroxyl (-OH), carboxyl (-COO-), sulfonic acid (-SO3-), and polyethoxy (-OCH2CH2-). On one hand, the main chain adsorbs onto the surface of cement particles, preventing contact between the particles and water. The high grafting density of carboxyl (-COO-) and sulfonic acid (-SO3-) groups provides electrostatic repulsion and simultaneously combines with calcium to form a calcium-rich protective layer. A small amount of hydroxyl (-OH) complexes with exposed silica hydrated ions, effectively reducing the concentration of calcium and silicon ions in the solution and preventing ion release. On the other hand, the long side chain of polyethoxy (-OCH2CH2-) and a small amount of hydroxyl (-OH) form hydrogen bonds with water, producing a three-dimensional water film protection and steric hindrance effect, increasing the thickness of the hydration layer, delaying cement hydration, effectively inhibiting the initial hydration of tricalcium aluminate (C3A) and tricalcium silicate (C3S), and delaying structural formation. In underwater concrete, the addition of polycarboxylate superplasticizer creates microbubbles within the concrete. These bubbles carry the same charge as the cement particles, resulting in electrostatic repulsion that disperses the cement particles. Furthermore, the bubbles physically isolate the cement particles, preventing agglomeration. Simultaneously, the bubbles themselves act like ball bearings, promoting the sliding of cement particles and improving the fluidity of the underwater concrete.

[0039] According to embodiments of this application, potassium polyacrylate is a cationic superabsorbent polymer with excellent water absorption and retention properties. The resin contains rattan-like polymer chains, and the hydrophilic groups on these chains ionize in water into carboxylate anions and potassium hydroxide ions. + Ions. Before absorbing water, these tightly packed, solid polymer chains intertwine and coil, forming an interlocking, cube-like grid between some chains, with gaps in the grid. + Ions enter the grid, leaving carboxylic acid anions on the molecular chain segments. Upon encountering water, the ions in the grid repel each other due to like charges, and the anions repel each other, fully expanding the polymer chains, causing the grid to enlarge and its volume to increase. Due to capillary action, water enters the interior of the grid; the K in the water within the grid... +Ions increase the concentration of the aqueous solution. Due to the osmotic pressure difference, water moves to areas with higher concentrations, causing water to continuously enter the water-absorbing resin and form a uniform gel-like substance. During drying, potassium polyacrylate gradually releases the absorbed water, overcoming the drawback of increasing the water content and water-cement ratio in underwater concrete to meet the workability requirements after adding bamboo chips, which leads to a decrease in the compressive strength of underwater concrete. This improves the performance of various materials. In underwater concrete, potassium polyacrylate reacts with calcium hydroxide (Ca(HO)2) in the cement to form potassium calcium polyacrylate gel, which fills the voids between cement particles, improving the strength and durability of the cement. Reducing the amount of water used in the cement voids creates more free water, which, when mixed with cement, fly ash, fine bamboo powder, and gypsum, forms a highly fluid cement slurry. This slurry not only coats and fills the voids between the mixed sand and gravel, improving the density, mechanical properties, and durability of the underwater concrete, but also reduces its permeability. Furthermore, it overcomes the drawback of increasing water content and water-cement ratio in underwater concrete to improve workability after adding bamboo powder, which leads to a decrease in compressive strength. It also improves the fluidity, pumpability, and processability of the cement slurry, reduces segregation, and increases the cohesiveness and water retention of the underwater concrete, thereby improving the quality of the concrete and construction efficiency.

[0040] This application verifies and designs the scheme from the following aspects: raw material selection and inspection, design of indoor components for underwater granite concrete, verification of mixing at the outdoor mixing plant for underwater granite concrete, verification of the first cast-in-place pile pouring at the construction site, and determination of the design components for underwater granite concrete.

[0041] I. Raw material selection and inspection.

[0042] The cement used is P.O42.5 ordinary Portland cement; the fly ash used is stable quality and uniform feed material of power plant Class F Grade I fly ash, with an admixture of 17.4% of the cementitious material mass; the manufactured sand is Zone II medium sand manufactured sand produced by multiple crushing processes of hard, dense, and high-strength acidic granite, with a fineness modulus of 2.3-3.0; the crushed stone is produced by multiple crushing processes of hard, dense, and high-strength acidic granite, producing continuous crushed stone with a nominal particle size of 5-25mm; bamboo chips are made from external materials. The bamboo shavings are made from clean, natural organic fibers, are environmentally friendly, and have strong stalk fiber, and are produced from bamboo stalks aged 3 years or older. The shavings are made from sawdust from the bamboo stalks, with a particle size of 4 mesh (4.75mm sieve opening). The 0-4.75mm particle size is composed of bamboo shavings with a particle size of 0.15-4.75mm and those smaller than 0.15mm, and their content is 0.3% of the total mass of sand and gravel. Nano-calcium carbonate is produced in Hebei Province with a particle size of 10-30nm and a density of 2.8-3.1g / cm³. 3The white powder is ultrafine calcium carbonate, with an admixture content of 2.5% of the cementitious material's mass; the gypsum is made from natural gypsum ore through calcination and pulverization, using materials produced in Shandong with a density of 2.31 g / cm³. 3 The following materials are used: white powdered gypsum, with an admixture dosage of 0.5% of the cementitious material's mass; potassium polyacrylate, a pale yellow powder with a density of 0.4 g / mL (25℃) produced in Henan Province, readily soluble in water, with an admixture dosage of 0.02% of the cementitious material's mass; a polycarboxylate-based HPWR-R type high-performance water-reducing agent (retarding type), an aqueous agent with a water reduction rate of 18%, with an admixture dosage of 2.0% of the cementitious material's mass; and drinking water. All the above raw materials must meet the requirements of the relevant current national product standards.

[0043] II. Interior component design of C35 underwater granite concrete.

[0044] The initial indoor composition of underwater granite concrete is a mixture made of cement, fly ash, manufactured sand, crushed stone, retarder, and mixing water. First, three initial compositions with different proportions are initially determined. Then, based on the test results of the concrete mixture's performance indicators, the initial indoor composition of underwater granite concrete that meets the technical requirements, economic efficiency, workability, durability, and strength requirements of the "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020) is selected. Finally, based on the initial indoor composition, a certain proportion of bamboo chips, nano-calcium carbonate, gypsum, and potassium polyacrylate are added and thoroughly mixed to obtain the designed indoor composition of the underwater granite concrete.

[0045] Preparation method of underwater granite concrete: First, add the weighed mass of manufactured sand and bamboo chips to an indoor concrete mixer and dry mix for 60 seconds to make mixed sand; second, add the weighed mass of cement, fly ash, nano-calcium carbonate, and gypsum to the mixed sand and dry mix for 30 seconds to make mixed fine aggregate; third, add the weighed mass of crushed stone to the mixed fine aggregate and dry mix for 60 seconds to make sand and gravel mixture; finally, add the weighed mass of potassium polyacrylate, retarder, and mixing water to the sand and gravel mixture and mix for 180 seconds to make underwater granite concrete mix.

[0046] The design composition (by mass method) for C35 underwater granite concrete interior is as follows: cement: fly ash: manufactured sand: crushed stone: bamboo chips: nano-calcium carbonate: gypsum: potassium polyacrylate: retarder: mixing water, with a mass ratio of 357:75:760:1008:5.304:10.80:2.16:0.087:8.64:172 (unit: kg / m³). 3 ).

[0047] III. Verification of outdoor mixing plant for C35 underwater granite concrete.

[0048] Based on the indoor component design of C35 underwater granite concrete, the mixing verification of the C35 underwater granite concrete mixing plant was carried out at the outdoor mixing plant, including the following technical contents: purchasing, commissioning and calibrating the mixing equipment; testing the moisture content of manufactured sand and crushed stone in the material preparation warehouse at the mixing plant; calculating the material supply amount of each material bin for each batch of concrete mixing; the feeding method and order of each component material of the concrete mixture; the mixing time of each component material of the underwater granite concrete mixture; inspecting the uniformity and color consistency of the underwater granite concrete mixture; inspecting the dispersibility of bamboo chips in the underwater granite concrete mixture; and conducting performance index tests on the concrete mixture according to the test methods in the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T 50080) and "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081), including apparent density, slump, slump change over 1 hour, cohesiveness, water retention, setting time, segregation, compressive strength and flexural strength.

[0049] IV. Verification of the first cast-in-place pile cast-in-place construction at the construction site.

[0050] The verification of the first cast-in-place pile at the construction site includes: engineering application implementation, cast-in-place pile pouring time, cast-in-place pile concrete strength testing, cast-in-place pile integrity testing, and cast-in-place pile concrete core sampling compressive strength testing.

[0051] V. Determine the design components of C35 underwater granite concrete.

[0052] The design composition (mass method) for C35 underwater granite concrete is determined as follows: cement: fly ash: manufactured sand: crushed stone: bamboo chips: nano-calcium carbonate: gypsum: potassium polyacrylate: retarder: mixing water, with a mass ratio of (354~360):(74.3~75.7):(746~774):(989~1027):(5.253~5.355):(10.70~10.90):(2.14~2.18):(0.0862~0.0878):(8.56~8.72):(171~173) (unit: kg / m³). 3 ).

[0053] Specifically, the embodiments of the present invention are based on the main bridge 7 of an A-shaped single-tower cable-stayed bridge in a bridge project in the Guangdong Delta Plain. #This paper takes the underwater concrete pouring construction of 30 bored piles (128m long, 2.2m diameter) of the pier, using C35 granite as an example. According to the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T3650-2020), the concrete mixture should have good workability, a slump of 160-220mm, and the underwater concrete pouring time should not exceed the initial setting time of the first batch of concrete. Furthermore, according to the engineering construction drawings, the main bridge of the A-shaped single-tower cable-stayed bridge has 7... # The pier set up with 30 bored cast-in-place piles, each with a diameter of 2.2m and a designed pile length of 128m, with a designed concrete strength grade of C35. The specific experimental procedure is as follows:

[0054] 1. Raw material selection and inspection.

[0055] Underwater granite concrete for bored piles refers to a mixture made from cement, fly ash, manufactured sand, crushed stone, bamboo shavings, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water in a specific ratio. Based on the determined types and specifications of the underwater granite concrete components, each component is prepared on-site at the mixing plant, categorized and stacked in separate bins according to type and specification, and properly labeled and protected against rainwater. Before entering the site, cement, fly ash, manufactured sand, crushed stone, bamboo shavings, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water undergo relevant quality indicator tests. All test results must meet the requirements of relevant national and industry construction technical specifications, product standards, or technical documents before use.

[0056] (1) Cement. P.O42.5 ordinary Portland cement was used. The test results showed a specific surface area of ​​346 m². 2 / kg, initial setting time is 184min, final setting time is 255min, soundness is qualified, 28-day compressive strength is 51.1MPa, 28-day flexural strength is 7.6MPa, all test indicators meet the technical requirements of P.O42.5 in the "General Portland Cement" (GB 175) standard.

[0057] (2) Fly ash. Stable quality and uniform feed quality of Class F, Grade I fly ash from power plants were used, with an admixture dosage of 17.4% of the cementitious material mass. The test results showed a fineness of 10.1%, a water requirement ratio of 92%, and a loss on ignition of 4.2%, meeting the Grade I technical requirements of the standard "Fly Ash for Cement and Concrete" (GB / T 1596).

[0058] (3) Manufactured sand. Manufactured sand is produced by repeatedly crushing and processing hard, dense, and high-strength acidic granite. Test results show a fineness modulus of 2.8 (classifying it as medium sand) and an apparent density of 2580 kg / m³. 3 The bulk density is 1450 kg / m³ 3The mud content is 0.9%; the methylene blue MB value test is qualified; the mud lump content is 0%; the maximum single-stage crushing value is 22.5%; all test indicators meet the technical requirements of Class II medium sand in Zone 2 of the "Construction Sand" (GB / T 14684) standard.

[0059] (4) Crushed stone. Hard, dense, and high-strength acidic granite was repeatedly crushed to produce continuously sized crushed stone with a nominal particle size of 5–25 mm. Test results showed: good particle size distribution; mud content of 0.7%, mud lump content of 0%, needle-like and flaky particle content of 7.3%, crushing value of 13.5%, and apparent density of 2680 kg / m³. 3 The bulk density is 1440 kg / m³ 3 Its rock saturated compressive strength is 99.5 MPa, and all test indicators meet the technical requirements of Class II crushed stone in the standard "Construction Pebbles and Crushed Stone" (GB / T 14685).

[0060] (5) Bamboo Shavings. Made from clean, natural organic fibers, environmentally friendly, and tough bamboo stalks from bamboo plants aged 3 years or older. The bamboo shavings are produced from sawdust on the bamboo stalks. The shavings have a particle size of 4 mesh (4.75mm sieve opening). The 0-4.75mm shavings consist of 0.15-4.75mm shavings and shavings smaller than 0.15mm shavings. The 0-4.75mm shavings are added at 0.3% of the total mass of sand and gravel. Before use, they must be soaked in a 10% A latex solution for 24 hours, then drained and allowed to air dry naturally.

[0061] (6) Nano-calcium carbonate. Nano-calcium carbonate, also known as ultrafine calcium carbonate, has the characteristics of high specific surface area and small particle size. Calcium carbonate is an inorganic compound with the chemical formula CaCO3. It is the main component of limestone. Calcium carbonate is usually a white crystal, tasteless, and basically insoluble in water. Calcium carbonate is composed of calcium ions and carbonate ions forming ionic bonds, with the carbonate ions consisting of carbon-oxygen covalent bonds. Nano-calcium carbonate produced in Hebei Province has a particle size of 20 nm and a density of 2.8–3.1 g / cm³. 3 The white powder is ultrafine calcium carbonate, and its dosage is 2.5% of the mass of the cementitious material.

[0062] (7) Gypsum. Gypsum, also known as calcium sulfate, is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O and a pH of 7. Gypsum is produced from natural gypsum ore through calcination and crushing. The gypsum produced in Shandong has a density of 2.31 g / cm³. 3 The white powdered gypsum is added at a rate of 0.5% of the mass of the cementitious material.

[0063] (8) Potassium polyacrylate. Potassium polyacrylate is a cationic superabsorbent polymer with good water absorption and retention properties. A light yellow powder of potassium polyacrylate with a density of 0.4 g / mL (25℃), produced in Henan Province, was used. It is easily soluble in water, and its dosage is 0.02% of the cementitious material mass. During testing, 1 g of potassium polyacrylate was added to 700 g of mixing water and stirred for 2 hours. The viscosity was measured using a funnel viscometer, and the molecular weight was compared to determine its molecular weight. Before use, potassium polyacrylate was prepared into a 1% aqueous solution for later use; when needed, it was added to the concrete mixture in the required amount.

[0064] (9) Retarder. High-performance water-reducing agent (retarded type) of polycarboxylate-based HPWR-R type is used. It is an aqueous agent with a water reduction rate of 18%. Its dosage is 2.0% of the mass of cementitious materials. Its quality meets the technical requirements of retarded high-efficiency water-reducing agent in the standard of "Concrete Admixtures" (GB 8076).

[0065] (10) Mixing water. Drinking water was used, and its quality met the requirements for water used in concrete as specified in the "Standard for Water Used in Concrete" (JGJ63).

[0066] 2. Example of indoor component design for C35 underwater granite concrete.

[0067] (1) Preparation and determination of initial indoor components.

[0068] Calculate the concrete composition. The initial composition of underwater granite concrete for indoor use is a mixture of cement, fly ash, manufactured sand, crushed stone, retarder, and mixing water. The following three mass ratios (cement:fly ash:manufactured sand:crushed stone:retar:mixing water) are used for mix design trials. The raw materials for each component are provided according to the following mass ratios:

[0069] Trial mix 1: The mass ratio of cement: fly ash: manufactured sand: crushed stone: retarder: mixing water is 406:85:717:991:9.82:172 (unit: kg / m³). 3 (Water-to-binder ratio is 0.35, sand content is 42%).

[0070] Trial mix design 2: The mass ratio of cement: fly ash: manufactured sand: crushed stone: retarder: mixing water is 357:75:760:1008:8.64:172 (unit: kg / m³). 3 (Water-to-binder ratio is 0.40, sand content is 43%).

[0071] Trial mix 3: The mass ratio of cement: fly ash: manufactured sand: crushed stone: retarder: mixing water is 316:66:800:1019:7.64:172 (unit: kg / m³). 3 (Water-to-binder ratio is 0.45, sand content is 44%).

[0072] Trial mixing of concrete. In the concrete composition design room where the indoor temperature is 5℃~35℃, 120L (0.12m³) of concrete was trial mixed. 3 For the concrete mixture, use a 150kg electronic scale with a sensitivity of 1g to weigh the following materials:

[0073] Trial mix 1: Weigh out the following quantities: cement 48.720 kg (dry weight), fly ash 10.200 kg (dry weight), manufactured sand 86.040 kg (dry weight), crushed stone 118.920 kg (dry weight), retarder 1.178 kg (aqueous solution), and mixing water 20.640 kg, and mix to prepare concrete mixture.

[0074] Trial mix 2: Weigh out the following quantities: cement 42.840 kg (dry weight), fly ash 9.000 kg (dry weight), manufactured sand 91.200 kg (dry weight), crushed stone 120.960 kg (dry weight), retarder 1.037 kg (aqueous solution), and mixing water 20.640 kg, and mix to prepare concrete mixture.

[0075] Trial mix 3: Weigh out the following quantities: cement 37.920 kg (dry weight), fly ash 7.920 kg (dry weight), manufactured sand 96.000 kg (dry weight), crushed stone 122.280 kg (dry weight), retarder 0.917 kg (aqueous solution), and mixing water 20.640 kg, and mix to prepare concrete mixture.

[0076] The concrete preparation method is as follows: First, weighed manufactured sand, cement, and fly ash are added sequentially to an indoor concrete mixer and dry-mixed for 60 seconds to form a fine aggregate mixture. Second, weighed crushed stone is added to the fine aggregate mixture and dry-mixed for 60 seconds to form a sand and gravel mixture. Finally, weighed retarder and mixing water are added sequentially to the sand and gravel mixture and mixed for 60 seconds to form an underwater granite concrete mix.

[0077] Quality inspection of performance indicators of concrete mixtures. For concrete mixtures from trial mix 1 to trial mix 3, the performance indicators of apparent density, slump, slump change over 1 hour, cohesiveness, water retention, setting time, segregation, compressive strength, and flexural strength were tested according to the test methods in the "Standard for Test Methods of Performance of Ordinary Concrete Mixes" (GB / T 50080) and "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081). The test results are shown in Table 1.

[0078] Table 1. Test results of performance indicators of concrete mixtures from Trial Mix 1 to Trial Mix 3

[0079]

[0080]

[0081] The initial indoor composition was determined. Based on the test results of apparent density, slump, slump change over 1 hour, cohesiveness, water retention, setting time, segregation, compressive strength, and flexural strength, combined with the design pile length and concrete strength grade in the engineering construction drawings, the technical requirements in the "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020), economic efficiency, workability, durability, and strength meeting design requirements, a comprehensive analysis was conducted. Trial mix two (comparative example) was selected as the initial indoor composition for underwater granite concrete, namely: cement: fly ash: manufactured sand: crushed stone: retarder: mixing water in a mass ratio of 357:75:760:1008:8.64:172 (unit: kg / m³). 3 (Water-to-binder ratio is 0.40, sand content is 43%).

[0082] (2) Interior component design of C35 underwater granite concrete.

[0083] Material usage per unit volume of C35 underwater granite concrete:

[0084] Calculate the concrete composition. Based on the test results of the concrete mix performance indicators in Table 1, the initial setting time of the underwater concrete in trial mix two (comparative example) is 619 min, which is shorter than the requirement of 15–17 h (900–1020 min) for underwater concrete in bored piles with a pile length of 128 m and a diameter of 2.2 m. Therefore, the initial indoor composition of this underwater granite concrete (comparative example: cement: fly ash: manufactured sand: crushed stone: retarder: mixing water mass ratio is 357:75:760:1008:8.64:172 (unit: kg / m³) 3 Based on the above, a certain proportion of bamboo shavings, nano-calcium carbonate, gypsum, and potassium polyacrylate are added and thoroughly mixed to prepare underwater granite concrete. The material content per unit volume of the underwater granite concrete is calculated according to the raw material mixing ratio.

[0085] The mass ratio of cement, fly ash, manufactured sand, crushed stone, bamboo chips, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water is 357:75:760:1008:5.304:10.80:2.16:0.087:8.64:172 (unit: kg / m³). 3 ).

[0086] Trial mixing of concrete. In the concrete composition design room with an indoor temperature of 5℃~35℃, 120L (0.12m) of concrete was trial-mixed according to the calculated composition of underwater granite concrete. 3 For the concrete mixture, use a 150kg electronic scale with a sensitivity of 1g to weigh the following materials:

[0087] Weigh out the following quantities separately: cement 42.840 kg (dry weight), fly ash 9.000 kg (dry weight), manufactured sand 91.200 kg (dry weight), crushed stone 120.960 kg (dry weight), bamboo chips 0.636 kg (dry weight), nano calcium carbonate 1.296 kg (dry weight), gypsum 0.259 kg (dry weight), potassium polyacrylate 0.010 kg (aqueous solution), retarder 1.037 kg (aqueous solution), and mixing water 20.640 kg, and mix to prepare concrete mixture.

[0088] The concrete preparation method is as follows: First, weighed manufactured sand and bamboo chips are added to an indoor concrete mixer and mixed for 60 seconds to form a mixed sand. Second, weighed cement, fly ash, nano-calcium carbonate, and gypsum are added to the mixed sand and mixed for 30 seconds to form a mixed fine aggregate. Third, weighed crushed stone is added to the mixed fine aggregate and mixed for 60 seconds to form a sand and gravel mixture. Finally, weighed potassium polyacrylate, retarder, and mixing water are added to the sand and gravel mixture and mixed for 180 seconds to form an underwater granite concrete mix.

[0089] Quality inspection of performance indicators of concrete mixtures. For concrete mixtures, the performance indicators of apparent density, slump, slump change over 1 hour, cohesiveness, water retention, setting time, segregation, compressive strength, and flexural strength were tested according to the test methods in the standards "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T 50080) and "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081). The test results are shown in Table 2.

[0090] Table 2 Test Results of Performance Indicators of Concrete Mixtures

[0091]

[0092] (3) Determine the design components of the indoor components of C35 underwater granite concrete.

[0093] Based on the test results of apparent density, slump, slump change over 1 hour, cohesiveness, water retention, initial setting time, final setting time, segregation, compressive strength, and flexural strength, the test results meet the technical requirements of the "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020) standard, and the construction operation requirement that the initial setting time of underwater concrete for a 128m long and 2.2m diameter bored pile should be between 15 and 17 hours (900 to 1020 minutes). The mass ratio of cement, fly ash, manufactured sand, crushed stone, bamboo chips, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water is 357:75:760:1008:5.304:10.80:2.16:0.087:8.64:172 (unit: kg / m³). 3 () as a component of the indoor design of C35 underwater granite concrete.

[0094] 3. Verification of mixing at an outdoor C35 underwater granite concrete mixing plant.

[0095] Based on the indoor component design composition of C35 underwater granite concrete, the mixing verification of the C35 underwater granite concrete mixing plant was carried out at an outdoor mixing plant, including the following technical contents:

[0096] (1) When purchasing mixing equipment, select and customize equipment with a concrete mixing output capacity of not less than 75m³ per hour. 3 The JS750 type forced concrete mixer is an automatic metering standard mixer with two batching bins.

[0097] (2) The mixing equipment must be properly adjusted. The measuring instruments of the mixing equipment must be statically calibrated by a legally authorized metrological verification agency on a regular basis, and the weighing accuracy of each silo of the mixing equipment must be dynamically calibrated during use. The allowable deviation of the weighing accuracy must comply with the relevant national and industry construction technical specifications.

[0098] (3) Detect the indoor temperature of the mixing plant and the storage silos of each component material, and control the temperature within the range of 5℃~35℃.

[0099] (4) Test the moisture content of manufactured sand and crushed stone in the material preparation warehouse of the mixing plant.

[0100] (5) Calculate the amount of material supplied to each silo in each batch of concrete mixing.

[0101] 1) The amount of material mixed per batch should not exceed 75% of the mixer's rated discharge capacity (i.e., 500L or 0.50m³). 3 ) Calculate, stir 1m 3 Concrete. Based on the measured moisture content of manufactured sand and crushed stone, calculate the mixing quantities per batch of cement, fly ash, manufactured sand, crushed stone, bamboo chips, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water.

[0102] 2) The amount of mixing water is calculated as follows: the amount of mixing water is calculated minus the water content in the manufactured sand and crushed stone.

[0103] 3) Allowable deviations in the batching of each component material in each batch (by mass): According to the provisions of the "Technical Specifications for Construction of Highway Bridges and Culverts" (JTG / T3650-2020) regarding the allowable mass deviations in the batching of concrete for "centralized batching plant mixing": the allowable deviation in the batching of coarse and fine aggregates is ±2%, and the allowable deviation in the batching of cement, dry admixtures, mixing water, and additives is ±1%.

[0104] (6) Methods and sequence of adding each component of concrete mixing:

[0105] 1) All materials are fed by weight. Specifically, cement, fly ash, manufactured sand, crushed stone, retarder, and mixing water are fed by electronic metering of the mixing equipment, while bamboo chips, nano calcium carbonate, gypsum, and potassium polyacrylate are fed by manual pre-weighing.

[0106] 2) In order to ensure that the bamboo chips are evenly dispersed in the concrete mixing, the order of adding each component material is as follows: manufactured sand (electronic metering) → bamboo chips (manual input) → cement (electronic metering) → fly ash (electronic metering) → nano calcium carbonate (manual input) → gypsum (manual input) → crushed stone (electronic metering) → potassium polyacrylate (manual input) → retarder (electronic metering) → mixing water (electronic metering) → mixing.

[0107] (7) The mixing time for each component of the underwater granite concrete is 330s.

[0108] First, manufactured sand and bamboo chips are added to a forced concrete mixer and mixed for 60 seconds to form a mixed sand. Then, cement, fly ash, nano-calcium carbonate, and gypsum are added to the mixed sand and mixed for 30 seconds to form a mixed fine aggregate. Next, crushed stone is added to the mixed fine aggregate and mixed for 60 seconds to form a sand and gravel mixture. Finally, potassium polyacrylate, retarder, and mixing water are added to the sand and gravel mixture and mixed for 180 seconds to form an underwater granite concrete mix.

[0109] (8) Inspect the uniformity and color consistency of the underwater granite concrete mixture.

[0110] (9) Test the dispersibility of bamboo chips in underwater granite concrete mixture.

[0111] For concrete mixtures, the performance indicators of apparent density, slump, slump change over 1 hour, cohesiveness, water retention, setting time, segregation, compressive strength, and flexural strength were tested according to the test methods in the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T 50080) and "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081). The test results are shown in Table 3.

[0112] Table 3 Test results of performance indicators of concrete mixtures

[0113]

[0114] 4. Verification of the first cast-in-place pile cast-in-place construction at the construction site.

[0115] (1) Engineering Application and Implementation. This application is based on the main bridge of a single-tower cable-stayed bridge of a bridge project in the Guangdong Delta Plain. # The pier consists of 30 bored cast-in-place piles, each with a diameter of 2.2m and a designed pile length of 128m. # The application and verification of the technology were demonstrated during the underwater concrete pouring construction of the first cast-in-place pile (-16).

[0116] (2) Cast-in-place pile grouting time. (This is from section 7.) # -16 cast-in-place piles were poured from the bottom to the top, totaling 537m³ of underwater granite concrete. 3 The total time was 822 minutes, shorter than the initial setting time of C35 underwater granite concrete (936–952 minutes). No blockage of the duct occurred during the underwater granite concrete pouring process.

[0117] (3) Concrete strength testing of cast-in-place piles. (This is part 7) # During the pouring of C35 underwater granite concrete for the -16 cast-in-place piles, representative samples of the underwater granite concrete mixture were extracted to prepare 6 sets of compressive strength specimens and 2 sets of flexural strength specimens. After 28 days of standard curing, the specimens were tested for compressive and flexural strength. The test results were as follows: compressive strength values ​​of 47.2 MPa, 46.0 MPa, 45.8 MPa, 46.5 MPa, 46.2 MPa, and 46.6 MPa; and flexural strength values ​​of 6.42 MPa and 6.38 MPa. # The compressive strength of the concrete in the -16 cast-in-place piles all meet the design requirements of C35.

[0118] (4) Integrity inspection of cast-in-place piles. (This refers to item 7) # The integrity of the -16 cast-in-place piles was tested using ultrasonic transmission method. The test results showed that the pile body was intact, with no mud inclusions, broken piles, or concrete segregation. The pile integrity category was Class I.

[0119] (5) Core sampling and compressive strength testing of cast-in-place pile concrete. (This is part 7) # -16 After the concrete of the cast-in-place pile was naturally cured for 28 days, core samples were taken for compressive strength testing. The test results were as follows: the compressive strength of the top concrete of the cast-in-place pile was 43.6 MPa, the compressive strength of the middle concrete was 45.4 MPa, and the compressive strength of the bottom concrete was 46.9 MPa. # The compressive strength of the concrete at the top, middle and bottom of the -16 cast-in-place piles all meet the design requirements of C35.

[0120] 5. Determine the design components of C35 underwater granite concrete.

[0121] The underwater granite concrete components, which have undergone mixing verification at an outdoor mixing plant and verification through the pouring of the first cast-in-place pile at the construction site, and meet the requirements specified in the "Technical Specifications for Highway Bridge and Culvert Construction" (JTG / T3650-2020), will be used as the design components for the main bridge 7 of the A-shaped single-tower cable-stayed bridge in this bridge project. # The remaining 29 large-diameter bored piles with a depth of over 100 meters serve as the basis for construction control.

[0122] The design components of C35 underwater granite concrete were determined. Based on indoor component design, outdoor mixing plant verification, on-site verification of the first cast-in-place pile pouring, and the allowable deviations (by mass) of the unit volume measurement of each component material (according to the allowable mass deviations for "centralized mixing plant" of concrete batching in the "Technical Specifications for Highway Bridge and Culvert Construction" (JTG / T3650-2020): the allowable deviation for coarse and fine aggregates is ±2%, and the allowable deviation for cement, dry admixtures, mixing water, and additives is ±1%), the design components of C35 underwater granite concrete (by mass method) were determined as follows:

[0123] The mass ratio of cement, fly ash, manufactured sand, crushed stone, bamboo chips, nano-calcium carbonate, gypsum, potassium polyacrylate, retarder, and mixing water is (354~360):(74.3~75.7):(746~774):(989~1027):(5.253~5.355):(10.70~10.90):(2.14~2.18):(0.0862~0.0878):(8.56~8.72):(171~173) (unit: kg / m³) 3 ).

[0124] 6. Technical effects.

[0125] The present invention, through the synergistic effect of the above-mentioned raw materials, prepares C35 underwater granite concrete. A comparison of Examples 1-2 and the comparative examples reveals the following technical effects:

[0126] (1) Apparent density increased by 10-20 kg / m³ 3 This can increase the free fall gravity of underwater granite concrete, overcoming the disadvantage of underwater granite concrete not being dense due to its small free fall gravity in the middle and top areas of the cast-in-place pile. This improves the compressive strength of underwater granite concrete, thereby increasing the vertical bearing capacity and deformation capacity of cast-in-place piles over 100 meters deep. It can also increase the lateral pressure of underwater granite concrete on the pile hole wall, making the pile hole wall more stable.

[0127] (2) The slump increased by 10-20 mm, which improved the fluidity of the underwater granite concrete. When the underwater granite concrete was poured with a pile length of 128 m, the underwater granite concrete was subjected to greater pressure due to its large free fall. This forced the underwater granite concrete to push the wall slurry in the pile hole to overflow and be discharged to the top of the pile and fill the pile hole. At the same time, it pushed the wall slurry in the pile hole to seep into the pile hole wall around the pile, forming a thin slurry layer between the underwater granite concrete and the soil layer of the pile hole wall. This prevented groundwater from seeping into the underwater granite concrete and wetting and corroding the bamboo chips in the underwater granite concrete, thus playing a role in corrosion protection for the bamboo chips. This improved the density, mechanical properties and durability of the underwater granite concrete.

[0128] (3) The initial setting time was extended by 317 to 333 minutes and the final setting time was extended by 323 to 345 minutes, so that the initial setting time of underwater granite concrete meets the requirements of underwater granite concrete pouring operation for large-diameter bored piles with a depth of over 100 meters, and ensures the quality of underwater granite concrete pouring for bored piles.

[0129] (4) The 7-day compressive strength increased by 2.3 to 3.0 MPa, and the 28-day compressive strength increased by 2.5 to 3.2 MPa, which improved the early and late compressive strength of underwater granite concrete in bored piles, thereby improving the density, mechanical properties and durability of underwater granite concrete, and further improving the vertical bearing capacity and deformation capacity of bored piles over 100 meters deep.

[0130] (5) The 28-day flexural strength increased by 0.34 to 0.44 MPa, overcoming the brittleness of underwater granite concrete, improving the flexural strength of cast-in-place piles over 100 meters deep, and thus improving the horizontal bearing capacity and deformation capacity of cast-in-place piles over 100 meters deep, which are affected by the flexural stiffness of the pile body section and the depth of the pile body into the soil.

[0131] (6) The C35 underwater granite concrete of this application was used in the main bridge of the A-shaped single-tower cable-stayed bridge of the aforementioned supporting project. #After the underwater granite concrete pouring construction of 30 Φ2.2m bored piles with a designed pile length of 128m, a comprehensive analysis was conducted and the following results were obtained: 1) The underwater granite concrete mixture exhibited good fluidity, cohesiveness, and water retention, with no segregation; 2) The initial setting time of the underwater granite concrete met the requirements for underwater granite concrete pouring operations for large-diameter bored piles exceeding 100 meters in depth; 3) The compressive strength and flexural strength of the underwater granite concrete were significantly improved, further enhancing the horizontal (vertical) bearing capacity and deformation capacity of the piles exceeding 100 meters in depth; 4) The bored piles were intact, without mud inclusions, broken piles, or concrete segregation, and the pouring quality was excellent. This effectively solved the technical problems of poor workability, short initial setting time, poor pouring quality, and low compressive and flexural strength of underwater concrete prepared using acidic granite as the concrete material.

[0132] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A C35 underwater granite concrete, characterized in that, The raw material components include the following mass ratios: Cement: Fly ash: Manufactured sand: Crushed stone: Bamboo chips: Nano calcium carbonate: Gypsum: Potassium polyacrylate Retarder The mass ratio of mixing water is (354-360):(74.3-75.7):(746-774):(989-1027):(5.253-5.355):(10.70-10.90):(2.14-2.18):(0.0862-0.0878):(8.56-8.72):(171-173), wherein the manufactured sand and crushed stone are both processed from crushed granite, and the density of the gypsum is 2.31 g / cm³. 3 White powdered gypsum; slow-release Agents include Polycarboxylate superplasticizer; the initial setting time of the granite concrete is 936-952 min; the bamboo chips include bamboo chips with a particle size of 0.15-4.75 mm and bamboo chips with a particle size of less than 0.15 mm; The method for preparing C35 underwater granite concrete is characterized by comprising the following steps: The manufactured sand and bamboo chips are mixed to obtain a mixed sand material; Cement, fly ash, nano-calcium carbonate and gypsum are added to the mixed sand in sequence, and the mixture is stirred to obtain fine material; Add crushed stone to the fine materials, stir and mix to make a mixture; Potassium polyacrylate, retarder, and mixing water are added to the mixture in sequence, and the mixture is stirred to obtain concrete mix. The concrete mix was poured to obtain C35 underwater granite concrete.

2. The C35 underwater granite concrete according to claim 1, characterized in that, The fineness modulus of the manufactured sand is 2.3~3.

0.

3. The C35 underwater granite concrete according to claim 1, characterized in that, The crushed stone is a continuous-sized crushed stone with a particle size of 5-25mm.

4. The C35 underwater granite concrete according to claim 1, characterized in that, The bamboo chips also undergo the following processing steps before use: soaking in a latex solution and drying.

5. The C35 underwater granite concrete according to claim 1, characterized in that, The nano-calcium carbonate has a particle size of 10-30 nm and a density of 2.8-3.1 g / cm³. 3 .

6. The C35 underwater granite concrete according to claim 1, characterized in that, Before adding the potassium polyacrylate, the process also includes preparing the potassium polyacrylate into an aqueous solution.

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