Self-compacting concrete mix proportion design method based on rheological property and strength of slurry

Abstract

The application relates to a self-compacting concrete mix proportion design method based on slurry rheology and strength, and belongs to the field of concrete mix proportion design, which comprises the following steps: initially drafting a self-compacting concrete mix proportion, determining rheological parameters thereof; testing cementitious material characteristics, calculating cement paste rheological characteristics; testing fine aggregate characteristics, calculating mortar rheological characteristics; testing coarse aggregate characteristics, calculating self-compacting concrete rheological characteristics; self-compacting concrete mix proportion optimization and adjustment; preparing self-compacting concrete according to the optimized mix proportion, and testing mechanical strength thereof. The self-compacting concrete is decomposed into solid-liquid two-phase bodies in three different scales of water-cementitious material, cement paste-fine aggregate and mortar-coarse aggregate, through the interaction between each two-phase body and the correlation between adjacent two levels, so that the accurate design of raw material components and the dynamic regulation and control of rheological properties in the self-compacting concrete can be realized, and the method is high in efficiency, low in cost and good in practicability.

Description

Technical Field

[0001] This invention relates to a method for designing mix proportions of self-compacting concrete based on the rheology and strength of slurry, belonging to the field of concrete mix proportion design technology. Background Technology

[0002] Self-compacting concrete has excellent construction and filling performance, which can solve the problems of insufficient vibration, over-vibration and difficulty in vibration due to dense reinforcement in traditional concrete construction. At the same time, the hardened self-compacting concrete has excellent mechanical and durability properties, so it is called "the most revolutionary development in concrete construction technology in recent decades". It has been widely used in new construction projects such as high-rise buildings, roads, bridges and tunnels, large-scale water conservancy and hydropower projects, as well as the reinforcement of old structures.

[0003] The design and control of the rheological properties of self-compacting concrete are crucial to achieving its self-compacting properties, and have a significant impact on concrete transportation, pumping, pouring, construction quality, post-hardening performance, and structural durability. Currently, the main methods for mix design of self-compacting concrete include: empirical derivation, fixed aggregate volume method, full calculation method, absolute volume method, and aggregate specific surface area method. However, these methods typically require multiple trial mixes and adjustments, consuming significant amounts of materials, manpower, and time. Furthermore, because they do not consider the complex interactions between various components in the raw materials of self-compacting concrete and their impact on its rheological properties, the prepared self-compacting concrete is prone to problems such as bleeding, insufficient segregation resistance, and poor fluidity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a mix design method for self-compacting concrete based on slurry rheology and strength. This method decomposes self-compacting concrete into three solid-liquid two-phase systems at different scales: water-cementing materials, cement paste-fine aggregate, and mortar-coarse aggregate. Through the interaction between each two-phase system and the correlation between adjacent two-phase systems, it is possible to achieve precise design of raw material components and dynamic control of rheological properties in self-compacting concrete. This method is also highly efficient, low-cost, and practical.

[0005] Terminology Explanation:

[0006] T500: T500, as a qualitative indicator of flow rate, has become a key indicator for evaluating self-compacting concrete. The currently used test method is to conduct slump and spread tests on a graduated plastic plate. Timing starts when the slump cone is lifted and ends when the concrete flows to the 500mm mark on the circle. The flow time is then recorded as T500.

[0007] Water-cementing material: This indicates that the mixture consists of two phases of materials: water and cementing material.

[0008] Cement paste-fine aggregate: This indicates that the mixture consists of two phases of materials: cement paste and fine aggregate.

[0009] Mortar-coarse aggregate: This indicates that the mixture consists of two phases of materials: mortar and coarse aggregate.

[0010] Cementitious materials: In building materials, substances that, through a series of physical and chemical processes, can transform from a paste into a solid, stone-like substance and bind other solid materials into a whole with a certain mechanical strength are collectively referred to as cementitious materials. This invention refers to cement and mineral admixtures such as fly ash, slag powder, silica fume, and limestone powder.

[0011] Cement paste: A mixture of cementitious materials and water, which has certain plasticity.

[0012] Cement mortar: A mixture with certain plasticity made by mixing cementitious materials, fine aggregates and water in a certain proportion.

[0013] The present invention adopts the following technical solution:

[0014] A method for designing mix proportions of self-compacting concrete based on slurry rheology and strength includes the following steps:

[0015] (1) Preliminary determination of the mix proportion of self-compacting concrete and determination of the rheological parameters of the target self-compacting concrete, including the target yield stress and the target plastic viscosity;

[0016] (2) Test the properties of cementitious materials and calculate the rheological properties of cement paste;

[0017] (3) Test the properties of fine aggregates and calculate the rheological properties of mortar;

[0018] (4) Test the properties of coarse aggregate and calculate the rheological properties of self-compacting concrete;

[0019] (5) Optimization and adjustment of mix proportions for self-compacting concrete;

[0020] The yield stress and plastic viscosity of the self-compacting concrete obtained in step (4) are compared with the target yield stress and target plastic viscosity in step (1). If the calculated value in step (4) is within the range of the target yield stress and target plastic viscosity in step (1), then step (6) is performed; otherwise, the mix proportion of the raw materials of the self-compacting concrete is optimized by changing the composition of cementitious materials, the amount of admixtures, the volume content of aggregates, the type of aggregates and the gradation, etc., and the yield stress and plastic viscosity of the self-compacting concrete are recalculated according to the above steps (1) to (4) until it can meet the target yield stress and target plastic viscosity range in step (1).

[0021] (6) Prepare self-compacting concrete according to the optimized mix proportion of self-compacting concrete in step (5), and test its mechanical strength according to the "Technical Specification for Application of Self-Compacting Concrete" JGT / T 283. If it meets the specification requirements, it can be directly used in actual projects; if it does not meet the requirements, the mix proportion should be further optimized. Specifically, when the strength is lower than the design value, its mechanical properties can be improved by increasing the amount of cementitious materials, reducing the amount of mineral admixtures, and reducing the water-cement ratio.

[0022] Preferably, step (1) includes the following sub-steps:

[0023] 1.1: Referring to the "Technical Specification for Application of Self-Compacting Concrete" JGT / T 283, the mix proportion of self-compacting concrete is initially proposed. The coarse and fine aggregates should be continuously graded, with the maximum nominal particle size of the coarse aggregate being less than 20cm. The fine aggregate should preferably be medium sand from gradation zone II. Mineral admixtures such as fly ash, slag powder, silica fume, and limestone powder can be used to partially replace cement, but their performance should meet the relevant current national standards. The water-reducing agents, thickeners, and other admixtures used should comply with the relevant provisions of the current national standards "Concrete Admixtures" GB 8076 and "Technical Specification for Application of Concrete Admixtures" GB 50119.

[0024] 1.2: Determine the rheological parameters of the target self-compacting concrete, including the target yield stress and target plastic viscosity, based on the actual needs of the project;

[0025] Alternatively, the rheological parameters of the target self-compacting concrete can be obtained through the spread and T500 calculations, and then calculated using formulas (1) and (2) respectively:

[0026] τ=853067e -0.014SF (1)

[0027] η=7.0645×T+6.8128 (2)

[0028] Where: τ is the yield stress; η is the plastic viscosity; SF is the target spread of fresh self-compacting concrete; T is the target T500 time of fresh self-compacting concrete;

[0029] Preferably, step (2) includes the following sub-steps:

[0030] 2.1: According to the national standard GB / T 16913-2008 "Test Methods for Physical Properties of Dust", the bulk density of the dry cementitious material was tested and the bulk porosity was calculated, i.e., p in formula (5);

[0031] 2.2: Since the interaction between cementitious material particles in cement paste is essentially achieved through particle-to-particle contact, the probability of any particle interacting with cement or mineral admixture particles can be considered as the probability of that particle contacting the surface of a certain type of material particle. That is, the probability of collision between each particle is calculated by combining the ratio of the surface area of ​​cement and mineral admixture to the total surface area in the system with a probability model. The equivalent Hamek constant of cementitious materials in cement paste is defined as the sum of the products of the Hamek constant between any two material particles and the probability of interaction between them. The equivalent Hamek constant between material particles used in multi-component cementitious material cement paste is calculated using equation (3):

[0032]

[0033] In the formula: N is the equivalent Hamek constant for cementitious materials. i P represents the proportion of the surface area of ​​any material particle in the total surface area of ​​all materials; n represents the types of multi-component cementitious materials in the cement paste; i-i A represents the contact probability between particles of the same cementitious material in cement paste. i-i P is the Hamelin constant between particles of the same cementitious material in cement paste; i-j A represents the contact probability between two different cementitious material particles in cement paste; i-j The Hamelck constant is the interparticle size distribution between two different cementitious materials in cement paste.

[0034] 2.3: Based on the cementitious material parameters obtained in steps 2.1 and 2.2, the yield stress and plastic viscosity of cement paste are predicted using equations (4) and (5), respectively:

[0035]

[0036]

[0037] In the formula: τ p The yield stress of cement paste is given in Pa; φ0 and φ max These are the minimum and maximum volume fractions of freshly mixed cement paste, approximately 0.03 and 0.7 in freshly mixed cement paste; φ is the volume fraction of freshly mixed cement paste (i.e., the volume fraction of solid materials in cement paste); Equivalent Hamek constant for cementitious materials; u k,k For relative volume increments, the literature recommends u k,k The value is set to 187.46, where f is the particle size distribution function, and the literature recommends a value of 1; R v,50 η is the average volume radius of the cementitious material (i.e., half of the median particle size of the cementitious material); H is the closest distance between particles in the suspension system, typically 3.2 nm; ... pρ is the plastic viscosity of cement paste, Pa·s; p is the packing porosity (obtained through step 2.1); w / b is the water-cement ratio.

[0038] Preferably, step (3) includes the following sub-steps:

[0039] 3.1: The aggregate particle characteristics of the aggregates used are quantitatively characterized by the Image Measurement System for Aggregates (AIMS), including the angularity GA of fine aggregates, the angularity GA of coarse aggregates, the texture TX of fine aggregates, the texture TX of coarse aggregates, the angular texture value CAAT of fine aggregates, and the angular texture value CAAT of coarse aggregates.

[0040] 3.2: According to fractal theory, the aggregate forming process has a certain degree of randomness and irregularity, but fine aggregates of different sizes have the same dynamic mechanism in the forming process, that is, the fine aggregate gradation is fractal. Therefore, the fractal dimension can be used to characterize the particle size distribution of aggregates. The fractal dimension of fine aggregates is calculated using equation (6).

[0041] When calculating the fractal dimension of aggregate gradation, equation (7) is obtained by taking the logarithm of both sides of equation (6). Obviously, log P * (x)∝log(x / x max This indicates a linear relationship between the two. A double logarithmic graph of x and x is plotted, with the horizontal axis representing the logarithm of the throughput when the fine aggregate size is x, and the vertical axis representing the logarithm of the volume fraction of the corresponding particle size, i.e., x / x. max The logarithm of the fine aggregate gradation is best linearly fitted using the least squares method. The slope of the resulting curve is k = 3 - D. Therefore, the fractal dimension of the fine aggregate gradation is D = 3 - k.

[0042]

[0043]

[0044] In the formula, P * (x, D) refers to the throughput when the particle size of the fine aggregate is x; x represents the different particle sizes of the fine aggregate; x max and x min These are the maximum and minimum particle sizes of the fine aggregate, respectively; D is the fractal dimension of the fine aggregate gradation.

[0045] 3.3: Based on the packing void ratio (which can be measured according to the specification), specific surface area, and total volume of cement paste of the fine aggregate in the mortar, the thickness of the excess paste layer between the fine aggregates is calculated using formula (8). The specific surface area of ​​the fine aggregate is simplified by assuming that the fine aggregate is a spherical particle. At the same time, the average value of the standard sieve aperture in the sieve test is taken as the representative particle size of the fine aggregate in a single particle size range. The specific surface area of ​​the fine aggregate is shown in formula (9):

[0046]

[0047] Where: TEP is the excess slurry layer thickness; V paste The total volume of the slurry (V) paste The volume sum (V) is calculated from the mass / density of all materials that make up the neat cement paste. void The volume of slurry filling the voids between fine aggregates (assuming all voids between fine aggregates are filled by neat slurry, therefore the volume of slurry filling the voids between fine aggregates is the total mass of fine aggregates × porosity); M s For fine aggregate quality; A S，C This represents the corrected actual specific surface area of ​​the fine aggregate.

[0048]

[0049] In the formula: A S D represents the specific surface area of ​​the fine aggregate. i M is the average standard sieve aperture value in interval i of the sieve test; M is the total mass of fine aggregate in the sieve test; m i ρ is the total mass of fine aggregate within the range i in the sieve analysis test; ρ is the apparent density of the fine aggregate; K i γ represents the relative content of fine aggregate within the range i in the sieve analysis test; γ is the correction factor for the specific surface area of ​​fine aggregate, which is taken as 1.05.

[0050] 3.4: Based on the rheological parameters of cement paste, the angle of fine aggregate, the fractal dimension of fine aggregate gradation, and the thickness of excess paste layer obtained in steps 2.3 and 3.1 to 3.3, the yield stress and plastic viscosity of the mortar are calculated using equations (10) and (11), respectively:

[0051] τ m =4.22τ p +136.83D+0.115GA-5.27TEP-398.77 (10)

[0052] η m =1.956η p -1.04D + 7.274 × 10 -4 GA-0.024TEP+2.219 (11)

[0053] In the formula: τ m η is the yield stress of the mortar. m τ is the plastic viscosity of the mortar. p η is the yield stress corresponding to the cement paste; p , where D is the plastic viscosity of the corresponding cement paste; D is the fractal dimension of the fine aggregate gradation; GA is the angle of the fine aggregate; TEP is the thickness of the excess paste layer.

[0054] Preferably, step (4) includes the following sub-steps:

[0055] 4.1: Based on the theory of excess mortar and two-phase material, freshly mixed self-compacting concrete can be considered as a combination of coarse aggregate and mortar. Part of the mortar fills the gaps between the coarse aggregates, and the other part of the mortar wraps the coarse aggregate particles, opening up the coarse aggregate skeleton structure to form a lubricating layer. The thickness of the excess mortar layer in the self-compacting concrete is calculated using formula (12):

[0056]

[0057] In the formula: V c δ represents the volume occupied by coarse aggregate in a unit volume of concrete. c H is the bulk porosity of the coarse aggregate (measured according to specifications); S is the thickness of the slurry coating on the coarse aggregate; C ρ is the corrected specific surface area of ​​the coarse aggregate; c S is the apparent density of the coarse aggregate; S is the specific surface area of ​​the coarse aggregate; k i d represents the relative content of coarse aggregate within the particle size range i; i ρ is the average aperture value of a standard sieve within the particle size range i; s γ represents the apparent density of the aggregate; b The specific surface area correction factor for coarse aggregate is 1.12 for crushed stone.

[0058] 4.2: Based on the rheological parameters of the mortar, the angular texture value (CAAT) of the coarse aggregate, and the mortar coating thickness of the coarse aggregate obtained in steps 3.1, 3.4, and 4.1, the yield stress and plastic viscosity of the self-compacting concrete are calculated using equations (13) and (14):

[0059] τ scc =0.1043τ m +0.0534CAAT-267.4581 / H+0.4139t+116.8454 (13)

[0060] η scc =28.6098η m +0.0112CAAT-246.0698 / H+0.4444t+17.1266 (14)

[0061] In the formula: τ scc η represents the yield stress of self-compacting concrete. scc The plastic viscosity of self-compacting concrete (SCC); τ m η is the yield stress of the mortar. m t represents the plastic viscosity of the mortar; CAAT represents the angular texture value of the coarse aggregate; H represents the mortar coating thickness of the coarse aggregate; and t represents the settling time of the fresh concrete.

[0062] Where this invention is not detailed, existing technologies may be used.

[0063] The beneficial effects of this invention are as follows:

[0064] This invention proposes a mix design method for self-compacting concrete based on slurry rheology and strength. This method decomposes self-compacting concrete into a solid-liquid two-phase system at three different scales: water-cement mix, cement paste-fine aggregate mix, and mortar-coarse aggregate mix. (The rheological prediction of self-compacting concrete is first performed at the microscopic level based on interparticle interaction forces and material properties to predict the rheology of the cement paste; then at the mesoscopic level based on the properties of the cement paste and fine aggregate to predict the rheology of the mortar; and finally at the macroscopic level based on the properties of the mortar and coarse aggregate to predict the rheology of the self-compacting concrete.) By establishing the relationship between raw material properties and the rheological properties of the concrete mixture, precise design of raw material components and dynamic control of rheological properties are achieved, resulting in the following beneficial effects:

[0065] 1. The self-compacting concrete mix design method proposed in this invention has a scientific and reasonable design process, a clear approach, and requires less testing. It can not only design and control the rheological properties of self-compacting concrete, but also significantly reduce the shortcomings of other design methods, such as high design blindness, uncontrollable performance, high time cost, heavy manpower burden, and serious material waste.

[0066] 2. In the design method proposed in this invention, self-compacting concrete is decomposed into water-cementing material, cement paste-fine aggregate, and mortar-coarse aggregate. The interaction between each two phase and the correlation between adjacent two phases are given through multiple mathematical relationships, which facilitates rapid optimization and dynamic control of its rheological properties.

[0067] 3. The rheological properties of cement paste largely determine the workability of fresh self-compacting concrete. As a high-concentration suspension system, cement paste contains various microscopic interaction forces, among which van der Waals forces are the main reason for the agglomeration of cementitious particles and the resulting reduction in the flowability of self-compacting concrete. The design method proposed in this invention uses an equivalent Hamelin constant to comprehensively quantify and characterize the van der Waals forces between various cementitious particles, improving the prediction accuracy of cement paste rheology. This, in turn, reduces the error between the calculated rheological parameters of self-compacting concrete and the measured values, ensuring the accuracy and practicality of the design method.

[0068] 4. Aggregates are another important component of self-compacting concrete. Their particle shape, surface texture, gradation, and volume content have a significant impact on the rheological properties of fresh self-compacting concrete. In the design method proposed in this invention, based on digital image processing technology, an aggregate image measurement system is used to quantitatively characterize the geometry and surface texture of the aggregates, thereby quantifying the degree of influence of aggregate characteristics on the rheological properties of self-compacting concrete.

[0069] 5. The self-compacting concrete mix design method proposed in this invention reflects a universal underlying mechanism. The method of expressing the intrinsic relationship between factors such as cementitious material properties, neat cement paste / mortar rheology, aggregate properties and the rheology of self-compacting concrete in a functional form has universality and is therefore applicable to the mix design of other fluid concretes and even ordinary concrete. Attached Figure Description

[0070] Figure 1 The relationship between yield stress and spread of self-compacting concrete;

[0071] Figure 2 The relationship between the plastic viscosity of self-compacting concrete and T500;

[0072] Figure 3 This is a double logarithmic plot used in the calculation of the fractal dimension of fine aggregate. Detailed Implementation

[0073] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. However, this description is not limited thereto. All aspects not described in detail in the present invention are based on conventional techniques in the field.

[0074] Example

[0075] A method for designing mix proportions of self-compacting concrete based on slurry rheology and strength includes the following steps:

[0076] (1) Preliminary determination of the mix proportion of self-compacting concrete and determination of the rheological parameters of the target self-compacting concrete, including the target yield stress and the target plastic viscosity;

[0077] 1.1: Referring to the "Technical Specification for Application of Self-Compacting Concrete" JGT / T 283, the mix proportion of self-compacting concrete is initially proposed. The coarse and fine aggregates should be continuously graded, with the maximum nominal particle size of the coarse aggregate being less than 20cm. The fine aggregate should preferably be medium sand from gradation zone II. Mineral admixtures such as fly ash, slag powder, silica fume, and limestone powder can be used to partially replace cement, but their performance should meet the relevant current national standards. The water-reducing agents, thickeners, and other admixtures used should comply with the relevant provisions of the current national standards "Concrete Admixtures" GB 8076 and "Technical Specification for Application of Concrete Admixtures" GB 50119.

[0078] 1.2: Determine the rheological parameters of the target self-compacting concrete, including the target yield stress and target plastic viscosity, based on the actual needs of the project;

[0079] Alternatively, the rheological parameters of the target self-compacting concrete can be obtained through the spread and T500 calculations, and then calculated using formulas (1) and (2) respectively:

[0080] τ=853067e -0.014SF (1)

[0081] η=7.0645×T+6.8128 (2)

[0082] Where: τ is the yield stress; η is the plastic viscosity; SF is the target spread of fresh self-compacting concrete; T is the target T500 time of fresh self-compacting concrete;

[0083] like Figure 1 , Figure 2 The figures shown are the relationship between yield stress and spread, and the relationship between plastic viscosity and T500, respectively. Based on the target spread and target T500, the range of yield stress and plastic viscosity of self-compacting concrete can be calculated and determined using equations (1) and (2).

[0084] (2) Test the properties of cementitious materials and calculate the rheological properties of cement paste;

[0085] 2.1: According to the national standard GB / T 16913-2008 "Test Methods for Physical Properties of Dust", the bulk density of the dry cementitious material was tested and the bulk porosity was calculated, i.e., p in formula (5);

[0086] 2.2: Since the interaction between cementitious material particles in cement paste is essentially achieved through particle-to-particle contact, the probability of any particle interacting with cement or mineral admixture particles can be considered as the probability of that particle contacting the surface of a certain type of material particle. That is, the probability of collision between each particle is calculated by combining the ratio of the surface area of ​​cement and mineral admixture to the total surface area in the system with a probability model. The equivalent Hamek constant of cementitious materials in cement paste is defined as the sum of the products of the Hamek constant between any two material particles and the probability of interaction between them. The equivalent Hamek constant between material particles used in multi-component cementitious material cement paste is calculated using equation (3):

[0087]

[0088] In the formula: N is the equivalent Hamek constant for cementitious materials. i P represents the proportion of the surface area of ​​any material particle in the total surface area of ​​all materials; n represents the types of multi-component cementitious materials in the cement paste; i-i A represents the contact probability between particles of the same cementitious material in cement paste. i-i P is the Hamelin constant between particles of the same cementitious material in cement paste; i-j A represents the contact probability between two different cementitious material particles in cement paste; i-j The Hamelck constant is the interparticle size distribution between two different cementitious materials in cement paste.

[0089] 2.3: Based on the cementitious material parameters obtained in steps 2.1 and 2.2, the yield stress and plastic viscosity of cement paste are predicted using equations (4) and (5), respectively:

[0090]

[0091]

[0092] In the formula: τ p The yield stress of cement paste is given in Pa; φ0 and φ max These are the minimum and maximum volume fractions of freshly mixed cement paste, approximately 0.03 and 0.7 in freshly mixed cement paste; φ is the volume fraction of freshly mixed cement paste (i.e., the volume fraction of solid materials in cement paste); Equivalent Hamek constant for cementitious materials; u k,k For relative volume increments, the literature recommends u k,k The value is set to 187.46, where f is the particle size distribution function, and the literature recommends a value of 1; R v,50 η is the average volume radius of the cementitious material (i.e., half of the median particle size of the cementitious material); H is the closest distance between particles in the suspension system, typically 3.2 nm; ... p ρ is the plastic viscosity of cement paste, Pa·s; p is the packing porosity (obtained through step 2.1); w / b is the water-cement ratio.

[0093] (3) Test the properties of fine aggregates and calculate the rheological properties of mortar;

[0094] 3.1: The aggregate particle characteristics of the aggregates used are quantitatively characterized by the Image Measurement System for Aggregates (AIMS), including the angularity GA of fine aggregates, the angularity GA of coarse aggregates, the texture TX of fine aggregates, the texture TX of coarse aggregates, the angular texture value CAAT of fine aggregates, and the angular texture value CAAT of coarse aggregates.

[0095] 3.2: According to fractal theory, the aggregate forming process has a certain degree of randomness and irregularity, but fine aggregates of different sizes have the same dynamic mechanism in the forming process, that is, the fine aggregate gradation is fractal. Therefore, the fractal dimension can be used to characterize the particle size distribution of aggregates. The fractal dimension of fine aggregates is calculated using equation (6).

[0096] When calculating the fractal dimension of aggregate gradation, equation (7) is obtained by taking the logarithm of both sides of equation (6). Obviously, log P * (x)∝log(x / x max This means that there is a linear relationship between the two, such as... Figure 3 As shown, a double logarithmic plot of x and x is plotted. The horizontal axis represents the logarithmic value of the throughput when the particle size of the fine aggregate is x, and the vertical axis represents the logarithmic value of the volume fraction of the corresponding particle size, i.e., x / x.max The logarithm of the fine aggregate gradation is best linearly fitted using the least squares method. The slope of the resulting curve is k = 3 - D. Therefore, the fractal dimension of the fine aggregate gradation is D = 3 - k.

[0097]

[0098]

[0099] In the formula, P * (x, D) refers to the throughput when the particle size of the fine aggregate is x; x represents the different particle sizes of the fine aggregate; x max and x min These are the maximum and minimum particle sizes of the fine aggregate, respectively; D is the fractal dimension of the fine aggregate gradation.

[0100] 3.3: Based on the packing void ratio (which can be measured according to the specification), specific surface area, and total volume of cement paste of the fine aggregate in the mortar, the thickness of the excess paste layer between the fine aggregates is calculated using formula (8). The specific surface area of ​​the fine aggregate is simplified by assuming that the fine aggregate is a spherical particle. At the same time, the average value of the standard sieve aperture in the sieve test is taken as the representative particle size of the fine aggregate in a single particle size range. The specific surface area of ​​the fine aggregate is shown in formula (9):

[0101]

[0102] Where: TEP is the excess slurry layer thickness; V paste The total volume of the slurry (V) paste The volume sum (V) is calculated from the mass / density of all materials that make up the neat cement paste. void The volume of slurry filling the voids between fine aggregates (assuming all voids between fine aggregates are filled by neat slurry, therefore the volume of slurry filling the voids between fine aggregates is the total mass of fine aggregates × porosity); M s For fine aggregate quality; A S，C This represents the corrected actual specific surface area of ​​the fine aggregate.

[0103]

[0104] In the formula: A S D represents the specific surface area of ​​the fine aggregate. i M is the average standard sieve aperture value in interval i of the sieve test; M is the total mass of fine aggregate in the sieve test; m i ρ is the total mass of fine aggregate within the range i in the sieve analysis test; ρ is the apparent density of the fine aggregate; K i γ represents the relative content of fine aggregate within the range i in the sieve analysis test; γ is the correction factor for the specific surface area of ​​fine aggregate, which is taken as 1.05.

[0105] 3.4: Based on the rheological parameters of cement paste, the angle of fine aggregate, the fractal dimension of fine aggregate gradation, and the thickness of excess paste layer obtained in steps 2.3 and 3.1 to 3.3, the yield stress and plastic viscosity of the mortar are calculated using equations (10) and (11), respectively:

[0106] τ m =4.22τ p +136.83D+0.115GA-5.27TEP-398.77 (10)

[0107] η m =1.956η p -1.04D + 7.274 × 10 -4 GA-0.024TEP+2.219 (11)

[0108] In the formula: τ m η is the yield stress of the mortar. m τ is the plastic viscosity of the mortar. p η is the yield stress corresponding to the cement paste; p , where D is the plastic viscosity of the corresponding cement paste; D is the fractal dimension of the fine aggregate gradation; GA is the angle of the fine aggregate; TEP is the thickness of the excess paste layer.

[0109] (4) Test the properties of coarse aggregate and calculate the rheological properties of self-compacting concrete;

[0110] 4.1: Based on the theory of excess mortar and two-phase material, freshly mixed self-compacting concrete can be considered as a combination of coarse aggregate and mortar. Part of the mortar fills the gaps between the coarse aggregates, and the other part of the mortar wraps the coarse aggregate particles, opening up the coarse aggregate skeleton structure to form a lubricating layer. The thickness of the excess mortar layer in the self-compacting concrete is calculated using formula (12):

[0111]

[0112] In the formula: V c δ represents the volume occupied by coarse aggregate in a unit volume of concrete. c H is the bulk porosity of the coarse aggregate (measured according to specifications); S is the thickness of the slurry coating on the coarse aggregate; C ρ is the corrected specific surface area of ​​the coarse aggregate; c S is the apparent density of the coarse aggregate; S is the specific surface area of ​​the coarse aggregate; k i d represents the relative content of coarse aggregate within the particle size range i; i ρ is the average aperture value of a standard sieve within the particle size range i; s γ represents the apparent density of the aggregate; b The specific surface area correction factor for coarse aggregate is 1.12 for crushed stone.

[0113] 4.2: Based on the rheological parameters of the mortar, the angular texture value (CAAT) of the coarse aggregate, and the mortar coating thickness of the coarse aggregate obtained in steps 3.1, 3.4, and 4.1, the yield stress and plastic viscosity of the self-compacting concrete are calculated using equations (13) and (14):

[0114] τ scc =0.1043τ m +0.0534CAAT-267.4581 / H+0.4139t+116.8454 (13)

[0115] η scc =28.6098η m +0.0112CAAT-246.0698 / H+0.4444t+17.1266 (14)

[0116] In the formula: τ scc η represents the yield stress of self-compacting concrete. scc The plastic viscosity of self-compacting concrete (SCC); τ m η is the yield stress of the mortar. m t represents the plastic viscosity of the mortar; CAAT represents the angular texture value of the coarse aggregate; H represents the mortar coating thickness of the coarse aggregate; and t represents the settling time of the fresh concrete.

[0117] (5) Optimization and adjustment of mix proportions for self-compacting concrete;

[0118] The yield stress and plastic viscosity of the self-compacting concrete obtained in step (4) are compared with the target yield stress and target plastic viscosity in step (1). If the calculated value in step (4) is within the range of the target yield stress and target plastic viscosity in step (1), then step (6) is performed; otherwise, the mix proportion of the raw materials of the self-compacting concrete is optimized by changing the composition of cementitious materials, the amount of admixtures, the volume content of aggregates, the type of aggregates and the gradation, etc., and the yield stress and plastic viscosity of the self-compacting concrete are recalculated according to the above steps (1) to (4) until it can meet the target yield stress and target plastic viscosity range in step (1).

[0119] (6) Prepare self-compacting concrete according to the optimized mix proportion of self-compacting concrete in step (5), and test its mechanical strength according to the "Technical Specification for Application of Self-Compacting Concrete" JGT / T 283. If it meets the specification requirements, it can be directly used in actual projects; if it does not meet the requirements, the mix proportion should be further optimized. Specifically, when the strength is lower than the design value, its mechanical properties can be improved by increasing the amount of cementitious materials, reducing the amount of mineral admixtures, and reducing the water-cement ratio.

[0120] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A mix design method for self-compacting concrete based on slurry rheology and strength, characterized in that, Includes the following steps: (1) Preliminary determination of the mix proportion of self-compacting concrete and determination of the rheological parameters of the target self-compacting concrete, including the target yield stress and the target plastic viscosity; (2) Test the properties of cementitious materials and calculate the rheological properties of cement paste; (3) Test the properties of fine aggregates and calculate the rheological properties of mortar; (4) Test the properties of coarse aggregate and calculate the rheological properties of self-compacting concrete; (5) Optimization and adjustment of mix proportions for self-compacting concrete; The yield stress and plastic viscosity of the self-compacting concrete obtained in step (4) are compared with the target yield stress and target plastic viscosity in step (1). If the calculated value in step (4) is within the range of the target yield stress and target plastic viscosity in step (1), then step (6) is performed; otherwise, the mix proportion of the self-compacting concrete raw materials is optimized, and the yield stress and plastic viscosity of the self-compacting concrete are recalculated according to the above steps (1) to (4) until it can meet the range of the target yield stress and target plastic viscosity in step (1). (6) Prepare self-compacting concrete according to the optimized mix proportion of self-compacting concrete in step (5) and test its mechanical strength. If it meets the specification requirements, it can be used directly in actual projects; if it does not meet the requirements, the mix proportion can be further optimized. Step (3) includes the following sub-steps: 3.1: The aggregate image measurement system is used to quantitatively characterize the particle characteristics of the aggregates used, including the angularity GA of fine aggregates, the angularity GA of coarse aggregates, the texture TX of fine aggregates, the texture TX of coarse aggregates, the angular texture value CAAT of fine aggregates, and the angular texture value CAAT of coarse aggregates. 3.2: According to fractal theory, the aggregate forming process is random and irregular, but fine aggregates of different sizes have the same dynamic mechanism in the forming process, that is, the fine aggregate gradation is fractal. Therefore, the fractal dimension can be used to characterize the particle size distribution of the aggregate. The fractal dimension of the fine aggregate is calculated using equation (6). When calculating the fractal dimension of aggregate gradation, equation (7) is obtained by taking the logarithm of both sides of equation (6). Obviously, This indicates a linear relationship between the two. A logarithmic plot of the sum and the value of the sum is drawn, with the horizontal axis representing the particle size of the fine aggregate. The vertical axis represents the logarithm of the throughput at a given time, and the vertical axis represents the logarithm of the volume fraction of the corresponding particle size, i.e., x / x. max The logarithm of the value is used to perform the best linear fit using the least squares method, and the slope of the resulting curve is... Therefore, the fractal dimension of the fine aggregate gradation is obtained. ; （6） （7） In the formula, The particle size of fine aggregate is The pass rate at that time; Different particle sizes of fine aggregate; and These are the maximum and minimum particle sizes of the fine aggregate, respectively. The fractal dimension of fine aggregate gradation; 3.3: Based on the porosity, specific surface area, and total volume of cement paste of the fine aggregate in the mortar, the thickness of the excess paste layer between the fine aggregates is calculated using formula (8). The specific surface area of ​​the fine aggregate is simplified by assuming that the fine aggregate is a spherical particle. At the same time, the average value of the standard sieve aperture in the sieve test is taken as the representative particle size of the fine aggregate in a single particle size range. The specific surface area of ​​the fine aggregate is shown in formula (9). （8） In the formula: This is to ensure sufficient slurry layer thickness; This represents the total volume of the slurry. The volume of the slurry used to fill the voids in the fine aggregate; For the quality of fine aggregate; This represents the corrected actual specific surface area of ​​the fine aggregate. （9） In the formula: is the specific surface area of ​​the fine aggregate; The average aperture of the standard sieve in interval i during the sieving test; The total mass of fine aggregate in the sieve analysis test; The total mass of fine aggregate within interval i in the sieve analysis test; The apparent density of fine aggregate; The relative content of fine aggregate in the range i during the sieve analysis test; The specific surface area correction factor for fine aggregate is set to 1.

05. 3.4: Based on the obtained rheological parameters of cement paste, the angle of fine aggregate, the fractal dimension of fine aggregate gradation, and the thickness of excess paste layer, the yield stress and plastic viscosity of the mortar are calculated using equations (10) and (11), respectively: （10） （11） In the formula: The yield stress of the mortar; The plastic viscosity of the mortar; This corresponds to the yield stress of cement paste; This corresponds to the plastic viscosity of neat cement paste; The fractal dimension of fine aggregate gradation; For the edges and corners of fine aggregate; This is to ensure sufficient slurry layer thickness; Step (4) includes the following sub-steps: 4.1: Based on the theory of excess mortar and two-phase composition, freshly mixed self-compacting concrete is considered to be composed of two phases of coarse aggregate and mortar. Part of the mortar fills the voids between the coarse aggregates, and the other part of the mortar wraps the coarse aggregate particles, expanding the coarse aggregate skeleton structure to form a lubricating layer. The thickness of the excess mortar layer in self-compacting concrete is calculated using formula (12): （12） In the formula: This refers to the volume occupied by coarse aggregate in a unit volume of concrete. The porosity of coarse aggregate; The thickness of the slurry coating on the coarse aggregate; The specific surface area of ​​the coarse aggregate after correction; The apparent density of coarse aggregate; is the specific surface area of ​​the coarse aggregate; The relative content of coarse aggregate within the particle size range i; The average aperture value of the standard sieve for particle size range i; The apparent density of the aggregate; The specific surface area correction factor for coarse aggregate is 1.12 for crushed stone. 4.2: Based on the obtained rheological parameters of the mortar, the angular texture value (CAAT) of the coarse aggregate, and the mortar coating thickness of the coarse aggregate, the yield stress and plastic viscosity of the self-compacting concrete are calculated using equations (13) and (14): （13） （14） In the formula: The yield stress of self-compacting concrete; The plastic viscosity of self-compacting concrete; The yield stress of the mortar; is the plastic viscosity of the mortar; CAAT is the angular texture value of the coarse aggregate; The thickness of the slurry coating on the coarse aggregate; This refers to the settling time for freshly mixed concrete.

2. The method for designing mix proportions of self-compacting concrete based on slurry rheology and strength according to claim 1, characterized in that, Step (1) includes the following sub-steps: 1.1: The mix proportion of self-compacting concrete is initially proposed with reference to the "Technical Specification for Application of Self-Compacting Concrete" JGT / T 283. The coarse and fine aggregates adopt continuous gradation, the maximum nominal particle size of the coarse aggregate should be less than 20cm, and the fine aggregate is medium sand of gradation zone II. The admixtures used comply with the current national standards. 1.2: Determine the rheological parameters of the target self-compacting concrete, including the target yield stress and target plastic viscosity, based on the actual needs of the project; Alternatively, the rheological parameters of the target self-compacting concrete can be obtained through the spread and T500 calculations, and then calculated using formulas (1) and (2) respectively: （1） （2） In the formula: The yield stress; is the plastic viscosity; SF is the target spread of fresh self-compacting concrete; T is the target T500 time of fresh self-compacting concrete.

3. The method for designing mix proportions of self-compacting concrete based on slurry rheology and strength according to claim 2, characterized in that, Step (2) includes the following sub-steps: 2.1: According to the national standard GB / T 16913-2008 "Test Methods for Physical Properties of Dust", the bulk density of the dry cementitious material was tested and the bulk porosity was calculated. 2.2: Since the interaction between cementitious material particles in cement paste is essentially achieved through particle-to-particle contact, the probability of any particle interacting with cement or mineral admixture particles is considered to be the probability of that particle contacting the surface of a certain type of material particle. That is, the probability of collision between each particle is calculated by combining the ratio of the surface area of ​​cement and mineral admixture to the total surface area in the system with a probability model. The equivalent Hamek constant of cementitious materials in cement paste is defined as the sum of the products of the Hamek constant between any two material particles and the probability of interaction between them. The equivalent Hamek constant between material particles used in multi-component cementitious material cement paste is calculated using equation (3): （3） In the formula: N is the equivalent Hamek constant for cementitious materials. i P represents the proportion of the surface area of ​​any material particle in the total surface area of ​​all materials; n represents the types of multi-component cementitious materials in the cement paste; i-i A represents the contact probability between particles of the same cementitious material in cement paste. i-i P is the Hamelin constant between particles of the same cementitious material in cement paste; i-j A represents the contact probability between two different cementitious material particles in cement paste; i-j The Hamelck constant is the interparticle size distribution between two different cementitious materials in cement paste. 2.3: Based on the cementitious material parameters obtained in steps 2.1 and 2.2, the yield stress and plastic viscosity of cement paste are predicted using equations (4) and (5), respectively: （4） （5） In the formula: Let be the yield stress of cement paste, in Pa; and These are the minimum and maximum volume fractions of freshly mixed cement paste, respectively, with values ​​of 0.03 and 0.7 for freshly mixed cement paste. This refers to the volume fraction of freshly mixed cement paste. Equivalent Hamek constant for cementitious materials; This represents the relative volume increment, with a value of 187.

46. This is the particle size distribution function, with a value of 1; The average volume radius of the cementitious material; The closest distance between particles in the suspension system is 3.2 nm; is the plastic viscosity of cement paste, Pa·s; Porosity; This refers to the water-to-binder ratio.

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