Methods for controlling the temperature at the outlet of a concrete mixing plant

Abstract

This invention provides a method for controlling the outlet temperature of a concrete mixing plant, namely: first, determining the temperature control information of the concrete mixing raw materials before they enter the storage area; calculating the outlet temperature of the concrete mixing plant; determining the upper and lower limits of water temperature and ice-water mass ratio, as well as the incremental values ​​for adjusting each parameter; prioritizing the adjustment of water temperature according to the set water temperature increment, and then adjusting the ice-water mass ratio until the outlet temperature meets the design requirements. If neither water temperature adjustment nor ice-water ratio adjustment can make the outlet temperature meet the design requirements, the aggregate cooling system is adjusted to lower the aggregate temperature or change the design value of the outlet temperature. The advantage of this invention is that it can accurately grasp the temperature of concrete aggregates before mixing, accurately calculate the concrete outlet temperature, and the required water temperature or amount of ice, overcoming the drawback of traditional outlet temperature calculations where errors in judging the concrete aggregate temperature lead to incorrect subsequent adjustments in ice amount or water temperature, resulting in the outlet temperature consistently failing to meet the design requirements.

Description

Technical Field

[0001] This invention relates to a method for controlling the temperature at the outlet of a concrete mixing plant. This invention belongs to the field of large-volume concrete construction technology. Background Technology

[0002] Because the heat generated by the hydration and temperature rise inside large-volume concrete cannot dissipate into the air in time after pouring, the internal temperature of the concrete structure undergoes a process of initial temperature rise followed by temperature drop. Consequently, the concrete initially exhibits compressive stress, which then transitions to tensile stress. Once the tensile stress inside the concrete exceeds its tensile strength, the large-volume concrete will crack.

[0003] One important factor affecting the tensile stress amplitude of concrete is the concrete pouring temperature, specifically the temperature at the outlet of the concrete mixing plant. This is the temperature of the concrete ready for pouring after the various raw materials have been mixed. The lower this temperature, the lower the peak temperature of the concrete hydration reaction, the smaller the temperature drop from the peak temperature to ambient temperature, the lower the final tensile stress inside the concrete, and the lower the risk of cracking.

[0004] However, there is currently no effective model or method for predicting and controlling the outlet temperature of concrete mixing plants, mainly because:

[0005] 1) The influence of the internal temperature of extra-large stone aggregate and large stone aggregate, as well as the temperature after air cooling, on the outlet temperature of the concrete mixing plant was ignored.

[0006] Currently, mass concrete typically uses four-level aggregate mixes: extra-large stone, large stone, medium stone, and small stone. For extra-large stone aggregate (i.e., coarse aggregate), the particle size can reach 12cm. There is a natural temperature difference between the surface and the interior of the aggregate. Therefore, when controlling the temperature at the outlet of the mixing plant, if the internal temperature of extra-large stone aggregate and large stone aggregate is not considered, and only the surface temperature is considered, it will inevitably lead to inaccurate control of the internal temperature rise of the poured concrete. This will result in an inadequate formulation of temperature control and crack prevention measures, and a high risk of concrete cracking.

[0007] Furthermore, due to the specific requirements for concrete temperature control in some projects, the extra-large stone and large stone aggregates used in concrete mixing undergo air-cooling treatment. A temperature gradient exists between the surface and internal temperatures of these aggregates, and the temperature of the air-cooled aggregates significantly impacts the outlet temperature of the concrete mixing plant. Ignoring these factors would undoubtedly lead to inaccurate design of the concrete mixing plant's outlet temperature, causing the maximum internal temperature rise after large-volume concrete pouring to differ from the predicted value. This results in inadequate temperature control and crack prevention measures, a high risk of concrete cracking, and compromised safety.

[0008] 2) The influence of the temperature of materials such as cement, mixing water, fly ash and admixtures on the outlet temperature of the concrete mixing plant was ignored.

[0009] When mixing concrete, materials such as cement, mixing water, fly ash and admixtures are also required. However, since the storage locations of each raw material are different and the paths they take to reach the mixing tank are also different, the temperature of the raw materials may change during the process. If these factors are ignored when calculating the temperature at the outlet of the mixing plant, it will also lead to the inability to effectively control the temperature at the outlet of the mixing plant. Summary of the Invention

[0010] For the reasons mentioned above, the purpose of this invention is to provide a model and method for effectively predicting and controlling the outlet temperature of a concrete mixing plant.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a method for controlling the temperature at the outlet of a concrete mixing plant, comprising the following steps:

[0012] S1. Determine the temperature control information before concrete mixing raw materials are placed in the storage area.

[0013] S1.1 Determine the surface temperature of extra-large stone aggregates and large stone aggregates after air cooling. The surface temperature after air cooling As its temperature before entering the warehouse

[0014] a) First, manually select several aggregates of different grades and locations from the aggregate pile, and drill holes in each aggregate up to its center. The number of holes is determined based on the actual amount required for concrete mixing. Temperature sensors are embedded on the surface and at the center of each aggregate, connected to a temperature acquisition device, to continuously collect temperature readings (T) of different grades of aggregates at different storage locations. 表 and T 内 The collection time varies depending on the season and time of day.

[0015] b) Establish a three-dimensional finite element model of the same size as the measured aggregate rockfill and divide it into meshes; assign the surface temperature and center temperature (i.e., internal temperature of aggregate) of several aggregates of different grades and locations to the measured temperature, and assign the surface temperature and center temperature of the remaining aggregates to the linear difference of the temperature of aggregates of the same grade.

[0016] c) The average temperature of the entire aggregate pile after temperature conduction between aggregates is calculated using finite element method, and this average temperature is used as the average temperature of extra-large and large stone aggregates before air cooling.

[0017] d) Based on multiple sets of T data collected at different time periods 表 and T 内The measured values ​​are input into the finite element model to calculate the average temperature of the extra-large stone aggregate and the large stone aggregate, i.e., the average temperature before air cooling. And calculate the temperature non-uniformity coefficient λ.

[0018]

[0019] e) For aggregate piles with different particle sizes, especially extra-large stone aggregates and large stone aggregates, the final temperature of the aggregate pile will be different due to the different heat transfer rates inside the pile. Therefore, steps a) to d) need to be repeated to determine the shape factor ζ of aggregates with different particle sizes. The calculation of this factor is based on the maximum particle size of 120mm for large-volume concrete aggregates.

[0020]

[0021] f) For extra-large and large stone aggregates that require air cooling, the surface temperature measured after air cooling shall be used as the basis for determining the air cooling temperature. The average temperature of extra-large stone aggregate and large stone aggregate after air cooling is calculated using the temperature non-uniformity coefficient λ.

[0022]

[0023] g) If extra-large stone aggregates and large stone aggregates undergo transportation and secondary screening before entering the mixing stage, the surface temperature T of the aggregates after transportation and secondary screening can be directly measured by actual measurement methods. i 运输筛分后 Calculate the surface temperature after air cooling to determine the corresponding temperature recovery coefficient.

[0024]

[0025] S1.2 Determine the temperature of medium and small stone aggregates before they are placed in the silo.

[0026] The surface temperature was measured directly using a field measurement method and used as the temperature before entering the warehouse.

[0027] S1.3 Determine the temperatures of cement, fly ash, water, and admixtures before they are placed in the silo for mixing.

[0028] The temperatures of cement, fly ash, water, and admixtures before mixing were measured directly and used as their temperatures before being placed in the storage silo.

[0029] S2. Establish a model for calculating the outlet temperature of the concrete mixing plant, and calculate the outlet temperature of the concrete mixing plant.

[0030] The calculation model for the outlet temperature of the concrete mixing plant is as follows:

[0031]

[0032] Where: T0—Temperature at the outlet of the concrete mixing plant (°C);

[0033] G i —The mass of the i-th material per cubic meter of concrete (kg / m³) 3 );

[0034] c i —Specific heat capacity of the i-th material (kJ / (kg·℃));

[0035] G c —Ice addition amount per cubic meter of concrete (kg / m³) 3 );

[0036] η—the utilization rate of ice's cold energy, expressed as a decimal; 1.0 can be taken for dry ice at sub-zero temperatures, and 0.9 for moist ice.

[0037] 335—Latent heat of fusion of ice (kJ / kg);

[0038] Q—Mechanical heat generated during the mixing of each cubic meter of concrete (kJ / m³) 3 Let Q = 42Pt / V, where P is the motor power of the mixer (kW), t is the mixing time (min), and V is the mixer capacity (m³). 3 (Calculated based on effective discharge volume);

[0039] T i —Temperature (°C) of the i-th material before it enters the warehouse, where the surface temperature of extra-large stone aggregate and large stone aggregate after air cooling is taken. As the temperature before storage;

[0040] λ i —Temperature non-uniformity coefficient, where i refers to extra-large stone aggregate and large stone aggregate;

[0041] —Heating coefficient, i refers to extra-large stone aggregate and large stone aggregate;

[0042] ζ i — Shape coefficient, i refers to extra-large stone aggregate and large stone aggregate;

[0043] S3. Adjust the mixing water temperature and / or ice-water mass ratio to ensure the mixing tower outlet temperature reaches the design temperature requirement.

[0044] S3.1. Collect the temperature T0 at the outlet of the concrete mixing plant;

[0045] S3.2 Determine the lower limit P0 and upper limit P1 of the water temperature and ice-water mass ratio, as well as the incremental values ​​of each parameter;

[0046] The lower limit P0 and upper limit P1 of water temperature are set to 5℃ and 10℃, respectively, and the lower limit P0 and upper limit P1 of ice-water mass ratio are set to 0% and 80%, respectively; in subsequent adjustment calculations, the water temperature increment is set to 0.5℃ and the ice-water mass ratio increment is set to 0.1.

[0047] S3.3 Adjust the water temperature and ice-water mass ratio to ensure that the temperature at the concrete mixing plant outlet meets the design requirements:

[0048] A. For pre-cooled concrete, i.e., concrete with air-cooled aggregate, the following priority adjustment shall be adopted:

[0049] According to step S3.2, the water temperature increment is adjusted first, and the ice temperature is directly adopted as the measured value. If the outlet temperature design requirement is met within the allowable ratio range, the adjustment ends. If the water temperature adjustment reaches the lower limit but still cannot meet the outlet temperature design requirement, the ice-water mass ratio is adjusted, with the amount of ice added not exceeding 80% of the mixing water volume, until the outlet temperature meets the design requirement, and the adjustment ends. When the water temperature is adjusted to the lower limit and the ice-water ratio is adjusted to the upper limit, and the outlet temperature still does not meet the requirement, the aggregate air cooling system is adjusted to further reduce the aggregate temperature or the outlet temperature design value is changed; or...

[0050] First, adjust the ice-to-water ratio, ensuring the amount of ice added does not exceed 80% of the mixing water volume. If the outlet temperature design requirements are met within the allowable ratio range, the adjustment is complete. If the outlet temperature still does not meet the design requirements after the ice-to-water mass ratio reaches its upper limit, adjust the water temperature within the specified range until the outlet temperature meets the design requirements, then the adjustment is complete. If the outlet temperature still does not meet the requirements even after the water temperature is adjusted to the lower limit and the ice-to-water ratio reaches its upper limit, then adjust the aggregate air-cooling system to further reduce the aggregate temperature or change the outlet temperature design value.

[0051] B. For preheated concrete:

[0052] If the outlet temperature is lower than the design requirement, the water temperature should be increased first; if the water temperature adjustment does not meet the requirements, the aggregate temperature should be adjusted through the aggregate air cooling system until the outlet temperature meets the design requirements. Attached Figure Description

[0053] Figure 1 This is a flowchart of the method for controlling the outlet temperature of a concrete mixing plant according to the present invention. Detailed Implementation

[0054] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0055] like Figure 1 As shown, the method for controlling the temperature at the outlet of the concrete mixing plant provided by this invention is as follows:

[0056] S1. Determine the temperature control information before concrete mixing raw materials are placed in the storage area.

[0057] Mixing concrete requires aggregates, cement, fly ash, water, and admixtures. Aggregates are classified into four grades: extra-large aggregates, large aggregates, medium aggregates, and small aggregates. Before these raw materials are transported to the mixing plant, the extra-large and large aggregates need to be cooled, i.e., air-cooled. To accurately control the temperature at the mixing plant outlet, it is necessary to know the temperature control information of these raw materials before they are transported to the mixing plant.

[0058] S1.1 Determine the surface temperature of extra-large stone aggregates and large stone aggregates after air cooling. The surface temperature after air cooling As its temperature before entering the warehouse

[0059] For extra-large and bulk stone aggregates requiring air cooling, due to the temperature gradient between the inside and outside of the rockfill, the surface temperature (T) of different grades of aggregates must be monitored simultaneously at the aggregate stockpile before entering the mixing plant. 表 and the internal temperature T of the aggregate 内 Calculate the average temperature of the extra-large and large stones before they are placed in the silo (i.e., the material silo of the mixing plant), and use this average temperature as the average temperature of the extra-large and large stones before air cooling. Then, based on the average temperature of the extra-large stone and large stone aggregates before air cooling, various parameters are calculated, and the surface temperature after air cooling is taken as the temperature before they are put into storage.

[0060] The average temperature of extra-large stone aggregates and large stone aggregates is usually obtained by combining on-site measured data with finite element calculations.

[0061] a) First, manually select several pieces of aggregate of different grades and from different locations in the aggregate pile (the particle size of the aggregate in the same batch can be assumed to be a fixed value d). i Holes are drilled into each aggregate piece until the center. The number of holes can be determined based on the actual amount required for concrete mixing. Temperature sensors are embedded on the surface and at the center of the aggregate pieces, connected to a temperature acquisition device to continuously collect temperature data of different grades of aggregates stored at different locations. 表 and T 内 The collection time can be varied depending on factors such as different seasons and different times of day.

[0062] b) Establish a three-dimensional finite element model of the same size as the measured aggregate rockfill and divide it into meshes; assign the surface temperature and center temperature (i.e., internal temperature of aggregate) of several aggregates of different grades and locations to the measured temperature, and assign the surface temperature and center temperature of the remaining aggregates to the linear difference of the temperature of aggregates of the same grade.

[0063] c) Because the internal and external temperatures of the aggregates differ at different depths, the temperatures between the aggregates also vary. Therefore, the average temperature of the entire aggregate pile after temperature conduction between the aggregates is calculated using finite element analysis and used as the average temperature of the extra-large stone aggregates and large stone aggregates before air cooling.

[0064] d) Based on multiple sets of T data collected at different time periods 表 and T 内 The measured values, when input into the finite element model, can be used to calculate the average temperature of the rockfill under the corresponding conditions (specific season, specific month, and specific day / time period), i.e., the average temperature before air cooling. At the same time, establish the average temperature and the surface temperature T of the rockfill body. 表 (The surface temperature of each aggregate at the surface of the rockfill can be approximated as the same)

[0065]

[0066] This leads to the introduction of a temperature non-uniformity coefficient λ.

[0067]

[0068] The advantage of formula (2) is that the surface temperature of the aggregate stockpile is easier to measure, avoiding the complicated work of drilling to measure the internal temperature; on the other hand, T 表 and T 内 It has a natural correlation (related to the thermal conductivity of aggregates), and formula (2) only considers T. 表 This is appropriate. Therefore, the measured surface temperature T of the rockfill can be used as a basis. 表 The average temperature of extra-large stone aggregates and large stones before air cooling is directly determined.

[0069] e) For aggregate piles with different particle sizes, especially extra-large stone aggregates and large stone aggregates, the final temperature of the aggregate pile will vary due to the different heat transfer rates inside the pile. Therefore, steps a) to d) need to be repeated to determine the influence of the shape factor ζ of different aggregate sizes on the average temperature. The calculation of this factor is based on a maximum aggregate size of 120 mm for large-volume concrete.

[0070]

[0071] f) For extra-large stone aggregates and large stone aggregates that require air cooling, the surface temperature measured after air cooling can be used as a reference. The average temperature of extra-large stone aggregate and large stone aggregate after air cooling was calculated using the temperature non-uniformity coefficient λ.

[0072]

[0073] g) If extra-large and large stone aggregates undergo transportation and secondary screening before entering the mixing stage, the increased mechanical heat should also be considered. The surface temperature T of the aggregates after transportation and secondary screening can be directly measured by actual measurement methods. i 运输筛分后 Calculate the surface temperature after air cooling to determine the corresponding temperature recovery coefficient.

[0074]

[0075] S1.2 Determine the temperature of medium and small stone aggregates before they are placed in the silo.

[0076] Since the particle size of medium and small stone aggregates is relatively small, their surface temperature can be measured directly as the temperature before they are put into storage.

[0077] S1.3 Determine the temperatures of cement, fly ash, water, and admixtures before they are placed in the silo for mixing.

[0078] The temperatures of cement, fly ash, water, and admixtures before mixing were measured directly and used as their temperatures before being placed in storage.

[0079] S2. Establish a model for calculating the outlet temperature of the concrete mixing plant, and calculate the outlet temperature of the concrete mixing plant.

[0080] Based on real-time monitoring of the ambient temperature and the temperatures of the aforementioned concrete raw materials (aggregates, water, cement, additives, etc.), the outlet temperature of the concrete mixing plant is calculated, enabling automatic prediction and control of the concrete temperature. The outlet temperature of the concrete mixing plant is calculated using the following formula:

[0081]

[0082] Where: T0—Temperature at the outlet of the concrete mixing plant (°C);

[0083] G i —The mass of the i-th material per cubic meter of concrete (kg / m³) 3 );

[0084] c i —Specific heat capacity of the i-th material (kJ / (kg·℃));

[0085] G c —Ice addition amount per cubic meter of concrete (kg / m³) 3 );

[0086] η—the utilization rate of ice's cold energy, expressed as a decimal; 1.0 can be taken for dry ice at sub-zero temperatures, and 0.9 for moist ice.

[0087] 335—Latent heat of fusion of ice (kJ / kg);

[0088] Q—Mechanical heat generated during the mixing of each cubic meter of concrete (kJ / m³) 3 Let Q = 42Pt / V, where P is the motor power of the mixer (kW), t is the mixing time (min), and V is the mixer capacity (m³). 3 (Calculated based on effective discharge volume);

[0089] T i —Temperature (°C) of the i-th material before it enters the warehouse, where the surface temperature of extra-large stone aggregate and large stone aggregate after air cooling is taken. As the temperature before storage;

[0090] λ i —Temperature non-uniformity coefficient, where i refers to extra-large stone aggregate and large stone aggregate;

[0091] —Heating coefficient, i refers to extra-large stone aggregate and large stone aggregate;

[0092] ζ i — Shape coefficient, i refers to extra-large stone aggregate and large stone aggregate;

[0093] S3. Adjust the mixing water temperature and / or ice-water mass ratio to ensure the mixing tower outlet temperature reaches the design temperature requirement.

[0094] To ensure the mixing plant outlet temperature reaches the design requirements, the water and ice temperatures need to be adjusted multiple times to guarantee the outlet temperature meets the requirements. The specific methods are as follows:

[0095] S3.1. Collect the temperature T0 at the outlet of the concrete mixing plant;

[0096] S3.2 Determine the lower limit P0 and upper limit P1 of the water temperature and ice-water mass ratio, as well as the incremental values ​​of each parameter;

[0097] The lower limit P0 and upper limit P1 of water temperature are set to 5℃ and 10℃, respectively, and the lower limit P0 and upper limit P1 of ice-water mass ratio are set to 0% and 80%, respectively; in subsequent adjustment calculations, the water temperature increment is set to 0.5℃ and the ice-water mass ratio increment is set to 0.1.

[0098] S3.3 Adjust the water temperature and ice-water mass ratio to ensure that the temperature at the concrete mixing plant outlet meets the design requirements:

[0099] A. For pre-cooled concrete, i.e., concrete with air-cooled aggregate, the following priority adjustment shall be adopted:

[0100] Option 1: Given that water temperature is easy to control, prioritize adjusting the water temperature according to the water temperature increment set in S3.2. The ice temperature is directly adopted from the measured value. If the outlet temperature meets the design requirements within the allowable range, the adjustment ends. If the water temperature adjustment reaches the lower limit but still cannot make the outlet temperature meet the design requirements, adjust the ice-water mass ratio, with the amount of ice added not exceeding 80% of the mixing water volume, until the outlet temperature meets the design requirements, and then end the adjustment.

[0101] If the water temperature is adjusted to the lower limit and the ice-water ratio is adjusted to the upper limit, but the outlet temperature still does not meet the requirements, the aggregate air cooling system should be adjusted to further reduce the aggregate temperature or the outlet temperature design value should be changed.

[0102] Option 2: Adjust the ice-to-water ratio, with the amount of ice added not exceeding 80% of the total water volume. If the outlet temperature meets the design requirements within the allowable ratio range, the adjustment is complete. If the outlet temperature still does not meet the design requirements after the ice-to-water mass ratio reaches its upper limit, adjust the water temperature within the specified range until the outlet temperature meets the design requirements, then the adjustment is complete.

[0103] If the water temperature is adjusted to the lower limit and the ice-water ratio is adjusted to the upper limit, but the outlet temperature still does not meet the requirements, the aggregate air cooling system should be adjusted to further reduce the aggregate temperature or the outlet temperature design value should be changed.

[0104] B. For preheated concrete:

[0105] If the outlet temperature is lower than the design requirement, the water temperature should be increased first; if the water temperature adjustment does not meet the requirements, the aggregate temperature should be adjusted through the aggregate air cooling system until the outlet temperature meets the design requirements.

[0106] The advantage of this invention is that by coupling finite element simulation calculation and measured temperature analysis before mixing, the temperature of concrete aggregate before mixing can be accurately determined, and the outlet temperature of concrete and the required water temperature or amount of ice can be calculated more precisely. This overcomes the defect of traditional outlet temperature calculation, which is caused by incorrect judgment of concrete aggregate temperature value, leading to subsequent incorrect adjustment of ice amount or water temperature, resulting in outlet temperature that is always difficult to meet design requirements or requires multiple adjustments to meet design requirements.

[0107] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 controlling the temperature at the outlet of a concrete mixing plant, characterized in that: It includes the following steps: S1. Determine the temperature control information before concrete mixing raw materials are placed in the storage area. S1.1 Determine the surface temperature of extra-large stone aggregates and large stone aggregates after air cooling. The surface temperature after air cooling As its temperature before entering the warehouse a) First, manually select several aggregates of different grades and locations from the aggregate pile, and drill holes in each aggregate up to its center. The number of holes is determined based on the actual amount required for concrete mixing. Temperature sensors are embedded on the surface and at the center of each aggregate, connected to a temperature acquisition device, to continuously collect temperature readings (T) of different grades of aggregates at different storage locations. 表 and T 内 The collection time varies depending on the season and time of day. b) Establish a three-dimensional finite element model of the same size as the measured aggregate rockfill and divide it into meshes; assign the surface temperature and center temperature (i.e., internal temperature of aggregate) of several aggregates of different grades and locations to the measured temperature, and assign the surface temperature and center temperature of the remaining aggregates to the linear difference of the temperature of aggregates of the same grade. c) The average temperature of the entire aggregate pile after temperature conduction between aggregates is calculated using finite element method, and this average temperature is used as the average temperature of extra-large and large stone aggregates before air cooling. d) Based on multiple sets of T data collected at different time periods 表 and T 内 The measured values ​​are input into the finite element model to calculate the average temperature of the extra-large stone aggregate and the large stone aggregate, i.e., the average temperature before air cooling. And calculate the temperature non-uniformity coefficient λ. e) For aggregate piles with different particle sizes, especially extra-large stone aggregates and large stone aggregates, the final temperature of the aggregate pile will be different due to the different heat transfer rates inside the pile. Therefore, steps a) to d) need to be repeated to determine the shape factor ζ of aggregates with different particle sizes. The calculation of this factor is based on the maximum particle size of 120mm for large-volume concrete aggregates. f) For extra-large and large stone aggregates that require air cooling, the surface temperature measured after air cooling shall be used as the basis for determining the air cooling temperature. The average temperature of extra-large stone aggregate and large stone aggregate after air cooling is calculated using the temperature non-uniformity coefficient λ. g) If extra-large stone aggregates and large stone aggregates undergo transportation and secondary screening before entering the mixing stage, the surface temperature T of the aggregates after transportation and secondary screening can be directly measured by actual measurement methods. i 运输筛分后 Based on the surface temperature after air cooling, the corresponding temperature recovery coefficient φ is determined. i ; S1.2 Determine the temperature of medium and small stone aggregates before they are placed in the silo. The surface temperature was measured directly using a field measurement method and used as the temperature before entering the warehouse. S1.3 Determine the temperatures of cement, fly ash, water, and admixtures before they are placed in the silo for mixing. The temperatures of cement, fly ash, water, and admixtures before mixing were measured directly and used as their temperatures before being placed in the storage silo. S2. Establish a model for calculating the outlet temperature of the concrete mixing plant, and calculate the outlet temperature of the concrete mixing plant. The calculation model for the outlet temperature of the concrete mixing plant is as follows: Where: T0—Temperature at the outlet of the concrete mixing plant (°C); G i —The mass of the i-th material per cubic meter of concrete (kg / m³) 3 ); c i —Specific heat capacity of the i-th material (kJ / (kg·℃)); G c —Ice addition amount per cubic meter of concrete (kg / m³) 3 ); η—the utilization rate of ice's cold energy, expressed as a decimal; 1.0 can be taken for dry ice at sub-zero temperatures, and 0.9 for moist ice. 335—Latent heat of fusion of ice (kJ / kg); Q—Mechanical heat generated during the mixing of each cubic meter of concrete (kJ / m³) 3 Let Q = 42Pt / V, where P is the motor power of the mixer (kW), t is the mixing time (min), and V is the mixer capacity (m³). 3 (Calculated based on effective discharge volume); T i —Temperature (°C) of the i-th material before it enters the warehouse, where the surface temperature of extra-large stone aggregate and large stone aggregate after air cooling is taken. As the temperature before storage; λ i —Temperature non-uniformity coefficient, where i refers to extra-large stone aggregate and large stone aggregate; —Heating coefficient, i refers to extra-large stone aggregate and large stone aggregate; ζ i — Shape coefficient, i refers to extra-large stone aggregate and large stone aggregate; S3. Adjust the mixing water temperature and / or ice-water mass ratio to ensure the mixing tower outlet temperature reaches the design temperature requirement. S3.

1. Collect the temperature T0 at the outlet of the concrete mixing plant; S3.2 Determine the lower limit P0 and upper limit P1 of the water temperature and ice-water mass ratio, as well as the incremental values ​​of each parameter; The lower limit P0 and upper limit P1 of water temperature are set to 5℃ and 10℃, respectively, and the lower limit P0 and upper limit P1 of ice-water mass ratio are set to 0% and 80%, respectively; in subsequent adjustment calculations, the water temperature increment is set to 0.5℃ and the ice-water mass ratio increment is set to 0.

1. S3.3 Adjust the water temperature and ice-water mass ratio to ensure that the temperature at the concrete mixing plant outlet meets the design requirements: A. For pre-cooled concrete, i.e., concrete with air-cooled aggregate, the following priority adjustment shall be adopted: According to step S3.2, the water temperature increment is adjusted first, and the ice temperature is directly adopted as the measured value. If the outlet temperature design requirement is met within the allowable ratio range, the adjustment ends. If the water temperature adjustment reaches the lower limit but still cannot meet the outlet temperature design requirement, the ice-water mass ratio is adjusted, with the amount of ice added not exceeding 80% of the mixing water volume, until the outlet temperature meets the design requirement, and the adjustment ends. When the water temperature is adjusted to the lower limit and the ice-water ratio is adjusted to the upper limit, and the outlet temperature still does not meet the requirement, the aggregate air cooling system is adjusted to further reduce the aggregate temperature or the outlet temperature design value is changed; or... First, adjust the ice-to-water ratio, ensuring the amount of ice added does not exceed 80% of the mixing water volume. If the outlet temperature design requirements are met within the allowable ratio range, the adjustment is complete. If the outlet temperature still does not meet the design requirements after the ice-to-water mass ratio reaches its upper limit, adjust the water temperature within the specified range until the outlet temperature meets the design requirements, then the adjustment is complete. If the outlet temperature still does not meet the requirements even after the water temperature is adjusted to the lower limit and the ice-to-water ratio reaches its upper limit, then adjust the aggregate air-cooling system to further reduce the aggregate temperature or change the outlet temperature design value. B. For preheated concrete: If the outlet temperature is lower than the design requirement, the water temperature should be increased first; if the water temperature adjustment does not meet the requirements, the aggregate temperature should be adjusted through the aggregate air cooling system until the outlet temperature meets the design requirements.

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