Specific volume weight stone powder content fluctuation machine-made sand concrete mix proportion design method for immersed tube tunnel

Abstract

The invention discloses a method for designing the mix proportion of machine-made sand concrete with fluctuation of the content of specific volume-weight stone powder for an immersed tunnel, which comprises the following steps of: determining the use amount of a cementing material according to the preparation strength of the concrete, calculating the water-binder ratio according to a water-binder ratio formula considering the fluidity, and solving the water consumption; according to the initial sand ratio, simultaneous solving is conducted based on a mass method, and the initial raw material dosage is obtained; adjusting the use amount of the cementing material, the water consumption and the sand ratio according to different contents of the machine-made sand powder to obtain the adjusted use amount of the raw material, and determining the use amount of the water reducing agent and the final water consumption on the basis of the adjusted use amount of the raw material; determining the type and the mixing amount range of the air entraining agent by combining the adaptability of the water reducing agent and the air entraining agent; and determining the relative volume based on the adjusted raw material dosage, calculating the gas content required by the concrete according to a volumetric method, and determining the mixing amount of the air entraining agent on the basis to obtain the final concrete mix proportion. According to the design method, the working performance, the mechanical performance and the volume weight of the immersed tube concrete with the mix proportion all meet the requirements of immersed tube tunnel engineering.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a method for designing a mix ratio of machine-made sand concrete with a specific bulk density and fluctuating stone powder content for an immersed tube tunnel. Background Art

[0002] As an important part of my country's cross-sea and cross-river channels, the safety and reliability of the structure in service has received extensive attention. Concrete immersed tube tunnels are widely used, and the mix design of immersed tube concrete is an important guarantee to ensure the safety of the immersed tube structure and improve the service life of the structure. Through a reasonable mix design method, it can not only ensure that the physical, mechanical and durability properties of the concrete material meet the design requirements, but also provide better working performance for on-site concrete mixing, transportation, pouring and other processes.

[0003] The immersed tube needs to be floated on the water to the designated location before it can be sunk and installed. During the floating process, the freeboard height of the pipe section needs to be kept at an appropriate height at all times. The bulk density of the immersed tube is the key factor in controlling the freeboard height. If the bulk density of the immersed tube is too large, it may cause the problem of natural floating. If the bulk density of the immersed tube is uneven, it may cause inclined floating. This puts higher requirements on the bulk density and bulk density deviation of the immersed tube concrete. Therefore, it is necessary to ensure the accuracy of bulk density control from the mix design stage to provide support for actual construction.

[0004] Faced with the problem of scarce river sand resources, the preparation of machine-made sand concrete has become the main means of saving river sand in the current construction engineering and building materials fields. At the same time, machine-made sand also has cost advantages. However, the production of machine-made sand requires screening, crushing and washing processes, which makes it inevitable that there is stone powder in the machine-made sand. At the same time, affected by different manufacturers, different equipment and processes, even the machine-made sand with the same source of material has a different stone powder content. The stone powder content will also bring negative effects such as poor compatibility with admixtures and affect the comprehensive performance of concrete. It is necessary to consider the actual content of stone powder and avoid the impact of stone powder in the mix design method.

[0005] At present, the bulk density control of immersed tube concrete mainly adopts the method of adjusting the mix ratio after a large number of tests and measurements. In addition to the problem of cumbersome workload and long time consumption, it is also easily affected by the environment, materials and casting process, and lacks theoretical guidance. At present, there are studies on regulating the bulk density of immersed tube concrete by controlling the air content of concrete, but the effect of air entrainment and foam stabilization in machine-made sand concrete is still inconclusive, and its application in immersed tube concrete is also rare, which may lead to the problem of insufficient precision of bulk density control. At the same time, the current domestic and foreign literature has not yet formed a systematic guidance method from the perspective of mix ratio design method, and more of them are determined by a large number of tests to determine the concrete mix ratio that meets the performance and bulk density requirements. At the same time, the presence of machine-made sand and stone powder will reduce the working performance of concrete, easily cause concrete non-uniformity, and cause the floating and deflection of the immersed tube. The presence of stone powder will also affect the effect of the air entraining agent, resulting in poor foam stabilization effect. The fluctuation of stone powder content in machine-made sand concrete further increases the above-mentioned influence. It can be seen that it is currently impossible to solve the problem of accurate bulk density control of machine-made sand concrete with different stone powder contents from the perspective of mix ratio design. Summary of the invention

[0006] In order to solve the problem that the bulk density of machine-made sand immersed tube concrete in the prior art cannot be accurately controlled and the negative impact of machine-made sand and stone powder content on concrete performance and bulk density, the present invention provides a method for designing a mix ratio of machine-made sand concrete with a specific bulk density and stone powder content fluctuation for immersed tube tunnels. The design method ensures the strength and working performance of concrete based on the amount of multi-component cementitious materials and the strength formula of machine-made sand concrete, determines the required air content based on the use of mass method and volume method, adjusts the amount of raw materials according to the stone powder content and considers the control effect and adaptability of the air entraining agent to accurately control the working performance of the mixture and the bulk density of concrete. Each calculation parameter is clear and easy to obtain, the calculation process is simple and clear, and the mix ratio of machine-made sand concrete with a specific bulk density and stone powder content fluctuation can be accurately calculated. Under this mix ratio, the working performance, mechanical properties and bulk density of the immersed tube concrete meet the requirements of immersed tube tunnel engineering.

[0007] In order to achieve the above technical objectives, the present invention proposes the following technical solutions:

[0008] A method for designing a mix ratio of machine-made sand concrete with a specific bulk density and a fluctuating stone powder content for an immersed tube tunnel comprises the following steps:

[0009] Determine the amount of cementitious materials according to the concrete configuration strength, calculate the water-binder ratio according to the water-binder ratio formula considering fluidity, and then calculate the water consumption;

[0010] According to the initial sand ratio, the initial raw material consumption is obtained by simultaneous solution and calculation based on the mass method;

[0011] According to the different contents of machine-made sand and gravel powder, the amount of cementitious materials, water consumption and sand ratio are adjusted to obtain the adjusted amount of raw materials, and the amount of water reducing agent and the final water consumption are determined based on the adjusted amount of raw materials;

[0012] Determine the type and dosage range of air-entraining agent based on the compatibility of water-reducing agent and air-entraining agent;

[0013] The relative volume is determined based on the adjusted raw material dosage, and the required air content of the concrete is calculated by the volume method. On this basis, the amount of air-entraining agent is determined to obtain the final concrete mix ratio.

[0014] Further, the amount of the gelling material W b The calculation formula is:

[0015]

[0016] Where: W b is the amount of cementitious material used, in kg / m 3 ;f cu,k is the concrete configuration strength, in MPa; f c,1 k is the 28-day compressive strength of cement mortar, in MPa; s The cement dosage for mortar test, in kg / m 3 ; α1 and α2 are regression coefficients.

[0017] Furthermore, the f cu,k The strength guarantee rate is 95%, f cu,k According to the "Ordinary Concrete Mix Design Code" JGJ 55-2011, the f c,1 It is determined by actual measurement using the test method of "Test method for strength of cement mortar (ISO method)" GB / T 17671-2021.

[0018] Furthermore, the values ​​of the regression coefficients α1 and α2 can be obtained by performing linear regression according to the least squares method based on the cementitious material dosage calculation formula when there is strength data of concrete of the same raw material and strength grade C15 to C60 in the last 1 to 3 months, and the number of groups is not less than 30 groups; when there is no recent data, for concrete of strength grade C15 to C25, α1 and α2 are taken as 0.9 and 1.1 respectively, and for concrete of strength grade C30 to C60, α1 and α2 are taken as 0.95 and 1.05 respectively.

[0019] Furthermore, the cementitious material is cement, fly ash, slag powder, and the cement is silicate cement or ordinary silicate cement;

[0020] The cement dosage W cem =η cem W b, fly ash dosage W fly =η fly W b , slag powder dosage W sla =η sla W b ;

[0021] Where: η cem , η fly , η sla are the proportion coefficients of cement, fly ash and slag powder respectively;

[0022] Among them, the proportionality coefficient η cem , η fly , η sla Determined according to test or experience requirements and meeting η cem Not less than 0.5, η fly and η sla No more than 0.45, η cem , η fly , η sla The sum of the three equals 1.0.

[0023] Furthermore, the water-binder ratio formula considering fluidity is:

[0024]

[0025] Where: w / b is the water-binder ratio; f b is the strength of cementitious materials at 28 days, in MPa, calculated according to the Code for Design of Ordinary Concrete Mix Proportion JGJ 55-2011; h tgt It is the target slump designed according to the mix ratio, in mm. If the target slump is lower than 160 mm, take 160 and substitute it in the calculation.

[0026] Furthermore, the initial sand ratio is determined according to the "Code for Design of Ordinary Concrete Mix" JGJ 55-2011, the assumed mass in the mass method is the target bulk density of the immersed tube tunnel, and the target bulk density of the immersed tube tunnel is determined according to the design requirements of the immersed tube tunnel concrete.

[0027] Furthermore, the adjustment of the amount of cementitious material, the amount of water and the sand ratio according to the different contents of the machine-made sand and gravel powder refers to:

[0028] When the content of machine-made sand and gravel powder is δ≤2%, the amount of cementitious materials, water consumption and sand ratio shall not be adjusted;

[0029] When 2%<δ≤10%, all stone powder is included in the amount of cementitious materials, the water-cement ratio remains unchanged, and the adjusted water consumption is calculated based on the cementitious materials amount and water-cement ratio at this time, and the sand ratio is not adjusted;

[0030] When 10%<δ≤20%, 10% of the stone powder will be included in the amount of cementitious materials. For the δ-10% part of the stone powder, for every 5% increase, the water-cement ratio will increase by 0.02, and the water consumption will be calculated based on the cementitious materials consumption and the water-cement ratio at this time; for the δ-10% part of the stone powder, for every 2% increase, the sand rate will increase by 0.01, and the adjusted raw material consumption will be calculated on this basis.

[0031] Furthermore, the machine-made sand needs to satisfy an MB value of no more than 1.4, and the machine-made sand and gravel powder content δ does not exceed 20%, and the machine-made sand and gravel powder content refers to the content of particles with a particle size of less than 0.075 mm in the machine-made sand.

[0032] Furthermore, the content of the machine-made sand and gravel powder is measured using the test method of "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52-2006.

[0033] Furthermore, the adjusted sand ratio ranges from 30% to 45%, and when the adjusted sand ratio exceeds 45%, 45% is taken.

[0034] Furthermore, the water reducing agent dosage and the final water consumption are determined by conducting concrete tests on a cementitious material system determined based on the adjusted raw material dosage.

[0035] Furthermore, the compatibility of the water reducing agent and the air entraining agent is determined by jointly testing the mortar fluidity of the water reducing agent and the air entraining agent and the surface tension of the air entraining agent and the water reducing agent solution;

[0036] Among them, the fluidity reduction rate of the mortar containing the water-reducing agent after adding the air-entraining agent shall not exceed 15%; the surface tension growth rate of the solution containing the air-entraining agent after adding the water-reducing agent shall not exceed 15%, and the surface tension of the solution containing the air-entraining agent after adding the water-reducing agent shall not be higher than 60mN / m;

[0037] When the above two conditions are met, the water reducing agent and the air entraining agent are judged to be well compatible, and the dosage range of the air entraining agent is determined based on the test results.

[0038] Furthermore, the tests of mortar fluidity and solution surface tension are carried out according to a cementitious material system determined by adjusted raw material dosage, and during the test, the deviation of the artificial sand and gravel powder content is selected to be no more than 0.2%, and the water reducer and air entraining agent are added according to the mass fraction of the cementitious material.

[0039] Furthermore, the required air content θ of the concrete is calculated according to the following formula based on the volume method:

[0040]

[0041] Where: V represents the relative volume, which is the ratio of the total mass of the adjusted raw material mix to the assumed mass, m i , iThey are the unit volume mass and density of each raw material except water reducing agent and air entraining agent, both in kg / m 3 .

[0042] Furthermore, the amount of air-entraining agent is determined by a concrete test in which only the amount of air-entraining agent is changed on the basis of determining the type and amount range of the air-entraining agent. The test can be carried out by the dichotomy principle on the basis of the amount range of the air-entraining agent until the required air content of the concrete is reached, or the amount of air-entraining agent can be gradually determined by a gradient test method. The amount of air-entraining agent at this time is the amount of air-entraining agent of the final concrete mix ratio.

[0043] Furthermore, the vibration time of the concrete test needs to be determined according to site requirements.

[0044] The concrete mix design method of the invention is suitable for machine-made sand immersed tube tunnel concrete with a machine-made sand and stone powder content not exceeding 20% ​​and a strength grade of C15 to C60.

[0045] The concrete mix design method proposed in the present invention has a simple calculation formula and process, and takes into account the performance change law of machine-made sand concrete due to stone powder content fluctuation and the requirements of immersed tube tunnel concrete for bulk density, workability and mechanical properties. Through a clear calculation method, the huge workload caused by repeated adaptation is reduced, the efficiency of mix design is greatly improved, and the quality of concrete is guaranteed from the calculation method level.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The concrete mix design method of the present invention can ensure that the mechanical properties, work performance and bulk density of the machine-made sand concrete meet the design requirements; the design of the present invention is to first determine the amount of cementitious material based on the concrete configuration strength, and then use the water-cement ratio formula considering the fluidity to determine the water-cement ratio, thereby ensuring sufficient slurry dosage and rheological properties, overcoming the problems of too little slurry and unsatisfactory workability caused by the prior art, and too much slurry resulting in excessive water reducer dosage, too high hydration heat and uneconomical conditions.

[0048] 2. The present invention uses different calculation methods for different contents of stone powder, thereby avoiding the performance difference caused by using the same ratio design method for machine-made sand with different stone powder contents. The present invention not only gives full play to the advantages of stone powder as an inert filler, but also avoids the problem of performance degradation caused by excessive stone powder content leading to a decrease in the actual water-binder ratio and thus performance degradation.

[0049] 3. The concrete mix design method of the present invention is adopted to determine the air content requirement for a specific bulk density by substituting the mass method of the target bulk density of the immersed tube tunnel and the volume method formula considering the air content. This overcomes the problem that the current technology cannot take into account both the bulk density and performance of machine-made sand concrete in the mix design stage, and ensures that the bulk density and performance of the configured concrete meet the design requirements.

[0050] 4. The concrete mix design method of the present invention adjusts the mix ratio according to different cementitious material systems, stone powder content and design requirements, which can reduce the carbon emission of concrete and reduce the hydration heat. The use of machine-made sand with different stone powder contents can help alleviate the problem of insufficient river sand and has a positive effect on the promotion and application of machine-made sand with different stone powder contents. The present invention has good operability and applicability, and has obvious economic and social benefits. DETAILED DESCRIPTION

[0051] The technical solution of the present invention will be clearly and completely described below in conjunction with this specific embodiment. Obviously, the described embodiment is only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0052] The raw materials used in the following examples 1 to 2 are: cement using P·Ⅱ42.5 grade cement with a specific surface area of ​​316m 2 / kg; the fly ash is Class F I fly ash, with a water requirement ratio of 95% and an activity index of 71%; the slag powder is S95 slag powder with a specific surface area of ​​436m 2 / kg, fluidity ratio 101%, activity index 101%; fine aggregate is machine-made sand with a fineness modulus of 2.8, stone powder content of 5.0-14.0%, methylene blue 1.0%, and crushing index 18%; coarse aggregate is 5-25mm continuously graded crushed stone, with a crushing value of 5% and a needle-like particle content of 3%; the water reducer is a slow-setting polycarboxylic acid water reducer; and the air entraining agent is a rosin thermal polymer air entraining agent.

[0053] Below, in conjunction with specific implementation modes, the present invention is further described in detail:

[0054] Example 1

[0055] The strength grade is C45, the slump is 200±20mm, and the bulk density is 2370±10kg / m 3 Taking the machine-made sand concrete of the immersed pipe section as an example, the mix design is carried out according to the following steps:

[0056] (1) Calculate the amount of cementitious materials based on the concrete mix strength: According to the "Ordinary Concrete Mix Design Code" JGJ55-2011, the concrete mix strength is calculated to be 53.225MPa. According to the "Test Method for Cement Mortar Strength (ISO Method)" GB / T 17671-2021, the 28-day compressive strength of cement mortar is 52.8MPa. The amount of cement used in the mortar test is 450kg / m 3 The regression coefficients α1 and α2 are 0.95 and 1.05 respectively, and the cementitious material dosage is calculated to be 410 kg / m 3 Based on the need to reduce the hydration heat of large-volume concrete of immersed tubes and the test experience of large-volume auxiliary cementitious materials, the proportion coefficients of cement, fly ash and slag powder are determined to be 0.5, 0.3 and 0.2 respectively.

[0057] (2) Calculate the water-binder ratio and determine the water consumption according to the water-binder ratio formula taking into account fluidity: Calculate the 28-day cementitious material strength f according to the "Ordinary Concrete Mix Design Code" JGJ 55-2011 b The target slump is 200 mm, the fly ash and slag powder ratios are 0.3 and 0.2 respectively, and the water-binder ratio is 0.38 when the water consumption is 156 kg / m 3 .

[0058] (3) Solve the initial raw material consumption by combining the initial sand ratio and mass method: According to the "Ordinary Concrete Mix Design Code" JGJ 55-2011, the initial sand ratio is 42%, combined with the target bulk density of 2370kg / m 3 , the mass method is used to solve the amount of machine-made sand, which is 758kg / m 3 , the amount of crushed stone is 1046kg / m 3 .

[0059] (4) Adjust the cementitious material dosage, water consumption and sand ratio according to the stone powder content of the machine-made sand: The test method of "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52-2006 was used for measurement, and the stone powder content of the machine-made sand was measured to be 8.9%. Therefore, only the water consumption was corrected, and the 8.9% stone powder was included in the cementitious material, that is, 67.46 kg / m 3 At this time, the total amount of cementitious materials is 477.46kg / m 3 , combined with the water-binder ratio, the water consumption is calculated to be 181kg / m 3 At this dosage, after concrete trial mixing, when the water reducing agent dosage was 1.1%, the water reduction rate was 15%, and the expected slump could be achieved under the condition of economic dosage, and the workability was good. The final water consumption was determined to be 154kg / m 3 .

[0060] (5) Determine the dosage range of air-entraining agent: The fluidity test of water-reducing agent-air-entraining agent mortar was designed with gradient tests of 0, 2.0 / 100000, 2.5 / 100000, 3.0 / 100000, 3.5 / 100000 and 4 / 100000. When the air-entraining agent dosage was 2.0 / 100000-3.5 / 100000, the fluidity reduction rate of the mortar did not exceed 15%. The surface tension of the air-entraining agent solution with an air-entraining agent dosage of 2.0 / 100000-3.5 / 100000 and the mixed solution with 1.1% water-reducing agent added were tested. The surface tension growth rate of the solution did not exceed 15%, and the surface tension of the solution after adding the water-reducing agent was not higher than 60mN / m. It was determined that the air-entraining agent met the requirements and the appropriate dosage was 2.0 / 100000-3.5 / 100000.

[0061] (6) Determine the required air content of concrete and the amount of air-entraining agent: The density of cement measured according to the relevant standards is 3.09 kg / dm 3 The density of fly ash is 2.3kg / dm 3 , the density of slag powder is 2.9kg / dm 3 , the density of machine-made sand is 2.82kg / dm 3 The density of crushed stone is 2.7kg / dm 3 , combined with the determined amounts of each raw material, substituted into the formula for the required air content of concrete, the relative volume V is 99.915%, and the required air content of concrete is calculated to be 4.1%. Through the concrete test of only changing the amount of air entraining agent, a gradient test of three air entraining agent contents of 2.0 / 100000, 2.5 / 100000, and 3.0 / 100000 was set. When the required air content of concrete was reached, the amount of air entraining agent was 2.5 / 100000.

[0062] The mix ratio of the machine-made sand concrete of this embodiment is shown in Table 1, and the working performance, mechanical properties and bulk density are shown in Table 2.

[0063] Example 2

[0064] The strength grade is C45, the slump is 200±20mm, and the bulk density is 2400±10kg / m 3 Taking the machine-made sand concrete of the immersed pipe section as an example, the mix design is carried out according to the following steps:

[0065] (1) Calculate the amount of cementitious materials based on the concrete mix strength: According to the "Ordinary Concrete Mix Design Code" JGJ55-2011, the concrete mix strength is calculated to be 53.225MPa. According to the "Cement Mortar Strength Test Method (ISO Method)" GB / T 17671-2021, the 28-day compressive strength of cement mortar is 51.6MPa. The amount of cement used in the mortar test is 450kg / m3 The regression coefficients α1 and α2 are 0.95 and 1.05 respectively, and the cementitious material dosage is calculated to be 420 kg / m 3 Based on the need to reduce the hydration heat of large-volume concrete of immersed tubes and the test experience of large-volume auxiliary cementitious materials, the proportion coefficients of cement, fly ash and slag powder are determined to be 0.5, 0.25 and 0.25 respectively.

[0066] (2) Calculate the water-binder ratio and determine the water consumption according to the water-binder ratio formula taking into account fluidity: Calculate the 28-day cementitious material strength f according to the "Ordinary Concrete Mix Design Code" JGJ 55-2011 b The target slump is 200 mm, the fly ash and slag powder ratio coefficients are 0.25 and 0.25 respectively, and the water-binder ratio is 0.39 when the water consumption is 164 kg / m 3 .

[0067] (3) Solve the initial raw material consumption by combining the initial sand ratio and mass method: The initial sand ratio is 42% according to the "Ordinary Concrete Mix Design Code" JGJ 55-2011, combined with the target bulk density of 2400kg / m 3 , the mass method is used to solve the amount of machine-made sand, which is 763kg / m 3 , the amount of crushed stone is 1053kg / m 3 .

[0068] (4) Adjust the cementitious material dosage, water consumption and sand ratio according to the stone powder content of machine-made sand: The test method of "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52-2006 was used for measurement. The stone powder content of machine-made sand was 12.0%, which was greater than 10%. Therefore, the water consumption, water-cement ratio and sand ratio were corrected, and the 10% stone powder was included in the cementitious material, that is, 76.3kg / m 3 At this time, the total amount of cementitious materials is 496.3kg / m 3 ; According to the requirement that the water-binder ratio increases by 0.02 for every 5% increase in the stone powder of δ-10%, the revised water-binder ratio is 0.398; According to the requirement that the sand ratio increases by 0.01 for every 2% increase in the stone powder of δ-10%, the revised sand ratio is 0.43. Based on the correction of the cementitious material dosage, water-binder ratio and sand ratio, the water consumption is calculated to be 198kg / m 3 , the amount of machine-made sand is 779kg / m 3 , the amount of crushed stone is 1032kg / m 3 At this dosage, after concrete trial mixing, when the water reducing agent dosage is 1.2%, the water reduction rate is 15%, and the expected slump can be achieved under the condition of economic dosage, and the workability is good. The final water consumption is determined to be 168kg / m 3.

[0069] (5) Determine the range of air-entraining agent dosage: For the fluidity test of water-reducing agent-air-entraining agent mortar, a gradient test was designed with the following values: 0, 2.0 / 100000, 2.5 / 100000, 3.0 / 100000, 3.5 / 100000 and 4 / 100000. When the air-entraining agent dosage was between 2.5 / 100000 and 3.5 / 100000, the reduction rate of mortar fluidity did not exceed 15%. The surface tension of the air-entraining agent solution with a dosage of 2.5 / 100000 and the mixed solution with 1.2% water-reducing agent added was tested. The results showed that the surface tension growth rate of the solution did not exceed 15% when the air-entraining agent dosage was 2.5 / 100000 to 3.5 / 100000, and the surface tension of the solution after adding the water-reducing agent was not higher than 60mN / m. It was determined that the air-entraining agent met the requirements and the appropriate dosage was 2.5 / 100000 to 3.5 / 100000.

[0070] (6) Determine the required air content of concrete and the amount of air-entraining agent: The density of cement measured according to the relevant standards is 3.09 kg / dm 3 The density of fly ash is 2.3kg / dm 3 , the density of slag powder is 2.9kg / dm 3 , the density of machine-made sand is 2.82kg / dm 3 The density of crushed stone is 2.7kg / dm 3 , combined with the determined amounts of each raw material, substituted into the formula for the required air content of concrete, the relative volume V is 99.958%, and the required air content of concrete is calculated to be 2.34%. Through the concrete test of only changing the amount of air entraining agent, a gradient test of three air entraining agent contents of 2.5 / 100000, 3.0 / 100000, and 3.5 / 100000 was set. When the required air content of concrete was reached, the air entraining agent content was determined to be 3.0 / 100000.

[0071] The mix ratio of the machine-made sand concrete of this embodiment is shown in Table 1, and the working performance, mechanical properties and bulk density are shown in Table 2.

[0072] Table 1 Mix ratio of machine-made sand concrete in Example 1 and Example 2

[0073]

[0074] Table 2 Working performance, mechanical properties and bulk density of machine-made sand concrete of Example 1 and Example 2

[0075]

[0076] Examples 1 and 2 show that: for the mix ratio of machine-made sand sedimentation tube concrete with fluctuating stone powder content, the mix ratio design method of the present invention can effectively solve the problem of incompatibility between admixtures and stone powder content and the problem of low bulk density control accuracy, and the working performance and mechanical properties of concrete meet the engineering requirements, with certain technical and economic rationality and significant social and economic benefits.

[0077] Comparative Example 1

[0078] The strength grade is C45, the slump is 200±20mm, and the bulk density is 2370±10kg / m 3 Taking the machine-made sand concrete of the immersed pipe section as an example, the raw materials used are the same as those in Example 1, and the mix ratio design is carried out according to the following steps:

[0079] (1) The test method of "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52-2006 was used for measurement, and the content of machine-made sand and stone powder was measured to be 8.9%.

[0080] (2) The concrete mix ratio was calculated according to the "Ordinary Concrete Mix Design Code" JGJ 55-2011. The proportion of cementitious materials was the same as that in Example 1. The mix ratio of machine-made sand concrete was shown in Table 3. The working performance, mechanical properties and bulk density were shown in Table 4.

[0081] Comparative Example 2

[0082] The strength grade is C45, the slump is 200±20mm, and the bulk density is 2400±10kg / m 3 Taking the machine-made sand concrete of the immersed pipe section as an example, the raw materials used are the same as those in Example 2, and the mix ratio design is carried out according to the following steps:

[0083] (1) The test method of "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52-2006 was used for measurement, and the content of machine-made sand and stone powder was measured to be 12%.

[0084] (2) The concrete mix ratio was calculated according to the "Ordinary Concrete Mix Design Code" JGJ 55-2011. The proportion of cementitious materials was the same as that in Example 2. The mix ratio of machine-made sand concrete was shown in Table 3. The working performance, mechanical properties and bulk density were shown in Table 4.

[0085] Table 3 Mix ratio of machine-made sand concrete in comparative example 1 and comparative example 2

[0086]

[0087] Table 4 Working performance, mechanical properties and bulk density of machine-made sand concrete of comparative example 1 and comparative example 2

[0088]

[0089] It can be seen from Comparative Examples 1 and 2 that: for machine-made sand containing stone powder, since the existing technical method does not consider the influence of the stone powder content of machine-made sand on the working performance, mechanical properties and bulk density of concrete, the mix ratio of cementitious materials calculated in the mix ratio design stage is too high, which brings about the problems of excessive hydration heat and increased cost, and the influence of the stone powder content leads to excessive use of water reducer and air entraining agent, and the working performance and mechanical properties are reduced; at the same time, since the existing technical method does not consider bulk density control, the influence of stone powder and the adaptability of air entraining agent-water reducer are not considered, the air content control is not accurate, so that the bulk density does not meet the design requirements.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing a mix ratio of machine-made sand concrete with a specific bulk density and fluctuating stone powder content for an immersed tube tunnel, characterized in that: The following steps are involved: Determine the amount of cementitious materials according to the concrete configuration strength, calculate the water-binder ratio according to the water-binder ratio formula considering fluidity, and then calculate the water consumption; According to the initial sand ratio, the initial raw material consumption is obtained by simultaneous solution and calculation based on the mass method; According to the different contents of machine-made sand and gravel powder, the amount of cementitious materials, water consumption and sand ratio are adjusted to obtain the adjusted amount of raw materials, and the amount of water reducing agent and the final water consumption are determined based on the adjusted amount of raw materials; Determine the type and dosage range of air-entraining agent based on the compatibility of water-reducing agent and air-entraining agent; The relative volume is determined based on the adjusted raw material dosage, and the required air content of the concrete is calculated by the volume method. On this basis, the amount of air-entraining agent is determined to obtain the final concrete mix ratio.

2. The method for designing the mix ratio of machine-made sand concrete with a specific bulk density and a fluctuating stone powder content for an immersed tube tunnel according to claim 1 is characterized in that: The amount of the gelling material W b The calculation formula is: Where: W b is the amount of cementitious material used, in kg / m 3 ; f cu,k is the concrete configuration strength, in MPa; f c,1 k is the 28-day compressive strength of cement mortar, in MPa; s The cement dosage for mortar test, in kg / m 3 ; α1, α2 are regression coefficients; The f cu,k The strength guarantee rate is 95%, f cu,k According to the "Ordinary Concrete Mix Design Code" JGJ 55-2011, the f c,1 Determined by actual measurement using the test method of "Test method for strength of cement mortar (ISO method)" GB / T 17671-2021; The values ​​of the regression coefficients α1 and α2 can be obtained by performing linear regression using the least squares method based on the cementitious material dosage calculation formula when there are strength data of concrete of the same raw material and strength grade C15 to C60 in the most recent 1 to 3 months, and the number of groups is not less than 30. When there are no recent data, for concrete of strength grade C15 to C25, α1 and α2 are taken as 0.9 and 1.1 respectively, and for concrete of strength grade C30 to C60, α1 and α2 are taken as 0.95 and 1.05 respectively.

3. The method for designing the mix ratio of machine-made sand concrete with a specific bulk density and fluctuating stone powder content for an immersed tube tunnel according to claim 2, characterized in that: The cementitious material is cement, fly ash, slag powder, and the cement is silicate cement or ordinary silicate cement; The cement dosage W cem =η cem W b , fly ash dosage W fly =η fly W b , slag powder dosage W sla =η sla W b ; Where: η cem , η fly , η sla are the proportion coefficients of cement, fly ash and slag powder respectively; Among them, the proportionality coefficient η cem , η fly , η sla Determined according to test or experience requirements and meeting η cem Not less than 0.5, η fly and η sla No more than 0.45, η cem , η fly , η sla The sum of the three equals 1.

0.

4. The method for designing mix proportion of machine-made sand concrete with fluctuating specific bulk density and stone powder content for immersed tube tunnel according to claim 3 is characterized in that: The water-binder ratio formula considering fluidity is: Where: w / b is the water-binder ratio; f b is the strength of cementitious materials at 28 days, in MPa, calculated according to the Code for Design of Ordinary Concrete Mix Proportion JGJ 55-2011; h tgt It is the target slump designed according to the mix ratio, in mm.

5. The method for designing mix proportion of machine-made sand concrete with fluctuating specific bulk density and stone powder content for immersed tube tunnel according to claim 1, characterized in that: The initial sand ratio is determined according to the "Code for Design of Ordinary Concrete Mix" JGJ 55-2011. The assumed mass in the mass method is the target bulk density of the immersed tube tunnel, and the target bulk density of the immersed tube tunnel is determined according to the design requirements of the immersed tube tunnel concrete.

6. The method for designing mix proportion of machine-made sand concrete with fluctuating specific bulk density and stone powder content for immersed tube tunnel according to claim 1, characterized in that: The adjustment of the amount of cementitious materials, water consumption and sand ratio according to the different contents of machine-made sand and gravel powder refers to: When the content of machine-made sand and gravel powder δ≤2%, the amount of cementitious materials, water consumption and sand ratio shall not be adjusted; When 2%<δ≤10%, all stone powder is included in the amount of cementitious materials, the water-cement ratio remains unchanged, and the adjusted water consumption is calculated based on the cementitious materials and water-cement ratio at this time, and the sand ratio is not adjusted; When 10%<δ≤20%, 10% of the stone powder will be included in the amount of cementitious materials. For the δ-10% part of the stone powder, for every 5% increase, the water-cement ratio will increase by 0.02, and the water consumption will be calculated based on the cementitious materials consumption and the water-cement ratio at this time; for the δ-10% part of the stone powder, for every 2% increase, the sand rate will increase by 0.01, and the adjusted raw material consumption will be calculated on this basis.

7. The method for designing the mix ratio of machine-made sand concrete with a specific bulk density and a fluctuating stone powder content for an immersed tube tunnel according to claim 6, characterized in that: The machine-made sand must satisfy the MB value of no more than 1.4, and the machine-made sand and stone powder content δ must not exceed 20%, where the machine-made sand and stone powder content refers to the content of particles with a particle size of less than 0.075 mm in the machine-made sand; The content of machine-made sand and stone powder is determined by the test method of "Standard for Quality and Inspection Methods of Sand and Stone for Ordinary Concrete" JGJ 52-2006; The adjusted sand ratio range is 30% to 45%. When the adjusted sand ratio exceeds 45%, 45% is taken. The amount of water reducing agent and the final amount of water are determined by concrete tests based on the cementitious material system determined by the adjusted raw material amounts.

8. The method for designing mix proportion of machine-made sand concrete with fluctuating specific bulk density and stone powder content for immersed tube tunnel according to claim 1, characterized in that: The compatibility of the water reducing agent and the air entraining agent is determined by jointly testing the mortar fluidity of the water reducing agent and the air entraining agent and the surface tension of the air entraining agent and the water reducing agent solution; Among them, the fluidity reduction rate of the mortar containing the water-reducing agent after adding the air-entraining agent shall not exceed 15%; the surface tension growth rate of the solution containing the air-entraining agent after adding the water-reducing agent shall not exceed 15%, and the surface tension of the solution containing the air-entraining agent after adding the water-reducing agent shall not be higher than 60mN / m; When the above two conditions are met, it is determined that the water reducing agent and the air entraining agent are well compatible, and the dosage range of the air entraining agent is determined according to the test results; The tests of mortar fluidity and solution surface tension are carried out according to the cementitious material system determined by the adjusted raw material dosage. During the test, the deviation of the machine-made sand and stone powder content is selected to be no more than 0.2%. The water reducer and air entraining agent are added according to the mass fraction of the cementitious material.

9. The method for designing mix proportion of machine-made sand concrete with fluctuating specific bulk density and stone powder content for immersed tube tunnel according to claim 1, characterized in that: The required air content θ of the concrete is calculated according to the volume method as follows: Where: V represents the relative volume, which is the ratio of the total mass of the adjusted raw material mix to the assumed mass, m i , i They are the unit volume mass and density of each raw material except water reducing agent and air entraining agent, both in kg / m 3 .

10. The method for designing mix proportion of machine-made sand concrete with fluctuating specific bulk density and stone powder content for immersed tube tunnel according to claim 1, characterized in that: The amount of air-entraining agent is determined by concrete testing by changing only the amount of air-entraining agent on the basis of determining the type and amount range of the air-entraining agent. The test can be conducted by the dichotomy principle on the basis of the amount range of the air-entraining agent until the required air content of the concrete is reached, or the amount of air-entraining agent can be gradually determined by a gradient test method. The amount of air-entraining agent at this time is the amount of air-entraining agent of the final concrete mix ratio.

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