An evaluation method and application of old asphalt contribution rate in cold recycled mixture

Abstract

The present invention discloses an evaluation method for the contribution rate of old asphalt in a cold recycled mixture and its application. The method is suitable for evaluating old asphalt materials that were previously considered to have no contribution in the cold recycled mixture. First, the recycled mixture mixed with the old asphalt is made into a test piece, and then a scatter plot of the splitting strength of the test piece and different emulsified asphalt contents is drawn, and a quadratic function and a linear function are fitted. Finally, the contribution rate of the cold recycled mixture is obtained by function calculation, and the contribution rate is used to guide the design of the proportion of the cold recycled mixture, so as to effectively and maximize the use of the old asphalt, thereby achieving the effect of improving the performance of the recycled pavement and reducing the cost.

Description

Technical Field

[0001] The invention relates to the technical field of asphalt pavement construction and maintenance, and in particular to an evaluation method for the contribution rate of old asphalt in a cold recycled mixture and its application. Background Art

[0002] Recycled mixture refers to the new pavement material for paving various types of roads obtained by reusing old asphalt road materials (RAP) and regenerating agents, new asphalt materials, new aggregates and other materials in a certain proportion. In recent years, the focus of my country's highway development has shifted from construction to maintenance, so the high-value utilization of RAP has become the trend of highway construction and development. For this reason, the industry has conducted many years of research and practice on RAP recycling technology, which can achieve green and high-value utilization of waste resources and solve some RAP dumping problems.

[0003] In traditional engineering, it is generally believed that RAP in cold recycling is a "black aggregate" and the old asphalt does not contribute to bonding. Existing studies have shown that the old asphalt in cold recycling contributes to the formation of strength. Therefore, the study of the contribution of the old asphalt in RAP to the cold recycled mixture is very important, which can prove that the emulsified asphalt cold recycling process is a fusion process of new and old asphalt. At the same time, the optimal new and old asphalt fusion ratio, optimal material selection and optimal preparation process of emulsified asphalt cold recycled mixture can also be further studied. Therefore, a set of methods to evaluate the extent to which the old asphalt in RAP plays a role is very important.

[0004] However, in the prior art, there is no reference ratio or method for the amount of old asphalt added to cold recycled mixtures. The reason why hot recycled mixtures cannot be referenced is that the old pavement material used in hot recycling technology is the surface layer, while cold recycling mainly uses the lower layer and the lower base layer. In addition, it is generally believed in the industry that the contribution rate of old asphalt in hot recycling technology can reach 100%, which has no reference value. Therefore, there is currently no relevant method to evaluate the addition of old asphalt to cold recycled mixtures. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for evaluating the contribution rate of old asphalt in cold recycled mixture, which can quantitatively evaluate the contribution rate of old asphalt in cold recycled mixture and provide guidance on how to maximize the use of old asphalt in cold recycled mixture.

[0006] The second purpose of the present invention is to provide an application of an evaluation method for the contribution rate of old asphalt in a cold recycled mixture, which can effectively adjust the optimal new and old asphalt fusion ratio, optimal material selection and optimal preparation process of the emulsified asphalt cold recycled mixture.

[0007] The first aspect of the present invention discloses a method for evaluating the contribution rate of old asphalt in a cold recycled mixture, comprising the following steps: Take the recycled mixture and make standard specimens.

[0008] A secondary compaction experiment was carried out on the specimens, and a scatter plot of the splitting strength of the specimens after the secondary compaction and different emulsified asphalt contents was drawn.

[0009] Determine the scatter plot fitting equation as ,in, is the oil-stone ratio corresponding to the quadratic function fitting, is the corresponding splitting strength after quadratic function fitting, , , is the coefficient of the quadratic fitting function. The splitting strength at the optimal emulsified asphalt dosage after function fitting is obtained by the quadratic function and recorded as A.

[0010] Take the points in the scatter plot from the zero point of emulsified asphalt to the optimal emulsified asphalt dosage range, perform a linear fit, and determine the fitting equation as follows: ,in is the oil-stone ratio corresponding to the linear function fitting, is the corresponding splitting intensity after linear function fitting, , is the coefficient of the linear fitting function. The splitting strength when the emulsified asphalt dosage is zero is obtained from the linear function and recorded as B.

[0011] In principle, after determining the splitting strength when the emulsified asphalt dosage is zero, the splitting strength value at the optimal emulsified asphalt dosage is used as a benchmark. The splitting strength value when the emulsified asphalt dosage is zero is determined to be mainly provided by the activated old asphalt cementation, so as to evaluate the contribution rate of the old asphalt.

[0012] The contribution rate is calculated according to the following formula: Contribution rate = (B ÷ A) × 100%.

[0013] Furthermore, the method to obtain the splitting strength at the optimal emulsified asphalt dosage after function fitting is: ,make , at this time, we obtain For the best oil-stone ratio, Substitute it into the quadratic fitting equation and obtain the highest splitting strength.

[0014] Furthermore, the method for selecting points in the range from the zero point of emulsified asphalt to the optimal emulsified asphalt dosage in the scatter plot is: ,make , to obtain The best oil-stone ratio is when the measured oil-stone ratio is greater than When the measured oil-stone ratio is less than , keep the corresponding points.

[0015] Preferably, in order to ensure the accuracy of the results and the repeatability of the test, the standard specimen is a Marshall standard specimen, which is compacted twice in a 25°C environment, compacted 100 times on both sides for the first time, and compacted 50 times on both sides again after curing.

[0016] Furthermore, the curing condition is 60° C. for 48 hours.

[0017] The second aspect of the present invention discloses the application of the evaluation method of the contribution rate of old asphalt in the cold recycled mixture in the preparation of the cold recycled mixture with old asphalt.

[0018] The present invention analyzes the contribution rate of old asphalt during the fusion of new and old asphalt in the cold regeneration process, and then evaluates the effect of old asphalt. By using the specific test and numerical fitting method, the Marshall specimen splitting strength when the emulsified asphalt dosage is zero can be estimated more accurately. By comparing the splitting strength of the specimen without adding emulsified asphalt with the splitting strength of the specimen with the optimal emulsified asphalt dosage, the contribution rate of old asphalt in RAP can be characterized.

[0019] Through this method, different processes, different emulsified asphalt dosages, or the interaction between new and old asphalt can be compared in engineering applications, and the application materials or methods that can maximize the contribution rate of old asphalt can be selected. At the same time, this method provides researchers with a new way to evaluate the application effect of emulsified asphalt cold recycling technology. Through a quantitative method, the originally abstract old asphalt effect is converted into a contribution rate indicator. In theory, while ensuring that the effect remains unchanged, the higher the contribution rate of old asphalt, the less resource waste.

[0020] The indicators for evaluating the contribution rate of old asphalt can also provide researchers with a new way to select materials. By increasing the contribution rate of old asphalt, the performance of recycled pavement can be effectively improved, and the use of old asphalt can be maximized, reducing resource waste and protecting the ecological environment.

[0021] In addition, there is currently no standardized evaluation method for the contribution rate of old asphalt in this field. The present invention adds an evaluation method for the optimal amount of new asphalt in the fusion of new and old asphalt, the optimal new asphalt type selection, etc., filling the gap in this area. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the relationship between the amount of emulsified asphalt and the splitting strength.

[0023] Figure 2 It is the regression relationship between emulsified asphalt type, dosage and splitting strength.

[0024] Figure 3It is less than the linear regression relationship between asphalt type, dosage and splitting strength when fitting the optimal emulsified asphalt dosage. DETAILED DESCRIPTION

[0025] The following embodiments and comparative examples are used to further describe the technical scheme of the present invention, so that those skilled in the art can understand and utilize the present invention well, but they are not intended to limit the scope of protection of the present invention.

[0026] The names and abbreviations of the experimental methods, production processes, instruments and equipment involved in the embodiments and comparative examples of the present invention are conventional names in the field and are very clear and unambiguous in the relevant application fields. Technicians in the field can understand the conventional process steps and apply the corresponding equipment based on the names and implement them according to conventional conditions or conditions recommended by the manufacturer.

[0027] The various raw materials or reagents used in the examples and comparative examples of the present invention are not particularly limited in their sources, and are all conventional products that can be purchased commercially. Example 1

[0028] Follow the steps below to conduct the test: 1) Take the recycled mixture and compact it twice in an environment of 25℃. That is, after compacting it 100 times on both sides for the first time, the specimen is cured at 60℃ for 48h and then compacted 50 times on both sides to make a Marshall standard specimen.

[0029] 2) The splitting strength test was carried out on the specimens, and the data obtained were shown in Table 1. A scatter plot of the splitting strength of the specimens and different emulsified asphalt contents was drawn, as shown in Table 1. Figure 1 Shown

[0030] 3) Determine the scatter plot fitting equation as ,in, is the oil-stone ratio corresponding to the quadratic function fitting, is the corresponding splitting intensity after quadratic function fitting.

[0031] Derivation ,make ,at this time, The optimal oil-stone ratio was obtained, and 3.07445 was substituted into the quadratic fitting equation to obtain the highest splitting strength of 0.69767.

[0032] 4) Take the points in the scatter plot from the zero point of emulsified asphalt to the optimal emulsified asphalt dosage range and perform a linear fit: Derivative ,make , to obtain The best oil-stone ratio is when the measured oil-stone ratio is greater than When the measured oil-stone ratio is less than , keep the corresponding points.

[0033] The fitting equation is determined as: ,in is the oil-stone ratio corresponding to the linear function fitting, It is the splitting strength corresponding to the linear function fitting. From this linear function, the splitting strength when the emulsified asphalt dosage is zero is 0.23371.

[0034] 5) Calculate contribution rate: Contribution rate = (0.23371 ÷ 0.69767) × 100% = 33.49865% It can be seen that the contribution rate of old asphalt in this cold recycled mixture is about 33.5%. Designing the cold recycled mixture according to this contribution rate can ensure the three-in-one superiority of environmental protection, cost and pavement performance.

[0035] It should be noted that 33.5% assumes that the cold recycled mixture is in the best condition. The contribution of old asphalt to strength formation is a concept under ideal conditions and does not mean that the actual addition amount is 33.5% of the total asphalt. Due to the huge total amount of various materials used in actual operations, the conventional system error will become larger as the total amount of materials increases, and the impurities in the old asphalt will also affect the test results. After testing, it is found that the optimal ratio is still around 33.5%, with a fluctuation of no more than 1%. Therefore, in practice, operators can directly use 33.5%, or they can take samples and conduct tests within the range of 33.5%±1% to obtain the actual optimal addition ratio. Example 2 Contribution of old asphalt in RAP to the cementing system

[0036] In this embodiment, three common emulsified asphalts (labeled as 1, 2, and 3) were selected for contribution rate detection test. Before the test, the raw materials of the recycled mixture were uniformly kept warm at 25°C.

[0037] Two compaction tests were carried out at 25°C. The first compaction test was 100 times on both sides. The specimens were cured at 60°C for 48 hours and then compacted 50 times on both sides to form Marshall standard specimens with different emulsified asphalt types and different asphalt contents. There were 5 parallel specimens under each test condition.

[0038] According to the method described in Example 1, the relationship between the type and content of different emulsified asphalts and the splitting strength of the mixture after secondary compaction was studied, and the measured values ​​of the splitting strength of the three asphalts were obtained as shown in Table 2. It was plotted into a scatter plot, and the result was Figure 2 .from Figure 2It can be seen that the splitting strength of each asphalt increases first and then decreases with the increase of the oil-stone ratio. In the interval where the emulsified asphalt dosage is less than the optimal emulsified asphalt content, the splitting strength gradually increases with the increase of the emulsified asphalt dosage. When the emulsified asphalt dosage is greater than the optimal content, the splitting strength begins to decrease. The corresponding value of the highest point of the fitting curve is calculated by polynomial fitting, that is, the splitting strength A at the optimal emulsified asphalt dosage before fitting. The optimal oil-stone ratios of emulsified asphalt 1, emulsified asphalt 2, and emulsified asphalt 3 are 3.1%, 3.4%, and 3.3%, respectively, and the corresponding splitting strengths are 0.70MPa, 0.78MPa, and 0.89MPa, respectively.

[0039] According to the evaluation steps, all measured numerical points after the maximum splitting strength of each asphalt are discarded, and the undiscarded points are used for further linear fitting. Figure 2 In fact, the regression line after linear regression extends in the opposite direction and crosses the coordinate axis vertically. At this time, the splitting strength when the oil-stone ratio is 0 is calculated, which is the splitting strength B when the emulsified asphalt dosage is 0 after fitting. The splitting strengths of emulsified asphalt 1, 2 and 3 mixtures are 0.22MPa, 0.22MPa and 0.35MPa respectively. The contribution rate is calculated by the formula, and the contribution rates of the old asphalt corresponding to the three emulsified asphalts are 31.4%, 28.2% and 39.3% respectively. Example 3

[0040] Test steps: 1) Take an unknown old asphalt sample and a new asphalt sample, and test them according to the steps described in Example 1. Calculate the contribution rate to be 31.4%. Prepare and obtain cold recycled mixture A according to the proportion described in the contribution rate, and prepare test pieces; 2) Set up a control group. The details of the control group are as follows: Positive control: Use new asphalt to prepare the specimen; Control group: The specimens were prepared using different proportions of new and old asphalt. In control group 1, the mass of old asphalt accounted for about 20.3% of the total mass, and the mass of new asphalt accounted for 79.7%. In control group 2, the mass of old asphalt accounted for about 34.0%, and the mass of new asphalt accounted for about 66%.

[0041] 3) Referring to the existing standards, the common test parameters of cold recycled mixture A, positive control and two control groups were compared. The results are shown in Table 3

[0042] Note: The data here refers to the mass of asphalt in 1kg of mixture (the same applies to the price calculation below) As can be seen from Table 3, the optimal amount of emulsified asphalt is 0.031kg of new asphalt added to every 1kg of mixture in Group A. The average amount of old asphalt is about 0.014kg per kilogram of old RAP material. The positive control is to remove the old asphalt in the mixture, and uniformly use 0.045kg (0.014+0.031) of new asphalt for testing. Control group 1 is a test group with the same amount of old asphalt and more new asphalt. At this time, about 0.014kg of old asphalt is still ignored in 1kg of old mixture, and 0.055kg of new asphalt is added on this basis. The old mixture used in control group 2 contains 0.016kg of old asphalt. Compared with group A, 0.031kg of new asphalt is also added. The four groups of samples were tested separately. After comparison, the test results of group A were the same as those of the positive control group, and the data difference was very small. The control groups 1 and 2 with the mass ratio of old asphalt to new asphalt of about 2:8 and 3.4:6.6 were far different from group A.

[0043] In addition, the data on the amount of new and old asphalt added and the contribution rate of Test Group A are not exactly the same. The reason is also mentioned in Example 1, that is, the amount added in actual operation will have a slight difference from the calculated contribution rate. Therefore, this test group simulated possible situations and conducted tests on values ​​near the calculated contribution rate to obtain the actual optimal addition amount affected by multiple factors, and applied it to Test Group A.

[0044] Then the cost of the above three groups of samples is calculated, and the results are shown in Table 4.

[0045] From the experience of technicians in this field, it is known that the performance of materials made of all new asphalt is of course better. However, from the test results in Table 3, it can be seen that the splitting strength and freeze-thaw splitting strength of the cold recycled mixture with the optimal proportion of old asphalt added are not much different from those made of all new asphalt.

[0046] In the actual pavement paving and maintenance operation site, one kilometer of two-way four-lane road requires about 350 tons of asphalt, two-way six-lane road requires about 500 tons, and two-way eight-lane road requires about 700 tons. Combined with the information in Table 4, it can be seen that after calculation, the mixture with a certain proportion of old asphalt has the lowest cost. The difference between Group A and the positive control group in this embodiment is only 60.2 yuan / ton. For only a 100-kilometer road in an ordinary province, the cost difference can reach at least 2.1 million yuan. What's more, the current domestic expressways have reached 184,000 kilometers, and national and provincial roads have reached a total of 788,100 kilometers. For renovating a road, the cost of paving new asphalt throughout the whole process is very high, especially when the old road surface needs maintenance and renovation. Using cold recycled mixture in combination with old asphalt can save operating costs and ensure the durability of the pavement, and achieve green development and sustainable development.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the contribution rate of old asphalt in cold recycled mixture, comprising the following steps: Take the recycled mixture and make a standard test piece; A secondary compaction experiment is performed on the specimen, and a scatter plot of the splitting strength of the specimen after the secondary compaction and different emulsified asphalt contents is drawn; Determine the scatter plot fitting equation as ,in, is the oil-stone ratio corresponding to the quadratic function fitting, is the corresponding splitting strength after quadratic function fitting, , , is the coefficient of the quadratic fitting function, and the splitting strength at the optimal emulsified asphalt dosage after function fitting is obtained by the quadratic function, which is recorded as A; Take the points in the scatter plot from the zero point of emulsified asphalt to the optimal emulsified asphalt dosage range, perform a linear fit, and determine the fitting equation as follows: ,in is the oil-stone ratio corresponding to the linear function fitting, is the corresponding splitting intensity after linear function fitting, , is the coefficient of the linear fitting function, and the splitting strength when the emulsified asphalt dosage is zero is obtained from the linear function, which is recorded as B; The contribution rate is calculated according to the following formula: Contribution rate = (B ÷ A) × 100%.

2. The evaluation method according to claim 1, wherein the method for obtaining the splitting strength at the optimal emulsified asphalt dosage after function fitting is: deriving ,make , at this time, we obtain For the best oil-stone ratio, Substitute it into the quadratic fitting equation and obtain the highest splitting strength.

3. The evaluation method according to claim 1, wherein the method for selecting points in the range from the zero point of emulsified asphalt to the optimal emulsified asphalt dosage in the scatter plot is: ,make , to obtain The best oil-stone ratio is when the measured oil-stone ratio is greater than When the measured oil-stone ratio is less than , keep the corresponding points.

4. The evaluation method according to claim 1, wherein the standard specimen is a Marshall standard specimen, which is compacted twice in a 25°C environment, compacted 100 times on both sides for the first time, and compacted 50 times on both sides again after curing.

5. The evaluation method according to claim 4, wherein the curing condition is 60°C for 48 hours.

6. An application of the evaluation method according to claim 1 in preparing cold recycled mixture from old asphalt.

Images