An evaluation method for determining the degree of asphalt adsorption by aggregates

Abstract

The present invention discloses an evaluation method for determining the degree of asphalt adsorption by aggregates, including: ultrasonic cleaning and flushing of aggregates; mixing two different masses of asphalt and a single particle size aggregate to obtain two asphalt-coated aggregate samples; cutting the two samples respectively to obtain cross sections; photographing the cross sections with SEM micro-areas to measure the thickness of the asphalt film on the surface of the two aggregate samples; and obtaining an evaluation index of the degree of asphalt adsorption by aggregates according to the mass of asphalt during mixing and the measured asphalt film thickness according to the following formula: #imgabs0# wherein C is an index characterizing the degree of asphalt adsorption by aggregates, the adsorption coefficient, which is defined as the mass of asphalt adsorbed per unit mass of aggregates; m1 and m2 are the asphalt dosages during the two mixings, in g; h1 and h2 are the asphalt film thicknesses measured by the two aggregate samples, in cm; and m is the mass of aggregates during mixing. The present invention can quantitatively evaluate the degree of asphalt adsorption by aggregates of different particle sizes through the adsorption coefficient C, which has guiding significance for determining the amount of asphalt in the preparation process of asphalt mixtures.

Description

Technical Field

[0001] The invention is an evaluation method for determining the degree of asphalt adsorption by aggregate, in particular, a method for solving the problem that the asphalt adsorption of aggregate itself cannot be determined when the asphalt dosage is considered in the current aggregate-asphalt mixing process, and belongs to the technical field of highway pavement materials. Background Art

[0002] Asphalt mixture is a pavement material that is made by mixing asphalt as a binder, coarse aggregate, fine aggregate, and mineral powder as aggregates according to a certain design and at a certain temperature. It is widely used in roads and railways because of its certain high temperature stability, no need to set construction joints, simple maintenance and recycling. When designing the asphalt dosage of the mixture, if the aggregate quality is certain, too much asphalt will lead to higher costs and may also cause serious diseases such as oil spilling, while too little asphalt will lead to insufficient adhesion between aggregates and serious problems such as aggregate shedding. Therefore, designing a reasonable asphalt dosage is the key to ensuring the quality of asphalt mixtures. Since there are many tiny pores on the surface of the aggregate, the asphalt material will be adsorbed in the pores of the aggregate. Therefore, the asphalt dosage consists of two parts, one is the adsorption amount absorbed by the aggregate into the internal pores, and the other is the effective asphalt amount filled between the gaps between the aggregates. At present, the asphalt adsorption amount of aggregates in asphalt mixtures is determined according to the "Technical Specifications for Highway Asphalt Pavement Construction". In this specification, according to the relationship: To determine the asphalt absorption coefficient C, where w x is the water absorption rate of aggregate. This relationship was derived by several professors of Tongji University based on a large number of experiments. The effective relative density of aggregate is determined by the apparent relative density, bulk density and asphalt absorption coefficient of aggregate. Finally, according to the formula Determine the proportion of asphalt binder absorbed by aggregate in asphalt mixture ba , where γ se is the effective relative density of aggregate, γ sb is the aggregate bulk density, γ b is the density of asphalt. From the above calculation process, it can be seen that the asphalt adsorption amount determined by this method mainly depends on the value of the asphalt absorption coefficient. Some scholars have found through experiments that when the water absorption rate of aggregates is the same, the asphalt absorption rate varies greatly. In other words, in addition to the water absorption rate of mineral materials, the type of mineral materials and the type of asphalt will affect the asphalt absorption rate of aggregates. Therefore, the asphalt adsorption amount calculated by the formula specified in the specification is not accurate, and a large number of tests are needed to confirm some parameters in the formula.

[0003] In summary, there is an urgent need for an accurate and efficient method to quantify the degree of asphalt adsorption by aggregates and determine the amount of asphalt adsorbed in aggregates, providing a necessary basis for the study of the interaction between asphalt and aggregates. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides an evaluation method for determining the degree of adsorption of asphalt by aggregates, by measuring the thickness of the asphalt film and calculating the adsorption coefficient C, an evaluation index of the adsorption degree, according to the difference between different asphalt dosages and corresponding film thicknesses.

[0005] In order to achieve the above object, the technical solution provided by the present invention is:

[0006] A method for evaluating the degree of asphalt adsorption by aggregates, characterized by: comprising ultrasonic cleaning and flushing of aggregates; mixing two asphalts of different masses and aggregates of a single particle size to obtain two asphalt-coated aggregate samples; cutting the two samples respectively to obtain cross sections; photographing the cross sections with SEM micro-areas to measure the thickness of the asphalt films on the surfaces of the two aggregate samples; and obtaining an evaluation index of the degree of asphalt adsorption by aggregates, an adsorption coefficient C, according to the mass of the asphalt during mixing and the measured asphalt film thickness according to the following formula:

[0007]

[0008] Where C is the adsorption coefficient, which is an indicator of the degree of asphalt adsorption by aggregate and is defined as the mass of asphalt adsorbed by unit mass of aggregate; m 1 、m 2 The amount of asphalt used in the two mixing operations, in g; h 1 、h 2 is the asphalt film thickness measured for the two aggregate samples, in cm; m is the mass of the aggregate during mixing.

[0009] Preferably, ultrasonic cleaning and flushing of aggregates includes using an ultrasonic cleaning machine to flush the aggregates, washing away dust and debris on the surface of the aggregates to prevent them from entering into tiny pores in the aggregates and affecting the asphalt adsorption results.

[0010] Preferably, the single particle size aggregate has a particle size of 4.75-9.5 mm and a mass of 1000 g.

[0011] Preferably, the masses of the two types of asphalt during mixing are 15g and 20g respectively.

[0012] Preferably, obtaining the cross section of the aggregate includes: cutting from the end of the aggregate with a small cutting machine to obtain a flat aggregate-asphalt cross section to obtain the aggregate-asphalt interface to measure the asphalt film thickness.

[0013] Preferably, determining the asphalt film thickness includes: performing a scanning electron microscope (SEM) micro-area photography experiment on the obtained aggregate-asphalt cross section, magnifying the sample, finding the interface between the aggregate and the asphalt, selecting a suitable position and using a measurement function to measure the thickness of the asphalt film according to a scale.

[0014] Preferably, in order to minimize variability and ensure the accuracy of the test, four aggregate samples with regular shapes are randomly selected for cutting, and three suitable areas are selected for each sample to test the asphalt film thickness.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0016] The present invention can quantify the degree of asphalt adsorption by aggregates, and the calculation formula for calculating the asphalt adsorption amount in the aggregates is simple, and the asphalt film thickness is obtained through actual measurement, so the calculation result is reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of asphalt adsorbed in the pores inside aggregate.

[0018] Figure 2 Aggregate-asphalt interface observed in SEM test. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in detail below with reference to certain examples:

[0020] The inventors have found through experiments that an environmental scanning electron microscope (SEM) can clearly observe the interface between asphalt and aggregate, and has a measurement function that can accurately measure the thickness of the asphalt film. In the design of asphalt mixtures, the asphalt dosage and the corresponding asphalt film thickness can be changed. For the same batch of aggregates, the asphalt adsorption amount is unchanged, so the asphalt adsorption amount can be calculated by the asphalt dosage and the corresponding asphalt film thickness difference. Specifically, the technical solution of the present invention is as follows:

[0021] A method for evaluating the degree of asphalt adsorption by aggregates, characterized by: comprising ultrasonic cleaning and flushing of aggregates; mixing two asphalts of different masses and aggregates of a single particle size to obtain two asphalt-coated aggregate samples; cutting the two samples respectively to obtain cross sections; photographing the cross sections with SEM micro-areas to measure the thickness of the asphalt films on the surfaces of the two aggregate samples; and obtaining an evaluation index of the degree of asphalt adsorption by aggregates - adsorption coefficient C - according to the mass of the asphalt during mixing and the measured asphalt film thickness according to the following formula:

[0022]

[0023] Where C is the adsorption coefficient, which is an indicator of the degree of asphalt adsorption by aggregate and is defined as the mass of asphalt adsorbed by unit mass of aggregate; m 1 、m 2 The amount of asphalt used in the two mixing operations, in g; h 1 、h 2 is the asphalt film thickness measured by the two aggregate samples, in cm; m is the mass of the aggregate during mixing. The present invention can quantitatively evaluate the degree of asphalt adsorption by aggregates of different particle sizes through the adsorption coefficient C, which has guiding significance for determining the amount of asphalt used in the preparation process of asphalt mixture.

[0024] In order to facilitate public understanding, the technical solution of the present invention is described in detail below with reference to a specific embodiment.

[0025] 1) Before the test, 2 portions of 1000 g of basalt aggregate with a particle size of 4.75-9.5 mm were weighed respectively, and the aggregates were first cleaned with an ultrasonic cleaner to remove dust and debris attached to the surface, and then placed in an oven to dry.

[0026] 2) Mix two portions of aggregate with 15 g and 20 g of No. 70 base asphalt respectively at 160°C for 100 seconds to obtain two portions of asphalt mixtures.

[0027] 3) Four aggregates with regular shapes were randomly selected from the two asphalt mixtures, for a total of eight aggregates. The eight aggregates were cut using a small cutting machine to obtain smooth asphalt-aggregate cross-section specimens.

[0028] 4) The 8 asphalt-aggregate cross-section samples were subjected to environmental scanning electron microscope (SEM) micro-area photography test. Since the asphalt surface is smooth and the aggregate surface is rough, the interface between asphalt and aggregate can be found quickly and clearly, such as Figure 2 As shown, three appropriate areas were selected to measure the asphalt film thickness and take the average value.

[0029] 5) The asphalt dosage of the samples and the measured asphalt film thickness are shown in Table 1 below.

[0030] Table 1. Asphalt film thickness (10-4cm) data table

[0031]

[0032] The amount of asphalt in the aggregate (M) consists of two parts, one is the amount adsorbed inside the aggregate (A), and the other is the amount wrapped on the surface of the aggregate (B = ρ × S × 1000 × h). The amount adsorbed inside the aggregate is only related to the aggregate, but not to the amount of asphalt. Therefore, the A values ​​in the two samples with different asphalt amounts are the same. Known asphalt density ρ = 1.03g / cm 3Then the asphalt coating amount of the first sample = 1.03 × S × 1000 × 50.3 × 10 -4 =5.18S, the asphalt coating amount of the second aggregate sample = 1.03×S×1000×67.8×10 -4 =6.98S, the amount of asphalt in the first batch of aggregate m 1 =15g, the amount of asphalt in the second batch of aggregate m 2 =20g, so we can get the following two formulas:

[0033] 5.18S+A=15 (1)

[0034] 6.98S+A=20 (2)

[0035] (2)-(1), we get 1.8S=5, then S=2.7cm 2 / g, substituting it into (1), we can get the asphalt adsorption amount of 1000g basalt aggregate with a particle size of 4.75-9.5mm A=15-5.18×2.7=1.01g.

[0036] The adsorption coefficient of basalt aggregate with a diameter of 4.75-9.5 mm to asphalt is

[0037] The above calculation process can be deduced through certain deductions to obtain the general formula of the adsorption coefficient C:

[0038]

[0039] The derivation process is as follows:

[0040] ρ×S×m×h 1 +A=m 1 (3)

[0041] ρ×S×m×h 2 +A=m 2 (4)

[0042] (3) ×h 2 -(4)×h 1 , we can get Ah 2 -Ah 1 =m 1 h 2 -m 2 h 1 (5)

[0043] but

[0044] The adsorption coefficient C is defined as the mass of asphalt adsorbed by unit mass of aggregate, then:

[0045]

[0046] According to the above process, the adsorption coefficient C is defined as:

[0047]

[0048] Where C is the adsorption coefficient, which is an indicator of the degree of aggregate adsorption to asphalt; m is the mass of aggregate during mixing, in g; m 1 、m 2 is the amount of asphalt used in the two mixings, in g; A is the mass of asphalt adsorbed by the aggregate, in g; h 1 、h 2 is the asphalt film thickness measured for the two aggregate samples, in cm; ρ is the density of the asphalt used, in g / cm 3 ; S is the specific surface area of ​​the aggregate used, in cm 2 / g.

Claims

1. A method for determining the degree of asphalt adsorption by aggregates, characterized in that: The method includes ultrasonic cleaning and flushing of aggregates; mixing two asphalts of different masses with a single-size aggregate of mass m to obtain two asphalt-coated aggregate samples; cutting the two samples to obtain cross sections; taking SEM micro-area photographs of the cross sections to measure the thickness of the asphalt film on the surface of the two aggregate samples; and obtaining an evaluation index of the degree of asphalt adsorption by aggregates - adsorption coefficient C according to the mass of asphalt during mixing and the measured asphalt film thickness: Among them, C is the index that characterizes the degree of asphalt adsorption by aggregate - the adsorption coefficient, which is defined as the mass of asphalt adsorbed by unit mass of aggregate; m1 and m2 are the asphalt consumption during the two mixings, in g; h1 and h2 are the asphalt film thickness measured for the two aggregate samples, in cm; m is the mass of aggregate during mixing.

2. The method for determining the degree of asphalt adsorption by aggregate according to claim 1, characterized in that: The ultrasonic cleaning and flushing of aggregates includes flushing the aggregates with an ultrasonic cleaning machine to wash away dust and debris on the surface to prevent them from entering into tiny pores in the aggregates and affecting the asphalt adsorption results.

3. The method for determining the degree of asphalt adsorption by aggregate according to claim 1, characterized in that: The particle size of the single-size aggregate is 4.75-9.5 mm and the mass is 1000 g.

4. The method for determining the degree of asphalt adsorption by aggregate according to claim 1, characterized in that: The masses of the two types of asphalt are taken as 15g and 20g respectively based on mixing experience.

5. The method for determining the degree of asphalt adsorption by aggregate according to claim 1, characterized in that: The two samples are cut respectively to obtain cross sections: since the selected aggregate particle size is small, a small cutting machine is selected to cut from the aggregate end to obtain a flat aggregate-asphalt cross section to obtain the aggregate-asphalt interface.

6. The method for determining the degree of asphalt adsorption by aggregates according to claim 1, characterized in that: The method for measuring the thickness of the asphalt film on the surface of the two aggregate samples includes: performing a scanning electron microscope (SEM) micro-area photography experiment on the obtained aggregate-asphalt cross section, magnifying the sample, finding the interface between the aggregate and the asphalt, selecting a suitable position and using the measurement function to measure the thickness of the asphalt film according to the scale.

7. The method for determining the degree of asphalt adsorption by aggregate according to claim 1, characterized in that: Four aggregate samples with regular shapes were randomly selected for cutting, and three suitable areas were selected for each sample to test the asphalt film thickness to ensure the accuracy of the experimental data.

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