Method for estimating asphalt content in asphalt pavement waste

Abstract

To provide an estimation method which can safely and relatively easily estimate the asphalt content rate in asphalt pavement waste in a short time.SOLUTION: An estimation method of an asphalt content rate in asphalt pavement waste irradiates a standard sample having the known asphalt content rate with the first infrared light being the absorption band common to asphalt and calcium carbonate and the second infrared light being the absorption band unique to the calcium carbonate, detects the first and second optical densities by receiving the respective diffuse reflection light, obtains a multiple regression expression by the linear multiple regression analysis from the first and second optical densities detected for each standard sample and the asphalt content rate of each standard sample, irradiates the sample having the unknown asphalt content rate with the first and second infrared light, detects the first and second optical densities by receiving the respective diffuse reflection light, and estimates the asphalt content rate on the basis of the first and second optical densities and the multiple regression expression.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating the asphalt content in waste asphalt pavement material excavated during road construction or the like. [Background technology]

[0002] In order to reuse waste asphalt pavement materials (hereinafter referred to as "waste materials") dug up during road construction work, etc., the crushed waste materials are heated to approximately 160°C and regenerated, and this heated and regenerated waste material, new aggregate, molten asphalt, etc. are mixed in a specified ratio to produce an asphalt mixture.

[0003] The waste materials include aggregates of various particle sizes, stone powder, asphalt, etc., but asphalt deteriorates over the years while in use as a road, and the original viscosity of asphalt cannot be restored by the heat treatment alone. For example, a recycling additive that has the effect of improving the viscosity of asphalt is added and mixed in, with the amount adjusted according to the degree of deterioration of the asphalt contained in the waste materials and its content, to produce an asphalt mixture (see Patent Documents 1 and 2).

[0004] As a method for measuring the amount (content rate) of asphalt contained in waste materials, for example, the Soxhlet extraction method is generally known, in which the asphalt in the waste materials is dissolved and extracted with a solvent and the amount of asphalt extracted is measured (see Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-112724 [Patent Document 2] Japanese Patent Application Publication No. 11-71710 [Patent Document 3] Japanese Utility Model Application Publication No. 63-35046 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the Soxhlet extraction method, many of the solvents used are flammable and toxic, and they have a high environmental impact. In addition, they require careful handling, and the measurement requires a certain amount of effort and time (several hours). On the other hand, since waste materials are collected from various construction sites, it is not uncommon for the asphalt content to vary. When trying to add and mix the appropriate amount of additives when manufacturing an asphalt mixture made from recycled waste materials, it would be best to take samples for each batch and check the asphalt content each time using the Soxhlet extraction method, but in reality, this is not realistic due to the effort and time constraints involved.

[0007] In view of the above, an object of the present invention is to provide a method for estimating the asphalt content in waste asphalt pavement safely, relatively easily, and in a short period of time. [Means for solving the problem]

[0008] In order to solve the above problems, the inventors of the present invention have conducted extensive research and have come to the conclusion that, for example, infrared spectroscopy may be used to estimate the asphalt content in waste materials relatively easily. Infrared spectroscopy is a method for qualitatively and quantitatively characterizing a substance by irradiating the substance to be measured with infrared light (near-infrared light or mid-infrared light), separating the transmitted or reflected light to obtain a spectrum, and detecting the absorbance at each wavelength.

[0009] The asphalt contained in the waste material has C-H (carbon-hydrogen) bonds as intermolecular bonds, and it was thought that if infrared light (mid-infrared light) with a wavelength of around 3.44 μm, which is the absorption band of this C-H bond, were irradiated onto the waste material to be measured, and the absorbance of the light transmitted or reflected from the waste material at that time was detected, it would be possible to estimate the asphalt content in the waste material safely, with low environmental impact, and relatively easily and in a short time.

[0010] There are various infrared spectroscopy methods, such as diffuse reflectance, ATR, and transmission, but among these, the method known as diffuse reflectance does not require the pre-processing required for other ATR and transmission methods (pulverizing the substance to be measured to a particle size of a few micrometers or less), and is therefore expected to be particularly effective when the goal is to estimate the asphalt content easily and quickly.

[0011] However, based on the above prediction, infrared light of 3.44 μm, which is the absorption band of asphalt, was irradiated onto multiple standard samples of waste materials with known asphalt content, and the diffuse reflection method was used to receive the diffuse reflected light from the standard samples (reflected light excluding specular reflected light that was not absorbed by the asphalt in the standard samples and was reflected from the surface of the standard samples) and detect its absorbance. A calibration curve was then created based on the absorbance detected for each standard sample and the asphalt content (true value) of each standard sample. However, contrary to prediction, the correlation between the absorbance and the asphalt content was low.

[0012] Therefore, the present inventors tried to clarify the cause and found that the absorption band of asphalt and the absorption band of calcium carbonate partially overlap near 3.44 μm. Calcium carbonate is the main component of stone powder, which is one of the materials of the waste material (asphalt mixture), but the stone powder content in the waste material also varies greatly depending on the waste material collection site, and it was thought that this overlap with the absorption band of asphalt reduces the correlation between the absorbance and the asphalt content (for example, even if the asphalt content is the same, if the calcium carbonate content is different, the absorbance near 3.44 μm may also vary).

[0013] This is not limited to the diffuse reflection method, and it is thought that the same phenomenon occurs in the ATR method, transmission method, etc., but since the absorbance of calcium carbonate appearing near 3.44 μm in the ATR method, transmission method, etc. is very weak (to a negligible extent), it is expected to have almost no effect on the absorbance of asphalt. On the other hand, in the diffuse reflection method, the absorbance of calcium carbonate appears relatively strongly near the aforementioned 3.44 μm, and therefore there is a possibility that it will have a large effect on the absorbance of asphalt in the same wavelength range.

[0014] Therefore, the inventor further conducted intensive research and, although he was ultimately unable to find an absorption band specific to asphalt (not overlapping with the absorption bands of other components in the waste material), he was able to find an absorption band specific to calcium carbonate (for example, around 3.97 μm).If that is the case, it is possible to irradiate a plurality of standard samples with known asphalt contents with a first infrared light of 3.44 μm, which is an absorption band common to the asphalt and calcium carbonate, and a second infrared light of 3.97 μm, which is an absorption band specific to calcium carbonate, and detect the first and second absorbances, which are the absorbances of the diffuse reflected light from the standard samples irradiated with the first and second infrared lights, using a diffuse reflection method, and create a highly correlated calibration curve from the first and second absorbances detected for each standard sample and the asphalt content of each standard sample, which led to the invention.

[0015] That is, in order to solve the above problem, the method for estimating the asphalt content in waste asphalt pavement according to the present invention, as described in claim 1, irradiates a standard sample of a plurality of waste asphalt pavement samples having known asphalt contents with a first infrared light, which is an absorption band common to asphalt and calcium carbonate contained in the waste asphalt pavement samples, and a second infrared light, which is an absorption band specific to calcium carbonate, and receives each diffuse reflected light from the standard sample irradiated with the first and second infrared lights, thereby detecting the first and second absorbances, which are the respective absorbances. a first infrared light ray and a second infrared light ray are received from the sample irradiated with the first and second infrared light rays, the first and second infrared light rays are detected as diffuse reflected light rays from the sample irradiated with the first and second infrared light rays, and the asphalt content of each of the standard samples is estimated based on the detected first and second absorbances and the multiple regression equation.

[0016] In addition, the method for estimating the asphalt content in asphalt pavement waste material described in claim 2 of the present invention is characterized in that the wavelength of the first infrared light is 3.44 μm and the wavelength of the second infrared light is 3.97 μm. Effect of the Invention

[0017] According to the method for estimating the asphalt content in waste asphalt pavement material of the present invention, the method does not require solvents, which reduces the environmental impact and allows safe processing, and also makes it possible to estimate the asphalt content relatively easily and in a short period of time. [Brief description of the drawings]

[0018] [Figure 1] 1 is a flowchart illustrating a method for estimating an asphalt content in waste asphalt pavement according to the present invention. [Diagram 2]1 is a graph showing the correlation between the estimated value of the asphalt content in a sample estimated using the method for estimating the asphalt content in waste asphalt pavement according to the present invention and the actual measured value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In the method of estimating the asphalt content in asphalt pavement waste material according to the present invention, standard samples of a plurality of waste materials having different asphalt contents and known asphalt contents are irradiated with a first infrared light having a wavelength of, for example, 3.44 μm, which is an absorption band common to the asphalt (C-H bonds) and calcium carbonate contained in the waste materials, and a second infrared light having a wavelength of, for example, 3.97 μm, which is an absorption band specific to calcium carbonate, and a diffuse reflection method is used to receive the diffuse reflected light from the standard samples irradiated with the first and second infrared lights, thereby detecting the first and second absorbances, respectively.

[0020] Next, a linear multiple regression equation expressing the relationship between the first and second absorbances and the asphalt content of each standard sample is determined in advance by linear multiple regression analysis using the first and second absorbances detected for each standard sample and the asphalt content of each standard sample. The linear multiple regression analysis determines a linear relational equation y=ax1+bx2+c...(1) (where a and b are regression coefficients, and c is an intercept) using the first absorbance x1 and the second absorbance x2 as explanatory variables and the asphalt content y as a response variable.

[0021] Then, for example, a first infrared light having a wavelength of 3.44 μm and a second infrared light having a wavelength of 3.97 μm are irradiated to a waste material sample with an unknown asphalt content, and the diffuse reflection method is used to receive the diffuse reflected light from the sample irradiated with the first and second infrared lights, and detect the first and second absorbances x1 and x2, which are the respective absorbances. Then, based on the detected first and second absorbances x1 and x2 and the multiple regression equation (1) previously obtained, the asphalt content y contained in the sample is estimated.

[0022] In this case, since there is no need to use solvents as in the conventional Soxhlet extraction method, the environmental impact is low and the process can be safely carried out, and since the waste material sample is simply irradiated with infrared light of a specified wavelength, the asphalt content can be estimated relatively easily and in a short time (instantaneously). This makes it possible, for example, to check the asphalt content for each batch when producing an asphalt mixture from recycled waste materials, and to add and mix the appropriate amount of additive according to the asphalt content contained in the waste material, making it ideal in terms of quality and cost.

[0023] In addition, the diffuse reflectance method used in the present invention has the advantage of not requiring pre-processing such as pulverizing the waste material. However, due to its characteristics, there is a possibility that the calcium carbonate (stone powder) also contained in the waste material may hinder the detection of the asphalt content in the waste material. However, with the estimation method of the present invention, it is possible to accurately estimate the asphalt content while appropriately correcting for the influence of calcium carbonate. EXAMPLES

[0024] An embodiment of the present invention will now be described with reference to the drawings.

[0025] FIG. 1 is a flow chart for explaining the method for estimating the asphalt content in waste material according to the present invention, in which S1 to S13 represent steps of each procedure.

[0026] First, a plurality of standard samples of waste materials are prepared in advance, the asphalt content of which has been measured using, for example, a conventional Soxhlet extraction method, etc. Then, as an initial setting, the standard samples, the asphalt content of which (true value) is known, are irradiated with a first infrared light (mid-infrared light) of a predetermined wavelength, for example, 3.44 μm, which is an absorption band common to asphalt (CH bonds) and calcium carbonate contained in the waste materials (S1), and are also irradiated with a second infrared light (mid-infrared light) of a predetermined wavelength, for example, 3.97 μm, which is an absorption band specific to calcium carbonate (S2).

[0027] Next, using a diffuse reflection method, the diffuse reflected light from the standard sample irradiated with the first and second infrared light is received (S3), and the first and second absorbances, which are the absorbances of the diffuse reflected light, are detected (S4). Note that, as a means for detecting the absorbance of the diffuse reflected light, for example, an appropriate infrared spectrophotometer or the like can be used.

[0028] Next, a linear multiple regression equation (1) expressing the relationship between the first and second absorbances and the asphalt content of each standard sample is determined by linear multiple regression analysis using the first and second absorbances detected for each standard sample and the asphalt content of each standard sample (S5).

[0029] The multiple regression equation (1) has the first absorbance x1 and the second absorbance x2 as explanatory variables and the asphalt content y as a response variable, and is expressed by a linear relational equation y=ax1+bx2+c...(1) (where a and b are regression coefficients, and c is an intercept). However, the regression coefficients a, b and the intercept c are not necessarily constant and vary depending on, for example, the measurement equipment, the measurement conditions, etc.

[0030] Then, it is confirmed whether or not the calculation of the multiple regression equation (1) is to be ended (S6). If it is to be ended, the process proceeds to END to end the initial setting, whereas if it is to be continued, the process returns to step 1 to reset the settings.

[0031] When estimating the asphalt content of a waste material sample with an unknown asphalt content, first, the multiple regression equation (1) calculated in advance is read (S7). Next, the waste material sample with an unknown asphalt content is irradiated with a first infrared light (mid-infrared light) of 3.44 μm, which is an absorption band common to asphalt (CH bond) and calcium carbonate contained in the waste material and has the same wavelength as that irradiated to the standard sample (S8), and is also irradiated with a second infrared light (mid-infrared light) of 3.97 μm, which is an absorption band specific to calcium carbonate (S9).

[0032] Next, using the diffuse reflectance method in the same manner as described above, the diffuse reflected light from the sample irradiated with the first and second infrared light is received (S10), and the first and second absorbances x1, x2, which are the absorbances of the diffuse reflected light, are detected, respectively (S11).

[0033] Then, based on the detected first and second absorbances x1, x2 and the previously obtained multiple regression equation (1), the asphalt content y contained in the sample is estimated (S12). Then, it is determined whether or not to end the estimation of the asphalt content in the waste material (S13), and if it is to be ended, the process proceeds to END and ends, whereas if it is to be continued (when estimating the asphalt content in another waste material sample), the process returns to step 8 and repeats the above series of steps.

[0034] FIG. 2 is a graph showing the correlation between the estimated values ​​of asphalt content (%) in multiple waste samples estimated using the estimation method of the present invention and the actual values ​​(true values) measured using the Soxhlet extraction method.

[0035] As can be seen from the graph in Figure 2, when an approximation line was drawn by using the least squares method from the multiple estimated values ​​estimated by the estimation method of the present invention and the actual measured values, the correlation coefficient R = 0.9422 and the coefficient of determination R2 = 0.8878 were obtained, indicating a strong correlation. [Industrial Applicability]

[0036] The present invention can be widely used not only for waste asphalt pavement materials, but also for confirming the asphalt content in a new asphalt mixture.

Claims

1. A method for estimating the asphalt content in asphalt pavement waste material, comprising: irradiating a first infrared light, which is an absorption band common to the asphalt and calcium carbonate contained in the asphalt pavement waste material, and a second infrared light, which is an absorption band specific to calcium carbonate, on a plurality of standard samples of asphalt pavement waste material having known asphalt content, with a first infrared light, which is an absorption band specific to calcium carbonate, with each diffuse reflected light from the standard samples irradiated with the first and second infrared lights, and detecting the first and second absorbances, which are the respective absorbances; determining a multiple regression equation by linear multiple regression analysis from the first and second absorbances detected for each of the standard samples and the asphalt content of each of the standard samples; irradiating a sample of asphalt pavement waste material having an unknown asphalt content with the first and second infrared lights, receiving each diffuse reflected light from the sample irradiated with the first and second infrared lights, and detecting the first and second absorbances, which are the respective absorbances; and estimating the asphalt content based on the detected first and second absorbances and the multiple regression equation.

2. 2. The method for estimating the asphalt content in waste asphalt pavement material according to claim 1, wherein the wavelength of the first infrared light is 3.44 μm and the wavelength of the second infrared light is 3.97 μm.

Images