A method for characterizing the cracking mechanism of a modified emulsified asphalt cold recycled mixture

Abstract

The application aims to provide a modified emulsified asphalt cold recycling mixture cracking mechanism characterization method, and belongs to the technical field of modified emulsified asphalt cold recycling mixture cracking mechanism research, and solves the problem that the internal crack development width and distribution of the modified emulsified asphalt cold recycling mixture cannot be effectively obtained. Hydrogenated epoxy modified emulsified asphalt and three groups of Marshall test pieces are prepared, and a semicircular bending test piece is prepared by using the first group of test pieces; the load-displacement curve of the semicircular bending test piece loaded to complete destruction is obtained by testing, and the remaining two groups of Marshall test pieces are subjected to splitting failure and CT scanning test, and the internal crack width and distribution before and after the test piece is broken are analyzed; and the cracking mechanism of the modified emulsified asphalt cold recycling mixture is summarized and analyzed. The method provided by the application can analyze the cracking mechanism of the modified emulsified asphalt cold recycling mixture when the modified emulsified asphalt cold recycling mixture is destroyed, and has very important reference value for improving the low-temperature performance and crack self-repairing of the modified emulsified asphalt cold recycling mixture.

Description

Technical Field

[0001] This invention is a characterization method for the cracking mechanism of modified emulsified asphalt cold recycled mixture, belonging to the field of modified emulsified asphalt cold recycling technology. Background Technology

[0002] Sustainable development of asphalt pavements is receiving increasing attention from road workers. In recent years, as a large number of asphalt pavements in my country have entered the maintenance and repair stage, a large amount of pavement waste has been generated, and its recycling and reuse have significant social and economic benefits. Cold recycling technology for asphalt pavements can reuse old asphalt mixtures and repair partially damaged asphalt pavements. It has advantages such as low energy consumption, resource conservation, and environmental friendliness, which has attracted the attention of road workers.

[0003] Ordinary emulsified asphalt suffers from insufficient strength and weak adhesion, resulting in poor low-temperature performance of cold-recycled emulsified asphalt mixtures, making them prone to low-temperature cracking. To address this poor low-temperature crack resistance, ordinary emulsified asphalt is primarily modified by adding different modifiers to improve its low-temperature performance. Therefore, most emulsified asphalt used in current cold recycling technology is modified emulsified asphalt. Modified emulsified asphalt exhibits altered crack resistance, leading to corresponding changes in its cracking mechanism. To better address the low-temperature cracking problem of modified emulsified asphalt cold-recycled mixtures, a deeper understanding of its cracking mechanism is necessary.

[0004] In recent years, different scholars have used various methods and indicators to study the cracking of emulsified asphalt cold recycled mixtures, and have achieved certain research results. One key method involves preparing semi-circular specimens of emulsified asphalt cold recycled mixtures and conducting semi-circular bending tests to investigate their cracking. By obtaining the load-displacement curves of the semi-circular specimens during loading to complete failure and the crack orientation on the fracture surface at the point of fracture, some information on the crack distribution during the cracking of emulsified asphalt cold recycled mixtures can be obtained.

[0005] CT scanning technology was first applied in the medical field. It can inspect various industrial products and ultimately display the internal structure of the tested object through computer image processing, making it widely used in industrial fields. By scanning modified emulsified asphalt cold recycled mixture specimens and damaged specimens using CT scanning technology, and processing the images by computer, the width and distribution of internal cracks in incompletely and completely damaged specimens can be obtained. This is an effective means of understanding the cracking mechanism of modified emulsified asphalt cold recycled mixtures.

[0006] Single tests can only obtain partial information about cracks in cold-recycled emulsified asphalt mixtures after cracking, which makes it difficult to analyze the cracking mechanism of these mixtures. The semi-circular bending test cannot effectively obtain the crack width and distribution within the mixture. Therefore, this invention combines the semi-circular bending test with CT scanning to study the crack width and distribution inside cracked specimens of modified cold-recycled emulsified asphalt mixtures, thereby analyzing the cracking mechanism. Based on a deeper understanding of the cracking mechanism of modified cold-recycled emulsified asphalt mixtures, this approach better addresses the problems of insufficient strength in ordinary emulsified asphalt, poor low-temperature performance of ordinary cold-recycled emulsified asphalt mixtures, and poor crack self-healing ability. Summary of the Invention

[0007] (1) Technical issues

[0008] The purpose of this invention is to provide a characterization method for the cracking mechanism of modified emulsified asphalt cold recycled mixtures, which solves the problem that it is difficult to effectively identify the development width and distribution of internal cracks in modified emulsified asphalt cold recycled mixtures.

[0009] (2) Technical solution

[0010] To address the difficulty in effectively identifying the width and distribution of internal cracks in modified emulsified asphalt cold recycled mixtures, the technical solution of this invention is as follows: First, hydrogenated epoxy-modified emulsified asphalt is prepared using a pre-emulsification and post-modification method, referring to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG). Marshall specimens (Groups A, B, and C) were prepared according to E20-2011. Group A Marshall specimens were symmetrically cut to prepare semi-circular bending specimens, and semi-circular bending tests were conducted to obtain load-displacement curves from loading to fracture. Group B Marshall specimens underwent splitting failure tests on a universal testing machine, obtaining load-displacement curves for the entire process from loading to failure. The critical points for initial and final failure of Group B Marshall specimens were determined based on these curves. The same splitting failure test was performed on Group C Marshall specimens as a control group. Loading was stopped at the critical points for initial and final failure of Marshall specimen B. CT scans were performed on these specimens at these critical points to obtain CT images of Group C Marshall specimens before and after fracture. The images were processed using a computer to obtain the width and distribution of internal cracks before and after fracture. Finally, the cracking mechanism of hydrogenated epoxy-modified emulsified asphalt cold recycled mixture was analyzed by combining the results of the two sets of tests.

[0011] (3) Beneficial effects

[0012] Emulsified asphalt has been widely used in asphalt pavement maintenance. As domestic roads gradually enter the maintenance phase, a large amount of pavement waste is generated. This waste, if not properly treated, not only pollutes the environment but also represents a significant waste of resources. Cold recycling technology uses emulsified asphalt as a binder to reuse pavement waste, greatly reducing pavement maintenance costs and minimizing resource waste. However, ordinary emulsified asphalt lacks sufficient strength, and the resulting cold recycled ordinary emulsified asphalt mixtures have poor low-temperature performance, making them prone to cracking and reducing pavement lifespan. Currently, the strength of ordinary emulsified asphalt is mainly improved through modification. To obtain better crack resistance, it is necessary to study the crack width and distribution of modified emulsified asphalt cold recycled mixtures upon failure.

[0013] However, current experiments primarily focus on determining the crack resistance of modified emulsified asphalt cold recycled mixtures, with limited research on the cracking mechanism. Studying this mechanism allows for better matching of appropriate modifiers to enhance the crack resistance of ordinary emulsified asphalt and extend the service life of cold recycled pavements. Therefore, this invention provides a method for characterizing the cracking mechanism of modified emulsified asphalt cold recycled mixtures. The method employs a semi-circular bending test and CT scanning to measure the cracking of damaged specimens from modified emulsified asphalt cold recycled mixtures. Analysis of the data reveals the cracking mechanism, which is of significant practical importance for improving the service life of cold recycled asphalt pavements and reducing pavement maintenance costs. Detailed Implementation

[0014] This invention provides a method for characterizing the cracking mechanism of modified emulsified asphalt cold recycled mixtures, the specific implementation steps of which are as follows:

[0015] (1) First, hydrogenated epoxy modified emulsified asphalt was prepared by emulsification followed by modification. Three groups of hydrogenated epoxy modified emulsified asphalt cold recycled mixture Marshall specimens A, B and C with a diameter of 101.6 mm and a height of 63.5 mm were prepared by the compaction method specified in the "Test Procedure for Asphalt and Asphalt Mixtures of Highway Engineering" (JTG E20-2011). The Marshall specimens of group A were symmetrically cut along the center line to prepare semi-circular bending specimens A1 and A2.

[0016] (2) Using a universal testing machine, select the controlled stress mode for loading. The test temperature is 15℃, the load frequency is 10Hz, and the loading method is uninterrupted. Load the semi-circular bending specimen A1 until the specimen completely breaks. Record the test process and draw the load-displacement relationship curve. Then repeat the test on the semi-circular bending specimen A2. Predict the critical point of crack initiation and fracture of the semi-circular specimen A2 based on the load-displacement curve of the semi-circular specimen A1. Take pictures of the specimen at the critical point of crack initiation and specimen fracture of the semi-circular specimen A2 and record the images of crack propagation on the specimen surface at the two critical points.

[0017] (3) The Marshall specimens of Group B were subjected to splitting failure test on a universal testing machine to obtain the full-process load-displacement failure curve of the Marshall specimens of Group B. Based on the full-process load-displacement failure curve, the load and displacement at the critical point when the Marshall specimens of Group B started to show cracks and finally failed were determined, and the load and displacement at the critical point when the Marshall specimens of Group C, which served as the control group, started to show cracks and finally failed were obtained.

[0018] (4) The first CT scan test was performed on the Marshall specimen of Group C, which served as the control group, to obtain the original scan image. The same splitting test was then performed on the Marshall specimen of Group C on a universal testing machine. When the critical point of cracking of the Marshall specimen of Group C began to appear, the loading was stopped, the specimen was removed, and the specimen was subjected to a second CT scan test to obtain the internal CT image of the specimen. Then the same splitting failure test was performed on the specimen. When the critical point of final failure of the Marshall specimen of Group C appeared, the loading was stopped, the specimen was removed, and the specimen was subjected to a third CT scan test to obtain the internal CT image of the specimen.

[0019] (5) The load-displacement curves of the semi-circular bending specimens A1 and A2 during the loading failure process, as well as the surface crack propagation images of the semi-circular specimen A2 taken at the time of crack initiation and final failure, were processed and compared to understand the crack propagation mode and crack width of the semi-circular bending specimens. At the same time, the CT scan images of the Marshall specimens in Group C at different cracking stages were analyzed and processed to clarify the propagation form and width of internal cracks in the hydrogenated epoxy modified emulsified asphalt cold recycled mixture at different cracking stages. The cracking mechanism of the hydrogenated epoxy modified emulsified asphalt cold recycled mixture was obtained through comprehensive analysis.

Claims

1. A method for characterizing the cracking mechanism of modified emulsified asphalt cold recycled mixture, characterized in that... The specific steps of this method are as follows: (1) First, hydrogenated epoxy modified emulsified asphalt was prepared by emulsification followed by modification. Three groups of Marshall specimens, group A, group B and group C, with a diameter of 101.6 mm and a height of 63.5 mm, were prepared by compaction method as specified in the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). The Marshall specimens in group A were symmetrically cut along the diameter to prepare semi-circular bending specimens A1 and A2. (2) Using a universal testing machine, select the controlled stress mode for loading, select the test temperature of 15℃, select the load frequency of 10Hz, and use the uninterrupted loading method to load the semi-circular bending specimen A1 until the specimen completely breaks. Record the test process and draw the load-displacement relationship curve. Then repeat the test on the semi-circular bending specimen A2. Based on the load-displacement curve of the semi-circular specimen A1, predict the critical point of crack initiation and fracture of the semi-circular specimen A2. Take pictures of the specimen at the critical point of crack initiation and specimen fracture of the semi-circular specimen A2 and record the images of crack propagation on the surface of the specimen at the two critical points. (3) The Marshall specimens of Group B were subjected to splitting failure test on a universal testing machine to obtain the full-process load-displacement failure curve of the Marshall specimens of Group B. Based on the full-process load-displacement failure curve, the critical point at which cracks first appeared and the final failure of the Marshall specimens of Group B were determined, and the optimal CT scan critical point of the Marshall specimens of Group C as the control group was obtained. (4) The first CT scan test was performed on the Marshall specimen of group C, which served as the control group, to obtain the initial scan image. The same splitting failure test was then performed on the Marshall specimen on the universal testing machine. Loading was stopped at the critical point when cracks began to appear in Marshall specimen B. The specimen was removed and a second CT scan test was performed on the specimen to obtain the internal CT image. After that, the same splitting failure test was performed on the specimen. Loading was stopped at the critical point when the final failure of Marshall specimen B occurred. The specimen was removed and a third CT scan test was performed on the specimen to obtain the internal CT image. (5) The load-displacement curves of the semicircular bending specimens A1 and A2 during the loading failure process, as well as the surface crack propagation images of the semicircular specimen A2 taken at the time of crack initiation and final failure, were analyzed and processed to understand the propagation mode and crack width of the semicircular bending specimens. At the same time, the CT scan images of the Marshall specimen C obtained at different stages were analyzed and processed to understand the propagation mode and width of the internal cracks of the hydrogenated epoxy modified emulsified asphalt cold recycled mixture at different stages. The cracking mechanism of the hydrogenated epoxy modified emulsified asphalt cold recycled mixture was obtained through comprehensive analysis.