WO2022227385A1 - Measurement method for water vapor diffusion coefficient of semi-rigid base - Google Patents

Abstract

A measurement method for a water vapor diffusion coefficient of a semi-rigid base, which method belongs to the technical field of road engineering. The measurement method comprises the following steps: S1, acquiring water vapor penetration amounts of semi-rigid base samples with different thicknesses and different temperatures; S2, according to relationships of the water vapor penetration amounts of the samples changing with time in a first experimental group and a second experimental group, respectively obtaining values of change slopes dWH2O/dt of the water vapor penetration amounts of the samples changing with time; S3, obtaining water vapor diffusion coefficients of the plurality of semi-rigid base samples according to the values of the change slopes dWH2O/dt in combination with relational expression (I); S4, according to relationships between the thicknesses and the water vapor diffusion coefficients D1 of the semi-rigid base samples in the first experimental group, obtaining a relational expression D1 = 0.2898·ln(x) - 0.2365; and S5, according to the thickness or temperature of a semi-rigid base sample to be tested being in combination with the corresponding relational expression in S4, obtaining a water vapor diffusion coefficient of the sample to be tested. By means of the measurement method, the water vapor diffusion coefficient of the sample to be tested can be directly obtained.

Description

A method for detecting the water vapor diffusion coefficient of a semi-rigid base technical field

The invention relates to the technical field of road engineering, in particular to a method for detecting the water vapor diffusion coefficient of a semi-rigid base.

Background technique

Asphalt pavement is directly exposed to the natural environment during the service period, and is subjected to the combined action of external factors such as temperature and humidity. Water damage is one of the most important diseases of asphalt pavement in the early stage. Pumping, rut grooves and other diseases seriously affect the service performance of asphalt pavement and shorten the service life of asphalt pavement. Existing research shows that the diffusion coefficient of water vapor in asphalt pavement is much larger than that of liquid water, that is, the water vapor moves faster in the asphalt pavement, and carries more water molecules into the asphalt pavement at the same time. It is a more important factor for the formation of water damage to asphalt pavement.

In the field of road engineering, the current research on water vapor diffusion mainly focuses on asphalt surface layer materials. Some experts and scholars have put forward theoretical models suitable for describing the movement of water vapor in asphalt mixtures through theoretical analysis and experimental verification. At the same time, some influencing factors of water vapor diffusion in asphalt mixture are analyzed. However, the existing researches on the movement of water and gas focus on the asphalt surface layer, and there are few studies on the movement laws and influencing factors of water and gas inside the base. A large number of studies have shown that due to the pavement covering effect, the relative humidity of the soil base is always greater than 97%, so the water vapor will move upward from the soil base through the base layer, providing a source of moisture for the asphalt surface layer. As the main form of asphalt pavement base in my country, the semi-rigid base will produce micro-cracks due to dry shrinkage and temperature shrinkage during the service period. These micro-cracks provide channels for the movement of water vapor in the semi-rigid base, which aggravates the water vapor in the semi-rigid base. exercise intensity. Based on the above reasons, the accurate measurement of the water vapor diffusion coefficient inside the semi-rigid base can be used to analyze the influence mechanism of micro-cracks in the semi-rigid base on the water and vapor movement, and to better quantify the effect of water vapor diffusion on asphalt pavement water from the overall perspective of the asphalt pavement. The degree of influence of the damage. At present, if you want to obtain the water vapor diffusion coefficient of the semi-rigid base at different temperatures or different thicknesses, it is necessary to obtain the water vapor diffusion coefficient at a certain temperature or a certain thickness after the corresponding number of experiments and the combination of the relationship formula. It takes a long time and the experimental process is complicated.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned technical deficiencies, and to provide a solution that solves the technical problems in the prior art that the process of obtaining the water vapor diffusion coefficient of the semi-rigid base layer at different temperatures or different thicknesses is complicated and time-consuming.

In order to achieve the above technical purpose, the technical scheme of the present invention provides a method for detecting the water vapor diffusion coefficient of a semi-rigid base layer.

A method for detecting the water vapor diffusion coefficient of a semi-rigid base layer, characterized in that it comprises the following steps:

S1. Conduct a water vapor diffusion test on a plurality of semi-rigid base samples with different thicknesses at the same temperature, marked as the first experimental group; perform a water vapor diffusion test on the semi-rigid base samples with the same thickness at different temperatures, marked as the first experimental group Two experimental groups; and detect and record the mass change every 1-2 days in the test, the reduced mass is the mass of water vapor lost through the semi-rigid base sample, that is, the water vapor penetration;

S2, according to the relationship of the water vapor penetration of the samples in the first experimental group and the second experimental group with time, obtain the value of the change slope dW _H2O/ dt of the water vapor penetration of the sample over time;

S3. Combine the relational expression according to the value of the change slope dW _H2O/ dt

obtaining the water vapor diffusion coefficients of a plurality of the semi-rigid base layer samples;

Among them, D _eff is the water vapor diffusion coefficient, L is the thickness of the sample, the unit is cm; C ₁ , C ₂ are the water vapor concentrations on both sides of the sample, the unit %; P ₁ , P ₂ are the water vapor pressures on both sides of the sample, unit %; R is the universal gas constant, and the value is 8.314J·mol ^-1 ; T is the Kelvin temperature, the unit is K; M _H2O is the relative molecular mass of water, and the value is 18.015g·mol ^-1 ;

S4. According to the relationship between the thickness of the semi-rigid base layer sample of the first experimental group and the water vapor diffusion coefficient D ₁ , the relational formula D ₁ =0.2898·ln(x)-0.2365 is obtained, where x represents the thickness of the semi-rigid base layer, in mm, according to The relationship between the temperature of the semi-rigid base sample of the second experimental group and the water vapor diffusion coefficient D ₂ is obtained by the relational formula D ₂ =0.163·e ^0.0504T , where T represents the temperature, in °C.

S5 , according to the thickness or temperature of the sample to be measured on the semi-rigid base layer combined with the corresponding relational expression in step S4 to obtain the water vapor diffusion coefficient of the sample to be measured.

Further, in step S1, performing the water vapor diffusion test includes:

Water is poured into the container, the top of the container is open, the semi-rigid base layer sample is fixed at the top opening of the container, and the gap between the semi-rigid base layer sample and the container is sealed to prevent water from diffusing and volatilizing from the gap; the There is a space between the bottom of the semi-rigid base sample and the water to prevent the water from contacting the bottom of the semi-rigid base sample.

Further, in step S1, the plurality of semi-rigid base layer samples with different thicknesses are semi-rigid base layer samples with different thicknesses between 10-50 mm.

Further, in step S1, the thicknesses of the plurality of semi-rigid base layer samples with different thicknesses are respectively 10 mm, 20 mm, 30 mm and 40 mm.

Further, in step S1, the water vapor diffusion test is performed at different temperatures of 10-30°C.

Further, the different temperatures are 10°C, 20°C and 30°C, respectively.

The present invention considers that both the water vapor diffusion coefficient and the water vapor diffusion flux are related to the change slope dW _H2O/ dt, and then obtains the value of the change slope dW _H2O/ dt and combines the relationship formula

Obtain the water vapor diffusion flux of a plurality of the semi-rigid base layer samples, and then obtain the relationship between the thickness of the sample and its water vapor diffusion flux, as well as the relationship between the temperature of the sample and its water vapor diffusion flux. The relational formula calculates the water vapor diffusion flux of the sample to be tested at different temperatures or different thicknesses, as follows:

Further, in step S3, it also includes combining the relationship formula according to the value of the change slope dW _H2O/ dt

obtaining a plurality of water vapor diffusion fluxes of the semi-rigid base layer samples;

Among them, J is the water vapor diffusion flux, A is the diffusion area, and the unit is m ² .

Further, in step S4 , it also includes obtaining a relational formula J ₁ =1.553·e ^−0.022x according to the relationship between the thickness of the semi-rigid base layer sample of the first experimental group and the water vapor diffusion flux J ₁ .

Further, in step S4, it also includes obtaining a corresponding relational formula J ₂ =0.4167·e ^0.0505T according to the relation between the temperature of the semi-rigid base layer sample in the second experimental group and the water vapor diffusion flux J ₂ .

Further, the water vapor diffusion flux of the sample to be measured is obtained according to the thickness or temperature of the sample to be measured on the semi-rigid base layer in combination with the corresponding relational expression in step S4.

Compared with the prior art, the beneficial effects of the present invention include: firstly, obtaining the water vapor permeability of each semi-rigid base layer samples with different thicknesses in the first experimental group and each semi-rigid base layer in the second experimental group at different temperatures. The water vapor penetration of the sample, according to the water vapor penetration, the value of the change slope dW _H2O/ dt of the water vapor penetration with time in the first experimental group and the second experimental group was obtained, and then according to the water vapor diffusion coefficient relationship. The water vapor diffusion coefficient of each semi-rigid base layer sample in the first experimental group and the second experimental group, and further, establish a correlation according to the relationship between the water vapor diffusion coefficient and the semi-rigid base layer samples of different thicknesses or the semi-rigid base layer samples of different temperatures Equations D ₁ =0.2898·ln(x)-0.2365 and D ₂ =0.163·e ^0.0504T , substituting the sample to be tested with the same temperature and different thickness into the relational formula D ₁ =0.2898·ln(x)-0.2365 can be obtained The water vapor diffusion coefficient of the sample to be tested can be obtained by substituting the sample to be tested with the same temperature and thickness of the sample into the relationship D ₂ =0.163·e ^0.0504T to obtain the water vapor diffusion coefficient of the sample to be tested. Calculation, the water vapor diffusion coefficient of the sample to be tested can be directly obtained.

Description of drawings

FIG. 1 is a schematic diagram of the preparation process of the semi-rigid base layer sample in Example 1 of the present invention.

FIG. 2 is a schematic diagram of a process of assembling a test device in Example 1 of the present invention.

FIG. 3 is a graph showing the change of the water vapor transmission amount with time for samples of semi-rigid base layers with different thicknesses in Example 1 of the present invention.

Figure 4a is a graph showing the relationship between the thickness of the semi-rigid base layer sample and the diffusion flux in Example 1 of the present invention.

Figure 4b is a graph showing the relationship between the thickness and the diffusion coefficient of the semi-rigid base layer sample in Example 1 of the present invention.

FIG. 5 is a graph showing the change of the water vapor transmission amount with time of the semi-rigid base layer samples at different temperatures in Example 1 of the present invention.

Fig. 6a is a graph showing the relationship between the temperature and the diffusion flux of the semi-rigid base layer sample of Example 1 of the present invention.

Fig. 6b is a graph showing the relationship between the temperature and the diffusion coefficient of the semi-rigid base layer sample of Example 1 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The specific embodiment provides a method for detecting the water vapor diffusion coefficient of a semi-rigid base layer, comprising the following steps:

S1. Conduct a water vapor diffusion test on a plurality of semi-rigid base samples with different thicknesses and thicknesses between 10-50 mm at the same temperature, marked as the first experimental group; Carry out the water vapor diffusion test at 30°C, marked as the second experimental group; and detect and record the mass change every 1-2 days in the test, the reduced mass is the mass of water vapor lost through the semi-rigid base sample, is the water vapor penetration;

S2, according to the relationship of the water vapor penetration of the samples in the first experimental group and the second experimental group with time, obtain the value of the change slope dW _H2O/ dt of the water vapor penetration of the sample over time;

S3. Combine the relational expression according to the value of the change slope dW _H2O/ dt

obtaining the water vapor diffusion coefficients of a plurality of the semi-rigid base layer samples;

Among them, D _eff is the water vapor diffusion coefficient, L is the thickness of the sample, the unit is cm; C ₁ , C ₂ are the water vapor concentrations on both sides of the sample, the unit %; P ₁ , P ₂ are the water vapor pressures on both sides of the sample, unit %; R is the universal gas constant, and the value is 8.314J·mol ^-1 ; T is the Kelvin temperature, the unit is K; M _H2O is the relative molecular mass of water, and the value is 18.015g·mol ^-1 ;

According to the value of the change slope dW _H2O/ dt combine the relationship

obtaining a plurality of water vapor diffusion fluxes of the semi-rigid base layer samples;

Among them, J is the water vapor diffusion flux, A is the diffusion area, the unit is m ² ;

S4. According to the relationship between the thickness of the semi-rigid base sample of the first experimental group and the water vapor diffusion coefficient D ₁ , the relational formula D ₁ =0.2898·ln(x)-0.2365 is obtained, where x represents the thickness of the semi-rigid base sample, in mm, According to the relationship between the temperature of the semi-rigid base layer sample of the second experimental group and the water vapor diffusion coefficient D ₂ , the relational formula D ₂ =0.163·e ^{0.0504T is obtained} , where T represents the temperature, in °C;

According to the relationship between the thickness of the semi-rigid base sample in the first experimental group and the water vapor diffusion flux J ₁ , the relational formula J ₁ =1.553·e ^{-0.022x is obtained} ; The relationship of the gas diffusion flux J ₂ is obtained by the corresponding relationship, J ₂ =0.4167·e ^0.0505T ;

S5 , according to the thickness or temperature of the sample to be measured on the semi-rigid base layer combined with the corresponding relational expressions in step S4 to obtain the water vapor diffusion coefficient and the water vapor diffusion flux of the sample to be measured.

Further, performing the water vapor diffusion test in this specific embodiment includes:

Water is poured into the container, the top of the container is open, the semi-rigid base layer sample is fixed at the top opening of the container, and the gap between the semi-rigid base layer sample and the container is sealed to prevent water from diffusing and volatilizing from the gap; the There is a space between the bottom of the semi-rigid base sample and the water to prevent the water from contacting the bottom of the semi-rigid base sample.

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

The method proposed in this example first analyzes the basic principles and theories of water vapor diffusion, and obtains the actual service semi-rigid base core samples from the core of the Hubei section of the Beijing-Hong Kong-Macao Expressway, and designs the test device and related test plans. The water vapor diffusion coefficient in the semi-rigid base layer was measured and studied under the conditions of temperature and temperature, and the general law of the influence of material thickness and temperature conditions on the water vapor diffusion in the semi-rigid base layer was obtained. It provides a theoretical basis for evaluating the water damage of asphalt pavement.

In the existing research, it is found that the penetrating water vapor diffusion coefficient is more than 1000 times that of the accumulating water vapor diffusion coefficient in the asphalt pavement, and the penetrating water vapor diffusion motion occupies the leading role of the water vapor motion. For the semi-rigid base material that has been in service for a long time, in this example, the penetrating water vapor diffusion motion of the semi-rigid base is studied. In the actual pavement structure, the semi-rigid base is located between the asphalt surface layer and the soil base layer. .

Research on the Theory of Water Vapour Diffusion

Since the semi-rigid base material is porous, Fick's law can be used to study the water-vapor movement in the semi-rigid base. According to Fick's first theorem, in a one-dimensional state, the diffusion flux per unit time through a unit cross-sectional area perpendicular to the diffusion direction is proportional to the concentration gradient at the cross-section. At this time, the diffusion flux is independent of time. Its theoretical The model can be expressed as:

Where: J is the water vapor diffusion flux, kg/m ² /s; D is the effective diffusion coefficient, kg/m ² ; dC/dy is the concentration gradient.

At the same time, from the definition of water vapor diffusion flux, it can be known that:

In the formula: A is the diffusion area, m ² ; t is the diffusion time, s; dW _H2O /dt is the water vapor penetration rate, that is, the mass of water vapor permeating the asphalt mixture per unit time, kg.

Simultaneous relations (1) and (2) can obtain the relational expression of the water vapor diffusion coefficient as follows:

In the formula: D _eff represents the water vapor diffusion coefficient, L represents the thickness of the sample, unit cm; C ₁ , C ₂ represent the water vapor concentration on both sides of the sample, unit %; P ₁ , P ₂ represent the water vapor partial pressure on both sides of the sample , in %; R is the universal gas constant, taking the value of 8.314J·mol ^-1 ; T is the Kelvin temperature, in K; M _H2O is the relative molecular mass of water, taking the value of 18.015g·mol ^-1 .

In relation (3), the partial pressure of water vapor can be expressed as:

P=H _r P _sat (4)

In the formula: Hr is the relative humidity, %; Psat is the saturated vapor pressure of water at a certain temperature, Pa.

It can be seen from the relational formula (4) that when the water vapor concentration on both sides of the sample remains stable, after the water vapor transmission rate of a certain material is measured, the water vapor transmission rate of the sample under a certain temperature condition can be calculated according to the relational formula (4). Water vapor diffusion coefficient.

In addition, since there is a relative humidity difference ΔRH between the upper and lower sides of the semi-rigid base material in the actual service environment, and there is also a water vapor concentration difference, the relationship between the relative humidity difference ΔRH and the water vapor concentration difference ΔC is established by transforming the ideal gas state equation as follows: Relational formula (5) shows:

In the formula: P ₀ is the saturated vapor pressure of water at 20℃, 2338.8Pa; P ₁ is the partial pressure of water vapor on the lower side of the sample, Pa; P ₂ is the partial pressure of water vapor on the upper side of the sample, Pa;

The partial pressure of water vapor can be expressed as:

Simultaneous relations (5) and (6) can obtain the expression of relative humidity ΔRH related to the difference of water vapor concentration on both sides as:

According to the existing research, the water vapor diffusion flux J has a linear relationship with the relative humidity difference ΔRH, and then the theoretical derivation shows that the water vapor diffusion flux and the water vapor concentration difference also have a linear relationship:

When the material thickness can be quantified, relation (1) can be transformed into relation (9):

Simultaneous relations (7) and (9) can obtain the expression of water vapor diffusion coefficient as shown in relation (10):

where k is the slope of the water vapor diffusion flux versus the relative humidity difference.

From relation (10), it can be seen that for the penetration process of water vapor diffusion, the water vapor diffusion coefficient of the semi-rigid base layer has nothing to do with the relative humidity difference ΔRH, that is, it should be constant under each relative humidity difference.

Therefore, we found that the material thickness and temperature are the main factors affecting the water vapor diffusion in the semi-rigid base layer. The material thickness and temperature do not need to consider the influence of the relative humidity difference on the water vapor diffusion in the semi-rigid base layer.

Design of Water Vapor Diffusion Test Device

The preparation process of the semi-rigid base test sample is shown in Figure 1. The test material is from the field core sample of the Hubei section of the Beijing-Hong Kong-Macao Expressway. The field core sample with a diameter of 150mm is obtained by drilling the core. For the 100mm semi-rigid base layer core sample, the field core sample is cut in layers with a cutting saw, and semi-rigid base layer test samples of different thicknesses can be obtained.

The preparation process of the water vapor diffusion test device is shown in Figure 2. A polypropylene plastic container is used as the water container, which does not absorb water and has good sealing performance. The volume is 250ml, the height is 50mm, and the opening diameter is 85mm. First, pour a sufficient amount of distilled water into the plastic container, and control the quality of distilled water in each plastic container to be consistent; apply high-vacuum silicone grease to the edge of the plastic container, and use a ring-shaped silicone sheet of sufficient size to adhere to the edge of the container to ensure The sealing of the container; secondly, the semi-rigid base sample is pasted at the opening of the plastic container; finally, the joints of the plastic container are smeared and sealed with molten wax to further ensure the sealing of the container, and try to ensure that the water vapor in the plastic container is only Can be dissipated through semi-rigid base samples.

At the same time, in order to ensure the sealing performance of the test device and ensure that the water vapor can only penetrate from the semi-rigid base sample to the external environment during the weighing process of the sample, a blank control group was also set up in this study, and the semi-rigid base sample was replaced with a sealed one. The protective cover is also sealed with wax to ensure the accuracy and scientificity of the test results.

When the test starts, weigh the initial mass of each group of test devices at this time, and weigh the test devices every day after 24 hours, and calculate the quality change of the test device every day, then the change quality of the test device at this time is the test. The mass of moisture lost in the device through the semi-rigid substrate sample.

Design of Water Vapor Diffusion Test Scheme

In order to explore the influence of the thickness and temperature conditions of the semi-rigid base layer on the water vapor diffusion of the semi-rigid base layer, the experimental plan is mainly designed for these two influencing factors. To ensure the scientificity and objectivity of the test results, three parallel test samples were set up for each group of experiments as the control group.

Test scheme of water vapor diffusion with different semi-rigid base thickness

Since the thickness of the actual semi-rigid base layer can reach about 30mm, samples of semi-rigid base layer similar to the actual thickness are used for the test, which are about 10mm, 20mm, 30mm and 40mm respectively. In order to adapt to the actual environment, the relative humidity difference ΔRH is controlled to be 50%-100%, and the temperature is 20°C. The water vapor diffusion test scheme of different material (semi-rigid base) thickness is shown in Table 1 below.

Table 1 Water vapor diffusion test scheme with different material thicknesses

Water vapor diffusion test scheme under different temperature conditions

During the actual service period, the maximum temperature of the asphalt pavement structure can reach 50 °C, but due to the low melting point of the sealing material wax, when the temperature reaches 40 °C, the wax will soften and deform, which will cause damage to the sealing energy of the test device. Therefore, the selection range of the test temperature is 10°C to 30°C, and a total of 3 temperatures of 10°C, 20°C, and 30°C are selected for the test, and the relative humidity difference ΔRH is set to 50%-100%. The water vapor diffusion test scheme under different temperature conditions is shown in Table 2 below.

Table 2 Water vapor diffusion test scheme under different temperature conditions

Analysis of Influence of Sample Thickness on Water Vapor Diffusion

Taking 50 days as a weighing cycle, calculate the average mass change of each group of samples and the average value of the mass change of each group of samples, and draw the relationship between the water vapor penetration of the base material with time under each thickness condition, As shown in Figure 3. After obtaining the relationship of the water vapor penetration with time of the semi-rigid base material of each material thickness, the diffusion flux J can be calculated according to the theoretical relationship (1), and the diffusion coefficient D _eff can be calculated according to the relationship (3).

According to the test results in Fig. 3, the change slope of the water vapor permeability of each group of base samples with time, that is, the value of dW _H2O /dt, the change slopes of the H1 group, H2 group, H3 group and H4 group are 0.2220× 10 ^-3 g/d, 0.1938×10 ^-3 g/d, 0.1416×10 ^-3 g/d and 0.1061×10 ^-3 g/d, in Table 3 below, the unit of water vapor transmission rate is converted into up to ×10 ^-3 g/h. Based on this, the diffusion flux and diffusion coefficient of each group of base materials can be calculated as shown in Table 3.

Table 3 Changes in quality of base samples with different thicknesses over time

According to the calculation results in Table 3, the relationship between the thickness of different semi-rigid base materials and the diffusion flux J and diffusion coefficient D _eff is plotted as shown in Figures 4a and 4b. It can be seen that there is a certain relationship between the diffusion coefficient J ₁ and the diffusion flux D ₁ and the thickness of the base material, and the relationship is shown in the relationship (11) and (12) respectively.

J ₁ =1.553·e ^-0.022x (11)

D ₁ =0.2898·ln(x)-0.2365 (12)

In the formula: x is the thickness of the base core sample, mm.

The applicability of relational formula (11) and relational formula (12) is verified. The semi-rigid base layer service core samples of Beijing-Zhuhai Expressway were used. After the core was cut, a set of parallel samples was obtained. The average thickness of the samples was 15.23mm. The diffusion flux J ₁ and diffusion coefficient D ₁ obtained by the relationship were 1.1109g/ m ² ·h and 0.553 mm ² /s, the actual measured diffusion flux J and diffusion coefficient D _eff are 1.0628 g/m ² ·h and 0.511 mm ² /s, the error values are 0.045 and 0.082, respectively, the goodness of fit Good, can be used to calculate diffusion flux J ₁ and diffusion coefficient D ₁ at different thicknesses.

According to the above relationship, it can be seen that the diffusion flux decreases with the increase of material thickness, and there is an exponential function relationship between the two, and the goodness of fit R ² is 0.9956; the diffusion coefficient increases with the increase of material thickness, and the two exist. Logarithmic function relationship, goodness of fit R ² was 0.9653. Based on the analysis of the above test results, the test results show that the diffusion flux decreases with the increase of the material thickness, which is caused by the increase of the thickness of the semi-rigid material, which reduces the amount of water vapor passing through in unit time. However, the water vapor moves inside the micro-crack channel of the semi-rigid base, and the diffusion coefficient increases with the increase of the material thickness, but the increase gradually slows down due to the limitation of the diffusion flux.

Analysis of Influence of Ambient Temperature on Water Vapour Diffusion

Calculate the average mass change of each sample and the average value of the mass change of each sample, and draw the relationship between the water vapor penetration of the base material over time under each temperature condition, as shown in Figure 5. After obtaining the relationship of the water vapor penetration of each sample with time, the diffusion flux J and the diffusion coefficient D _eff can be calculated according to the theoretical relationship (1) and (3).

According to the test results in Fig. 5, the change ^slopes of the water vapor permeability ^of the base samples in each group with time can be obtained. ³ g/d and 0.3515×10 ⁻³ g/d, the unit of water vapor transmission rate in Table 4 below was converted to ×10 ⁻³ g/h. Based on this, the diffusion flux J and diffusion coefficient D _eff of each group of base materials can be calculated, as shown in Table 4.

Table 4 Changes in quality of base samples at different temperatures with time

According to the calculation results in Table 4, the relationship between different temperatures and diffusion flux and diffusion coefficient are plotted as shown in Figures 6a and 6b, respectively. There is a certain relationship between the diffusion coefficient J ₂ and the diffusion flux D ₂ and the temperature of the base material, and their relationships are shown in the following equations (13) and (14), respectively.

J=0.4167·e ^0.0505T (13)

D=0.163·e ^0.0504T (14)

In the formula: T is the temperature, °C.

The applicability of relational formula (13) and relational formula (14) is verified. The semi-rigid base service core samples of Beijing-Zhuhai Expressway were used. After the core was cut, a set of parallel samples were obtained. The average thickness of the samples was 12.13m and the ambient temperature was 25°C. _The diffusion fluxes J and The diffusion coefficient D ₂ is 1.473g/m ² ·h and 0.575mm ² /s, the actual measured diffusion flux J and diffusion coefficient D _eff are 1.358g/m ² ·h and 0.534mm ² /s, the error value They are 0.085 and 0.077, respectively, and the fitting degree is good, which can be used to calculate the water vapor diffusion flux J ₂ and the water vapor diffusion coefficient D ₂ at different temperatures.

According to the above relationship, it can be seen that the water vapor diffusion flux increases with the increase of temperature, and there is a logarithmic function relationship between the two, and the goodness of fit R ² is 0.9973; the water vapor diffusion coefficient increases with the increase of temperature, There is a logarithmic function relationship between the two, and the goodness of fit R ² is 0.9978.

Based on the analysis of the above test results, the test results show that the water vapor diffusion flux increases with the increase of temperature, which is because the increase of temperature provides energy for water molecules and improves the activity of water vapor molecules. At the same time, since the activity of water vapor molecules intensifies with the increase of temperature, the water vapor diffusion coefficient also increases, and its variation trend also increases with the increase of temperature. Through this conclusion, the water vapor diffusion flux and water vapor diffusion coefficient of the semi-rigid base at actual temperature can be obtained respectively. The influence results of the two influencing factors of material thickness and temperature conditions on the water vapor diffusion carried out in the present invention can provide design parameters for the numerical simulation of the asphalt pavement humidity field, and at the same time provide a theoretical basis for quantifying the influence of water vapor on the water damage of the asphalt pavement , has certain theoretical and engineering practical value.

In this method, by analyzing the principle of water vapor diffusion and related theories, it is found that the penetrating water vapor diffusion movement is in the dominant position. It is of great significance to analyze the influence mechanism of micro-cracks in semi-rigid base course on water vapor movement, and to better quantify the influence of water vapor diffusion on asphalt pavement water damage from the overall perspective of asphalt pavement.

details as follows:

1) It can be used to measure the water vapor diffusion coefficient of semi-rigid base

The method is based on the theoretical relationship to deduce and analyze the relationship of the water vapor diffusion coefficient. The test device and scheme are designed. The daily mass loss of the test device in the health environment box is weighed in a period of 50 days, and the data is sorted and calculated to obtain different conditions. The water vapor diffusion coefficient under the semi-rigid base.

2) It can be used to analyze the water vapor diffusion movement of the Beijing-Zhuhai high-speed semi-rigid base

This method is to study the water vapor diffusion motion of the Beijing-Zhuhai high-speed semi-rigid base. The water vapor diffusion coefficient of the sample under different thicknesses and different ambient temperatures is measured by the test device, so as to establish the thickness of the sample, the ambient temperature and the water vapor diffusion coefficient. The relationship model is used to evaluate the water vapor diffusion movement law of Beijing-Zhuhai Expressway, and provides a theoretical basis for better evaluating the water damage of Beijing-Zhuhai Expressway asphalt pavement under actual service conditions from the perspective of water vapor diffusion.

3) Provide design parameters for numerical simulation of asphalt pavement humidity field

The results of the two influencing factors of material thickness and temperature conditions on the water vapor diffusion can provide design parameters for the numerical simulation of the asphalt pavement humidity field, and provide a theoretical basis for quantifying the impact of water vapor on the water damage of the asphalt pavement. Certain theoretical and engineering practical value.

The specific embodiments of the present invention described above do not limit the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (10)

1. A method for detecting the water vapor diffusion coefficient of a semi-rigid base layer, characterized in that it comprises the following steps:

   S1. Conduct a water vapor diffusion test on a plurality of semi-rigid base samples with different thicknesses at the same temperature, marked as the first experimental group; perform a water vapor diffusion test on the semi-rigid base samples with the same thickness at different temperatures, marked as the first experimental group Two experimental groups; and detect and record the mass change every 1-2 days in the test, the reduced mass is the mass of water vapor lost through the semi-rigid base sample, that is, the water vapor penetration;

   S2, according to the relationship of the water vapor penetration of the samples in the first experimental group and the second experimental group with time, obtain the value of the change slope dW _H2O/ dt of the water vapor penetration of the sample over time;

   S3. Combine the relational expression according to the value of the change slope dW _H2O/ dt

   

   obtaining the water vapor diffusion coefficients of a plurality of the semi-rigid base layer samples;

   Among them, D _eff is the water vapor diffusion coefficient, L is the thickness of the sample, the unit is cm; C ₁ , C ₂ are the water vapor concentrations on both sides of the sample, the unit %; P ₁ , P ₂ are the water vapor pressures on both sides of the sample, unit %; R is the universal gas constant, and the value is 8.314J·mol ^-1 ; T is the Kelvin temperature, the unit is K; M _H2O is the relative molecular mass of water, and the value is 18.015g·mol ^-1 ;

   S4. According to the relationship between the thickness of the semi-rigid base layer sample of the first experimental group and the water vapor diffusion coefficient D ₁ , the relational formula D ₁ =0.2898·ln(x)-0.2365 is obtained, where x represents the thickness of the semi-rigid base layer, in mm, according to The relationship between the temperature of the semi-rigid base sample of the second experimental group and the water vapor diffusion coefficient D ₂ is obtained by the relational formula D ₂ =0.163·e ^0.0504T , where T represents the temperature, in °C;

   S5 , according to the thickness or temperature of the sample to be measured on the semi-rigid base layer combined with the corresponding relational expression in step S4 to obtain the water vapor diffusion coefficient of the sample to be measured.
2. The detection method according to claim 1, wherein in step S1, performing the water vapor diffusion test comprises:

   Water is poured into the container, the top of the container is open, the semi-rigid base layer sample is fixed at the top opening of the container, and the gap between the semi-rigid base layer sample and the container is sealed to prevent water from diffusing and volatilizing from the gap; the There is a space between the bottom of the semi-rigid base sample and the water to prevent the water from contacting the bottom of the semi-rigid base sample.
3. The detection method according to claim 1, characterized in that, in step S1, the plurality of semi-rigid base layer samples with different thicknesses are semi-rigid base layer samples with different thicknesses between 10-50 mm.
4. The detection method according to claim 3, wherein in step S1, the thicknesses of the plurality of semi-rigid base layer samples with different thicknesses are respectively 10 mm, 20 mm, 30 mm and 40 mm.
5. The detection method according to claim 1, characterized in that, in step S1, the water vapor diffusion test is performed at different temperatures of 10-30°C.
6. The detection method according to claim 5, wherein the different temperatures are 10°C, 20°C and 30°C, respectively.
7. The detection method according to claim 1, characterized in that, in step S3, it further comprises combining the relational expression according to the value of the change slope dW _H2O/ dt

   

   obtaining a plurality of water vapor diffusion fluxes of the semi-rigid base layer samples;

   Among them, J is the water vapor diffusion flux, A is the diffusion area, and the unit is m ² .
8. The detection method according to claim 7, characterized in that, in step S4, further comprising obtaining a relational formula J ₁ =1.553 according to the relationship between the thickness of the semi-rigid base layer sample of the first experimental group and the water vapor diffusion flux J ₁ ·e ^-0.022x .
9. The detection method according to claim 8, characterized in that, in step S4, further comprising obtaining a corresponding relational formula J according to the relation between the temperature of the semi-rigid base layer sample in the second experimental group and the water vapor diffusion flux J _{2 2} = 0.4167·e ^0.0505T .
10. The detection method according to claim 9, wherein the water vapor diffusion flux of the sample to be measured is obtained according to the thickness or temperature of the sample to be measured on the semi-rigid base layer in combination with the corresponding relational expression in step S4.

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