Method for determining maintenance parameters of precast concrete product

Abstract

The invention discloses a method for determining maintenance parameters of a precast concrete product, which comprises the following steps: acquiring a relation curve of concrete strength and maintenance age under a laboratory standard maintenance condition, and calculating to obtain a relation graph of strength and maturity; on the basis of hydration heat release of multiple ages at different temperatures, the maximum heat release, hydration activation energy and pre-exponential factors of a unit cementing material are solved through a nonlinear least square method; predicting the temperature development history, and calculating the temperature difference between the central point of the precast concrete product and the protective layer and the temperature difference between the protective layer and the environment; calculating the maturity of the concrete at different ages under the temperature history; on the basis of the maturity theory of the same maturity and the same strength, according to the strength and maturity relation graph, the relation of the strength of the precast concrete product along with the age is inquired and obtained; and determining a precast concrete product curing system according to the predicted temperature, temperature difference and strength requirements of the precast concrete product. By reasonably arranging parameters such as steam curing temperature and time, energy consumption in the curing process of the precast concrete product is reduced, social and economic benefits are increased, and the carbon reduction effect is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of cement concrete, in particular to a method for predicting temperature history, strength and temperature difference development based on maturity theory and determining a maintenance system for precast concrete products. Background Art

[0002] The present invention mainly focuses on the selection of steam curing system for precast concrete products under different ambient temperatures in actual production. Precast concrete products have been widely used in infrastructure construction due to their advantages such as fast production speed and controllable quality. However, in actual production, there are certain technical difficulties in predicting the strength development of concrete products and determining the steam curing system. Especially under different external ambient temperature conditions, the adjustment of the steam curing system has become a key factor in ensuring the quality of precast concrete products.

[0003] In view of the above problems, the present invention proposes a method for predicting the temperature history, strength and temperature difference development of concrete products and determining the curing parameters of precast concrete products based on maturity theory. The method aims to accurately predict the temperature development history of precast concrete products through a scientific theoretical calculation model, calculate the strength and temperature difference development at different positions, and optimize the steam curing system accordingly, so as to achieve quality assurance such as crack control of concrete products and resource and energy conservation. Summary of the invention

[0004] Technical problem: The purpose of the present invention is to propose a method for determining the curing parameters of precast concrete products in view of the difficulty in real-time measurement of concrete strength development at different positions of precast products and the need for adjustment during steam curing at different external ambient temperatures. The method predicts temperature history, strength and temperature difference development based on maturity theory and determines the curing parameters of precast concrete products.

[0005] Technical solution: A method for determining the curing parameters of precast concrete products adopted by the present invention comprises the following steps:

[0006] Step 1: Prepare concrete specimens according to the engineering mix ratio and cure the concrete specimens under standard conditions;

[0007] Step 2: Test the strength of concrete specimens at different ages and calculate the maturity of concrete specimens at different ages;

[0008] Step 3: According to the strength and maturity of different ages, fit the strength-maturity relationship curve under standard conditions;

[0009] Step 4: Prepare cementitious material samples according to the engineering mix ratio of the raw materials of precast concrete products and test the heat release at multiple ages at three temperatures;

[0010] Step 5: According to the heat release at different temperatures and at multiple ages, the maximum heat release Q per unit cementitious material is obtained by fitting using the nonlinear least squares method. max , hydration reaction activation energy E a and pre-exponential factor A;

[0011] Step 6: According to the fitting maximum heat release Q max , hydration reaction activation energy E a and pre-exponential factor A, predict the temperature development history of precast concrete products and calculate the maturity-time relationship diagram;

[0012] Step 7: Based on the strength-maturity relationship under standard conditions and the maturity-time relationship under the predicted temperature development history, the strength-time relationship diagram under the predicted temperature development history is converted;

[0013] Step 8: According to the predicted temperature development history in step 6, according to the predicted temperature development history of different positions of precast concrete products and the average ambient temperature, calculate the temperature difference between the center and surface of the precast products, the temperature difference between the surface and the environment, and the strength development curve, and adjust and determine the temperature, time and other parameters in the maintenance system according to the requirements of the standard (TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels").

[0014] in,

[0015] The standard conditions of step 1 are temperature of 20°C ± 2°C and humidity ≥ 95%.

[0016] The different ages of step 2 are 1d, 3d, 7d and 28d; the maturity calculation formula is: M = (tt 0 )T;

[0017] Where M is the maturity, ℃·h or ℃·d; h is hours, d is days; T is the average temperature of the concrete during the time interval, ℃; t 0 is the final setting time, h or d; t is the age of concrete.

[0018] The step 3 of fitting to obtain the strength-maturity relationship curve under standard conditions is based on the strength and maturity of different ages obtained by testing and calculating in step 2, and using nonlinear curve fitting to obtain the strength-maturity relationship curve under standard conditions;

[0019] The three temperatures in step 4 are 20°C, 40°C and 60°C respectively, and the different ages are 1d, 3d and 7d respectively;

[0020] The nonlinear least squares fitting formula in step 5 is: The fitting accuracy is greater than 0.9;

[0021] Where q(t,T) is the heat released by unit mass of cementitious material at temperature T after age t, kJ / kg; Q max is the total heat released by complete hydration of unit mass of cementitious material, kJ / kg; K T is the hydration exothermic rate constant, 1 / h; A is the pre-exponential factor; E a is the hydration activation energy, kJ / mol; R is the universal gas constant, kJ / (K·mol); T is the average temperature of the concrete during the time interval, K.

[0022] The step six predicts the temperature development history of precast concrete products, wherein the temperature field control equation is:

[0023]

[0024] Where, λ is the thermal conductivity, kJ / (m·h·℃); c p is the specific heat capacity, kJ / kg·℃; ρ is the density, kg / m 3 ; mq is the rate at which energy is generated per unit volume of concrete, kJ / (m 3 ·h); m is the mass of cementitious material per unit volume of concrete, kg / m 3 , q is the hydration heat released per unit mass of cementitious material per unit time, kJ / (kg·h); T is the temperature; t is the age; x, y, z are the positions of the characteristic points in the precast concrete product.

[0025] The step seven calculates the strength-time relationship diagram under the predicted temperature, which is based on the strength-maturity relationship under standard conditions and the maturity-time relationship under the predicted temperature development history, thereby converting to obtain the strength-time relationship diagram under the predicted temperature development history.

[0026] The step eight calculates the temperature difference between the center and the surface of the precast product, the temperature difference between the surface and the environment, and the strength development curve according to the predicted temperature development history in step six, the predicted temperature development history at different positions of the precast concrete product and the average ambient temperature, and adjusts and determines the temperature, time and other parameters in the maintenance system according to the requirements of standard TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels".

[0027] Beneficial effects: The present invention measures and calculates the relationship between concrete strength and maturity under standard curing conditions, calculates the concrete strength and temperature difference at a certain age under the predicted temperature history according to the maturity theory, and determines the curing temperature and time parameters of precast concrete products at different ambient temperatures according to the standard (TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels") precast concrete product strength and temperature difference requirements. The present invention determines the steam curing temperature and time and other curing systems of precast concrete products according to the accurately predicted concrete strength and temperature difference, which can significantly increase economic benefits, achieve carbon reduction results, prevent cracking of concrete products, and improve quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart for predicting concrete strength and temperature difference and determining a curing system for the present invention;

[0029] Figure 2 It is the relationship curve between concrete strength and maturity under standard conditions;

[0030] Figure 3 The results of constant temperature calorimetry of cementitious materials at different temperatures;

[0031] Figure 4 It is the temperature prediction point of precast concrete segment; Figure 4 (a) is the overall diagram of the segment. Figure 4 (b) is a midline cross-sectional view of the segment, which includes: segment center point 1, center surface point 2, and longitudinal end point 3;

[0032] Figure 5 Temperature prediction results for precast concrete products at different curing temperatures and durations;

[0033] Figure 6 It is a temperature difference curve diagram of precast concrete products under different steam curing temperatures and durations;

[0034] Figure 7 Predict the strength curve of precast concrete products at different curing temperatures and times. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1: This example takes the ambient temperature of 5°C, the mold entry temperature of 20°C, the constant temperature steam curing temperature of the precast concrete segment of 40°C, and the constant temperature curing duration of 1 hour as an example.

[0037] Example 2: This example takes the ambient temperature of 5°C, the mold entry temperature of 20°C, the constant temperature steam curing temperature of the precast concrete segment of 40°C, and the constant temperature curing duration of 2 hours as an example.

[0038] Example 3: This embodiment takes the ambient temperature of 5°C, the mold temperature of 20°C, the constant temperature steam curing temperature of the precast concrete segment of 40°C, and the constant temperature curing duration of 3 hours as an example.

[0039] Example 4: This embodiment takes the ambient temperature of 5°C, the mold temperature of 20°C, the constant temperature steam curing temperature of the precast concrete segment of 40°C, and the constant temperature curing duration of 4 hours as an example.

[0040] Example 5: This embodiment takes the ambient temperature as 5°C, the mold temperature as 20°C, the constant temperature steam curing temperature of the precast concrete segment as 45°C, and the constant temperature curing duration as 1 hour as an example.

[0041] Example 6: This embodiment takes the ambient temperature of 5°C, the mold temperature of 20°C, the constant temperature steam curing temperature of the precast concrete segment of 45°C, and the constant temperature curing duration of 2 hours as an example.

[0042] Example 7: This embodiment takes the ambient temperature of 5°C, the mold temperature of 20°C, the constant temperature steam curing temperature of the precast concrete segment of 45°C, and the constant temperature curing duration of 3 hours as an example.

[0043] Example 8: This example takes the ambient temperature of 5°C, the mold temperature of 20°C, the constant temperature steaming temperature of the precast concrete segment of 45°C, and the constant temperature curing duration of 4 hours as an example.

[0044] Step 001: Prepare multiple concrete specimens according to the engineering mix ratio, and cure the concrete specimens under standard conditions of temperature of 20℃±2℃ and humidity ≥95%. Figure 1 shown.

[0045] Table 1 Mixing ratio (kg / m 3 )

[0046]

[0047] Step 002: Test the strength of the concrete specimens at 1d, 3d, 7d and 28d. According to the formula M = (tt 0 )T, calculate the maturity of concrete specimens at 1d, 3d, 7d and 28d; where M is maturity, ℃·h or ℃·d; h is hours, d is days; T is the average temperature of concrete in the time interval, ℃; t 0 is the final setting time, h or d; t is the age of concrete.

[0048] Step 003: According to the relationship between strength and maturity at 1d, 3d, 7d and 28d, the strength-maturity relationship curve under standard conditions is fitted;

[0049] Step 004: Prepare cementitious material samples according to the engineering proportion and test the heat release at 20°C, 40°C and 60°C for 1 day, 3 days and 7 days;

[0050] Step 005: Based on the heat release at 20℃, 40℃ and 60℃ at 1d, 3d and 7d respectively, use the formula The maximum heat release Q of unit cementitious material is obtained by fitting using nonlinear least squares method. max , hydration reaction activation energy E a and pre-exponential factor A, the fitting accuracy is greater than 0.9. Among them, Q(t,T) is the heat released by unit mass of cementitious material at temperature T after age t, kJ / kg; Q max is the total heat released by complete hydration of unit mass of cementitious material, kJ / kg; K T is the hydration exothermic rate constant, 1 / h; A is the pre-exponential factor; E a is the hydration activation energy, kJ / mol; R is the universal gas constant, kJ / (K·mol);

[0051] Step 006: Based on the strength-maturity relationship under standard conditions and the maturity-time relationship under the predicted temperature development history, the strength-time relationship diagram under the predicted temperature development history is converted, where the temperature field control equation is Where, λ is the thermal conductivity, kJ / (m·h·℃); c p is the specific heat capacity, kJ / kg·℃; ρ is the density, kg / m 3 ; mq is the rate at which energy is generated per unit volume of concrete, kJ / (m 3 ·h); m is the mass of cementitious material per unit volume of concrete, kg / m 3 , q is the hydration heat released per unit mass of cementitious material per unit time, kJ / (kg·h);

[0052] Step 007: Based on the strength-maturity relationship under standard conditions and the maturity-time relationship under the predicted temperature development history, a strength-time relationship diagram under the predicted temperature development history is obtained by conversion;

[0053] Step 008: According to the predicted temperature development history in step 6, according to the predicted temperature development history of different positions of the precast concrete products and the average ambient temperature, calculate the temperature difference between the center and surface of the precast products, the temperature difference between the surface and the environment, and the strength development curve, and adjust and determine the temperature, time and other parameters in the maintenance system according to the requirements of the standard (TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels").

[0054] According to the embodiments and the accompanying drawings, when the ambient temperature is low, the constant temperature steaming time should be appropriately extended to ensure that the tube segment has sufficient demoulding strength and factory strength; when the ambient temperature is high, the constant temperature steaming time can be appropriately shortened to reduce the large hydration temperature and temperature difference of the tube segment and ensure the overall performance of the tube segment.

[0055] In summary, the present invention discloses a method for predicting the development of temperature history, strength and temperature difference and determining the curing system of precast concrete products based on maturity theory, the method comprising: preparing concrete specimens according to the mix ratio and curing them to different ages under standard conditions, establishing the relationship between the strength and maturity of concrete under standard conditions; preparing cementitious material samples according to the mix ratio, measuring the heat release at different temperatures and different ages, and fitting to obtain the maximum heat release per unit of cementitious material, the activation energy of hydration reaction and the pre-exponential factor; predicting the temperature development history of precast concrete products; calculating the maturity of precast concrete products under the predicted temperature history; calculating the strength and temperature difference of precast concrete products under the predicted temperature history according to the relationship between strength and maturity under standard conditions; and determining the steam curing temperature, time and other parameters according to the requirements for the predicted strength and temperature difference of precast concrete products in the standard (TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels").

[0056] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for determining curing parameters of precast concrete products, characterized in that: The following steps are involved: Step 1: Prepare concrete specimens according to the engineering mix ratio and cure the concrete specimens under standard conditions; Step 2: Test the strength of concrete specimens at different ages and calculate the maturity of concrete specimens at different ages; Step 3: According to the strength and maturity of different ages, fit the strength and maturity relationship curve under standard conditions; Step 4: Prepare cementitious material samples according to the engineering mix ratio of the raw materials of precast concrete products and test the heat release at multiple ages at three temperatures; Step 5: According to the heat release at different temperatures and at multiple ages, the maximum heat release Q per unit cementitious material is obtained by fitting using the nonlinear least squares method. max , hydration reaction activation energy E a and pre-exponential factor A; Step 6: According to the fitting maximum heat release Q max , hydration reaction activation energy E a and pre-exponential factor A, predict the temperature development history of precast concrete products and calculate the maturity-time relationship diagram; Step 7: Based on the strength-maturity relationship under standard conditions, calculate the strength-time relationship diagram at the predicted temperature; Step 8: Based on the predicted temperature development history in step 6, calculate the strength and temperature difference of precast concrete products. According to the strength and temperature difference requirements of precast concrete products in the standard (TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels"), determine the steam curing temperature, time and other parameters.

2. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: The standard conditions described in step 1 are a temperature of 20°C ± 2°C and a humidity of ≥ 95%.

3. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: The different ages described in step 2 are 1d, 3d, 7d and 28d; the maturity calculation formula is: M = (t-t0)T; Where, M is maturity, ℃·h or ℃·d; h is hours, d is days; T is the average temperature of concrete in the time interval, ℃; t0 is the final setting time, h or d; t is the age of concrete.

4. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: The strength-maturity relationship curve under standard conditions is obtained by fitting in step 3, which is based on the strength and maturity of different ages tested and calculated in step 2, and the strength-maturity relationship curve under standard conditions is obtained by using nonlinear curve fitting.

5. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: The three temperatures in step 4 are 20° C., 40° C. and 60° C., and the different ages are 1 day, 3 days and 7 days.

6. A method for determining curing parameters of precast concrete products according to claim 4, characterized in that: The nonlinear least squares fitting formula in step 5 is: The fitting accuracy is greater than 0.9; Where q(t,T) is the heat released by unit mass of cementitious material at temperature T after age t, kJ / kg; Q max is the total heat released by complete hydration of unit mass of cementitious material, kJ / kg; K T is the hydration exothermic rate constant, 1 / h; A is the pre-exponential factor; E a is the hydration activation energy, kJ / mol; R is the universal gas constant, kJ / (K·mol); T is the average temperature of the concrete during the time interval, K.

7. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: Step 6 predicts the temperature development history of precast concrete products, where the temperature field control equation is: Where, λ is the thermal conductivity, kJ / (m·h·℃); c p is the specific heat capacity, kJ / kg·℃; ρ is the density, kg / m 3 ; mq is the rate at which energy is generated per unit volume of concrete, kJ / (m 3 ·h); m is the mass of cementitious material per unit volume of concrete, kg / m 3 , q is the hydration heat released per unit mass of cementitious material per unit time, kJ / (kg·h); T is the temperature; t is the age; x, y, z are the positions of the characteristic points in the precast concrete product.

8. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: The calculation of the strength-time relationship diagram under the predicted temperature in step seven is based on the strength-maturity relationship under standard conditions and the maturity-time relationship under the predicted temperature development history, thereby converting the strength-time relationship diagram under the predicted temperature development history.

9. A method for determining curing parameters of precast concrete products according to claim 1, characterized in that: Step eight describes that according to the predicted temperature development history in step six, according to the predicted temperature development history at different positions of the precast concrete product and the average ambient temperature, the temperature difference between the center and the surface, the temperature difference between the surface and the environment, and the strength development curve of the precast product are calculated, and according to the requirements of standard TB / T 3353-2014 "Reinforced Concrete Segments for Railway Tunnels", the temperature and time parameters in the maintenance system are adjusted and determined.

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