A strength assessment method for precast coarse aggregate ultra-high performance concrete bridge deck

Abstract

The present invention provides a method for evaluating the strength of a precast coarse aggregate ultra-high performance concrete bridge deck, which is applicable to the field of quality inspection of precast concrete components. The present invention includes preliminary preparation, concrete pouring, concrete curing and concrete strength assessment. The quality of the precast coarse aggregate ultra-high performance concrete bridge deck is assessed by assessing the degree of concrete hydration. The method assesses the heat released by the hydration reaction of the cementitious material by monitoring the temperature during the pouring and curing of the bridge deck. When the heat released by the hydration reaction of the cementitious material is greater than a critical value, it is considered that the degree of hydration reaction is sufficient to provide a bridge deck strength that meets the design requirements. When the heat released by the hydration reaction of the cementitious material is less than a critical value, the strength of the bridge deck is further checked. The method for evaluating the quality of a precast coarse aggregate ultra-high performance concrete bridge deck provided by the present invention has the advantages of being economical, convenient and reliable, and can be widely used in the field of quality inspection of precast concrete components.

Description

Technical Field

[0001] The invention relates to a method for evaluating the strength of a prefabricated coarse aggregate ultra-high performance concrete bridge deck, which is applicable to the field of quality inspection of 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 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 quality evaluation of ultra-high performance concrete bridge decks faces great challenges. The traditional rebound test method has been difficult to evaluate the ultra-high performance concrete bridge decks whose strength far exceeds the detection limit. For prefabricated components, if core drilling is performed on each prefabricated coarse aggregate ultra-high performance concrete bridge deck, although it can provide direct and reliable strength data, the core sampling and laboratory pressure testing methods are cumbersome and expensive, especially for components with destructive sampling, even if the strength is qualified, they need to be repaired before they can be used.

[0003] Therefore, there is a need for an economical, convenient and reliable method for evaluating the quality of precast coarse aggregate ultra-high performance concrete bridge decks. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the strength of ultra-high performance concrete exceeds the limit of traditional rebound test method and the core drilling detection method is cumbersome and expensive. A precast coarse aggregate ultra-high performance concrete bridge deck strength assessment method is provided, which has the advantages of being economical, convenient and reliable, and can be widely used in the field of quality inspection of precast concrete components.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for evaluating the strength of a precast coarse aggregate ultra-high performance concrete bridge deck comprises the following steps:

[0007] S101 Preliminary preparation;

[0008] The preliminary preparation includes determining the mix ratio of ultra-high performance concrete, determining the temperature measuring point L on the upper surface of the bridge deck according to the length, width and thickness h of the prefabricated coarse aggregate ultra-high performance concrete bridge deck, and determining the temperature measuring point L on the upper surface of the bridge deck. 1 , L 2 , ..., L n Arrangement position, every two adjacent temperature measurement points are divided by the central axis, and the area represented by each temperature measurement point is S 1 , S 2 , ..., S n, and then determine whether the temperature, humidity and wind speed in the current maintenance area are within the range required by the standard maintenance conditions according to the ambient temperature, humidity and wind speed sensors set in the maintenance area. If not, adjust the temperature, humidity and wind speed in the current maintenance area until the standard maintenance conditions are met;

[0009] S102 concrete pouring;

[0010] The concrete pouring includes mixing the raw materials of the prefabricated coarse aggregate ultra-high performance concrete bridge deck at a preset temperature, stirring them at a fixed stirring time and stirring speed, pouring them into the bridge deck mold after stirring, and then using parallel multi-row infrared thermometers to synchronously measure the temperature of each measuring point of the bridge deck to obtain t 0 The temperature distribution on the bridge deck surface at time T 1,0 , T 2,0 , ..., T n,0 , corresponding to the temperature measurement point L 1 , L 2 , ..., L n , after covering the bridge deck, the bridge deck together with the bridge deck mold is transported to a maintenance area for maintenance;

[0011] S103 Concrete curing;

[0012] The concrete curing includes strictly curing according to the prescribed curing requirements of the prefabricated coarse aggregate ultra-high performance concrete bridge deck, using parallel multi-row infrared thermometers to synchronously measure the temperature of each measuring point of the bridge deck with ΔT as a fixed period to obtain t 0 The temperature distribution T on the upper surface of the bridge deck at time +i×ΔT 1,i , T 2,i , ..., T n,i , corresponding to the temperature measurement point L 1 , L 2 , ..., L n , i represents the i-th temperature measurement cycle;

[0013] S104 Concrete strength assessment;

[0014] The concrete strength assessment includes the hydration heat reference value Q of the precast coarse aggregate ultra-high performance concrete bridge deck whose strength meets the design requirements according to the test. b And judge inequality (1) to evaluate whether the concrete strength meets the design requirements;

[0015]

[0016] Where, k is the total number of temperature measurement cycles during the 28d curing period, C c -Specific heat capacity of concrete, kJ / (kg·℃), ρ c-Concrete mass density, kg / m 3 , K-evaluation risk control index, take 1.02, T 0 - Average temperature of raw materials;

[0017] When it is determined that inequality (1) holds true, it is considered that the strength of the ultra-high performance concrete bridge deck meets the design requirements and is a qualified product. When it is determined that inequality (1) does not hold true, the core drilling method is used to further test the concrete strength. If the test result meets the design requirements, the strength of the ultra-high performance concrete bridge deck after repair is considered to meet the design requirements and is a qualified product. If the test result does not meet the design requirements, it is considered that the strength does not meet the design requirements and is an unqualified product.

[0018] As a preferred technical solution of the present invention, in step S101, the area represented by each temperature measuring point is not greater than 0.1m 2 .

[0019] As a preferred technical solution of the present invention, in step S103, the fixed period ΔT is no more than 4 hours.

[0020] As a preferred technical solution of the present invention, in step S104, the test measures the bridge deck hydration heat reference value Q whose strength meets the design requirements. b , m groups of ultra-high performance concrete bridge decks of the same specifications were obtained under the same mix ratio, the same pouring and curing conditions. After 28 days of concrete curing age, the core drilling method was used to test the concrete strength. Then, the surface temperature distribution T' of the m' group of bridge decks whose concrete strength reached the design requirements was calculated. j,i , calculate the total hydration heat Q', and select the average of the m" group values ​​with the smaller total hydration heat Q' as the hydration heat reference value Q of the bridge deck whose strength meets the design requirements measured in the test b .

[0021]

[0022] As a preferred technical solution of the present invention, the average temperature of the raw material T 0 According to formula (3),

[0023]

[0024] In the formula, C x -Specific heat capacity of raw materials of x-th precast coarse aggregate ultra-high performance concrete, kJ / (kg·℃), W x -Ultra-high performance concrete raw material consumption of the xth precast coarse aggregate per cubic meter of concrete, kg / m 3 , T x -The xth precast coarse aggregate ultra-high performance concrete raw material preset temperature, °C.

[0025] The beneficial effects of the present invention are as follows: a quality assessment method for prefabricated coarse aggregate UHPC bridge deck based on concrete hydration degree assessment is proposed. Since the strength of UHPC components mainly comes from the hydration degree of cementitious materials therein, the quality of prefabricated coarse aggregate UHPC bridge deck is assessed by assessing the hydration degree of concrete. The method assesses the heat released by the hydration reaction of cementitious materials by monitoring the temperature during the pouring and curing of UHPC. When the heat released by the hydration reaction of cementitious materials is less than a critical value, it is considered that the hydration reaction degree is insufficient to provide the strength of the UHPC bridge deck that meets the design requirements. The advantages of this method are: 1. It is non-destructive and can determine the strength qualification of the UHPC bridge deck under the premise of ensuring the integrity of the UHPC structure; 2. It is reliable and takes the UHPC bridge deck data whose strength meets the design requirements under the same conditions as a benchmark, and considers the uncertainty risk index, so as to leave a certain safety reserve in the evaluation process of subsequent prefabricated components. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of the quality assessment method of precast coarse aggregate ultra-high performance concrete bridge deck of the present invention; DETAILED DESCRIPTION

[0027] 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.

[0028] This embodiment 1 is based on the T15 contract section 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 prefabricated coarse aggregate ultra-high performance concrete bridge deck quality assessment method are as follows:

[0029] S101 Preliminary preparation;

[0030] The mix ratio of ultra-high performance concrete is 750:40:50:200:1040:157:40:160:13, and the temperature measuring point L on the upper surface of the bridge deck is determined according to the length, width and thickness of the prefabricated coarse aggregate ultra-high performance concrete bridge deck h = 180mm. 1 , L 2 , ..., L nArrangement position, every two adjacent temperature measuring points are divided by the central axis, and the adjacent temperature measuring points are arranged at a distance of 300mm. In this embodiment, a total of 81 measuring points are arranged, and the area represented by each temperature measuring point is S 1 , S 2 , ..., S n , in this embodiment, the arrangement is uniform, that is, S 1 =S 2 =... =S n =0.09m 2 To ensure that the temperature measurement density can correctly reflect the temperature distribution of the current bridge deck, the area represented by each temperature measurement point is no larger than 0.1m 2 The ambient temperature of the maintenance area is set at 20°C, the humidity is 90%, and the wind speed sensor measures a wind speed of 0.52m / s. The temperature, humidity and wind speed in the maintenance area are within the range required by standard maintenance conditions.

[0031] S102 concrete pouring;

[0032] The raw materials of the prefabricated coarse aggregate ultra-high performance concrete bridge deck are mixed at a preset temperature. In this embodiment, the preset temperature of the raw materials is 10°C except for the crushed ice, and the preset temperature of the crushed ice is -20°C. The raw materials are mixed at a fixed stirring time of 10 minutes and a stirring speed of 25 revolutions per minute. After stirring, the raw materials are poured into the bridge deck mold. Then, the temperature of each measuring point of the bridge deck is synchronously measured using a multi-row infrared thermometer connected in parallel to obtain t 0 The temperature distribution on the bridge deck surface at time T 1,0 , T 2,0 , ..., T n,0 , some data are shown in Table 1, distributed in 30℃~38℃, corresponding to the temperature measurement points L 1 , L 2 , ..., L n , after covering the bridge deck, the bridge deck together with the bridge deck mold is transported to a maintenance area for maintenance;

[0033] Table 1 t 0 The upper surface temperature of the bridge deck at the moment

[0034]

[0035] S103 Concrete curing;

[0036] The maintenance is strictly carried out in accordance with the prescribed requirements for the maintenance of prefabricated coarse aggregate ultra-high performance concrete bridge decks. The temperature of each measuring point of the bridge deck is synchronously measured using a multi-row infrared thermometer in parallel at a fixed period of ΔT = 4h. In order to accurately evaluate the heat generated by the hydration heat reaction of the bridge deck, the measurement period should not exceed 4h. 0The temperature distribution T on the upper surface of the bridge deck at time +i×ΔT 1,i , T 2,i , ..., T n,i , corresponding to the temperature measurement point L 1 , L 2 , ..., L n , i represents the i-th temperature measurement cycle, and some data are shown in Table 2;

[0037] Table 2 t i The upper surface temperature of the bridge deck at the moment

[0038]

[0039]

[0040] S104 Concrete strength assessment;

[0041] Average temperature of raw materials T 0 , calculated according to formula (1);

[0042]

[0043] In the formula, C x -The specific heat capacity of raw materials of the x-th precast coarse aggregate ultra-high performance concrete, cement, expansion agent, fly ash, silica fume, quartz sand, steel fiber, water, crushed ice, and water reducing agent are 0.9 kJ / (kg·℃), 1 kJ / (kg·℃), 0.75 kJ / (kg·℃), 0.7 kJ / (kg·℃), 0.84 kJ / (kg·℃), 0.49 kJ / (kg·℃), 4.18 kJ / (kg·℃), 2.1 kJ / (kg·℃), and 1 kJ / (kg·℃), respectively, W x - The raw material consumption of prefabricated coarse aggregate ultra-high performance concrete for each cubic meter of concrete is 750 kg / m for cement, expansion agent, fly ash, silica fume, quartz sand, steel fiber, water, crushed ice and water reducing agent. 3 , 40kg / m 3 , 50kg / m 3 , 200kg / m 3 、1040kg / m 3 、157kg / m 3 , 40kg / m 3 , 160kg / m 3 , 13kg / m 3 , T x - The xth precast coarse aggregate ultra-high performance concrete raw material preset temperature, °C;

[0044] According to the test, the hydration heat reference value Q of the precast coarse aggregate ultra-high performance concrete bridge deck with strength that meets the design requirementsb And judge inequality (2) to evaluate whether the concrete strength meets the design requirements;

[0045]

[0046] Where, the total number of temperature measurement cycles during the k-28d curing period is 141 in this embodiment, C c -Specific heat capacity of concrete, kJ / (kg·℃), 375 kJ / (kg·℃) in this embodiment, ρ c -Concrete mass density, kg / m 3 , in this embodiment, 2450kg / m 3 , K-evaluation risk control index, take 1.02;

[0047] Inequality (1) is determined to be true, and it is considered that the strength of the ultra-high performance concrete bridge deck meets the design requirements and is a qualified product;

[0048] This embodiment 2 is based on the T15 contract section of the Shiziyang Channel project. The Shiziyang Channel starts at Xinnian, Humen Town, Dongguan City, and ends at Dagang Town. The hydration heat reference value Q of the prefabricated coarse aggregate ultra-high performance concrete bridge deck with strength that meets the design requirements is obtained through experiments. b :

[0049] Ten groups of ultra-high performance concrete bridge decks of the same specifications were obtained according to the same mix ratio, the same pouring and curing conditions as in Example 1. After 28 days of concrete curing, the core drilling method was used to test the concrete strength. Then, the surface temperature distribution T' of the nine groups of bridge decks whose concrete strength reached the design requirements was calculated. j,i According to formula (3), the total hydration heat Q' is 205984kJ, 223941kJ, 206814kJ, 201893kJ, 214541kJ, 226283kJ, 202813kJ, 210870kJ, and 206475kJ, respectively. The average of the five groups with the smallest total hydration heat Q' is selected as the hydration heat reference value Q of the bridge deck whose strength meets the design requirements. b , in this embodiment it is 204796kJ.

[0050]

[0051] The third embodiment of this invention is based 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 method for making the prefabricated coarse aggregate ultra-high performance concrete bridge deck is consistent with that of the first embodiment. The temperature measurement data of the upper surface of the bridge deck are shown in the following table.

[0052] Table 3 Bridge deck upper surface temperature

[0053]

[0054] According to the test, the hydration heat reference value Q of the precast coarse aggregate ultra-high performance concrete bridge deck with strength that meets the design requirements b And judging inequality (4), evaluate whether the concrete strength meets the design requirements;

[0055]

[0056] It is determined that inequality (4) is not true. The core drilling method is used to further test the concrete strength. The test results meet the design requirements. After the ultra-high performance concrete bridge deck is repaired, it is considered that its strength meets the design requirements and is a qualified product.

[0057] In summary, the quality assessment method of prefabricated coarse aggregate ultra-high performance concrete bridge deck of the present invention has the advantages of being economical, convenient and reliable in the field of quality inspection of prefabricated concrete components, and can determine the strength qualification of UHPC bridge decks while ensuring the integrity of the UHPC structure.

[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 evaluating the strength of a precast coarse aggregate ultra-high performance concrete bridge deck, characterized in that The specific steps include: S101 Preliminary preparation; The preliminary preparation includes determining the mix ratio of ultra-high performance concrete, determining the temperature measuring points L1, L2, ..., L on the upper surface of the bridge deck according to the length, width and thickness h of the prefabricated coarse aggregate ultra-high performance concrete bridge deck, n Arrangement position, every two adjacent temperature measurement points are divided by the central axis, and the area represented by each temperature measurement point is S1, S2, ..., S n , and then determine whether the temperature, humidity and wind speed in the current maintenance area are within the range required by the standard maintenance conditions according to the ambient temperature, humidity and wind speed sensors set in the maintenance area. If not, adjust the temperature, humidity and wind speed in the current maintenance area until the standard maintenance conditions are met; S102 concrete pouring; The concrete pouring includes mixing the raw materials of the prefabricated coarse aggregate ultra-high performance concrete bridge deck at a preset temperature, stirring them at a fixed stirring time and stirring speed, and pouring them into the bridge deck mold after stirring, and then using parallel multi-row infrared thermometers to synchronously measure the temperature of each measuring point of the bridge deck to obtain the upper surface temperature distribution T of the bridge deck at time t0. 1,0 , T 2,0 , ..., T n,0 , corresponding to the temperature measurement points L1, L2, ..., L n , after covering the bridge deck, the bridge deck together with the bridge deck mold is transported to a maintenance area for maintenance; S103 concrete curing; The concrete curing includes strictly curing according to the prescribed curing requirements of the prefabricated coarse aggregate ultra-high performance concrete bridge deck, using a plurality of parallel rows of infrared thermometers to synchronously measure the temperature of each measuring point of the bridge deck with a fixed period of ΔT to obtain the upper surface temperature distribution T of the bridge deck at time t0+i×ΔT 1,i , T 2,i , ..., T n,i , corresponding to the temperature measurement points L1, L2, ..., L n , i represents the i-th temperature measurement cycle; S104 Concrete strength assessment; The concrete strength assessment includes the hydration heat reference value Q of the precast coarse aggregate ultra-high performance concrete bridge deck whose strength meets the design requirements according to the test. b And judge inequality (1) to evaluate whether the concrete strength meets the design requirements; Where, k is the total number of temperature measurement cycles during the 28d curing period, C c -Specific heat capacity of concrete, kJ / (kg·℃), ρ c -Concrete mass density, kg / m 3 , K-evaluation risk control index, take 1.02, T0-average temperature of raw materials; The hydration heat reference value Q b , m groups of ultra-high performance concrete bridge decks of the same specifications were obtained under the same mix ratio, the same pouring and curing conditions. After 28 days of concrete curing age, the core drilling method was used to test the concrete strength. Then, the surface temperature distribution T' of the m' group of bridge decks whose concrete strength reached the design requirements was calculated. j,i , calculate the total hydration heat Q', The average value of the m" group with the smallest total hydration heat Q' is selected as the hydration heat reference value Q b ; When it is determined that inequality (1) holds true, it is considered that the strength of the ultra-high performance concrete bridge deck meets the design requirements and is a qualified product. When it is determined that inequality (1) does not hold true, the core drilling method is used to further test the concrete strength. If the test result meets the design requirements, the strength of the ultra-high performance concrete bridge deck after repair is considered to meet the design requirements and is a qualified product. If the test result does not meet the design requirements, it is considered that the strength does not meet the design requirements and is an unqualified product.

2. The method for evaluating the strength of a precast coarse aggregate ultra-high performance concrete bridge deck according to claim 1, characterized in that: In step S101, the area represented by each temperature measurement point is no larger than 0.1m 2 .

3. The method for evaluating the strength of a precast coarse aggregate ultra-high performance concrete bridge deck according to claim 1, characterized in that: In step S103, the fixed period ΔT is no greater than 4 hours.

4. The method for evaluating the strength of a precast coarse aggregate ultra-high performance concrete bridge deck according to any one of claim 1 and claim 3, characterized in that: The average temperature T0 of the raw material is calculated according to formula (3): In the formula, C x -Specific heat capacity of raw materials of x-th precast coarse aggregate ultra-high performance concrete, kJ / (kg·℃), W x -Ultra-high performance concrete raw material consumption of the xth precast coarse aggregate per cubic meter of concrete, kg / m 3 , T x -The xth precast coarse aggregate ultra-high performance concrete raw material preset temperature, °C.

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