A method for pouring and maintaining temperature control of prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment

Abstract

The present invention provides a method for pouring and curing temperature control of a prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment, which is applicable to the field of concrete prefabricated component production technology. The present invention includes temperature control in the concrete pouring stage, temperature control in the initial and mid-term curing stages of the concrete, curing in the late curing stage of the concrete, data acquisition and bridge deck maintenance. By adding crushed ice of a specific proportion and a specific temperature to the raw materials of ultra-high performance concrete, the hydration heat in the concrete pouring stage is effectively reduced. By controlling the spraying time and spraying amount in the curing stage, the temperature rise of the concrete in the initial and mid-term curing stages is limited. At the same time, the water evaporated from the ultra-high performance concrete bridge deck in a high temperature environment is supplemented to ensure the smooth development of strength. During the pouring and curing process, the temperature rise of the concrete is strictly and quantitatively controlled by the control equation, reducing the risk of concrete cracking.

Description

Technical Field

[0001] The invention relates to a method for pouring and maintaining a temperature-controlling prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high-temperature environment, and is applicable to the field of production technology for prefabricated concrete components. Background Art

[0002] In the field of building materials, concrete is the most widely used one, and its performance directly affects the safety and durability of building structures. Among them, Ultra-High Performance Concrete (UHPC) is widely used in super high-rise buildings, large infrastructure and other structures due to its high strength, high toughness and high durability. However, the pouring and maintenance of UHPC in high temperature environment is a problem, because high temperature will significantly accelerate the hydration reaction of cement, causing the temperature inside the concrete to rise faster and higher, which will further cause the concrete to crack.

[0003] At present, there are measures such as adjusting the mix ratio of UHPC, using low-heat cement, adding mineral admixtures such as fly ash, and using high-efficiency water reducing agents to reduce the hydration heat of concrete, thereby slowing down and reducing the internal temperature rise of concrete. In addition, phase change materials can be added during the preparation of UHPC to use their heat absorption and heat release characteristics during the phase change process to adjust the internal temperature of concrete.

[0004] However, existing solutions require major adjustments to the mix ratio of concrete, which will affect the strength and durability of the concrete. Phase change materials will also cause dispersion and stability problems in concrete. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of reduced strength and durability caused by traditional ultra-high performance concrete casting and maintenance temperature control methods, as well as the dispersion and stability problems caused by adding phase change materials. A method for casting and maintaining temperature control of prefabricated coarse aggregate ultra-high performance concrete bridge decks in a high-temperature environment is provided. The method can avoid concrete cracking caused by concrete hydration heat while ensuring the strength and durability of ultra-high performance concrete bridge decks. The method can be widely used in the field of concrete prefabricated component production technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for pouring and maintaining temperature control of a prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment, specifically comprising the following steps:

[0008] S101 Temperature control during concrete pouring;

[0009] The temperature control during the concrete pouring stage includes using industrial temperature control equipment to control the ambient temperature of the closed pouring area at the local annual average temperature T1, ° C, and then preparing water, cement, river sand, fly ash, mineral powder, silica fume, steel fiber, additives and coarse aggregate according to the mix ratio, wherein the water-cement ratio is ω, pouring the above raw materials into a stirring device, except for water, the rest of the raw materials are at room temperature, water is added in a water-to-crushed ice mass ratio of 2:8 and then stirred, the temperature of the crushed ice is T2, ° C, and T2 should meet conditions (1), (2), (3), and (4);

[0010] Q i =0.8ω(C w T1-C i T2+L i ) (1)

[0011] T1≥0, T2<0 (2)

[0012]

[0013]

[0014] In the formula, C w -Specific heat capacity of water, kJ / (kg·℃), C i -Specific heat capacity of ice, kJ / (kg·℃), L i - melting heat of ice, kJ / kg, α- linear expansion coefficient of concrete, 1 / ℃, E(t1)- elastic modulus of concrete at age t1, MPa, k- hydration heat adjustment coefficient of different admixtures, Q0- total hydration heat of cement, kJ / kg, W- cementitious material dosage per cubic meter of concrete, kg / m 3 , C c -Specific heat capacity of concrete, kJ / (kg·℃), ρ c -Mass density of concrete, kg / m 3 , μ-Poisson's ratio of concrete, m-corresponding coefficient of unilateral cementitious material related to cement type, dosage and mold temperature, t1-age from the beginning of concrete mixing to the disappearance of the gloss of concrete bridge deck bleeding, d, f tk (t1)-standard value of tensile strength of concrete at age t1, MPa, K-anti-cracking safety factor, taken as 1.5;

[0015] The temperature control during the concrete pouring stage also includes placing the tied steel bars in the mold, pouring the mixed concrete into the mold, vibrating and compacting the concrete in the mold, flattening the concrete bridge deck, covering it with a film and placing it in the maintenance area;

[0016] S102 Temperature control during the initial and mid-term curing stages of concrete;

[0017] The temperature control of the concrete in the initial and mid-term curing stages includes: when the gloss of the concrete bridge deck disappears due to water seepage, the concrete bridge deck cover is opened, the surface temperature of the concrete bridge deck is measured, T3, °C, and spray curing is performed immediately after the temperature measurement. After that, the interval between each spraying is Δt, h, and the spraying amount per cubic meter of concrete is Δm j ,kg / m 3 , j represents the jth spray curing, the spray temperature is lower than T3 but not lower than (T3-15)℃, Δt, Δm j Conditions (5), (6), (7), and (8) must be met;

[0018] ΔQ f =ηΔm j L v (5)

[0019]

[0020] ΔQ a =[ΔT1h+εσ(T1+ΔT1) 4 ]AΔt (7)

[0021] ΔQ a +ΔQ f >ΔQ j (8)

[0022] Where, η is the ratio of actual evaporated water volume to spray volume, L v -The amount of heat that a unit mass of water needs to absorb when evaporating, kJ / kg, h-Convection heat transfer coefficient, W / m 2 ·℃, ε-emissivity of ultra-high performance concrete bridge deck, A-surface area of ​​bridge deck per cubic meter of concrete, σ-Sterfan-Boltzmann constant;

[0023] S103 Concrete late curing stage curing;

[0024] The concrete late curing stage curing includes confirming that the ultra-performance concrete bridge deck has been finally set according to the touch of the ultra-performance concrete bridge deck, removing surface debris, ensuring that the concrete surface is clean and pollution-free, placing the ultra-performance concrete bridge deck in a water curing pool, and transporting it to a storage area by a transfer vehicle after a water curing period of t days;

[0025] S104 data acquisition and bridge deck maintenance;

[0026] The data collection and bridge deck maintenance include collecting the ambient temperature and humidity during the entire maintenance process, as well as the strength of the ultra-high performance concrete bridge deck after the maintenance is completed, and determining whether further covering maintenance is needed based on the collected data.

[0027] Furthermore, in step S101, the local annual average temperature is obtained by dividing the sum of the local daily average temperatures in a year by the number of days in that year. When the calculated result is less than 10°C, the local annual average temperature is taken as 10°C.

[0028] Furthermore, in step S102, the droplet size of the spray curing is not more than 100 μm, the spray interval is not more than 1 hour, and the spray amount per cubic meter of concrete is not less than 10 kg.

[0029] Furthermore, it is characterized in that: in step S103, the water immersion curing period t is at least 15 days.

[0030] The beneficial effects of the present invention are: 1. By adding crushed ice of a specific proportion and a specific temperature to the raw materials of ultra-high performance concrete, the hydration heat in the concrete pouring stage is effectively reduced, the amplitude of the temperature rise inside the concrete is reduced, and the temperature of the concrete entering the mold is limited by industrial temperature control equipment, thereby avoiding the risk of concrete cracking caused by excessive concrete temperature entering the mold in a high temperature environment; 2. By controlling the spraying time and spraying amount in the curing stage, the temperature rise of the concrete caused by the hydration heat in the early and middle stages of coagulation is limited, and at the same time, the water evaporated from the ultra-high performance concrete bridge deck in a high temperature environment is supplemented to ensure the smooth development of strength; 3. Strict quantitative control of the temperature rise of the concrete during the pouring and curing process reduces the risk of concrete cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart of the method for pouring and maintaining temperature control of a prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given here are only used to illustrate and explain the present invention and cannot be used to limit the present invention. It should be noted that many specific details are set forth in the following description to facilitate a full understanding of the present invention, but the present invention may also have other embodiments and variations thereof, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0033] This embodiment relies on the T15 contract section of the civil engineering construction of the Shiziyang Channel project. The Shiziyang Channel starts at Xinnian, Humen Town, Dongguan City, and ends at Dagang Town. The specific steps of the ultra-high performance concrete bridge deck pouring and curing temperature control method are as follows:

[0034] S101 Temperature control during concrete pouring;

[0035] The ambient temperature of the closed casting area is controlled at the local annual average temperature T1 = 22°C by using industrial temperature control equipment. The annual average temperature is obtained by dividing the sum of the local daily average temperatures in a year by the number of days in that year. When the calculated result is less than 10°C, the local annual average temperature is taken as 10°C. Then, water, cement, river sand, fly ash, mineral powder, silica fume, steel fiber, additives and coarse aggregate are prepared according to the mix ratio, wherein the water-cement ratio is ω = 0.15. The above raw materials are poured into a stirring device. Except for water, the rest of the raw materials are at room temperature. Water is added in a water-to-crushed ice mass ratio of 2:8 and stirred. The temperature of the crushed ice is T2 = -10°C. T2 satisfies conditions (1), (2), (3) and (8);

[0036] Q i =0.8ω(C w T1-C i T2+L i )=53.63kJ / kg (1)

[0037] T1≥0, T2<0 (2)

[0038]

[0039] k=k1+k2-1=0.89 (4)

[0040] m=k(λA0W C +B)=0.81 (5)

[0041]

[0042]

[0043]

[0044] In the formula, C w -The specific heat capacity of water is 4.2 kJ / (kg·℃), C i -The specific heat capacity of ice is 2.1 kJ / (kg·℃), L i - Melting heat of ice 333.55 kJ / kg, α-linear expansion coefficient of concrete 0.00001 / ℃, E(t1)-elastic modulus of concrete at age t1, MPa, k-hydration heat adjustment coefficient of different admixtures, Q0-total hydration heat of cement 375 kJ / kg, W-cementitious material dosage per cubic meter of concrete 1000 kg / m 3 , C c -Specific heat of concrete 1kJ / (kg·℃), ρ c -Concrete mass density 2500kg / m 3, μ-Poisson's ratio of concrete 0.2, m-corresponding coefficient of unilateral cementitious material related to cement type, dosage and mold temperature, t1-the age from the beginning of concrete mixing to the disappearance of the gloss of the concrete bridge deck is conservatively taken as 0.5d, f tk (t1)-standard value of tensile strength when concrete age is t1, MPa, K-anti-cracking safety factor 1.5, k1-hydration heat adjustment coefficient corresponding to fly ash content, 0.96 for this project, k2-hydration heat adjustment coefficient corresponding to mineral powder content, 0.93 for this project, λ-correction coefficient, 0.65 for this project, A0, B-coefficients related to concrete construction mold temperature, 0.0024, 0.5159 for this project, respectively, W c - The amount of other silicate cement per cubic meter is 250kg for this project, β1-the corresponding coefficient of fly ash dosage is 1.0 for this project, β2-the corresponding coefficient of mineral powder dosage is 1.02 for this project, E0-the elastic modulus of concrete under standard curing conditions of 28 days, 5.6×10 4 MPa, -Empirical coefficient, take 0.15, f tk -Concrete tensile strength standard value, this project takes 26MPa, γ-tensile strength standard value empirical coefficient, take 0.3;

[0045] Place the tied steel bars in the mold, then pour the mixed concrete into the mold, vibrate and compact the concrete in the mold, flatten the concrete bridge deck, cover it with film and place it in the maintenance area;

[0046] S102 Temperature control during the initial and mid-term curing stages of concrete;

[0047] When the gloss of the concrete bridge deck disappears due to water seepage, the concrete bridge deck cover is opened and the surface temperature of the concrete bridge deck is measured as T3 = 52°C. After the temperature measurement, spray curing is carried out immediately. The interval between each spraying is Δt, h, and the spraying amount per cubic meter of concrete is Δm j ,kg / m 3 , j represents the jth spray curing, the spray temperature is 37°C, the droplet size of the spray curing does not exceed 100 μm, the spray interval time is not more than 1 hour, and the spray volume per cubic meter of concrete is not less than 10 kg. Take j = 1 for calculation, Δt and Δm1 meet the conditions (5), (6), (7), and (8);

[0048] ΔQ f =ηΔm j L v =4800kJ / m 3 (5)

[0049]

[0050] ΔQa =[ΔT1h+εσ(T1+ΔT1) 4 ]AΔt=1836.2kJ / m 3 (7)

[0051] ΔQ a +ΔQ f =6636.2kJ / m 3 >ΔQ j =6313.92kJ / m 3 (8)

[0052] In the formula, η is the ratio of the actual evaporated water volume to the spray volume. In this project, it is taken as 0.2. v -The amount of heat that a unit mass of water needs to absorb when evaporating. In this project, 2400 kJ / kg is used. h-Convection heat transfer coefficient is 8.7 W / (m 2 ·℃), ε-emissivity of ultra-high performance concrete bridge deck 0.85, A-surface area of ​​bridge deck per cubic meter of concrete 5.55m 2 / m 3 ,σ-Stefan-Boltzmann constant 5.67×10 -8 W / m 2 ℃ 4 ;

[0053] S103 Concrete late curing stage curing;

[0054] Confirming that the ultra-performance concrete bridge deck has been finally set based on the touch of the ultra-performance concrete bridge deck, removing surface debris to ensure that the concrete surface is clean and pollution-free, placing the ultra-performance concrete bridge deck in a water curing pool, and transporting it to a storage area by a transfer vehicle after a 15-day water curing period;

[0055] S104 data acquisition and bridge deck maintenance;

[0056] The ambient temperature and humidity during the entire curing process, as well as the strength of the ultra-high performance concrete bridge deck after curing were collected. After some of the ultra-high performance concrete bridge decks were cured, they were close to but not yet at the design strength. After water was sprinkled on these ultra-high performance concrete bridge decks, they were further covered and cured, and eventually reached the design strength.

[0057] In summary, the method for casting and curing temperature control of prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment of the present invention has the advantages of controlling the temperature of ultra-high performance concrete entering the mold, reducing the risk of concrete cracking, and ensuring the strength of concrete in the field of concrete prefabricated component production technology.

[0058] It should be understood that the above-mentioned embodiments are one or more embodiments of the present invention, and there are many other embodiments and variations thereof based on the present invention; the variations and modifications made by ordinary technicians in this industry through the present invention without making pioneering innovations all fall within the scope of protection of the present invention.

Claims

1. A method for pouring and maintaining temperature control of prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment, characterized in that The specific steps include: S101 Temperature control during concrete pouring; The temperature control during the concrete pouring stage includes using industrial temperature control equipment to control the ambient temperature of the closed pouring area to the local annual average temperature. T 1, ℃, then prepare water, cement, river sand, fly ash, mineral powder, silica fume, steel fiber, additives and coarse aggregate according to the mix ratio, where the water-binder ratio is ω , pour the above raw materials into a stirring device, except water, the rest of the raw materials are at room temperature, water is added in a mass ratio of 2:8 to crushed ice, and then stirred. The temperature of the crushed ice is T 2,℃, T 2. Conditions (1), (2), (3), and (4) should be met; （1） （2） （3） （4） In the formula, C w -Specific heat capacity of water, kJ / (kg·℃), C i -Specific heat capacity of ice, kJ / (kg·℃), L i - heat of fusion of ice, kJ / kg, α -Linear expansion coefficient of concrete, 1 / ℃, E ( t 1)-Concrete age is t Elastic modulus at 1, MPa, k -Adjustment coefficient of hydration heat of admixtures with different dosages, Q 0-Total heat of cement hydration, kJ / kg, W -Amount of cementitious material per cubic meter of concrete, kg / m 3 , C c -Specific heat capacity of concrete, kJ / (kg·℃), ρ c -Mass density of concrete, kg / m 3 , μ - Poisson's ratio of concrete, m - The corresponding coefficient of unilateral cementitious materials related to cement type, dosage and mold entry temperature, t 1- The age from the beginning of concrete mixing to the disappearance of the gloss of the concrete bridge deck, d, f tk ( t 1)-Concrete age is t Standard value of tensile strength at 1, MPa, K - Anti-cracking safety factor is 1.5; The temperature control during the concrete pouring stage also includes placing the tied steel bars in the mold, pouring the mixed concrete into the mold, vibrating and compacting the concrete in the mold, flattening the concrete bridge deck, covering it with a film and placing it in the maintenance area; S102 Temperature control during the initial and mid-term curing stages of concrete; The temperature control of the concrete in the initial and mid-term curing stages includes: when the gloss of the concrete bridge deck disappears due to water seepage, the concrete bridge deck covering is opened, and the surface temperature of the concrete bridge deck is measured. T 3, ℃, spray maintenance is carried out immediately after temperature measurement, and the interval between each spray is Δt , h, the spray volume per cubic meter of concrete is Δm j ,kg / m 3 , j Indicates j Spray curing, the spray temperature is lower than T 3 but not less than ( T 3-15)℃, Δt , Δm j Conditions (5), (6), (7), and (8) must be met; （5） （6） （7） （8） In the formula, η -The ratio of the actual evaporated water volume to the spray volume, L v -The amount of heat that a unit mass of water needs to absorb when evaporating, kJ / kg, h -Convection heat transfer coefficient, W / m²·℃, ε - emissivity of ultra-high performance concrete bridge decks, A -Surface area of ​​the bridge deck per cubic meter of concrete, σ - Stefan-Boltzmann constant; The droplet size of the spray curing is no more than 100 μm, the spray interval is no more than 1 hour, and the spray volume per cubic meter of concrete is no less than 10 kg; S103 Concrete late curing stage curing; The concrete late curing stage curing includes confirming that the ultra-performance concrete bridge deck has been finally set according to the touch of the ultra-performance concrete bridge deck, removing surface debris to ensure that the concrete surface is clean and pollution-free, placing the ultra-performance concrete bridge deck in a water curing tank, and undergoing a water curing cycle. t After a few days, it is transported to the storage area by a transfer vehicle; S104 data acquisition and bridge deck maintenance; The data collection and bridge deck maintenance include collecting the ambient temperature and humidity during the entire maintenance process, as well as the strength of the ultra-high performance concrete bridge deck after the maintenance is completed, and determining whether further covering maintenance is needed based on the collected data.

2. The method for pouring and maintaining temperature control of prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment according to claim 1, characterized in that: In step S101, the local annual average temperature is obtained by dividing the sum of the local daily average temperatures in a year by the number of days in that year. When the calculated result is less than 10°C, the local annual average temperature is taken as 10°C.

3. The method for pouring and maintaining temperature control of prefabricated coarse aggregate ultra-high performance concrete bridge deck in a high temperature environment according to claim 1, characterized in that: In step S103, the water immersion curing period t is at least 15 days.

Images