CN109164005B - Method for Determining Condensed Water Proportion in Asphalt Mortar - Google Patents

Abstract

Method for determining the proportion of condensed water in asphalt mortar. It belongs to the field of road building material testing. There is currently no method for determining the proportion of condensed water in asphalt mortar. The invention measures the equilibrium adsorption amount of the asphalt mortar specimen under various humidity under dry conditions; calculates the equilibrium desorption amount of the specimen under each humidity; uses data analysis software to obtain the adsorption-desorption curve of the asphalt mortar specimen; and then calculates the water The thickness of the molecular layer is obtained, and the relationship between the thickness of the water molecular layer and the water content in the asphalt mortar under this humidity condition is obtained, and the curve diagram of the equilibrium water content and the thickness of the water molecular layer is drawn. Subtract the difference obtained, and the ratio of the total area to obtain the proportion of condensed water in the test piece. The invention realizes the division of the proportion of condensed water in the asphalt mortar, provides a method for studying the damage mechanism of the asphalt mixture under the action of gaseous water, and has reference significance for improving the durability of the asphalt pavement.

Description

Method for Determining Condensed Water Proportion in Asphalt Mortar

technical field

The invention belongs to the field of road building material detection methods, in particular to a method for determining the proportion of condensed water in asphalt mortar.

Background technique

Moisture is one of the important factors affecting the durability of asphalt pavement. Since the adsorption of water to the stone is greater than that of the asphalt binder, the water will enter the joint between the asphalt and the stone to peel off the two, resulting in cracks, loosening and pits. In addition, water will also penetrate into the asphalt. The inside of the binder reduces the viscosity of the asphalt. The combined action of these two aspects reduces the strength and durability of the asphalt pavement and shortens the service life of the asphalt pavement.

It is generally believed that liquid water is the only cause of water damage to asphalt pavement, but a large number of engineering practices show that water damage to asphalt pavement does not only occur in wet and rainy areas, but also in arid areas with little rainfall. For example, my country's Gansu Province, Inner Mongolia and Xinjiang Autonomous Region, Arizona, USA, etc. The reason for the damage of pavement water in these arid areas is that the groundwater diffuses upward in the form of gaseous water driven by the humidity gradient and accumulates inside the pores of the asphalt pavement due to the extremely low atmospheric moisture content. Therefore, the study of gaseous water damage to asphalt pavement is an important branch of asphalt pavement water damage, but this mechanism has not been paid attention to for a long time.

In addition, gaseous water has different degrees of condensation in the adsorption process. Since condensation is one of the key characteristics of gaseous water transport in porous media, it is particularly important to study the condensation of gaseous water in asphalt mortar; The proportion of condensed water is an evaluation index for the condensation characteristics of gaseous water, but there is no method to divide the proportion of condensed water in asphalt mortar. This patent will adopt the method of combining test and theoretical analysis to realize the division of the proportion of condensed water in asphalt mortar.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for determining the proportion of condensed water in asphalt mortar in order to solve the problem that the method for determining the proportion of condensed water in asphalt mortar is currently lacking.

A method for determining the proportion of condensed water in asphalt mortar is realized through the following technical solutions:

Step 1. Prepare a φ100mm×80mm cylindrical asphalt mortar specimen with a rotary compaction method, and then use a cutting machine to make a φ100mm×4±1mm sheet specimen, and the specimen diameter-height ratio is 10-40, which can realize the water vapor along the axis. one-dimensional diffusion in the direction;

Step 2: Carry out an adsorption test in the full humidity range of RH30%～RH90% under the condition of any temperature value determined in the range of 0～50℃:

计算各湿度下薄片试件的平衡吸附量；First, measure the mass w ₀ of the dried sheet specimen, then measure the mass when it reaches the adsorption equilibrium in an environment with a relative humidity of 30%, the relative humidity is increased by 10% in turn, and then the sheet specimen is measured every time the relative humidity is increased The mass w _∞ of the specimen when the humidity reaches the adsorption equilibrium, according to the formula

Calculate the equilibrium adsorption capacity of the thin specimens under each humidity;

Step 3: Carry out the desorption test in the full humidity range of RH90%~RH30% under the condition of determining any temperature value in the range of 0~50℃:

计算各湿度下薄片试件的平衡脱附量；First, place the sheet specimens in an environment with a relative humidity of RH95% for 12 hours, and measure the mass w' ₀ when the relative humidity reaches a stable state. mass, the two can be subtracted to obtain the desorption amount of the sheet specimen at a relative humidity of 90%, and then the humidity is reduced to 30% with a 10% decrease in turn, and the desorption of the sheet specimen when it reaches equilibrium under each relative humidity condition is determined. Mass w' _∞ , according to the formula

Calculate the equilibrium desorption amount of the thin specimen under each humidity;

Step 4. After the adsorption test of step 2 and the desorption test of step 3 are completed, use data analysis software to fit the data in the process of adsorption test and desorption test to obtain the adsorption-desorption cycle curve of the thin specimen;

Step 5: Calculate the statistical thickness of the water molecule layer, use the Origin software to draw the curve relationship between the water content of the asphalt mortar specimen and the thickness of the water molecule layer, and calculate the proportion of condensed water to the amount of absorbed water; so far, the division of the proportion of condensed water in the asphalt mortar is completed.

The beneficial effects of the present invention are:

The invention draws the curve of the equilibrium water content in the asphalt mortar with the thickness of the water molecule layer through the method of adsorption-desorption cycle test and data analysis. When the relative humidity is low, the equilibrium water content and the thickness of the water molecule layer are in a linear relationship. , as the relative humidity gradually increases, the slope of the relationship line gradually increases. When the relative humidity exceeds a certain value, the equilibrium water content deviates significantly from the respective linear relationship, that is, the equilibrium water content is higher than the point on the final line, this When the equilibrium water content and the thickness of the water molecule layer show a curve relationship, the difference obtained by subtracting the integral area of the curve and the integral area of the straight line with the largest slope is used to calculate the condensed water content, and then divide the difference by the area of the integral curve to get the condensation In addition, the present invention theoretically proposes a method for determining the proportion of condensed water in asphalt mortar, which enriches the analysis method for heat and mass transfer of asphalt mixtures; this method can determine the actual proportion of condensed water in asphalt mortar and each The minimum environmental humidity of the condensation water generated by the asphalt mixture provides a method for studying the damage mechanism of the asphalt mixture under the action of gaseous water, enriches the research content of the water damage of the asphalt pavement, and has reference significance for improving the durability of the asphalt pavement.

Description of drawings

Fig. 1 is the top view of adsorption test and desorption test specimen of the present invention;

Fig. 2 is the side view of adsorption test and desorption test specimen of the present invention;

Fig. 3 is the fitting curve diagram of adsorption test and desorption test data of the present invention;

4 is a schematic diagram of the proportion of condensed water in the present invention;

Detailed ways

Specific implementation one:

This embodiment provides a method for dividing the proportion of condensed water in asphalt mortar, which is specifically carried out according to the following steps

Step 1. Prepare a φ100mm×80mm cylindrical asphalt mortar specimen with a rotary compaction method, and then use a cutting machine to make a φ100mm×4±1mm sheet specimen, and the specimen diameter-height ratio is 10-40, which can realize the water vapor along the axis. The one-dimensional diffusion in the direction means that the water vapor is transported from the upper and lower surfaces rather than the side surfaces;

Step 2: Carry out an adsorption test in the full humidity range of RH30%～RH90% under the condition of any temperature value determined in the range of 0～50℃:

计算各湿度下薄片试件的平衡吸附量；First, measure the mass w ₀ of the dried sheet specimen, then measure the mass when it reaches the adsorption equilibrium in an environment with a relative humidity of 30%, the relative humidity is increased by 10% in turn, and then the sheet specimen is measured every time the relative humidity is increased The mass w _∞ of the specimen when the humidity reaches the adsorption equilibrium, according to the formula

Calculate the equilibrium adsorption capacity of the thin specimens under each humidity;

Step 3: Carry out the desorption test in the full humidity range of RH90%~RH30% under the condition of determining any temperature value in the range of 0~50℃:

计算各湿度下薄片试件的平衡脱附量；In order to measure the desorption amount of the test piece at the point of RH90%, first, the thin piece test piece was placed in an environment with a relative humidity of RH95% for 12 hours, and the mass w' ₀ when it reached a stable state was measured, and then the relative humidity was reduced to 90%, measure the mass of the sheet specimen when the humidity is stable, subtract the two to obtain the desorption amount of the sheet specimen at 90% relative humidity, and then reduce the humidity to the lowest 30% by 10%. %, determine the mass w' _∞ of the thin specimen when it reaches equilibrium under each relative humidity condition, according to the formula

Calculate the equilibrium desorption amount of the thin specimen under each humidity;

Step 4. After the adsorption test of step 2 and the desorption test of step 3 are completed, use data analysis software to fit the data in the process of adsorption test and desorption test to obtain the adsorption-desorption cycle curve of the thin specimen. The specific process is:

Using the data analysis software, the equilibrium adsorption capacity and equilibrium desorption capacity were calculated by the GAB model formula, as shown in formula 1:

计算所得，平衡脱附量为

计算所得，W_m表示单分子层饱和吸附量或者单分子层饱和脱附量，是水分子仅以单层吸附、脱附方式完全覆盖吸附界面时对应的吸附量、脱附量；C表示第一层水分子吸附能常数或第一层水分子脱附能常数，K为多层水分子吸附能常数，或多层水分子脱附常数，是外层水分子与液态水能量状态的差异，取值范围为0～1，越接近于1表明外层水分子(即第1层水分子之外的水分子层)与液态水分子之间能量状态更为接近；P表示水蒸气压力，P₀表示水蒸气饱和压力；P/P₀表示相对蒸气压，水蒸气相对湿度，以小数形式表示，取值范围为0～1。步骤五、计算水分子层统计厚度，运用Origin软件绘制沥青砂浆试件含水量和水分子层厚度的曲线关系，计算冷凝水占吸附水量的比例具体为：In the formula, W represents the equilibrium adsorption capacity or equilibrium desorption capacity, and the equilibrium adsorption capacity is

Calculated, the equilibrium desorption amount is

Calculated, W _m represents the saturated adsorption capacity of the monolayer or the saturated desorption capacity of the monomolecular layer, which is the corresponding adsorption capacity and desorption capacity when the water molecule only completely covers the adsorption interface in the form of monolayer adsorption and desorption; C represents the first The adsorption energy constant of one layer of water molecules or the desorption energy constant of the first layer of water molecules, K is the adsorption energy constant of multi-layer water molecules, or the desorption constant of multi-layer water molecules, which is the difference between the energy states of outer water molecules and liquid water, The value ranges from 0 to 1, and the closer it is to 1, the closer the energy state between the outer water molecules (that is, the water molecule layer other than the first layer of water molecules) and the liquid water molecules is; P represents the water vapor pressure, and P ₀ represents the saturation pressure of water vapor; P/P ₀ represents the relative vapor pressure, the relative humidity of water vapor, expressed in decimal form, the value range is 0～1. Step 5: Calculate the statistical thickness of the water molecule layer, use the Origin software to draw the curve relationship between the water content of the asphalt mortar specimen and the thickness of the water molecule layer, and calculate the proportion of condensed water to the amount of adsorbed water as follows:

Step 51. The thickness of the water molecule layer is calculated by the Harkins-Jura equation, and the relative humidity data in steps 2 and 3 are used for calculation, as shown in formula (2):

Among them, t represents the statistical thickness of the adsorbed water molecule layer, the unit is ^10-10 m, and RH is the relative humidity;

Step 52. Using the relative humidity as a bridge, use Origin software to convert the isothermal adsorption and desorption curve data into the relationship between the equilibrium water content in the asphalt mortar and the thickness of the water molecule layer under the humidity conditions, and draw the relationship curve between the two. ; Origin software has a curve fitting function, and the curve fitting in Origin adopts the nonlinear least squares fitting based on the Levernberg-Marquardt algorithm (LMA);

Step 53: When the relative humidity is low, there is a linear relationship between the equilibrium water content and the thickness of the water molecule layer. As the relative humidity gradually increases, the slope of the relationship line gradually increases. When the relative humidity exceeds a certain value, The equilibrium water content deviates significantly from the respective linear relationships, that is, the equilibrium water content is higher than the point on the final straight line. At this time, when the equilibrium water content and the thickness of the water molecule layer show a curve relationship, the integral area of the curve and the integral area of the line with the largest slope are subtracted. Calculate the condensed water content from the difference of , and then obtain the condensed water proportion in the thin specimen from the ratio of the difference to the total area, that is, the condensed water proportion in the asphalt mortar. The specific relationship is shown in Figure 4.

So far, the division of the proportion of condensed water in the asphalt mortar is completed.

Specific implementation two:

Different from the specific embodiment 1, in the method for determining the proportion of condensed water in the asphalt mortar of this embodiment, the tests in steps 2 and 3 use a constant temperature and humidity box to provide constant temperature and humidity conditions, and the relative humidity inside the container is determined by saturated salt. The solution or distilled water is maintained, and the relative humidity outside the container is maintained by a constant temperature and humidity box;

Other steps and parameters are the same as in the first embodiment.

The following examples are used to verify the beneficial effects of the present invention:

Example: The raw materials of the asphalt mortar specimen are andesite, SBS modified asphalt and elemental mineral powder. The material parameters are shown in Table 1.

Table 1 Material parameters of asphalt mortar specimens

Step 1. Prepare a cylindrical asphalt mortar specimen of φ100mm×80mm by rotary compaction, and then use a cutting machine to form a thin specimen of φ100mm×4±1mm, which satisfies the diameter-height ratio of 10-40, and can realize one-dimensional axial direction. diffusion;

The test gradation is based on the median value of AC-13 grading recommended in "Asphalt Pavement Construction and Acceptance Specifications" (GBJ 50092-1996), the particle size range is selected from 1.18mm to 0.075mm, and the internal proportion of the gradation is kept unchanged and recalculated to obtain the test. The gradation used; the powder-to-binder ratio is 1.2:1; the cylindrical specimen is prepared by the rotary compaction molding method, and the size is φ100mm×63.5mm.

According to "Highway Engineering Asphalt and Asphalt Mixture Test Regulations" (JTG E20-2011) T0705-2011 Compacted Asphalt Mixture Density Test (Surface Dry Method), the physical parameters of the specimen were measured and the porosity and theoretical maximum relative density were calculated. Then, the cylindrical specimen was cut into a thin plate of φ100mm×2～5mm to realize one-dimensional water vapor diffusion. The specimen is shown in Figure 1 and Figure 2.

计算各湿度下的平衡吸附量，如表2所示。Step 2: Carry out a gaseous water adsorption test with a constant temperature of 303K (30°C) and relative humidity conditions of 0.4, 0.5, 0.7, 0.9 and 1 (water immersion), respectively. Determine the mass w ₀ (kg) of the dry specimen and the mass w _∞ (kg) of the specimen when the adsorption equilibrium is reached under each humidity condition (the weight gain of the specimen at an interval of more than 24 hours does not exceed the measurement accuracy of the electronic balance), according to the formula

The equilibrium adsorption capacity under each humidity was calculated, as shown in Table 2.

Table 2 Adsorption capacity under various humidity conditions

计算各湿度下试件的平衡脱附量，如表3所示。Step 3: Carry out a gaseous water desorption test with a constant temperature of 303K (30°C) and relative humidity conditions of 1 (water immersion), 0.9, 0.7, 0.5 and 0.4, respectively. Determine the maximum mass w' ₀ of the specimen under the condition of maximum humidity and the mass w' _∞ of the specimen whose weight gain does not exceed the measurement accuracy of the electronic balance when the desorption equilibrium is reached under each humidity condition at an interval of more than 24 hours, According to the formula

The equilibrium desorption amount of the specimen under each humidity was calculated, as shown in Table 3.

Table 3 Desorption amount under various humidity conditions

Step 4. After the adsorption and desorption test, use the data analysis software to fit the data in the adsorption and desorption process to obtain the adsorption-desorption cycle curve of the asphalt mortar specimen, as shown in Figure 3.

Step 5. Calculate the thickness of the water molecule layer through the Harkins-Jura equation, and use the Origin software to convert the adsorption-desorption curve data into the relationship between the thickness of the water molecule layer and the water content in the asphalt mortar under the humidity conditions, and draw the equilibrium water content. The graph with the thickness of the water molecule layer is shown in Figure 4. The proportion of condensed water in the asphalt mortar is obtained by calculating the ratio of the area difference between the integral of the curve and the integral of the straight line to the total area. It is calculated from Figure 4 that the proportion of condensed water accounts for 8% of the total adsorbed water. So far, the condensed water in the asphalt mortar is divided Proportional task accomplished.

The present invention can also have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations are all It should belong to the protection scope of the appended claims of the present invention.

Claims (2)

1. The method for determining the proportion of the condensed water in the asphalt mortar is characterized by comprising the following steps:

preparing a phi 100mm multiplied by 80mm cylindrical asphalt mortar test piece by using a rotary compaction method, and then preparing a phi 100mm multiplied by 4 +/-1 mm sheet test piece by using a cutting machine, wherein the height ratio of the test piece diameter is 10-40, so that one-dimensional diffusion of water vapor along the axial direction can be realized;

step two, carrying out an adsorption test of RH 30% -RH 90% in a full humidity range under the condition that any temperature value is determined within the range of 0-50 ℃:

first, the mass w of a dried sheet specimen is measured₀Then measuring the mass when the relative humidity reaches the adsorption balance under the environment with the relative humidity of 30 percent, sequentially increasing the relative humidity by 10 percent, and then measuring the mass w of the test piece when the relative humidity of the thin sheet test piece reaches the adsorption balance after each increase of the relative humidity_∞According to the formula

Calculating the equilibrium adsorption capacity of the sheet test piece under each humidity;

step three, carrying out a desorption test of RH 90% -RH 30% in a full humidity range under the condition that any temperature value is determined within the range of 0-50 ℃:

first, a sheet specimen was placed in an atmosphere having a relative humidity of RH 95% for 12 hours, and its mass w 'at the time of stabilization was measured'₀Then, the relative humidity was reduced to 90%, the mass of the sheet specimen at a stable humidity was measured, the desorption amount of the sheet specimen at a relative humidity of 90% was obtained by subtracting the two, and then the humidity was reduced to 30% by a reduction amount of 10%, and the mass w 'at equilibrium of the sheet specimen was measured for each relative humidity condition'_∞According to the formula

Calculating the equilibrium desorption amount of the sheet test piece under each humidity;

after the adsorption test in the step two and the desorption test in the step three are finished, fitting data in the adsorption test and the desorption test by using data analysis software to obtain an adsorption-desorption cycle curve of the sheet test piece, wherein the specific process is as follows:

calculating the equilibrium adsorption amount and the equilibrium desorption amount by a water adsorption fitting formula of the GAB model, wherein the formula is shown as formula 1:

wherein W represents an equilibrium adsorption amount or an equilibrium desorption amount, W_mThe adsorption capacity and desorption capacity are corresponding to the adsorption capacity and desorption capacity when water molecules completely cover the adsorption interface only in a single-layer adsorption and desorption mode; c represents the adsorption energy constant or desorption energy constant of the first layer of water molecules, K is the adsorption energy constant or desorption constant of the multiple layers of water molecules, which is the difference of the water energy states of the outer layer of water molecules and the liquid water, the value range is 0-1, and the closer to 1, the more the value is, the outer layer of water molecules and the liquid water are shownThe energy states of the liquid water molecules are closer; p represents the water vapor pressure, P₀Represents the water vapor saturation pressure; P/P_OThe relative humidity of the water vapor is expressed in a decimal form, and the value range is 0-1;

step five, calculating the statistical thickness of the water content layer, drawing a curve relation between the water content of the asphalt mortar test piece and the thickness of the water content layer by using Origin software, and calculating the proportion of condensed water in the adsorbed water quantity as follows:

step five, calculating the thickness of the water molecular layer by using the relative humidity data in the step two and the step three through a Harkins-Jura equation, wherein the formula (2) is as follows:

wherein t represents the statistical thickness of the adsorbed water molecular layer and has a unit of 10^-10m, RH is relative humidity;

step two, taking the relative humidity as a bridge, converting isothermal adsorption and desorption curve data into a relation between the equilibrium water content and the thickness of a water molecular layer in the asphalt mortar under the humidity condition by using Origin software, and drawing a relation curve graph between the isothermal adsorption and desorption curve data and the water molecular layer;

step three, when the equilibrium water content and the thickness of the water molecular layer present a curve relationship, calculating the condensed water content through a difference value obtained by subtracting the integral area of the curve from the integral area of the straight line with the maximum slope, and obtaining the condensed water proportion in the slice test piece according to the proportion of the difference value in the total area, namely obtaining the condensed water proportion in the asphalt mortar;

so far, the division of the proportion of the condensed water in the asphalt mortar is completed.

2. The method for determining the proportion of the condensed water in the asphalt mortar according to claim 1, wherein the tests in the second step and the third step are carried out by using a constant temperature and humidity chamber to provide constant temperature and humidity conditions, the relative humidity inside the container is maintained by saturated salt solution or distilled water, and the relative humidity outside the container is maintained by the constant temperature and humidity chamber.

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