CN116486943B - Freeze thawing cycle test system design method considering regional air temperature characteristics - Google Patents
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Abstract
The invention relates to the technical field of concrete freezing resistance evaluation, and provides a freeze-thawing cycle test system design method considering regional air temperature characteristics. According to the invention, based on statistical analysis of historical air temperature data for many years, statistical indexes such as daily temperature difference, positive and negative temperature alternation times and cooling rate are considered, and a freeze-thawing cycle test system design method considering regional climate characteristics is established by combining a hydrostatic pressure theory, so that the freeze-thawing effect suffered by concrete in real service environments of different regions can be reproduced in a laboratory, the degradation process of the concrete under different freeze-thawing systems can be more accurately evaluated, and the problem that the original standard recommends that a single freeze-thawing effect system is inaccurate in evaluating the frost resistance of the concrete is solved.
Description
Technical Field
The invention relates to the technical field of concrete freezing resistance evaluation, in particular to a freeze-thawing cycle test system design method considering regional air temperature characteristics.
Background
The freezing and thawing damage of concrete refers to the phenomena of peeling off of the concrete surface layer, loose materials and strength degradation under the alternating action of positive and negative temperature.
The artificial simulated freeze thawing is usually carried out according to a quick freezing method in GB50082-2009, wherein the freeze thawing cycle is completed every 2-4 hours at the positive and negative temperature of (-18+/-2) DEG C to (5+/-2) DEG C, and the freezing resistance of the concrete is evaluated according to the change condition of indexes such as a dynamic elastic mold and the like along with the number of the freeze thawing cycles.
However, in the actual service environment, the daily temperature difference, the positive and negative temperature alternation times, the cooling rate, the freezing and thawing month and the like in different areas have larger differences, the standard recommended quick freezing method is a standardized method, the freezing and thawing system of each freezing and thawing cycle test in the method is the same, the freezing and thawing degradation process of concrete in the actual environment is difficult to be truly reflected, and the obvious error exists in the concrete freezing resistance test result by the quick freezing method for guiding engineering practice.
Disclosure of Invention
In view of the above, the invention provides a freeze-thawing cycle test system design method considering regional air temperature characteristics. The invention can realize the repeated freezing and thawing actions suffered by the concrete in the real service environment of different regions in a laboratory, and the evaluation result is more accurate.
In order to achieve the above object, the present invention provides the following technical solutions:
a freeze thawing cycle test system design method considering regional air temperature characteristics comprises the following steps:
(1) Counting historical temperature data of the test region for m years, and screening out representative freezing and thawing months according to the temperature data; the representative freezing and thawing months are the first n months with the largest times of freezing and thawing cycle of concrete; n is more than or equal to 1, m is more than or equal to 10;
(2) Dividing each representative freeze-thawing month into three time periods of the last ten days, the middle ten days and the last ten days, and counting the maximum value and the minimum value of the historical daily temperature of each time period; performing frequency analysis on the minimum value of the historical daily temperature in each time period, and calculating the average value of the minimum value of the daily temperature as the minimum temperature representative value of the freeze thawing cycle test; performing frequency analysis on the maximum value of the historical daily temperature in each time period, and calculating the average value of the maximum value of the daily temperature as the highest temperature representative value of the freeze thawing cycle test; taking the minimum temperature representative value and the maximum temperature representative value selected in each time period as a group of freeze-thawing cycle test temperature data to obtain 3n groups of freeze-thawing cycle test temperature data;
(3) Determining the number of freeze-thaw cycle tests performed in an indoor acceleration environment for each set of freeze-thaw cycle test temperature data according to equation 1:
in formula 1: n (N) s N is the number of times of freeze thawing cycle in each time period in the practical environment acc The number of freeze-thawing cycle tests is the number of times in an indoor accelerated environment; t is t s The extreme temperature change time of each freeze thawing cycle in the actual environment is expressed in units of h and t acc The cooling time of each freeze thawing cycle in the indoor environment is expressed in h;
(4) And (3) according to the time sequence of the freeze-thawing cycle test temperature data, carrying out the freeze-thawing cycle test of the concrete according to the times of carrying out the freeze-thawing cycle test in the indoor accelerating environment under each group of freeze-thawing cycle temperature data calculated in the step (3).
Preferably, m is 10 to 20.
Preferably, the screening method of the representative freeze-thawing month comprises the following steps: counting the maximum value and the minimum value of the historical daily temperature in m years, determining whether the concrete has freeze thawing cycles in the same day according to the maximum value and the minimum value of the daily temperature, calculating the average freeze thawing cycle times of each month, and selecting the first n months with the maximum average freeze thawing cycle times as representative freeze thawing months; the criteria for determining the occurrence of a freeze-thaw cycle are: the highest daily temperature is more than 0 ℃ and the lowest daily temperature is less than-3 ℃.
Preferably, the method for determining the number of the representative freeze-thawing months comprises the following steps: according to the historical temperature data of the test area for m years, the annual average freeze thawing cycle times of the test area are counted and recorded as N year The number of representative freeze-thaw months, on a 30 day per month basis, was calculated by formula 2:
n＝N year 30 formula 2;
in the formula 2, n is an integer.
Preferably, when the frequency analysis is performed on the minimum value of the historical daily temperature in each time period, if the result shows that the frequency distribution of the daily temperature minimum value approximately accords with the normal distribution, the average value of the daily temperature minimum value is an arithmetic average value or a weighted average value, and if the result shows that the frequency distribution of the daily temperature minimum value does not accord with the normal distribution, the average value of the daily temperature minimum value is a weighted average value;
when the frequency analysis is carried out on the maximum value of the historical daily temperature in each time period, if the result shows that the frequency distribution of the maximum value of the daily temperature approximately accords with the normal distribution, the average value of the maximum value of the daily temperature is an arithmetic average value or a weighted average value, and if the result shows that the frequency distribution of the maximum value of the daily temperature does not accord with the normal distribution, the average value of the maximum value of the daily temperature is a weighted average value.
Preferably, in the formula 1, t s The difference between the time of occurrence of the highest day temperature and the lowest day temperature of the freeze thawing cycle in the actual environment.
Preferably, in formula 1, t s The acquisition method of (1) comprises the following steps: counting the occurrence time of the daily highest air temperature in the historical temperature with the average freeze thawing cycle time of the maximum month in the test area, taking the occurrence time with the maximum occurrence time as the occurrence time of the daily highest air temperature of the freeze thawing cycle, and marking as t High height The method comprises the steps of carrying out a first treatment on the surface of the Counting the occurrence time of the lowest daily air temperature in the historical temperature of the test area, taking the time with the highest occurrence times as the occurrence time of the lowest daily air temperature of freeze thawing circulation, and marking as t Low and low The method comprises the steps of carrying out a first treatment on the surface of the Calculating t High height To t Low and low Temperature drop time of t Low and low To t High height Taking the smaller value of the temperature drop time and the temperature rise time as t s Is a value of (a).
Preferably, in the formula 1, N s The value of (2) is 10, t acc The value of (2) is 1-2 h.
Preferably, the test area is a plateau area.
The invention provides a freeze-thawing cycle test system design method considering regional air temperature characteristics, which is characterized in that historical temperature data of an experimental region in m years are counted, n representative freeze-thawing months are screened out, the representative freeze-thawing months are divided into three time periods of the last ten days, the middle ten days and the last ten days, the maximum value and the minimum value of daily temperatures of each time period are counted, the average value and the standard deviation of the maximum temperature and the minimum temperature of a freeze-thawing cycle test are determined through frequency analysis, 3n groups of freeze-thawing cycle test temperature data are obtained, and then the number of times of freeze-thawing cycle tests in an indoor accelerating environment is calculated under each group of freeze-thawing cycle temperature data based on the maximum hydrostatic pressure theory through a formula 1, so that the freeze-thawing cycle test system is determined. According to the invention, based on statistical analysis of historical air temperature data for many years, statistical indexes such as daily temperature difference, positive and negative temperature alternation times and cooling rate are considered, and a freeze-thawing cycle test system design method considering regional climate characteristics is established by combining a hydrostatic pressure theory, so that the freeze-thawing effect suffered by concrete in real service environments of different regions can be reproduced in a laboratory, the degradation process of the concrete under different freeze-thawing systems can be more accurately evaluated, and the problem that the original standard recommends that a single freeze-thawing effect system is inaccurate in evaluating the frost resistance of the concrete is solved.
Drawings
FIG. 1 is a plot of the present invention on a plateau;
FIG. 2 is a plot of sample point threshold temperature interval frequency statistics;
FIG. 3 is a graph showing extreme temperature frequency distribution in the top, middle and bottom 4 months of the Point37 region;
FIG. 4 is a graph showing extreme temperature frequency distribution in the top, middle and bottom 10 months of the Point37 region;
FIG. 5 is a graph showing the comparison of the freeze-thaw temperatures of the Point37 region and the quick freeze method determined in example 1.
Detailed Description
The invention provides a freeze-thawing cycle test system design method considering regional air temperature characteristics, which comprises the following steps:
(1) Counting historical temperature data of the test region for m years, and screening out representative freezing and thawing months according to the temperature data; the representative freezing and thawing months are the first n months with the largest times of freezing and thawing cycle of concrete; n is more than or equal to 1, m is more than or equal to 10;
(2) Dividing each representative freeze-thawing month into three time periods of the last ten days, the middle ten days and the last ten days, and counting the maximum value and the minimum value of the historical daily temperature of each time period; performing frequency analysis on the minimum value of the historical daily temperature in each time period, and calculating the average value of the minimum value of the daily temperature as the minimum temperature representative value of the freeze thawing cycle test; performing frequency analysis on the maximum value of the historical daily temperature in each time period, and calculating the average value of the maximum value of the daily temperature as the highest temperature representative value of the freeze thawing cycle test; taking the minimum temperature representative value and the maximum temperature representative value selected in each time period as a group of freeze-thawing cycle test temperature data to obtain 3n groups of freeze-thawing cycle test temperature data;
(3) Determining the number of freeze-thaw cycle tests performed in an indoor acceleration environment for each set of freeze-thaw cycle test temperature data according to equation 1:
in formula 1: n (N) s N is the number of times of freeze thawing cycle in each time period in the practical environment acc The number of freeze-thawing cycle tests is the number of times in an indoor accelerated environment; t is t s The extreme temperature change time of each freeze thawing cycle in the actual environment is expressed in units of h and t acc The cooling time of each freeze thawing cycle in the indoor environment is expressed in h;
(4) And (3) according to the time sequence of the freeze-thawing cycle test temperature data, carrying out the freeze-thawing cycle test of the concrete according to the times of carrying out the freeze-thawing cycle test in the indoor accelerating environment under each group of freeze-thawing cycle temperature data calculated in the step (3).
According to the invention, historical temperature data of the experimental region for m years are counted, and representative freezing and thawing months are screened out according to the temperature data; the representative freezing and thawing months are the first n months with the largest times of freezing and thawing cycle of concrete; n is more than or equal to 1, and m is more than or equal to 10. The freeze-thawing cycle of the invention refers to the freeze-thawing cycle of concrete, and the subsequent description is omitted; in the invention, the test area is preferably a plateau area (area with the altitude higher than 1000 m), 153 sampling points are distributed in the plateau area of China in total, the meteorological data are extracted and analyzed, and the freeze-thawing circulation effect is not considered for the distribution point with the average daily air temperature higher than-3 ℃. In the present invention, m is preferably 10 to 20, more preferably 15 to 20, and even more preferably 19, and in the specific embodiment of the present invention, historical temperature data of 2000 to 2018 (total 19) are counted, and the historical temperature data can be obtained from the following three ways: 1. national Qinghai-Tibet plateau science data center https:// data.tpdc.ac.cn/zh-hans/data/8028b944-daaa-4511-8769-965612652c49/; 2. http:// data. Cma. Cn/national weather science data center; 3. https:// www.resdc.cn/defaults. Aspx national academy of sciences resource environment science and data center; in a specific embodiment of the present invention, raster data from the national Qinghai-Tibet plateau science data center is employed. In the invention, the historical temperature data are all the historical temperature data of m years, and the description is omitted.
In the present invention, the screening method of the representative freeze-thawing month preferably comprises: counting the maximum value and the minimum value of the historical daily temperature in m years, determining whether the concrete has freeze thawing cycles in the same day according to the maximum value and the minimum value of the daily temperature, calculating the average freeze thawing cycle times of each month, and selecting the first n months with the maximum average freeze thawing cycle times as representative freeze thawing months; the criteria for determining the occurrence of a freeze-thaw cycle are: the highest daily temperature is more than 0 ℃ and the lowest daily temperature is less than-3 ℃. From the relationship of Clapeyron-Clausius with respect to the freezing point of water and pressure, it is known that the water inside the capillary pores of concrete freezes at-3℃and melts at 0℃and therefore the present invention treats the day maximum temperature above 0℃and the day minimum temperature below-3℃as a freeze-thaw cycle when determining a representative freeze-thaw month. In the specific embodiment of the invention, 8 data (one every 3 hours) can be obtained in a certain area every day, 55520 data are obtained in total in 19 years, the maximum value and the minimum value in the 8 data every day are extracted, the maximum value and the minimum value of 6940 groups of daily temperatures are obtained in total, the group number meeting the conditions that the daily maximum temperature is more than 0 ℃ and the daily minimum temperature is less than-3 ℃ is selected from 6940 groups of data, the average number of times of occurrence of freeze thawing cycle coefficients in each month is calculated by combining with specific months, the average number of freeze thawing cycles in each month is ordered from large to small, and the first n months are selected as representative freeze thawing months, wherein n meets the following conditions in the specific embodiment of the invention: the number of times of freeze thawing cycles of the annual average is not less than n times of monthly days.
In the present invention, the method for determining the number of representative freeze-thaw months includes: according to the historical temperature data of the test area for m years, the annual average freeze thawing cycle times of the test area are counted and recorded as N year The number of representative freeze-thaw months, on a 30 day per month basis, was calculated by formula 2:
n＝N year 30 formula 2;
in the formula 2, n is an integer.
For example, in the statistical process, of the 19 years of historical temperature data, 2223 groups of data meet the criteria that "day maximum temperature is greater than 0 ℃ and day minimum temperature is less than-3 ℃, then N year =2223/19=117, then n=117/30=3.9, n being the integer 4. In the invention, the number of representative freeze thawing months is calculated according to the number of annual average freeze thawing cycles in the region, and is related to the annual average freeze thawing in the test region, the number of annual average freeze thawing times in different regions is different, the calculated result is also different, and when n is smaller than 1, the region is considered to be unnecessary to consider the freeze thawing action.
After the representative freeze-thawing months are obtained, each representative freeze-thawing month is divided into three time periods of the last ten days, the middle ten days and the last ten days, and the maximum value and the minimum value of the historical daily temperature of each time period are counted; performing frequency analysis on the minimum value of the historical daily temperature in each time period, and calculating the average value of the minimum value of the daily temperature as the minimum temperature representative value of the freeze thawing cycle test; performing frequency analysis on the maximum value of the historical daily temperature in each time period, and calculating the average value of the maximum value of the daily temperature as the highest temperature representative value of the freeze thawing cycle test; and taking the minimum temperature representative value and the maximum temperature representative value selected in each time period as a group of freeze-thawing cycle test temperature data to obtain 3n groups of freeze-thawing cycle test temperature data. In the present invention, each time period comprises 10 to 11 days, and the time of a single freeze-thawing cycle is recorded as 24 hours (i.e. 1 freeze-thawing cycle occurs per day) in each time period; the method has no special requirement on the calculation mode of the frequency, and adopts a conventional method, for example, taking the last ten days (10 days) of a certain representative freeze thawing month and selecting the historical data of m years as an example, counting the highest temperature of the last ten days of the month in m years to obtain a data in total, and if b times occur at the temperature of minus 3 ℃, the frequency at the temperature of minus 3 ℃ is b/a.
In the invention, when the minimum value of the historical daily temperature in each time period is subjected to frequency analysis, if the result shows that the frequency distribution of the minimum value of the daily temperature approximately accords with normal distribution, the mean value of the minimum value of the daily temperature is preferably an arithmetic mean value or a weighted mean value, more preferably the arithmetic mean value, and when the frequency distribution approximately shows normal distribution, the arithmetic mean value and the weighted mean value are similar, in order to simplify the calculation process, the arithmetic mean value is preferably adopted, and the standard deviation can be calculated while the arithmetic mean value is calculated, and the floating range of the experimental temperature can be controlled according to the standard deviation; if the result shows that the frequency distribution of the daily temperature minimum does not conform to the normal distribution, the average value of the daily temperature minimum is preferably a weighted average value.
In the present invention, when the maximum value of the historical daily temperature in each period is analyzed for frequency, if the result shows that the frequency distribution of the daily temperature maximum value approximately matches the normal distribution, the average value of the daily temperature maximum value is an arithmetic average value or a weighted average value, more preferably an arithmetic average value (the principle is the same as the above), and if the result shows that the frequency distribution of the daily temperature maximum value does not match the normal distribution, the average value of the daily temperature maximum value is a weighted average value.
The calculation mode of the arithmetic mean value and the weighted mean value is not particularly required, and calculation methods well known to those skilled in the art can be adopted.
In the invention, after the freeze-thawing cycle test temperature data are obtained, 3n groups of freeze-thawing cycle test temperature data are drawn into a freeze-thawing extremum temperature change curve according to time sequence.
After obtaining the temperature data of each set of freeze-thawing cycle test, the invention determines the times of freeze-thawing cycle test in the indoor accelerating environment under the temperature data of each set of freeze-thawing cycle test according to the formula 1:
the meaning of each symbol in formula 1 is not repeated, wherein N is calculated according to formula 1 acc The value is an integer.
In the present invention, in the formula 1, t s The difference between the time of occurrence of the highest day temperature and the lowest day temperature of the freeze thawing cycle in the actual environment.
In the present invention, the t s The acquisition method of (a) preferably includes: counting the occurrence time of the daily highest air temperature in the historical temperature with the average freeze thawing cycle times of the maximum month in the test area, taking the occurrence time with the maximum occurrence times as the occurrence time of the daily highest air temperature of the freeze thawing cycle, and marking as t High height The method comprises the steps of carrying out a first treatment on the surface of the Counting the occurrence time of the lowest daily air temperature in the historical temperature of the test area, taking the time with the highest occurrence times as the occurrence time of the lowest daily air temperature of freeze thawing circulation, and marking as t Low and low Calculating t High height To t Low and low Temperature drop time of t Low and low To t High height Taking the smaller value of the temperature drop time and the temperature rise time as t s Is a value of (a). The time interval of the solar extreme temperature is particularly important for 24 hours a day, because the smaller the time interval, the larger the temperature rate and the larger the damage caused by freeze thawing to the concrete under the condition of the same extreme temperature. Therefore, the time difference of the extreme temperature of the day of the month with the most frequent freezing and thawing is counted, and the time required by temperature rise and temperature drop is often different.
In the present invention, N in formula 1 s Preferably 10 (28-31 days per month, for ease of calculation, the invention is similar to regards each month as 30 days, i.e. each time period is 10 days, 1 freeze-thawing cycle per day), t acc The value of (2) is preferably 1 to 2 hours.
The invention relates to a method for accelerating the efficiency of an indoor test, which is characterized in that a formula 1 is deduced based on a hydrostatic pressure theory, and the number of freeze thawing cycles in each time period is reduced by improving the cooling rate of the indoor test under the condition that the internal and external accumulated maximum hydrostatic pressures in each time period are ensured to be the same.
In the present invention, the derivation process of formula 1 is specifically as follows:
according to the hydrostatic pressure theory, as shown in formula (3), for the same concrete material and environmental temperature difference, the maximum hydrostatic pressure is proportional to the cooling rate, as shown in formula (4).
In the formulae (3) to (4), P max The maximum hydrostatic pressure under the action of concrete freeze thawing is represented by R, the cooling rate is represented by delta T, the temperature difference is represented by T, the cooling time is represented by eta, the dynamic viscosity coefficient of capillary pore water is represented by eta, the maximum icing rate is represented by U, the permeability coefficient of concrete is represented by K, and the capillary pore shape factor is represented by phi (L).
And defining the maximum hydrostatic pressure multiplied by the number of freeze-thawing cycles under a single freeze-thawing cycle as the accumulated hydrostatic pressure, wherein in order to realize the freeze-thawing action suffered by the recycled concrete in the actual environment in the indoor acceleration test, the same accumulated maximum hydrostatic pressure between the indoor and the outdoor is required to be ensured, as shown in the formulas (6) to (8).
σ＝P max N (5)
σ s ＝σ acc (6)
P max,s N s ＝P max,acc N acc (7)
In the formulas (5) to (8), σ represents the cumulative maximum hydrostatic pressure, subscripts s and acc represent the actual environment and the indoor acceleration environment, respectively, and N represents the number of freeze-thawing cycles.
In order to improve the efficiency of the freeze thawing test in the laboratory, the time required for single freeze thawing is shortened as much as possible under the condition of not changing the freeze thawing temperature difference (formula (9)). And (3) performing test design according to the freezing and thawing cycle temperature specified by the quick freezing method in the specification for 2-4 h (the cooling time is 1-2 h), and deducing the formula (1) according to the formula (9) and the formula (8).
ΔT s ＝ΔT acc (9)
In the formulas (9) and (1), subscripts s and acc represent the actual environment and the indoor acceleration environment, respectively, N represents the number of freeze-thawing cycles, and Δt represents the temperature difference.
According to formula 1, the number of times of performing freeze thawing cycle test in indoor acceleration environment under each group of freeze thawing cycle test temperature data can be calculated, if calculated, N acc If the value of (2) is 2, the test is carried out twice under each group of freeze-thawing cycle temperature data, namely the test can simulate the actual environment for 10 days (N s The value of (2) is 10), 3n groups of freeze-thawing cycle test temperature data are obtained through the scheme, then 2 freeze-thawing cycle tests are carried out under each group of freeze-thawing cycle test temperature data, the cooling time of each time is set to be 1-2 h, and 6n times of tests are carried out, so that the freeze-thawing cycle effect suffered by the concrete in the test area in one year can be simulated.
And after the freeze-thawing cycle temperature data and the times of performing freeze-thawing cycle in an indoor accelerating environment under each group of data are obtained, performing a freeze-thawing cycle test on the concrete according to the calculated test times according to the time sequence of the freeze-thawing cycle test temperature data. In the invention, the time sequence of the freeze-thawing cycle test temperature data specifically refers to the time sequence of the time periods corresponding to each group of temperature data, for example, if four representative freeze-thawing months of 4 months, 10 months, 5 months and 3 months are obtained through screening, each month is divided into three time periods, 12 groups of freeze-thawing cycle test temperature data are obtained in total, and the time periods are respectively corresponding to 4 months, middle and lower ten days, 10 months, middle and lower ten days, 5 months, middle and lower ten days and 3 months, then when the freeze-thawing cycle test is performed, the test is performed according to the time sequence of the freeze-thawing cycle test temperature data, namely, the test is performed under the test temperature data corresponding to 3 months, middle and lower ten days, and then the test is performed sequentially over 4 months, middle and lower ten daysPerforming test at test temperature data corresponding to the last, middle and last ten days of 5 months and the last, middle and last ten days of 10 months, and calculating N according to the number of times of each test acc And (5) value determination.
By adopting the method provided by the invention to design a system of the freeze-thawing cycle test, the obtained freeze-thawing positive and negative extremum temperature of each time period changes along with time, and is closer to the actual environment than the normal constant freeze-thawing test temperature, and the artificial simulation test realizes the simulation of the freeze-thawing effect suffered by the actual service concrete by setting different freeze-thawing cycle positive and negative extremum temperatures, so that the reality and reliability of the indoor freeze-thawing test are improved.
The following description of the embodiments of the present invention will clearly and fully describe the technical solutions of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
1. Research scope and distribution point
In the embodiment, historical air temperature data of 19 years total from 2000 to 2018 are adopted for analysis, the research range is a plateau area of China, 153 sampling points are distributed for meteorological data extraction and re-analysis, for the distribution point with the average daily minimum air temperature of more than-3 ℃, the specific distribution point under the freeze thawing cycle action is not considered, and the distributed sampling points are shown in figure 1;
2. representative freeze-thaw month screening
From Clapeyron-Clausius regarding the relationship of the freezing point of water to pressure, it is known that the water within the capillary pores of concrete freezes at-3℃and melts at 0 ℃. Thus, when determining the month of the freeze-thaw cycle, the day maximum temperature is above 0 ℃ and the day minimum temperature is below-3 ℃ is considered as a freeze-thaw cycle. The program statistics of Python is adopted to obtain the number of times of freezing and thawing of each sampling point in 19 years in each month, and the statistics is carried out to obtain the number of times of annual average freezing and thawing cycle N of each sampling point year . In order to ensure that the number of freeze-thaw cycles contemplated by the present invention matches the actual freeze-thaw conditions,the number of annual average freeze-thaw cycles was divided by 30 (30 days were assumed per month) to calculate the number of annual average freeze-thaw cycles months. Taking Point37 as an example, the number of annual average freeze-thawing cycles counted by the Point is 117 times, so that the first 4 months (117/30 approximately 4) with the maximum number of freeze-thawing cycles of the Point are selected as representative freeze-thawing months to be analyzed, and the months with the maximum number of freeze-thawing cycles of the Point37 are 4 months, 10 months, 5 months and 3 months after counting, and the number of days of the freeze-thawing is shown in table 1.
TABLE 1Point37 major freeze thawing cycle months and month average number of freeze thawing
3. The moment of day at which the highest and lowest air temperatures occur
The time of day extreme temperature of the most frequent month of freeze thawing is counted by taking Point37 as an example, and the result is shown in Table 2, and the result shows that the time of day extreme temperature of the most frequent month of freeze thawing is mostly 9:00 am, not usually 14:00 am, and the lowest temperature is mostly 0:00 am, not 3:00 am. The time required by temperature rise and temperature drop is often different, the invention takes the smaller time of temperature rise and temperature drop as the time (t) s ) I.e. in Point37, t s The value of (2) is 9;
TABLE 2 time at which the extreme temperature of day, for example Point37, is located
In addition, statistics were made on the time intervals at which the extreme daily temperatures of the most frequent months of freeze thawing at 153 sampling points occur, and the results are shown in fig. 2. From the statistical results in fig. 2, the extreme temperature time interval mainly includes 6h, 9h and 12h, and is most frequent by 78% at the time interval of 9h, among 153 sampling points.
4. Extreme temperature frequency distribution and positive and negative temperature determination in freeze thawing test
The representative freezing and thawing months of each region are divided into three time periods of the last ten days, the middle ten days and the last ten days, the daily maximum temperature and the daily minimum temperature of each time period are respectively extracted, and the frequency analysis is carried out by adopting Python programming, so that the daily maximum air temperature and the daily minimum air temperature frequency distribution map of different time periods of each region are obtained. Taking Point37 as an example, the main freezing and thawing cycle months in the area are 4 months, 10 months, 5 months and 3 months in sequence, extreme temperature frequency distribution diagrams of 4 months and 10 months in different time periods in the Point37 area are shown in fig. 3-4, wherein (a) is the highest temperature frequency distribution diagram of the last ten days of 4 months, (b) is the lowest temperature frequency distribution diagram of the last ten days of 4 months, (c) is the highest temperature frequency distribution diagram of the last ten days of 4 months, and (d) is the lowest temperature frequency distribution diagram of the last ten days of 4 months; (e) The distribution map is the highest temperature frequency distribution map of the day in the last ten days of 4 months, and the distribution map is the lowest temperature frequency distribution map of the day in the last ten days of 4 months; in fig. 4, (a) is a distribution diagram of the highest temperature frequency of the last ten days of 10 months, (b) is a distribution diagram of the lowest temperature frequency of the last ten days of 10 months, (c) is a distribution diagram of the highest temperature frequency of the last ten days of 10 months, and (d) is a distribution diagram of the lowest temperature frequency of the last ten days of 10 months; (e) The highest temperature frequency distribution map of the day in the last 10 months, and the lowest temperature frequency distribution map of the day in the last 10 months. In fig. 3 to 4, the broken line is a Kernel density curve (Kernel density), the solid line is a normal distribution curve (Normal distribution), the Kernel density curve is a curve fitted according to the frequency distribution, and the closer the Kernel density curve is to the normal distribution curve, the more data conforms to the normal distribution.
According to the frequency distribution of the extreme temperature, the main positive and negative temperature distribution during the freeze thawing action of the region can be obtained, and the design of an indoor freeze thawing cycle test system can be guided. According to the frequency distribution result of the polar temperature, the frequency distribution of the maximum daily temperature value and the minimum daily temperature value are approximately in normal distribution, so that an arithmetic average value or a weighted average value can be selected when the average value is calculated (as can be seen from the table 3, the results of the arithmetic average value and the weighted average value are close, and the subsequent experiment is based on the arithmetic average value); in order to ensure the design of an indoor freeze-thawing test system, the severe degree of test conditions is improved on the premise of ensuring universality, the arithmetic average value of the daily minimum value is selected as the minimum temperature representative value of the freeze-thawing cycle test for the daily minimum temperature, and the arithmetic average value of the daily maximum value is selected as the maximum temperature representative value of the freeze-thawing cycle test for the daily maximum temperature. Table 3 shows the mean and standard deviation (standard deviation is the standard deviation of arithmetic mean) of the extreme temperatures for each time period of a representative freeze-thaw month in Point37 region.
TABLE 3 highest temperature and lowest temperature mean and standard deviation for Point37 freeze-thaw cycle test
5. Freeze-thaw cycle regime determination
Taking Point37 as an example, the obtained extreme temperatures of the freezing and thawing months are drawn into a freezing and thawing extreme temperature change curve according to a time sequence, so that the annual freezing and thawing cycle temperature change condition of the region is obtained, and compared with a laboratory quick freezing method, as shown in fig. 5.
In fig. 5, each freeze-thaw cycle was continued for 10 days (11 days) without indoor acceleration, so for Point37, the test regime set up a number of annual freeze-thaw cycles of 120 days (30×4=120 days), one set of freeze-thaw temperatures every 10 days, for a total of 12 sets of 10 freeze-thaw cycles. The maximum and minimum temperatures for each freeze-thaw cycle are shown in table 3 and fig. 5.
The time of the Point37 day temperature change is 9 hours (0:00-9:00) according to the statistics of the time when the highest temperature and the lowest temperature occur in 3 days, and in order to improve the indoor freeze-thawing cycle test efficiency, namely to shorten the time required by a single freeze-thawing cycle, the times of each group of freeze-thawing cycles need to be reduced. Based on hydrostatic pressure theory (see the derivation process of the above formula 1 for details), test design is performed according to the cooling time 1-2 h specified by the quick freezing method in the specification, and the test design is substituted into the formula 1 to perform calculation, specifically as follows:
calculated N acc 1.11 to 2.22 times and 2 times.
To sum up, taking Point37 as an example, according to the setting of the freeze thawing temperature in fig. 5, the indoor cooling time is set to 1-2 h, and each group of freeze thawing cycle is repeated 2 times, so that the freeze thawing cycle effect suffered by the concrete in the Point37 area in one year can be simulated.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (9)
1. A freeze-thawing cycle test system design method considering regional air temperature characteristics is characterized by comprising the following steps:
(1) Counting historical temperature data of the test region for m years, and screening out representative freezing and thawing months according to the temperature data; the representative freezing and thawing months are the first n months with the largest times of freezing and thawing cycle of concrete; n is more than or equal to 1, m is more than or equal to 10;
(2) Dividing each representative freeze-thawing month into three time periods of the last ten days, the middle ten days and the last ten days, and counting the maximum value and the minimum value of the historical daily temperature of each time period; performing frequency analysis on the minimum value of the historical daily temperature in each time period, and calculating the average value of the minimum value of the daily temperature as the minimum temperature representative value of the freeze thawing cycle test; performing frequency analysis on the maximum value of the historical daily temperature in each time period, and calculating the average value of the maximum value of the daily temperature as the highest temperature representative value of the freeze thawing cycle test; taking the minimum temperature representative value and the maximum temperature representative value selected in each time period as a group of freeze-thawing cycle test temperature data to obtain 3n groups of freeze-thawing cycle test temperature data;
(3) Determining the number of freeze-thaw cycle tests performed in an indoor acceleration environment for each set of freeze-thaw cycle test temperature data according to equation 1:
in formula 1: n (N) s For every time period in the actual environmentNumber of freeze thawing cycles, N acc The number of freeze-thawing cycle tests is the number of times in an indoor accelerated environment; t is t s The extreme temperature change time of each freeze thawing cycle in the actual environment is expressed in units of h and t acc The cooling time of each freeze thawing cycle in the indoor environment is expressed in h;
(4) And (3) according to the time sequence of the freeze-thawing cycle test temperature data, carrying out the freeze-thawing cycle test of the concrete according to the times of carrying out the freeze-thawing cycle test in the indoor accelerating environment under each group of freeze-thawing cycle temperature data calculated in the step (3).
2. The method for designing a freeze-thawing cycle test system taking into consideration regional air temperature characteristics according to claim 1, wherein m is 10-20.
3. The method for designing a freeze-thaw cycle test system considering regional air temperature characteristics according to claim 1 or 2, wherein the method for screening representative freeze-thaw months comprises: counting the maximum value and the minimum value of the historical daily temperature in m years, determining whether the concrete has freeze thawing cycles in the same day according to the maximum value and the minimum value of the daily temperature, calculating the average freeze thawing cycle times of each month, and selecting the first n months with the maximum average freeze thawing cycle times as representative freeze thawing months; the criteria for determining the occurrence of a freeze-thaw cycle are: the highest daily temperature is more than 0 ℃ and the lowest daily temperature is less than-3 ℃.
4. The method for designing a freeze-thaw cycle test system considering regional air temperature characteristics according to claim 1, wherein the method for determining the number of representative freeze-thaw months comprises: according to the historical temperature data of the test area for m years, the annual average freeze thawing cycle times of the test area are counted and recorded as N year The number of representative freeze-thaw months, on a 30 day per month basis, was calculated by formula 2:
n＝N year 30 formula 2;
in the formula 2, n is an integer.
5. The method for designing a freeze-thawing cycle test system taking regional air temperature characteristics into consideration according to claim 1, wherein when the minimum value of the historical daily temperature in each time period is subjected to frequency analysis, if the result shows that the frequency distribution of the daily temperature minimum value approximately accords with normal distribution, the average value of the daily temperature minimum value is an arithmetic average value or a weighted average value, and if the result shows that the frequency distribution of the daily temperature minimum value does not accord with normal distribution, the average value of the daily temperature minimum value is a weighted average value;
when the frequency analysis is carried out on the maximum value of the historical daily temperature in each time period, if the result shows that the frequency distribution of the maximum value of the daily temperature approximately accords with the normal distribution, the average value of the maximum value of the daily temperature is an arithmetic average value or a weighted average value, and if the result shows that the frequency distribution of the maximum value of the daily temperature does not accord with the normal distribution, the average value of the maximum value of the daily temperature is a weighted average value.
6. The method for designing a freeze-thaw cycle test system considering regional air temperature characteristics according to claim 1, wherein in the formula 1, t s The difference between the time of occurrence of the highest day temperature and the lowest day temperature of the freeze thawing cycle in the actual environment.
7. The method for designing a freeze-thaw cycle test system considering regional air temperature characteristics according to claim 1 or 6, wherein in the formula 1, t s The acquisition method of (1) comprises the following steps: counting the occurrence time of the daily highest air temperature in the historical temperature with the average freeze thawing cycle time of the maximum month in the test area, taking the occurrence time with the maximum occurrence time as the occurrence time of the daily highest air temperature of the freeze thawing cycle, and marking as t High height The method comprises the steps of carrying out a first treatment on the surface of the Counting the occurrence time of the lowest daily air temperature in the historical temperature of the test area, taking the time with the highest occurrence times as the occurrence time of the lowest daily air temperature of freeze thawing circulation, and marking as t Low and low The method comprises the steps of carrying out a first treatment on the surface of the Calculating t High height To t Low and low Temperature drop time of t Low and low To t High height Taking the smaller value of the temperature drop time and the temperature rise time as t s Is a value of (a).
8. The method for designing a freeze-thaw cycle test system considering regional air temperature characteristics according to claim 1, wherein in the formula 1, N s The value of (2) is 10, t acc The value of (2) is 1-2 h.
9. The method for designing a freeze-thaw cycle test system considering regional air temperature characteristics according to claim 1, wherein the test region is a plateau region.
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| CN108709980A (en) * | 2018-07-03 | 2018-10-26 | 三峡大学 | A kind of determination method of fast freeze-thaw cycle and natural Frozen-thawed cycled relationship in concrete room |
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