A method for determining the construction retention time of a polyurethane mixture

Abstract

The present invention provides a method for determining the construction retention time of a polyurethane mixture, which comprises the following steps: preparing a polyurethane mixture; placing the polyurethane mixture in a constant temperature and humidity environment, and measuring the CO2 concentration value in the constant temperature and humidity environment; obtaining a relationship curve between the CO2 concentration value and time; and determining the construction retention time of the polyurethane mixture based on the relationship curve. The method for determining the construction retention time of the polyurethane mixture of the present invention is simple to operate, can more truly reflect the construction retention characteristics under actual external environmental conditions, and can fully ensure the compaction quality of the polyurethane pavement; the present invention provides a simple and quantifiable operation method for determining the construction retention time of the polyurethane mixture, avoids the influence of human factors, guarantees the optimal compaction quality of the polyurethane pavement, and improves the service performance of the polyurethane pavement.

Description

Technical Field

[0001] The present invention relates to a method for determining the construction retention time of polyurethane mixture, belonging to the field of road engineering materials. Background Art

[0002] Petroleum asphalt is one of the most widely used binder materials for highway pavements in China. However, as a by-product of the petroleum refining industry, petroleum asphalt is not a high-performance binder material and has many disadvantages such as high temperature sensitivity and poor adhesion to aggregates. As a result, asphalt pavements with petroleum asphalt as the binder are prone to diseases such as cracks, rutting, loose potholes, etc. under the combined action of heavy traffic volume, heavy traffic load, and complex climate environment, with a short design life and a less-than-satisfactory actual service life. In addition, as a by-product of the petroleum refining industry, petroleum asphalt will inevitably be gradually replaced as the "dual carbon goal" and the acceleration of the pace of fossil energy substitution progress. Therefore, to achieve the sustainable development of highway traffic infrastructure, it is urgent to research and develop a new generation of environmentally friendly and high-performance binder materials that can replace traditional asphalt binders in the post-petroleum era and change the road material technology system.

[0003] In recent years, road-use polyurethane binders have attracted extensive attention in the domestic and foreign highway engineering fields. Polyurethane (PU) is a general term for a class of synthetic polymer compounds with diverse forms and wide applications, containing repeating urethane groups (-NHCOO-) in the main chain. Research has found that polyurethane is formed by mixing polyol and isocyanate in a certain ratio and curing at room temperature. It has a strong bond with aggregates and exhibits excellent mechanical strength, wear resistance, elasticity, and resilience. Therefore, polyurethane has the technical characteristics to become a high-performance pavement binder.

[0004] Polyurethane mixtures are produced and constructed at room temperature, which can greatly reduce the energy consumption, pollutants, and greenhouse gas emissions during the construction process of traditional asphalt pavements, and contribute to the realization of the "dual carbon" goal in the highway engineering field. At the same time, polyurethane mixtures have excellent mechanical properties, and the durability and service life of polyurethane pavements will be significantly improved compared with asphalt pavements.

[0005] However, as a new type of polymer material, the formation of the strength of polyurethane requires a certain time of curing reaction, and this curing reaction is greatly affected by environmental temperature and humidity, which is completely different from asphalt mixtures. And the progress of this curing reaction will directly affect the construction retention time of polyurethane mixtures, and then affect the compaction quality of polyurethane pavements. At present, the determination of the construction retention time of asphalt mixtures mainly relies on the viscosity-temperature curve, and the compaction timing is determined by testing the viscosity in different temperature ranges. However, as a cold mix and cold lay material, polyurethane mixtures cannot use the viscosity-temperature curve to determine the compaction timing.

[0006] Therefore, researching a method for determining the construction retention time of polyurethane mixture has become a technical problem to be solved urgently. Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] During the curing reaction process of polyurethane, isocyanate will react with water to generate unstable carbamic acid, and then carbamic acid decomposes into other substances such as CO2 gas. If the polyurethane mixture is compacted too early after mixing, it will be difficult for the generated CO2 to be released, resulting in swelling after the road surface is formed. If it is compacted too late, the compaction degree will be poor due to a high degree of curing. Therefore, combining the material characteristics of the polyurethane mixture to determine the retention time of the polyurethane mixture, that is, the compaction timing, is crucial for ensuring the quality of the polyurethane road surface.

[0009] In view of the technical problems existing in the prior art, the present invention utilizes the characteristic that CO2 is generated during the curing reaction process of the polyurethane mixture. By detecting the CO2 release amount of the polyurethane mixture and combining the actual construction temperature and humidity conditions, a method for determining the construction retention time of the polyurethane mixture is proposed.

[0010] The operation method for determining the construction retention time of the polyurethane mixture of the present invention is simple, can more truly reflect the construction retention characteristics under the actual external environmental conditions, and can fully ensure the compaction quality of the polyurethane road surface.

[0011] The present invention provides a simple and quantifiable operation method for determining the construction retention time of the polyurethane mixture, avoiding the influence of human factors, ensuring the optimal compaction quality of the polyurethane road surface, improving the service performance of the polyurethane road surface, and having important significance for promoting the application of polyurethane, an environmentally friendly and high-performance binder material, in the post-petroleum era.

[0012] Solutions for Solving the Problems

[0013] The present invention provides a method for determining the construction retention time of a polyurethane mixture, which includes the following steps:

[0014] Prepare the polyurethane mixture;

[0015] Place the polyurethane mixture in a constant temperature and humidity environment, and measure the CO2 concentration value in the constant temperature and humidity environment;

[0016] Obtain the relationship curve between the CO2 concentration value and time;

[0017] Based on the relationship curve, determine the construction retention time of the polyurethane mixture.

[0018] The method according to the present invention, wherein the temperature of the constant temperature and humidity environment is the same as the average temperature of the construction environment; the humidity of the constant temperature and humidity environment is the same as the average humidity of the construction environment.

[0019] The method according to the present invention, wherein the CO2 concentration value in the constant temperature and humidity environment is measured at the same time interval to obtain a relationship curve between the CO2 concentration value and time.

[0020] The method according to the present invention, wherein the time interval is 1 - 60 min.

[0021] The method according to the present invention, wherein the construction residence time is near the inflection point of the relationship curve.

[0022] The method according to the present invention, wherein the polyurethane mixture includes mineral aggregate, mineral powder and polyurethane.

[0023] The method according to the present invention, wherein in the polyurethane mixture, based on the total mass of the mineral aggregate and the mineral powder being 100%, the content of the mineral aggregate is 90 - 99%; the content of the mineral powder is 1 - 10%; the addition amount of the polyurethane is 1 - 10%.

[0024] The method according to the present invention, wherein the preparation method of the polyurethane mixture includes the step of mixing the mineral aggregate, the mineral powder and the polyurethane.

[0025] The method according to the present invention, wherein the preparation method includes first mixing the mineral aggregate and then mixing it with the polyurethane, and finally mixing it with the mineral powder.

[0026] The method according to the present invention, wherein based on the total mass of the mineral aggregate and the mineral powder being 100%, the content of the mineral aggregate with a particle size of 11 - 16 mm is 20 - 40%; the content of the mineral aggregate with a particle size of 6 - 11 mm is 20 - 40%; the content of the mineral aggregate with a particle size of 3 - 6 mm is 1 - 20%; the content of the mineral aggregate with a particle size of 0 - 3 mm is 20 - 40%.

[0027] Advantages of the Invention

[0028] The method for the construction residence time of the polyurethane mixture of the present invention is simple to operate, can more truly reflect the construction residence characteristics under actual external environmental conditions, and can fully ensure the compaction quality of the polyurethane pavement;

[0029] The present invention provides a simple and quantifiable operation method for determining the construction residence time of the polyurethane mixture, avoids the influence of human factors, ensures the optimal compaction quality of the polyurethane pavement, and improves the service performance of the polyurethane pavement. Brief Description of the Drawings

[0030] Figure 1 Schematic diagram showing the change of CO2 concentration over time in an embodiment of the present invention;

[0031] Figure 2 Showing the change of CO2 concentration over time in the polyurethane mixture of Embodiment 1 of the present invention;

[0032] Figure 3 Showing the change of CO2 concentration over time in the polyurethane mixture of Embodiment 2 of the present invention;

[0033] Figure 4 Showing the change of CO2 concentration over time in the polyurethane mixture of Embodiment 1 of the present invention. Detailed implementation manners

[0034] The following will detail various exemplary embodiments, features and aspects of the present invention. The special word "exemplary" here means "serving as an example, embodiment or illustrative". Any embodiment described as "exemplary" here does not have to be construed as superior or better than other embodiments.

[0035] In addition, for better illustration of the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present invention can also be implemented without some specific details. In other instances, methods, means, equipment and steps well-known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

[0036] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0037] In this specification, the meaning expressed by using "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0038] In this specification, the "some specific / preferred implementation manners", "other specific / preferred implementation manners", "implementation manners", etc. mentioned refer to the specific elements (for example, features, structures, properties and / or characteristics) related to the implementation manner described, which are included in at least one of the implementation manners described here, and may or may not exist in other implementation manners. In addition, it should be understood that the elements can be combined in various implementation manners in any suitable way.

[0039] In this specification, the numerical range represented by using "numerical value A~numerical value B" refers to the range including the endpoint numerical values A and B.

[0040] In this specification, when "normal temperature" or "room temperature" is used, the temperature can be 10 - 25°C.

[0041] The present invention provides a method for determining the construction retention time of a polyurethane mixture, which comprises the following steps:

[0042] Prepare the polyurethane mixture;

[0043] Place the polyurethane mixture in a constant temperature and humidity environment, and measure the CO2 concentration value in the constant temperature and humidity environment;

[0044] Obtain the relationship curve between the CO2 concentration value and time;

[0045] Based on the relationship curve, determine the construction retention time of the polyurethane mixture.

[0046] The present invention utilizes the characteristic that CO2 is generated during the curing process of the polyurethane mixture. By testing the change data of the CO2 release amount over time, a change curve is plotted, and the construction retention time of the polyurethane mixture is determined through a set CO2 release amount range. The method is simple, reliable, easy to operate, and can effectively ensure the compaction quality of the polyurethane pavement in the later stage.

[0047] In some specific embodiments, the temperature of the constant temperature and humidity environment is the same as the average temperature of the construction environment; the humidity of the constant temperature and humidity environment is the same as the average humidity of the construction environment. By making the temperature and humidity of the constant temperature and humidity environment the same as the average temperature and average humidity of the construction environment, the measurement results can be made as accurate as possible. The meaning of the construction environment is the external environment on the day of construction.

[0048] Regarding the provision of the constant temperature and humidity environment, the present invention does not make a special limitation. Generally, a constant temperature and humidity control box can be used to provide the constant temperature and humidity environment. By adjusting the control parameters of the constant temperature and humidity control box, the internal temperature and humidity of the constant humidity control box can reach the predetermined values.

[0049] In some specific embodiments, the CO2 concentration value in the constant temperature and humidity environment is measured at the same time interval to obtain the relationship curve between the CO2 concentration value and time. By measuring the CO2 concentration value in the constant temperature and humidity environment at the same time interval, the measurement results can be made more accurate. Specifically, in the present invention, the time interval is 1 - 60 min, preferably 5 - 30 min, for example: 10 min, 15 min, 20 min, 25 min, 35 min, 40 min, 45 min, 50 min, 55 min, etc. When the interval time is 1 - 60 min, the time interval is appropriate, which will not cause the test process to be too long and can also obtain accurate measurement results.

[0050] For the detection of CO2 concentration values, a fully automatic real-time CO2 detector can be used for detection. Initially, a fully automatic real-time CO2 detector can be placed inside the constant temperature and humidity environment, and after waiting for 10 - 60 s, the CO2 concentration value displayed by the fully automatic real-time CO2 detector inside the constant temperature and humidity control box can be read. To facilitate the observation of the data of the fully automatic real-time CO2 detector, the fully automatic real-time CO2 detector can be placed at a position close to the glass door inside the constant temperature and humidity control box.

[0051] Specifically, the construction retention time is near the inflection point of the relationship curve. The inventor found that the time corresponding to the position near the inflection point is the construction retention time. For the confirmation near the inflection point, generally two tangents can be drawn on the curve, and the time corresponding to the intersection position of the tangents is the inflection point. The vicinity of the inflection point is generally about plus or minus 15 min from the inflection point position.

[0052] Furthermore, for the polyurethane mixture, the present invention is not particularly limited and can be a polyurethane mixture commonly used in the art. Specifically, the polyurethane mixture may include mineral aggregates, mineral powder, and polyurethane. For the polyurethane, it can be a two-component polyurethane or a one-component polyurethane, and the present invention preferably uses a one-component polyurethane.

[0053] In some specific embodiments, in the polyurethane mixture, based on the total mass sum of the mineral aggregates and the mineral powder being 100%, the content of the mineral aggregates is 90 - 99%, for example: 92%, 94%, 96%, 98%, etc.; the content of the mineral powder is 1 - 10%, for example: 2%, 4%, 6%, 8%, etc.; the addition amount of the polyurethane is 1 - 10%, for example: 2%, 4%, 6%, 8%, etc.

[0054] For the selection of the mineral aggregates, the present invention is not particularly limited and can be any commonly used mineral aggregates in the art as long as the corresponding polyurethane mixture can be prepared, for example: AC-13 graded mineral aggregates.

[0055] Specifically, in the present invention, the proportion of the mineral material grading is as follows: based on the total mass of the mineral material and the mineral powder as 100%, the content of the mineral material with a particle size of 11-16 mm is 20-40%, for example: 22%, 25%, 28%, 30%, 32%, 35%, 38% and the like; the content of the mineral material with a particle size of 6-11 mm is 20-40%, for example: 22%, 25%, 28%, 30%, 32%, 35%, 38% and the like; the content of the mineral material with a particle size of 3-6 mm is 1-20%, for example: 2%, 5%, 8%, 10%, 12%, 15%, 18% and the like; the content of the mineral material with a particle size of 0-3 mm is 20-40%, for example: 22%, 25%, 28%, 30%, 32%, 35%, 38% and the like. When the above-mentioned graded mineral material ratio is used, the test results are more accurate.

[0056] The present invention does not particularly limit the preparation method of the polyurethane mixture, and the polyurethane mixture can be prepared as required. Specifically, the preparation method of the polyurethane mixture includes the steps of mixing mineral material, mineral powder and polyurethane.

[0057] Furthermore, in the present invention, the method for preparing the polyurethane mixture includes first mixing the mineral material, then mixing it with the polyurethane, and finally mixing it with the mineral powder.

[0058] Specifically, the mineral material is poured into a mixing pot and stirred for 10 to 15 seconds; then the polyurethane is added and stirred for 15 to 25 seconds; finally, the mineral powder is added and stirred for 20 to 30 seconds, thereby preparing a polyurethane mixture.

[0059] Specifically, the method for determining the construction residence time of the polyurethane mixture comprises the following steps:

[0060] 1. Select the polyurethane, various grades of mineral materials and mineral powder used in the project and set them aside.

[0061] 2. Select a constant temperature and humidity control box with a glass door and keep it for future use.

[0062] 3. Check the average temperature and humidity on the day of polyurethane mixture construction, and use this temperature and humidity as the temperature and humidity environment for the polyurethane mixture construction retention time test. Adjust the control parameters of the constant temperature and humidity control box so that the temperature and humidity inside the constant humidity control box reach the preset values.

[0063] 4. At room temperature, pour each grade of mineral material into the mixing pot according to the set ratio and mix for 10 to 15 seconds; then add the set proportion of polyurethane and mix for 15 to 25 seconds; finally add the set proportion of mineral powder and mix for 20 to 30 seconds. At this point, the mixing process of the polyurethane mixture is completed.

[0064] 5. Immediately scoop out the mixed polyurethane mixture and place it in a dry and clean stainless-steel tray. Then, immediately place the stainless-steel tray containing the polyurethane mixture at the central position of a constant temperature and humidity control box that has reached the preset temperature and humidity. Place a CO2 full-automatic real-time detector at a position close to the glass door of the box. Then close the box door and wait for 10 - 60 s, and then read the CO2 concentration value displayed by the CO2 full-automatic real-time detector inside the constant temperature and humidity control box.

[0065] 6. Subsequently, read and record the CO2 concentration value every 1 - 60 min until the CO2 concentration value tends to be stable, and then end the test.

[0066] 7. Plot the curve of the CO2 concentration value changing with time, and inversely deduce the time inflection point t c (as Figure 1 shown), and take the time range of t c ±15 min as the construction tolerance time of the polyurethane mixture.

[0067] Example

[0068] The following will describe the implementation scheme of the present invention in detail in combination with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0069] In the example, the manufacturer of the one-component polyurethane is Wanhua Chemical Group Co., Ltd.

[0070] Example 1

[0071] 1. Select the one-component polyurethane, various grades of aggregates and mineral powder used in the project for standby. The gradation of the polyurethane mixture is shown in Table 1 below. Among them, the meaning of the rubber-aggregate ratio is based on the total mass of the aggregates and mineral powder being 100%, and the content of the one-component polyurethane is 4.8%.

[0072] Table 1 Gradation of the polyurethane mixture

[0073]

[0074] 2. Select a constant temperature and humidity control box with a glass door for standby.

[0075] 3. Query the average temperature and humidity on the day of the polyurethane mixture construction. The temperature is 23 °C and the humidity is 65%. Use this temperature and humidity as the temperature and humidity environment during the test of the construction tolerance time of the polyurethane mixture. Adjust the control parameters of the constant temperature and humidity control box to a temperature of 23 °C and a humidity of 65% so that the internal temperature and humidity of the constant humidity control box reach the set value.

[0076] 4. At room temperature, pour each grade of mineral material into the mixing pot according to the set ratio, including 6 kg of mineral material with a particle size of 11-16 mm, 4.8 kg of mineral material with a particle size of 6-11 mm, 3 kg of mineral material with a particle size of 3-6 mm, and 5.4 kg of mineral material with a particle size of 0-3 mm. Mix for 12 seconds; then add 0.96 kg of single-component polyurethane and mix for 20 seconds; finally add 0.8 kg of mineral powder and mix for 25 seconds. At this point, the mixing process of the polyurethane mixture is completed.

[0077] 5. Immediately scoop out the mixed polyurethane mixture and put it into a dry and clean stainless steel tray, and immediately place the stainless steel tray containing the polyurethane mixture into the center of the constant temperature and humidity control box that has reached the set temperature and humidity. Place a CO2 fully automatic real-time detector near the glass door, then close the door, wait for 30 seconds and read the CO2 concentration value displayed by the CO2 fully automatic real-time detector in the constant temperature and humidity control box. At this time, the CO2 concentration value is 517ppm.

[0078] 6. Then read and record the CO2 concentration value every 10 minutes until the CO2 concentration value stabilizes, then end the test.

[0079] 7. Draw a curve of CO2 concentration versus time, such as Figure 2 shown.

[0080] 8. Basis Figure 2 The relationship curve shown in the figure obtains the time inflection point t c (like Figure 2 As shown), determine t c It is 163min, so the construction residence time of the polyurethane mixture is 148min~178min, that is, within this time range, the polyurethane mixture can obtain excellent compaction quality from the completion of mixing to the completion of paving and rolling.

[0081] 9. To verify the compaction quality within this time range, repeat steps 1 to 4 above.

[0082] 10. Immediately scoop out the mixed polyurethane mixture and put it into a dry and clean stainless steel tray, and immediately put the stainless steel tray containing the polyurethane mixture into the center of a constant temperature and humidity control box that has reached the set temperature and humidity, then close the box door, take it out after 160 minutes (i.e., the retention time is 160 minutes), and compact it to form a Marshall specimen. The molding method refers to T0702-2011 in the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). The molded specimens are cured at room temperature for 48 hours, and then demolded to test the void ratio of the specimens.

[0083] 11. Repeat steps 9 to 10 to test the void ratio of the specimen when the retention time is 60 min, 120 min, 210 min, and 260 min respectively. The test results are shown in Table 2.

[0084] Table 2 Void ratio of polyurethane mixture under different residence time conditions

[0085]

[0086] It is known that the design void ratio of polyurethane mixture is 3% to 5%. As shown in Table 2, when the construction retention time is 160 minutes, the void ratio of polyurethane mixture meets the design requirements, thus effectively ensuring the performance of polyurethane pavement. When the retention time is less than 148 minutes or greater than 178 minutes, the void ratio of polyurethane mixture does not meet the requirements. On the one hand, because the retention time is short, the release of CO2 after compaction is still large, resulting in the volume expansion of polyurethane mixture, reflecting the increase of void ratio; on the other hand, because the retention time is too long, the degree of curing of polyurethane is high at this time, and it has a certain strength, which makes it difficult to compact the polyurethane mixture, reflecting the increase of void ratio.

[0087] Example 2

[0088] 1. Select the single-component polyurethane, various grades of mineral materials and mineral powder used in the project and set them aside. The gradation of the polyurethane mixture is shown in Table 3 below, where the rubber-stone ratio means that the total mass of the mineral materials and mineral powder is 100%, and the content of the single-component polyurethane is 5.5%.

[0089] Table 3 Grading of polyurethane mixture

[0090]

[0091] 2. Select a constant temperature and humidity control box with a glass door and keep it for future use.

[0092] 3. Check the average temperature and humidity on the day of polyurethane mixture construction. The temperature is 35°C and the humidity is 85%. This temperature and humidity are used as the temperature and humidity environment for the polyurethane mixture construction retention time test. Adjust the control parameters of the constant temperature and humidity control box to 35°C and 85% so that the temperature and humidity inside the constant humidity control box reach the set values.

[0093] 4. At room temperature, pour each grade of mineral material into the mixing pot according to the set ratio, including 4.4kg of mineral material with a particle size of 11-16mm, 7kg of mineral material with a particle size of 6-11mm, 1.2kg of mineral material with a particle size of 3-6mm, and 6kg of mineral material with a particle size of 0-3mm. Mix for 14s; then add 1.1kg of single-component polyurethane and mix for 23s; finally add 1.4kg of mineral powder and mix for 22s. At this point, the mixing process of the polyurethane mixture is completed.

[0094] 5. Immediately scoop out the mixed polyurethane mixture and place it in a dry and clean stainless-steel tray. Then, immediately place the stainless-steel tray containing the polyurethane mixture at the center position of a constant temperature and humidity control box that has reached the set temperature and humidity. Place a CO2 fully automatic real-time detector near the glass door of the box. Then close the box door. After waiting for 30 s, read the CO2 concentration value displayed by the CO2 fully automatic real-time detector in the constant temperature and humidity control box. At this time, the CO2 concentration value is 703 ppm.

[0095] 6. Subsequently, read and record the CO2 concentration value every 10 min until the CO2 concentration value tends to be stable, and then end the test.

[0096] 7. Plot the relationship curve of the CO2 concentration value versus time, as Figure 3 shown.

[0097] 8. Obtain the time inflection point t c based on the curve, and determine that t c is 116 min. Therefore, the construction retention time of the polyurethane mixture is 101 min - 131 min. That is, within this time range, excellent compaction quality can be obtained from the completion of mixing to the completion of paving and rolling of the polyurethane mixture.

[0098] 9. To verify the compaction quality within this time range, repeat steps 1 - 4 above.

[0099] 10. Immediately scoop out the mixed polyurethane mixture and place it in a dry and clean stainless-steel tray. Then, immediately place the stainless-steel tray containing the polyurethane mixture at the center position of a constant temperature and humidity control box that has reached the set temperature and humidity. Then close the box door and take it out at 115 min (i.e., the retention time is 115 min) to compact and form Marshall specimens. The forming method refers to T0702 - 2011 in the "Test Procedures for Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E20 - 2011). The formed specimens are cured at room temperature for 48 h, and then the void ratio of the specimens is measured after demolding.

[0100] 11. Repeat steps 9 - 10, and measure the void ratio of the specimens at retention times of 55 min, 115 min, 175 min, and 235 min respectively. The test results are shown in Table 4.

[0101] Table 4 Void ratios of polyurethane mixtures under different retention time conditions

[0102]

[0103] It is known that the design void ratio of polyurethane mixture is 3% to 5%. It can be seen from Table 4 that when the construction retention time is 115 minutes, the void ratio of polyurethane mixture meets the design requirements, thereby effectively ensuring the performance of polyurethane pavement. When the retention time is less than 101 minutes or greater than 131 minutes, the void ratio of polyurethane mixture does not meet the requirements. On the one hand, because the retention time is short, the release of CO2 after compaction is still large, resulting in the volume expansion of polyurethane mixture, reflecting the increase of void ratio; on the other hand, because the retention time is too long, the degree of curing of polyurethane is high at this time, and it has a certain strength, which makes it difficult to compact the polyurethane mixture, reflecting the increase of void ratio.

[0104] Example 3

[0105] 1. Select the single-component polyurethane, various grades of mineral materials and mineral powder used in the project and set them aside. The gradation of the polyurethane mixture is shown in Table 5 below, where the rubber-stone ratio means that the total mass of the mineral materials and mineral powder is 100%, and the content of the single-component polyurethane is 4.7%.

[0106] Table 5 Grading of polyurethane mixture

[0107]

[0108] 2. Select a constant temperature and humidity control box with a glass door and keep it for future use.

[0109] 3. Check the average temperature and humidity on the day of polyurethane mixture construction. The temperature is 16°C and the humidity is 32%. This temperature and humidity are used as the temperature and humidity environment for the polyurethane mixture construction retention time test. Adjust the control parameters of the constant temperature and humidity control box to 16°C and 32% so that the temperature and humidity inside the constant humidity control box reach the set values.

[0110] 4. At room temperature, pour each grade of mineral material into the mixing pot according to the set ratio, including 6 kg of mineral material with a particle size of 11-16 mm, 7.6 kg of mineral material with a particle size of 6-11 mm, 0.6 kg of mineral material with a particle size of 3-6 mm, and 5 kg of mineral material with a particle size of 0-3 mm. Mix for 15 seconds; then add 0.94 kg of single-component polyurethane and mix for 21 seconds; finally add 0.8 kg of mineral powder and mix for 24 seconds. At this point, the mixing process of the polyurethane mixture is completed.

[0111] 5. Immediately take out the mixed polyurethane mixture and put it into a dry and clean stainless steel tray, and immediately put the stainless steel tray containing the polyurethane mixture into the center of the constant temperature and humidity control box which has reached the set temperature and humidity. Place a CO2 automatic real-time detector near the glass door, and then close the door. Wait for 30 seconds and read the CO2 concentration value displayed by the CO2 automatic real-time detector in the constant temperature and humidity control box. At this time, the CO2 concentration value is 359ppm.

[0112] 6. Subsequently, read and record the CO2 concentration value every 10 minutes until the CO2 concentration value tends to be stable, and then end the test.

[0113] 7. Plot the relationship curve of the CO2 concentration value versus time, as Figure 4 shown.

[0114] 8. Obtain the time inflection point t c based on the curve, and determine that t c is 212 minutes. Therefore, the construction retention time of the polyurethane mixture is 197 minutes to 227 minutes. That is, within this time range, excellent compaction quality can be obtained from the completion of mixing to the completion of paving and rolling of the polyurethane mixture.

[0115] 9. To verify the compaction quality within this time range, repeat steps 1 - 4 above.

[0116] 10. Immediately scoop out the mixed polyurethane mixture and place it in a dry and clean stainless - steel tray. Then, immediately place the stainless - steel tray containing the polyurethane mixture at the center position of a constant - temperature and humidity - controlled chamber that has reached the set temperature and humidity. Then close the chamber door, take it out at 210 minutes (i.e., the retention time is 210 minutes), and compact and form Marshall specimens. The forming method refers to T0702 - 2011 in the "Test Procedures for Bitumen and Bituminous Mixtures for Highway Engineering" (JTG E20 - 2011). The formed specimens are cured at room temperature for 48 hours, and then the void ratio of the specimens is tested after demolding.

[0117] 11. Repeat steps 9 - 10, and test the void ratio of the specimens at retention times of 110 minutes, 160 minutes, 210 minutes, and 260 minutes respectively. The test results are shown in Table 6.

[0118] Table 6 Void ratios of polyurethane mixtures under different retention time conditions

[0119]

[0120] It is known that the designed void ratio of the polyurethane mixture is 3% - 5%. From Table 6, it can be seen that when the construction retention time is 115 minutes, the void ratio of the polyurethane mixture meets the design requirements, thus effectively ensuring the service performance of the polyurethane pavement. When the retention time is less than 197 minutes or greater than 227 minutes, the void ratio of the polyurethane mixture does not meet the requirements. On the one hand, because the retention time is short, the release amount of CO2 after compaction is still large, resulting in the volume expansion of the polyurethane mixture, reflecting an increase in the void ratio; on the other hand, because the retention time is too long, at this time the degree of curing of the polyurethane is relatively high and it already has a certain strength, resulting in difficulty in compacting the polyurethane mixture, reflecting an increase in the void ratio.

[0121] Therefore, reasonably determining the construction retention time of the polyurethane mixture is crucial for ensuring the compaction quality of the polyurethane mixture. The method proposed by the present invention is simple, scientific and reliable. Generally, the lower the temperature and humidity, the longer the construction retention time, and the same variation law is presented for different aggregate gradations and binder-aggregate ratios. Moreover, it can more realistically simulate the actual external temperature and humidity environmental conditions during the construction period of the polyurethane pavement, having direct engineering guiding significance.

[0122] It should be noted that although the technical solutions of the present invention are introduced by specific examples, those skilled in the art can understand that the present invention should not be limited thereto.

[0123] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is also not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications or improvements in the market, or to enable other ordinary skilled persons in the technical field to understand the embodiments disclosed herein.

Claims

1. A method for determining the construction retention time of a polyurethane mixture, characterized in that, It includes the following steps: Prepare a polyurethane mixture; Place the polyurethane mixture in a closed constant temperature and humidity environment, and measure the CO2 concentration value in the constant temperature and humidity environment; Obtain the relationship curve between the CO2 concentration value and time; Based on the relationship curve, determine the construction retention time of the polyurethane mixture, and the construction retention time is near the inflection point of the relationship curve; The temperature of the constant temperature and humidity environment is the same as the average temperature of the construction environment; the humidity of the constant temperature and humidity environment is the same as the average humidity of the construction environment.

2. The method according to claim 1, characterized in that, Measure the CO2 concentration value in the constant temperature and humidity environment at the same time interval to obtain the relationship curve between the CO2 concentration value and time.

3. The method according to claim 2, wherein The time interval is 1 - 60 min.

4. The method according to any one of claims 1 to 3, characterized in that The polyurethane mixture includes mineral aggregate, mineral powder and polyurethane.

5. The method according to claim 4, wherein In the polyurethane mixture, based on the total mass of the mineral aggregate and the mineral powder being 100%, the content of the mineral aggregate is 90 - 99%; the content of the mineral powder is 1 - 10%; the addition amount of the polyurethane is 1 - 10%.

6. The method according to claim 4, characterized in that, The preparation method of the polyurethane mixture includes the step of mixing the mineral aggregate, the mineral powder and the polyurethane.

7. The method according to claim 6, wherein The preparation method includes first mixing the mineral aggregate and then mixing it with the polyurethane, and finally mixing it with the mineral powder.

8. The method according to claim 4, characterized in that, Based on the total mass of the mineral aggregate and the mineral powder being 100%, the content of the mineral aggregate with a particle size of 11 - 16 mm is 20 - 40%; the content of the mineral aggregate with a particle size of 6 - 11 mm is 20 - 40%; the content of the mineral aggregate with a particle size of 3 - 6 mm is 1 - 20%; the content of the mineral aggregate with a particle size of 0 - 3 mm is 20 - 40%.

Images