Low-rebound-rate wet-sprayed concrete and its mix proportion design method

Abstract

The application belongs to the technical field of concrete materials, and particularly relates to low-rebound-rate wet-spraying concrete and a mix proportion design method thereof. Components of the low-rebound-rate wet-spraying concrete of the application include cementitious materials, aggregates and water, and the water-binder ratio is 0.35-0.40; the full grading close void ratio of the aggregates is A, and the slurry volume ratio of the low-rebound-rate wet-spraying concrete is B, and 1.05<=B / A<=1.10. The low-rebound-rate wet-spraying concrete of the application has good pumpability and cohesion (the pumpability of the wet-spraying concrete is characterized by the slump and inverted slump emptying time indexes), can ensure the continuity of the spraying jet, and reduces the rebound rate of the wet-spraying concrete.

Description

Technical Field

[0001] This invention belongs to the field of concrete material technology, specifically relating to a low-resilience wet-sprayed concrete and its mix design method. Background Technology

[0002] With the rapid development of highways, railway tunnels, urban subways, and underground engineering in China, shotcrete has become an indispensable part of these construction projects. Wet shotcrete technology, due to its low dust and high strength during construction, is widely used in support engineering. However, due to factors such as wet shotcrete mix design and wet spraying operation processes, the rebound rate remains high, resulting in significant material waste and low construction efficiency, while also impacting project safety, quality, and the natural environment.

[0003] The mix design of shotcrete directly determines its performance. Strong cohesion and maintaining jet continuity can reduce the rebound rate of wet shotcrete; therefore, pumpability and cohesion have become crucial indicators of shotcrete mix performance.

[0004] Current methods for designing wet-mix shotcrete proportions rely on empirical data for key parameters such as cementitious material content and sand ratio, and use indicators like strength and slump to verify the suitability of the mix design. However, this approach fails to scientifically design concrete mix proportions from a fundamental perspective. Wet-mix shotcrete is a fine-aggregate concrete, and conventional slump tests are insufficient to accurately characterize its workability. Furthermore, laboratory tests cannot adequately characterize the pumpability and resilience of wet-mix shotcrete. Excessive concrete viscosity makes pumping difficult, while insufficient viscosity easily leads to rebound.

[0005] Therefore, an improved technical solution is needed to address the aforementioned problems. This solution should include a scientific concrete mix design method that fundamentally improves the pumpability and cohesiveness of the concrete mixture, thereby reducing rebound rate, minimizing material waste, increasing construction efficiency, and simultaneously ensuring project safety, quality, and environmental protection. Summary of the Invention

[0006] The purpose of this invention is to provide a low-rebound wet-mix shotcrete and its mix design method, so as to help solve or improve the problems of poor pumpability or excessive rebound rate of wet-mix shotcrete.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a low-resilience wet-sprayed concrete, wherein the components of the low-resilience wet-sprayed concrete include cementitious materials, aggregates and water, and the water-cement ratio is 0.35-0.40; the full-graded compact void ratio of the aggregate is A, and the slurry volume ratio of the low-resilience wet-sprayed concrete is B, where 1.05≤B / A≤1.10.

[0008] Preferably, the cementitious material includes cement and / or fly ash; the components of the low-resilience wet-sprayed concrete further include admixtures and / or rebound inhibitors; the admixtures include water-reducing agents and / or quick-setting agents.

[0009] Preferably, the amount of cementitious material is calculated based on the aggregate gradation, the total aggregate gradation density (A), and the range of B / A values:

[0010] ;

[0011] Wherein, cement usage = total amount of cementitious materials × (1- P 1);

[0012] Fly ash = Total amount of cementitious materials × P 1;

[0013] In the above formula, P 1 represents the mass percentage of fly ash in the cementitious material; ρ p1 ρ is the apparent density of fly ash, expressed in kilograms per cubic meter. c This is the apparent density of cement, expressed in kilograms per cubic meter.

[0014] Preferably, the fly ash content is 10%-20% of the total cementitious material content, the rebound inhibitor content is 5%, and the water-reducing agent content is 0.8%-1.2%.

[0015] Preferably, the rebound inhibitor comprises component X, component Y and water; component X is nano-calcium carbonate; component Y is a polystyrene-butadiene copolymer emulsion; and the mass ratio of component X, component Y and water is 3:1:7.

[0016] Preferably, the water-reducing agent has a water reduction rate of ≥25% and an air content of ≤6.0%; the water-reducing agent is a polycarboxylate water-reducing agent.

[0017] Preferably, the amount of the quick-setting agent is 2%-9% of the cementitious material; the quick-setting agent is an alkali-free quick-setting agent.

[0018] Preferably, the aggregate includes coarse aggregate and fine aggregate, wherein the coarse aggregate is crushed stone and the fine aggregate is river sand or manufactured sand; the particle size of the crushed stone is ≤16 mm.

[0019] Preferably, the low-rebound wet-mixed concrete comprises the rebound inhibitor, the pump slump of the low-rebound wet-mixed concrete is 210-230 mm, the slump emptying time is 4-10 s, and the concrete is in a continuous fluid state when being pumped; or, the low-rebound wet-mixed concrete comprises not including the rebound inhibitor, the pump slump of the low-rebound wet-mixed concrete is 160-200 mm, the slump emptying time is 4-10 s, and the concrete is in a continuous fluid state when being pumped.

[0020] The present invention also provides a low rebound shotcrete mix design method, which adopts the following technical solution: A low rebound shotcrete mix design method, comprising the following steps: (1) designing the mix composition based on at least slump and slump emptying time as control indicators; (2) determining a reasonable sand ratio by using the aggregate full-gradation particle analysis method and the minimum compact void ratio index; (3) using the ratio of the slurry volume ratio to the aggregate full-gradation compact void ratio as the basis for adjusting the slurry-aggregate ratio; (4) adding a rebound inhibitor; (5) determining a suitable water-cement ratio.

[0021] Beneficial effects:

[0022] The low-rebound wet-mix shotcrete provided by this invention has many advantages, such as good workability, low rebound rate, and strong applicability, making it suitable for various types of materials. Furthermore, the low-rebound wet-mix shotcrete of this invention has good pumpability and cohesive properties (characterized by slump and slump emptying time), ensuring the continuity of the sprayed jet and thus reducing the rebound rate of the wet-mix shotcrete. Attached Figure Description

[0023] 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. Wherein:

[0024] Figure 1 This is a schematic diagram of the structure of low-rebound wet-sprayed concrete used for spraying in different directions, according to an embodiment of the present invention.

[0025] Figure 2 This is the Fuller theory curve;

[0026] Figure 3 This is the porosity curve for a fully graded, tightly packed system.

[0027] Figure label:

[0028] 1-Arch; 2-Side wall; 3-Arch base. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0030] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0031] This invention addresses the problems of poor pumpability or high rebound rate in current wet-mixed shotcrete by providing a low-rebound-rate wet-mixed shotcrete. The components of the low-rebound-rate wet-mixed shotcrete in this embodiment include cementitious materials, aggregates, and water. The water-cement ratio (mass ratio of water to cementitious materials) is 0.35-0.40 (e.g., 0.35, 0.36, 0.37, 0.38, 0.39, or 0.40). The aggregate has a fully graded compact void ratio A, and the paste volume of the low-rebound-rate wet-mixed shotcrete is B, with 1.05 ≤ B / A ≤ 1.10 (e.g., B / A is 1.05, 1.055, 1.06, 1.065, 1.07, 1.075, 1.08, 1.085, 1.09, 1.095, or 1.10).

[0032] This invention aims to improve the pumpability and reduce the rebound rate of wet-mix shotcrete by achieving a B / A ratio (slurry volume ratio / full-graded compacted void fraction) ≥ 1.05. The low-rebound wet-mix shotcrete provided by this invention has many advantages, such as good workability, low rebound rate, and wide applicability, suitable for various types of materials. Furthermore, the low-rebound wet-mix shotcrete of this invention exhibits good pumpability (characterized by slump and slump emptying time) and cohesive properties, ensuring the continuity of the sprayed jet, thereby reducing the rebound rate of the wet-mix shotcrete.

[0033] Preferably, when calculating the volume ratio (B) of wet-mixed shotcrete, the overall air content of the low-rebound wet-mixed shotcrete is controlled to be 2%-4% (e.g., 2%, 2.3%, 2.8%, 3%, 3.4%, 3.7% or 4%), and the volume ratio of the slurry is limited to 0.33-0.38 (e.g., 0.33, 0.34, 0.35, 0.36, 0.37 or 0.38).

[0034] In a preferred embodiment of the low-rebound wet-mixed shotcrete of the present invention, the cementitious material includes cement and / or fly ash; the components of the low-rebound wet-mixed shotcrete also include admixtures and / or rebound inhibitors; the admixtures include water-reducing agents and / or accelerators. Fly ash in this invention mainly serves to replace cement and improve the cohesion and workability of the wet-mixed shotcrete; the rebound inhibitor in this invention can improve the weak links in the structure of the wet-mixed shotcrete, namely the voids between cement hydration products (or secondary hydration products), thereby improving various properties of the wet-mixed shotcrete, such as mixture properties, mechanical properties, and long-term durability.

[0035] In a preferred embodiment of the low-resilience wet-sprayed concrete of the present invention, the amount of cementitious material is calculated based on the aggregate gradation, the total aggregate gradation density A, and the range of B / A values:

[0036] The volume ratio of the slurry (B) = k × A (k = B / A, with a selection range of 1.05-1.10)

[0037] ;

[0038] Wherein, cement usage = total amount of cementitious materials × (1- P 1);

[0039] Fly ash = Total amount of cementitious materials × P 1;

[0040] In the above formula, P 1 represents the mass percentage of fly ash in the cementitious material; ρ p1 ρ is the apparent density of fly ash, expressed in kilograms per cubic meter. c This is the apparent density of cement, expressed in kilograms per cubic meter.

[0041] In a preferred embodiment of the low-rebound wet-mixed shotcrete of the present invention, the amount of fly ash is 10%-20% of the total amount of cementitious materials (e.g., 10%, 13%, 15%, 17% or 20%), the amount of water-reducing agent is 0.8%-1.2% of the total amount of cementitious materials (e.g., 0.8%, 0.9%, 1.0%, 1.1% or 1.2%), and the amount of rebound inhibitor is 5%.

[0042] In a preferred embodiment of the low-rebound wet-mixed shotcrete of the present invention, the rebound inhibitor comprises component X, component Y, and water; wherein component X is nano-calcium carbonate, component Y is polystyrene-butadiene copolymer emulsion, and the mass ratio of component X, component Y, and water is 3:1:7. Specifically: 1) The present invention obtains the rebound inhibitor by preparing components X, Y, and water in a specific ratio. Component B can demulsify to form an adhesive, improving the adhesion between the shotcrete and the tunnel substrate. The hydrated component X (nano-calcium carbonate) can form a composite material with component Y (polystyrene-butadiene copolymer emulsion). According to composite material theory, the hydrated nanoparticles are a flocculated structure, dispersed in the demulsified polystyrene-butadiene copolymer emulsion, improving the viscosity and viscosity of the demulsified polystyrene-butadiene copolymer emulsion, thereby further improving the adhesion between the shotcrete and the tunnel substrate. 2) When no quick-setting agent is added, the polymer emulsion (especially the excess emulsifier in the polymer emulsion) can be adsorbed around the nanoparticles. X and Y form a synergistic effect, which improves the dispersibility of nano-calcium carbonate, thereby improving the filling of voids, water reduction, flocculation network, and cohesiveness of nano-calcium carbonate in concrete.

[0043] In a preferred embodiment of the low-resilience wet-mixed shotcrete of the present invention, the water reduction rate of the polycarboxylate superplasticizer is ≥25%, and the air content is ≤6.0%. Preferably, the air content of the polycarboxylate superplasticizer is ≤3.0%.

[0044] In a preferred embodiment of the low-resilience wet-sprayed concrete of the present invention, the aggregate includes coarse aggregate and fine aggregate, wherein the coarse aggregate is crushed stone and the fine aggregate is river sand or manufactured sand; the particle size of the crushed stone is ≤16 mm.

[0045] In a preferred embodiment of the low-resilience wet-sprayed concrete of the present invention, the components of the low-resilience wet-sprayed concrete further include an accelerator; the amount of the accelerator is 2%-9% of the total amount of cementitious materials (e.g., 2%, 4%, 6%, 8% or 9%); the accelerator is an alkali-free accelerator.

[0046] In a preferred embodiment of the present invention, when the low-resilience wet-sprayed concrete of the present invention is used for horizontal spraying (such as sidewall construction), the amount of quick-setting agent is 2%-4% (e.g., 2%, 2.5%, 3%, 3.5% or 4%); when the low-resilience wet-sprayed concrete of the present invention is used for upward-angle spraying (such as tunnel arch construction), the amount of quick-setting agent can be 7%-9% (e.g., 7%, 7.5%, 8%, 8.5% or 9%).

[0047] In a preferred embodiment of the present invention, the low-resilience wet-mixed shotcrete comprises a rebound inhibitor, has an initial slump of 210-230 mm (e.g., 210 mm, 215 mm, 220 mm, 225 mm, or 230 mm), a slump emptying time of 4-10 s (e.g., 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, or 10 s), and is in a continuous fluid state during slump emptying; or, in a low-resilience wet-mixed shotcrete, does not comprise a rebound inhibitor, has an initial slump of 160-200 mm (e.g., 160 mm, 170 mm, 180 mm, 190 mm, or 200 mm), a slump emptying time of 4-10 s, and is in a continuous fluid state during slump emptying. The resulting low-resilience wet-mixed shotcrete exhibits better homogeneity.

[0048] The present invention also proposes a mix design method for low rebound rate wet shotcrete. The mix design method for low rebound rate shotcrete in the embodiments of the present invention includes the following steps: (1) adjusting the proportion of each material component with at least slump and slump emptying time as control indicators; (2) determining a reasonable sand ratio by aggregate full gradation particle analysis method and minimum compact void ratio index; (3) using the ratio of paste volume ratio to aggregate compact void ratio as the basis for adjusting paste-aggregate ratio; (4) adding rebound inhibitor; (5) determining a suitable water-cement ratio.

[0049] This invention relates to a mix design method for low-rebound shotcrete, focusing on properties such as pumpability and low rebound rate. Based on the principles of concrete fluidity and the differences in raw material characteristics, it proposes key indicators (characterizing the pumpability of wet-mixed shotcrete) such as the ratio of slurry volume ratio to aggregate porosity and the concrete inversion voiding time. By selecting an appropriate slurry volume ratio and aggregate porosity ratio, the amount of slurry filling and wrapping the aggregate gaps is controlled, and the thickness of the cementitious material slurry filling layer and lubrication layer in the concrete is optimized. The concrete viscosity is characterized by the concrete inversion voiding time, which serves as the main control indicator in mix design. This method then enables the design of the concrete mix proportion, resulting in concrete with good fluidity and cohesiveness, ensuring the continuity of the sprayed jet, thereby reducing the rebound rate of wet-mixed shotcrete. This method produces wet-mixed shotcrete with good workability, low rebound, and strong applicability, suitable for various different materials.

[0050] The mix design method for low-rebound shotcrete of the present invention is a volumetric method derived from the "Specification for Mix Design of Ordinary Concrete". The method in the specification is to first calculate the water-cement ratio based on the strength, determine the water consumption by referring to tables based on experience, then calculate the cementitious materials, and finally calculate the amount of sand and crushed stone. This method empirically fixes the amount of cementitious materials, neglecting the influence of sand and crushed stone properties on shotcrete. Shotcrete mix designs based on this method are essentially unapplicable. The method described in this invention emphasizes the filling effect of slurry volume on aggregate voids and the thickness of the lubricating layer. It sets a range for the ratio of slurry volume to aggregate compaction porosity and calculates the amount of cementitious materials based on this ratio. The calculation process involves first calculating the water-cement ratio, obtaining a reasonable sand ratio based on particle size analysis and aggregate full-grade compaction porosity tests, then calculating the slurry volume ratio based on the selected ratio of (slurry volume ratio / aggregate full-grade compaction porosity), then calculating the amount of cementitious materials and water, and finally calculating the amount of sand and crushed stone based on the volumetric method in the specifications and the known sand ratio. This method fully considers the differences in the properties of sand and crushed stone, ensuring the workability of shotcrete. Concrete viscosity and slump are used as test indicators, and the amount of polycarboxylate superplasticizer is fine-tuned.

[0051] In some preferred embodiments of the present invention, the main materials used in the mix design of shotcrete include:

[0052] I. In some embodiments, the ratio of slurry volume ratio (B) to aggregate full-grade compact void ratio (A) is used as a key parameter for concrete mix design, and is a key indicator affecting concrete pumping and jetting:

[0053] B / A = 1.05 - 1.10

[0054] The volume of the slurry, comprising cementitious materials (cement and / or fly ash are used as cementitious materials in this invention), water, admixtures (water-reducing agents and / or accelerators are used as admixtures in this invention), the volume of gas in the concrete, and the slurry's ability to fill the voids in the aggregate and the lubrication layer, directly affects the workability of the concrete. If the B / A ratio is too low, the slurry will have difficulty filling the voids in the aggregate or the lubrication layer will be thin, making concrete pumping difficult or prone to clogging. A suitable ratio makes the concrete easy to work with, and the shotcrete will also have greater adhesion. If the B / A ratio is too high, it results in economic waste and makes the shotcrete too viscous, affecting its workability.

[0055] II. In some embodiments, material parameters are calculated by using the ratio of slurry volume ratio (B) to aggregate full-gradation compact void ratio (A). The specific calculation process is as follows:

[0056] Cement: Grade 42.5 ordinary Portland cement or Portland cement

[0057] Mineral admixtures: Fly ash, Class F, Grade II

[0058] River sand: Medium sand (fineness modulus of 2.3-3.0)

[0059] Crushed stone: 5-16 mm

[0060] Water-cement ratio: The water-cement ratio for concrete should be selected as 0.35 to 0.40;

[0061] Types and dosages of admixtures: 0.8% to 1.2% polycarboxylate superplasticizer; the dosage of alkali-free quick-setting agent (manufacturer: Anhui Zhongtie Engineering Materials Technology Co., Ltd.) in the sidewall area can be controlled at 2% to 4%, and the dosage in the arch area should be controlled at 7% to 9%.

[0062] The wet-mix shotcrete mix design method of the present invention mainly includes the following steps:

[0063] Step 1: Determine the apparent density of various raw materials. The test results are shown in Table 1 below:

[0064] Table 1

[0065]

[0066] Step 2: Based on Fuller's maximum theoretical density principle, select n=0.3 and n=0.6 as the upper and lower limits of the wet-mixed shotcrete gradation to achieve a relatively dense state. Simultaneously, based on aggregate sieve analysis data and past construction experience, select different "crushed stone-sand sample" mixing ratios to plot gradation curves and determine the mixing ratio range.

[0067] Table 2

[0068]

[0069] Table 3 Example of coarse aggregate gradation and screening calculation

[0070]

[0071] Among them, G1, G2, G3, G4, G5, G6, G7, and G8 are the cumulative sieve residues (%) of each stage of the crushed stone screening process.

[0072] S1, S2, S3, S4, S5, and S6 represent the cumulative sieve residue (%) of each grade of the sand sieve.

[0073] β1, β2, and β3 are the estimated sand ratios;

[0074] P 1-1 P 1-2 P 1-3 P 1-4 P 1-5 P 1-6 P1-7 P 1-8 The passing rates of each sieve, calculated for sand and gravel with a simulated sand ratio of 1, are respectively.

[0075] P 1-1 =G1×(1-β1),P 1-2 =G2×(1-β1),P 1-3 =G3×(1-β1)+S1×β1;

[0076] P 1-4 =G4×(1-β1)+S2×β1、P 1-5 =G5×(1-β1)+S3×β1;

[0077] P 1-6 =G6×(1-β1)+S4×β1、P 1-7 =G7×(1-β1)+S5×β1;

[0078] P 1-8 =G8×(1-β1)+S6×β1;

[0079] Based on past construction experience, different "crushed stone-sand sample" mixing ratios were selected to draw gradation curves (e.g., Figure 2 As shown in the figure, the curve is compared with the maximum theoretical density of FULLER, and a smooth curve between the upper and lower limits of the reference is selected to determine a more suitable range of coarse and fine aggregate blending ratios; by detecting the compact porosity under different "crushed stone-sand sample" blending ratios, the optimal coarse and fine aggregate blending ratio is determined.

[0080] Step 3: Aggregate full-gradation compact void ratio

[0081] In this invention, based on sieving results, we pre-select 3-5 groups of well-graded sand ratios, namely sand ratio 1, sand ratio 2, sand ratio 3, sand ratio 4, and sand ratio 5. For each sand ratio, samples are weighed and mixed according to the ratio of sand:gravel = sand ratio:(1-sand ratio), stirred evenly, and then filled into a 5 L volumetric cylinder in three layers. After each layer is filled, the cylinder is agitated 25 times from side to side. The weight of the filled mixture, m, is then obtained. 混 Calculate the total porosity of aggregates across all gradations:

[0082] Pj=Vm 混 ×

[0083] Fully graded compact porosity under different sand ratios, such as Figure 3 As shown.

[0084] By drawing a graph, we can find the sand ratio corresponding to the minimum compaction void ratio, which is the sand ratio selected for this mix design.

[0085] Step 4: Select the water-to-glue ratio, which should be between 0.35 and 0.40.

[0086] Step 5: Determine the slurry volume ratio

[0087] Based on past construction experience and data analysis, this invention adds the slurry volume ratio index to the mix design. It proposes that when the colloid volume ratio is 1.05 to 1.10 times the full-graded compact void ratio of the aggregate, the designed mix concrete has better pumpability and cohesive properties, can ensure the continuity of the sprayed jet, and reduce the rebound rate of wet-sprayed concrete.

[0088] (Because the air content in concrete is unstable, the volume of gas is not considered in the volume of the grout.) V 砼 =1);

[0089] Slurry volume ratio = k × Pj (k=1.05-1.10, Pj (for aggregate full gradation and compacted void ratio).

[0090] ;

[0091] ;

[0092] (V) 砼 1m 3 );

[0093] m c m p1 m w m a m s m g —These represent the masses of cement, mineral admixtures (fly ash is used as a mineral admixture in this invention), water, additives (water-reducing agents and additives are used in this invention), sand, and crushed stone in concrete, in kilograms (kg).

[0094] ρ c ρ p1 ρ w ρ a ρ s ρ g —These represent the densities of cement, mineral admixtures, water, additives, sand, and crushed stone in concrete, expressed in kilograms per cubic meter (kg / m³). 3 );

[0095] α — Air content of concrete, in cubic meters (m³) 3 The air content of concrete should be controlled at 2%-4%.

[0096] Step 6: Calculate the total amount of cementitious materials.

[0097] The percentage of the mass of the mineral admixture (fly ash is used as the mineral admixture in this invention) to the total mass of the cementitious material is denoted as: P 1. It is recommended to use 0-20% air content; in the initial calculation, the air content can be initially set at 2% (the air content of sprayed concrete is usually 1.5%-4%, so setting it to 2% will result in a smaller deviation).

[0098] ;

[0099] Calculate cement usage = Total amount of cementitious materials × (1- P 1);

[0100] Fly ash dosage = Total amount of cementitious materials × P 1.

[0101] Understandably, by using the full-graded compaction void ratio, the optimal sand ratio can be selected, which is more precise and quantitative than traditional empirical or graphical methods. Different sand coarseness and large differences in coarse aggregate particle shape result in different corresponding amounts of cementitious materials. This method can quickly and accurately calculate the appropriate amount of cementitious materials, which is faster and more convenient than traditional empirical methods.

[0102] Step 7 In some embodiments, the shotcrete mix design includes workability parameters.

[0103] The operating performance parameters are as follows:

[0104] Slump 210-230mm (with rebound inhibitor, suitable for upward spraying areas)

[0105] Slump 160-200mm (without rebound inhibitor, suitable for horizontal or downward spraying).

[0106] The slump discharge time is 4-10 seconds, and the outflow is a continuous fluid.

[0107] Slump is used to characterize the workability of concrete, and its range is relatively broad. Generally speaking, a large slump indicates good concrete fluidity, thin paste, and weak paste binding force on aggregates. After spraying, the concrete will flow or the aggregates will easily rebound during spraying. If the slump is too small, the concrete will be difficult to pump and the spray jet speed will be slow.

[0108] The slump test reflects the viscosity of concrete to a certain extent. After adding rebound inhibitors, the viscosity of shotcrete increases significantly, which is also a key way to control the rebound rate of shotcrete. Therefore, controlling the slump test time is a key indicator of the workability of shotcrete.

[0109] Slump and slump discharge time are both easy to operate and reliable indicators in mix design and construction quality control, and the methods have very strong practical value.

[0110] Based on the above research, this invention focuses on the material parameters and workability of shotcrete. Based on the theory of concrete material filling, a new material usage design method is constructed, and workability indicators such as slump and slump emptying time are introduced, which effectively ensures the pumping and rebound effect of shotcrete.

[0111] Step 9 In some embodiments, a rebound inhibitor is used, which is in a liquid state.

[0112] The rebound inhibitor comprises component X, component Y, and water; wherein, component X is nanomaterial (nano-calcium carbonate), component Y is polymer (polystyrene-butadiene copolymer emulsion) that improves bonding strength, and the mass ratio of component X, component Y, and water is 3:1:7.

[0113] Step 10: In some embodiments, a water-reducing agent is used, which is a polycarboxylate high-performance water-reducing agent, at 1% of the amount of cementitious material, with a water reduction rate of more than 25%. The dosage is adjusted according to the performance of the water-reducing agent, the adaptability of the cementitious material, and the performance indicators of the concrete.

[0114] Step 11 In some instances, a accelerator, specifically an alkali-free accelerator, was used.

[0115] The low-resilience wet-sprayed concrete of the present invention is sprayed horizontally or downwards, and the quick-setting agent is added at a dosage of 2%-4% of the total amount of cementitious materials.

[0116] The low-resilience wet-sprayed concrete of the present invention is sprayed upward, and the dosage of the quick-setting agent is 7%-9% of the total amount of cementitious materials.

[0117] Among them, the rebound rate = total rebound mass / total concrete volume.

[0118] The mix design method for low-rebound shotcrete of this invention considers the design and construction requirements of different parts. Different structural parts have different characteristics, such as the mechanical behavior of the structure, which places different requirements on the mechanical properties, workability, and durability of concrete. Mechanical properties mainly include the cubic compressive strength, flexural strength, and deformation capacity of concrete. Therefore, the mix design should be adjusted according to the characteristics of different structural parts. This method determines the appropriate amount of cementitious materials, the amount of mineral admixtures (fly ash is used as a mineral admixture in this invention), the full gradation method of aggregates, and the minimum porosity index to determine a reasonable sand ratio. By adjusting the ratio of the paste volume ratio to the aggregate compaction porosity, the amount of cementitious materials and water-reducing agent is adjusted to determine the appropriate water-cement ratio range. Different amounts of accelerators are determined according to the requirements of different construction parts.

[0119] The following detailed description of the low-resilience wet-sprayed concrete and its mix design method of the present invention is provided through specific embodiments.

[0120] The water-reducing agent used in the following examples is a polycarboxylate water-reducing agent; the quick-setting agent is an alkali-free quick-setting agent.

[0121] Example 1

[0122] The components of the low-resilience wet-mixed shotcrete in this embodiment include: coarse sand (fineness modulus of 3.4) and cement dosage of 477 kg / m³. 3 The fly ash usage is 53 kg / m³. 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 185 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 5.30 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and coarse sand, with coarse sand dosage at 963 kg / m³. 3 The amount of crushed stone used is 727 kg / m³. 3 The aggregate has a fully graded compact void ratio (A) of 35%, a paste volume ratio (B) of 37.8%, and a B / A ratio of 1.08. The accelerator dosage is 7% of the total cement and fly ash content.

[0123] In this embodiment, the low-rebound wet-sprayed concrete is used for upward spraying construction (i.e., arch construction).

[0124] The preparation method of low rebound wet sprayed concrete in this embodiment is as follows: at the concrete mixing plant, concrete is mixed according to the materials and dosages mentioned in this example, such as cement, fly ash, sand, crushed stone, water, and water-reducing agent. The mixing time is 180 seconds. The concrete is transported to the construction site by a concrete mixer truck and sprayed using a wet spraying robot. At the end of the spraying, the wet spraying robot sprays out an alkali-free quick-setting agent according to the dosage requirements. The concrete and quick-setting agent mix in the air and adhere to the sprayed surface.

[0125] Example 2

[0126] The components of the low-resilience wet-mixed shotcrete in this embodiment include: coarse sand (fineness modulus of 3.2), cement dosage of 450 kg / m³, and fly ash dosage of 50 kg / m³. 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 175 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 5.00 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and coarse sand, with coarse sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 790 kg / m³. 3The aggregate's overall gradation density (A) is 33%, the paste volume ratio (B) is 35.8%, and B / A = 1.09. The accelerator dosage is 7% of the total cement and fly ash content.

[0127] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0128] Example 3

[0129] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 478 kg / m³. 3 The fly ash content is 0, and the water consumption is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³. 3 The aggregate has a full-graded compact void ratio (A) of 32%, a paste volume ratio (B) of 34.4%, B / A = 1.07, and the accelerator dosage is 7% of the total cement and fly ash content.

[0130] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0131] Example 4

[0132] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 430 kg / m³. 3 The fly ash usage is 48 kg / m³ 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³. 3 The aggregate has a full-graded compact void ratio (A) of 32%, a paste volume ratio (B) of 34.7%, B / A = 1.08, and the accelerator dosage is 7% of the total cement and fly ash content.

[0133] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0134] Example 5

[0135] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³. 3 The aggregate has a full-graded compact void ratio (A) of 32%, a paste volume ratio (B) of 34.9%, B / A = 1.09, and the accelerator dosage is 7% of the total cement and fly ash content.

[0136] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0137] Example 6

[0138] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The dosage of quick-setting agent is 7% of the total amount of cement and fly ash; among which, the full-grade compact void ratio (A) of aggregate is 32%, the slurry volume ratio (B) is 34.9%, and B / A=1.09.

[0139] The rebound inhibitor dosage is 24 kg / m² 3 Component X is nano-calcium carbonate, and component Y is a polystyrene-butadiene copolymer emulsion; the mass ratio of component X: component Y: water is 3:1:7.

[0140] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Embodiment 1.

[0141] Example 7

[0142] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 4% of the total cement and fly ash content.

[0143] The low-rebound wet-sprayed concrete of this embodiment is used for horizontal spraying construction (such as sidewall construction), and the preparation method is the same as in Embodiment 1.

[0144] Comparative Example 1

[0145] The components of the low-resilience wet-mix shotcrete in this comparative example include:

[0146] Coarse sand (fineness modulus 3.4) was used, and the cement dosage was 490 kg / m³. 3 The fly ash usage is 54 kg / m³. 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 190 kg / m³. 3 The water-cement ratio is 0.35, the water-reducing agent dosage is 5.40 kg / m³, and the water-reducing agent dosage is 1% of the cementitious material; the aggregates used are crushed stone and sand, with a sand dosage of 963 kg / m³. 3 The amount of crushed stone used is 727 kg / m³. 3 The aggregate's overall compact porosity (A) is 35%, the paste volume ratio (B) is 38.8%, and B / A = 1.11. The accelerator dosage is 7% of the total cement and fly ash content.

[0147] The low-rebound wet-sprayed concrete in this comparative example is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Example 1.

[0148] Comparative Example 2

[0149] The components of the low-rebound wet-mix shotcrete in this comparative example include: coarse sand (fineness modulus of 3.4), and cement content of 460 kg / m³. 3 The fly ash usage is 51 kg / m³. 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 178 kg / m³. 3The water-cement ratio is 0.35, and the water-reducing agent dosage is 5.10 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and coarse sand, with coarse sand dosage at 963 kg / m³. 3 The amount of crushed stone used is 727 kg / m³. 3 The aggregate has a full-graded compact void ratio (A) of 35%, a paste volume ratio (B) of 36.5%, B / A = 1.04, and the accelerator dosage is 7% of the total cement and fly ash content.

[0150] The low-rebound wet-sprayed concrete in this comparative example is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Example 1.

[0151] Comparative Example 3

[0152] The components of the low-resilience wet-mix shotcrete in this comparative example include: coarse sand (fineness modulus of 3.2) and cement dosage of 459 kg / m³. 3 The fly ash usage is 51 kg / m³. 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 179 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 5.10 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and coarse sand, with coarse sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 790 kg / m³. 3 The aggregate's overall compact porosity (A) is 33%, the paste volume ratio (B) is 36.5%, and B / A = 1.11. The accelerator dosage is 7% of the total cement and fly ash content.

[0153] The low-rebound wet-sprayed concrete in this comparative example is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Example 1.

[0154] Comparative Example 4

[0155] The components of the low-resilience wet-mix shotcrete in this comparative example include: coarse sand (fineness modulus of 3.2) and cement dosage of 430 kg / m³. 3 The fly ash usage is 48 kg / m³ 3 The amount of pulverized coal added is 10% of the total amount of cementitious materials, and the water usage is 168 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and coarse sand, with coarse sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 790 kg / m³. 3The aggregate's overall compact porosity (A) is 33%, the paste volume ratio (B) is 34.4%, and B / A = 1.04. The accelerator dosage is 7% of the total cement and fly ash content.

[0156] The low-rebound wet-sprayed concrete in this comparative example is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Example 1.

[0157] Comparative Example 5

[0158] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 358 kg / m³. 3 The fly ash usage is 120 kg / m³ 3 The amount of pulverized coal added is 25% of the total amount of cementitious materials, and the water usage is 170 kg / m³. 3 The water-cement ratio is 0.36, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³. 3 The aggregate has a full-graded compact void ratio (A) of 32%, a paste volume ratio (B) of 35.0%, B / A = 1.09, and the accelerator dosage is 7% of the total cement and fly ash content.

[0159] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0160] Comparative Example 6

[0161] The components of the low-rebound wet-mix shotcrete in this comparative example include: medium sand (fineness modulus of 2.8), and cement dosage of 463 kg / m³. 3 No fly ash was added, and the water consumption was 164 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.63 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate has a full-graded compact void ratio (A) of 32%, a paste volume ratio (B) of 33.4%, B / A = 1.04, and the accelerator dosage is 7% of the total cement and fly ash content.

[0162] The low-rebound wet-sprayed concrete in this comparative example is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Example 1.

[0163] Comparative Example 7

[0164] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 5.73 kg / m³. 3 The water-reducing agent dosage is 1.2% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's total gradation density (A) is 32%, the paste volume ratio (B) is 34.9%, B / A = 1.09, and the accelerator dosage is 7% of the total cement and fly ash content.

[0165] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0166] Comparative Example 8

[0167] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.30 kg / m³. 3 The water-reducing agent dosage is 0.9% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) was 32%, its paste volume ratio (B) was 34.9%, and B / A = 1.09. The accelerator dosage was 7% of the total cement and fly ash content.

[0168] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0169] Comparative Example 9

[0170] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.30 kg / m³. 3 The water-reducing agent dosage is 0.9% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 7% of the total cement and fly ash content.

[0171] The rebound inhibitor dosage is 24 kg / m² 3 Component X is nano-calcium carbonate, and component Y is a polystyrene-butadiene copolymer emulsion; the mass ratio of component X: component Y: water is 3:1:7.

[0172] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0173] Comparative Example 10

[0174] The components of the low-rebound wet-mix shotcrete in this comparative example include: medium sand (fineness modulus of 2.8), and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.36, and the water-reducing agent dosage is 5.73 kg / m³. 3 The water-reducing agent dosage is 1.2% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 7% of the total cement and fly ash content.

[0175] The rebound inhibitor dosage is 24 kg / m² 3 Component X is nano-calcium carbonate, and component Y is a polystyrene-butadiene copolymer emulsion; the mass ratio of component X: component Y: water is 3:1:7.

[0176] The low-rebound wet-sprayed concrete in this comparative example is used for upward spraying construction (such as arch construction), and the preparation method is the same as in Example 1.

[0177] Comparative Example 11

[0178] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.36, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 5% of the total cement and fly ash content.

[0179] The rebound inhibitor dosage is 24 kg / m² 3 Component X is nano-calcium carbonate, and component Y is a polystyrene-butadiene copolymer emulsion; the mass ratio of component X: component Y: water is 3:1:7.

[0180] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0181] Comparative Example 12

[0182] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.36, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and medium sand, with the medium sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 10% of the total cement and fly ash content.

[0183] The rebound inhibitor dosage is 24 kg / m² 3 Component X is nano-calcium carbonate, and component Y is a polystyrene-butadiene copolymer emulsion; the mass ratio of component X: component Y: water is 3:1:7.

[0184] The low-rebound wet-sprayed concrete in this embodiment is used for upward spraying construction (i.e., arch construction), and the preparation method is the same as in Embodiment 1.

[0185] Comparative Example 13

[0186] The only difference between this embodiment and Example 6 is that the rebound inhibitor consists only of component X and water (the mass ratio of component X to water is 3:7); all other aspects are the same as in Example 6.

[0187] Comparative Example 14

[0188] The only difference between this embodiment and Embodiment 6 is that the rebound inhibitor consists only of component Y and water (the mass ratio of component Y to water is 1:7); all other aspects are consistent with Embodiment 6.

[0189] Comparative Example 15

[0190] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and sand, with sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 2% of the total cement and fly ash content.

[0191] The low-rebound wet-sprayed concrete of this embodiment is used for horizontal spraying construction (such as sidewall construction), and the preparation method is the same as in Embodiment 1.

[0192] Comparative Example 16

[0193] The components of the low-resilience wet-mixed shotcrete in this embodiment include: medium sand (fineness modulus of 2.8) and cement dosage of 382 kg / m³. 3 The fly ash usage is 96 kg / m³ 3 The amount of pulverized coal added is 20% of the total amount of cementitious materials, and the water usage is 169 kg / m³. 3 The water-cement ratio is 0.35, and the water-reducing agent dosage is 4.78 kg / m³. 3 The water-reducing agent dosage is 1% of the cementitious material; the aggregate consists of crushed stone and sand, with sand dosage at 910 kg / m³. 3 The amount of crushed stone used is 840 kg / m³ 3 The aggregate's overall compact porosity (A) is 32%, the paste volume ratio (B) is 34.9%, and B / A = 1.09. The accelerator dosage is 6% of the total cement and fly ash content.

[0194] The low-rebound wet-sprayed concrete of this embodiment is used for horizontal spraying construction (such as sidewall construction), and the preparation method is the same as in Embodiment 1.

[0195] The main parameters of the wet-mixed shotcrete in Examples 1-7 and Comparative Examples 1-16 are summarized in Table 4 below:

[0196]

[0197] It can be seen from Table 4 above:

[0198] Three types of sand with different fineness were used in the examples. The comparison revealed that variations in sand fineness affected the overall compactness and porosity of the aggregate. To ensure good workability of the concrete, the amount of cementitious material increased with increasing overall compactness and porosity of the aggregate, which aligns with practical experience.

[0199] Comparative Example 1, Example 1, and Comparative Example 2 all used coarse sand with a fineness modulus of 3.4. The total compacted void ratio of the crushed stone and coarse sand was 35%, requiring a large amount of slurry to fill the voids. When the ratio of the slurry volume ratio to the total compacted void ratio was less than 1.05 (Comparative Example 2), the wet-mixed shotcrete exhibited poor cohesion and was in a loose state. During the slump test, it showed discontinuous flow, a long slump test time, and difficulty in wet-mixed pumping, easily causing pipe blockage. When the ratio of the slurry volume ratio to the total compacted void ratio was greater than 1.10 (Comparative Example 1), the amount of cementitious material used in the concrete was large, the concrete viscosity increased, the slump test time was long, the viscosity was high, the pumping speed was slow, and the rebound rate was high.

[0200] Comparative Examples 3, 2, and 4 used coarse sand with a fineness modulus of 3.2 and a total aggregate compaction void ratio of 33%. When the slurry volume ratio / compaction void ratio was less than 1.05 (Comparative Example 4), the wet-mixed sprayed concrete slump flow was discontinuous, the slump flow time was 22 s, pumping was difficult, and the rebound rate was 23%. When the slurry volume ratio / compaction void ratio was greater than 1.10 (Comparative Example 3), too much cementitious material was used, the wet-mixed sprayed concrete slump flow time was 16 s, the concrete viscosity was high, the pumping speed was slow, and the rebound rate was 19%.

[0201] Examples 3, 4, 5, and Comparative Example 5 used the same amount of cementitious material, but with fly ash content of 0%, 10%, 20%, and 25%, respectively. The slurry volume ratio gradually increased, and the slurry volume ratio / dense porosity value was greater than 1.05. The slump time was 7-9 seconds. However, when the fly ash content was 25%, the rebound rate was 19%. This was mainly because the increased fly ash content resulted in low early setting strength of the wet-mixed shotcrete, insufficient to support its own weight, leading to easy breakage. When the cementitious material content was 478 kg / m³... 3At that time, the fly ash content should be controlled within 20%.

[0202] Compared with Comparative Example 3 and Comparative Example 6, the cementitious material in Example 3 was 478 kg / m³. 3 The slurry volume ratio / compressed porosity value was 1.07; the cementitious material dosage in Comparative Example 6 was 460 kg / m³. 3 At that time, the slurry volume ratio / dense porosity was 1.04. In Example 3, the concrete in the slump evacuation test chamber was in a continuous flow state, with an evacuation time of 8 seconds, smooth pumping, and a rebound rate of 13%. In contrast, in Comparative Example 6, the slump evacuation time was 22 seconds, the flow was discontinuous, the pumping speed was slow, and the rebound rate was 23%. In Example 3, the slurry volume in the concrete could fully fill the aggregate voids and form a thicker lubricating layer between the aggregates, which could significantly improve the workability of the concrete. The jet velocity of the shotcrete pump has a significant impact on the rebound rate; a lower jet velocity results in a higher concrete rebound rate.

[0203] Comparing Example 5 with Comparative Examples 7 and 8, Comparative Example 7 achieved a slump of 210 mm by adjusting the water-reducing agent dosage. The wet-mixed sprayed concrete had a short slump emptying time of only 4 seconds, exhibiting high fluidity and low viscosity. After being sprayed onto the wall, the wet-mixed sprayed concrete continued to flow, resulting in a rebound rate of 26%. Comparative Example 8, with a slump of 160 mm and a slump emptying time of 14 seconds, showed poor fluidity, flowing continuously, but with high viscosity. This made pumping the wet-mixed sprayed concrete difficult, resulting in discontinuous jetting and a rebound rate of 18%. The slump test reflects the viscosity of concrete. When the concrete viscosity is too high and the slump time exceeds 10 seconds, the concrete pumping is slow, reducing the jet velocity. The concrete is not dense and is prone to falling off, resulting in a high rebound rate. When the concrete viscosity is too low and the slump time is 4 seconds, the concrete pumping is convenient, but the adhesion between the slurry and aggregate is low, making it easy to disperse. The aggregate is prone to rebound during spraying and is easy to flow after spraying, resulting in a high rebound rate.

[0204] Comparing Examples 3, 4, 5, and 6, Example 6 incorporated a rebound inhibitor, which increased the cohesiveness of the concrete and gave the slurry stronger adhesion. To ensure smooth pumping, the slump emptying time in both examples was within 4-10 seconds. The slump of Example 6 was 220 mm, which was greater than that of Example 5. The rebound rate in Example 6 was 5%, in Example 3 it was 13%, in Example 4 it was 8%, and in Example 5 it was 9%. It can be seen that incorporating a rebound inhibitor into shotcrete can significantly reduce the concrete rebound rate.

[0205] According to Examples 6, 9, and 10, all three examples incorporated rebound inhibitors, which increased the cohesiveness of the concrete and resulted in a stronger adhesiveness of the slurry. In Comparative Example 9, the concrete slump was 200 mm, the concrete backflow time was 12 s, the pumping was slow, and the rebound rate was 9%. In Example 6, the concrete slump was 220 mm, the concrete backflow time was 8 s, the pumping was smooth, and the rebound rate was 5%. In Comparative Example 10, the concrete slump was 240 mm, the concrete backflow time was 4 s, the pumping was smooth, and the rebound rate was 15%. The addition of rebound inhibitors significantly reduced the rebound rate of shotcrete; however, excessively high or low concrete viscosity increased the rebound rate. Following the same analytical principle, excessively high viscosity affects the spray jet velocity, while excessively low viscosity causes the concrete to continue flowing after spraying, both leading to an increased rebound rate.

[0206] According to Examples 6, 11, and 12, decreasing or increasing the dosage of the accelerator (5% and 10%) both increased the rebound rate (18.6% and 13.8%, respectively). When the dosage of the accelerator was too low, the shotcrete slurry continued to flow on the wall surface, resulting in a large rebound of the aggregate; when the dosage of the accelerator was too high, the shotcrete hardened quickly, and subsequent shotcrete spraying resulted in a high surface stiffness and an increased rebound rate.

[0207] According to Examples 6, 13, and 14, Comparative Examples 13 and 14, which lacked component Y and component X respectively in their rebound inhibitors, had rebound rates of 11% and 9% respectively. The absence of component Y reduced the internal bonding force of the concrete after spraying, making it more susceptible to being broken up or crumbling by subsequent concrete, thus increasing the rebound rate. The absence of component X reduced the cohesiveness of the concrete, weakening its ability to overcome aggregate rebound upon impact with the structure, also leading to an increased rebound rate. Components X and Y work synergistically, improving the cohesiveness and bonding force in the concrete, thereby reducing the rebound rate of the sprayed concrete.

[0208] According to Comparative Examples 7, 15, and 16, the rebound rate increases with decreasing or increasing the accelerator dosage (2% and 6%). Compared to upward spraying, horizontally sprayed concrete resists gravity more after molding. In horizontal spraying, when the accelerator dosage is too low, the sprayed concrete slurry continues to flow on the wall surface, resulting in greater stone rebound. When the accelerator dosage is too high, the cost is higher to achieve the same effect, which is inconsistent with the concept of green and low-carbon development.

[0209] In summary, this invention, through a novel shotcrete mix design method, proposes parameters characterizing the good workability of shotcrete, introduces new materials to suppress concrete rebound, and proposes different mix design schemes for different spraying directions. It achieves a rebound rate of nearly 5% for upward spraying (tunnel arch) and nearly 2% for horizontal spraying (sidewall). Furthermore, the design of shotcrete mix proportions for different spraying directions significantly reduces mix design costs. Compared to existing shotcrete control technologies, this invention is more refined, more operable, and less costly, making it worthy of engineering application and promotion.

[0210] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-resilience wet-sprayed concrete, characterized in that, The components of the low-resilience wet-mixed shotcrete include cementitious materials, aggregates, and water, with a water-cement ratio of 0.35-0.

40. The aggregate has a full-graded compact void ratio of A, and the low-resilience wet-sprayed concrete has a paste volume ratio of B, where 1.05 ≤ B / A ≤ 1.

10. The cementitious material includes cement and / or fly ash; the total amount of the cementitious material is calculated according to the following formula: ； Wherein, cement usage = total amount of cementitious materials × (1- P 1); Fly ash dosage = Total amount of cementitious materials × P 1; In the above formula, P 1 represents the mass percentage of fly ash in the cementitious material; ρ p1 ρ is the apparent density of fly ash, expressed in kilograms per cubic meter. c ρ is the apparent density of cement, expressed in kilograms per cubic meter. 水 The density of water is expressed in kilograms per cubic meter; the total amount of cementitious materials is expressed in kilograms per cubic meter.

2. The low-resilience wet-sprayed concrete according to claim 1, characterized in that, The components of the low-rebound wet-sprayed concrete also include admixtures and / or rebound inhibitors; The admixtures include water-reducing agents and / or quick-setting agents.

3. The low-resilience wet-sprayed concrete according to claim 2, characterized in that, The fly ash content is 10%-20% of the total cementitious material content, the rebound inhibitor content is 5%, and the water-reducing agent content is 0.8%-1.2%.

4. The low-resilience wet-sprayed concrete according to claim 2, characterized in that, The rebound inhibitor comprises component X, component Y, and water; The component X is nano-calcium carbonate; Component Y is a polystyrene-butadiene copolymer emulsion; The mass ratio of component X, component Y and water is 3:1:

7.

5. The low-resilience wet-sprayed concrete according to claim 2, characterized in that, The water reduction The water reduction rate of the agent is ≥25%, and the air content is ≤6.0%; The water-reducing agent is a polycarboxylate water-reducing agent.

6. The low-resilience wet-sprayed concrete according to claim 2, characterized in that, The amount of the quick-setting agent is 2%-9% of the cementitious material; the quick-setting agent is an alkali-free quick-setting agent.

7. The low-resilience wet-sprayed concrete according to claim 1, characterized in that, The aggregate includes coarse aggregate and fine aggregate, wherein the coarse aggregate is crushed stone and the fine aggregate is river sand and / or manufactured sand; the particle size of the crushed stone is ≤16 mm.

8. The low-resilience wet-sprayed concrete according to any one of claims 2-6, characterized in that, The low-resilience wet-mixed concrete comprises the rebound inhibitor, and the pump slump of the low-resilience wet-mixed concrete is 210-230 mm, the slump discharge time is 4-10 s, and the concrete is in a continuous fluid state during discharge; or, The composition of the low-rebound wet-sprayed concrete does not include the rebound inhibitor. The slump of the low-rebound wet-sprayed concrete upon entering the pump is 160-200 mm, the slump emptying time is 4-10 s, and the concrete is in a continuous fluid state when being discharged.

9. A mix design method for low-resilience wet-mix shotcrete as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) The material composition should be designed with at least slump and slump discharge time as control indicators; (2) Determine the reasonable sand ratio by using the aggregate full-gradation particle size analysis method and the minimum compacted void ratio index; (3) The ratio of the slurry volume ratio to the total gradation density of the aggregate is used as the basis for adjusting the slurry-aggregate ratio; (4) Incorporate rebound inhibitors; (5) Determine the appropriate water-to-glue ratio.

Images